A liquid silicone rubber system for heat conducting gaskets and a method for producing same

Abstract

This invention belongs to the field of organosilicon thermally conductive materials, and provides a liquid silicone rubber system for thermally conductive pads and its preparation method. The system comprises vinyl-terminated dimethyl polysiloxane, MQ / phenyl-enriched pre-crosslinked polysiloxane microgel, vinyltrimethoxysilane-modified hexagonal boron nitride, alumina, trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex, and 1-ethynyl-1-cyclohexanol, forming a two-component packaging. This system is advantageous in balancing thermal conductivity, electrical insulation, flowability, defoaming, softness and fit, and long-term stability, making it suitable for the preparation of thermally conductive pads.

Description

Technical Field

[0001] This invention relates to the field of organosilicon thermal conductive materials, specifically to a liquid silicone rubber system for thermal pads and its preparation method. Background Technology

[0002] As electronic devices evolve towards higher power density, miniaturization, and higher integration, the interfacial heat transfer between heat-generating and heat-dissipating components in power modules, communication equipment, automotive electronic control units, and precision heat dissipation assemblies increasingly relies on the comprehensive adaptability of thermal pads. Thermal pads typically need to simultaneously perform heat transfer, gap filling, electrical insulation, and buffering functions within a limited space. Therefore, the material must not only possess stable thermal conductivity and electrical insulation but also maintain suitable flowability during mixing, degassing, and molding, and retain softness, low interfacial stress, and stable shape after curing. For liquid silicone rubber systems, only by considering filler loading, system rheology, cured network, and interfacial contact state can an effective heat transfer path and reliable performance be maintained continuously under thermal cycling, compression assembly, and long-term service conditions.

[0003] Existing technologies have focused on improving thermally conductive liquid silicone rubber and thermally conductive silicone compositions. For example, Chinese patent CN110845852A discloses a high thermal conductivity liquid silicone rubber, its preparation method, and its application. It employs an A / B glue structure and introduces spherical alumina, alkyltrimethoxysilane, and alkynyl alcohol compounds into the system to balance thermal conductivity, flowability, and injection molding applicability. Another example is Chinese patent CN113454165A, which discloses a thermally conductive silicone composition that aims to obtain a low-oil-permeability thermally conductive silicone system by controlling the alkenyl group, Si-H component, and thermally conductive particles. Therefore, existing solutions often focus on either high thermal conductivity flow systems or low-oil-permeability thermally conductive systems. However, for the dual constraints of flowability and defoaming, and soft adhesion and low migration long-term stability under high-filling conditions in thermally conductive pad applications, a systematic design synergistically combining multiple thermally conductive fillers with pre-crosslinked polysiloxane structures is still lacking. Summary of the Invention

[0004] The purpose of this invention is to provide a liquid silicone rubber system for thermally conductive pads and its preparation method. This addresses the problem that in the prior art, to obtain high thermal conductivity and maintain electrical insulation, it is usually necessary to increase the filling amount of insulating and thermally conductive fillers such as alumina and hexagonal boron nitride, and enhance the overlap contact between fillers to construct a thermally conductive network. This often leads to increased system viscosity, poor flowability, difficulty in degassing, and a narrowing of the processing window. Furthermore, to improve the flowability and molding processability of highly filled systems, it is often achieved by increasing the proportion of continuous polysiloxane phase, reducing filler load, or weakening the degree of structure, resulting in a decrease in the continuity of the thermal conductive path and impaired thermal conductivity. Meanwhile, in order to improve the softness and low interfacial stress of thermally conductive pads, existing technologies often adopt methods such as reducing cross-linking constraints or increasing flexible continuous phases. However, this can easily lead to the migration and precipitation of low molecular weight components, pumping out under hot-pressing cycles, and a decrease in long-term thermal conductivity. In order to suppress migration, reduce oil precipitation, and improve long-term interfacial thermal conductivity reliability, it is often necessary to enhance the network structure and interfacial anchoring of the system, which further leads to an increase in modulus, a decrease in compression compliance, and an increase in contact thermal resistance. Therefore, it is difficult to achieve both the inherent contradictions of high filling, low viscosity, and wide processing window with high thermal conductivity and insulation performance, and soft, low-stress bonding with low migration and long-term thermal conductivity reliability.

