An elastomer-based glass-like thermal interface material and method of making the same

Abstract

The application discloses a kind of based on elastomer class glass thermal interface material and preparation method thereof.The thermal interface material is prepared from raw materials including diglycidyl ether-terminated liquid polythioether prepolymer, methyl tetrahydrophthalic anhydride, ethylene glycol diglycidyl ether, catalyst and heat-conducting filler.The application realizes the high vertical orientation of heat-conducting filler by the process of hot-pressing and stack welding, and has very high thermal conductivity in the vertical direction.The R c of the thermal interface material is much lower than that of commercial thermal interface material using traditional silicon matrix, and has spontaneous contact behavior on the surface of substrate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of organic-inorganic composite materials, in particular to a kind of based on elastomer glass thermal interface material and preparation method thereof. BACKGROUND

[0002] With the surge in power and heat of electronic equipment, the heat dissipation problem has become the bottleneck hindering the development of advanced electronic equipment. It is worth noting that when heat passes through the macroscopic interface between heat source and heat sink, the air slot generated by incomplete interface contact will seriously hinder heat transfer. Using thermal interface material (TIM) to enhance interface heat transfer is the most common engineering strategy, and developing high-performance TIM has become the common goal of global practitioners.

[0003] However, high thermal conductivity composites usually require a large amount of thermal conductive fillers to build a complete heat transfer path, which leads to an increase in the hardness of the composite and a serious weakening of the three-dimensional consistency. And the most common in the thermal conductive pad is the thermal conductive silicone pad, in order to have good flexibility, usually reduce the crosslinking density of the silicone matrix, so that it is not completely cured, there is a certain oil leakage phenomenon. Even though high-filled TIM has high κ ⊥ , its thermal conductivity performance will be affected by high interface thermal resistance (R c ). Obviously, more research reports on flexible TIM with low thermal resistance. Some researchers try to build a continuous filler network at low filling through specific methods, such as ice template method, polymer template method and foam template method. Zhao et al. prepared a new type of polymer composite composed of foam graphene (GF), carbon black (CB) and polydimethylsiloxane (PDMS) by foam template method. When the filler content reaches 8wt%, GF and CB form an effective thermal transport double network inside the composite, and the thermal conductivity of 8wt% CB / GF / PDMS composite reaches 0.686W m -1 K -1 . Although the thermal conductivity efficiency of the filler is improved through these methods, the low content of the thermal conductive filler limits κ ⊥ . SUMMARY

[0004] In view of the problems existing in the prior art, the purpose of the present application is to provide a kind of based on elastomer glass thermal interface material and preparation method thereof.

[0005] The present application is based on a high-flexibility vitreous matrix prepared from a diglycidyl ether-terminated liquid polythioether prepolymer (EPS) with a large number of dynamic disulfide bonds. At the same time, the highly vertical orientation of the thermally conductive filler is realized through the process combining hot pressing and stack welding, thereby realizing effective through-plane thermal conduction. Due to the bond exchange reaction of a large number of active disulfide bonds in the matrix, the customized vitreous matrix has good self-repairing performance, and especially the hot-pressed film filled with graphite shows excellent weldability, which is the basis for the feasibility of the vertical orientation process. When the amount of the thermally conductive filler is 80 parts, the κ ⊥ up to 25.0 W·m -1 K -1 More importantly, a unique spontaneous interfacial contact behavior is discovered on this vitreous composite under the driving of high surface free energy relying on time-temperature-dependent unstable kinetics and thermodynamics. Therefore, the R c of this vitreous TIM is much lower than that of commercial TIMs using traditional silicon matrix.

[0006] One of the purposes of the present application is to provide an elastomer vitreous thermal interface material prepared from raw materials including a diglycidyl ether-terminated liquid polythioether prepolymer, methyl tetrahydrophthalic anhydride, ethylene glycol diglycidyl ether, a catalyst and a thermally conductive filler.

[0007] In the thermal interface material, the diglycidyl ether-terminated liquid polythioether prepolymer is 100 parts by weight, the methyl tetrahydrophthalic anhydride is 20-50 parts by weight, the ethylene glycol diglycidyl ether is 2-20 parts by weight, the catalyst is 0.5-2 parts by weight, and the thermally conductive filler is 20-100 parts by weight.

