High-thermal-conductivity flame-retardant silicon-based EMI shielding adhesive as well as preparation method and application thereof
By leveraging the synergistic effect of organosilicon-phosphorus-nitrogen synergistic modification of boron nitride nanosheets and siloxane-boronate ester modification of silicon carbide nanowires, the problems of low thermal conductivity, poor flame retardancy, and weak adhesion of silicon-based EMI shielding materials were solved, achieving a comprehensive performance improvement of high thermal conductivity, high flame retardancy, and strong adhesion.
Patent Information
- Application Number
- CN202511049325.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-29
- Publication Date
- 2025-12-05
AI Technical Summary
Existing silicon-based EMI shielding materials suffer from low thermal conductivity, poor flame retardancy, and weak adhesion to the substrate, making it difficult to meet the comprehensive performance requirements of high-end electronic devices.
Organosilicon-phosphorus-nitrogen synergistic modification of boron nitride nanosheets and siloxane-boron ester modification of silicon carbide nanowires were used as modifying fillers. Through the synergistic effect of chemical bonding and physical filling, the thermal conductivity, flame retardancy and adhesion properties of the materials were improved.
The thermal conductivity of the material was significantly improved to 6.2-7.1 W/(m·K), achieving a V-0 flame retardant rating, and the tensile shear strength was increased to 6.8-7.9 MPa, meeting the heat dissipation and reliability requirements of high-power electronic devices.
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Figure CN121064784A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of electronic materials, in particular to a high-thermal-conductivity flame-retardant silicon-based EMI shielding adhesive as well as a preparation method and application thereof. BACKGROUND
[0002] With the rapid iteration of information technology and the deep popularization of electronic equipment, the influence of electromagnetic interference (EMI) on precision electronic equipment is increasingly significant, and has become a key problem restricting the performance improvement of 5G communication, new energy vehicles, consumer electronics and other products. Traditional electromagnetic interference shielding materials mainly rely on metal foils, conductive coatings and the like, which have certain shielding efficiency, but generally have defects such as high density, insufficient flexibility, weak adhesion to the substrate, and are difficult to meet the needs of emerging fields such as flexible electronic devices and lightweight equipment. For example, metal shielding materials increase the weight of the equipment due to their high density, and are prone to breakage and failure during repeated bending; conductive coatings often cause the shielding layer to fall off due to insufficient adhesion, affecting long-term reliability. These problems have promoted the research of polymer-based shielding materials, but their comprehensive performance is still difficult to break through.
[0003] Polymer-based electromagnetic interference shielding materials have become the mainstream direction of current research due to their advantages of light weight, easy processing, corrosion resistance and the like. However, such materials generally face the dual bottleneck of thermal conductivity and flame retardancy. On the one hand, the intrinsic thermal conductivity of polymers is low, which is difficult to meet the heat dissipation demand of high-power electronic equipment, leading to heat accumulation and causing performance degradation or even failure of the device; on the other hand, polymer materials are flammable, and traditional flame retardants (such as aluminum hydroxide and red phosphorus) can improve the fireproof performance, but the addition amount is often too high to damage the original mechanical properties of the material, and it is difficult to synergize with thermal conductive fillers, so it is difficult to achieve high thermal conductivity and high flame retardancy. In addition, the modification method of single filler also has the problems of poor dispersibility and weak interface bonding with the matrix, which makes it difficult to balance the mechanical properties and shielding efficiency, limiting its application in high-end electronic equipment.
[0004] Silicon-based materials are considered as an ideal matrix for preparing high-performance electromagnetic interference shielding adhesives due to their good weather resistance, high biocompatibility and excellent thermal stability. However, their intrinsic thermal conductivity is extremely low, and they lack effective flame-retardant mechanisms, so they need to be modified by fillers to improve their performance. Existing modification methods mostly use single thermal conductive fillers or flame retardants, but there are problems such as uneven dispersion of fillers, weak interfacial bonding, and difficulty in optimizing multiple properties synergistically, making it difficult to meet the comprehensive needs of high thermal conductivity, high flame retardancy and strong adhesion. Therefore, it is of great significance to develop a silicon-based electromagnetic interference shielding adhesive that can synergistically improve the thermal conductivity, flame retardancy and adhesion performance by using a new type of modified compound, which can promote the miniaturization, lightweight and reliability improvement of high-end electronic equipment. SUMMARY
[0005] The present application aims to provide a high-thermal-conductivity flame-retardant silicon-based EMI shielding adhesive as well as a preparation method and application thereof, which solves the technical problems of low thermal conductivity, poor flame retardancy and weak adhesion to the base material of the existing silicon-based EMI shielding material.
