Epoxy resin heat conductive composite material and preparation method thereof

Abstract

The present application relates to a kind of epoxy resin heat conducting composite material and its preparation method, belong to heat conducting composite material field.The modified boron nitride, polyamide acid and amino-terminated amide acid are built three-dimensional skeleton by ice template method in the present application, after skeleton imidization, epoxy resin is perfused, and the epoxy resin heat conducting composite material is obtained after curing.The skeleton provides a way for phonon transport, reduces the interfacial thermal resistance between skeleton and matrix, and achieves the purpose of improving the thermal conductivity of composite material at low filler load.The epoxy resin heat conducting composite material prepared in the present application improves the interfacial thermal resistance between skeleton and matrix by building continuous boron nitride skeleton in polymer at the same time through covalent bond.

Description

Technical Field

[0001] This invention relates to a method for preparing a thermally conductive composite material, specifically an epoxy resin thermally conductive composite material and its preparation method, belonging to the field of thermally conductive composite materials. Background Technology

[0002] The rapid development of electronic technology has driven electronic products towards greater compactness and higher power density. This has also led to a rise in the heat generated by electronic components, causing a rapid increase in device temperature. High temperatures not only threaten the stability and reliability of electronic products but may also shorten their lifespan and create safety hazards. Therefore, it is necessary to use composite materials with excellent thermal conductivity to effectively dissipate heat from within electronic products, ensuring that the equipment maintains good performance and improves durability while operating at high efficiency.

[0003] Epoxy resin is widely used as a matrix for thermally conductive composite materials due to its advantages such as corrosion resistance, good electrical insulation properties, ease of processing and molding, and high strength. Currently, a common practice is to add highly thermally conductive inorganic fillers to the polymer matrix to improve the polymer's thermal conductivity and thus solve the heat dissipation problem.

[0004] Chinese invention patent CN112175238A discloses a method for preparing a boron nitride nanosheet-carbon nanotube thermally conductive filler and a thermally conductive composite material. This invention modifies hexagonal boron nitride through exfoliation, allowing it to coordinate with metal ions. The resulting carbon nanotubes are tightly connected to a three-dimensional framework structure between the boron nitride nanosheets. An epoxy resin mixture is then infused to form the thermally conductive composite material. This structure reduces phonon scattering and solves the problem of high contact thermal resistance within the framework. However, the preparation method is relatively complex, focusing on solving the interfacial thermal resistance within the framework, without addressing the interfacial thermal resistance between the matrix and the framework.

[0005] Chinese invention patent CN112552648A discloses a three-dimensional ordered and controllable carbon fiber thermally conductive composite material and its preparation method. This invention utilizes the cation-π interaction between an amine-containing imidazole ionic liquid and carbon fibers to reduce the interfacial thermal resistance between carbon fibers and between carbon fibers and the polymer matrix, thereby improving the interfacial bonding force between the carbon fibers and the polymer matrix. Simultaneously, an ice-template method is used to construct a three-dimensional ordered and controllable carbon fiber skeleton, increasing the orientation degree of the carbon fibers and providing a pathway for phonon transport, thus achieving the goal of improving the thermal conductivity of the composite material with low carbon fiber loading. However, this invention only improves the interfacial thermal resistance between the skeleton and the matrix in a non-covalent manner, and its effect on reducing interfacial thermal resistance is limited compared to covalent bond modification. Summary of the Invention

[0006] To address the aforementioned issues, this invention employs amino-terminated ammonium acids. A three-dimensional framework is prepared from an aqueous solution of polyamic acid containing ammonium acids and boron nitride nanosheets using an ice template method. Epoxy resin is then infused into the framework to obtain a thermally conductive epoxy resin composite material, thereby resolving the problem of excessively high thermal resistance at the interface between the epoxy resin matrix and the framework.

[0007] To achieve the above objectives, this invention discloses a method for preparing an epoxy resin thermally conductive composite material, comprising the following steps:

[0008] S1. Hexagonal boron nitride was exfoliated to prepare aminated boron nitride nanosheets;

[0009] S2. Dissolve polyamic acid and amino-terminated amic acid to obtain an aqueous solution of polyamic acid; mix the amino-terminated boron nitride nanosheets and the aqueous solution of polyamic acid evenly to obtain a mixed solution;

[0010] S3. The mixture is prepared into a three-dimensional skeleton by ice template method, and after imidization, epoxy resin is injected and cured to obtain an epoxy resin thermally conductive composite material.

