Modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient, preparation method and application thereof

Abstract

This invention provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient, its preparation method, and its application, relating to the technical field of polymer materials. The modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient comprises the following raw material components: polypropylene resin, high thermal conductivity insulating filler, and additives; wherein the high thermal conductivity insulating filler includes spherical or near-spherical insulating thermally conductive fillers, as well as sheet-like insulating thermally conductive fillers. This invention provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient for automotive exterior parts, possessing both high thermal conductivity (λ), high thermal diffusivity (α, reflecting transient heat dissipation response), and low linear expansion coefficient (CLTE), thereby improving the reliability of automotive exterior parts in high-temperature environments, extending their service life, and improving the overall vehicle thermal management performance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient, its preparation method, and its application. Background Technology

[0002] With the increasing popularity of electric vehicles, automotive exterior components need to balance lightweight design, weather resistance, and thermal management capabilities. At high temperatures, polypropylene-based components such as bumpers and wheel arches are prone to heat accumulation due to their low thermal conductivity (typically <0.5 W / (m·K)), leading to thermal deformation, accelerated aging, and affecting the heat dissipation of surrounding electronic components. Furthermore, their high coefficient of linear expansion (CLTE) can cause changes in assembly gaps, abnormal noises, and appearance defects.

[0003] Current methods for thermal conductivity modification employ metal powders, carbon materials, or ceramic fillers. Metal powders decrease material insulation, increase density, and worsen corrosion resistance; carbon materials are costly, difficult to disperse, and prone to increasing electrical conductivity; the dispersion, orientation, and interfacial bonding of ceramic fillers within the polymer matrix remain technical challenges, making it difficult to construct an efficient thermal conductivity network, resulting in limited thermal conductivity improvement, and even compromising the material's mechanical properties and dimensional stability. While CN110628131A effectively reduces CLTE, its focus is on improving dimensional stability and does not provide a significant enhancement in thermal conductivity.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] One of the objectives of this invention is to provide a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient, so as to at least solve one of the technical problems existing in the prior art.

[0006] The second objective of this invention is to provide a method for preparing a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient.

[0007] The third objective of this invention is to provide a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient, or a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient prepared by the aforementioned preparation method, for use in the preparation of automotive exterior products.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient, comprising the following raw material components: Polypropylene resin, high thermal conductivity insulating filler and additives; The high thermal conductivity insulating filler includes spherical or near-spherical insulating thermal conductive fillers and sheet-like insulating thermal conductive fillers.

[0009] In an optional embodiment, the sheet-like insulating thermally conductive filler comprises one or both of boron nitride and aluminum nitride; Preferably, the sheet-like insulating and thermally conductive filler has an average particle size of 10~50 μm, a thickness of 0.5~5 μm, and an aspect ratio ≥10.

[0010] In an optional embodiment, the spherical or near-spherical insulating thermally conductive filler comprises one or both of alumina and silicon nitride; Preferably, the average particle size of the spherical or near-spherical insulating thermally conductive filler is 1~20 μm.

[0011] In an optional embodiment, the polypropylene resin comprises highly crystalline homopolymer polypropylene or block copolymer polypropylene, and the melt index of the polypropylene resin is 20-60 g / 10min.

[0012] In an optional embodiment, the additives include one or more of toughening agents, lubricants, antioxidants, and light stabilizers; Preferably, the modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient comprises, by weight parts: 40-70 parts polypropylene resin, 20-40 parts sheet-like insulating and thermally conductive filler, 5-15 parts spherical or near-spherical insulating and thermally conductive filler, 5-15 parts toughening agent, 0.1-0.5 parts lubricant, 0.2-0.8 parts antioxidant and 0.1-0.5 parts light stabilizer; Preferably, the toughening agent comprises an ethylene-octene copolymer; Preferably, the Mooney viscosity of the ethylene-octene copolymer is 30~70 MU; Preferably, the lubricant comprises zinc stearate and / or ethylene bis-stearamide; Preferably, the antioxidant includes one or two of hindered phenolic antioxidants and / or phosphite antioxidants; Preferably, the light stabilizer includes hindered amine light stabilizers.

