CN113788986B - Modified graphite-based functional filler, thermal interface material and preparation method of thermal interface material - Google Patents

Abstract

The invention discloses a modified graphite-based functional filler, a thermal interface material and a preparation method thereof, wherein the modified graphite-based functional filler comprises vermicular expanded graphite, and the surface of the vermicular expanded graphite is provided with a chemical active plating layer; the chemical active coating is used for introducing active groups to improve the polarity of the vermicular expanded graphite; the thermal interface material comprises the modified graphite-based functional filler and liquid rubber; the problem that the application of the conventional thermal interface material is limited because the multiple coupling balance of the flexible characteristic, the heat conduction performance and the electromagnetic shielding effect cannot be achieved is solved.

Description

Modified graphite-based functional filler, thermal interface material and preparation method of thermal interface material

Technical Field

The present disclosure relates to thermal management functional materials, and in particular to a functional filler, a thermal interface material using the functional filler, and a method of making the same.

Background

As 5G mobile communication technology and integrated circuit fabrication technology further develop, modern electronic devices are moving toward high operating frequencies and miniaturization. However, high integration, accompanied by high power density, accelerates the burn-in process of the core electronics and raises a serious problem in the field of thermal management. In addition, complex electromagnetic waves generated by the operation of part of radio frequency chips not only can influence the operation of adjacent electronic modules, but also can cause harm to human health, and because most electromagnetic shielding materials at present achieve the purpose of electromagnetic shielding by absorbing, reflecting and converting electromagnetic waves into heat energy, the electromagnetic shielding materials ignore a large amount of heat accumulation generated in the electromagnetic energy conversion process. Even if the electromagnetic shielding requirements can be met, the large accumulation of converted thermal energy can still cause serious damage to the electronic device. Therefore, the electromagnetic shielding performance is considered, and the thermal management performance of the material is also considered, so that the material for specific application is required to have high thermal conductivity and electromagnetic shielding resistance.

Compared with the traditional metal base electricityMagnetic shielding materials and thermal management materials, polymeric materials have attracted considerable attention due to their processability, light weight, corrosion resistance. However, the low intrinsic thermal conductivity of the polymer (0.1 to 0.5W m ^-1 K ^-1 ) And the low electromagnetic shielding effectiveness (10-20%) still limits the wide application of the electromagnetic shielding material in the field of thermal management and electromagnetic shielding coupling to a great extent.

In the first aspect, the problem of the existing thermal management materials in terms of thermal management is that the assembly thermal resistance caused by the material characteristics during the assembly process of the materials is also a significant factor affecting the actual effect of the materials. In practical application, when the heat sink is in direct contact with the heat source device, a large number of micro-voids are generated due to insufficient bonding interface, and the thermal conductivity of air is extremely low (about 0.023W m ^-1 K ^-1 ) Thereby creating a non-negligible interfacial thermal resistance.

Many of the current studies use resin substrates that do not have flexibility and application interface adhesion properties, and therefore, even if some degree of heat conduction enhancement is obtained, the core problem of interface thermal resistance due to assembly in practical applications is not solved. For example, the epoxy resin heat-conducting material has no flexible characteristic after being molded, so that the heat dissipation groove cannot be fully contacted with a heat source in the assembly process, a large number of micro-area gaps cannot be effectively filled, and finally the actual heat management performance is greatly influenced. Therefore, developing a flexible thermal interface material that can fill micro-region voids is a more practical solution to this problem.

In the second aspect, in the aspect of electromagnetic shielding resistance, the existing thermal management material is generally used in a method of introducing functional filler into a polymer matrix so as to improve heat conduction performance and electromagnetic shielding efficiency, but the problem of high interface thermal resistance cannot be effectively solved due to common mixed fusion molding, and it is difficult to construct a layered filler network with developed orientation so as to improve heat transmission efficiency and electromagnetic shielding efficiency. Therefore, there is a need to develop a flexible thermal interface material with excellent thermal conductivity and electromagnetic shielding performance to efficiently solve the multiple coupling problems of integrated circuit device heat accumulation and dissipation, high frequency electromagnetic wave pollution and practical thermal interface application bonding.

