Thermally conductive epoxy potting adhesive and preparation method thereof

Abstract

This invention discloses a thermally conductive epoxy potting compound and its preparation method. The thermally conductive epoxy potting compound is composed of component A and component B in a mass ratio of 100:(8-15). Component A, by mass, includes 80-120 parts of main epoxy resin, 3-10 parts of silicone-modified toughening agent DEP, 2-5 parts of coupling agent, 800-860 parts of filler, and 5-15 parts of additives. Component B, by mass, includes 80-100 parts of main curing agent, 0-20 parts of auxiliary curing agent, and 0.3-2 parts of curing accelerator. By constructing a flexible interface layer using the silicone-modified toughening agent DEP, the traditional toughening mechanism is fundamentally changed. While maintaining a high-filler system and high thermal conductivity, the thermal shock resistance of the epoxy potting compound is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of epoxy potting compound technology, and more particularly to a thermally conductive epoxy potting compound and its preparation method. Background Technology

[0002] Epoxy potting compounds are widely used in the insulation and heat dissipation encapsulation of power semiconductor modules, new energy vehicle electronic control systems, high-temperature sensors and aerospace electronic devices. One of the important indicators for evaluating their performance in the industry is the thermal conductivity of the adhesive.

[0003] To achieve excellent thermal conductivity in potting compounds, the industry often uses a large amount of filler to construct thermal conduction paths, with heavy powders such as alumina and aluminum nitride typically accounting for more than 60% by mass. Related solutions have been disclosed in numerous patents, industry literature, and commercial products.

[0004] However, the filler and the resin itself have a large difference in their coefficients of thermal expansion. Combined with the potential heterogeneity of the system, a large amount of residual internal stress will be generated at the interface during curing and high-low temperature alternation. At the same time, high filler content of powder will break the resin molecular chains, significantly increasing the rigidity of the system. Under thermal shock, it is very easy to generate microcracks and exacerbate cracking.

[0005] In existing technologies, toughening is typically achieved by adding liquid rubber toughening agents (such as CTBN and ATBN), which rely on "reaction-induced phase separation" to form island structures to absorb impact energy. However, in ultra-high filler systems with 800+ parts of filler, a large number of filler particles break and isolate the rubber phase, making it difficult to form continuous island structures and significantly reducing toughening efficiency.

[0006] Chinese patent document CN119799234A discloses a two-component thermally conductive epoxy potting compound resistant to thermal shock. It discloses a compound system of epoxy polybutadiene rubber and bridge shell toughening agents, which improves the thermal shock resistance of the epoxy potting compound by forming a special island structure. This island-structure toughening is a traditional rubber phase separation pathway. Liquid rubber dissolves in epoxy, and reaction-induced phase separation (RIPS) occurs during curing, precipitating 0.5-5μm rubber particles ("islands") dispersed in the continuous epoxy phase ("sea"). In high-filler systems (800+ parts, volume fraction > 60%), the filler physically isolates and blocks the aggregation of rubber droplets, preventing the rubber phase from growing. This reduces the toughening efficiency by 70-80%, easily leading to an imbalance between rigidity and toughness in the thermally conductive epoxy potting compound, resulting in poor thermal shock resistance.

[0007] The inherent thermodynamic parameters of inorganic fillers and resin matrices are naturally mismatched; the dispersion of toughening components is limited in high-filler systems. How to improve the thermal shock resistance of high thermal conductivity and high-filler epoxy potting compounds is a technical problem that urgently needs to be solved in the industry. Summary of the Invention

[0008] The purpose of this invention is to provide a thermally conductive epoxy potting compound and its preparation method, so as to enhance the thermal shock resistance of thermally conductive epoxy potting compounds in high-filler systems.

