Highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive material and preparation method thereof

Abstract

This invention provides a highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive material and its preparation method. The method involves melt-blending polyethylene grafted with maleic anhydride at 1% and 8% grafting rates to obtain a blend. This blend is then mixed with graphite filler and kneaded to obtain a composite material. Finally, the composite material is rolled using a two-roll mill to obtain the highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive material. This invention significantly improves the processability of the rolling process by directly using polyethylene grafted with maleic anhydride within a certain average grafting rate range as the polymer matrix instead of a compatibilizer, and then kneading it with highly filled graphite and rolling it to obtain the composite thermal conductive material. It was also discovered that this significantly reduces interfacial thermal resistance and increases thermal conductivity. The resulting composite thermal conductive material is uniform and complete, has a high thermal conductivity, and is suitable for industrial-scale production.

Description

Technical Field

[0001] This invention belongs to the technical field of polymer thermal conductive film materials, and relates to a highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive material and its preparation method. This composite thermal conductive material can be used as a heat dissipation material for electronic appliances. Background Technology

[0002] In polyethylene-based composite materials, high-filler graphite-based fillers are often added to impart functionalities such as high electrical conductivity, high thermal conductivity, and electromagnetic shielding properties. The resulting highly filled polyethylene / graphite composite materials, due to their mechanical properties, flexibility, stability, and functionality, have broad application prospects in fields such as antistatic packaging, heat dissipation for electronic devices, and shielding layers for wires and cables.

[0003] However, due to the poor interfacial compatibility between the polyethylene matrix and the graphite filler, numerous voids and defects exist at the interface, leading to severe phonon scattering and significant interfacial thermal resistance, which limits the improvement of the composite material's thermal conductivity. This is particularly true in highly filled materials, where numerous matrix-filler interfaces severely restrict interfacial heat transport. Furthermore, high-content graphite fillers are prone to agglomeration, making homogenization difficult during extrusion, mixing, and other blending processes, resulting in significant stress concentration and extremely poor mechanical properties.

[0004] Existing technologies often employ chemical modifications to graphite fillers, such as silane coupling agents and surface coating with dopamine, to enhance the interaction between the matrix and filler by introducing polar groups. However, surface silane or dopamine modification of fillers only significantly improves thermal conductivity at low filler concentrations. At high filler concentrations, the filler-filler interactions form thermal pathways, carrying the majority of the heat flux. While filler modification can reduce matrix-filler thermal resistance, the surface silane or polydopamine layer becomes a thermal resistance layer, increasing the filler-filler interfacial thermal resistance and often leading to a decrease in thermal conductivity. Introducing polymer compatibilizers to enrich the polymer matrix can effectively improve processability at high filler concentrations, but there are no reports of it enhancing the thermal conductivity of such materials. Theoretically, the addition of compatibilizers reduces the proportion of graphite fillers, which is detrimental to improving thermal conductivity.

[0005] Therefore, traditional matrix compatibilization and filler modification methods are insufficient to enhance the thermal conductivity of graphite / polyethylene composites with high filler content. Summary of the Invention

[0006] To overcome the problems in the prior art, this invention provides a highly filled graphite / polyethylene grafted maleic anhydride composite thermally conductive material and its preparation method. This invention involves melt-blending polyethylene grafted maleic anhydride with a specific grafting ratio. The resulting polyethylene grafted maleic anhydride with an average grafting ratio within a certain range is directly used as the polymer matrix rather than a compatibilizer. This matrix is ​​then mixed with highly filled graphite and rolled to obtain the composite thermally conductive material. This significantly improves the processability of the rolling process and, incidentally, it was discovered that it can significantly reduce interfacial thermal resistance and increase thermal conductivity. The prepared composite thermally conductive material is uniform and complete, possesses high thermal conductivity, and is suitable for industrial-scale production.

[0007] To achieve the above objectives, the present invention employs a technical solution consisting of the following technical measures.

