Silicone rubber composition for electrical insulation

Abstract

The present invention discloses a silicone rubber composition for electrical insulation. The composition comprises, by mass, 55-65 parts of vinyl-terminated polydimethylsiloxane, 8-15 parts of polyurethane microcapsules containing 4-cyano-4'-pentylbiphenyl, 5-10 parts of ZrO2 nanoparticles, 5-10 parts of aluminum hydroxide, 2-4 parts of hydrogen-containing siloxane, and 0.01-0.03 parts of a platinum-based catalyst. The preparation method includes the steps of filler dispersion, mixing of microcapsules and a crosslinker, coating and curing, and a secondary heat treatment. The composition dynamically regulates the thermal expansion coefficient through liquid crystal microcapsules, synergistically forms a dense carbonized layer with ZrO2 and aluminum hydroxide, significantly improving tensile strength, flame retardancy, and low toxicity. The composition is suitable for high-voltage cables, transformer insulation, and electronic component packaging.

Description

Technical Field

[0001] The present invention relates to the technical field of silicone rubber, in particular to a silicone rubber composition for electrical insulation. Background Art

[0002] Silicone rubber, a high-performance polymer material, has been widely used in the power, electronics, and cable industries due to its excellent electrical insulation properties, heat resistance, and weather resistance. In recent years, with the increasing safety and reliability requirements for electrical equipment, demand for silicone rubber compositions in the electrical insulation field has continued to grow. Conventional silicone rubber compositions are often enhanced by adding inorganic fillers (such as alumina and silica) or flame retardants (such as halogen compounds or phosphorus-based flame retardants) to improve their flame retardancy to meet international fire safety standards such as UL 94 V-0 or IEC 60695. Early research focused on improving the thermal stability and flame retardancy of silicone rubber through physical blending or chemical modification while maintaining its flexibility and dielectric properties. Furthermore, the introduction of nanotechnology has further promoted the optimization of silicone rubber compositions, for example, by adding nanofillers (such as montmorillonite or graphene oxide) to enhance the thermal barrier effect and flame retardancy. These technological advances have significantly improved the applicability of silicone rubber in high-temperature and fire environments, showing promising application prospects in high-voltage cables, transformer insulation, and electronic component packaging.

[0003] However, the fire resistance of existing silicone rubber compositions still has significant deficiencies, especially under extreme fire conditions. First, while traditional flame retardants such as halogen compounds can effectively inhibit flame spread, they may release toxic gases during combustion, posing a potential threat to the environment and human health, limiting their use in applications with strict environmental requirements. Second, existing silicone rubber compositions often struggle to form a stable charred layer in high-intensity fires, leading to accelerated thermal decomposition and rapid degradation of insulation properties, making them ineffective in protecting electrical equipment. Summary of the Invention

[0004] The present application provides a composition for preparing high-performance silicone rubber, which comprises, in parts by mass:

[0005] 55 to 65 parts vinyl terminated polydimethylsiloxane

[0006] 8 to 15 parts of polyurethane microcapsules containing liquid crystal molecules

[0007] ZrO2 nanoparticles 5 to 10 parts

[0008] 5 to 10 parts of aluminum hydroxide

[0009] 2 to 4 parts of hydrogen siloxane

[0010] 0.01 to 0.03 parts of platinum-based catalyst.

[0011] Preferably, the liquid crystal molecules in the polyurethane microcapsules are 4-cyano-4'-pentylbiphenyl.

[0012] Preferably, the hydrogen-containing siloxane is polymethyl hydrogen siloxane, and the hydrogen content is 0.5 wt % to 1.6 wt %.

[0013] A method for preparing the above composition comprises the following technical steps:

[0014] Step 1. Add ZrO2 nanoparticles and aluminum hydroxide to vinyl-terminated polydimethylsiloxane and disperse them using a high shear mixer at 2000-3000 rpm for 30-60 minutes to uniformly disperse the filler in the matrix to obtain a PDMS-filler mixture;

[0015] Step 2. Add the polyurethane microcapsules containing liquid crystal molecules to the PDMS-filler mixture and stir at a low speed of 100-200 rpm for 20-30 minutes until uniform. Then add the hydrogenated siloxane and platinum-based catalyst and continue stirring for 10-15 minutes to obtain a uniform mixture.

[0016] Step 3. Apply the uniform mixture obtained in step 2 on the target substrate and heat-cure at 90-130°C for 1-2 hours to complete the cross-linking reaction;

[0017] Step 4. Place the cured material at 150-180°C for a secondary heat treatment for 10-20 minutes.