[0009] To solve the above-mentioned technical problems, the embodiments of the present invention provide a technical solution as follows: a thermally conductive epoxy potting compound, composed of component A and component B, wherein the mass ratio of component A to component B is 100:(8-15); component A, by mass, includes the following raw materials: 80-120 parts of main epoxy resin, 3-10 parts of organosilicon modified toughening agent DEP, 2-5 parts of coupling agent, 800-860 parts of filler, and 5-15 parts of additives; component B, by mass, includes the following raw materials: 80-100 parts of main curing agent, 0-20 parts of auxiliary curing agent, and 0.3-2 parts of curing accelerator.

[0010] Furthermore, the main epoxy resin is composed of 30-50 parts by weight of bisphenol F type epoxy resin and 50-70 parts by weight of alicyclic epoxy resin.

[0011] Furthermore, the organosilicon-modified toughening agent DEP is an epoxy-terminated polydimethylsiloxane-polyether block copolymer with a number-average molecular weight of 2000-5000 g / mol, an epoxy equivalent of 500-1000 g / eq, and a viscosity of 500-2000 mPa·s at 25°C.

[0012] Furthermore, the filler is composed of modified compound spherical alumina and aluminum hydroxide.

[0013] Furthermore, the mass ratio of the modified compound spherical alumina to the aluminum hydroxide is (780-830):(20-30).

[0014] Furthermore, the main curing agent is one or more of methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, and hydrogenated methylnadic anhydride.

[0015] Furthermore, the auxiliary curing agent is a long-chain aliphatic anhydride.

[0016] Furthermore, the additives, by weight, include 0.5-1 parts of defoamer, 0.2-0.6 parts of wetting and dispersing agent, 2.5-5 parts of pigment, and 3-8 parts of flame retardant.

[0017] To solve the above-mentioned technical problems, the present invention also provides a method for preparing a thermally conductive epoxy potting compound, which is used to prepare the thermally conductive epoxy potting compound described in any of the above-mentioned claims, comprising the following steps: mixing and stirring the main epoxy resin, silicone-modified toughening agent DEP, coupling agent, filler, and additives evenly according to the formulation amount of component A, and then performing vacuum degassing treatment to obtain component A; mixing and stirring the main curing agent, auxiliary curing agent, and curing accelerator evenly according to the formulation amount of component B, and then performing vacuum degassing treatment to obtain component B.

[0018] Furthermore, it also includes mixing component A and component B at a mass ratio of 100:(8-15) and then curing them using a stepped temperature increase process: first stage: curing at 80-100℃ for 2-3 hours; second stage: curing at 120-150℃ for 2-4 hours.

[0019] The thermally conductive epoxy potting compound and its preparation method provided by this invention, compared with the prior art, fundamentally change the traditional toughening mechanism by constructing a flexible interface layer using a silicone-modified toughening agent (DEP). While maintaining a high-filling system and high thermal conductivity, it significantly improves the epoxy potting compound's resistance to thermal shock, making it particularly suitable for power device packaging under harsh conditions such as new energy vehicles and aerospace. Specifically, a rigid heat-resistant skeleton is provided by the main curing agent (such as methylhexahydrophthalic anhydride), while an auxiliary curing agent (such as long-chain aliphatic anhydrides) introduces flexible segments, increasing the space for segment movement and improving stress relaxation ability. These two components, together with the silicone-modified toughening agent DEP, form a synergistic effect, resulting in an elongation at break of 23-28% and a tensile strength ≥60 MPa, achieving a balance between rigidity and toughness in a high-filling system. Furthermore, a stepped temperature curing process is employed, with pre-gelation in the first stage to release initial stress, and complete cross-linking in the second stage to avoid concentrated heat release, further reducing internal stress during curing and ensuring the reliability of large-size device packaging. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the preparation steps of the thermally conductive epoxy potting compound in this embodiment of the invention. Detailed Implementation To make the objectives, technical solutions, and advantages of this invention clearer, the various embodiments of this invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the various embodiments of this invention to facilitate a better understanding of this application. However, the technical solutions claimed in the claims of this application can be implemented even without these technical details and with various variations and modifications based on the following embodiments.

