Interface-crosslinked high-thermal-conductivity flexible-elastic thermal interface composite material and preparation method thereof

Abstract

The invention discloses an interface-crosslinked high-thermal-conductivity flexible-elastic thermal interface composite material and a preparation method thereof. The preparation method comprises the following steps: firstly, carrying out high-temperature banburying processing reaction on a carboxyl compound containing a sulfydryl (including a breakable polysulfide bond) functional group and epoxidized ethylene propylene diene monomer to prepare sulfhydrylated ethylene propylene diene monomer (eEPDM-S); a beta-hydroxyl ester bond dynamic covalent self-adaptive network is generated by utilizing the reaction of carboxyl in a carboxyl compound containing a sulfydryl functional group and an epoxy group, and meanwhile, a sulfydryl reaction site is endowed to the ethylene propylene diene monomer, so that the sulfydryl reaction site is used as a flexible elastic matrix; bN (boron nitride) and liquid metal are self-assembled and positioned under the action of mechanical force, the surface (LM-BN) of the BN is coated with the liquid metal, further, the LM-BN and eEPDM-S are subjected to blending processing, and the flexible and elastic thermal interface composite material with high thermal conductivity is prepared through hot press molding. Mechanical deformable LM is used as a buffer layer between boron nitride and a polymer matrix, stress transfer between a polymer and filler is effectively transited, modulus matching of a heterogeneous interface is improved, and meanwhile liquid metal in LM-BN can react with sulfydryl on an eEPDM-S molecular chain to form a metal-sulfur (LM-S) coordinate bond. No extra catalyst or cross-linking agent is added in the system, that is, beta-hydroxyl ester bond and LM-S bond interface cross-linking effect is constructed at a heat-conducting filler-matrix interface, so that the interface thermal resistance between the heat-conducting filler and a matrix is reduced, and the contradiction between high heat conductivity and mechanical flexibility and elasticity is well balanced. The prepared thermal interface composite material is used for heat dissipation of LED chips in the field of thermal management, temperature rise can be remarkably reduced in the working operation state, and the heating condition of devices is obviously reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermally conductive rubber, and particularly relates to an interface-crosslinked highly thermally conductive flexible thermal interface composite material and a preparation method thereof. Background Art

[0002] With the advent of the post-Moore era, the size of transistors has reached the physical limit, and the serious heat generation problem has become an urgent problem to be solved. Advanced packaging technologies have gradually been pushed to the center of the era. The increasingly serious heat generation problem has threatened the normal use of chips. Therefore, advanced thermal management technologies and efficient thermal management materials have become the key technologies for the normal operation of chips. Usually, thermally conductive materials that can fill the microstructures under a certain pressure are used to squeeze air, connect the heat source and the radiator, so as to assist rapid heat dissipation and extend the service life of electronic devices.

[0003] Rubber materials have excellent soft elasticity, electrical insulation, and chemical stability, and are ideal materials for thermal interface materials. However, rubber materials do not have freely movable electrons and only rely on phonon vibration to transfer heat. They are also limited by the chaotic entanglement of molecular chain segments, resulting in serious phonon scattering and unable to transfer heat quickly in an orderly direction, resulting in an extremely low intrinsic thermal conductivity of rubber, only 0.2 W / mK. Traditional polymer-based thermal interface materials are mechanically blended with high-thermal-conductivity fillers to achieve the effect of rapid heat conduction, which is simple to operate and low in cost. However, simple mixing inevitably brings interface problems. Due to the poor interface compatibility between the high-thermal-conductivity inorganic fillers and the polymer, phonon vibrations do not match, and phonons are severely scattered at the interface, resulting in limited thermal conductivity. In order to further improve the thermal conductivity, a large amount of thermally conductive particles are filled to form a thermal conduction path. However, too high a filler content will cause serious agglomeration phenomena, sacrificing the elasticity and mechanical properties of the rubber, resulting in poor mechanical flexibility, and at the same time, the large amount of filler used increases the cost. Therefore, the research on the interface bonding between the rubber matrix and the thermally conductive filler and its influence on the thermal conductivity is an important development direction and has important research significance and practical significance for the thermal management of electronic devices.