[0005] This invention employs MQ / phenyl-enriched pre-crosslinked polysiloxane microgel, vinyltrimethoxysilane-modified hexagonal boron nitride, and alumina in a proportionally matched manner, and uses a two-component packaging form of component A and component B. This allows for the simultaneous adjustment of interfacial interactions, system flow, and the stability of the cured network, thereby improving the reliability of thermal conductivity pathway construction and use.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A liquid silicone rubber system for thermal pads, comprising, by weight, 100 parts by weight of vinyl-terminated dimethyl polysiloxane, 8-35 parts by weight of MQ / phenyl-enriched pre-crosslinked polysiloxane microgel, 2-12 parts by weight of vinyltrimethoxysilane-modified hexagonal boron nitride, 180-450 parts by weight of alumina, 0.5-6 parts by weight of trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer, 2-80 ppm of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex based on the total mass of the composition (calculated as platinum), and 0.01-0.20 parts by weight of 1-ethynyl-1-cyclohexanol;

[0008] Furthermore, the MQ / phenyl enriched pre-crosslinked polysiloxane microgel is prepared by pre-reaction of vinyl-terminated dimethylpolysiloxane, divinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer, trimethylsiloxysilicate, and trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer; the vinyltrimethoxysilane-modified hexagonal boron nitride is prepared by reacting hexagonal boron nitride with vinyltrimethoxysilane; the D50 of the microgel is 0.5-5.0µm, and the gel fraction measured by organic solvent extraction is 10-45wt%; the surface grafting amount of the vinyltrimethoxysilane-modified hexagonal boron nitride is 0.3-5.0wt%; the alumina exhibits a bimodal particle size distribution, including a first peak alumina and a second peak alumina, the D50 of the first peak alumina is 0.3-5µm, and the D50 of the second peak alumina is 10-60µm.

[0009] Furthermore, the MQ / phenyl-enriched pre-crosslinked polysiloxane microgel was prepared by the following method:

[0010] A1. 100 parts by weight of vinyl-terminated dimethylpolysiloxane, 8-30 parts by weight of vinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer, 5-25 parts by weight of trimethylsiloxysilicate, and 0.4-2.5 parts by weight of trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer are added to 40-120 parts by weight of xylene and stirred at 25-35°C for 10-40 min to obtain the oil phase.

[0011] A2, add 0.5-4.0 parts by weight of polyvinyl alcohol to 100-300 parts by weight of water, stir at 80-95℃ for 30-90 minutes until completely dissolved, cool to 25-40℃ to obtain the aqueous phase;

[0012] A3, under nitrogen protection, the oil phase is added to the aqueous phase. After all the oil phase has been added, the mixture is sheared at 3000-8000 rpm for 5-20 min to form droplets. Then, 10-60 ppm of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex (based on the total mass of the organosilicon components in step A1 and calculated as platinum) is added. The mixture is reacted at 55-75°C for 1-4 h, and the gel content, as measured by organic solvent extraction, is 10-45 wt%.

[0013] A4. The reaction system obtained in A3 is subjected to xylene removal at 60-75℃ and -0.06 to -0.095 MPa, washed 1-3 times with 60-90wt% ethanol aqueous solution, and dried at 40-60℃ and -0.06 to -0.095 MPa for 6-18 h until the difference between two consecutive weighings is no greater than 0.5wt%, to obtain the microgel.

[0014] Furthermore, the microgel meets the following requirements: D50 is 0.8-3.0µm; gel content measured by organic solvent extraction is 15-35wt%; volatile matter is not higher than 2.0wt%; residual Si-H content is 0.01-0.20mmol / g; and in step A1, the mass ratio of the divinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer to the trimethylsiloxysilicate is 0.32:1 to 2:1.

[0015] Furthermore, the vinyltrimethoxysilane-modified hexagonal boron nitride is prepared by the following method:

[0016] B1, dispersing 100 parts by weight of hexagonal boron nitride in a mixed solvent consisting of 300-1000 parts by weight of ethanol and 10-120 parts by weight of water;

[0017] B2, after adjusting the pH of the system to 4.0-5.5 with acetic acid, add 1-10 parts by weight of vinyltrimethoxysilane, reflux at 65-80℃ for 1-6 hours, and stir at 200-800 rpm;

[0018] B3 was filtered, washed 2-4 times with ethanol, and dried at 80-110℃ and -0.06 to -0.095 MPa for 4-12 hours until the difference between two consecutive weighings was no more than 0.5 wt%, to obtain the vinyltrimethoxysilane modified hexagonal boron nitride.

[0019] Furthermore, the vinyltrimethoxysilane-modified hexagonal boron nitride meets the following requirements: surface grafting amount is 0.5-3.0 wt%; residual free vinyltrimethoxysilane is not higher than 0.5 wt%; D50 is 0.5-8 µm; sheet thickness is 80-500 nm; lateral dimension is 0.5-15 µm; and the mass ratio of the MQ / phenyl enriched pre-crosslinked polysiloxane microgel to the vinyltrimethoxysilane-modified hexagonal boron nitride is 1.5:1 to 6:1.

[0020] Furthermore, the amount of the MQ / phenyl enriched pre-crosslinked polysiloxane microgel is 10-25 parts by mass, the amount of the vinyltrimethoxysilane modified hexagonal boron nitride is 3-8 parts by mass, the amount of alumina is 220-380 parts by mass, and the amount of the trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer is 0.8-3.0 parts by mass; the mass ratio of the first peak alumina to the second peak alumina is 20:80 to 50:50; the D50 of the first peak alumina is 0.5-3µm; and the D50 of the second peak alumina is 20-45µm.