[0021] One embodiment of the present invention relates to a thermally conductive epoxy potting compound, comprising component A and component B, wherein the mass ratio of component A to component B is 100:(8-15); component A, by mass, comprises the following raw materials: 80-120 parts of main epoxy resin, 3-10 parts of silicone-modified toughening agent DEP, 2-5 parts of coupling agent, 800-860 parts of filler, and 5-15 parts of additives; component B, by mass, comprises the following raw materials: 80-100 parts of main curing agent, 0-20 parts of auxiliary curing agent, and 0.3-2 parts of curing accelerator. Preferably, the main epoxy resin, by mass, is a compound composed of 30-50 parts of bisphenol F type epoxy resin and 50-70 parts of alicyclic epoxy resin. By compounding bisphenol F epoxy and alicyclic epoxy at a mass ratio of (30-50):(50-70), the former provides a low viscosity window to ensure high filling processability, while the latter provides a high glass transition temperature to ensure heat resistance. The two are mutually soluble at the molecular level to form a uniform matrix, avoiding the phase separation defects common in physical blending.

[0022] In one example, the organosilicon-modified toughening agent DEP is an epoxy-terminated polydimethylsiloxane-polyether block copolymer, abbreviated as PDMS-PEO-EP, with a number-average molecular weight of 2000-5000 g / mol, an epoxy equivalent of 500-1000 g / eq, and a viscosity of 500-2000 mPa·s at 25°C. The PDMS segments (-Si(CH3)2-O-) have an ultra-low surface energy of approximately 20 mN / m and a Tg ≈ -120°C, allowing them to preferentially wet the filler surface; the PEO polyether segments (-CH2CH2-O-) provide compatibility with the epoxy matrix, preventing macroscopic phase separation; and the epoxy-terminated groups participate in the curing agent anhydride crosslinking reaction, covalently embedding themselves into the epoxy crosslinking network.

[0023] In existing technologies, the mechanism of liquid rubber toughening agents involves the dissolution of liquid rubber in epoxy. During curing, reaction-induced phase separation occurs, resulting in the precipitation of 0.5-5 μm rubber particles ("islands") dispersed in the continuous epoxy phase ("sea"). Under stress, rubber cavitation / interfacial debonding induces matrix shear yielding. In particular, in high-filler systems with >800 parts and >60% volume fraction of filler, the physical isolation of the filler prevents the rubber droplet coalescence, hindering rubber phase growth and reducing toughening efficiency by 70-80%, thus creating a bottleneck for toughening failure. In contrast, the silicone-modified toughening agent DEP used in this application has an ultra-low surface energy of approximately 20 mN / m for its PDMS segments, far lower than the epoxy surface energy of 40-50 mN / m and the filler surface energy of 50-60 mN / m. This allows the silicone-modified toughening agent DEP to spontaneously migrate and adsorb onto the high surface energy filler surface during mixing, forming a 5-20 nm thick flexible silicone coating layer. This interface layer achieves three functions: First, interface stress buffering: the free rotation of Si-O-Si bonds causes elastic / viscoelastic deformation of the interface layer, absorbing the strain caused by the thermal expansion mismatch between the filler and the matrix, and the modulus changes from abrupt change to gradient transition, reducing stress by 40-60%; Second, chemical bonding anchoring: the terminal epoxy participates in cross-linking, covalently connecting the filler and epoxy network at the same time, that is, the filler-DEP-matrix trinity, which is fundamentally different from physical interlocking; Third, active toughening: a low-stress interface is constructed from the initial stage of curing, reducing the thermodynamic driving force for microcrack initiation from the source, which is different from the passive triggering mechanism.

