Epoxy resin-based heat-conducting insulating composite material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of coatings for battery cooling plates, and particularly relates to an epoxy resin-based heat-conducting insulating composite material as well as a preparation method and application thereof. Aiming at the defect of relatively insufficient flexibility, 3-5% of flexible chain segment flexibilizer (such as carboxyl-terminated nitrile rubber CTBN or polyurethane prepolymer) is added, and the toughness is improved by 20% on the premise that the heat conductivity is not reduced. Or a low-temperature pre-curing and high-temperature post-curing two-step method (such as 80 DEG C / 2h and 120 DEG C / 2h) is adopted to regulate and control the density distribution of the cross-linked network and balance the hardness and the flexibility.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coatings for battery cooling plates, and particularly relates to an epoxy resin-based thermal conductive and insulating composite material, a preparation method thereof and an application thereof. BACKGROUND

[0002] As a core component of the power battery thermal management system, the battery cooling plate needs to meet multiple requirements such as high thermal conductivity, high insulation, corrosion resistance and construction convenience. At present, the following technical solutions are mainly used in the industry: 1. Solvent-based epoxy resin coating Solvent-based coatings can reduce the viscosity of the system by adding organic solvents (such as xylene and butanone), which can achieve medium-temperature curing at 120-150°C or room-temperature catalytic curing, avoiding thermal damage to the battery module. The thermal conductivity is improved by adding thermal conductive fillers. This technology realizes weather resistance and heat dissipation, but solvent volatilization can increase the porosity of the coating, affecting the compactness, and there is a problem of volatile organic compound (VOC) emission, which does not meet environmental protection requirements. In addition, solvent residues may reduce the long-term insulation stability of the coating.

[0003] 2. Epoxy resin powder coating Powder coatings can be applied without solvent (VOC≈0) through electrostatic spraying process, avoiding environmental pollution and health risks of traditional solvent-based coatings, meeting the requirements of green manufacturing in the battery industry. Powder coatings do not need to be diluted and can be directly applied to the surface of metal substrates through spraying or fluidized bed process, reducing coating waste and post-processing costs. Epoxy resin itself has good electrical insulation and chemical corrosion resistance, which can meet the basic requirements of insulation and electrolyte corrosion resistance of battery cooling plates. However, the poor flowability of molten resin makes it difficult to achieve ultra-thin coatings, increasing the thermal resistance and material cost. Air bubbles may be formed when powder particles melt, or pinholes may be caused by oil stains on the substrate surface, leading to insulation failure. It is difficult to uniformly coat the dead angle area of complex structures (such as micro-channel cooling plates), and there is a risk of local non-coating.

[0004] 3. Composite phase change material technology By using the characteristics of phase change materials (such as paraffin, fatty acids or metal alloys) to absorb / release latent heat when they undergo solid-liquid phase change at a specific temperature range, the battery operating temperature can be stabilized in the optimal range, solving the limitation of passive heat dissipation of traditional thermal conductive coatings. After compounding with the epoxy resin matrix, a uniform coating can be formed through spraying or molding process, which is suitable for complex micro-channel structures. However, the phase change process needs to reach a threshold temperature to start, and when a sudden large current discharge occurs, the temperature rise rate may exceed the heat absorption rate of the phase change, causing local hot spots. Moreover, the cycle stability of the phase change material is insufficient, and long-term use may cause performance degradation due to phase change fatigue.

[0005] 4. Solventless liquid epoxy resin coating Advantages: (1) Zero VOC emissions: Direct compounding of low viscosity epoxy resin with room temperature curing agent without adding organic solvents, in line with "Low Volatile Organic Compound Content Coating Product Technical Requirements" (GB / T 38597-2020). (2) Simplify the construction process: can be directly coated by spraying, dipping or scraping process, without complex VOC treatment equipment, the production cost is reduced by more than 30%. (3) No solvent residue: no porosity or micropore defects after curing, high density of coating, reducing the risk of insulation performance deterioration caused by solvent volatilization. (4) Introducing silane coupling agent to modify the filler, enhance the interfacial bonding force between filler and resin matrix.