[0008] Preferably, the diglycidyl ether-terminated liquid polythioether prepolymer is 100 parts by weight, the methyl tetrahydrophthalic anhydride is 30-40 parts by weight, the ethylene glycol diglycidyl ether is 10-15 parts by weight, the catalyst is 1-1.5 parts by weight, and the thermally conductive filler is 60-80 parts by weight.

[0009] Specifically, the methyl tetrahydrophthalic anhydride can be 20, 25, 30, 35, 40, 45, 50 parts by weight, etc., based on 100 parts by weight of the diglycidyl ether-terminated liquid polythioether prepolymer.

[0010] Specifically, the ethylene glycol diglycidyl ether can be 2, 5, 10, 15, 20 parts by weight, etc., based on 100 parts by weight of the diglycidyl ether-terminated liquid polythioether prepolymer.

[0011] Specifically, the catalyst can be 0.5, 1, 1.5, 2 parts by weight, etc., based on 100 parts by weight of the diglycidyl ether-terminated liquid polythioether prepolymer.

[0012] Specifically, the heat-conducting filler can be 20, 30, 40, 50, 60, 70, 80, 90, 100 parts by weight, etc. based on 100 parts by weight of the liquid polythioether prepolymer capped with diglycidyl ether.

[0013] The heat-conducting filler is selected from at least one of graphite, carbon nanotube whiskers, and carbon fibers.

[0014] The heat-conducting filler has a particle size of 50 nm to 600 μm.

[0015] The catalyst is 2,4,6-tris(dimethylaminomethyl)phenol.

[0016] The heat-conducting filler is orderly arranged in any direction relative to the thickness of the thermal interface material.

[0017] Various types of additives commonly used in the art can also be added to the thermal interface material as needed.

[0018] Under the action of the catalyst, the methyl tetrahydrophthalic anhydride can promote the ring opening of the epoxy groups in the liquid polythioether prepolymer capped with diglycidyl ether and crosslinking, and in order to improve the toughness and elasticity of the epoxy group crosslinking product, the ethylene glycol diglycidyl ether is added to increase the content and reactivity of the epoxy groups in the reactants.

[0019] The second object of the present application is to provide a preparation method of the thermal interface material, which comprises hot pressing and stack welding of raw materials including the liquid polythioether prepolymer capped with diglycidyl ether, the methyl tetrahydrophthalic anhydride, the ethylene glycol diglycidyl ether, the catalyst, and the heat-conducting filler.

[0020] Preferably, the preparation method comprises the following steps:

[0021] (1) uniformly mixing raw materials including the liquid polythioether prepolymer capped with diglycidyl ether, the methyl tetrahydrophthalic anhydride, the ethylene glycol diglycidyl ether, the catalyst, and the heat-conducting filler to obtain a premix;

[0022] (2) hot pressing the premix at high temperature to prepare a composite material film;

[0023] (3) stack welding the composite material film to obtain a composite material block;

[0024] (4) cutting the composite material block.

[0025] In the step (2), the temperature for high-temperature hot pressing is 100-170℃, for example, it can be 100℃, 120℃, 150℃, 170℃, etc.

[0026] The temperature for high-temperature hot pressing is 100-170℃, for example, it can be 100℃, 120℃, 150℃, 170℃, etc.

[0027] The time of high-temperature hot pressing is 0.5-2h;

[0028] The thickness of the composite film is 0.08-2mm, for example, 0.08mm, 0.1mm, 0.5mm, 1mm, 1.5mm, 2mm, etc.

[0029] In the step (3):

[0030] The temperature of welding is 100-150℃, for example, 100℃, 120℃, 150℃, etc.

[0031] The thickness of the composite block is greater than or equal to 4cm.

[0032] The key of the novel TIM in the application is that liquid polythioether prepolymer (EPS) terminated by diglycidyl ether is used as a base material, the EPS mixture is obtained by stirring uniformly with methyl tetrahydrophthalic anhydride and ethylene glycol diglycidyl ether (EDGE) and 2,4,6-tris(dimethylaminomethyl) phenol as a catalyst; the mixture is heated and cured at 100-170℃ under normal pressure in a vacuum drying box for 0.5-2h to obtain a high-flexibility EPS glass-like matrix.