[0008] This invention provides a method for preparing a highly filled graphite / polyethylene grafted maleic anhydride composite thermally conductive material, comprising the following steps:

[0009] (1) Based on a total mass of 100 parts, 72-86 parts of polyethylene grafted maleic anhydride with a grafting rate of 1% and 14-28 parts of polyethylene grafted maleic anhydride with a grafting rate of 8% are melt-blended, extruded and granulated to prepare a polyethylene grafted maleic anhydride blend.

[0010] (2) Based on a total of 100 parts by weight, 10-50 parts of the polyethylene-grafted maleic anhydride blend obtained in step (1) are mixed with 50-90 parts of graphite filler and kneaded to prepare the composite material.

[0011] (3) The composite material obtained in step (2) is rolled using a two-roll mill to prepare a high-filled graphite / polyethylene grafted maleic anhydride composite thermal conductive material.

[0012] The prepared highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive material can be a sheet or a film material, based on the roll gap control of a two-roll mill. For example, when the roll gap is controlled at 0.1~0.2 mm, a highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive film with a thickness of about 0.1~0.2 mm can be prepared.

[0013] The invention originated from an accidental discovery by the inventors when solving the problem of poor processability when blending highly filled graphite with polyethylene for roll forming.

[0014] In the early stages of research and development, the inventors blended highly filled (70 wt%) graphite nanosheets with polyethylene and used a two-roll mill for roll forming to prepare a film material, such as... Figure 2 , Figure 3As shown, the blend does not stick to the rollers, making feeding difficult and causing it to easily peel off. Simultaneously, the poor adhesion between polyethylene and graphite nanosheets results in extremely low film strength, making it highly brittle and difficult to detach completely from the rollers. Even by adjusting the roller pressing process parameters, such as forcibly reducing the roller gap to squeeze the material into the rollers, only broken samples can be obtained. Figure 3 ).

[0015] To address the aforementioned poor processability issue, the inventors considered introducing polymer compatibilizers to enhance the polymer matrix. However, due to the small proportion of the polymer matrix itself, they attempted to directly use relatively inexpensive polyethylene grafted with maleic anhydride at a 1% grafting rate as the polymer matrix instead of a compatibilizer. This was then combined with highly filled graphite through intensive mixing and roll forming to prepare a composite thermally conductive film. This method significantly improved processability, enabling the preparation of complete film materials. However, the product's microstructure still exhibited certain voids and defects, such as... Figure 4 As shown.

[0016] Based on the above situation, the inventors attempted to use polyethylene grafted with maleic anhydride with a higher grafting rate as the polymer matrix. However, the purchase cost of such high-grafting-rate polyethylene grafted with maleic anhydride is relatively high. Therefore, they tried to first melt-blend low-grafting-rate polyethylene grafted with maleic anhydride and high-grafting-rate polyethylene grafted with maleic anhydride to prepare polyethylene grafted with maleic anhydride with an average grafting rate within a certain range as the polymer matrix. It was found that when the average grafting rate is about 2-3%, it is sufficient to prepare a uniform, complete, and highly processable composite thermally conductive film.

[0017] When a polyethylene-grafted maleic anhydride blend with an average grafting rate of about 2-3% was selected as the polymer matrix, it was accidentally discovered during testing that the cross-sectional thermal conductivity of the prepared composite film was significantly enhanced, achieving an unexpected technical effect.

[0018] In this article, the polyethylene-grafted maleic anhydride (MAH-g-PE) is a functional polymer in which maleic anhydride polar groups are introduced into the polyethylene backbone through a chemical grafting reaction. It is a conventional commercially available chemical raw material. Typically, the polyethylene-grafted maleic anhydride with a 1% grafting rate and the polyethylene-grafted maleic anhydride with an 8% grafting rate mentioned in step (1) are both commercially available, such as the polyethylene-grafted maleic anhydride used in the examples below, or can be obtained by self-production. Those skilled in the art can refer to the records in the prior art literature to prepare polyethylene-grafted maleic anhydride with a specific grafting rate.

[0019] In this paper, the graphite filler is selected from conventional thermally conductive functional fillers, such as graphite nanosheets, natural flake graphite, expandable graphite sheets, expanded graphite microspheres, worm-like expanded graphite, conductive graphite powder, graphene nanosheets, etc. Those skilled in the art can select appropriate graphite fillers based on actual needs and cost considerations, as well as common knowledge in the field and existing technical literature.