In the third aspect, the functional filler used in the current thermal management material is partially researched to prepare the functional filler by adopting a chemical vapor deposition method, a plasma vapor deposition method, an ice template method and other processes, but the process technologies cannot be practically applied in a large scale due to high cost and complex process. Although some researches are currently attempted to use transition metal carbonitrides (MXENEs) as functional fillers to improve the electromagnetic shielding properties of thermal interface materials, the high purity transition metal carbonitrides are complicated and costly to synthesize and cannot be applied in large quantities to synergistically enhance the thermal conductivity of the thermal interface materials. Most of the thermal interface materials obtained by the method have thermal conductivity lower than 20W m ^-1 K ^-1 Meanwhile, the ideal electromagnetic shielding capability is lacked, so that the current multiple requirements of light weight, high heat conduction and high electromagnetic shielding of the thermal interface material are hardly met.

In the fourth aspect, the traditional mechanical stirring and mixing method is difficult to uniformly mix the high-viscosity polymer matrix with the functional filler, and the problem of filler aggregation and uneven distribution is often caused in the actual operation process, so that a large number of gaps exist in the nano-microstructure in the forming process, and micro-region interface defects are caused, so that the overall mechanical property of the material is reduced.

Thus, the various technical challenges described above result in a failure to achieve multiple coupling balances of flexibility characteristics, thermal conductivity, and electromagnetic shielding effectiveness in thermal interface materials.

Disclosure of Invention

In view of the above, the present disclosure provides a modified graphite-based functional filler and a thermal interface material using the same, which solve the problem that the application of the existing thermal interface material is limited because the multiple coupling balance of the flexibility, the heat conduction performance and the electromagnetic shielding performance cannot be achieved.

In addition, the present disclosure also provides methods of preparing the functional filler and the thermal interface material.

In a first aspect, the modified graphite-based functional filler is characterized by comprising:

the shape of the vermiform expanded graphite,

the surface of the vermicular expanded graphite is provided with a chemical active plating layer;

the chemically active coating is used for introducing active groups to improve the polarity of the vermicular expanded graphite.

The second aspect of the preparation method of the modified graphite-based functional filler is characterized by comprising the following steps:

obtaining vermiform expanded graphite;

and carrying out in-situ polymerization reaction on the vermicular expanded graphite and a modifier in a biochemical buffer solution to form a chemical active coating on the surface of the vermicular expanded graphite, thereby obtaining the modified graphite-based functional filler.

Further, the chemical active coating is a nano-scale chemical active coating.

Further, the vermicular expanded graphite is the product of in situ thermal expansion of crystalline flake graphite, graphite intercalation compounds, graphitic carbon tubes or graphite-based carbon fibers.

The vermicular expanded graphite retains the inherent van der Waals forces in the graphite structure and has a porous, three-dimensional structure.

Further, the modifier is a coupling agent;

the biochemical buffer solution is used for mixing the modifier and the vermiform expanded graphite.

Further, the modifier comprises 4- (2-amino ethyl) -1, 2-benzenediol hydrochloride, vinyl methoxy silane or amino ethoxy silane;

the biochemical buffer solution comprises a mixed solution of tris hydrochloride and ethanol, a mixed solution of isopropanol and sodium hydroxide or a mixed solution of absolute ethyl alcohol and ammonia water;

and/or the number of the groups of groups,

the vermicular expanded graphite: the biochemical buffer solution: the mass ratio of the modifier is 1: 100-300: 0.2-1.5;

and/or the number of the groups of groups,

the in-situ polymerization reaction condition is that mechanical stirring is carried out for 12-48 h at room temperature;

the pH value of the reaction is 7-12.

Further, after forming a chemical active coating on the surface of the vermicular expanded graphite, washing the vermicular expanded graphite with a detergent, and drying the vermicular expanded graphite to obtain the final modified graphite-based functional filler.

Further, the detergent comprises deionized water, absolute ethyl alcohol or isopropanol;

and/or the number of the groups of groups,

the drying mode is freeze drying, and the drying time is controlled to be 12-72 h.

In a third aspect, the thermal interface material includes:

the modified graphite-based functional filler of the first aspect.

Further, the thermal interface material also includes a liquid rubber.

Further, the liquid rubber comprises one or a mixture of more than one of nitrile rubber, natural rubber, ethylene propylene rubber, butadiene rubber or styrene butadiene rubber.

In a fourth aspect, the method for preparing a thermal interface material is characterized by comprising:

the liquid rubber of the third aspect and the modified graphite-based functional filler;

and vulcanizing and adding a mixture containing the liquid rubber and the modified graphite-based functional filler to obtain the thermal interface material.

Further, the solid mass percentage of the mixture is 10-40 wt%.