[0006] The present application achieves the above-mentioned purpose through the following technical solutions: The high-thermal-conductivity flame-retardant silicon-based EMI shielding adhesive comprises the following raw materials in parts by weight: hydroxyl-terminated polydimethylsiloxane: 80-120 parts by weight; silicon-phosphorus-nitrogen synergistically modified boron nitride nanosheet: 5-15 parts by weight; siloxane-borate modified silicon carbide nanowire: 3-10 parts by weight; conductive carbon black: 5-10 parts by weight; aluminum hydroxide: 10-20 parts by weight; tetraethyl orthosilicate: 3-8 parts by weight; dibutyltin dilaurate: 0.1-0.5 parts by weight; xylene: 20-40 parts by weight; The preparation steps of the silicon-phosphorus-nitrogen synergistically modified boron nitride nanosheet include: A1, dispersing boron nitride nanosheet in anhydrous ethanol, ultrasonic treatment to obtain a uniform dispersion liquid; adding 3-aminopropyltriethoxysilane to the dispersion liquid, refluxing at 80-82 DEG C, centrifuging after cooling, washing with anhydrous ethanol, and vacuum drying at 60-62 DEG C to obtain amino-modified boron nitride nanosheet; A2, dispersing the amino-modified boron nitride nanosheet in deionized water, adding ammonium polyphosphate and dimethyl methylphosphonate, and stirring at 60-62 DEG C; adding dimethylsiloxane oligomer to the system, and distilling under reduced pressure at 120-122 DEG C; and finally vacuum drying at 150-155 DEG C.
[0007] In the present application, the preparation of the boron nitride nanosheet modified by organic silicon-phosphorus-nitrogen synergistically is divided into three stages of amination, phosphorus-nitrogen flame-retardant layer construction and organic silicon coating. First, after ultrasonic dispersion, the surface active site of the boron nitride nanosheet is exposed, and the hydrolysis product (containing silanol group) of 3-aminopropyl triethoxysilane reacts with the silanol group (-Si-OH) and the amino group (-NH2) to form a covalent bond (-Si-O-NH-), so as to graft amino on the surface of the boron nitride, improve its polarity and reactivity. Then, when the amino-modified boron nitride nanosheet is mixed with ammonium polyphosphate and dimethyl methylphosphonate in water, the amino group and the hydroxyl group of the phosphoric acid group condense to form a phosphorus-nitrogen synergistic flame-retardant network, in which the phosphorus element decomposes to generate phosphorus-containing free radicals at high temperature, which can capture the active substances of combustion chain reaction, and the nitrogen element promotes carbonization and delays the spread of fire. Finally, the dimethylsiloxane oligomer is hydrolyzed to generate silanol (-Si-OH), which further condenses with the amino group or the residual hydroxyl group to form an organic silicon coating layer, which not only enhances the thermal stability of the boron nitride nanosheet, but also improves the interfacial compatibility of the boron nitride nanosheet with the silicon matrix.
[0008] According to a preferred embodiment of the present application, the hydroxy-terminated polydimethylsiloxane is purchased from Huatian New Materials (model number: 107-200).
[0009] According to a preferred embodiment of the present application, the boron nitride nanosheet is purchased from Suzhou Nanomicro Technology (model number: N-BN-510, average thickness 5-10 nm, lateral size 5-10 μm).
[0010] According to a preferred embodiment of the present application, the anhydrous ethanol is purchased from Jiangsu Lunfeng Synthetic Technology (model number: RE-001, analytical pure).
[0011] According to a preferred embodiment of the present application, the 3-aminopropyl triethoxysilane is purchased from Nanjing Youpu Chemical (model number: Y-503, analytical pure).
[0012] According to a preferred embodiment of the present application, the ammonium polyphosphate is purchased from Jiangsu Tianteng Chemical (model number: APP-1000, degree of polymerization 1000).
[0013] According to a preferred embodiment of the present application, the dimethyl methylphosphonate is purchased from Jiangsu Feixiang Chemical (model number: DMMP-99, industrial grade).
[0014] According to a preferred embodiment of the present application, the dimethylsiloxane oligomer is purchased from Zhejiang Xin'an Chemical (model number: PDMS-5000, number average molecular weight 5000).
[0015] According to a preferred embodiment of the present application, the conductive carbon black is purchased from Shanghai Cabot Chemical (model number: Conductex 975, conductive carbon black).
[0016] According to the preferred embodiment of the present application, the aluminum hydroxide is purchased from Hebei Xintao New Material (Model: AH-1000, high purity grade).
[0017] According to the preferred embodiment of the present application, the tetraethyl orthosilicate is purchased from Jiangsu Lunfeng Synthetic Technology (Model: TEOS-28, analytical pure).
[0018] According to the preferred embodiment of the present application, the dibutyltin dilaurate is purchased from Jiangsu Feixiang Chemical Industry (Model: DBTDL-95, chemical pure).
[0019] According to the preferred embodiment of the present application, the dimethylbenzene is purchased from Jiangsu Lunfeng Synthetic Technology (Model: XY-100, analytical pure).
[0020] According to the preferred embodiment of the present application, in step A1, the time for ultrasonic treatment is 30-40 min, and the frequency is 30-40 kHz; the time for reflux reaction is 2-4 h; the speed for centrifugation after cooling is 8000-8200 rpm, and the time is 10-20 min; the time for vacuum drying is 6-8 h.