[0013] Secondly, the present invention provides a method for preparing a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient, comprising the following steps: (a) Premixing polypropylene resin, toughening agent, lubricant, antioxidant and light stabilizer; (b) Add the premixed material obtained in step (a) into the main feed port of the extruder; (c) Add spherical or near-spherical insulating and thermally conductive filler from the first side feed port of the extruder, and add sheet-like insulating and thermally conductive filler from the second side feed port of the extruder, the second side feed port being downstream of the first side feed port; (d) The modified polypropylene composite material is obtained by melt extrusion and granulation.

[0014] In an optional embodiment, the spherical or near-spherical insulating thermally conductive filler and the sheet-like insulating thermally conductive filler are both surface-treated with a silane coupling agent before being added.

[0015] In an optional embodiment, the temperature from the feed section to the die head of the extruder is 170-210°C.

[0016] In an optional embodiment, the screw speed of the extruder is 300-500 rpm.

[0017] Thirdly, the present invention provides the application of a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient, or a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient prepared by the aforementioned preparation method, in the preparation of automotive exterior products.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient provided by this invention constructs a three-dimensional thermally conductive network with directional thermal conduction paths within the polypropylene matrix by synergistically introducing spherical or near-spherical insulating thermally conductive fillers and sheet-like insulating thermally conductive fillers. The spherical or near-spherical insulating thermally conductive fillers help improve melt flowability and serve as connection points in the thermally conductive network. The sheet-like insulating thermally conductive fillers are easily oriented under shear and tensile flow fields, and their later addition helps reduce excessive breakage. Furthermore, the pre-dispersed spherical or near-spherical insulating thermally conductive fillers promote dispersion and overlap, forming a three-dimensional thermally conductive network with sheet-like insulating thermally conductive fillers as the backbone and spherical or near-spherical insulating thermally conductive fillers as nodes. This network not only significantly improves the material's steady-state thermal conductivity (λ) but also enhances the thermal diffusivity (α), giving the material excellent transient heat dissipation response capabilities and enabling rapid heat conduction and dissipation from the surface of exterior components. Meanwhile, spherical or near-spherical insulating and thermally conductive fillers and sheet-like insulating and thermally conductive fillers have low coefficients of thermal expansion. Their uniform dispersion and good interfacial bonding in the matrix can effectively constrain the thermal motion of polymer molecular chains, thereby significantly reducing the CLTE of the composite material and ensuring the dimensional stability of the exterior parts at high temperatures. Detailed Implementation

[0019] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0021] The first aspect of this invention provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient, comprising the following raw material components: polypropylene resin (PP), high thermal conductivity insulating filler, and additives; wherein the high thermal conductivity insulating filler includes spherical or near-spherical insulating thermal conductive filler, as well as sheet-like insulating thermal conductive filler. Optionally, the additives include one or more of toughening agents, lubricants, antioxidants, and light stabilizers.

[0022] This invention provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient for automotive exterior parts. The modified polypropylene composite material has high thermal conductivity (λ), high thermal diffusivity (α, reflecting transient heat dissipation response capability) and low linear expansion coefficient (CLTE), which improves the reliability of automotive exterior parts in high-temperature environments, extends service life and improves the thermal management performance of the whole vehicle.

[0023] To further explain, this invention constructs a highly efficient and stable three-dimensional thermally conductive network within the matrix by selecting superior insulating high thermal conductivity fillers and their compounding, and optimizing filler surface treatment and dispersion orientation processes, while ensuring that mechanical properties are essentially unaffected. Through the combination of spherical or near-spherical insulating thermally conductive fillers and sheet-like insulating thermally conductive fillers (high aspect ratio, high in-plane thermal conductivity), along with optimized processing techniques (stepwise feeding, shear orientation), a highly efficient three-dimensional thermally conductive network is constructed within the polypropylene matrix. This network not only significantly improves the material's steady-state thermal conductivity (λ) but also enhances the thermal diffusivity (α), giving it excellent steady-state and transient heat dissipation capabilities, rapidly dissipating heat accumulated on the surface of the exterior components. While improving thermal conductivity, it maintains or further reduces the material's coefficient of linear thermal expansion (CLTE), ensuring dimensional stability of the parts under high-temperature conditions and preventing thermal deformation.