Further, the method for obtaining the mixture adopts a vacuum multi-stage mixing mode.

The vacuum multi-stage mixing is implemented under the negative pressure condition, and the mixture is uniformly dispersed by means of the mixing and stirring action of different gradients, and the micron-sized air gaps in the functional filler are cooperatively eliminated, so that the rubber matrix is fully filled in the functional filler microcell.

Further, the mixture further comprises a vulcanization accelerator and an anti-aging agent;

the vulcanization accelerator comprises sulfur or 2, 2' -dithiodibenzothiazyl;

the anti-aging agent comprises 2, 4-trimethyl-1, 2-dihydroquinoline polymer (RD), 2-Mercaptobenzimidazole (MB) or 6-ethoxy-2, 4-trimethyl-1, 2-dihydroquinoline;

the vulcanization accelerator: the anti-aging agent comprises the following components: the mass ratio of the liquid rubber is 0.5-2: 0.5-2: 100.

further, the conditions of the vulcanization addition are: pressurizing at the temperature of 120-180 ℃ for 6-8 MPa for one time, and pressure-maintaining for 1-3 min and then releasing pressure; pressurizing for 10-12 MPa for the second time, and pressure-maintaining for 2-5 min and then pressure-releasing; pressurizing for 14-18 MPa for three times, maintaining the pressure for 4-6 min, releasing pressure, cooling to normal temperature, and demoulding.

The vulcanization addition operation promotes the modified graphite-based functional filler to be arranged in a directional manner in the rubber matrix through gradient pressure induction, so as to construct a multilayer oriented network structure; and then, by means of the coupling of temperature and pressure, the crosslinking degree between the rubber chain segments is enhanced, and the effect of improving the integral mechanical property of the thermal interface material is achieved.

Further, the vacuum multi-stage mixing mode adopts a vacuum third-stage stirring mixing mode; wherein, the vacuum degree during mixing is-90-100 kPa; the rotation speed of the first-order mixing is 200-500 rpm, and the stirring time is 30-60 s; the rotation speed of the second-order mixing is 600-1200 rpm, and the stirring time is 60-180 s; the rotation speed of the third-order mixing is 1500-2500 rpm, and the stirring time is 120-240 s.

Further, a diluent is added during the vacuum multi-stage mixing;

the diluent comprises one or more of xylene, ethyl acetate, acetone or cyclohexanone;

the mass ratio of the diluent to the liquid rubber is 0.3-1.8: 1.

further, venting the mixture to volatilize the diluent prior to the vulcanization addition, the solvent volatilization process conditions: and (3) carrying out ventilation and standing for 12-72 h at the temperature of 40-70 ℃.

The invention has the following beneficial effects:

1. the thermal interface material has high electromagnetic shielding effectiveness

1. The modified graphite-based functional filler disclosed by the disclosure forms a nano-scale chemical active coating on the surface of a graphite-based material with a vermicular three-dimensional structure through an in-situ polymerization reaction, the nano-scale chemical active coating can introduce active groups such as amino groups, hydroxyl groups, vinyl groups, catecholamine structures and the like, the introduction of the active groups can improve the polarity of the vermicular expanded graphite, more polarization centers are formed, and more dipoles are provided through asymmetric charge distribution. The dipoles can absorb electromagnetic energy, break freely and rotate, thereby enhancing the electromagnetic shielding effectiveness of the thermal interface material.

According to the preparation method of the thermal interface material, through a vacuum multi-stage mixing mode, liquid rubber and modified graphite-based functional filler are uniformly dispersed, micron-sized air gaps in the modified graphite-based functional filler are cooperatively eliminated, and rubber matrixes are promoted to be fully filled in functional filler micro-areas; and in the vulcanization operation process, gradient pressure is utilized for induction, so that the modified graphite-based functional filler is directionally arranged in the rubber matrix, a multilayer oriented network structure is constructed, multiple interfaces in unit volume are provided, multiple reflection of electromagnetic waves is promoted to be attenuated, and the electromagnetic shielding efficiency of the thermal interface material is improved.

2. The thermal interface material has high heat conduction performance

According to the thermal interface material disclosed by the disclosure, the liquid rubber matrix is uniformly filled in the intrinsic gaps (micro-areas) of the modified graphite-based functional filler, the nano chemical active coating of the modified graphite-based functional filler reduces the space density of the micro-area interface (filler-matrix) contact thermal resistance, and the bridging effect of the micro-area interface is enhanced.