[0024] In one example, the filler used in component A consists of modified compound spherical alumina and aluminum hydroxide. The spherical morphology of the alumina reduces interparticle friction and improves the filling density, while the aluminum hydroxide synergistically provides flame retardancy. A preferred configuration is a mixture of modified compound spherical alumina (DRHY-392) and aluminum hydroxide (WA-1) at a mass ratio of (780-830):(20-30), thereby constructing a dense, highly thermally conductive pathway at an ultra-high filler content of 800-860 parts, which is beneficial for improving the thermal conductivity of the thermally conductive epoxy potting compound.

[0025] In one example, the primary curing agent is selected from one or more of methylhexahydrophthalic anhydride (MHHPA), methyltetrahydrophthalic anhydride (MeTHPA), methylnadic anhydride (MNA), and hydrogenated methylnadic anhydride (HMNA). The secondary curing agent is selected from long-chain aliphatic anhydrides, such as dodecenylsuccinic anhydride (DDSA). The curing accelerator is selected from one or more of 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), benzyldimethylamine (BDMA), and 1-cyanoethyl-2-ethyl-4-methylimidazolium (2E4MZ-CN). Preferably, the primary curing agent is methylhexahydrophthalic anhydride, which has no unsaturated double bonds in its molecular structure, resulting in excellent heat aging resistance of the cured product and giving the system a basic temperature resistance rating. The secondary curing agent, a long-chain aliphatic anhydride, introduces flexible segments embedded in the cross-linking network, increasing the segment mobility space and enhancing stress relaxation ability within the cross-linking structure. The two work synergistically to adjust the rigidity-toughness balance from within the cross-linking network, rather than relying solely on external toughening agents.

[0026] In one example, the coupling agent is selected from γ-glycidoxypropyltrimethoxysilane (KH-560), and the additives, by weight, include 0.5-1 parts of defoamer selected from 6800, 0.2-0.6 parts of wetting and dispersing agent selected from phosphate ester dispersants (BYK W9010), 2.5-5 parts of pigment selected from Mitsubishi MA100 carbon black, and 3-8 parts of flame retardant selected from red phosphorus.

[0027] One embodiment relates to a method for preparing a thermally conductive epoxy potting compound, comprising the following steps: mixing and stirring the main epoxy resin, silicone-modified toughening agent DEP, coupling agent, filler, and additives according to the formulation amount of component A, followed by vacuum degassing to obtain component A; mixing and stirring the main curing agent, auxiliary curing agent, and curing accelerator according to the formulation amount of component B, followed by vacuum degassing to obtain component B. In use, component A and component B are mixed at a mass ratio of 100:(8-15), and cured using a stepped temperature increase process: first stage: 80-100℃ for 2-3 hours; second stage: 120-150℃ for 2-4 hours. The thermally conductive epoxy potting compound is pre-cured and initially gelled in the first stage by a stepped temperature curing process. At this stage, the viscosity of the system gradually increases but it is not yet fully cross-linked, which is conducive to the initial release of residual stress. In the second stage, the temperature is gradually increased to complete the cross-linking, avoiding thermal stress caused by concentrated heat release and avoiding problems such as thermal runaway caused by curing at a single temperature.

[0028] The present invention will be further described below with reference to specific embodiments. Unless otherwise specified, all raw materials involved in the embodiments are commercially available.

[0029] Example 1 This embodiment provides a thermally conductive epoxy potting compound with the following formulation: Component A: 40 parts bisphenol F type epoxy 170, 60 parts alicyclic epoxy 21P, 6 parts silicone-modified toughening agent DEP, 3 parts coupling agent KH-560, 0.7 parts defoamer, 0.4 parts phosphate ester wetting and dispersing agent, 3.5 parts carbon black, 5 parts red phosphorus, 800 parts modified spherical alumina, and 25 parts aluminum hydroxide. Component B: 85 parts methylhexahydrophthalic anhydride, 10 parts dodecenyl succinic anhydride, and 1 part curing accelerator. The mass ratio of A to B is 100:10.