[0024] Furthermore, while achieving high thermal conductivity and low CLTE, this invention maintains good impact toughness, processing flowability, and weather resistance through POE toughening and filler surface treatment, meeting the comprehensive usage requirements of automotive exterior parts. It also provides insulation and safety; the spherical or near-spherical insulating thermally conductive fillers and sheet-like insulating thermally conductive fillers in this invention are all insulating fillers, ensuring high volume resistivity of the composite material, suitable for various electrically charged or insulation-requiring parts of automotive exterior parts. Simultaneously, polypropylene resin provides the main structure and processing basis, toughening agents mitigate the embrittlement tendency that may be caused by high filler content, lubricants optimize melt flowability to ensure uniform dispersion and orientation of the fillers, and antioxidants and light stabilizers synergistically resist thermal-oxidative and UV aging, jointly maintaining the overall performance balance and long-term reliability of the material in the harsh service environment of automotive exterior parts.

[0025] Optionally, the aspect ratio (longest axis / shortest axis) of a sphere is 1.0; for near-spherical (quasi-spherical) shapes, the aspect ratio is required to be ≤2.0.

[0026] In some preferred embodiments, the modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient comprises, by weight: 40 to 70 parts of polypropylene resin, for example, 40, 45, 50, 55, 60, 65, 70 parts, etc., more preferably 50 to 60 parts.

[0027] 20 to 40 parts of sheet-like insulating and thermally conductive filler, for example, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, etc., more preferably 20 to 30 parts.

[0028] 5 to 15 parts of spherical or near-spherical insulating and thermally conductive filler, for example, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, etc., and more preferably 10 parts.

[0029] 5 to 15 parts of toughening agent, for example, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 parts, etc., more preferably 8 parts.

[0030] 0.1 to 0.5 parts of lubricant, for example, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, etc., more preferably 0.3 parts.

[0031] 0.2 to 0.8 parts of antioxidant, for example, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, etc., more preferably 0.5 parts.

[0032] 0.1 to 0.5 parts of light stabilizer, for example, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, etc., more preferably 0.2 parts.

[0033] In some preferred embodiments, the sheet-like insulating thermally conductive filler comprises one or both of hexagonal boron nitride (h-BN) lamellar crystals and sheet-like aluminum nitride (AlN). The average particle size D50 of the sheet-like insulating thermally conductive filler is 10~50 μm, for example, it can be 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, etc., and the thickness is 0.5~5 μm, for example, it can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc., with an aspect ratio ≥10. More preferably, the sheet-like insulating thermally conductive filler is hexagonal boron nitride (h-BN) lamellar crystals, which possess extremely high in-plane thermal conductivity (approximately 300 W / (m·K)) and good electrical insulation properties.

[0034] In some preferred embodiments, the spherical or near-spherical insulating thermally conductive filler comprises one or both of alumina (Al2O3) powder and silicon nitride (Si3N4) powder, and the average particle size D50 of the spherical or near-spherical insulating thermally conductive filler is 1~20 μm, for example, it can be 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, etc. Alumina has a high thermal conductivity (approximately 30 W / (m·K)), good insulation, and low cost.

[0035] In some preferred embodiments, the polypropylene resin comprises highly crystalline homopolymer polypropylene or block copolymer polypropylene, with a melt index (230°C, 2.16 kg) of 20-60 g / 10 min. The highly crystalline homopolymer polypropylene and / or the highly crystalline block copolymer polypropylene both have a crystallinity ≥ 55%.

[0036] Further preferably, the highly crystalline homopolymer polypropylene is selected from one or more of Lanzhou Petrochemical H9018 (melt index 54~56 g / 10min, 230℃ / 2.16kg) and the highly crystalline block copolymer polypropylene is selected from ExxonMobil AP03B (melt index 30 g / 10min, 230℃ / 2.16kg).

[0037] In some preferred embodiments, the toughening agent comprises ethylene-octene copolymer (POE).