[0018] Preferably, the preparation method of the liquid crystal microcapsules includes: mixing 4-cyano-4'-pentylbiphenyl with water and an emulsifier, forming a stable emulsion by high-speed stirring, adding isocyanate and polyol, performing interfacial polymerization in the emulsion to polymerize it into a polyurethane shell on the surface of the liquid crystal droplets, filtering, washing and drying the microcapsules, and controlling the particle size to be between 10-50 μm.

[0019] Preferably, in step 1, the rotation speed of the high-speed shear mixer is 2000-3000 rpm, and the dispersion time is 30-60 minutes.

[0020] Preferably, in step 2, when the polyurethane microcapsules containing liquid crystal molecules are added, the stirring speed is 100-200 rpm.

[0021] Preferably, the target substrate is a metal or ceramic material used in electronic devices.

[0022] The silicone rubber composition provided by the present invention achieves excellent electrical insulation properties, mechanical strength, and flame retardancy by introducing polyurethane microcapsules containing liquid crystal molecules, ZrO2 nanoparticles, and aluminum hydroxide. The liquid crystal microcapsules dynamically regulate the thermal expansion coefficient through phase transition, effectively alleviating thermal stress and enhancing interfacial stability with metal / ceramic substrates. ZrO2 and aluminum hydroxide synergistically promote the formation of a dense carbonized layer at high temperatures, significantly reducing toxic gas release (e.g., CO concentration to 700-850 ppm) and increasing the residual carbon rate (30-35%), thereby enhancing flame retardancy and thermal stability. At the same time, the composition maintains high tensile strength (6.9-7.2 MPa) and meets fire protection standards such as UL 94 V-0. It is suitable for use in applications with high safety and reliability requirements in the power, electronics, and cable industries, and has significant environmental friendliness and application prospects. DETAILED DESCRIPTION

[0023] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0024] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0025] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it constitute a separate or selective embodiment that is mutually exclusive with other embodiments.

[0026] Preparation Example

[0027] Preparation Example 1

[0028] The preparation method for liquid crystal microcapsules involves mixing 4-cyano-4'-pentylbiphenyl (5CB) and an emulsifier (e.g., Tween 80, 2 wt%) in a mass ratio of 1:10. The mixture is stirred at high speed (10,000 rpm for 5-10 minutes) to form a stable water-in-oil emulsion. The 5CB acts as the oil phase and is dispersed into micron-sized droplets. The emulsifier ensures droplet stability by reducing interfacial tension. Subsequently, an isocyanate (e.g., diphenylmethane diisocyanate, MDI, 1 wt%) and a polyol (e.g., ethylene glycol, 0.8 wt%) are added. A rapid polymerization reaction is initiated at the emulsion interface via interfacial polymerization (reaction temperature 60-70°C, pH 4-5, for 2-3 hours), generating a polyurethane shell that encapsulates the 5CB to form microcapsules. The filtration was performed using a 200-mesh nylon filter to remove large particles of impurities, and the unreacted products and emulsifiers were removed by washing with deionized water for three times. The product was vacuum dried at 60° C. for 12 hours to control the particle size of the microcapsules to be 10-50 μm.

[0029] Example

[0030] Example 1

[0031] Formula (by mass):

[0032] Vinyl-terminated polydimethylsiloxane: 60 parts

[0033] Polyurethane microcapsules containing liquid crystal molecules (the liquid crystal molecules are 4-cyano-4'-pentylbiphenyl): 10 parts

[0034] ZrO2 nanoparticles: 8 parts

[0035] Aluminum hydroxide: 8 parts

[0036] Hydrogenated siloxane (polymethylhydrogen siloxane, hydrogen content 1.0 wt%): 3 parts

[0037] Platinum-based catalyst: 0.02 parts

[0038] Preparation steps:

[0039] 1. Filler dispersion: Take 60 parts of vinyl-terminated polydimethylsiloxane and place it in a high-shear mixer. Add 8 parts of ZrO2 nanoparticles (average particle size 20 nm) and 8 parts of aluminum hydroxide (average particle size 1 μm). Disperse at 2500 rpm for 40 minutes to ensure that the filler is evenly dispersed in the matrix to obtain a PDMS-filler mixture.