[0033] The beneficial effects of the application are:

[0034] (1) The EPS prepared by the application is used as a matrix of TIM, has good flexibility, and the EPS matrix has excellent self-healing performance and good adhesion.

[0035] (2) The TIM of the application is oriented by hot pressing, and the TIM of the application can be prepared into a glass-like TIM with vertically arranged heat-conducting fillers by using the "stack-welding method" and changing the orientation direction of the heat-conducting fillers, and the TIM has extremely high thermal conductivity in the vertical direction.

[0036] (3) Different from the physical flexibility of the traditional heat-conducting pad, the TIM of the glass-like body of the application has spontaneous contact behavior on the surface of the substrate under the joint driving of stress relaxation and high surface free energy. Therefore, the TIM of the glass-like body has low R c。 BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 (a) is a typical stress-strain curve of the EPS glass-like body with different crosslinking degrees in examples 3, 4 and 5; Figure 1 (b) is the Young's modulus of the EPS glass-like body with different crosslinking degrees in examples 3, 4 and 5.

[0038] Figure 2 (a) is an optical microscope image of the self-healing phenomenon of EV-1 in example 3 at 60℃; Figure 2(b) is a typical stress-strain curve for the original and healed samples of the EPS-based glass of Examples 3, 4, 5; Figure 2 (c) is the healing efficiency for the EPS-based glass of Examples 3, 4, 5.

[0039] Figure 3 (a) is the adhesive shear strength between EV-1 and different substrates of Example 3; Figure 3 (b) is a picture of the lap shear test between EV-1 and different substrates of Example 3.

[0040] Figure 4 (a) is the kappa of the VAGC of Examples 1, 2, 4 with different size graphite ⊥ and kappa ∥ and its kappa ⊥ / kappa ∥ ; Figure 4 (b) is the kappa ⊥ of 600 pm graphite composites with different filler distribution.

[0041] Figure 5 is the kappa ⊥ of the VAGC of Example 4 compared to previously reported materials.

[0042] Figure 6 (a) is the R c of the TIM of Example 4 under 1 psi pressure; Figure 6 (b) is the R t of the TIM under 1 psi pressure. DETAILED DESCRIPTION

[0043] It is necessary to point out that the following examples are only used to further illustrate the present application and should not be understood as limiting the scope of the present application. Some non-essential improvements and adjustments to the present application made by those skilled in the art based on the content of the present application are still within the scope of the present application.

[0044] In addition, various embodiments of the present application can also be combined arbitrarily, as long as they do not deviate from the idea of the present application, and the technical solutions thus formed are part of the original disclosure of the present specification and also fall within the scope of the present application.

[0045] The raw materials used in the examples and comparative examples, if not specifically limited, are disclosed in the prior art, for example, can be directly purchased or prepared according to the preparation method disclosed in the prior art.

[0046] According to a preferred embodiment of the present application, the method for preparing the thermal interface material comprises the following steps:

[0047] ① EPS matrix, methyltetrahydrophthalic anhydride, ethylene glycol diglycidyl ether, 2,4,6-tris(dimethylaminomethyl)phenol catalyst, and thermally conductive filler are mixed uniformly using common polymer mixing methods to obtain a TIM premix; ② The premix is ​​hot-pressed at 100–170℃ to prepare parallel-aligned graphite composite materials with a thickness of 0.08–2 mm; ③ After stacking the graphite composite film to a certain thickness (≥4 cm), the stacked film is pressed tightly with two steel plates with positioning holes at the top and bottom, and fixed with bolts. The fixed stacked film is welded in a drying oven at a welding temperature of 100–150℃ for 0.5–2 hours to obtain a complete composite material block; ④ The block material is longitudinally cut in a specific direction to obtain vertically oriented TIM (VAGC), where the thickness of the TIM can be adjusted according to the actual situation.