[0021] Furthermore, based on the composition after mixing components A and B, the molar ratio of reactive Si-H functional groups to reactive vinyl functional groups is 0.85:1 to 1.20:1; the amount of the 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex added is 10-40 ppm based on the total mass of the composition after mixing components A and B, expressed as platinum; the amount of 1-ethynyl-1-cyclohexanol added is 0.02-0.10 parts by mass; the composition uses components A and B. The product is packaged in a two-component form. Component A comprises vinyl-terminated dimethyl polysiloxane, the microgel, the vinyltrimethoxysilane-modified hexagonal boron nitride, the alumina, and the 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex. Component B comprises vinyl-terminated dimethyl polysiloxane, the trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer, and the 1-ethynyl-1-cyclohexanol. The mass ratio of component A to component B is 1:0.9 to 1:1.1.

[0022] As a concept of this invention, the present invention employs a design that combines MQ / phenyl-enriched pre-crosslinked polysiloxane microgel, vinyltrimethoxysilane-modified hexagonal boron nitride, and alumina with vinyl-terminated dimethyl polysiloxane, primarily to achieve a synergistic balance between flowability and thermal conductivity. In existing technologies, to obtain higher thermal conductivity and maintain electrical insulation, the filling amounts of alumina and hexagonal boron nitride are typically increased, and filler contact is enhanced. However, this easily leads to increased system viscosity, difficulty in degassing, and a narrowing of the processing window. Conversely, to improve flowability, softness, and low interfacial stress, the proportion of continuous phases is often increased or network constraint is weakened, thereby weakening the continuity of the thermal conductivity pathway and inducing the migration and precipitation of low-molecular-weight components. This invention, through the proportional matching and interfacial synergistic design of MQ / phenyl-enriched pre-crosslinked polysiloxane microgel, vinyltrimethoxysilane-modified hexagonal boron nitride, and alumina, cross-mitigates the side effects of high filling and low constraint, achieving simultaneous improvement in thermal conductivity, processing, and long-term service performance.

[0023] This invention also discloses a method for preparing a liquid silicone rubber system for thermal pads, comprising the following steps:

[0024] S1 provides the prepared MQ / phenyl-enriched pre-crosslinked polysiloxane microgel;

[0025] S2 provides a prepared vinyltrimethoxysilane-modified hexagonal boron nitride;

[0026] S3, vinyl-terminated dimethyl polysiloxane, the microgel, the vinyltrimethoxysilane-modified hexagonal boron nitride, the alumina, and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex are mixed to obtain component A;

[0027] S4, vinyl-terminated dimethylpolysiloxane, trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer and 1-ethynyl-1-cyclohexanol are mixed to obtain component B;

[0028] S5, mix component A and component B at a mass ratio of 1:0.9 to 1:1.1, degas, mold, and cure at 110-140℃ for 10-30 min to obtain the cured liquid silicone rubber system for the thermal pad.

[0029] Further, in step S3, the vinyltrimethoxysilane-modified hexagonal boron nitride is first pre-dispersed with 5-20 parts by weight of vinyl-terminated dimethyl polysiloxane for 5-20 minutes, and then the microgel is added; in step S3, the alumina is added in two stages in the order of adding the second peak alumina first and the first peak alumina later; the mixing temperature in steps S3 and S4 is 20-45℃, the mixing speed is 200-1200 rpm, and the mixing time is 10-40 minutes; the degassing pressure in step S5 is -0.06 to -0.095 MPa, and the degassing time is 5-30 minutes.

[0030] The molding method in step S5 is one of calendering, compression molding, or liquid silicone rubber injection molding; the curing conditions in step S5 are 120-135℃ for 10-25 min; the thickness of the resulting thermal pad is 0.3-5.0 mm; after step S5, there is also a post-curing step of holding at 80-120℃ for 0.5-2 h.

[0031] Furthermore, in step A1, the stirring is carried out by mechanical stirring at a speed of 200-500 rpm.

[0032] Furthermore, in step A2, the stirring is carried out by mechanical stirring at a speed of 200-500 rpm.

[0033] Furthermore, in step A2, the criterion for complete dissolution is that the system has no visible particles and the solution is clear and transparent.

[0034] Furthermore, in step A3, the oil phase is gradually added to the aqueous phase over 10-40 minutes, and shearing is performed simultaneously at 3000-8000 rpm during the addition process. The shearing time of 5-20 minutes is calculated from the completion of the addition of all the oil phase.

[0035] Furthermore, in step A4, the time for removing xylene is 1-3 hours.

[0036] Furthermore, in step A4, when washing with a 60-90 wt% ethanol aqueous solution, the amount of washing solution used each time is 100-400 parts by weight relative to the microgel solids, and the washing is carried out by resuspension followed by centrifugation.

[0037] Furthermore, in step B1, the hexagonal boron nitride is dispersed by mechanical stirring for 10-40 minutes.