In addition, the multilayer orientation structure formed by the oriented arrangement of the modified graphite-based functional filler in the rubber matrix promotes a developed space heat conduction path, and is favorable for the efficient diffusion and transmission of heat flow so as to greatly improve the heat conduction performance of the thermal interface material.

The vulcanization treatment promotes the addition reaction of chemical bonds in the modified graphite-based functional filler and the rubber matrix chain segments, so that the interface bridging effect is enhanced to form a crosslinked network, and the flexibility and the mechanical property are further improved; the optimized flexibility characteristic enables the thermal interface material to effectively fill the micro air gap of the element interface in the application process, and the overall heat transfer effect after assembly is enhanced.

Because the thermal interface material disclosed by the invention has the advantages that the coupling enhancement of the heat conduction performance and the electromagnetic shielding performance is obtained, the flexibility characteristics and the mechanical properties which are lacked by most thermal interface materials are ensured, the application range of the front-edge thermal management field is further widened, and the thermal interface material has application value in the traditional thermal management field and the emerging comprehensive thermomagnetic coupling radio frequency system; the special flexible characteristic ensures the full contact between the heat radiation module and the heat-generating electronic element, and greatly improves the interface adhesion problem of the heat-accumulating element in practical application; its excellent thermal conductivity exceeds that of many commercial thermal interface materials, even some metal alloys; simultaneously has electromagnetic shielding efficiency exceeding 99.9999 percent and electromagnetic shielding value reaching 79.0dB, and is far more than the electromagnetic shielding efficiency (99 percent) required by the current commercial standard; in addition, its electromagnetic shielding value is twice that of part of the military and space electronic equipment requirements (30 dB). The heat conduction performance and electromagnetic shielding performance synergistic coupling enhancement is achieved, and meanwhile excellent flexibility characteristics and mechanical properties are maintained.

Drawings

The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of embodiments thereof with reference to the accompanying drawings in which:

FIG. 1A is a HRTEM diagram of the graphite-based filler of example 1;

FIG. 1B is a HRTEM diagram of the modified graphite-based functional filler of example 2;

as can be seen from fig. 1A and fig. 1B, after in-situ polymerization, the modified graphite-based functional filler prepared by the present disclosure forms a chemical plating layer with a thickness of about 3nm on the surface of the graphite-based filler, and after introducing active groups, the chemical affinity of the filler is improved, and as can also be seen from diffraction spot diagrams, the in-situ polymerization treated filler still well retains the crystal structure.

FIG. 2A is a cross-sectional SEM of a thermal interface material of example 1;

FIG. 2B is a cross-sectional SEM of a thermal interface material of example 2;

FIG. 2C is a high magnification cross-sectional SEM magnified view of the thermal interface material of example 2;

as can be seen from fig. 2B, the thermal interface material prepared by the present disclosure possesses excellent in-plane alignment and forms a multi-layer aligned network structure. The microstructure feature is favorable for efficient phonon transmission, and the modified graphite-based functional filler in close contact between layers also has a nano-coating to reduce interface thermal resistance and bring high heat conductivity. In addition, the multilayer oriented network structure can provide multiple interfaces in unit volume to promote the electromagnetic wave to generate multi-order reflection so as to achieve the purpose of attenuation, and the nano-plating layer formed by in-situ polymerization reaction introduces a large number of active groups to form more polarization centers and provides more dipoles by asymmetric charge distribution. The dipole can absorb electromagnetic energy, break freely and rotate, thereby enhancing electromagnetic shielding effectiveness.

As can be seen from fig. 2C, a superior in-plane orientation arrangement is observed even in the high magnification SEM image and no apparent interface defects; as can be seen from fig. 2A, the graphite-based filler lacking the nano-active coating layer cannot be sufficiently fused with the rubber matrix, and obvious cavity and interface defects appear in the prepared thermal interface material.

FIG. 3A is a graph showing the effect of the flexibility characteristics of the thermal interface material of example 2;

FIG. 3B is a graph comparing the flexibility characteristics and practical properties of the thermal interface material of example 2;

as can be seen from fig. 3A and 3B, the thermal interface material prepared by the method of the present disclosure has better flexibility, can be folded and bent at will, and has excellent tensile strength; the method can meet the requirements of the front-end field heat management field, such as a wearable device heat management application.