[0021] According to the preferred embodiment of the present application, in step A2, the time for stirring reaction is 4-6 h; the time for vacuum drying is 12-14 h.
[0022] According to the preferred embodiment of the present application, the preparation method of the siloxane-boronic ester modified silicon carbide nanowire comprises: B1, dispersing the silicon carbide nanowire in toluene, ultrasonic treatment to obtain a uniform dispersion liquid; adding γ-glycidyl ether propyltrimethoxysilane to the dispersion liquid, heating to 100-102℃ for reflux reaction, centrifuging after cooling, washing with toluene, and vacuum drying at 80-82℃ to obtain epoxy modified silicon carbide nanowire; B2, dispersing the epoxy modified silicon carbide nanowire in N,N-dimethylformamide, adding triethyl borate and dibutyltin dilaurate, and heating to 80-82℃ for reaction; adding vinyltrimethoxysilane to the system, heating to 110-112℃ for reaction; and finally distilling under reduced pressure at 120-122℃.
[0023] In the present application, the preparation of siloxane-borate modified silicon carbide nanowires includes three steps of silane modification, borate grafting and vinyl introduction. After ultrasonic dispersion of the surface of the silicon carbide nanowires, the weak polar groups (such as hydroxyl groups) on the surface of the silicon carbide nanowires undergo ring-opening reaction with the epoxy groups (-C-O-C-) generated by hydrolysis of γ-glycidyloxypropyltrimethoxysilane, and the epoxy groups after ring-opening reaction are combined with the hydroxyl groups on the surface of the silicon carbide to form stable ether bonds (-O-), thereby grafting epoxy groups on the surface of the silicon carbide to increase the reaction sites. Subsequently, the epoxy group modified silicon carbide nanowires and triethyl borate undergo condensation reaction of the epoxy groups and the hydroxyl groups of the borate to generate borate bonds (-B-O-C-), forming a grafted layer containing borate, which can promote carbon formation on the surface of the material at high temperature and inhibit smoke release. Finally, the hydrolysis of vinyltrimethoxysilane generates silanol containing vinyl groups (-CH=CH2), which reacts with the remaining active sites or epoxy groups on the surface of the silicon carbide to introduce vinyl functional groups, facilitating subsequent crosslinking reaction with the silicon matrix and enhancing the chemical bonding force between the filler and the matrix.
[0024] According to a preferred embodiment of the present application, the silicon carbide nanowires are purchased from Suzhou Nanomicro Technology (model: N-SiC-100, diameter 50-100 nm, length 10-20 μm).
[0025] According to a preferred embodiment of the present application, the toluene is purchased from Jiangsu Lunfeng Synthetic Technology (model: RE-002, analytical pure).
[0026] According to a preferred embodiment of the present application, the γ-glycidyloxypropyltrimethoxysilane is purchased from Nanjing Youpuhua Chemical (model: Y-560, analytical pure).
[0027] According to a preferred embodiment of the present application, the N,N-dimethylformamide is purchased from Jiangsu Lunfeng Synthetic Technology (model: RE-003, analytical pure).
[0028] According to a preferred embodiment of the present application, the triethyl borate is purchased from Jiangsu Feixiang Chemical (model: TEB-99, industrial grade).
[0029] According to a preferred embodiment of the present application, the vinyltrimethoxysilane is purchased from Nanjing Youpuhua Chemical (model: Y-571, analytical pure).
[0030] According to a preferred embodiment of the present application, in step B1, the ultrasonic treatment time is 1-2 h, and the frequency is 30-40 kHz; the reflux reaction time is 6-8 h; and the vacuum drying time is 2-4 h.
[0031] According to a preferred embodiment of the present application, in step B2, the reaction time is 8-10 h; and the heating to 110-112 °C reaction time is 4-6 h.
[0032] This invention also provides a method for preparing the aforementioned high thermal conductivity and flame retardant silicon-based EMI shielding adhesive, comprising the following steps: S1. In a planetary ball mill, add hydroxyl-terminated polydimethylsiloxane, organosilicon-phosphorus nitrogen synergistic modified boron nitride nanosheets, siloxane-boron ester modified silicon carbide nanowires, conductive carbon black, aluminum hydroxide, tetraethyl orthosilicate and xylene, and add agate balls to mix. S2. Transfer the mixture to the coating mold and vulcanize at 120-122°C.