[0038] Furthermore, in step B2, the pH of the system is adjusted to 4.0-5.5 using a 10-50 wt% aqueous acetic acid solution.

[0039] Furthermore, in step B2, the 10-50wt% acetic acid aqueous solution is added dropwise under stirring, and the pH value of the system is monitored in real time using a pH meter.

[0040] Furthermore, in step B2, the reflux is carried out in an atmospheric pressure device equipped with a reflux condenser and circulating cooling water, and the timing begins after the reflux state stabilizes.

[0041] Furthermore, in step B3, when washing with ethanol, the amount of washing liquid used each time is 100-300 parts by mass relative to the amount of hexagonal boron nitride fed, and the washing is carried out by resuspension followed by vacuum filtration.

[0042] Furthermore, the total amount of vinyl-terminated dimethyl polysiloxane in components A and B is 100 parts by mass.

[0043] Furthermore, in step S3, 5-20 parts by mass of vinyl-terminated dimethyl polysiloxane pre-dispersed with vinyltrimethoxysilane-modified hexagonal boron nitride are included in the total amount of vinyl-terminated dimethyl polysiloxane.

[0044] Furthermore, the molar ratio of the reactive Si-H functional group to the reactive vinyl functional group is calculated based on the composition after mixing component A and component B, and the reactive vinyl functional group does not include the vinyl functional group in the 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex ligand.

[0045] Furthermore, the D50 of the microgel and the D50 of the vinyltrimethoxysilane-modified hexagonal boron nitride were determined by laser particle size analysis, the gel fraction of the microgel was determined by organic solvent extraction, and the surface grafting amount of the vinyltrimethoxysilane-modified hexagonal boron nitride was determined by thermogravimetric analysis.

[0046] As another aspect of this invention, a preparation method employing a stepwise construction of components A and B, followed by mixing and curing before molding, is primarily used to achieve, fix, or amplify the aforementioned synergistic effect. In existing technologies, pursuing thermal conductivity solely by increasing the amount of alumina and hexagonal boron nitride or simply shortening the mixing path often leads to instability in the mixing, degassing, and molding processes. Conversely, improving processability solely by reducing the degree of structure or relaxing curing constraints can result in insufficient thermal conductivity pathways and long-term interfacial stability. This invention, by first providing MQ / phenyl-enriched pre-crosslinked polysiloxane microgels and vinyltrimethoxysilane-modified hexagonal boron nitride, then sequentially distributing them to components A and B, and coordinating the segmented addition of the second-peak alumina and the first-peak alumina, along with controlled degassing and curing conditions, allows the processing window, thermal conductivity pathways, and curing network to be simultaneously established within the same process path, thereby enabling the aforementioned synergistic relationship to form and be stably maintained.

[0047] MQ / phenyl-enriched pre-crosslinked polysiloxane microgels primarily function to improve system flow, stabilize the cured network, and control the migration of low-molecular-weight components. Vinyltrimethoxysilane-modified hexagonal boron nitride (BNN) mainly functions to build thermally conductive pathways and facilitate heat transfer under electrically insulating conditions. Increasing only the proportion of MQ / phenyl-enriched pre-crosslinked polysiloxane microgels, while beneficial for enhancing network constraint and inhibiting migration and precipitation, can easily increase interfacial constraint and affect the effective overlap of thermally conductive fillers. Similarly, increasing only the proportion of vinyltrimethoxysilane-modified BNN, while beneficial for forming thermally conductive contact paths, can easily deteriorate processing and usage conditions due to agglomeration of sheet-like fillers, increased rheological properties, and decreased adhesion. This invention, by limiting the mass ratio of the two and combining the interfacial effects of vinyltrimethoxysilane-modified BNN with the particle size distribution design of alumina, allows the former's stabilizing effect on the network and interface to mutually correct the latter's role in building thermally conductive pathways, thus achieving a balance between flowability, soft adhesion, and reliable thermal conductivity.

[0048] Beneficial technical effects

[0049] 1. This invention introduces MQ / phenyl-enriched pre-crosslinked polysiloxane microgels into a vinyl-terminated dimethyl polysiloxane system, and combines them with vinyltrimethoxysilane-modified hexagonal boron nitride and alumina. This allows the system under high-filling conditions to no longer rely solely on increasing alumina loading to achieve thermal conductivity, thereby facilitating the balance between maintaining electrical insulation and flowability and molding processability.

[0050] 2. The present invention adopts a particle size distribution design of first peak alumina and second peak alumina, and limits the molar ratio of reactive Si-H functional groups to reactive vinyl functional groups and the mass ratio of component A to component B, which is beneficial to maintain a stable operating window after mixing, reduce fluctuations in the degassing and molding process, and improve the consistency of thermal pad preparation.