[0038] The Mooney viscosity (ML 1+4 @121℃) of the ethylene-octene copolymer is 30~70 MU.

[0039] In some preferred embodiments, the lubricant comprises zinc stearate and / or ethylene bis-stearamide (EBS).

[0040] In some preferred embodiments, the antioxidant includes hindered phenolic antioxidants (such as 1010) and / or phosphite antioxidants (such as 168).

[0041] In some preferred embodiments, the light stabilizer includes hindered amine light stabilizers (HALS).

[0042] A second aspect of the present invention provides a method for preparing a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient, comprising the following steps: (a) Premixing polypropylene resin, toughening agent, lubricant, antioxidant and light stabilizer; (b) Add the premixed material obtained in step (a) into the main feed port of the extruder; (c) Add spherical or near-spherical insulating and thermally conductive filler from the first side feed port of the extruder, and add sheet-like insulating and thermally conductive filler from the second side feed port of the extruder, the second side feed port being downstream of the first side feed port; (d) The modified polypropylene composite material is obtained by melt extrusion and granulation.

[0043] In some preferred embodiments, the spherical or near-spherical insulating thermally conductive filler and the sheet-like insulating thermally conductive filler may be surface-treated with a silane coupling agent (such as KH-550, KH-560) before being added to improve their interfacial compatibility and dispersibility with the polypropylene matrix.

[0044] In some preferred embodiments, the temperature from the feed section to the die head of the extruder is 170-210°C, and the screw speed of the extruder is 300-500 rpm.

[0045] In a preferred embodiment of the present invention, the preparation method of the modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient specifically includes the following steps: S1. Surface treatment: The sheet-like insulating thermally conductive filler (hereinafter referred to as filler A) and the spherical or near-spherical insulating thermally conductive filler (hereinafter referred to as filler B) are respectively surface treated with silane coupling agent ethanol solution and dried for later use.

[0046] S2. Premixing: Add polypropylene resin, toughening agent, lubricant, antioxidant, and light stabilizer to a high-speed mixer and mix for 2-4 minutes.

[0047] S3. Step-by-step addition and mixing: a. Add the premixed material (S2) to the main feed port of the twin-screw extruder.

[0048] b. Add the surface-treated filler B through the first feed port of the extruder.

[0049] c. Add the surface-treated filler A from the middle and rear section of the extruder (second side feed port).

[0050] S4. Melt Extrusion: The twin-screw extruder temperature setting from the feeding section to the die head is 170-210℃, and the screw speed is 300-500 rpm. A combination of high-shear kneading blocks and appropriate vacuum venting (vacuum degree ≤ -0.07 MPa) is employed to ensure sufficient dispersion and orientation of the filler and to remove volatiles.

[0051] S5. Granulation and post-treatment: The modified polypropylene composite material is obtained by extrusion, water cooling, pelletizing and drying.

[0052] The third aspect of this invention provides the application of a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient, or a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient prepared by the aforementioned preparation method, in the preparation of automotive exterior products.

[0053] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0054] The polypropylene resin used in the following examples is a highly crystalline block copolymer polypropylene selected from ExxonMobil AP03B (melt index 30 g / 10min, 230℃ / 2.16kg).

[0055] Example 1 This embodiment provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient. Its formulation composition is shown in Table 1. Filler A is hexagonal boron nitride (h-BN) lamellar crystals with a D50 of 30 μm, a thickness of 3 μm, and an aspect ratio ≥10. Filler B is spherical or near-spherical Al2O3 powder with a D50 of 10 μm.

[0056] The modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient was prepared according to the formulation table. The process is as follows: S1. Surface-treat filler A and filler B with an ethanol solution of 1 wt% KH-550 silane coupling agent and dry at 80°C.

[0057] S2. Add PP, POE, EBS, antioxidant, and light stabilizer to a high-speed mixer and premix for 3 minutes to obtain a premix.

[0058] S3. Use a co-rotating twin-screw extruder (length-to-diameter ratio 40:1), set the temperature of the temperature zone, and set the screw speed of the extruder to 400 rpm.