[0033] In this invention, the synergistic effect of the two modified compounds with the basic silicon matrix and other components is key to the breakthrough in material performance. Organosilicon-phosphorus-nitrogen synergistic modified boron nitride nanosheets significantly reduce the interfacial thermal resistance between the filler and the matrix through the condensation reaction of amino groups with the hydroxyl groups of the silicon matrix and the interfacial transition effect of the organosilicon coating layer. Simultaneously, the phosphorus-nitrogen flame-retardant layer and aluminum hydroxide form a dual flame-retardant mechanism of "capturing free radicals and promoting char formation." Siloxane-boronate modified silicon carbide nanowires further enhance interfacial bonding and supplement flame-retardant performance through the covalent cross-linking of vinyl groups with the silicon matrix and the high-temperature char formation characteristics of the boronate. Conductive carbon black forms a continuous conductive network in the silicon matrix, achieving electromagnetic interference shielding. Tetraethyl orthosilicate acts as a cross-linking agent, promoting the vulcanization and curing of the silicon matrix and improving the material's mechanical strength. Through the synergistic effect of chemical bonding and physical filling, the components ultimately enable the material to possess high thermal conductivity, excellent flame retardancy, and strong adhesion.
[0034] According to a preferred embodiment of the present invention, in step S1, the mixing speed is 500-520 rpm and the mixing time is 2-4 h.
[0035] According to a preferred embodiment of the present invention, in step S2, the vulcanization time is 4-6 hours.
[0036] This invention also provides the application of the high thermal conductivity and flame retardant silicon-based EMI shielding adhesive described above, or the high thermal conductivity and flame retardant silicon-based EMI shielding adhesive prepared by the aforementioned preparation method, in the sealing of electronic device housings, circuit board encapsulation, electromagnetic shielding coatings, and bonding of high-end electronic components.
[0037] The beneficial effects of this invention are as follows: Traditional silicon-based materials have low thermal conductivity due to intrinsic structure limitations, which is difficult to meet the heat dissipation requirements of high-power electronic devices. The present application effectively solves this problem by introducing two new types of modified fillers. Among them, the organic silicon-phosphorus-nitrogen synergistically modified boron nitride nanosheet takes the high thermal conductivity boron nitride nanosheet as the substrate, and after being treated by silane modification and phosphorus-nitrogen compound synergistically, an organic-inorganic hybrid layer with stronger affinity to the silicon matrix is formed on its surface, reducing the interfacial thermal resistance between the filler and the matrix; the siloxane-borate modified silicon carbide nanowire introduces active functional groups through silane modification, and forms a more intimate chemical bond with the silicon matrix, while its high aspect ratio characteristics promote the formation of a thermal conduction network. The synergistic effect of the two fillers significantly improves the thermal conductivity efficiency of the material, which can effectively meet the heat dissipation performance requirements of high-power devices.
[0038] Traditional polymer-based materials are flammable, and conventional flame-retardant methods often damage the original performance of the material due to excessive addition. The present application realizes high-efficiency flame retardation through a dual flame-retardant mechanism. In the organic silicon-phosphorus-nitrogen synergistically modified boron nitride nanosheet, phosphorus-nitrogen compounds decompose to generate phosphorus-containing free radicals at high temperatures, which can effectively capture active substances in the combustion chain reaction and delay the spread of fire; at the same time, the glassy protective layer formed by the dehydration of ammonium polyphosphate can isolate oxygen and inhibit further combustion. The borate in the siloxane-borate modified silicon carbide nanowire generates borate at high temperatures, which can promote the formation of carbon on the surface of the material and inhibit the release of smoke. Combined with the flame retardant synergist aluminum hydroxide, a multi-level flame-retardant system is formed, making the material achieve a high flame-retardant grade, and the synergistic effect of the flame retardant does not significantly reduce the mechanical properties of the material.
[0039] The present application optimizes the interfacial bonding between the filler and the silicon matrix through silane modification treatment, significantly improving the adhesion performance. The amino group of the organic silicon-phosphorus-nitrogen synergistically modified boron nitride nanosheet reacts with the hydroxyl group of the silicon matrix to form a stable chemical bond; the vinyl group of the siloxane-borate modified silicon carbide nanowire forms a covalent bond with the silicon matrix, both of which enhance the interfacial bonding force between the filler and the matrix, greatly improving the bonding strength of the material with different substrates such as metals and plastics. At the same time, the material maintains the weather resistance, biocompatibility and thermal stability of the silicon matrix, and is not prone to aging in long-term use, and has excellent electromagnetic interference shielding performance, which can meet the stringent requirements of electronic device shell sealing, circuit board packaging and other scenarios for comprehensive performance. BRIEF DESCRIPTION OF DRAWINGS
[0040] Figure 1 Preparation flow chart of high-thermal-conductivity flame-retardant silicon-based EMI shielding adhesive. DETAILED DESCRIPTION
[0041] The application will be described in further detail below with reference to the drawings. It is necessary to point out here that the following specific embodiments are only used to further illustrate the application and cannot be understood as limiting the scope of protection of the application. Those skilled in the art can make some non-essential improvements and adjustments to the application according to the above application content.