[0051] 3. This invention, through the interface regulation of vinyltrimethoxysilane-modified hexagonal boron nitride and the ratio matching with MQ / phenyl-enriched pre-crosslinked polysiloxane microgel, helps to weaken the adverse effects of filler agglomeration and interface mismatch, so that the construction of thermal conductive pathways and interface bonding no longer significantly hinder each other.

[0052] 4. This invention adopts a two-component packaging form, and in the curing stage, it is combined with trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex and 1-ethynyl-1-cyclohexanol, which helps to reduce the risk of low molecular weight component migration and precipitation and pumping out under thermo-pressing cycles, and improves long-term thermal conductivity stability and interface reliability. Attached Figure Description

[0053] Figure 1 The images are FTIR overlays of samples from Example 1, Comparative Example 1, and Comparative Example 10.

[0054] Figure 2 The images shown are XPS high-resolution B1s images of samples from Example 1, Comparative Example 1, and Comparative Example 9.

[0055] Figure 3 The images shown are XPS high-resolution N1s images of samples from Example 1, Comparative Example 1, and Comparative Example 9.

[0056] Figure 4 The images shown are XPS high-resolution Si2p images of the samples from Example 1, Comparative Example 1, and Comparative Example 9.

[0057] Figure 5 This is the XPS Si2p peak fitting diagram of the sample from Example 1.

[0058] Figure 6 The rheological flow curves of the uncured systems of Example 1, Comparative Example 5, and Comparative Example 6 are shown.

[0059] Figure 7 The thermal resistance-pressure curves of the cured thermally conductive pads in Examples 1, 5, and 6 are shown.

[0060] Figure 8 The figures show the compression stress relaxation curves of the cured thermally conductive pads in Examples 1, 7, and 8.

[0061] Figure 9 The graph shows the thermal conductivity retention rate of the cured thermally conductive pads after thermal cycling in Examples 1, 8, and 10.

[0062] Figure 10 The original scatter plot with mean ± SD of the post-cured thermal pad sheets of Example 1, Comparative Example 8, and Comparative Example 10 is shown.

[0063] Figure 11 Macroscopic optical photograph of the thermally conductive pad prepared in Example 1.

[0064] Figure 12 This is a scanning electron microscope image of the liquid silicone rubber composite material used in the thermal pad of Example 1.

[0065] Figure 12 (a) is a low-magnification scanning electron microscope image of the liquid silicone rubber composite material for the thermal pad in Example 1.

[0066] Figure 12 (b) is a high-magnification scanning electron microscope image of the liquid silicone rubber composite material for the thermal pad in Example 1. Detailed Implementation

[0067] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0068] Example 1

[0069] The liquid silicone rubber system for the thermal pad in this embodiment is prepared according to the following method:

[0070] Step S1: Preparation of MQ / phenyl-enriched pre-crosslinked polysiloxane microgels

[0071] A1. 100 parts by weight of vinyl-terminated dimethylpolysiloxane, 8 parts by weight of a vinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer, 5 parts by weight of trimethylsiloxysilicate, and 0.4 parts by weight of a trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer were added to 40 parts by weight of xylene. The mixture was stirred mechanically at 300 rpm for 25 minutes at 30°C to obtain the oil phase.

[0072] A2, add 0.5 parts by weight of polyvinyl alcohol to 100 parts by weight of water, and stir mechanically at 350 rpm for 60 min at 85°C until completely dissolved (the system has no visible particles and the solution is clear and transparent), cool to 30°C to obtain the aqueous phase;

[0073] A3, under nitrogen protection, the oil phase was gradually added to the aqueous phase over 25 minutes, with simultaneous shearing at 5000 rpm during the addition process. After all the oil phase was added, shearing at 5000 rpm continued for 12 minutes to form droplets. Then, 30 ppm of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex (based on the total mass of the organosilicon components in step A1 and calculated as platinum) was added. The reaction was carried out at 65°C for 2.5 hours, and the gel content, measured by organic solvent extraction, was 15 wt%.

[0074] A4. The reaction system obtained from A3 was subjected to xylene removal at 65℃ and -0.08MPa for 2 hours, washed twice with 75wt% ethanol aqueous solution (each washing solution was 250 parts by weight relative to the microgel solids, and the washing was performed by resuspension followed by centrifugation), and dried at 50℃ and -0.08MPa for 12 hours until the difference between two consecutive weighings was no greater than 0.5wt%, thus obtaining the microgel.

[0075] The obtained microgel had a D50 of 0.8 µm, and the gel fraction, measured by organic solvent extraction, was 15 wt%, the volatile content was 1.2 wt%, and the residual Si-H content was 0.08 mmol / g. In step A1, the mass ratio of the divinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer to trimethylsiloxysilicate was 0.32:1.