[0011] Preferably, the preparation method of the aminated boron nitride nanosheets in S1 includes the following steps:

[0012] Hexagonal boron nitride powder, modified solution, and milling beads were mixed evenly and then ball-milled under ultrasonic conditions. After the ball milling was completed, the milling beads were removed to obtain a milling slurry. The milling slurry was then centrifuged, washed, and vacuum-dried to obtain aminated boron nitride nanosheets.

[0013] Preferably, the modified solution is a urea solution, and the mass ratio of urea to hexagonal boron nitride powder in the urea solution is (30-100):1.

[0014] Preferably, the mass ratio of the grinding beads to the hexagonal boron nitride powder is (1-2):1.

[0015] The grinding balls are zirconia grinding balls with diameters of 0.15 mm and 0.3 mm, and the mass ratio of zirconia grinding balls with diameters of 0.15 mm and 0.3 mm is (1~2):1.

[0016] The ball milling process takes 18 to 36 hours.

[0017] Preferably, the preparation of the polyamic acid aqueous solution in S2 involves dissolving polyamic acid and amino-terminated amic acid in triethylamine and deionized water to obtain the polyamic acid aqueous solution.

[0018] Preferably, the mass ratio of triethylamine to polyamic acid in S2 is (0.4-1.2):1; the mass ratio of deionized water to polyamic acid is (20-50):1. The mass ratio of amino-terminated ammonium acid to polyamic acid is (0.05-0.20):1.

[0019] Preferably, the mass ratio of the aminated boron nitride nanosheets to polyamic acid in S2 is (0.01-0.2):1.

[0020] Preferably, the freeze-drying time in S3 is 24–48 hours.

[0021] Preferably, the imidization conditions in S3 are: treatment at 150–180°C for 1–3 hours, followed by treatment at 200–250°C for 1–3 hours. The curing conditions for the epoxy resin composite material are: treatment at 60–120°C for 1–3 hours, followed by treatment at 150–180°C for 1–3 hours.

[0022] The present invention also discloses an epoxy resin thermally conductive composite material prepared by the above method.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. Introducing imide into the three-dimensional framework can cause ring-opening reactions with epoxy groups, linking the framework and matrix with covalent bonds. This can reduce phonon scattering and interfacial thermal resistance within the three-dimensional framework, thus contributing to the improvement of the thermal conductivity of the composite material.

[0025] 2. This invention mixes aminated boron nitride nanosheets with an aqueous solution of polyamic acid. Utilizing the dissociation of the carboxyl groups in the amic acid with triethylamine, both the amic acid and polyamic acid can be completely dissolved in water. After the amic acid aqueous solution and the aminated boron nitride nanosheets are uniformly dispersed in water, an aerogel is prepared using the ice-templating method.

[0026] 3. The operation steps of this invention are easy to control, the processing cost is low, and it is expected to achieve industrial production after appropriate processing. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 Process flow diagram for the preparation of epoxy resin thermally conductive composite materials;

[0029] Figure 2The NMR spectrum of the amic acid in Example 1;

[0030] Figure 3 The NMR spectrum of the imide after imidization in Example 1;

[0031] Figure 4 The images are scanning electron microscope (SEM) images of the three-dimensional skeletons prepared in Examples 1 to 4, with a to d corresponding to Examples 1 to 4 respectively. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The amino-terminated ammonium acid of the present invention can be prepared by the following method:

[0034] S1. Under a nitrogen atmosphere, the diamine is dissolved in an organic solvent by magnetic stirring, and dianhydride is added and stirred for 3-12 hours to obtain an amic acid solution; the molar ratio of the diamine to the dianhydride is (5-2):1;

[0035] S2. Pour the solution into a solvent, wash the precipitate with deionized water, and freeze-dry to obtain the ammonium acid powder. The solvent is selected from at least one of water, methanol, and ethanol.

[0036] The synthesis reaction mechanism diagram is as follows:

[0037]

[0038] The polyamic acid of this invention can be prepared by the following method:

[0039] S1. The diamine is dissolved in an organic solvent by mechanical stirring under an ice bath and a flowing nitrogen atmosphere, and dianhydride is added and stirred for 0.5-6 hours to obtain a polyamic acid solution; the molar ratio of the diamine to the dianhydride is 0.8-1.2.

[0040] S2. After coating the polyamic acid film with the polyamic acid solution, place it in deionized water to replace the organic solvent. After drying the polyamic acid film to remove water, the polyamic acid is obtained.