[0004] Chinese Patent CN202410041552.0 discloses a regenerated highly thermally conductive rubber and its preparation method. By using the volume exclusion effect, the crushed waste rubber powder particles are filled into the desulfurized rubber, and the three-dimensional thermal conduction path is constructed by extruding the added two-dimensional thermally conductive particles. However, the inherent three-dimensional cross-linked network of the waste rubber powder in this thermally conductive rubber composite leads to poor compatibility with the desulfurized rubber, resulting in serious mechanical losses and having an adverse impact on the service life of the thermal conductive gasket. Ji et al., Composites Part B: Engineering, 2025, 290: 111965, can adjust the vertical arrangement of boron nitride in the silicone rubber composite by controlling the flow pattern in the specially designed microchannels. When the boron nitride content is 34.3 wt%, the thermal conductivity can reach 5.08 W / mK, effectively improving the thermal conductivity, and the boron nitride loading is also very high. Chinese Patent CN202410994340.4 discloses a graphene thermally conductive rubber composite material for electric heating pads and its preparation method. By the action of compatibilizing silicone rubber and styrene-butadiene rubber, and the copolymer contains amino groups, which can react with the active epoxy groups of epoxypropyl graphene during the mixing and high-temperature vulcanization processes, improving the compatibility between graphene and silicone rubber and styrene-butadiene rubber, enhancing the dispersion of graphene, and significantly enhancing the mechanical properties and thermal conductivity of the composite material, preparing a rubber composite material with both high thermal conductivity and excellent mechanical properties. Although the filling content is low, the preparation process of the composite material is complex and the steps are cumbersome, limiting its wide application in industry. Based on this, further research is still needed to prepare a thermal interface material with high thermal conductivity and mechanical flexibility by regulating the interface structure. Summary of the Invention

[0005] The object of the present invention is to provide an interface-crosslinked highly thermally conductive flexible elastic thermal interface composite material and its preparation method in view of the deficiencies of the prior art. Its characteristics are as follows: First, a carboxyl compound containing a mercapto group (including a cleavable polysulfide bond) is reacted with epoxidized ethylene propylene diene monomer rubber through high-temperature internal mixing processing to prepare mercapto-functionalized ethylene propylene diene monomer rubber (eEPDM-S), while endowing the ethylene propylene diene monomer rubber with a dynamic covalent adaptive network and mercapto reaction sites, which is used as a flexible elastic matrix; Boron nitride (BN) is self-assembled and coordinated with liquid metal under mechanical force to coat the liquid metal on the surface of boron nitride (LM@BN). Further, LM@BN and eEPDM-S are blended and processed and hot-pressed to prepare a flexible elastic thermal interface composite material with high thermal conductivity. The mechanically deformable LM is used as a buffer layer between boron nitride and the polymer matrix to effectively transfer the stress between the polymer and the filler, improve the modulus matching of the heterogeneous interface, and at the same time, the liquid metal in LM@BN can react with the mercapto group on the molecular chain of eEPDM-S to form a metal-sulfur (LM-S) coordination bond. Interface crosslinking of β-hydroxy ester bonds and LM-S bonds is constructed at the interface of the thermally conductive filler-matrix, balancing the contradiction between high thermal conductivity and mechanical flexibility. The prepared thermal interface composite material can be used in the field of thermal management and can significantly reduce the low temperature rise of electronic devices.

[0006] The object of the present invention is achieved by the following technical solutions, where the raw material fractions are all in parts by mass unless otherwise specified.