[0059] The temperature zones are specifically defined as follows: Zone 1 (Feeding Section): 180℃; Zones 2 to 4 (melting and mixing sections): Zone 2 is set at 190°C, Zone 3 at 195°C, and Zone 4 at 200°C; Zone 5 (first side feeding port, spherical Al2O3 added): Temperature appropriately reduced (set to 195℃); Zone 6 (Second kneading and dispersing zone): 200℃; Zone 7 (second side feeding port, flaky BN added): 195℃; Zone 8 (Homogenization / Exhaust Section): Set as the highest temperature zone (200℃); Zone 9 (Melting Conveying Section): Temperature dropped slightly (195℃); Zone 10 (Head): Temperature further decreased (185℃).

[0060] S4. Add the premixed material from the main feed port, add the surface-treated filler B from the first side feed port (about 1 / 3 of the screw length), and add the surface-treated filler A from the second side feed port (about 2 / 3 of the screw length).

[0061] S5. Melt extrusion, water cooling, pelletizing, and drying are performed to obtain modified polypropylene granules, which are then injection molded into test specimens (size: 80*10*4mm; when testing thermal conductivity, the specimens can be cut from the above specimens to 10*10*4mm).

[0062] Example 2 This embodiment provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient. The difference between this embodiment and Example 1 is that the formulation composition is different, as shown in Table 1; the preparation process is the same as that of Example 1.

[0063] Example 3 This embodiment provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient. The difference between this embodiment and Example 1 is that the formulation composition is different, as shown in Table 1; the preparation process is the same as that of Example 1.

[0064] Example 4 This embodiment provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient. The difference between this embodiment and Example 1 is that the formulation composition is different, as shown in Table 1; the preparation process is the same as that of Example 1.

[0065] Example 5 This embodiment provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient. The difference between this embodiment and Example 1 is that the formulation composition is different, as shown in Table 1; the preparation process is the same as that of Example 1.

[0066] Example 6 This embodiment provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient. The formulation composition is shown in Table 1. The difference between this and Example 1 is that: filler A is flake aluminum nitride (AlN) with a D50 of 30 μm, a thickness of 3 μm, and an aspect ratio ≥10; filler B is silicon nitride (Si3N4) powder with a D50 of 10 μm; and its preparation process is the same as that of Example 1.

[0067] Comparative Example 1 This comparative example provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient. The difference between this example and Example 1 is that the formulation composition is different, as shown in Table 1; the preparation process is the same as that of Example 1.

[0068] Comparative Example 2 This comparative example provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient. The difference between this example and Example 1 is that the formulation composition is different, as shown in Table 1; the preparation process is the same as that of Example 1.

[0069] Comparative Example 3 This comparative example provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient. The difference between this example and Example 1 is that the formulation composition is different, as shown in Table 1; the preparation process is the same as that of Example 1.

[0070] Comparative Example 4 This comparative example provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient. The formulation composition is shown in Table 1. The difference between this and Example 1 is that filler A is hexagonal boron nitride whiskers; and its preparation process is the same as that of Example 1.

[0071] Comparative Example 5 This comparative example provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient. The formulation composition is shown in Table 1. The difference from Example 1 is that in S4, surface-treated filler A is added from the first side feed port, and surface-treated filler B is added from the second side feed port (about 2 / 3 of the screw length). The rest is the same as in Example 1.

[0072] Comparative Example 6 This comparative example provides a modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient. The formulation composition is shown in Table 1. The difference from Example 1 is that in S4, BN and Al2O3 are all added from the main feed port, while the rest is the same as in Example 1.

[0073] Table 1

[0074] The splines obtained from the examples and comparative examples were tested for their corresponding performance using the following methods: Thermal conductivity (λ): Tested using the laser flare method (LFA) according to ISO 22007-2 standard.

[0075] Thermal diffusivity (α): It can be directly measured by the laser flare method (LFA) or calculated by the formula α=λ / (ρ* Cp), where ρ is density and Cp is specific heat capacity.

[0076] Coefficient of linear expansion (CLTE): Tested using a thermomechanical analyzer (TMA) in accordance with ISO 11359-2, within a temperature range of -30 to 85°C.