[0048] The formula consists of 100 parts EPS matrix, 20-50 parts methyltetrahydrophthalic anhydride, 2-20 parts ethylene glycol diglycidyl ether, 0.5-2 parts 2,4,6-tris(dimethylaminomethyl)phenol, and 20-100 parts of one or more of graphite (75-600 μm), carbon fiber (200 μm), and whisker carbon nanotubes (75 nm) with different particle sizes.

[0049] In the following examples, the thickness of the TIM is 2 mm.

[0050] Example 1

[0051] 100 parts EPS rubber, 40 parts methyltetrahydrophthalic anhydride, 2 parts EDGE, 0.5 parts 2,4,6-tris(dimethylaminomethyl)phenol, and 50 parts graphite with a particle size of 75 μm were uniformly mixed in a non-invasive material homogenizer. The mixture was then hot-pressed at 100°C for 2 hours to obtain a 0.1 mm thick film. The films were stacked and welded at 120°C to form a complete block. The block material was cut into TIM of the required thickness, with the cutting direction perpendicular to the orientation direction of the two-dimensional filler. The thermal conductivity of the prepared TIM in the vertical direction was 16.9 W / mK.

[0052] Example 2

[0053] 100 parts of EPS rubber, 40 parts of methyl tetrahydrophthalic anhydride, 5 parts of EDGE, 0.5 parts of 2,4,6-tris(dimethylaminomethyl) phenol, 50 parts of graphite with a particle size of 200 μm were mixed uniformly in a non-intrusive material homogenizer. Then it was hot-pressed at 140°C for 0.5h to obtain a 0.1mm thick film. The film was stacked and welded at 120°C to form a complete block. The block material was cut into TIMs of the required thickness, and the cutting direction was perpendicular to the orientation direction of the two-dimensional filler. The TIM prepared has a thermal conductivity of 17.8 W / mK in the vertical direction.

[0054] Example 3

[0055] 100 parts of EPS rubber, 40 parts of methyl tetrahydrophthalic anhydride, 5 parts of EDGE, 1 part of 2,4,6-tris(dimethylaminomethyl) phenol, 50 parts of graphite with a particle size of 600 μm were mixed uniformly in a non-intrusive material homogenizer. Then it was hot-pressed at 100°C for 1h to obtain a 0.1mm thick film. The film was stacked and welded at 120°C to form a complete block. The block material was cut into TIMs of the required thickness, and the cutting direction was perpendicular to the orientation direction of the two-dimensional filler. The TIM prepared has a thermal conductivity of 21 W / mK in the vertical direction.

[0056] 100 parts of EPS rubber, 40 parts of methyl tetrahydrophthalic anhydride, 5 parts of EDGE, 1 part of 2,4,6-tris(dimethylaminomethyl) phenol were mixed uniformly in a non-intrusive material homogenizer. Then it was hot-pressed at 100°C for 1h to obtain an EPS glass body (EV-1).

[0057] Example 4

[0058] 100 parts of EPS rubber, 40 parts of methyl tetrahydrophthalic anhydride, 10 parts of EDGE, 1 part of 2,4,6-tris(dimethylaminomethyl) phenol, 50 parts of graphite with a particle size of 600 μm were mixed uniformly in a non-intrusive material homogenizer. Then it was hot-pressed at 100°C for 1h to obtain a 0.1mm thick film. The film was stacked and welded at 120°C to form a complete block. The block material was cut into TIMs of the required thickness, and the cutting direction was perpendicular to the orientation direction of the two-dimensional filler, to obtain VAGC. The TIM prepared has a thermal conductivity of 25 W / mK in the vertical direction.

[0059] 100 parts of EPS rubber, 40 parts of methyl tetrahydrophthalic anhydride, 10 parts of EDGE, 1 part of 2,4,6-tris(dimethylaminomethyl) phenol were mixed uniformly in a non-intrusive material homogenizer. Then it was hot-pressed at 100°C for 1h to obtain an EPS glass body (EV-2).

[0060] Example 5

[0061] 100 parts of EPS rubber, 40 parts of methyltetrahydrophthalic anhydride, 15 parts of EDGE, 1 part of 2,4,6-tris(dimethylaminomethyl)phenol, 50 parts of graphite with a particle size of 600 μm were mixed uniformly in a non-intrusive material homogenizer. Then it was hot-pressed at 100°C for 1 h to obtain a 0.1 mm thick film. The film was stacked and welded at 120°C to form a complete block. The block material was cut into TIMs of the required thickness, and the cutting direction was perpendicular to the orientation direction of the two-dimensional filler. The TIM prepared had a thermal conductivity of 20 W / mK in the vertical direction.