[0042] I. Example Example 1 Preparation of silicone-phosphorus-nitrogen synergistically modified boron nitride nanosheets: 5 g of boron nitride nanosheets were dispersed in 50 mL of anhydrous ethanol and ultrasonically treated for 35 min (frequency 35 kHz) to obtain a uniform dispersion liquid; 2.5 g of 3-aminopropyl triethoxysilane was added to the dispersion liquid, and the temperature was raised to 81°C for reflux reaction for 3 h. After cooling, centrifugation (speed 8100 rpm, time 15 min) was performed, and anhydrous ethanol was used for washing, and 61°C vacuum drying was performed for 7 h to obtain amino-modified boron nitride nanosheets; 5 g of amino-modified boron nitride nanosheets were dispersed in 100 mL of deionized water, 3 g of ammonium polyphosphate and 1 g of dimethyl methylphosphonate were added, and the temperature was raised to 61°C for stirring reaction for 5 h. 10 g of dimethylsiloxane oligomer was added to the system, and the temperature was raised to 121°C for distillation under reduced pressure. Finally, vacuum drying was performed at 153°C for 13 h.
[0043] Preparation of siloxane-boron ester modified silicon carbide nanowires: 3 g of silicon carbide nanowires were dispersed in 30 mL of toluene and ultrasonically treated for 1.5 h (frequency 35 kHz) to obtain a uniform dispersion liquid; 1.5 g of γ-glycidyloxypropyltrimethoxysilane was added to the dispersion liquid, and the temperature was raised to 101°C for reflux reaction for 7 h. After cooling, centrifugation (speed 8100 rpm, time 15 min) was performed, and toluene was used for washing, and 81°C vacuum drying was performed for 3 h to obtain epoxy-modified silicon carbide nanowires; 5 g of epoxy-modified silicon carbide nanowires were dispersed in 50 mL of N,N-dimethylformamide, 2 g of triethyl borate and 0.1 g of dibutyltin dilaurate were added, and the temperature was raised to 81°C for reaction for 9 h. 1 g of vinyltrimethoxysilane was added to the system, and the temperature was raised to 111°C for reaction for 5 h. Finally, distillation was performed under reduced pressure at 121°C.
[0044] Preparation of high-thermal-conductivity flame-retardant silicone-based EMI shielding adhesive: In a planetary ball mill, 100 g of hydroxy-terminated polydimethylsiloxane, 5 g of silicone-phosphorus-nitrogen synergistically modified boron nitride nanosheets, 3 g of siloxane-boron ester modified silicon carbide nanowires, 5 g of conductive carbon black, 10 g of aluminum hydroxide, 3 g of tetraethyl orthosilicate and 20 g of xylene were added, and mixed (speed 510 rpm, time 3 h) with agate balls. The mixed system was transferred to a coating mold and vulcanized at 121°C for 5 h.
[0045] Example 2 The specific implementation is the same as Example 1, except that the preparation of silicone-boronate modified silicon carbide nanowires: 8 g of silicon carbide nanowires were dispersed in 80 mL of toluene, ultrasonic treatment for 2 h (frequency 38 kHz) to obtain a uniform dispersion; 4 g of γ-glycidyloxypropyltrimethoxysilane was added to the dispersion, heated to 102°C and refluxed for 8 h, cooled and centrifuged (speed 8200 rpm, time 20 min), washed with toluene, and vacuum dried at 82°C for 4 h to obtain epoxy-modified silicon carbide nanowires; 8 g of epoxy-modified silicon carbide nanowires were dispersed in 80 mL of N,N-dimethylformamide, 5 g of triethyl borate and 0.3 g of dibutyltin dilaurate were added, heated to 82°C and reacted for 10 h, 2 g of vinyltrimethoxysilane was added to the system, heated to 112°C and reacted for 6 h, and finally distilled under reduced pressure at 122°C.
[0046] The specific implementation is the same as Example 1, except that the preparation of silicone-boronate modified silicon carbide nanowires: 8 g of silicon carbide nanowires were dispersed in 80 mL of toluene, ultrasonic treatment for 2 h (frequency 38 kHz) to obtain a uniform dispersion; 4 g of γ-glycidyloxypropyltrimethoxysilane was added to the dispersion, heated to 102°C and refluxed for 8 h, cooled and centrifuged (speed 8200 rpm, time 20 min), washed with toluene, and vacuum dried at 82°C for 4 h to obtain epoxy-modified silicon carbide nanowires; 8 g of epoxy-modified silicon carbide nanowires were dispersed in 80 mL of N,N-dimethylformamide, 5 g of triethyl borate and 0.3 g of dibutyltin dilaurate were added, heated to 82°C and reacted for 10 h, 2 g of vinyltrimethoxysilane was added to the system, heated to 112°C and reacted for 6 h, and finally distilled under reduced pressure at 122°C.