[0076] Step S2: Preparation of vinyltrimethoxysilane-modified hexagonal boron nitride

[0077] B1, 100 parts by weight of hexagonal boron nitride are dispersed in a mixed solvent consisting of 300 parts by weight of ethanol and 10 parts by weight of water, and dispersed by mechanical stirring for 25 min;

[0078] B2, a 20wt% acetic acid aqueous solution was added dropwise under stirring, and the pH of the system was adjusted to 4.5 by real-time monitoring with a pH meter. Then, 1 part by mass of vinyltrimethoxysilane was added, and the mixture was refluxed at 70°C in an atmospheric pressure device equipped with a reflux condenser and circulating cooling water for 3.5 hours (timing started after the reflux state stabilized), with a stirring speed of 500 rpm.

[0079] B3 was filtered and washed three times with ethanol (each time the washing liquid was 200 parts by weight relative to the amount of hexagonal boron nitride fed, and the washing was carried out by resuspension and vacuum filtration), and dried at 95℃ and -0.08MPa for 8 hours until the difference between two consecutive weighings was no more than 0.5wt%, to obtain vinyltrimethoxysilane modified hexagonal boron nitride.

[0080] The obtained vinyltrimethoxysilane-modified hexagonal boron nitride has a surface grafting amount of 0.5 wt%, a residual free vinyltrimethoxysilane amount of 0.3 wt%, a D50 of 0.5 µm, a sheet thickness of 80 nm, and a lateral dimension of 0.5 µm.

[0081] Step S3: Prepare component A

[0082] First, 2 parts by mass of vinyltrimethoxysilane-modified hexagonal boron nitride and 10 parts by mass of vinyl-terminated dimethyl polysiloxane were pre-dispersed for 12 min, and then 8 parts by mass of the microgel prepared above were added. Then, 180 parts by mass of alumina were added in two stages, with the second peak alumina added first and the first peak alumina added later (36 parts by mass of the first peak alumina with a D50 of 0.5 µm and 144 parts by mass of the second peak alumina with a D50 of 20 µm, the mass ratio of the first peak alumina to the second peak alumina being 20:80). Finally, 15 ppm of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex, based on the total mass of the mixture of components A and B and calculated as platinum, was added. The mixing temperature was 30 °C, the mixing speed was 600 rpm, and the mixing time was 25 min to obtain component A.

[0083] Ten parts by mass of vinyl-terminated dimethyl polysiloxane pre-dispersed with vinyltrimethoxysilane are included in the total amount of vinyl-terminated dimethyl polysiloxane.

[0084] Step S4: Preparation of Component B

[0085] 80 parts by weight of vinyl-terminated dimethylpolysiloxane, 0.5 parts by weight of trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer, and 0.02 parts by weight of 1-ethynyl-1-cyclohexanol were mixed. The mixing temperature was 30°C, the mixing speed was 600 rpm, and the mixing time was 25 min to obtain component B.

[0086] The total amount of vinyl-terminated dimethyl polysiloxane in components A and B is 100 parts by mass.

[0087] Step S5: Curing and molding

[0088] Component A and component B were mixed at a mass ratio of 1:0.9, degassed for 15 minutes under a pressure of -0.08 MPa, calendered into sheets, and cured at 125°C for 18 minutes to obtain a cured liquid silicone rubber system for thermal pads with a thickness of 2.0 mm. Subsequently, it was post-cured at 100°C for 1 hour.

[0089] Based on the composition after mixing components A and B, the molar ratio of reactive Si-H functional groups to reactive vinyl functional groups is 1.00:1 (the reactive vinyl functional groups do not include the vinyl functional groups in the 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex ligand). The mass ratio of MQ / phenyl-enriched pre-crosslinked polysiloxane microgel to vinyltrimethoxysilane-modified hexagonal boron nitride is 4:1.

[0090] Features of Example 1:

[0091] This embodiment employs a design scheme with proportions in the low-end range. The amounts of core components such as MQ / phenyl-enriched pre-crosslinked polysiloxane microgel, vinyltrimethoxysilane-modified hexagonal boron nitride, alumina, and crosslinking agent are all selected at proportions close to the lower end of the range. The mass ratio of alumina in the first peak to the second peak is chosen to favor the second peak. The amounts of each raw material added during microgel preparation and the amounts of solvent and modifier used in the preparation of modified boron nitride are all in the low-end range. This scheme features relatively low raw material costs, moderate system viscosity, and ease of processing, making it suitable for conventional thermal pad manufacturing scenarios with moderate thermal conductivity requirements and cost control considerations, such as general heat dissipation applications in consumer electronics.