[0007] The main raw materials of an interface-crosslinked highly thermally conductive flexible elastic thermal interface composite material are composed of the following components: Epoxidized ethylene propylene diene monomer rubber 100 parts Boron nitride nanosheets 10 - 25 parts Carboxyl compound containing a mercapto group 3 - 10 parts Liquid metal 1 - 4 parts Among them, the carboxyl compound containing a mercapto group is any one of cysteine, mercaptoacetic acid, o-mercaptobenzoic acid, and lipoic acid; The liquid metal is any one of gallium-indium-tin alloy, gallium-indium alloy, gallium-tin alloy, gallium-indium-zinc alloy, and gallium-bismuth alloy.

[0008] The preparation method of this interface-crosslinked highly thermally conductive flexible elastic thermal interface composite material includes the following steps: Preparation of mercapto-functionalized ethylene propylene diene monomer rubber (eEPDM-S) 100 parts of epoxidized EPDM (eEPDM) were placed in a torque rheometer and kneaded at 120 - 170 °C and 60 r / min for 1 min. Then, 3 - 10 parts of a carboxyl compound containing a mercapto functional group were added and kneaded for 10 - 18 min to ensure complete grafting reaction, obtaining mercapto-functionalized ethylene propylene diene monomer rubber (eEPDM-S).

[0009] Preparation of High Thermal Conductivity Flexible Elastic Thermal Interface Composite Material 1 - 4 parts of liquid metal (LM) and 10 - 25 parts of boron nitride (BN) were placed in a mortar and ground under mechanical force for 20 - 80 min to wrap LM on the surface of BN, obtaining boron nitride encapsulated by liquid metal (LM@BN). The prepared LM@BN was added to eEPDM-S and kneaded at room temperature on an open mill for 10 - 15 min to ensure sufficient reaction between the mercapto functional group and the liquid metal. Then, the mixture was placed in a hot press and hot-pressed at 150 - 170 °C and 10 - 15 MPa for 4 - 10 min to ensure complete association of the dynamic adaptive network, finally obtaining the thermal interface composite material.

[0010] The following beneficial effects can be obtained through the above technical solutions: Dynamic adaptive β-hydroxy ester bonds are formed between the epoxy groups on the epoxidized ethylene propylene diene monomer rubber and the carboxyl compound containing a mercapto functional group. At the same time, the mercapto functional group is introduced into the molecular chain of the ethylene propylene diene monomer rubber to obtain mercapto-functionalized ethylene propylene diene monomer rubber; under the action of mechanical force, the liquid metal is wrapped on the surface of the boron nitride lamella. On the one hand, it can form an interfacial crosslinking with the mercapto-functionalized ethylene propylene diene monomer rubber at the interface, establishing strong interactions, significantly improving the dispersion of boron nitride, reducing the interfacial thermal resistance between boron nitride and the rubber matrix, and significantly improving the thermal conductivity at low boron nitride loading; on the other hand, the liquid metal with good deformation ability can effectively transfer the stress between the matrix and the thermal conductive filler and can maintain the good movement ability of the molecular chain, thus effectively overcoming the stress concentration problem of the composite material, while reducing the interfacial mismatch between boron nitride and the rubber matrix, balancing the contradiction between high thermal conductivity and mechanical flexibility, and having a significant effect in the field of thermal management temperature control. This preparation method is simple, the conditions are mild, the thermal conductivity is significantly improved, and it has obvious advantages. Description of the Drawings

[0011] Figure 1 It is a scanning electron microscope image of the brittle fracture cross-section of the high thermal conductivity flexible elastic thermal interface composite material.

[0012] Figure 2 It is the heat dissipation assembly and temperature control effect of the thermal interface composite material in the LED chip. Detailed Embodiments

[0013] The present invention will be further described below through specific embodiments. It should be noted here that the embodiments are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Those skilled in the art can make non-essential improvements and adjustments to the present invention based on the above content of the present invention. Example 1

[0014] Put 100 parts of eEPDM into a torque rheometer, knead at 120 °C and 60 r / min for 1 min, add 3 parts of mercaptoacetic acid and carry out a kneading reaction for 10 min to ensure that the grafting reaction is complete, and obtain mercapto-functionalized ethylene propylene diene monomer rubber (eEPDM-S).