FIG. 4 is a graph showing in-plane thermal conductivity and electromagnetic shielding effectiveness comparison of comparative examples 1-2 and examples 1-2;

as can be seen from fig. 4, the thermal interface material prepared by the method of the present disclosure greatly improves the heat conducting performance and simultaneously optimizes the electromagnetic shielding effectiveness.

FIG. 5 is a graph showing the mechanical properties of comparative examples 1-2 and examples 1-2;

as can be seen from fig. 5, the tensile strength of the thermal interface material prepared by the method of the present disclosure is greatly enhanced. Wherein the tensile strength of example 2 is approximately 10-fold enhanced compared to comparative example 1 to 23.3 MPa; and elongation at break is also maintained at a good level (> 130%).

Detailed Description

The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the following detailed description of the present disclosure, certain specific details are set forth in detail. However, for portions not described in detail, those skilled in the art can also fully understand the present disclosure.

Furthermore, those of ordinary skill in the art will appreciate that the drawings are provided solely for purposes of illustrating the objects, features, and advantages of the disclosure and that the drawings are not necessarily drawn to scale.

Meanwhile, unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, it is the meaning of "including but not limited to".

Comparative example 1

Step (1): adding proper amount of ethyl acetate into 30g of liquid nitrile rubber, 0.06g of sulfur, 0.06g of 2, 2' -dithiodibenzothiazyl and 0.06g of 2, 4-trimethyl-1, 2-dihydroquinoline polymer to obtain a liquid rubber mixture;

step (2): carrying out vacuum multi-stage mixing assembly on the liquid rubber mixture to obtain a homogeneous mixture; wherein, the vacuum degree during mixing is-100 kPa; the rotation speed of the first-order mixing is 500rpm, and the stirring time is 45s; the rotation speed of the second-order mixing is 1200rpm, and the stirring time is 90s; the rotation speed of the third-stage mixing was 1800rpm, and the stirring time was 120s.

Step (3): placing the obtained homogeneous mixture into a 60 ℃ oven for solvent volatilization for 48 hours, and removing residual ethyl acetate and volatile matters to obtain cured rubber;

step (4): vulcanizing the obtained cured rubber, pressurizing at a time of 6MPa at a temperature of 150 ℃, and pressure releasing after pressure maintaining for 2 min; pressurizing for 10MPa for the second time, and pressure releasing after pressure maintaining for 4 min; pressurizing for 14MPa for three times, maintaining the pressure for 5min, releasing pressure, cooling to normal temperature, and demolding to obtain vulcanized rubber.

Comparative example 2

Step (1): 10g of liquid nitrile rubber, 0.02g of sulfur, 0.02g of 2, 2' -dithiodibenzothiazole, 0.02g of 2, 4-trimethyl-1, 2-dihydroquinoline polymer and 3g of graphite compound are added with proper amount of ethyl acetate to obtain a liquid rubber mixture;

step (2): carrying out vacuum multi-stage mixing assembly on the liquid rubber mixture to obtain a homogeneous mixture; wherein, the vacuum degree during mixing is-100 kPa; the rotation speed of the first-order mixing is 500rpm, and the stirring time is 45s; the rotation speed of the second-order mixing is 1200rpm, and the stirring time is 90s; the rotation speed of the third-stage mixing was 1800rpm, and the stirring time was 120s.

Step (3): placing the obtained homogeneous mixture into a 60 ℃ oven for solvent volatilization for 48 hours, removing residual ethyl acetate and volatile matters, and curing to obtain a composite material precursor;

step (4): vulcanizing the obtained precursor material, pressurizing at 160 ℃ for 6MPa once, and depressurizing after pressure maintaining for 2 min; pressurizing for 10MPa for the second time, and pressure releasing after pressure maintaining for 4 min; pressurizing for 15MPa for three times, maintaining the pressure for 5min, releasing the pressure, cooling to normal temperature, and demolding to obtain the flexible thermal interface material.

Example 1

Step (1): rapidly and in-situ thermally expanding 5g of graphite compound at 700 ℃ for 80 seconds to obtain porous worm graphite;

step (2): 10g of liquid nitrile rubber, 0.02g of sulfur, 0.02g of 2, 2' -dithiodibenzothiazole, 0.02g of 2, 4-trimethyl-1, 2-dihydroquinoline polymer and 3.2g of worm graphite filler are added with proper amount of ethyl acetate to obtain a liquid rubber mixture;

step (3): carrying out vacuum multi-stage mixing assembly on the liquid rubber mixture to obtain a homogeneous mixture; wherein, the vacuum degree during mixing is-100 kPa; the rotation speed of the first-order mixing is 500rpm, and the stirring time is 45s; the rotation speed of the second-order mixing is 1200rpm, and the stirring time is 90s; the rotation speed of the third-stage mixing was 1800rpm, and the stirring time was 120s.