[0030] The preparation steps for thermally conductive epoxy potting compound are as follows: Preparation of Component A: Bisphenol F type epoxy 170, alicyclic epoxy 21P, organosilicon modified toughening agent DEP, coupling agent KH-560, defoamer, and wetting and dispersing agent are added to the reaction vessel according to the formula amount and stirred at 400-600 r / min for 5-10 minutes; carbon black, red phosphorus, modified spherical alumina, and aluminum hydroxide are added according to the formula amount and stirred at 9000-1100 r / min for 40-80 minutes; transferred to a vacuum device and stirred at 200-400 r / min, degassing for 15 minutes under a vacuum degree ≤-0.095 MPa; filtered, sealed and packaged to obtain Component A.

[0031] Preparation of Component B: Methylhexahydrophthalic anhydride, dodecenylsuccinic anhydride, and curing accelerator are mixed at room temperature for 40-60 minutes according to the formula. The mixture is then degassed for 10-20 minutes under a vacuum of ≤-0.095MPa, sealed, and packaged to obtain Component B.

[0032] After mixing component A and component B at a ratio of 100:10, a stepped temperature curing process is used: the temperature is raised to 80°C and held for 2 hours, then raised to 130°C and held for 3 hours to complete the curing.

[0033] Example 2 The difference between this embodiment and Example 1 is that the amount of organosilicon-modified toughening agent DEP is 3 parts, the auxiliary curing agent dodecenylsuccinic anhydride is not added, and the curing process is to heat to 80°C and hold for 2 hours, then heat to 130°C and hold for 3 hours. The rest of the formulation and preparation method are the same as in Example 1.

[0034] Example 3 The difference between this embodiment and Example 1 is that the amount of organosilicon-modified toughening agent DEP is 10 parts, the amount of modified spherical alumina is 830 parts, the amount of aluminum hydroxide is 30 parts, and the amount of auxiliary curing agent dodecenyl succinic anhydride is 20 parts. The rest of the formulation and preparation method are the same as in Example 1.

[0035] Example 4 The difference between this embodiment and Embodiment 1 is that the amount of modified spherical alumina is 780 parts, the amount of aluminum hydroxide is 20 parts, and the amount of coupling agent is 2 parts. The rest of the formulation and preparation method are the same as in Embodiment 1.

[0036] Comparative Example 1 The difference between this comparative example and Example 1 is that the organosilicon-modified toughening agent DEP is not added; the rest of the formulation and preparation method are the same as in Example 1.

[0037] Comparative Example 2 The difference between this comparative example and Example 1 is that the organosilicon-modified toughening agent DEP is replaced in equal amounts with carboxyl-terminated butadiene-acrylonitrile rubber CTBN 1300X8, while the rest of the formulation and preparation method are the same as in Example 1.

[0038] Comparative Example 3 The difference between this comparative example and Example 1 is that the organosilicon-modified toughening agent DEP is replaced with an equal amount of the core-shell toughening agent Kane Ace MX-154, while the rest of the formulation and preparation method are the same as in Example 1.

[0039] Comparative Example 4 The difference between this comparative example and Example 1 is that methyl hexahydrophthalic anhydride and benzyl alcohol were esterified in a molar ratio of 2:1 under nitrogen protection to prepare a modified curing agent, which replaced the curing combination of methyl hexahydrophthalic anhydride and dodecenyl succinic anhydride in equal amounts. The rest of the formulation and preparation method are the same as in Example 1.

[0040] The thermally conductive epoxy potting compounds obtained in Examples 1-4 and Comparative Examples 1-4 were tested for performance according to conventional testing methods and standards in the field. The results are shown in Table 1, Epoxy Potting Compound Performance Test Record Table.