[0015] Put 1 part of gallium-indium alloy and 10 parts of boron nitride (BN) into a mortar and grind for 20 min under the action of mechanical force to obtain boron nitride encapsulated by liquid metal (LM@BN). Add the prepared LM@BN to eEPDM-S, carry out mixing and processing on an open mill at room temperature for 10 min to ensure sufficient reaction of mercapto functional groups with liquid metal, and then hot press at 150 °C and 10 MPa for 4 min to obtain a thermal interface composite material.

[0016] After testing, the thermal conductivity of the thermal interface composite material is 1.347 W / mK, the tensile strength is 0.78 MPa, the fracture strain is 397%, and the Young's modulus is 125 kPa; when connected to an LED chip, the operating temperature is reduced by 4 °C. Example 2

[0017] Put 100 parts of eEPDM into a torque rheometer, knead at 140 °C and 60 r / min for 1 min, add 6 parts of cysteine and carry out a kneading reaction for 13 min to ensure that the grafting reaction is complete, and obtain mercapto-functionalized ethylene propylene diene monomer rubber (eEPDM-S).

[0018] Put 2 parts of gallium-indium-tin alloy and 15 parts of boron nitride (BN) into a mortar and grind for 40 min under the action of mechanical force to obtain boron nitride encapsulated by liquid metal (LM@BN). Add the prepared LM@BN to eEPDM-S, carry out mixing and processing on an open mill at room temperature for 10 min to ensure sufficient reaction of mercapto functional groups with liquid metal, and then hot press at 150 °C and 10 MPa for 6 min to obtain a thermal interface composite material.

[0019] After testing, the thermal conductivity of the thermal interface composite material is 2.139 W / mK, the tensile strength is 0.92 MPa, the fracture strain is 452%, and the Young's modulus is 136 kPa; when connected to an LED chip, the operating temperature is reduced by 6 °C. Example 3

[0020] 100 parts of eEPDM were placed in a torque rheometer and kneaded at 150 °C and 60 r / min for 1 min. Then, 10 parts of lipoic acid were added and the kneading reaction was carried out for 15 min to ensure complete grafting reaction, and thiolated ethylene propylene diene monomer rubber (eEPDM-S) was obtained.

[0021] 3 parts of gallium-indium-zinc alloy and 15 parts of boron nitride (BN) were placed in a mortar and ground under mechanical force for 50 min to obtain boron nitride encapsulated by liquid metal (LM@BN). The prepared LM@BN was added to eEPDM-S and kneaded at room temperature on an open mill for 12 min to ensure sufficient reaction between the mercapto functional group and the liquid metal. Then, it was hot-pressed at 160 °C and 12 MPa for 6 min to obtain a thermal interface composite material.

[0022] After testing, the thermal conductivity of the thermal interface composite material was 2.664 W / mK, the tensile strength was 1.15 MPa, the fracture strain was 523%, and the Young's modulus was 112 kPa; when connected to an LED chip, the operating temperature decreased by 7 °C. Example 4

[0023] 100 parts of eEPDM were placed in a torque rheometer and kneaded at 160 °C and 60 r / min for 1 min. Then, 8 parts of o-mercaptobenzoic acid were added and the kneading reaction was carried out for 15 min to ensure complete grafting reaction, and thiolated ethylene propylene diene monomer rubber (eEPDM-S) was obtained.

[0024] 3 parts of gallium-indium-zinc alloy and 20 parts of boron nitride (BN) were placed in a mortar and ground under mechanical force for 60 min to obtain boron nitride encapsulated by liquid metal (LM@BN). The prepared LM@BN was added to eEPDM-S and kneaded at room temperature on an open mill for 15 min to ensure sufficient reaction between the mercapto functional group and the liquid metal. Then, it was hot-pressed at 160 °C and 12 MPa for 8 min to obtain a thermal interface composite material.