[0047] The specific implementation is the same as Example 1, except that the preparation of silicone-boronate modified silicon carbide nanowires: 8 g of silicon carbide nanowires were dispersed in 80 mL of toluene, ultrasonic treatment for 2 h (frequency 38 kHz) to obtain a uniform dispersion; 4 g of γ-glycidyloxypropyltrimethoxysilane was added to the dispersion, heated to 102°C and refluxed for 8 h, cooled and centrifuged (speed 8200 rpm, time 20 min), washed with toluene, and vacuum dried at 82°C for 4 h to obtain epoxy-modified silicon carbide nanowires; 8 g of epoxy-modified silicon carbide nanowires were dispersed in 80 mL of N,N-dimethylformamide, 5 g of triethyl borate and 0.3 g of dibutyltin dilaurate were added, heated to 82°C and reacted for 10 h, 2 g of vinyltrimethoxysilane was added to the system, heated to 112°C and reacted for 6 h, and finally distilled under reduced pressure at 122°C.
[0048] Example 3 The specific implementation is the same as Example 1, except that the preparation of silicone-boronate modified silicon carbide nanowires: 6 g of silicon carbide nanowires were dispersed in 60 mL of toluene, ultrasonic treatment for 1.8 h (frequency 36 kHz) to obtain a uniform dispersion; 3 g of γ-glycidyloxypropyltrimethoxysilane was added to the dispersion, and the temperature was raised to 101.5 °C to reflux for 7.5 h. After cooling, centrifugation (speed 8180 rpm, time 19 min), washing with toluene, and vacuum drying at 81.5 °C for 3.5 h, epoxy-modified silicon carbide nanowires were obtained; 6 g of epoxy-modified silicon carbide nanowires were dispersed in 60 mL of N,N-dimethylformamide, 3.8 g of triethyl borate and 0.2 g of dibutyltin dilaurate were added, and the temperature was raised to 81.5 °C to react for 9.5 h. 1.5 g of vinyltrimethoxysilane was added to the system, and the temperature was raised to 111.5 °C to react for 5.5 h. Finally, vacuum distillation was carried out at 121.5 °C.
[0049] The specific implementation is the same as Example 1, except that the preparation of silicone-boronate modified silicon carbide nanowires: 6 g of silicon carbide nanowires were dispersed in 60 mL of toluene, ultrasonic treatment for 1.8 h (frequency 36 kHz) to obtain a uniform dispersion; 3 g of γ-glycidyloxypropyltrimethoxysilane was added to the dispersion, and the temperature was raised to 101.5 °C to reflux for 7.5 h. After cooling, centrifugation (speed 8180 rpm, time 19 min), washing with toluene, and vacuum drying at 81.5 °C for 3.5 h, epoxy-modified silicon carbide nanowires were obtained; 6 g of epoxy-modified silicon carbide nanowires were dispersed in 60 mL of N,N-dimethylformamide, 3.8 g of triethyl borate and 0.2 g of dibutyltin dilaurate were added, and the temperature was raised to 81.5 °C to react for 9.5 h. 1.5 g of vinyltrimethoxysilane was added to the system, and the temperature was raised to 111.5 °C to react for 5.5 h. Finally, vacuum distillation was carried out at 121.5 °C.
[0050] The specific implementation is the same as Example 1, except that the preparation of silicone-boronate modified silicon carbide nanowires: 6 g of silicon carbide nanowires were dispersed in 60 mL of toluene, ultrasonic treatment for 1.8 h (frequency 36 kHz) to obtain a uniform dispersion; 3 g of γ-glycidyloxypropyltrimethoxysilane was added to the dispersion, and the temperature was raised to 101.5 °C to reflux for 7.5 h. After cooling, centrifugation (speed 8180 rpm, time 19 min), washing with toluene, and vacuum drying at 81.5 °C for 3.5 h, epoxy-modified silicon carbide nanowires were obtained; 6 g of epoxy-modified silicon carbide nanowires were dispersed in 60 mL of N,N-dimethylformamide, 3.8 g of triethyl borate and 0.2 g of dibutyltin dilaurate were added, and the temperature was raised to 81.5 °C to react for 9.5 h. 1.5 g of vinyltrimethoxysilane was added to the system, and the temperature was raised to 111.5 °C to react for 5.5 h. Finally, vacuum distillation was carried out at 121.5 °C.
[0051] Comparative Example 1 The specific implementation is the same as Example 1, except that the preparation of the high-thermal-conductive flame-retardant silicone-based EMI shielding adhesive: 100 g of hydroxyl-terminated polydimethylsiloxane, 5 g of unmodified boron nitride nanosheet, 3 g of siloxane-borate-modified silicon carbide nanowire, 5 g of conductive carbon black, 10 g of aluminum hydroxide, 3 g of tetraethyl orthosilicate, and 20 g of dimethylbenzene were added to a planetary ball mill, mixed with agate balls (rotation speed 510 rpm, time 3 h), and the mixed system was transferred to a coating mold and vulcanized at 121 °C for 5 h.