Step (4): placing the obtained homogeneous mixture into a 60 ℃ oven for solvent volatilization for 48 hours, removing residual ethyl acetate and volatile matters, and curing to obtain a composite material precursor;

step (5): vulcanizing the obtained precursor material, pressurizing at 160 ℃ for 6MPa once, and depressurizing after pressure maintaining for 2 min; pressurizing for the second time to 12MPa, maintaining the pressure for 4min, and then releasing the pressure; pressurizing for 15MPa for three times, maintaining the pressure for 5min, releasing the pressure, cooling to normal temperature, and demolding to obtain the flexible thermal interface material.

Example 2

Step (1): rapidly and in-situ thermally expanding 5g of graphite compound at 700 ℃ for 80 seconds to obtain porous worm graphite;

step (2): 3.6g of porous worm graphite and 0.75g of 4- (2-aminoethyl) -1, 2-benzenediol hydrochloride are mixed in 500g of tris (hydroxymethyl) aminomethane hydrochloride and ethanol buffer solution, and in-situ polymerization reaction is carried out for 36h at room temperature to obtain a functional filler precursor; fully washing the functional filler precursor, and freeze-drying for 48 hours to obtain the in-situ polymerization modified graphite-based functional filler;

step (3): adding proper amount of ethyl acetate into 10g of liquid nitrile rubber, 0.02g of sulfur, 0.02g of 2, 2' -dithiodibenzothiazole, 0.02g of 2, 4-trimethyl-1, 2-dihydroquinoline polymer and 3.2g of in-situ polymerization modified graphite-based functional filler to obtain a liquid rubber mixture;

step (4): carrying out vacuum multi-stage mixing assembly on the liquid rubber mixture to obtain a homogeneous mixture; wherein, the vacuum degree during mixing is-100 kPa; the rotation speed of the first-order mixing is 500rpm, and the stirring time is 45s; the rotation speed of the second-order mixing is 1200rpm, and the stirring time is 90s; the rotation speed of the third-stage mixing was 1800rpm, and the stirring time was 120s.

Step (5): placing the obtained homogeneous mixture into a 60 ℃ oven for solvent volatilization for 48 hours, removing residual ethyl acetate and volatile matters, and curing to obtain a composite material precursor;

step (6): vulcanizing the obtained precursor material, pressurizing at 160 ℃ for 6MPa once, and depressurizing after pressure maintaining for 2 min; pressurizing for the second time to 12MPa, maintaining the pressure for 4min, and then releasing the pressure; pressurizing for 15MPa for three times, maintaining the pressure for 5min, releasing the pressure, cooling to normal temperature, and demolding to obtain the flexible thermal interface material.

Example 3

Step (1): mixing 5g of crystalline flake graphite with 0.75g of gamma-aminopropyl triethoxysilane in 400g of 25wt% isopropanol buffer solution, and carrying out in-situ polymerization reaction for 36h at room temperature to obtain a functional filler precursor; fully washing the functional filler precursor, and freeze-drying for 48 hours to obtain the in-situ polymerization modified graphite-based functional filler;

step (2): adding a proper amount of dimethylbenzene into 10g of liquid rubber, 0.02g of sulfur, 0.02g of 2, 2' -dithiodibenzothiazole, 0.02g of 2, 4-trimethyl-1, 2-dihydroquinoline polymer and 3.2g of in-situ polymerization modified graphite-based functional filler to obtain a liquid rubber mixture;

step (3): carrying out vacuum multi-stage mixing assembly on the liquid rubber mixture to obtain a homogeneous mixture; wherein, the vacuum degree during mixing is-100 kPa; the rotation speed of the first-order mixing is 500rpm, and the stirring time is 45s; the rotation speed of the second-order mixing is 1200rpm, and the stirring time is 90s; the rotation speed of the third-stage mixing was 1800rpm, and the stirring time was 120s.

