A method for preparing high-filled low-modulus stretchable thermal interface material based on physical loose entanglement

Abstract

A method for preparing high-filled, low-modulus stretchable thermal interface materials based on physical loose entanglement belongs to the field of thermal interface thermal conductive material preparation. The method involves: preparing polyurethane acrylate using isophorone diisocyanate, polytetrahydrofuran-2000, and hydroxyethyl acrylate; drying to remove the solvent used in the reaction process; weighing 10g of polyurethane acrylate, 1.21-3.63g of hydroxyethyl acrylate, and 2.136-5.20g of pentaerythritol tetrakis(3-mercaptopropionic acid); adding a mixture of 13.35-18.83g of polypropylene glycol 400 and polypropylene glycol 3000; then adding 106.8-150.64g of spherical alumina thermally conductive particles; mixing thoroughly; adding 0.03g of catalyst; pouring into a mold; and allowing to cure at room temperature. This invention introduces internal dispersion media of different molecular weights into the thermal interface material to adjust the physical cross-linking and entanglement of the thermal interface material, thereby preparing a stretchable thermal interface material that balances high thermal conductivity particle filling amount and low modulus flexibility. Under a high load of 80% alumina, it achieves a high elongation at break of 694% and a low Young's modulus of 72.6 kPa.

Description

Technical Field

[0001] This invention belongs to the field of thermal interface thermal conductive material preparation, specifically relating to a method for preparing high-filling, low-modulus stretchable thermal interface material based on physical loose entanglement. Background Technology

[0002] Typically, thermal interface materials are elastomeric composite materials composed of an elastomeric matrix and thermally conductive particles. They are used to fill the space between a radiator and a heat-generating device to reduce contact thermal resistance.

[0003] To ensure the normal operation of the heating element, the thermal interface material used must have high thermal conductivity to meet the requirement of quickly transferring heat from the heating element to the heat sink.

[0004] However, in the actual application scenarios of thermal interface materials, during the heating and cooling process of chips, thermal interface materials will generate thermal stress and deformation due to the different coefficients of thermal expansion. In order to avoid uneven surfaces between the chip and the heat sink, and to avoid leaving thermal insulation gaps in rigid contact, the expected requirements are put forward for the low modulus and high ductility of the thermal interface.

[0005] To achieve higher thermal conductivity, researchers often add ultra-high amounts of thermally conductive fillers to the elastomer matrix. This creates thermal pathways between particles, improving the thermal conductivity of the interface material. Studies have shown that the thermal conductivity of interface materials increases exponentially with the amount of thermally conductive particles added; that is, the more filler added and the higher the filler density per unit volume, the more exponentially the thermal conductivity increases, and the significantly lower the contact thermal resistance. Therefore, to achieve high thermal conductivity, interface materials often require ultra-high amounts of thermally conductive particles. However, increasing the filler inevitably leads to an increase in the Young's modulus. Thus, high thermal conductivity and good flexibility are generally mutually exclusive. However, to meet the increasingly diverse heat dissipation requirements of today's electronic devices, a balance must be found between the flexibility and thermal conductivity of interface materials. Therefore, the seemingly contradictory coexistence of low modulus, high ductility, and high thermally conductive particle content remains a continuing challenge for existing interface materials.

[0006] Previous studies have demonstrated that, despite their low content, polymer matrices play a decisive role in the mechanical properties of thermal interface materials. Research has shown that entanglement within the polymer acts as a slip chain, allowing forces to be transmitted along the chain to many other chains. Through the synergistic effect of crosslinking and entanglement, excellent elasticity and stretchability of the elastomer can be achieved. Therefore, controlling the appropriate degree of physical entanglement in thermal interface materials to ensure their excellent stretchability is undoubtedly a promising direction. Summary of the Invention

[0007] The purpose of this invention is to resolve the contradiction between low modulus and high ductility and high thermal conductivity particle filling amount, and to provide a method for preparing high-filling low-modulus stretchable thermal interface material based on physical loose entanglement.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing high-filled, low-modulus stretchable thermal interface materials based on physical loose entanglement, the method comprising:

[0010] Step 1: Dissolve isophorone diisocyanate in an organic solvent to obtain solution A; dissolve polytetrahydrofuran-2000 in an organic solvent to obtain solution B; dissolve hydroxyethyl acrylate in an organic solvent to obtain solution C; under a nitrogen atmosphere, heat at 75°C with magnetic stirring, and add solution A dropwise to solution B over 10 minutes. The reaction is allowed to proceed for 4 hours. During this process, the hydroxyl groups in the diol (polytetrahydrofuran-2000) react with the isocyanate functional groups of the diisocyanate (isophorone diisocyanate) to produce... An isocyanate-terminated polyurethane prepolymer was formed. Under a nitrogen atmosphere, the mixture was heated at 75°C with magnetic stirring. Solution C was added dropwise to the aforementioned solution within 10 minutes, and the reaction was allowed to proceed for 2 hours. During this process, the hydroxyl groups in hydroxyethyl acrylate reacted with the isocyanate functional groups in the prepolymer, thus end-capping the prepolymer and yielding acrylate-terminated polyurethane acrylate. The organic solvent served to reduce viscosity and prevent excessively high concentrations from causing a violent reaction, but it did not participate in the reaction. Therefore, there were no requirements regarding the concentrations of solutions A, B, and C.

[0011] Step 2: Pour out the reaction solution obtained in Step 1, dry it in a vacuum oven at 80°C for 24 hours, and then dry it in a forced-air drying oven at 80°C for 24 hours to obtain polyurethane acrylate (PUA); the two drying steps are to remove the solvent completely.

[0012] Step 3: Weigh 10g of polyurethane acrylate (PUA), 1.21-3.63g of hydroxyethyl acrylate (HEA), and 2.136-5.20g of pentaerythritol tetrakis(3-mercaptopropionic acid) ester (PETMP). Add a mixture of 13.35-18.83g of polypropylene glycol 400 (PPG-400) and polypropylene glycol 3000 (PPG3000). Then add 106.8-150.64g of spherical alumina thermally conductive particles. After mixing evenly, add 0.03g of catalyst, pour into a mold, and allow to cure at room temperature. Step 1 synthesized the polymer backbone. Based on this, the hydroxyethyl acrylate in Step 3 forms a pendant side chain, and PETMP, a tetrafunctional thiol curing agent, undergoes a thiol-olefin click reaction with the double bond.

[0013] Furthermore, in step one, the organic solvent is one or more of tetrahydrofuran (THF), dioxane, pyridine, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0014] Furthermore, in step one, the molar ratio of isophorone diisocyanate, polytetrahydrofuran-2000 and hydroxyethyl acrylate is 20:10:20.

[0015] Furthermore, in step three, the mass ratio of polypropylene glycol 3000 (PPG3000) to polypropylene glycol 400 (PPG-400) is 3:0 to 3.

[0016] Furthermore, in step three, the spherical alumina thermally conductive particles contain 50μm spherical alumina with a proportion of 52.5wt%, 20μm spherical alumina with a proportion of 13.5wt%, and 10μm spherical alumina with a proportion of 34wt%.

[0017] Further, in step three, the catalyst is one or more of 1,8-diazabicyclo[5.4.0]undec-7-ene DBU, triethylamine, tetramethylguanidine, hexahydropyridine, tetrahydropyridine, and triethylenediamine.

[0018] The advantages of this invention over the prior art are as follows:

[0019] (1) Under the condition of ensuring the same filler content, the present invention uses small-sized particles to fill the gaps between large-sized particles, making the fillers pack more tightly, thereby reducing the thermal resistance between the fillers and improving the thermal conductivity of the thermal interface material.