[0092] Example 2

[0093] The liquid silicone rubber system for the thermal pad in this embodiment is prepared according to the following method:

[0094] Step S1: Preparation of MQ / phenyl-enriched pre-crosslinked polysiloxane microgels

[0095] A1, 100 parts by weight of vinyl-terminated dimethylpolysiloxane, 30 parts by weight of divinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer, 25 parts by weight of trimethylsiloxysilicate, and 2.5 parts by weight of trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer were added to 120 parts by weight of xylene and stirred at 350 rpm for 25 min at 30 °C to obtain the oil phase;

[0096] A2, add 4.0 parts by weight of polyvinyl alcohol to 300 parts by weight of water, and stir mechanically at 350 rpm for 60 min at 85°C until completely dissolved (the system has no visible particles and the solution is clear and transparent), cool to 30°C to obtain the aqueous phase;

[0097] A3, under nitrogen protection, the oil phase was gradually added to the aqueous phase over 25 minutes, with simultaneous shearing at 5000 rpm during the addition process. After all the oil phase was added, shearing at 5000 rpm continued for 12 minutes to form droplets. Then, 30 ppm of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex (based on the total mass of the organosilicon components in step A1 and calculated as platinum) was added. The reaction was carried out at 65°C for 2.5 hours, and the gel content, measured by organic solvent extraction, was 35 wt%.

[0098] A4. The reaction system obtained from A3 was subjected to xylene removal at 65℃ and -0.08MPa for 2 hours, washed twice with 75wt% ethanol aqueous solution (each washing solution was 250 parts by weight relative to the microgel solids, and the washing was performed by resuspension followed by centrifugation), and dried at 50℃ and -0.08MPa for 12 hours until the difference between two consecutive weighings was no greater than 0.5wt%, thus obtaining the microgel.

[0099] The obtained microgel had a D50 of 3.0 µm, a gel fraction of 35 wt% and a volatile fraction of 2.0 wt% as determined by organic solvent extraction, and a residual Si-H content of 0.20 mmol / g. In step A1, the mass ratio of the divinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer to trimethylsiloxysilicate was 2:1.

[0100] Step S2: Preparation of vinyltrimethoxysilane-modified hexagonal boron nitride

[0101] B1, 100 parts by weight of hexagonal boron nitride are dispersed in a mixed solvent consisting of 1000 parts by weight of ethanol and 120 parts by weight of water, and dispersed by mechanical stirring for 25 min;

[0102] B2, a 20wt% acetic acid aqueous solution was added dropwise under stirring, and the pH of the system was adjusted to 4.5 by real-time monitoring with a pH meter. Then, 10 parts by mass of vinyltrimethoxysilane were added, and the mixture was refluxed at 70°C in an atmospheric pressure device equipped with a reflux condenser and circulating cooling water for 3.5 hours (timing started after the reflux state stabilized), with a stirring speed of 500 rpm.

[0103] B3 was filtered and washed three times with ethanol (each time the washing liquid was 200 parts by weight relative to the amount of hexagonal boron nitride fed, and the washing was carried out by resuspension and vacuum filtration), and dried at 95℃ and -0.08MPa for 8 hours until the difference between two consecutive weighings was no more than 0.5wt%, to obtain vinyltrimethoxysilane modified hexagonal boron nitride.

[0104] The obtained vinyltrimethoxysilane-modified hexagonal boron nitride has a surface grafting amount of 3.0 wt%, a residual free vinyltrimethoxysilane amount of 0.5 wt%, a D50 of 8 µm, a sheet thickness of 500 nm, and a lateral dimension of 15 µm.

[0105] Step S3: Prepare component A

[0106] First, 12 parts by mass of vinyltrimethoxysilane-modified hexagonal boron nitride and 10 parts by mass of vinyl-terminated dimethyl polysiloxane were pre-dispersed for 12 min, and then 35 parts by mass of the microgel prepared above were added. Then, 450 parts by mass of alumina were added in two stages, first the second peak alumina and then the first peak alumina (225 parts by mass of the first peak alumina with a D50 of 3 µm, and 225 parts by mass of the second peak alumina with a D50 of 45 µm, the mass ratio of the first peak alumina to the second peak alumina was 50:50). Finally, 15 ppm of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex, based on the total mass of the mixture of components A and B and calculated as platinum, was added. The mixing temperature was 30 °C, the mixing speed was 600 rpm, and the mixing time was 25 min to obtain component A.

[0107] Ten parts by mass of vinyl-terminated dimethyl polysiloxane pre-dispersed with vinyltrimethoxysilane are included in the total amount of vinyl-terminated dimethyl polysiloxane.

[0108] Step S4: Preparation of Component B

[0109] 80 parts by weight of vinyl-terminated dimethylpolysiloxane, 6 parts by weight of trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer, and 0.02 parts by weight of 1-ethynyl-1-cyclohexanol were mixed. The mixing temperature was 30°C, the mixing speed was 600 rpm, and the mixing time was 25 min to obtain component B.

[0110] The total amount of vinyl-terminated dimethyl polysiloxane in components A and B is 100 parts by mass.

[0111] Step S5: Curing and molding

[0112] Component A and component B were mixed at a mass ratio of 1:1.1, degassed under a pressure of -0.08 MPa for 15 min, calendered into sheets, and cured at 125℃ for 18 min to obtain a cured liquid silicone rubber system for thermal pads with a thickness of 2.0 mm. Subsequently, it was post-cured at 100℃ for 1 h.