[0006] Disadvantages: (1) Filler dispersion process complexity: uniform dispersion of high proportion of fillers (60-70 wt%) depends on high precision grinding equipment (such as three roll mill) and vacuum defoaming process, the equipment investment cost is high, and it is sensitive to operating parameters (such as grinding pressure, speed), which may affect batch stability. (2) Interface matching with metal substrate: the difference in thermal expansion coefficient between epoxy resin and aluminum substrate may cause interface stress concentration after long-term cycling, which needs to be relieved by interface transition layer or gradient elastic modulus design. (3) Curing condition sensitive: latent curing agent is sensitive to temperature / humidity, precise control of curing parameters is needed to avoid incomplete curing or premature reaction. (4) High crosslinking density of epoxy resin, after curing, the hardness is high, in the scene of frequent cold and hot cycle or mechanical vibration, microcracks may appear due to stress concentration. SUMMARY

[0007] Therefore, the technical problem to be solved by the present application is mainly to overcome the defects described in the background art, and to provide an epoxy resin-based thermal conductive insulation composite material, its preparation method and application, to solve the problems of complex high proportion of filler dispersion process, poor interface matching with metal substrate, sensitive to curing conditions and prone to microcracks under cold and hot / mechanical cycles of the current epoxy resin-based composite material.

[0008] To achieve the above technical purposes, the technical scheme adopted by the present application is as follows: The first technical purpose of the present application is to provide an epoxy resin-based thermal conductive insulation composite material, the preparation raw materials of the material are as follows in terms of weight fraction: Epoxy resin: 30~60 parts; Curing agent: 2~4 parts; Promoter: 0~1 part; Filler: 30~50 parts; Leveling agent: 0.5~2 parts; Toughening agent: 3~12 parts; Silane coupling agent: 0~1 part; Preferably, the epoxy resin is bisphenol F type epoxy resin, and the epoxy equivalent weight is 156 g / eq-165 g / eq.

[0009] Preferably, the curing agent is micro powder dicyandiamide, and the particle size is 5-10 μm.

[0010] Preferably, the accelerator is one or a mixture of several of N-(2-hydroxyphenyl)-N',N'-dimethylurea, N-(2-hydroxy-4-nitrophenyl)-N',N'-dimethylurea, N-(5-chloro-2-hydroxyphenyl)-N',N'-dimethylurea, N-(4-chlorophenyl)-N',N'-dimethylurea, N-(4-chloro-2-hydroxyphenyl)-N',N'-dimethylurea, 2-methylimidazole, 2-isopropylimidazole, 2-propylimidazole, 2-isopropylimidazole, 2-propylimidazole.

[0011] Preferably, the filler is one or a mixture of several of alumina, boron nitride, and the particle size is 0.5-120 μm.

[0012] Preferably, the leveling agent is at least one of acrylate leveling agent, silicone leveling agent, and preferably polyether-modified polydimethylsiloxane.

[0013] Preferably, the toughening agent is at least one of carboxyl-terminated liquid nitrile rubber, amino-terminated liquid nitrile rubber, and epoxy-terminated liquid nitrile rubber.

[0014] Preferably, the silane coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

[0015] A second technical object of the present application is to provide a method for preparing the epoxy resin-based thermal conductive and insulating composite material as described above, and the method specifically comprises the following steps: (1) dissolving a proper amount of silane coupling agent in deionized water, adding a filler dispersion liquid after hydrolysis, refluxing at 80°C for 4 h, centrifuging, washing and drying to obtain a modified filler; (2) mixing the modified filler obtained in step (1) with an epoxy resin, and stirring at a uniform speed of 300-600 r / min for 30 min; (3) adding the mixture of step (2) to a curing agent, an accelerator and other additives, and stirring at a uniform speed of 1000-1500 r / min for 30 min; (4) putting the mixture of step (3) into a planetary gravity stirrer, and mixing for 5 min at a vacuum degree of 1.5 kPa and a rotation speed of 1500 rpm to finally obtain the epoxy resin-based thermal conductive and insulating composite material.

[0016] Compared with the prior art, the present application has the following advantages: (1) The thermal conductivity is significantly improved: The surface of the alumina filler is modified by silane coupling agent in the present application. The modified alumina can be better dispersed in the epoxy resin, which makes the thermal conductivity of the composite material increase by 10% compared with the material prepared by unmodified filler. In practical application in battery cooling plate, it can more efficiently conduct the heat generated by the battery, ensure the battery to work in a suitable temperature environment, prolong the service life of the battery, and improve the performance and safety of the battery. When the content of modified filler is 50 parts, the thermal conductivity of the composite material can reach 0.56 W / m・K, which meets the requirements of high power density battery thermal management on thermal conductivity.