[0041] The organic solvent mentioned above is selected from at least one of N,N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide and dimethyl sulfoxide. Example 1

[0042] A method for preparing an epoxy resin thermally conductive composite material, comprising the following steps:

[0043] (1) The preparation of aminated boron nitride nanosheets includes the following steps:

[0044] S1. Dissolve 48g of urea in 400ml of deionized water and stir until homogeneous to obtain a urea solution; add 0.6g of zirconia grinding beads with a diameter of 0.15mm and 1.2g of hexagonal boron nitride powder with a diameter of 0.3mm to the urea solution, stir until homogeneous, and then place the mixture in an ultrasonic machine for ball milling at an ultrasonic frequency of 60kHz for 36h.

[0045] S2. After ball milling, remove the milling beads to obtain the milling liquid. Centrifuge the milling liquid at 2500 rpm for 10 min, remove the supernatant, and wash with water 3 times to obtain the water-washed product. Dry the water-washed product under vacuum at 70℃ for 24 h to obtain aminated boron nitride nanosheets.

[0046] (2) Add 1g of the synthesized polyamic acid and 0.05g of amino-terminated amic acid to a mixture of 23.52g of deionized water and 0.48g of triethylamine, and stir until completely dissolved. Then add 0.03g of amino-terminated boron nitride nanosheets and stir until homogeneous.

[0047] (3) Pour the mixture into a mold, place the mold on liquid nitrogen, and freeze it directionally from bottom to top for 0.5 h. After freeze-drying in a freeze dryer for 36 h, a three-dimensional skeleton is obtained. The three-dimensional skeleton is imidized. The imidization procedure is 2 h at 180 °C and 1 h at 220 °C. 1.377 g of 4,4'-diaminodiphenylmethane is dissolved in 5 g of E51 type epoxy resin at 60 °C. The solution is then vacuum-injected into the three-dimensional skeleton. After curing at 120 °C for 1 h and then at 180 °C for 3 h, an epoxy resin thermally conductive composite material is obtained.

[0048] The amino-terminated amide acid (a) and the imide (b) synthesized in this embodiment were characterized by NMR, and the results are as follows: Figure 2 and Figure 3 As shown; the three-dimensional skeleton prepared in this embodiment was scanned by electron microscopy, and the results are as follows. Figure 4 As shown in (a). Example 2

[0049] The epoxy resin thermally conductive composite material was prepared using the same method as in Example 1, except that:

[0050] (2) Add 1g of the synthesized polyamic acid and 0.10g of amino-terminated amic acid to a mixture of 23.52g of deionized water and 0.4g of triethylamine, and stir until completely dissolved. Then add 0.03g of amino-terminated boron nitride nanosheets and stir until homogeneous.

[0051] (3) The imidization conditions are 3 hours at 150°C and 3 hours at 200°C. The curing conditions are 3 hours at 60°C and 1 hour at 150°C.

[0052] The three-dimensional skeleton prepared in this embodiment was scanned by electron microscopy, and the results are as follows: Figure 4 As shown in (b). Example 3

[0053] The epoxy resin thermally conductive composite material was prepared using the same method as in Example 1, except that:

[0054] (2) Add 1g of the synthesized polyamic acid and 0.15g of amino-terminated amic acid to a mixture of 23.52g of deionized water and 0.8g of triethylamine, and stir until completely dissolved. Then add 0.03g of amino-terminated boron nitride nanosheets and stir until homogeneous.

[0055] (3) The imidization conditions are 160℃ for 1 hour and 250℃ for 1 hour. The curing conditions are 90℃ for 3 hours and then 150℃ for 3 hours.

[0056] The three-dimensional skeleton prepared in this embodiment was scanned by electron microscopy, and the results are as follows: Figure 4 As shown in (c). Example 4

[0057] The epoxy resin thermally conductive composite material was prepared using the same method as in Example 1, except that:

[0058] (2) Add 1g of the synthesized polyamic acid and 0.20g of amino-terminated amic acid to a mixture of 23.52g of deionized water and 1.2g of triethylamine, and stir until completely dissolved. Then add 0.03g of amino-terminated boron nitride nanosheets and stir until homogeneous.

[0059] The three-dimensional skeleton prepared in this embodiment was scanned by electron microscopy, and the results are as follows: Figure 4 As shown in (d). Example 5

[0060] The epoxy resin thermally conductive composite material was prepared using the same method as in Example 1, except that:

[0061] (2) Add 1g of the synthesized polyamic acid and 0.2g of amino-terminated amic acid to a mixture of 23.52g of deionized water and 0.48g of triethylamine, and stir until completely dissolved. Then add 0.01g of amino-terminated boron nitride nanosheets and stir until homogeneous. Example 6

[0062] The epoxy resin thermally conductive composite material was prepared using the same method as in Example 1, except that:

[0063] Add 1g of the synthesized polyamic acid and 0.20g of amino-terminated amic acid to a mixture of 23.52g of deionized water and 0.48g of triethylamine, and stir until completely dissolved. Then add 0.2g of amino-terminated boron nitride nanosheets and stir until homogeneous. Example 7

[0064] The epoxy resin thermally conductive composite material was prepared using the same method as in Example 1, except that:

[0065] (2) Add 1g of the synthesized polyamic acid and 0.20g of amino-terminated amic acid to a mixture of 20.0g of deionized water and 0.48g of triethylamine, and stir until completely dissolved. Then add 0.03g of amino-terminated boron nitride nanosheets and stir until homogeneous. Example 8

[0066] The epoxy resin thermally conductive composite material was prepared using the same method as in Example 1, except that:

[0067] (2) Add 1g of the synthesized polyamic acid and 0.20g of amino-terminated amic acid to a mixture of 50.0g of deionized water and 0.48g of triethylamine, and stir until completely dissolved. Then add 0.03g of amino-terminated boron nitride nanosheets and stir until homogeneous. Comparative Example 1

[0068] Thermal conductivity of pure epoxy resin samples was tested: 1.377 g of 4,4'-diaminodiphenylmethane was dissolved in 5 g of E51 type epoxy resin at 60℃, and the cured epoxy resin was obtained after being cured at 120℃ for 1 h and 180℃ for 3 h. Comparative Example 2

[0069] The epoxy resin thermally conductive composite material was prepared using the same method as in Example 1, except that:

[0070] (2) Add 1g of polyamic acid to a mixture of 23.52g of deionized water and 0.48g of triethylamine and stir until completely dissolved. Comparative Example 3

[0071] The epoxy resin thermally conductive composite material was prepared using the same method as in Example 1, except that:

[0072] Add 1g of polyamic acid to a mixture of 23.52g of deionized water and 0.48g of triethylamine, and stir until completely dissolved. Then add 0.03g of amino-modified boron nitride nanosheets and stir until homogeneous.

[0073] Table 1 shows the thermal conductivity test results of Examples 1-8 and Comparative Examples 1-3.

[0074]

[0075] Table 1 shows that the thermal conductivity can be increased to 0.85 W / (m·K) with the increase of imide in the skeleton. Example 6 showed a 325% increase in thermal conductivity compared to Comparative Example 1. It can be concluded that constructing a three-dimensional skeleton in epoxy resin to form a continuous thermally conductive pathway, this porous skeleton with a directional structure can effectively improve the thermal conductivity of the composite in the vertical direction. Introducing imide and a small amount of BN into the three-dimensional skeleton allows the imide to undergo a ring-opening reaction with the epoxy groups, covalently linking the skeleton and matrix. BN provides transport pathways, reducing phonon scattering and interfacial thermal resistance within the three-dimensional skeleton, thus contributing to the improvement of the composite material's thermal conductivity.

[0076] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing an epoxy resin thermally conductive composite material, characterized in that, Includes the following steps: S1. Hexagonal boron nitride was exfoliated to prepare aminated boron nitride nanosheets; S2. Dissolve polyamic acid and amino-terminated amic acid to obtain an aqueous solution of polyamic acid, wherein the mass ratio of amino-terminated amic acid to polyamic acid is (0.05~0.20):1; mix the amino-terminated boron nitride nanosheets and the aqueous solution of polyamic acid evenly to obtain a mixed solution, wherein the mass ratio of amino-terminated boron nitride nanosheets to polyamic acid is (0.01~0.2):1; S3. The mixture is prepared into a three-dimensional skeleton by ice template method, and after imidization, epoxy resin is injected and cured to obtain an epoxy resin thermally conductive composite material.

2. The method for preparing the epoxy resin thermally conductive composite material according to claim 1, characterized in that, In S2, polyamic acid and amino-terminated amic acid are dissolved in triethylamine and deionized water to obtain an aqueous solution of polyamic acid, wherein the mass ratio of triethylamine to polyamic acid is (0.4-1.2):1; and the mass ratio of deionized water to polyamic acid is (20-50):

1.

3. The method for preparing the epoxy resin thermally conductive composite material according to claim 1, characterized in that, The imidization conditions in S3 are: treatment at 150–180℃ for 1–3 hours, followed by treatment at 200–250℃ for 1–3 hours.

4. The method for preparing the epoxy resin thermally conductive composite material according to claim 1, characterized in that, The curing conditions for S3 are: treatment at 60–120°C for 1–3 hours, followed by treatment at 150–180°C for 1–3 hours.

5. An epoxy resin thermally conductive composite material prepared by the method according to any one of claims 1-4.

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