[0041] Table 1. Epoxy Potting Compound Performance Test Record As shown in Table 1, the thermal conductivity of Examples 1-4 is ≥1.95 W / m·K, with Example 3 reaching 2.12 W / m·K, indicating that the present invention constructs an efficient thermal conductivity pathway under ultra-high filler filling. The thermal shock cracking cycles of Examples 1-4 are all >140, while the thermal shock cracking test results of Comparative Examples 1-4 show cracking after 90-108 cycles, indicating that the present invention has a significant toughening effect through the DEP flexible interface layer, significantly improving the thermal shock resistance of the high thermal conductivity, high filler epoxy potting compound. As can be seen from Comparative Example 4, its elongation at break is significantly lower than that of Examples 1, 3, and 4. This indicates that the curing agent used in Comparative Example 4, which is a pre-chemically modified acid anhydride product, can play a certain role in auxiliary toughening, but its process is complex and the toughening effect is limited. It is also prone to imbalance in the high-filler epoxy potting compound system. In this invention, a commercially available acid anhydride physical blending curing system is used. The process is simple and can synergistically regulate the balance between toughness and rigidity of the high-filler epoxy potting compound with the flexible interface toughening of the organosilicon-modified toughening agent DEP, so that its elongation at break reaches 23%-28%.

[0042] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications and improvements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be defined by the claims.

Claims

1. A thermally conductive epoxy potting compound, characterized in that, It is composed of component A and component B, wherein the mass ratio of component A to component B is 100:8-15; Component A, by mass, comprises the following raw materials: The main component is epoxy resin (80-120 parts), organosilicon-modified toughening agent DEP (3-10 parts), coupling agent (2-5 parts), filler (800-860 parts), and additives (5-15 parts). Component B, by weight, comprises the following raw materials: 80-100 parts of main curing agent, 0-20 parts of auxiliary curing agent, and 0.3-2 parts of curing accelerator.

2. The thermally conductive epoxy potting compound according to claim 1, characterized in that, The main epoxy resin is composed of 30-50 parts by weight of bisphenol F type epoxy resin and 50-70 parts by weight of alicyclic epoxy resin.

3. The thermally conductive epoxy potting compound according to claim 1, characterized in that, The organosilicon-modified toughening agent DEP is an epoxy-terminated polydimethylsiloxane-polyether block copolymer with a number-average molecular weight of 2000-5000 g / mol, an epoxy equivalent of 500-1000 g / eq, and a viscosity of 500-2000 mPa·s at 25°C.

4. The thermally conductive epoxy potting compound according to claim 1, characterized in that, The filler is composed of modified compound spherical alumina and aluminum hydroxide.

5. The thermally conductive epoxy potting compound according to claim 4, characterized in that, The mass ratio of the modified compound spherical alumina to the aluminum hydroxide is (780-830):(20-30).

6. The thermally conductive epoxy potting compound according to claim 1, characterized in that, The main curing agent is one or more of methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, and hydrogenated methylnadic anhydride.

7. The thermally conductive epoxy potting compound according to claim 1, characterized in that, The auxiliary curing agent is a long-chain aliphatic acid anhydride.

8. The thermally conductive epoxy potting compound according to claim 1, characterized in that, The additives, by weight, include 0.5-1 parts of defoamer, 0.2-0.6 parts of wetting and dispersing agent, 2.5-5 parts of pigment, and 3-8 parts of flame retardant.

9. A method for preparing a thermally conductive epoxy potting compound, characterized in that, The preparation of the thermally conductive epoxy potting compound as described in any one of claims 1-8 comprises the following steps: mixing and stirring the main epoxy resin, silicone-modified toughening agent DEP, coupling agent, filler, and additives according to the formulation amount of component A, and then performing vacuum degassing treatment to obtain component A; mixing and stirring the main curing agent, auxiliary curing agent, and curing accelerator according to the formulation amount of component B, and then performing vacuum degassing treatment to obtain component B.

10. The method for preparing the thermally conductive epoxy potting compound according to claim 9, characterized in that, It also includes mixing component A and component B at a mass ratio of 100:(8-15) and then curing them using a stepped temperature increase process: first stage: curing at 80-100℃ for 2-3 hours; second stage: curing at 120-150℃ for 2-4 hours.

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