[0020] It should be noted that the choice of specific type of graphite filler usually does not have a significant impact on the technical contribution of this invention. Therefore, although the same type of graphite nanosheets are used as graphite filler in the following embodiments, this does not mean that the graphite filler of this invention is the only specified / limited.

[0021] It should be further noted that, under normal circumstances, other processing aids / fillers may be added to the raw materials specified in the technical solution of this invention. However, it is currently unknown whether this will have a significant impact on the technical contribution of this invention. Therefore, based on the principle of seeking truth from facts, this invention only limits polyethylene grafted with maleic anhydride and graphite filler to the raw materials. Under the condition of this raw material selection, a composite thermally conductive material with limited cost, uniform integrity and high thermal conductivity can be prepared.

[0022] In this article, the melt blending extrusion granulation described in step (1) is a conventional processing technology in the chemical industry. Those skilled in the art can directly refer to the melt blending extrusion granulation process of polyethylene recorded in existing technical literature for actual operation.

[0023] To better illustrate the present invention and provide a technical solution for reference, the melt blending extrusion granulation described in step (1) specifically uses a twin-screw extruder, with the temperature of zone one set to 120~130 ℃, the temperature of zone two set to 130~140 ℃, and the temperatures of zones three to six all set to 180~200 ℃, and the screw speed being 30~70 r / min.

[0024] In this paper, the mixing process described in step (2) is to perform mixing processing using conventional torque rheometry mixing equipment. Those skilled in the art can directly refer to the mixing process of polyethylene recorded in existing technical literature for actual operation.

[0025] To better illustrate the present invention and provide a technical solution for reference, the mixing process in step (2) includes the following process parameters: mold cavity temperature 180~200 ℃, rotor speed 30~50 r / min, and mixing time 5~15 min.

[0026] In this document, the roll forming process described in step (3) using a two-roll mill involves shearing, plasticizing, and mixing the material using two counter-rotating inward-rotating rolls based on the roll gap, temperature, and relative speed, thereby forming the material into sheets or films. Typically, those skilled in the art can determine the specific roll forming process parameters based on the choice of the polymer matrix, such as the melt parameters of polyethylene, and the processing methods described in the instruction manual or existing literature of the two-roll mill.

[0027] To better illustrate the present invention and provide a reference technical solution, in order to prepare a highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive film, step (3) involves roll forming using a two-roll mill. The process parameters include: roll temperature of 130~150 ℃ (higher than the melting point of polyethylene), and roll gap control of 0.1~0.2 mm. After the blend melts and uniformly coats the surface of the roll, it is peeled off and cooled to obtain the highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive film.

[0028] The present invention has the following beneficial effects:

[0029] 1. This invention provides a high-filled graphite / polyethylene grafted maleic anhydride composite thermal conductive material and its preparation method. Specifically, a high content of maleic anhydride groups is introduced onto a polyethylene matrix. The polyethylene grafted maleic anhydride with a specific grafting rate is melt-blended, and the resulting polyethylene grafted maleic anhydride with an average grafting rate within a certain range is directly used as the polymer matrix rather than a compatibilizer. This is then mixed with high-filled graphite and rolled to obtain the composite thermal conductive material. This significantly improves the processability of the roll forming process and, incidentally, it was discovered that it can significantly reduce interfacial thermal resistance and increase thermal conductivity.

[0030] 2. The highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive film prepared based on the technical solution of this invention is uniform and complete, and can have an ultra-high thermal conductivity of 44.7 W / mK in-plane and 4.14 W / mK across planes. It has potential application value in LED arrays and thermal management of electronic systems, and is suitable for industrial-scale production. Attached Figure Description

[0031] Figure 1 This is a comparative bar chart showing the in-plane thermal conductivity (K||) and transplane thermal conductivity (K⊥) of the composite thermal conductive film samples prepared in Examples 1-2 and Comparative Examples 1-3 of the present invention.

[0032] Figure 2 This is a photograph taken between the rollers during the roll forming process of the blended material in the two-roll open mill during the preparation of Comparative Example 1 of this invention.