[0052] Comparative Example 2 The specific implementation is the same as Example 1, except that the preparation of the high-thermal-conductive flame-retardant silicone-based EMI shielding adhesive: 100 g of hydroxyl-terminated polydimethylsiloxane, 5 g of unmodified boron nitride nanosheet, 3 g of siloxane-borate-modified silicon carbide nanowire, 5 g of conductive carbon black, 10 g of aluminum hydroxide, 3 g of tetraethyl orthosilicate, and 20 g of dimethylbenzene were added to a planetary ball mill, mixed with agate balls (rotation speed 510 rpm, time 3 h), and the mixed system was transferred to a coating mold and vulcanized at 121 °C for 5 h.
[0053] Comparative Example 3 The specific implementation is the same as Example 1, except that the preparation of the high-thermal-conductive flame-retardant silicone-based EMI shielding adhesive: 100 g of hydroxyl-terminated polydimethylsiloxane, 5 g of unmodified boron nitride nanosheet, 3 g of siloxane-borate-modified silicon carbide nanowire, 5 g of conductive carbon black, 10 g of aluminum hydroxide, 3 g of tetraethyl orthosilicate, and 20 g of dimethylbenzene were added to a planetary ball mill, mixed with agate balls (rotation speed 510 rpm, time 3 h), and the mixed system was transferred to a coating mold and vulcanized at 121 °C for 5 h (without using two modified compounds).
[0054] Performance Test The adhesives prepared in each example and comparative example were tested according to the following steps: 1. Thermal conductivity test: Laser flash method (LFA 467 HyperFlash®) was used to test 3 samples of 10 mm x 10 mm x 2 mm, and the samples were dried at 120 °C for 2 h to remove moisture before testing. The test temperature range was 25-100 °C, and the average value was taken as the thermal conductivity.
[0055] 2. Flame retardant performance test: according to UL94 vertical burning standard (ASTM D3641), take 10 samples of 127mm x 12.7mm x 3mm, ignite from one end with an igniter, record the ignition time (t1), the second ignition time (t2) and the time of burning to the clamp (t3), and determine the flame retardant grade according to the standard (V-0: t1≤10s, t2≤30s, no dripping; V-1: t1≤30s, t2≤250s, no dripping; V-2: t1≤30s, t2≤250s, with dripping igniting cotton).
[0056] 3. Adhesion strength test: according to GB / T 3903.3-2011 standard, the sample is bonded with aluminum alloy substrate (surface polished with sandpaper and cleaned with ethanol) at an area ratio of 1:1 to prepare a test sample of 25mm x 25mm x 5mm, and the tensile shear strength is tested by a universal material testing machine (load rate 1mm / min), and the average value of 5 test samples is taken.
[0057] 4. Electromagnetic shielding effectiveness test: a vector network analyzer (Keysight N5247B) is used to test the electromagnetic shielding effectiveness (SE) in the frequency range of 100MHz-10GHz, the sample is prepared into a sheet of 50mm x 50mm x 2mm, and is placed in a shielding darkroom, the reflection loss (R.L.) and transmission loss (T.L.) are measured by the coaxial transmission line method, and the total shielding effectiveness SE=20lg(E_unshielded / E_shielded), wherein E is the electric field intensity.
[0058] 6. Test results: Table 1: Test results of each example and comparative example Group Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Thermal conductivity (W / (m·K)) 6.2 6.8 7.1 3.5 4.1 2.8 UL94 flame retardant grade V-0 V-0 V-0 V-2 V-1 V-2 Tensile shear strength (MPa) 6.8 7.5 7.9 4.2 5.1 3.8 Electromagnetic shielding effectiveness (dB, 100MHz-10GHz) 65 (peak 72) 68 (peak 75) 70 (peak 78) 45 (peak 50) 52 (peak 58) 39 (peak 42) As can be seen from Table 1, the present application effectively solves the problems of low thermal conductivity, poor flame retardancy and weak adhesion to the substrate of the existing silicon-based EMI shielding materials through the synergistic effect of two completely new modified compounds. In the examples, the organosilicon-phosphorus-nitrogen synergistically modified boron nitride nanosheet utilizes the high thermal conductivity of boron nitride (lateral size 5-10 μm) and the active sites after silane modification to form a close interfacial bond with the silicon matrix. At the same time, the aspect ratio characteristics of the siloxane-borate modified silicon carbide nanowires (diameter 50-100 nm, length 10-20 μm) promote the extension of the thermal conduction network, and the two synergistically make the thermal conductivity of Examples 1-3 increase to 6.2-7.1 W / (m·K) (Comparative Examples 1-3 only 2.8-4.1 W / (m·K)). In terms of flame retardancy, the phosphorus-nitrogen components of the organosilicon-phosphorus-nitrogen modified layer decompose to generate phosphorus-containing free radical capture active substances at high temperatures, and form a glassy protective layer with ammonium polyphosphate to synergistically isolate oxygen; the borate of the siloxane-borate modified layer promotes surface carbonization, combined with the synergistic effect of aluminum hydroxide, so that the flame retardant grade of Examples 1-3 is stably reached V-0 (Comparative Examples 1-3 are mostly V-2 or V-1). In terms of adhesion, the amino, epoxy and other functional groups introduced by silane modification form covalent bonds with the silicon matrix, enhancing the interfacial bonding force between the filler and the matrix, and the tensile shear strength of Examples 1-3 is increased to 6.8-7.9 MPa (Comparative Examples 1-3 only 3.8-5.1 MPa), effectively solving the problem of weak adhesion of traditional materials to the substrate.