[0017] (2) The mechanical properties are optimized: By adding appropriate amount of toughening agent, the impact resistance of the coating is significantly improved while maintaining the insulation performance of the composite material. Carboxyl-terminated liquid nitrile rubber can form micro-phase separation structure in the epoxy resin matrix. When impacted, these micro-phase structures can absorb and disperse energy, thereby improving the toughness and impact resistance of the coating, and making the impact resistance of the coating break through 50 cm (positive impact). In addition, the addition of toughening agent also alleviates the problem of coating embrittlement caused by high filler load to a certain extent, improves the comprehensive mechanical properties of the coating, and makes the composite material more durable in actual use, reducing the damage of the coating caused by external impact.

[0018] (3) Excellent environmental resistance: The composite material prepared in the present application has good acid and alkali resistance. There is no coating falling phenomenon after soaking in 10% H2SO4 / NaOH solution for 240 hours. This indicates that the composite material can maintain stable performance in a relatively harsh chemical environment, and is suitable for various complex use scenarios, such as outdoor energy storage systems, electric vehicles, etc. which may come into contact with acid and alkali substances. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the present application, and those skilled in the art can obtain other drawings according to the provided drawings without creating any inventive labor.

[0020] Figure 1 The structure diagram of the KH-550 modified spherical alumina involved in the present application.

[0021] Figure 2 The scanning electron microscope (SEM) images of the epoxy resin and its composite material, and the spherical alumina before and after modification involved in the present application. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0023] Herein, the term "embodiment" is not necessarily construed as superior or better than other embodiments. In the performance index test of the embodiments of the present application, unless otherwise specified, the conventional test method in the art is adopted. It should be understood that the terms described in the present application are only for describing the specific embodiments, and are not used to limit the disclosure of the present application.

[0024] Unless otherwise specified, the technical and scientific terms used herein have the same meanings as generally understood by a person of ordinary skill in the art to which the present application belongs; and the test methods and technical means not specifically noted in the present application refer to the test methods and technical means generally used by a person of ordinary skill in the art.

[0025] In order to better illustrate the content of the present application, numerous specific details are given in the specific embodiments below. A person of ordinary skill in the art should understand that the present application can also be implemented without some specific details. In the embodiments, some methods, means, instruments, devices and the like which are well known to a person of ordinary skill in the art are not described in detail, in order to highlight the main idea of the present application.

[0026] The technical features disclosed in the embodiments of the present application can be combined in any manner without conflict, and the technical solutions obtained by the combination belong to the disclosure of the embodiments of the present application.

[0027] The present application discloses an epoxy resin-based heat-conducting and insulating composite material and a preparation method thereof.

[0028] It should be noted that the bisphenol F reaction solution used in the following embodiments is a reaction solution synthesized in the laboratory; and the reagents or instruments not marked with the manufacturer are conventional reagent products that can be obtained by purchase in the market.

[0029] In order to better understand the present application, the following embodiments are further specifically described below, but it should not be understood as limiting the present application. Some non-essential improvements and adjustments made by a person of ordinary skill in the art based on the above disclosure are also considered to fall within the scope of protection of the present application. Embodiment

[0030] The present embodiment provides an epoxy resin-based heat-conducting and insulating composite material and a preparation method thereof, specifically comprising the following steps: (1) A certain amount of γ-aminopropyl triethoxysilane (KH-550) is dissolved in deionized water, and after hydrolysis, alumina dispersion liquid is added, and refluxed at 80°C for 4h, centrifuged, washed and dried to obtain modified alumina; (2) The modified alumina obtained in step (1) is mixed with epoxy resin, and stirred at a uniform speed of 300-600r / min for 30min; (3) The mixture of step (2) is added with dicyandiamide curing agent, accelerant and other additives, and stirred at a uniform speed of 1000-1500r / min for 30min; (4) The mixture of step (3) is put into a planetary gravity stirrer, with a vacuum degree of 1.5kPa and a rotation speed of 1500rpm, and mixed for 5min, to finally obtain the epoxy resin-based thermal conductive and insulating composite material.

[0031] The present comparative example provides an epoxy resin-based thermal conductive and insulating composite material and a preparation method thereof, specifically comprising the following steps: (1) Alumina is mixed with epoxy resin, and stirred at a uniform speed of 300-600r / min for 30min; (2) The mixture of step (1) is added with dicyandiamide curing agent, accelerant and other additives, and stirred at a uniform speed of 1000-1500r / min for 30min; (3) The mixture of step (2) is put into a planetary gravity stirrer, with a vacuum degree of 1.5kPa and a rotation speed of 1500rpm, and mixed for 5min, to finally obtain the epoxy resin-based thermal conductive and insulating composite material.