[0033] Figure 3This is a photograph of a broken composite thermal conductive film sample obtained by forcibly reducing the roller gap during the preparation process of Comparative Example 1 of this invention to squeeze the blended material into the roller.

[0034] Figure 4 This is a SEM image of the microstructure of the highly filled graphite / polyethylene composite thermally conductive film prepared in Comparative Example 2 of this invention.

[0035] Figure 5 This is a photograph of the roller surface during the roll forming process of the blended material in the two-roll open mill during the preparation of Example 1 of the present invention.

[0036] Figure 6 This is a photograph of the composite thermal conductive film sample prepared in Example 1 of the present invention.

[0037] Figure 7 This is a photograph of the composite thermal conductive film sample prepared in Comparative Example 3 of this invention. Detailed Implementation

[0038] To further understand the present invention, preferred embodiments are described below with reference to examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. Those skilled in the art can refer to the content of this document to appropriately improve the process parameters. In particular, it should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the scope of the present invention. The methods and applications of the present invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate changes and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present invention to realize and apply the technology of the present invention. Although it is believed that those skilled in the art will fully understand the following terms, the following definitions are set forth to help illustrate the subject matter disclosed in the present invention.

[0039] This invention provides a method for preparing a highly filled graphite / polyethylene grafted maleic anhydride composite thermally conductive material, comprising the following steps:

[0040] (1) Based on a total mass of 100 parts, 72-86 parts of polyethylene grafted maleic anhydride with a grafting rate of 1% and 14-28 parts of polyethylene grafted maleic anhydride with a grafting rate of 8% are melt-blended, extruded and granulated to prepare a polyethylene grafted maleic anhydride blend.

[0041] (2) Based on a total of 100 parts by weight, 10-50 parts of the polyethylene-grafted maleic anhydride blend obtained in step (1) are mixed with 50-90 parts of graphite filler and kneaded to prepare the composite material.

[0042] (3) The composite material obtained in step (2) is rolled using a two-roll mill to prepare a high-filled graphite / polyethylene grafted maleic anhydride composite thermal conductive material.

[0043] The prepared highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive material can be a sheet or a film material, based on the roll gap control of a two-roll mill. For example, when the roll gap is controlled at 0.1~0.2 mm, a highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive film with a thickness of about 0.1~0.2 mm can be prepared.

[0044] The invention originated from an accidental discovery by the inventors when solving the problem of poor processability when blending highly filled graphite with polyethylene for roll forming.

[0045] In the early stages of research and development, the inventors blended highly filled (70 wt%) graphite nanosheets with polyethylene and used a two-roll mill for roll forming to prepare a film material, such as... Figure 2 , Figure 3 As shown, the blend does not stick to the rollers, making feeding difficult and causing it to easily peel off. Simultaneously, the poor adhesion between polyethylene and graphite nanosheets results in extremely low film strength, making it highly brittle and difficult to detach completely from the rollers. Even by adjusting the roller pressing process parameters, such as forcibly reducing the roller gap to squeeze the material into the rollers, only broken samples can be obtained. Figure 3 ).

[0046] To address the aforementioned poor processability issue, the inventors considered introducing polymer compatibilizers to enhance the polymer matrix. However, due to the small proportion of the polymer matrix itself, they attempted to directly use relatively inexpensive polyethylene grafted with maleic anhydride at a 1% grafting rate as the polymer matrix instead of a compatibilizer. This was then combined with highly filled graphite through intensive mixing and roll forming to prepare a composite thermally conductive film. This method significantly improved processability, enabling the preparation of complete film materials. However, the product's microstructure still exhibited certain voids and defects, such as... Figure 4 As shown.

[0047] Based on the above situation, the inventors attempted to use polyethylene grafted with maleic anhydride with a higher grafting rate as the polymer matrix. However, the purchase cost of such high-grafting-rate polyethylene grafted with maleic anhydride is relatively high. Therefore, they tried to first melt-blend low-grafting-rate polyethylene grafted with maleic anhydride and high-grafting-rate polyethylene grafted with maleic anhydride to prepare polyethylene grafted with maleic anhydride with an average grafting rate within a certain range as the polymer matrix. It was found that when the average grafting rate is about 2-3%, it is sufficient to prepare a uniform, complete, and highly processable composite thermally conductive film.