[0020] (2) By introducing free macromolecular chains and free small molecules into the polymer matrix, the physical entanglement and cross-linking of the thermal interface material are adjusted. Tensile strength and elasticity are achieved by lengthening the free polymer chains to form appropriate entanglement. Loose entanglement transfers the applied force to a large area, while rigid cross-linking prevents the entanglement from unraveling. Specifically, by adjusting the ratio of polypropylene glycol 400 and polypropylene glycol 3000—two internal dispersion media with different molecular weights—in the thermal interface material, loose physical entanglement is achieved, solving the flexibility problem of the thermal interface material under high thermal conductivity particle filling, thereby realizing the coupling relationship between high filling amount and low modulus high ductility.

[0021] (3) This invention introduces internal dispersion media of different molecular weights into the thermal interface material to adjust the physical cross-linking and entanglement of the thermal interface material, and prepares a soft and stretchable thermal interface material that takes into account both high thermal conductivity particle filling amount and low modulus, flexibility and extensibility. The final prepared thermal interface material achieves a high elongation at break of 694% and a low Young's modulus of 72.6kPa under a high load of 80% alumina. Attached Figure Description

[0022] Figure 1 A schematic diagram of the synthesis scheme for the polymer backbone;

[0023] Figure 2 The graph shows the Fourier transform infrared (FTIR) test data before and after the polymer backbone is cured.

[0024] Figure 3 Particle size distribution of spherical alumina with different particle sizes;

[0025] Figure 4 Tensile curves of thermal interface materials obtained with different mass ratios of polypropylene glycol 3000 / polypropylene glycol 400;

[0026] Figure 5 A comparison chart of the tensile modulus of thermal interface materials obtained by different mass ratios of polypropylene glycol 3000 / polypropylene glycol 400;

[0027] Figure 6 The graph shows the fitting analysis of chemical crosslinking modulus and physical entanglement modulus when the mass ratio of polypropylene glycol 3000 / polypropylene glycol 400 is 1:0.

[0028] Figure 7 The graph shows the fitting analysis of chemical crosslinking modulus and physical entanglement modulus when the mass ratio of polypropylene glycol 3000 / polypropylene glycol 400 is 3:1.

[0029] Figure 8 The graph shows the fitting analysis of chemical crosslinking modulus and physical entanglement modulus when the mass ratio of polypropylene glycol 3000 / polypropylene glycol 400 is 1:1.

[0030] Figure 9 A comparison of chemical crosslinking modulus and physical entanglement modulus for different mass ratios of polypropylene glycol 3000 / polypropylene glycol 400;

[0031] Figure 10 An illustration of the effect of using thermal interface materials for heat dissipation of 1W LED beads;

[0032] Figure 11 This is a schematic diagram of the loose entanglement mechanism of polymer networks in thermal interface materials. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to the embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0034] The formulation of thermally conductive particles: Considering that smaller particle size thermally conductive fillers improve toughness but exhibit weaker thermal conductivity, while larger particle size thermally conductive fillers impair toughness but exhibit higher thermal conductivity, three types of spherical alumina powder with different particle sizes were selected. Their particle size distribution was characterized using a laser powder particle size analyzer. Figure 3 As shown, the particle size distributions of the three different alumina powders are all unimodal, with no overlap in the main particle size distributions. The optimal ratio of the three particle sizes was obtained by calculating the particle size distribution using the Dinger-Funk equation: 50μm spherical alumina accounted for 52.5wt%, 20μm spherical alumina accounted for 13.5wt%, and 10μm spherical alumina accounted for 34wt%. Under this particle size distribution, the three particles are closely packed, achieving the most compact arrangement and thus providing a better thermal conductivity pathway.

[0035] Example 1:

[0036] Synthesis of polymer backbone polyurethane acrylate (PUA): The synthetic route is as follows Figure 1 As shown. First, 20 mmol of isophorone diisocyanate was weighed and dissolved in 80 ml of N,N-dimethylformamide. Under a nitrogen atmosphere, the mixture was heated at 75 °C with magnetic stirring. Over 10 min, 10 mmol of polytetrahydrofuran ether diol dissolved in 20 ml of N,N-dimethylformamide was added dropwise, and the reaction was allowed to proceed for 4 h. Subsequently, under a nitrogen atmosphere, under a heating condition of 75 °C with magnetic stirring, 20 mmol of hydroxyethyl acrylate dissolved in 20 ml of N,N-dimethylformamide was added dropwise over 10 min, and the reaction was allowed to proceed for 2 h.