Step (4): placing the obtained homogeneous mixture into a 60 ℃ oven for solvent volatilization for 48 hours, removing residual xylene and volatile matters, and curing to obtain a composite material precursor;

step (5): vulcanizing the obtained precursor material, pressurizing at 160 ℃ for 6MPa once, and depressurizing after pressure maintaining for 2 min; pressurizing for the second time to 12MPa, maintaining the pressure for 4min, and then releasing the pressure; pressurizing for 15MPa for three times, maintaining the pressure for 5min, releasing the pressure, cooling to normal temperature, and demolding to obtain the flexible thermal interface material.

Example 4

Step (1): 1.8g of crystalline flake graphite, 1.8g of graphite compound and 0.72g of 4- (2-amino ethyl) -1, 2-benzenediol hydrochloride are mixed in 500g of tris (hydroxymethyl) aminomethane hydrochloride and ethanol buffer solution, and in-situ polymerization reaction is carried out for 36h at room temperature to obtain a composite functional filler precursor; fully washing the composite functional filler precursor, and freeze-drying for 48 hours to obtain the in-situ polymerization modified graphite-based functional filler;

step (2): adding a proper amount of dimethylbenzene into 10g of liquid nitrile rubber, 0.02g of sulfur, 0.02g of 2, 2' -dithiodibenzothiazole, 0.02g of 2, 4-trimethyl-1, 2-dihydroquinoline polymer and 3.2g of in-situ polymerization modified graphite-based functional filler to obtain a liquid rubber mixture;

step (3): carrying out vacuum multi-stage mixing assembly on the liquid rubber mixture to obtain a homogeneous mixture; wherein, the vacuum degree during mixing is-100 kPa; the rotation speed of the first-order mixing is 500rpm, and the stirring time is 45s; the rotation speed of the second-order mixing is 1200rpm, and the stirring time is 90s; the rotation speed of the third-stage mixing was 1800rpm, and the stirring time was 120s.

Step (4): placing the obtained homogeneous mixture into a 60 ℃ oven for solvent volatilization for 48 hours, removing residual xylene and volatile matters, and curing to obtain a composite material precursor;

step (5): vulcanizing the obtained precursor material, pressurizing at 160 ℃ for 6MPa once, and depressurizing after pressure maintaining for 2 min; pressurizing for the second time to 12MPa, maintaining the pressure for 4min, and then releasing the pressure; pressurizing for 15MPa for three times, maintaining the pressure for 5min, releasing the pressure, cooling to normal temperature, and demolding to obtain the flexible thermal interface material.

TABLE 1 thermal conductivity, electromagnetic Shielding Properties and mechanical Properties of comparative examples 1-2 and examples 1-2

Note that: the thermal conductivity of the main body is measured by adopting a Hot Disk-TPS method based on the standard ISO 22007-2; the anisotropic thermal conductivity is tested based on standard ISO 22007-4-2017 by adopting a laser flash LFA method; the mechanical property test is based on ASTM D638; electromagnetic shielding effectiveness was tested using an Agilent PNA-N5244A vector network analyzer in the frequency domain range of 8.2-12.4 GHz.

As shown in table 1, example 1 and example 2 showed better overall performance than comparative example 1 and comparative example 2; and compared with the embodiment 1, the embodiment 2 has obviously improved heat conduction performance, electromagnetic shielding performance and mechanical performance, and shows excellent anisotropic heat conduction performance.

Example 2 the excellent thermal conductivity was also far beyond the current commercial thermal interface material level (5-10W m ^-1 K ^-1 ) The method comprises the steps of carrying out a first treatment on the surface of the The excellent electromagnetic shielding performance of the electromagnetic shielding material exceeds the current commercial standard electromagnetic shielding value by 20dB and is twice as high as the required value of partial military industry and space electronic equipment by 30dB. The high-efficiency balance between the heat conducting performance and the electromagnetic shielding performance is achieved, the excellent mechanical performance is maintained, and the application range is widened for more heat management examples.

The bulk thermal conductivity of both example 3 and example 4 exceeds 30W m ^-1 K ^-1 Wherein example 3 has an electromagnetic shielding index exceeding 40dB; example 4 electromagnetic shielding index exceeding 60dB, and tensile strength exceeding 25MPa; the information shows that the coupling enhancement of the thermal interface material in heat conduction performance, electromagnetic shielding performance and mechanical performance.

The foregoing examples have expressed only a few embodiments of the present disclosure, which are described in more detail and detail, but are not to be construed as limiting the scope of the present disclosure. It should be noted that modifications, equivalent substitutions, improvements, etc. can be made by those skilled in the art without departing from the spirit of the present disclosure, which are all within the scope of the present disclosure. Accordingly, the scope of protection of the present disclosure should be determined by the following claims.