[0048] When a polyethylene-grafted maleic anhydride blend with an average grafting rate of about 2-3% was selected as the polymer matrix, it was accidentally discovered during testing that the cross-sectional thermal conductivity of the prepared composite film was significantly enhanced, achieving an unexpected technical effect.

[0049] In this article, the polyethylene-grafted maleic anhydride (MAH-g-PE) is a functional polymer in which maleic anhydride polar groups are introduced into the polyethylene backbone through a chemical grafting reaction. It is a conventional commercially available chemical raw material. Typically, the polyethylene-grafted maleic anhydride with a 1% grafting rate and the polyethylene-grafted maleic anhydride with an 8% grafting rate mentioned in step (1) are both commercially available, such as the polyethylene-grafted maleic anhydride used in the examples below, or can be obtained by self-production. Those skilled in the art can refer to the records in the prior art literature to prepare polyethylene-grafted maleic anhydride with a specific grafting rate.

[0050] In this document, the graphite filler is selected from conventional thermally conductive functional fillers. In one embodiment, the graphite filler may include graphite nanosheets, natural flake graphite, expandable graphite sheets, expanded graphite microspheres, worm-like expanded graphite, conductive graphite powder, graphene nanosheets, etc. Those skilled in the art can select appropriate graphite fillers based on actual needs and cost considerations, as well as common knowledge in the field and existing technical literature.

[0051] It should be noted that the choice of specific type of graphite filler usually does not have a significant impact on the technical contribution of this invention. Therefore, although the same type of graphite nanosheets are used as graphite filler in the following embodiments, this does not mean that the graphite filler of this invention is the only specified / limited.

[0052] It should be further noted that, under normal circumstances, other processing aids / fillers may be added to the raw materials specified in the technical solution of this invention. However, it is currently unknown whether this will have a significant impact on the technical contribution of this invention. Therefore, based on the principle of seeking truth from facts, this invention only limits polyethylene grafted with maleic anhydride and graphite filler to the raw materials. Under the condition of this raw material selection, a composite thermally conductive material with limited cost, uniform integrity and high thermal conductivity can be prepared.

[0053] In this article, the melt blending extrusion granulation described in step (1) is a conventional processing technology in the chemical industry. Those skilled in the art can directly refer to the melt blending extrusion granulation process of polyethylene recorded in existing technical literature for actual operation.

[0054] To better illustrate the present invention and provide an embodiment for reference, the melt blending extrusion granulation described in step (1) specifically uses a twin-screw extruder, with the temperature of zone one set to 120~130 ℃, the temperature of zone two set to 130~140 ℃, and the temperatures of zones three to six all set to 180~200 ℃, and the screw speed being 30~70 r / min.

[0055] In one embodiment, the polyethylene grafted with maleic anhydride with a 1% grafting rate in step (1) is 72 to 86 parts, for example, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86 parts or any range or point value therebetween; the polyethylene grafted with maleic anhydride with an 8% grafting rate is 14 to 28 parts, for example, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28 parts or any range or point value therebetween.

[0056] In this paper, the mixing process described in step (2) is to perform mixing processing using conventional torque rheometry mixing equipment. Those skilled in the art can directly refer to the mixing process of polyethylene recorded in existing technical literature for actual operation.

[0057] To better illustrate the present invention and provide an embodiment for reference, the mixing process in step (2) includes the following process parameters: mold cavity temperature of 180~200 ℃, rotor speed of 30~50 r / min, and mixing time of 5~15 min.

[0058] In one embodiment, the polyethylene-grafted maleic anhydride blend in step (2) is 10-50 parts, for example, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 parts. Any range or point value between them; the graphite filler is 50 to 90 parts, for example 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts, 60 parts, 61 parts, 62 parts, 63 parts, 64 parts, 65 parts, 66 parts, 67 parts, 68 parts, 69 parts, 70 parts, 71 parts, 72 parts, 73 parts, 74 parts, 75 parts, 76 parts, 77 parts, 78 parts, 79 parts, 80 parts, 81 parts, 82 parts, 83 parts, 84 parts, 85 parts, 86 parts, 87 parts, 88 parts, 89 parts, 90 parts or any range or point value between them.