[0062] 100 parts of EPS rubber, 40 parts of methyltetrahydrophthalic anhydride, 15 parts of EDGE, 1 part of 2,4,6-tris(dimethylaminomethyl)phenol were mixed uniformly in a non-intrusive material homogenizer. Then it was hot-pressed at 100°C for 1 h to obtain an EPS vitreous body (EV-3).

[0063] Example 6

[0064] 100 parts of EPS rubber, 40 parts of methyltetrahydrophthalic anhydride, 10 parts of EDGE, 1 part of 2,4,6-tris(dimethylaminomethyl)phenol, 30 parts of graphite with a particle size of 600 μm were mixed uniformly in a non-intrusive material homogenizer. Then it was hot-pressed at 120°C for 1 h to obtain a 0.1 mm thick film. The film was stacked and welded at 120°C to form a complete block. The block material was cut into TIMs of the required thickness, and the cutting direction was perpendicular to the orientation direction of the two-dimensional filler. The TIM prepared had a thermal conductivity of 15 W / mK in the vertical direction.

[0065] Example 7

[0066] 100 parts of EPS rubber, 40 parts of methyltetrahydrophthalic anhydride, 15 parts of EDGE, 2 parts of 2,4,6-tris(dimethylaminomethyl)phenol, 40 parts of graphite with a particle size of 600 μm were mixed uniformly in a non-intrusive material homogenizer. Then it was hot-pressed at 130°C for 0.5 h to obtain a 0.1 mm thick film. The film was stacked and welded at 120°C to form a complete block. The block material was cut into TIMs of the required thickness, and the cutting direction was perpendicular to the orientation direction of the two-dimensional filler. The TIM prepared had a thermal conductivity of 19 W / mK in the vertical direction.

[0067] Comparative Example 1

[0068] The coefficient of thermal conductivity in the vertical direction is 5 W / mK using Tflex 740 of Laird Technologies Company.

[0069] Comparative Example 2

[0070] 100 parts of EPS rubber, 40 parts of methyl tetrahydrophthalic anhydride, 10 parts of EDGE, 1 part of 2,4,6-tris(dimethylaminomethyl) phenol, and 50 parts of graphite with a particle size of 600 μm were uniformly mixed in a non-intervention material homogenizer. Then, it was hot-pressed at 120°C for 1h to obtain a 2mm film, which is a randomly distributed graphite composite (RAGC). The prepared TIM has a coefficient of thermal conductivity in the vertical direction of 11.1 W / mK.

[0071] According to the drawings of the present application, it can be seen that:

[0072] (1) The present application prepares a matrix of EPS used as a TIM, which has good flexibility and increases with the decrease of the amount of EDGE Figure 1 ). Among them, EV-1, EV-2, EV-3 correspond to Examples 3, 4, 5 respectively. Figure 2 From (a), it can be observed that the self-healing phenomenon caused by the dynamic network of the EPS matrix at 60°C, the scratches on the sample completely disappear after 60min, and the EPS matrix has excellent self-healing performance. Figure 2 (b) is the stress-strain curve of the original sample and the healed sample, and the ratio of the tensile strength of the two is calculated, Figure 2 (c) it can be seen that EV-1 has the highest tensile strength recovery rate, reaching 99.9%. Figure 3 The lap shear test of the EPS matrix on different substrates was carried out, and the adhesion of the EPS matrix was evaluated by its shear strength, and it was found that the EPS matrix has good adhesion.

[0073] (2) The composite material is oriented by hot pressing, and the graphite is oriented in the vertical direction by "stack-welding method", and a glass-like TIM with vertically arranged graphite is prepared, which has very high coefficient of thermal conductivity in the vertical direction. Among all the reported graphite composites, the κ⊥ of VAGC is very outstanding, especially with less filler and the EPS matrix itself has a lower coefficient of thermal conductivity (0.12 W·m -1 ·K -1 ).