[0025] After testing, the thermal conductivity of the thermal interface composite material was 2.311 W / mK, the tensile strength was 1.54 MPa, the fracture strain was 458%, and the Young's modulus was 151 kPa; when connected to an LED chip, the operating temperature decreased by 6 °C. Example 5

[0026] 100 parts of eEPDM were placed in a torque rheometer and kneaded at 170 °C and 60 r / min for 1 min. Then, 10 parts of lipoic acid were added and the kneading reaction was carried out for 16 min to ensure complete grafting reaction, and thiolated ethylene propylene diene monomer rubber (eEPDM-S) was obtained.

[0027] Place 4 parts of gallium-indium alloy and 25 parts of boron nitride (BN) in a mortar and grind them under mechanical force for 80 min to obtain boron nitride encapsulated by liquid metal (LM@BN). Add the prepared LM@BN to eEPDM-S and carry out mixing and processing on an open mill at room temperature for 16 min to ensure sufficient reaction between the mercapto functional group and the liquid metal. Then, hot press at 170 °C and 15 MPa for 8 min to obtain a thermal interface composite material.

[0028] After testing, the thermal conductivity of the thermal interface composite material is 3.128 W / mK, the tensile strength is 0.81 MPa, the fracture strain is 647%, and the Young's modulus is 97 kPa; when connected to an LED chip, the operating temperature is reduced by 9 °C.

[0029] In summary, the thermal interface composite material prepared in the embodiment of the present invention has a high thermal conductivity and excellent mechanical flexibility and can be applied to the field of heat dissipation of electronic components.

[0030] The above embodiments have described the specific content of the present invention in detail, but the present invention is not limited to the described embodiments. Those skilled in the art can make equivalent substitutions, which should all be covered within the protection scope of the present invention. The above are all preferred embodiments of the present invention. For those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, the modifications of various equivalent forms of the present invention all fall within the protection scope of the appended claims of this application.

Claims

1. An interface cross-linked high thermal conductivity flexible elastic thermal interface composite material, characterized in that: The main raw materials of the composite material are composed of the following components, calculated by weight: Epoxidized EPDM rubber 100 parts Boron nitride nanosheets 10-25 parts 3-10 parts of carboxyl compounds containing thiol functional groups Liquid metal 1-4 parts Wherein, the carboxyl compound containing a thiol functional group is any one of cysteine, thioglycolic acid, o-mercaptobenzoic acid, and lipoic acid; The liquid metal is any one of gallium-indium-tin alloy, gallium-indium alloy, gallium-tin alloy, gallium-indium-zinc alloy and gallium-bismuth alloy.

2. A method for preparing the interface cross-linked high thermal conductivity flexible elastic thermal interface composite material as shown in claim 1, characterized in that: Here’s how: Preparation of mercaptolated ethylene propylene diene monomer rubber eEPDM-S 100 parts of epoxidized EPDMeEPDM were placed in a torque rheometer, and kneaded at 120-170°C and 60 r / min for 1 min, and 3-10 parts of a carboxyl compound containing a thiol functional group were added to carry out kneading reaction for 10-18 min to ensure that the grafting reaction was complete, thereby obtaining thiolated ethylene propylene diene monomer rubber eEPDM-S; Preparation of high thermal conductivity flexible elastic thermal interface composite materials 1-4 parts of liquid metal LM and 10-25 parts of boron nitride BN are placed in a mortar and ground under mechanical force for 20-80 min to wrap LM on the surface of BN to obtain liquid metal-wrapped boron nitride LM@BN; the prepared LM@BN is added to eEPDM-S and mixed in an open mill at room temperature for 10-15 min to ensure sufficient reaction between the thiol functional group and the liquid metal; then the mixture is placed in a hot press and hot pressed at 150-170°C and 10-15 MPa for 4-10 min to ensure that the dynamic adaptive network is completely associated, and finally a thermal interface composite material is obtained.

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