[0077] Notched impact strength of cantilever beam: tested according to ISO 180 standard.

[0078] Bending performance: Tested according to ISO 178 standard.

[0079] The performance test results are shown in Table 2.

[0080] Table 2

[0081] As shown in Table 2, compared with the comparative examples, the embodiments provided by the present invention maintain high thermal conductivity, high thermal diffusivity and low linear expansion coefficient, while the notched impact strength does not decrease significantly, and the overall comprehensive performance is better than that of the comparative examples.

[0082] Examples 1-3 all employed a compounding process of spherical Al2O3 and flake-shaped BN, with a stepwise feeding method, resulting in a complete thermally conductive network. As the total filler content decreased from 40 parts to 30 parts, the thermal conductivity and heat dissipation decreased, while the CLTE (Coefficient of Thermal Expansion) increased accordingly, achieving high thermal conductivity, rapid heat dissipation, and low thermal expansion. In Example 4, the upper limit of the total filler content (45 parts) and the lower limit of PP (40 parts) resulted in a decrease in impact strength despite the increased filler content. In Example 5, the upper limit of PP content (70 parts) and the upper limit of POE content (15 parts) resulted in slightly inferior thermal conductivity compared to the high-filler scheme. However, the overall performance of Examples 4-5 was still better than the comparative example, verifying the rationality of the optimized parameter range in this invention. Example 6, using BN and Al2O3 with different particle size distributions and equal limiting conditions, still achieved excellent overall performance.

[0083] Comparative Example 1, without any thermally conductive filler, exhibited extremely poor thermal conductivity and thermal diffusivity, with a high CLTE (Coefficient of Thermal Dispersion). Comparative Example 2, with only BN added and no Al2O3 added, showed lower thermal conductivity and thermal diffusivity than Example 1 with the same amount of BN, and a higher CLTE and lower impact strength. This indicates that the combination of BN and spherical Al2O3, along with the corresponding stepwise processing technology, plays a crucial role in constructing a more complete thermally conductive network and balancing various performance characteristics. In Comparative Example 3, without BN, the spherical filler alone could not form an efficient thermally conductive path, demonstrating the key role of plate-like BN. Therefore, through Examples 1, 2, and 3, it is evident that the combination of BN plates and spherical Al2O3 to construct a three-dimensional thermally conductive network with a plate-like backbone and spherical nodes significantly outperforms the single-filler scheme in both thermal conductivity and thermal diffusivity.

[0084] Comparative Example 4 uses BN whiskers instead of BN lamellar crystals. Although whiskers have some thermal conductivity, they severely impair impact toughness, demonstrating the advantage of the lamellar crystal morphology. Therefore, as shown in Example 1 and Comparative Example 4, high aspect ratio (≥10) BN lamellar crystals are superior to BN whiskers, maintaining good impact toughness while ensuring thermal conductivity.

[0085] In Comparative Example 5, BN (filler A) was added first, followed by Al2O3 (filler B) to verify the effect of the feeding order on the construction of the thermally conductive network. The difference between this comparative example and Example 1 lies in the adjustment of the feeding order. Specifically, hexagonal boron nitride (BN, filler A) was added from the first feeding port, and spherical alumina (Al2O3, filler B) was added from the second feeding port; that is, flake-shaped BN was added first, followed by spherical Al2O3. All other components and process conditions were the same as in Example 1. The performance test results of the resulting composite material are shown in Table 2: the thermal conductivity was 2.2 W / (m·K), and the thermal diffusivity was 1.3 mm. 2 / s, the linear expansion coefficient (CLTE) is 4.3×10 -5 / K, notched impact strength is 6.5 kJ / m 2 Compared to Example 1, because the BN flakes underwent a longer shearing process when added first, some flakes broke, resulting in an incomplete thermal network structure, decreased thermal conductivity and dimensional stability, and reduced impact toughness.