[0040] 2. Mixing Microcapsules and Crosslinker: Add 10 parts of polyurethane microcapsules containing 4-cyano-4'-pentylbiphenyl (prepared according to Preparation Example 1, particle size approximately 30 μm) to the PDMS-filler mixture and stir at 150 rpm for 25 minutes until uniform. Then, add 3 parts of polymethylhydrogensiloxane (hydrogen content 1.0 wt%) and 0.02 parts of a platinum-based catalyst (chloroplatinic acid type). Continue stirring at 150 rpm for 12 minutes to obtain a uniform mixture.

[0041] 3. Coating and curing: The mixture obtained in step 2 was evenly coated on a metal substrate (copper plate, thickness 0.5 mm) and placed in an oven at 110°C for heating and curing for 1.5 hours to complete the cross-linking reaction.

[0042] 4. Secondary heat treatment: Place the cured material in a 160°C oven for secondary heat treatment for 15 minutes to enhance the stability of the carbonized layer and flame retardant properties.

[0043] Example 2

[0044] Formula (by mass):

[0045] Vinyl-terminated polydimethylsiloxane: 55 parts

[0046] Polyurethane microcapsules containing liquid crystal molecules (the liquid crystal molecules are 4-cyano-4'-pentylbiphenyl, with a particle size of 10-50 μm): 10 parts

[0047] ZrO2 nanoparticles: 10 parts

[0048] Aluminum hydroxide: 5 parts

[0049] Hydrogenated siloxane (polymethylhydrogen siloxane, hydrogen content 0.5 wt%): 2 parts

[0050] Platinum-based catalyst: 0.01 parts

[0051] Preparation steps:

[0052] 1. Filler dispersion: Take 55 parts of vinyl-terminated polydimethylsiloxane and place it in a high-shear mixer. Add 10 parts of ZrO2 nanoparticles (average particle size 15 nm) and 5 parts of aluminum hydroxide (average particle size 0.8 μm). Disperse at 2000 rpm for 50 minutes to ensure that the filler is evenly dispersed to obtain a PDMS-filler mixture.

[0053] 2. Mixing Microcapsules and Crosslinker: Add 12 parts of polyurethane microcapsules containing 4-cyano-4'-pentylbiphenyl (prepared according to Preparation Example 1, particle size approximately 20 μm) to the PDMS-filler mixture and stir at 100 rpm for 30 minutes until uniform. Then, add 2 parts of polymethylhydrogensiloxane (hydrogen content 0.5 wt%) and 0.01 parts of a platinum-based catalyst and continue stirring at 100 rpm for 15 minutes to obtain a uniform mixture.

[0054] 3. Coating and curing: The mixture obtained in step 2 was coated on a ceramic substrate (alumina ceramic, thickness 1 mm), and placed in an oven at 90°C for heating and curing for 2 hours to complete the cross-linking reaction.

[0055] 4. Secondary heat treatment: Place the cured material in a 150°C oven for secondary heat treatment for 20 minutes to optimize flame retardant properties.

[0056] Example 3

[0057] Formula (by mass):

[0058] Vinyl-terminated polydimethylsiloxane: 65 parts

[0059] Polyurethane microcapsules containing liquid crystal molecules (the liquid crystal molecules are 4-cyano-4'-pentylbiphenyl, with a particle size of 10-50 μm): 8 parts

[0060] ZrO2 nanoparticles: 5 parts

[0061] Aluminum hydroxide: 10 parts

[0062] Hydrogenated siloxane (polymethylhydrogen siloxane, hydrogen content 1.6 wt%): 4 parts

[0063] Platinum-based catalyst: 0.03 parts

[0064] Preparation steps:

[0065] 1. Filler dispersion: Take 65 parts of vinyl-terminated polydimethylsiloxane and place it in a high-shear mixer. Add 5 parts of ZrO2 nanoparticles (average particle size 25 nm) and 10 parts of aluminum hydroxide (average particle size 1.2 μm). Disperse at 3000 rpm for 30 minutes to ensure that the filler is evenly dispersed to obtain a PDMS-filler mixture.

[0066] 2. Mixing Microcapsules and Crosslinker: Add 8 parts of polyurethane microcapsules containing 4-cyano-4'-pentylbiphenyl (prepared according to Preparation Example 1, particle size approximately 40 μm) to the PDMS-filler mixture and stir at 200 rpm for 20 minutes until uniform. Then, add 4 parts of polymethylhydrogensiloxane (hydrogen content 1.6 wt%) and 0.03 parts of a platinum-based catalyst and continue stirring at 200 rpm for 10 minutes to obtain a uniform mixture.