[0032] The raw materials used in the examples and comparative examples are as follows: The epoxy resin is ZLF-160B produced by Zilun Super Pure Epoxy Resin (Xi'an) Co., Ltd., with an epoxy equivalent weight of 156-165g / eq; the filler is alumina produced by Xi'an Keneng Material Technology Co., Ltd., and boron nitride produced by Shanghai Maikelin Biochemical Technology Co., Ltd.; the toughening agent is carboxyl-terminated liquid nitrile rubber produced by Dongguan Hongcheng High Polymer Material Co., Ltd.; the leveling agent is polyether modified polydimethylsiloxane produced by Wuhan Kemik Biological Medicine Technology Co., Ltd.; the silane coupling agent is γ-aminopropyl triethoxysilane produced by Kangjin New Material Technology Co., Ltd.; the curing agent dicyandiamide is produced by Aladdin Reagent (China) Co., Ltd.; the accelerant is N-(2-hydroxyphenyl)-N', N'-dimethylurea produced by Shijiazhuang Kunxianda Technology Co., Ltd., and 2-propylimidazole produced by Wuhan Xinyangruihe Chemical Technology Co., Ltd.

[0033] Table 1

[0034] Figure 1The schematic diagram of the structure of the KH-550 modified spherical alumina involved in the present application is used to clearly show the connection relationship between KH-550 and the spherical alumina and the overall structure morphology after modification. The spherical alumina is the matrix, and the KH-550 is grafted on the surface of the spherical alumina through a chemical bond, and the amino functional group thereof faces outward.

[0035] Figure 2 The scanning electron microscope (SEM) images of the epoxy resin and its composite material before and after modification of the spherical alumina involved in the present application are as follows: Figure 2 (a)-(d) respectively correspond to the cross-sectional SEM images of the pure epoxy resin, the epoxy resin composite material containing 30% of the spherical alumina, the epoxy resin composite material containing 50% of the spherical alumina, and the epoxy resin composite material containing 70% of the spherical alumina, which are used to show the microstructure morphology of the composite material under different contents of the alumina. Figure 2 (e) is the surface SEM image of the unmodified spherical alumina, Figure 2 (f) is the surface SEM image of the spherical alumina after modification by KH-550, which is used to compare the surface structure difference of the alumina before and after modification.

[0036] Thermal conductivity: compared with the comparative example (containing KH-550) and the comparative example (without KH-550), when the content of the filler (alumina) increases, the thermal conductivity of the example rises more significantly and is higher. For example, the thermal conductivity of the comparative example 4 is 0.53 W / m・K when the filler content is 50%, while the thermal conductivity of the example 7-9 is 0.68 W / m・K when the filler content is 50%, which shows that the KH-550 can enhance the interface bonding between the alumina and the epoxy resin, reduce the interface thermal resistance, more efficiently build a heat conduction path, and improve the thermal conductivity.

[0037] Mechanical properties: in the example, the bending strength under a reasonable formula shows the effect of KH-550 improving the interface, making the alumina better dispersed and transmitting stress. For example, the bending strength of the example 4 is 80.5 MPa when the filler content is 40%, which is much higher than 74.2 MPa of the comparative example 3; in terms of impact resistance, some examples (such as 3, 5, and 8) pass the test, and the comparative examples also pass the test, but the examples still have good performance under high filler content, which shows that under the assistance of KH-550, the crack propagation is more difficult when the material is stressed, and the toughness is better.

[0038] Chemical and other properties: the adhesion of the examples were all 0 level, better than 1 level of Comparative Example 1; the acid resistance (10% H2SO4, 240h), alkali resistance (10% NaOH, 240h), electrolyte resistance (60°C, 24h) performance, the examples all passed or performed excellently, Comparative Example 1 did not pass the acid and alkali resistance. The modification of KH-550 made the combination of alumina and resin more firm, the coating formed was more dense, the ability to resist chemical medium erosion was stronger, and the adhesion, pencil hardness and other properties were improved, ensuring the comprehensive quality of the coating. The coating obtained after curing of the epoxy resin-based thermal conductive and insulating composite material obtained in Example 1 to Example 9 and Comparative Example 1 to Comparative Example 4 was tested for performance, and the specific test standards and corresponding indexes are shown in Table 2.