[0086] In Comparative Example 6, both BN and Al2O3 were added from the main feed inlet to verify the necessity of stepwise feeding (B first, then A). The difference between this comparative example and Example 1 lies in the feeding method. Specifically, hexagonal boron nitride (BN, filler A) and spherical alumina (Al2O3, filler B) were both added simultaneously from the main feed inlet, rather than being fed stepwise from the side. The remaining components and process conditions were the same as in Example 1. The performance test results of the resulting composite material are shown in Table 2: the thermal conductivity was 1.9 W / (m·K), and the thermal diffusivity was 1.1 mm.2 / s, the linear expansion coefficient (CLTE) is 5.3×10 -5 / K, notched impact strength is 7.5 kJ / m 2 Compared to Example 1, the BN flakes, subjected to intense shearing throughout the extrusion process, lose their high aspect ratio characteristics, making it difficult to form effective orientation and overlap; premature addition of spherical Al2O3 may also lead to agglomeration. Neither method can construct a complete three-dimensional thermally conductive network, resulting in significant deterioration of thermal conductivity and dimensional stability.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient, characterized in that, Includes the following raw material components: Polypropylene resin, high thermal conductivity insulating filler and additives; The high thermal conductivity insulating filler includes spherical or near-spherical insulating thermal conductive fillers and sheet-like insulating thermal conductive fillers.

2. The modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient according to claim 1, characterized in that, The sheet-like insulating and thermally conductive filler includes boron nitride and / or aluminum nitride; Preferably, the sheet-like insulating and thermally conductive filler has an average particle size of 10~50 μm, a thickness of 0.5~5 μm, and an aspect ratio ≥10.

3. The modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient according to claim 1, characterized in that, The spherical or near-spherical insulating and thermally conductive filler includes alumina and / or silicon nitride; Preferably, the average particle size of the spherical or near-spherical insulating thermally conductive filler is 1~20 μm.

4. The modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient according to claim 1, characterized in that, The polypropylene resin includes highly crystalline homopolymer polypropylene or block copolymer polypropylene, and the melt index of the polypropylene resin is 20-60 g / 10min.

5. The modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient according to claim 1, characterized in that, The additives include one or more of toughening agents, lubricants, antioxidants, and light stabilizers; Preferably, the modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient comprises, by weight parts: 40-70 parts polypropylene resin, 20-40 parts sheet-like insulating and thermally conductive filler, 5-15 parts spherical or near-spherical insulating and thermally conductive filler, 5-15 parts toughening agent, 0.1-0.5 parts lubricant, 0.2-0.8 parts antioxidant and 0.1-0.5 parts light stabilizer; Preferably, the toughening agent comprises an ethylene-octene copolymer; Preferably, the Mooney viscosity of the ethylene-octene copolymer is 30~70 MU; Preferably, the lubricant comprises zinc stearate and / or ethylene bis-stearamide; Preferably, the antioxidant includes hindered phenolic antioxidants and / or phosphite antioxidants; Preferably, the light stabilizer includes hindered amine light stabilizers.

6. The method for preparing the modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient as described in any one of claims 1-5, characterized in that, Includes the following steps: (a) Premixing polypropylene resin, toughening agent, lubricant, antioxidant and light stabilizer; (b) Add the premixed material obtained in step (a) into the main feed port of the extruder; (c) Add spherical or near-spherical insulating and thermally conductive filler from the first side feed port of the extruder, and add sheet-like insulating and thermally conductive filler from the second side feed port of the extruder, the second side feed port being downstream of the first side feed port; (d) The modified polypropylene composite material is obtained by melt extrusion and granulation.

7. The preparation method according to claim 6, characterized in that, Before being added, both the spherical or near-spherical insulating and thermally conductive fillers and the sheet-like insulating and thermally conductive fillers are surface-treated with silane coupling agents.

8. The preparation method according to claim 6, characterized in that, The temperature from the feed section to the die head of the extruder is 170-210℃.

9. The preparation method according to claim 6, characterized in that, The screw speed of the extruder is 300-500 rpm.

10. The application of the modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient as described in any one of claims 1-5, or the modified polypropylene composite material with high thermal conductivity and low linear expansion coefficient prepared by the preparation method described in any one of claims 6-9, in the preparation of automotive exterior products.

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