[0067] 3. Coating and curing: The mixture obtained in step 2 was coated on a metal substrate (aluminum plate, thickness 0.8 mm), and placed in an oven at 130°C for heating and curing for 1 hour to complete the cross-linking reaction.

[0068] 4. Secondary heat treatment: Place the cured material in an oven at 180°C for secondary heat treatment for 10 minutes to enhance the density of the carbonized layer and the flame retardant effect.

[0069] Example 4

[0070] Formula (by mass):

[0071] Vinyl-terminated polydimethylsiloxane: 62 parts

[0072] Polyurethane microcapsules containing liquid crystal molecules (the liquid crystal molecules are 4-cyano-4'-pentylbiphenyl, with a particle size of 10-50 μm): 15 parts

[0073] ZrO2 nanoparticles: 7 parts

[0074] Aluminum hydroxide: 7 parts

[0075] Hydrogenated siloxane (polymethylhydrogen siloxane, hydrogen content 1.2 wt%): 3.5 parts

[0076] Platinum-based catalyst: 0.02 parts

[0077] Preparation steps:

[0078] 1. Filler dispersion: Take 62 parts of vinyl-terminated polydimethylsiloxane and place it in a high-shear mixer. Add 7 parts of ZrO2 nanoparticles (average particle size 18 nm) and 7 parts of aluminum hydroxide (average particle size 1 μm) and disperse it at 2700 rpm for 45 minutes to ensure that the filler is evenly dispersed to obtain a PDMS-filler mixture.

[0079] 2. Microcapsule and crosslinker mixture: Add 15 parts of polyurethane microcapsules containing 4-cyano-4'-pentylbiphenyl (prepared according to Preparation Example 1, particle size approximately 25 μm) to the PDMS-filler mixture and stir at 120 rpm for 28 minutes until uniform. Then, add 3.5 parts of polymethylhydrogensiloxane (hydrogen content 1.2 wt%) and 0.02 parts of a platinum-based catalyst and continue stirring at 120 rpm for 13 minutes to obtain a uniform mixture.

[0080] 3. Coating and curing: The mixture obtained in step 2 was coated on a ceramic substrate (silicon nitride ceramic, thickness 0.7 mm), and placed in an oven at 120°C for heating and curing for 1.2 hours to complete the cross-linking reaction.

[0081] 4. Secondary heat treatment: Place the cured material in a 170°C oven for secondary heat treatment for 12 minutes to improve flame retardancy and material stability.

[0082] Control Example

[0083] Comparative Example 1

[0084] The difference between this control example and Example 2 is that the ZrO2 nanoparticles are removed and replaced with 10 parts of vinyl-terminated polydimethylsiloxane, while keeping the total amount of the composition unchanged, and the preparation method is changed accordingly.

[0085] Comparative Example 2

[0086] The difference between this control example and Example 2 is that the polyurethane microcapsules containing liquid crystal molecules are removed and replaced with 10 parts of vinyl-terminated polydimethylsiloxane, while keeping the total amount of the composition unchanged and changing the preparation method accordingly.

[0087] Comparative Example 3

[0088] The difference between this control example and Example 2 is that the aluminum hydroxide is removed and replaced by 3 parts of vinyl-terminated polydimethylsiloxane, the total amount of the composition remains unchanged, and the preparation method is changed accordingly.

[0089] Performance testing methods

[0090] 1. Tensile Strength: The following are test methods for three performance indicators: tensile strength, toxic gas concentration, and carbon residue rate. Based on the background and requirements of the high-performance silicone rubber composition described in the document, each indicator is clearly explained in a paragraph, including the test method, standard, and expected results, to ensure that the method is suitable for verifying the performance improvement of the material in electrical insulation applications.

[0091] 2. Toxic gas concentration: The toxic gas concentration test adopts ISO 19702 standard and uses Fourier transform infrared spectroscopy (FTIR) to analyze the gas composition of the combustion products. Take about 5g of silicone rubber sample and burn it in a tube furnace or cone calorimeter at 600-800℃ in air atmosphere. The combustion gas is collected through the gas line to the FTIR spectrometer (wave number range 400-4000 cm -1 ), detects the concentration of toxic gases such as CO (unit: ppm). The test requires baseline calibration and quantitative analysis using a standard gas curve. Each formulation is repeated three times and the average value is taken.