[0059] In this document, the roll forming process described in step (3) using a two-roll mill involves shearing, plasticizing, and mixing the material using two counter-rotating inward-rotating rolls based on the roll gap, temperature, and relative speed, thereby forming the material into sheets or films. Typically, those skilled in the art can determine the specific roll forming process parameters based on the choice of the polymer matrix, such as the melt parameters of polyethylene, and the processing methods described in the instruction manual or existing literature of the two-roll mill.

[0060] To better illustrate the present invention and provide a reference technical solution, in order to prepare a highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive film, step (3) involves roll forming using a two-roll mill. The process parameters include: roll temperature of 130~150 ℃ (higher than the melting point of polyethylene), and roll gap control of 0.1~0.2 mm. After the blend melts and uniformly coats the surface of the roll, it is peeled off and cooled to obtain the highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive film.

[0061] The present application will be further explained in detail below with reference to embodiments. However, those skilled in the art should understand that these embodiments are provided for illustrative purposes only and are not intended to limit the present application.

[0062] Example

[0063] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the scope of this application. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all commercially available conventional products. This application should not be construed as being limited to the specific embodiments described.

[0064] 1. Raw materials

[0065] 1% grafted polyethylene grafted with maleic anhydride, FUSABOND E-226 Functional Polymer, melt index 1.75 g / 10 min, DOW Company.

[0066] 8% grafting rate polyethylene grafted with maleic anhydride, Shanghai Aladdin Co., Ltd.

[0067] Polyethylene, DGDX-6095, melt index 10.4 g / 10min, China Petroleum Xinjiang Dushanzi Petrochemical Company.

[0068] Graphite nanosheets, HGP-50, 50 μm in size, 1~15 nm in thickness, Qingdao Yanhai Carbon Materials Co., Ltd., require no pretreatment steps.

[0069] 2. Preparation method

[0070] (1) Based on a total mass of 100 parts, 72-86 parts of polyethylene grafted maleic anhydride with a grafting rate of 1% and 14-28 parts of polyethylene grafted maleic anhydride with a grafting rate of 8% are melt-blended, extruded and granulated to prepare a polyethylene grafted maleic anhydride blend.

[0071] The melt blending extrusion granulation is specifically carried out using a twin-screw extruder, with the temperature set to 120 ℃ in zone one, 140 ℃ in zone two, and 180 ℃ in zones three to six, and the screw speed being 50 r / min.

[0072] (2) Based on a total mass of 100 parts, 30 parts of the polyethylene-grafted maleic anhydride blend obtained in step (1) are mixed with 70 parts of graphite nanosheets and kneaded to prepare a composite material.

[0073] The mixing process parameters include: mold cavity temperature 180 ℃, rotor speed 50 r / min, and mixing time 15 min.

[0074] (3) The composite material obtained in step (2) is rolled using a two-roll mill (LRMR-S-150 / EW type) to prepare a high-filled graphite / polyethylene grafted maleic anhydride composite thermal conductive material.

[0075] The process involves roll forming using a two-roll open mill, with the following parameters: roll temperature of 145 ℃, roll gap of 0.2 mm, and front / rear roll speed ratio of 5:3. After the blend melts and evenly coats the roll surface, it is peeled off and cooled to obtain a highly filled graphite / polyethylene grafted maleic anhydride composite thermally conductive film with a thickness of approximately 0.2 mm.

[0076] 3. Testing Methods

[0077] The thermal conductivity of the samples was determined by laser flare analysis (LFA 467, Netzsch AG, Germany) according to standard ISO 22007-2. The samples were 25 mm diameter discs coated with a thin layer of graphite on both sides to ensure complete and uniform light absorption. The in-plane and through-plane thermal diffusivity (α) was measured separately. The thermal conductivity Tc was then calculated using the following formula:

[0078] Tc = α × ρ × Cp

[0079] Wherein, Cp (joules / gram Kelvin) is the specific heat capacity, and ρ (grams / cubic centimeter) is the composite density measured by a GH-120M density meter (Matharp, China).