[0039] Table 2

[0040] It should be noted that in Table 2, the impact resistance test refers to GB / T 91732; the adhesion test refers to GB / T 9286; the pencil hardness test refers to GB / T 6739; the acid and alkali resistance test refers to GB / T 9274; the breakdown voltage test refers to GB / T 1408.1; the electrolyte used in the electrolyte resistance test is composed of organic solvents including ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate, and the volume ratio of the three is 1:1:1. The bending strength test refers to GB / T 2567; the thermal conductivity performance test is based on the ISO22007-2-2015 standard.

[0041] In summary, as shown in Table 1 and Table 2, compared with Comparative Example 1, the addition of fillers greatly improves the thermal conductivity, adhesion and medium resistance of the composition. Compared with Comparative Examples 2, 3 and 4 respectively by Examples 3, 5 and 8, after the filler is treated by the silane coupling agent, the thermal conductivity of the epoxy resin thermal conductive and insulating composite material is obviously increased; compared with Examples 8 and 9 by Example 7, when the toughening agent content is 6%, the impact resistance of the composition is improved, but the addition of the toughening agent causes a certain loss to the bending strength of the composition.

[0042] The above description of disclosed examples enables one of ordinary skill in the art to make or use the application. Various modifications to these examples will be readily apparent to those of ordinary skill in the art, and the generic principles defined herein can be applied to other examples without departing from the spirit or scope of the application. Therefore, the application is not to be limited to the examples shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An epoxy resin-based thermally conductive and insulating composite material, characterized in that, The raw materials for preparing the material, in parts by weight: Epoxy resin: 30-60 parts; Hardener: 2-4 parts; Accelerator: 0-1 part; Filler: 30-50 parts; Leveling agent: 0.5~2 parts; Toughening agent: 3-12 parts; Silane coupling agent: 0~1 part.

2. The epoxy resin-based thermally conductive and insulating composite material according to claim 1, characterized in that, The epoxy resin is a bisphenol F type epoxy resin with an epoxy equivalent of 156 g / eq-165 g / eq.

3. The epoxy resin-based thermally conductive and insulating composite material according to claim 1, characterized in that, The curing agent is micronized dicyandiamide with a particle size of 5~10 μm.

4. The epoxy resin-based thermally conductive and insulating composite material according to claim 1, characterized in that, The accelerator is one or a mixture of several of the following: N-(2-hydroxyphenyl)-N',N'-dimethylurea, N-(2-hydroxy-4-nitrobenzene)-N',N'-dimethylurea, N-(5-chloro-2-hydroxyphenyl)-N',N'-dimethylurea, N-(4-chlorophenyl)-N',N'-dimethylurea, N-(4-chloro-2-hydroxyphenyl)-N',N'-dimethylurea, 2-methylimidazole, 2-isopropylimidazole, 2-propylimidazole, 2-isopropylimidazole, and 2-propylimidazole.

5. The epoxy resin-based thermally conductive and insulating composite material according to claim 1, characterized in that, The filler is one or a mixture of alumina and boron nitride, with a particle size of 0.5~120μm.

6. The epoxy resin-based thermally conductive and insulating composite material according to claim 1, characterized in that, The leveling agent is at least one of acrylate leveling agents and silicone leveling agents, preferably polyether-modified polydimethylsiloxane.

7. The epoxy resin-based thermally conductive and insulating composite material according to claim 1, characterized in that, The toughening agent is at least one of carboxyl-terminated liquid nitrile rubber, amino-terminated liquid nitrile rubber, and epoxy-terminated liquid nitrile rubber.

8. The epoxy resin-based thermally conductive and insulating composite material according to claim 1, characterized in that, The silane coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

9. A method for preparing an epoxy resin-based thermally conductive and insulating composite material as described in claim 1, characterized in that, The method specifically includes the following steps: (1) Dissolve an appropriate amount of silane coupling agent in deionized water, hydrolyze it, add it to the filler dispersion, reflux at 80°C for 4 hours, centrifuge, wash and dry to obtain the modified filler. (2) Mix the modified filler obtained in step (1) with epoxy resin and stir at a constant speed of 300~600r / min for 30min. (3) Add the mixture from step (2) to the curing agent, accelerator and other additives, and stir at a constant speed of 1000~1500r / min for 30min; (4) The mixture from step (3) is placed in a planetary gravity mixer with a vacuum of 1.5 kPa and a rotation speed of 1500 rpm for 5 min to finally obtain the epoxy resin-based thermally conductive and insulating composite material.

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