[0092] 3. Carbon Residue: The carbon residue test follows ASTM E1131 and is performed using a thermogravimetric analyzer (TGA, such as the TAInstruments Q500). A 5-10 mg sample is heated in a nitrogen or air atmosphere from room temperature to 800°C at a heating rate of 10°C / min. The remaining carbon residue (%) at 800°C is recorded. During the test, ensure the sample is homogeneous, the atmosphere flow rate is stable (approximately 50 mL / min), and the instrument is calibrated to eliminate baseline drift. Each formulation is tested three times, and the average value is calculated.

[0093] Table 1

[0094]

[0095] Combining Examples 1 to 4 and Table 1, it can be seen that the tensile strength of Examples 1 to 4 ranges from 6.9 to 7.2 MPa, the toxic gas concentration (taking CO as an example) ranges from 700 to 850 ppm, and the carbon residue rate ranges from 30 to 35%.

[0096] Combining Example 2, Control Example 1, and Table 1, it can be seen that Example 2 exhibits a tensile strength of 6.9 MPa, a toxic gas concentration (CO) of 750 ppm, and a carbon residue of 30%. In contrast, Control Example 1 (based on Example 2, but with the ZrO2 nanoparticles removed and replaced with 10 parts of vinyl-terminated PDMS) exhibits a tensile strength drop to 6.0 MPa, a CO concentration increase to 900 ppm, and a carbon residue drop to 20%. The ZrO2 nanoparticles (10 parts) in Example 2 enhance the compatibility between the polyurethane microcapsules and the PDMS matrix through interfacial interactions (such as hydrogen bonding or van der Waals forces), significantly reducing the coefficient of thermal expansion (CTE) and increasing the mechanical strength of the cross-linked network, thereby maintaining high tensile strength and interfacial stability. Furthermore, the ZrO2 and aluminum hydroxide (5 parts) synergistically promote the formation of a dense carbonized layer at high temperatures, reducing volatile decomposition products (low CO concentration), increasing the carbon residue, and enhancing flame retardancy and thermal stability. After removing ZrO2 from Control Example 1, the CTE increased (estimated to be 150 ppm / °C, close to that of conventional silicone rubber, as shown in Table 1). Thermal stress could not be effectively alleviated, resulting in decreased interfacial compatibility and lower tensile strength. Furthermore, the lack of ZrO2's thermal barrier effect loosened the carbonization layer, significantly reducing the residual carbon yield and increasing combustion volatiles (CO concentration). Therefore, the absence of ZrO2 weakened the material's synergistic optimization effects in mechanical properties, flame retardancy, and thermal stability, resulting in significantly inferior performance of Control Example 1 compared to Example 2.

[0097] A comparison of Example 2, Comparative Example 2, and Table 1 shows that Example 2 exhibits a tensile strength of 6.9 MPa, a toxic gas concentration (CO) of 750 ppm, and a carbon residue of 30%. In contrast, Comparative Example 2 (based on Example 2, but with the polyurethane microcapsules containing liquid crystal molecules removed and replaced with 10 parts vinyl-terminated PDMS) exhibits a tensile strength drop to 5.8 MPa, a CO concentration increase to 1000 ppm, and a carbon residue drop to 15%. The polyurethane microcapsules (12 parts) containing 4-cyano-4'-pentylbiphenyl in Example 2 undergo a volume change through a nematic to isotropic phase transition at around 35°C, dynamically regulating the coefficient of thermal expansion (CTE; 72 ppm / °C in Table 1), effectively alleviating thermal stress and enhancing interfacial stability with the metal / ceramic substrate, thereby maintaining high tensile strength. The microcapsules synergistically interact with ZrO2 (10 parts) and aluminum hydroxide (5 parts) to promote the formation of a dense carbonized layer at high temperatures, reduce volatile decomposition products (low CO concentration), and increase the carbon residue, thereby enhancing flame retardancy and thermal stability. After removing the microcapsules from Control Example 2, the lack of dynamic CTE control led to a significant increase in CTE (estimated to be 200 ppm / °C based on Table 1, close to the 220 ppm / °C of pure PDMS). This increased thermal stress led to interfacial cracking and a significant decrease in tensile strength. Simultaneously, the stability of the carbonized layer decreased, volatiles increased (CO concentration increased), and the residual carbon yield decreased significantly. Therefore, the absence of liquid crystal microcapsules weakened CTE control, mechanical properties, and flame retardancy, resulting in Control Example 2 performing significantly worse than Example 2.