[0080] Tensile strength tests were performed on an Inston 5966 universal testing machine (Inston Corporation, USA). Dumbbell-shaped specimens (75.0 mm total length, 25.0 mm gauge length) were cut from the samples. At least five specimens were tested for each formulation, according to ASTM D638, at a speed of 5 mm / min.

[0081] Example 1

[0082] Example 1 is based on the steps in "2. Preparation method" above, wherein step (1) involves melting and extruding 86 parts of polyethylene grafted maleic anhydride with a grafting rate of 1% and 14 parts of polyethylene grafted maleic anhydride with a grafting rate of 8% to prepare a polyethylene grafted maleic anhydride blend; finally, a highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive film with a thickness of about 0.2 mm is prepared as a sample for testing.

[0083] Example 2

[0084] Example 2 is based on the steps in "2. Preparation method" above, wherein step (1) involves melting and extruding 72 parts of polyethylene grafted maleic anhydride with a grafting rate of 1% and 28 parts of polyethylene grafted maleic anhydride with a grafting rate of 8% to prepare a polyethylene grafted maleic anhydride blend; finally, a high-filled graphite / polyethylene grafted maleic anhydride composite thermal conductive film with a thickness of about 0.2 mm is prepared as a sample for testing.

[0085] Comparative Example 1

[0086] Comparative Example 1 was prepared by replacing the polyethylene-grafted maleic anhydride blend with polyethylene, and included the following steps:

[0087] (I) By mass fraction, 30 parts of polyethylene and 70 parts of graphite nanosheets were mixed and kneaded to prepare a composite material;

[0088] The mixing process parameters include: mold cavity temperature 180 ℃, rotor speed 50 r / min, and mixing time 15 min.

[0089] (II) The composite material obtained in step (I) is rolled using a two-roll mill (LRMR-S-150 / EW type) to prepare a high-filled graphite / polyethylene composite thermal conductive material.

[0090] The process of roll forming using a two-roll open mill includes the following parameters: roll temperature of 145 ℃, front / rear roll speed ratio of 5:3, forcibly reducing the roll gap to squeeze the material into the rolls, and after the blend melts and does not uniformly coat the roll surface, it is peeled off and cooled to obtain a highly filled graphite / polyethylene composite thermally conductive film with a thickness of approximately 0.08 mm, which is then used as a sample for testing.

[0091] Comparative Example 2

[0092] Comparative Example 2 follows the steps in "2. Preparation Method" above, but in step (1), 8% grafted maleic anhydride of polyethylene was not added. Instead, 100 parts of 1% grafted maleic anhydride of polyethylene were melt-blended, extruded and granulated to prepare polyethylene grafted maleic anhydride granules. The polyethylene grafted maleic anhydride granules were then used as polyethylene grafted maleic anhydride blends to continue the subsequent steps. Finally, a high-filled graphite / polyethylene grafted maleic anhydride composite thermal conductive film with a thickness of about 0.2 mm was prepared as a sample for testing.

[0093] Comparative Example 3

[0094] Comparative Example 3 follows the steps in "2. Preparation Method" above, but in step (1), 1% grafted maleic anhydride of polyethylene was not added. Instead, 100 parts of 8% grafted maleic anhydride of polyethylene were melt-blended, extruded and granulated to prepare polyethylene grafted maleic anhydride granules. The polyethylene grafted maleic anhydride granules were then used as polyethylene grafted maleic anhydride blends to continue the subsequent steps. Finally, a high-filled graphite / polyethylene grafted maleic anhydride composite thermal conductive film with a thickness of about 0.2 mm was prepared as a sample for testing.

[0095] Test results are as follows Figures 1-7 As shown.