[0074] The coefficient of thermal conductivity of graphite is anisotropic, its κ ⊥ (vertical thermal conductivity) is different from the excellent κ ∥ (parallel thermal conductivity), and its κ⊥ is only 2.0 W·m -1 ·K -1This also leads to a significant anisotropy in thermal conductivity for VAGC (Example 4) compared to RAGC (Comparative Example 2) and PAGC (Example 4, 0.1 mm thick film directly stacked to 2 mm), with K1= 25.0 W-m -1 ·K -1 , which is much higher than RAGC and PAGC. Figure 4 b)

[0075] (3) Unlike the physical flexibility of traditional thermal pads, the glassy composite material has a spontaneous contact behavior on the substrate surface under the joint driving of stress relaxation and high surface free energy. The EPS glassy TIM also has a temperature-dependent R c ( Figure 6 ) at 1 psi low pressure. As the temperature rises from 30°C to 85°C, the R c of RAGC (Comparative Example 2) and VAGC (Example 4) drops by more than 40%, only 131.4 mm 2 ·W·K -1 and 165.9 mm 2 ·W·K -1 . While the Rcof the commercially available silicone rubber TIM (Tflex 740) is stable at around 880.0 mm 2 ·W·K -1 in this temperature range. Compared with Tflex 740, the R c of the EPS glassy TIM at 85°C drops by more than 81.1%.

Claims

1. A thermally conductive interface material based on elastomer-like glass, prepared by hot-pressing and stack welding of raw materials comprising a liquid polythioether prepolymer capped with diglycidyl ether, methyltetrahydrophthalic anhydride, ethylene glycol diglycidyl ether, a catalyst and a thermally conductive filler; in which, based on 100 parts by weight of the liquid polythioether prepolymer capped with diglycidyl ether, the methyltetrahydrophthalic anhydride is 20-50 parts by weight, the ethylene glycol diglycidyl ether is 2-20 parts by weight, the catalyst is 0.5-2 parts by weight, and the thermally conductive filler is 20-100 parts by weight. 2.The thermally conductive interface material of claim 1, wherein: in which, based on 100 parts by weight of the liquid polythioether prepolymer capped with diglycidyl ether, the methyltetrahydrophthalic anhydride is 30-40 parts by weight, the ethylene glycol diglycidyl ether is 10-15 parts by weight, the catalyst is 1-1.5 parts by weight, and the thermally conductive filler is 60-80 parts by weight. 3.The thermally conductive interface material of claim 1, wherein: the thermally conductive filler is selected from at least one of graphite, carbon nanotube whiskers, and carbon fibers; and / or, the thermally conductive filler has a particle size of 50 nm-600 μm. 4.The thermally conductive interface material of claim 1, wherein: the catalyst is 2,4,6-tris(dimethylaminomethyl)phenol. 5.The thermally conductive interface material of claim 1, wherein: the thermally conductive filler is orderly arranged in any direction relative to the thickness of the thermally conductive interface material. 6.A method for preparing the thermally conductive interface material of any one of claims 1-5, comprising hot-pressing and stack welding of raw materials comprising a liquid polythioether prepolymer capped with diglycidyl ether, methyltetrahydrophthalic anhydride, ethylene glycol diglycidyl ether, a catalyst and a thermally conductive filler. comprising the following steps: (1) mixing the raw materials comprising a liquid polythioether prepolymer capped with diglycidyl ether, methyltetrahydrophthalic anhydride, ethylene glycol diglycidyl ether, a catalyst and a thermally conductive filler to obtain a premix; (2) hot-pressing the premix at high temperature to prepare a composite film; (3) stack welding the composite film to obtain a composite block; (4) cutting the composite block.

7. The method of claim 6, wherein in step (2): the hot-pressing temperature is 100-170 ℃; and / or, the hot-pressing time is 0.5-2 h; and / or, the thickness of the composite film is 0.08-2 mm. in step (3): the welding temperature is 100-150 ℃; and / or, the thickness of the composite block is ≥ 4 cm. ​ ​ ​ 8. The method of claim 7, wherein ​ ​ ​ 9. The method of claim 7, wherein ​ ​

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