[0098] Combining Example 2, Comparative Example 3, and Table 1, shows that Example 2 achieved a tensile strength of 6.9 MPa, a toxic gas concentration (CO) of 750 ppm, and a carbon residue of 30%. In contrast, Comparative Example 3 (based on Example 2, but with the aluminum hydroxide removed and replaced with 3 parts of vinyl-terminated PDMS) exhibited a tensile strength drop to 6.2 MPa, a CO concentration increase to 950 ppm, and a carbon residue drop to 18%. Mechanistically, the aluminum hydroxide (5 parts) in Example 2, acting as a flame-retardant filler, synergizes with ZrO2 nanoparticles (10 parts) and polyurethane microcapsules containing 4-cyano-4'-pentylbiphenyl (12 parts), promoting the formation of a dense and stable carbonized layer at high temperatures, reducing volatile decomposition products (low CO concentration), and increasing the carbon residue, thereby enhancing flame retardancy and thermal stability. Furthermore, the aluminum hydroxide's filling effect enhances the mechanical strength of the cross-linked network, which, combined with the microcapsules' dynamically controlled CTE (72 ppm / °C in Table 1) and the interfacial reinforcement of ZrO2, maintains high tensile strength and thermal cycling stability. After removing aluminum hydroxide from Control Example 3, the stability of the carbonized layer decreased significantly, resulting in a lower carbon residue rate (18%) and an increase in volatile matter (CO concentration rose to 950 ppm). Furthermore, the lack of aluminum hydroxide's filling and flame retardant properties weakened the cross-linked network, reduced tensile strength, slightly increased CTE (estimated to be 100 ppm / °C according to Table 1), and caused microcracks to appear during thermal cycling. Therefore, the absence of aluminum hydroxide weakened flame retardancy, carbonized layer stability, and mechanical properties, resulting in significantly inferior performance of Control Example 3 compared to Example 2.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A silicone rubber composition for electrical insulation, characterized in that: In terms of mass, it includes: 55 to 65 parts vinyl terminated polydimethylsiloxane 8 to 15 parts of polyurethane microcapsules containing liquid crystal molecules ZrO2 nanoparticles 5 to 10 parts 5 to 10 parts of aluminum hydroxide 2 to 4 parts of hydrogen siloxane 0.01 to 0.03 parts of a platinum-based catalyst; The liquid crystal molecules in the polyurethane microcapsules are 4-cyano-4'-pentylbiphenyl. The preparation method of the polyurethane microcapsules includes: mixing 4-cyano-4'-pentylbiphenyl with water and an emulsifier, forming a stable emulsion through high-speed stirring, adding isocyanate and polyol, performing interfacial polymerization in the emulsion to polymerize the liquid crystal droplets into a polyurethane shell, filtering, washing and drying the microcapsules, and controlling the particle size to be between 10 and 50 μm.

2. The composition according to claim 1, characterized in that The hydrogen-containing siloxane is polymethyl hydrogen siloxane, and the hydrogen content is 0.5 wt % to 1.6 wt %.

3. The method for preparing the composition according to claim 1, wherein The following technical steps are included: Step 1. Add ZrO2 nanoparticles and aluminum hydroxide to vinyl-terminated polydimethylsiloxane and disperse them using a high shear mixer at 2000-3000 rpm for 30-60 minutes to uniformly disperse the filler in the matrix to obtain a PDMS-filler mixture; Step 2. Add the polyurethane microcapsules containing liquid crystal molecules to the PDMS-filler mixture and stir at a low speed of 100-200 rpm for 20-30 minutes until uniform. Then add the hydrogenated siloxane and platinum-based catalyst and continue stirring for 10-15 minutes to obtain a uniform mixture. Step 3. Apply the uniform mixture obtained in step 2 on the target substrate and heat-cure at 90-130°C for 1-2 hours to complete the cross-linking reaction; Step 4. Place the cured material at 150-180°C for a secondary heat treatment for 10-20 minutes.

4. The preparation method according to claim 3, characterized in that In step 1, the rotation speed of the high shear mixer is 2000-3000 rpm, and the dispersion time is 30-60 minutes.

5. The preparation method according to claim 3, characterized in that In step 2, when adding the polyurethane microcapsules containing liquid crystal molecules, the stirring speed is 100-200 rpm.

6. The preparation method according to claim 3, characterized in that The target substrate is a metal or ceramic material used in electronic devices.

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