The above examples are merely representative of embodiments of the present disclosure, which are described in more detail and are not to be construed as limiting the scope of the present disclosure. It should be noted that modifications, equivalent substitutions, improvements, etc. can be made by those skilled in the art without departing from the spirit of the present disclosure, which are all within the scope of the present disclosure. Accordingly, the scope of protection of the present disclosure should be determined by the following claims.

Claims (8)

1. A method of preparing a thermal interface material, comprising:

liquid rubber and modified graphite-based functional filler;

vulcanizing and adding a mixture containing the liquid rubber and the modified graphite-based functional filler to obtain the thermal interface material;

the liquid rubber comprises one or more of nitrile rubber, natural rubber, ethylene propylene rubber, butadiene rubber or styrene butadiene rubber;

the preparation method of the modified graphite-based functional filler comprises the following steps:

obtaining vermiform expanded graphite;

performing in-situ polymerization reaction on the vermicular expanded graphite and a modifier in a biochemical buffer solution to form a chemical active coating on the surface of the vermicular expanded graphite so as to obtain the modified graphite-based functional filler;

the modifier comprises 4- (2-amino ethyl) -1, 2-benzenediol hydrochloride, vinyl methoxy silane or amino ethoxy silane;

the biochemical buffer solution comprises a mixed solution of tris hydrochloride and ethanol, a mixed solution of isopropanol and sodium hydroxide or a mixed solution of absolute ethyl alcohol and ammonia water;

the method for obtaining the mixture adopts a vacuum multi-stage mixing mode;

the vacuum multi-stage mixing mode adopts a vacuum three-stage stirring mixing mode; wherein, the vacuum degree during mixing is-90-100 kPa; the rotation speed of the first-order mixing is 200-500 rpm, and the stirring time is 30-60 s; 600-1200 rpm of second-order mixing, and stirring time is 60-180 s; the rotating speed of the third-order mixing is 1500-2500 rpm, and the stirring time is 120-240 s;

the conditions of the vulcanization addition are: pressurizing at the temperature of 120-180 ℃ for 6-8 MPa for one time, and pressure-maintaining for 1-3 min and then releasing pressure; pressurizing for 10-12 MPa for the second time, and pressure-maintaining for 2-5 min and then pressure-releasing; pressurizing for 14-18 MPa for three times, maintaining the pressure for 4-6 min, releasing pressure, cooling to normal temperature, and demoulding.

2. The method for preparing a thermal interface material according to claim 1, wherein:

the chemical active coating is a nano-scale chemical active coating.

3. The method for preparing a thermal interface material according to claim 2, wherein:

the vermicular expanded graphite is the product of in situ thermal expansion of crystalline flake graphite, graphite intercalation compounds, graphitic carbon tubes or graphite-based carbon fibers.

4. The method for preparing a thermal interface material according to claim 1, wherein:

the vermicular expanded graphite: the biochemical buffer solution: the mass ratio of the modifier is 1: 100-300: 0.2 to 1.5.

5. The method for preparing a thermal interface material according to claim 1, wherein:

the in-situ polymerization reaction condition is that mechanical stirring is carried out for 12-48 h at room temperature;

the pH value of the reaction is 7-12.

6. The method for preparing a thermal interface material according to claim 1, wherein:

the solid mass percentage content of the mixture is 10-40wt%.

7. The method for preparing a thermal interface material according to claim 1, wherein:

the mixture also comprises a vulcanization accelerator and an anti-aging agent;

the vulcanization accelerator comprises sulfur or 2, 2' -dithiodibenzothiazyl;

the anti-aging agent comprises 2, 4-trimethyl-1, 2-dihydroquinoline polymer (RD), 2-Mercaptobenzimidazole (MB) or 6-ethoxy-2, 4-trimethyl-1, 2-dihydroquinoline;

the vulcanization accelerator: the anti-aging agent comprises the following components: the mass ratio of the liquid rubber is 0.5-2: 0.5-2: 100.

8. the method for preparing a thermal interface material according to claim 1, wherein:

adding a diluent during the vacuum multi-stage mixing;

the diluent comprises one or more of xylene, ethyl acetate, acetone or cyclohexanone;

the mass ratio of the diluent to the liquid rubber is 0.3-1.8: 1.

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