[0096] Comparative analysis during processing revealed that when the average grafting rate reached approximately 2% (Example 1), a uniform, complete, and highly processable composite thermal conductive film could be prepared. Surprisingly, the thermal conductivity of the sample prepared in Example 1 was significantly higher than that of the graphite / polyethylene composite thermal conductive film with the same filler content (Comparative Example 1). The in-plane thermal conductivity increased from 36.5 W / mK to 44.7 W / mK, and the transplane thermal conductivity increased from 3.0 W / mK to 4.1 W / mK. Example 1 showed the best test results, outperforming Comparative Examples 2 and 3. However, when the average grafting rate reached approximately 3% (Example 2), the thermal conductivity decreased. This indicates that there is a limit to the improvement in the thermal conductivity of the composite material by maleic anhydride groups, approximately 2%. It is speculated that when the maleic anhydride grafting rate is around 2%, the segments containing maleic anhydride groups encapsulate the GNP. The hydrogen bonds formed between the maleic anhydride groups and the oxygen-containing functional groups on the GNP surface improve interfacial compatibility. When the maleic anhydride grafting rate exceeds a critical value, the grafted chains form a thicker polymer interfacial layer on the GNP surface. Since the thermal conductivity of the polymer segments is much lower than that of the GNP, the excessively thick interfacial layer actually becomes an obstacle to heat flow, reducing the thermal conductivity.

[0097] Furthermore, although the sample prepared in Comparative Example 2 had a complete morphology, the microstructure of the product still contained certain voids and defects, such as... Figure 4 As shown.

[0098] The sample prepared in Comparative Example 3 exhibited flaking and powdering, and had very poor mechanical properties, failing to meet the usability requirements for commercial products. Figure 7 As shown. This may be because the molecular weight of maleic anhydride grafted onto polyethylene with a grafting rate of 8% is only 3000~5000, and the molecular chain is too short to bridge the filler particles.

[0099] Regarding tensile strength, tests showed that the tensile strength of the highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive films prepared in Examples 1 and 2 was not less than 18 MPa.

[0100] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a highly filled graphite / polyethylene grafted maleic anhydride composite thermally conductive material, characterized in that... Includes the following steps: (1) Based on a total mass of 100 parts, 72-86 parts of polyethylene grafted maleic anhydride with a grafting rate of 1% and 14-28 parts of polyethylene grafted maleic anhydride with a grafting rate of 8% are melt-blended, extruded and granulated to prepare a polyethylene grafted maleic anhydride blend. (2) Based on a total of 100 parts by weight, 10-50 parts of the polyethylene-grafted maleic anhydride blend obtained in step (1) are mixed with 50-90 parts of graphite filler and kneaded to prepare the composite material. (3) The composite material obtained in step (2) is rolled using a two-roll mill to prepare a high-filled graphite / polyethylene grafted maleic anhydride composite thermal conductive material.

2. The preparation method according to claim 1, characterized in that: The graphite filler includes at least one of graphite nanosheets, natural flake graphite, expandable graphite sheets, expanded graphite microspheres, worm-like expanded graphite, conductive graphite powder, and graphene nanosheets.

3. The preparation method according to claim 1, characterized in that: The melt blending extrusion granulation described in step (1) specifically uses a twin-screw extruder, with the temperature of zone one set to 120~130 ℃, the temperature of zone two set to 130~140 ℃, and the temperatures of zones three to six all set to 180~200 ℃, and the screw speed to 30~70 r / min.

4. The preparation method according to claim 1, characterized in that: The mixing process described in step (2) includes the following parameters: mold cavity temperature of 180~200 ℃, rotor speed of 30~50 r / min, and mixing time of 5~15 min.

5. The preparation method according to claim 1, characterized in that: In step (3), the rolling process using a two-roll open mill includes the following parameters: the roll temperature is 130~150 ℃.

6. The preparation method according to claim 1, characterized in that: In step (3), the rolling process using a two-roll open mill includes the following parameters: the roll gap is controlled to be 0.1~0.2 mm.

7. The highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive material prepared by the preparation method of the highly filled graphite / polyethylene grafted maleic anhydride composite thermal conductive material as described in claim 1.

8. The application of the highly filled graphite / polyethylene grafted maleic anhydride composite thermally conductive material as described in claim 7 as a heat dissipation material for electronic appliances.

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