[0037] Post-processing: Pour out the reaction solution and dry it in a vacuum oven at 80°C for 24 hours, then dry it in a forced-air drying oven at 80°C for 24 hours to obtain the product polyurethane acrylate (PUA).

[0038] Preparation of multi-scale composite thermally conductive particles: Take 52.5g of 50μm spherical alumina, 13.5g of 20μm spherical alumina, and 34g of 10μm spherical alumina, mix them thoroughly and evenly to obtain multi-scale composite spherical alumina powder.

[0039] Preparation of thermal interface material: Weigh 10g PUA, 2.66g hydroxyethyl acrylate, 3.98g pentaerythritol tetrakis(3-mercaptopropionic acid) ester, add 16.64g polypropylene glycol 3000, then weigh out multi-scale composite thermally conductive particles accounting for 80% of the total mass of the system, mix evenly, add 0.03g catalyst DBU, pour into a silicone mold and let it cure at room temperature.

[0040] The prepared thermal interface material was subjected to mechanical tensile testing, such as... Figure 4 As shown, for Figure 4The tensile modulus is obtained by calculating the obtained data, such as Figure 5 As shown, for Figure 4 The obtained data is used for fitting calculations, such as Figure 6 As shown, the physical entanglement modulus / chemical crosslinking modulus is obtained, as follows: Figure 9 As shown in the figure. Analysis shows that when the ratio of free macromolecules to free small molecules is 3:0, that is, relying solely on the strong physical entanglement brought about by the free macromolecules, the prepared thermal interface material has a large tensile modulus and a low elongation at break.

[0041] Through Fourier transform infrared testing, such as Figure 2 As shown in the infrared spectrum, no peak was observed at 2200 cm⁻¹. -1 The characteristic absorption peak of isocyanate at 3300 cm⁻¹ is due to the reaction of -NCO and -OH to form an urethane bond. -1 The appearance of a new absorption peak nearby indicates the successful synthesis of polyurethane acrylate (PUA). Furthermore, the peak at 1640 cm⁻¹ in the infrared spectrum confirms this. -1 The disappearance of the absorption peak in the vicinity indicates that the carbon-carbon double bond has been successfully reacted.

[0042] Example 2:

[0043] The difference between this embodiment and Embodiment 1 is that the polypropylene glycol 3000 added in Embodiment 1 is replaced with a mixture of polypropylene glycol 3000 and polypropylene glycol 400, while the total mass remains the same, wherein the mass ratio of polypropylene glycol 3000 to polypropylene glycol 400 is 3:1.

[0044] The prepared thermal interface material was subjected to mechanical tensile testing, such as... Figure 4 As shown, for Figure 4 The tensile modulus is obtained by calculating the obtained data, such as Figure 5 As shown, for Figure 4 The obtained data is used for fitting calculations, such as Figure 7 As shown, the physical entanglement modulus / chemical crosslinking modulus is obtained, as follows: Figure 9 As shown in the analysis, compared to Experiment 1, Experiment 2 introduces a non-reactive free small molecule dispersion medium to reduce the adverse effects of rigid physical entanglement on tensile properties, improve polymer chain fluidity, and thus improve tensile properties, thereby reducing the physical entanglement modulus of the thermal interface material while keeping the chemical crosslinking modulus essentially unchanged. Polypropylene glycol 3000 acts as a free macromolecule, and polypropylene glycol 400 acts as a free small molecule; together they create a loose physical entanglement to facilitate chain segment slippage during material stretching. The mechanism of action is as follows: Figure 11 As shown.

[0045] Example 3:

[0046] The difference between this embodiment and Embodiment 1 is that the polypropylene glycol 3000 added in Embodiment 1 is replaced with a mixture of polypropylene glycol 3000 and polypropylene glycol 400, while the total mass remains the same, wherein the mass ratio of polypropylene glycol 3000 to polypropylene glycol 400 is 1:1.