[0059] The above-described examples only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application.
Claims
1. A high thermally conductive, flame retardant, silicone-based EMI shielding adhesive characterized in that, The raw materials include the following weight parts: Hydroxyl-terminated polydimethylsiloxane: 80-120 parts by weight; Silicone-phosphorus-nitrogen synergistically modified boron nitride nanosheet: 5-15 parts by weight; Siloxane-borate modified silicon carbide nanowire: 3-10 parts by weight; Conductive carbon black: 5-10 parts by weight; Aluminum hydroxide: 10-20 parts by weight; Ethyl silicate: 3-8 parts by weight; Dibutyltin dilaurate: 0.1-0.5 parts by weight; Xylene: 20-40 parts by weight; The preparation steps of the silicone-phosphorus-nitrogen synergistically modified boron nitride nanosheet include: A1, dispersing boron nitride nanosheet in anhydrous ethanol, ultrasonic treatment to obtain a uniform dispersion; adding 3-aminopropyl triethoxysilane to the dispersion, refluxing at 80-82℃, cooling, centrifuging, washing with anhydrous ethanol, and vacuum drying at 60-62℃ to obtain amino-modified boron nitride nanosheet; A2, dispersing the amino-modified boron nitride nanosheet in deionized water, adding ammonium polyphosphate and dimethyl methylphosphonate, and stirring at 60-62℃; adding dimethylsiloxane oligomer to the system, and distilling under reduced pressure at 120-122℃; and finally vacuum drying at 150-155℃.
2. The high thermally conductive flame retardant silicone-based EMI shielding adhesive of claim 1, wherein, In step A1, the ultrasonic treatment time is 30-40 min, and the frequency is 30-40 kHz; the refluxing time is 2-4 h; the centrifuging speed after cooling is 8000-8200 rpm, and the time is 10-20 min; and the vacuum drying time is 6-8 h.
3. The high thermally conductive flame retardant silicone-based EMI shielding adhesive of claim 1, wherein, In step A2, the stirring time is 4-6 h; and the vacuum drying time is 12-14 h.
4. The high thermally conductive flame retardant silicone-based EMI shielding adhesive of claim 1, wherein, The preparation method of the siloxane-borate modified silicon carbide nanowire includes: B1, dispersing silicon carbide nanowire in toluene, ultrasonic treatment to obtain a uniform dispersion; adding γ-glycidyloxypropyltrimethoxysilane to the dispersion, refluxing at 100-102℃, cooling, centrifuging, washing with toluene, and vacuum drying at 80-82℃ to obtain epoxy-modified silicon carbide nanowire; B2, dispersing the epoxy-modified silicon carbide nanowire in N,N-dimethylformamide, adding triethyl borate and dibutyltin dilaurate, and reacting at 80-82℃; adding vinyltrimethoxysilane to the system, and reacting at 110-112℃; and finally distilling under reduced pressure at 120-122℃.
5. The high thermally conductive, flame retardant, silicone-based EMI shielding adhesive of claim 4, wherein, In step B1, the ultrasonic treatment time is 1-2 h, and the frequency is 30-40 kHz; the refluxing time is 6-8 h; and the vacuum drying time is 2-4 h.
6. The high thermally conductive flame retardant silicone-based EMI shielding adhesive of claim 4, wherein, In step B2, the reaction time is 8-10 h; and the reaction time at 110-112℃ is 4-6 h.
7. A process for preparing the high thermally conductive flame retardant silicon-based EMI shielding adhesive according to any one of claims 1-6, characterized by the steps of It includes: S1, adding hydroxyl-terminated polydimethylsiloxane, silicone-phosphorus-nitrogen synergistically modified boron nitride nanosheet, siloxane-borate modified silicon carbide nanowire, conductive carbon black, aluminum hydroxide, ethyl silicate, and xylene in a planetary ball mill, and mixing with agate balls; S2, transferring the mixed system to a coating mold, and vulcanizing at 120-122℃.
8. The preparation method according to claim 7, characterized in that, In step S1, the rotation speed of mixing is 500-520 rpm, and the mixing time is 2-4 h.
9. The preparation method according to claim 7, characterized in that, In step S2, the vulcanization time is 4-6 h.
10. Use of the high thermally conductive flame retardant silicone-based EMI shielding adhesive according to any one of claims 1 to 6 or prepared according to the method of any one of claims 7 to 9, characterized in that, The application of the high-thermal-conductivity flame-retardant silicon-based EMI shielding adhesive in electronic device shell sealing, circuit board packaging, electromagnetic shielding coating and high-end electronic component bonding.