[0047] The prepared thermal interface material was subjected to mechanical tensile testing to obtain stress-strain curves, such as... Figure 4 As shown, for Figure 4 The tensile modulus is obtained by calculating the obtained data, such as Figure 5 As shown, for Figure 4 The obtained data is used for fitting calculations, such as Figure 8 As shown, the physical entanglement modulus / chemical crosslinking modulus is obtained, as follows: Figure 9 As shown in the figure. Analysis shows that, compared with Experimental Example 2, Experimental Example 3 introduces more non-reactive free small molecule dispersion media, which significantly reduces the adverse effects of rigid physical entanglement on tensile properties, creates loose physical entanglement, so that chain segments can slip during the material stretching process, improve the fluidity of polymer chains, and thus significantly improve tensile properties. The elongation at break is twice that of Example 1, the tensile modulus and physical entanglement modulus are significantly reduced, while the chemical crosslinking modulus remains basically unchanged, which meets the requirements of high filling and low modulus stretchability.

[0048] The prepared thermal interface material was used for heat dissipation testing of a 1W LED chip, such as... Figure 10 As shown, by comparing with materials without thermal interfaces, the analysis shows that the prepared thermal interface material has excellent heat dissipation capabilities.

Claims

1. A method for preparing high-filled, low-modulus stretchable thermal interface materials based on physical loose entanglement, characterized in that: The method is as follows: Step 1: Dissolve isophorone diisocyanate in an organic solvent to obtain solution A; dissolve polytetrahydrofuran-2000 in an organic solvent to obtain solution B; dissolve hydroxyethyl acrylate in an organic solvent to obtain solution C; Under a nitrogen atmosphere, the mixture was heated at 75°C with magnetic stirring. Solution A was added dropwise to solution B within 10 minutes, and the reaction was carried out for 4 hours. Under a nitrogen atmosphere, the mixture was heated at 75°C with magnetic stirring. Solution C was added dropwise to the aforementioned solution within 10 minutes, and the reaction was carried out for 2 hours. The molar ratio of isophorone diisocyanate, polytetrahydrofuran-2000, and hydroxyethyl acrylate was 20:10:

20. Step 2: Pour out the reaction solution obtained in Step 1, dry it in a vacuum oven at 80°C for 24 hours, and then dry it in a forced-air drying oven at 80°C for 24 hours to obtain polyurethane acrylate. Step 3: Weigh 10 g of polyurethane acrylate, 1.21~3.63 g of hydroxyethyl acrylate, and 2.136~5.20 g of pentaerythritol tetrakis(3-mercaptopropionic acid). Add 13.35~18.83 g of a mixture of polypropylene glycol 400 (PPG-400) and polypropylene glycol 3000 (PPG3000). Then add 106.8~150.64 g of spherical alumina thermally conductive particles. After mixing evenly, add 0.03 g of catalyst and pour into a mold. Allow to cure at room temperature. The mass ratio of polypropylene glycol 3000 (PPG3000) to polypropylene glycol 400 (PPG-400) is 3:1~3.

2. The method for preparing a high-filling, low-modulus stretchable thermal interface material based on physical loose entanglement according to claim 1, characterized in that: In step one, the organic solvent is one or more of tetrahydrofuran, dioxane, pyridine, N,N-dimethylformamide, and N,N-dimethylacetamide.

3. The method for preparing a high-filling, low-modulus stretchable thermal interface material based on physical loose entanglement according to claim 1, characterized in that: In step three, among the spherical alumina thermally conductive particles, 50 μm spherical alumina accounts for 52.5 wt%, 20 μm spherical alumina accounts for 13.5 wt%, and 10 μm spherical alumina accounts for 34 wt%.

4. The method for preparing a high-filling, low-modulus stretchable thermal interface material based on physical loose entanglement according to claim 1, characterized in that: In step three, the catalyst is one or more of 1,8-diazabicyclo[5.4.0]undec-7-ene, triethylamine, tetramethylguanidine, hexahydropyridine, tetrahydropyridine, and triethylenediamine.

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