[0113] Based on the composition after mixing components A and B, the molar ratio of reactive Si-H functional groups to reactive vinyl functional groups is 1.00:1 (the reactive vinyl functional groups do not include the vinyl functional groups in the 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex ligand). The mass ratio of MQ / phenyl-enriched pre-crosslinked polysiloxane microgel to vinyltrimethoxysilane-modified hexagonal boron nitride is 2.92:1.

[0114] Features of Example 2:

[0115] This embodiment employs a design scheme with proportions in the high-value range. The amounts of core components such as MQ / phenyl-enriched pre-crosslinked polysiloxane microgel, vinyltrimethoxysilane-modified hexagonal boron nitride, alumina, and crosslinking agent are all selected in proportions close to the upper end of the range. The mass ratio of alumina in the first peak to the second peak is balanced. The amounts of each raw material added during microgel preparation and the amounts of solvent and modifier used in the preparation of modified boron nitride are all in the high-value range. This scheme features high filler content, excellent thermal conductivity, and good mechanical strength, making it suitable for high-end heat dissipation applications such as high-power-density electronic devices, new energy vehicle battery packs, and server chips, where extremely high thermal conductivity is required.

[0116] Example 3

[0117] The liquid silicone rubber system for the thermal pad in this embodiment is prepared according to the following method:

[0118] Step S1: Preparation of MQ / phenyl-enriched pre-crosslinked polysiloxane microgels

[0119] A1, 100 parts by weight of vinyl-terminated dimethylpolysiloxane, 18 parts by weight of divinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer, 12 parts by weight of trimethylsiloxysilicate, and 1.2 parts by weight of trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer were added to 70 parts by weight of xylene and stirred mechanically at 200 rpm for 10 min at 25°C to obtain the oil phase;

[0120] A2, add 2.0 parts by weight of polyvinyl alcohol to 180 parts by weight of water, and stir mechanically at 200 rpm for 30 minutes at 80°C until completely dissolved (the system has no visible particles and the solution is clear and transparent), cool to 25°C to obtain the aqueous phase;

[0121] A3, under nitrogen protection, the oil phase was gradually added to the aqueous phase over 10 minutes, with simultaneous shearing at 3000 rpm during the addition process. After all the oil phase was added, shearing at 3000 rpm continued for 5 minutes to form droplets. Then, 10 ppm of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex (based on the total mass of the organosilicon components in step A1 and calculated as platinum) was added. The reaction was carried out at 55°C for 1 hour, and the gel content, measured by organic solvent extraction, was 22 wt%.

[0122] A4. The reaction system obtained in A3 was subjected to xylene removal at 60℃ and -0.06MPa for 1 h, washed once with 60wt% ethanol aqueous solution (the washing solution volume was 100 parts by weight relative to the microgel solid content, and the washing was carried out by resuspension and centrifugation), and dried at 40℃ and -0.06MPa for 6 h until the difference between two consecutive weighings was no greater than 0.5wt%, thus obtaining the microgel.

[0123] The obtained microgel had a D50 of 1.5 µm, a gel fraction of 22 wt% and a volatile fraction of 1.5 wt% as determined by organic solvent extraction, and a residual Si-H content of 0.12 mmol / g. In step A1, the mass ratio of the divinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer to trimethylsiloxysilicate was 1:0.67.

[0124] Step S2: Preparation of vinyltrimethoxysilane-modified hexagonal boron nitride

[0125] B1, disperse 100 parts by weight of hexagonal boron nitride in a mixed solvent consisting of 600 parts by weight of ethanol and 50 parts by weight of water, and disperse by mechanical stirring for 10 min;

[0126] B2, a 10wt% acetic acid aqueous solution was added dropwise under stirring, and the pH of the system was adjusted to 4.0 by real-time monitoring with a pH meter. Then, 5 parts by mass of vinyltrimethoxysilane were added, and the mixture was refluxed at 65°C in an atmospheric pressure device equipped with a reflux condenser and circulating cooling water for 1 hour (timing started after the reflux state stabilized), with a stirring speed of 200 rpm.

[0127] B3 was filtered and washed twice with ethanol (each washing solution was 100 parts by weight relative to the amount of hexagonal boron nitride fed, and the washing was carried out by resuspension followed by vacuum filtration), and dried at 80℃ and -0.06MPa for 4 hours until the difference between two consecutive weighings was no more than 0.5wt%, thus obtaining vinyltrimethoxysilane modified hexagonal boron nitride.

[0128] The obtained vinyltrimethoxysilane-modified hexagonal boron nitride has a surface grafting amount of 1.5 wt%, a residual free vinyltrimethoxysilane amount of 0.2 wt%, a D50 of 3 µm, a sheet thickness of 250 nm, and a lateral dimension of 6 µm.

[0129] Step S3: Prepare component A

[0130] First, 6 parts by mass of vinyltrimethoxysilane-modified hexagonal boron nitride and 5 parts by mass of vinyl-terminated dimethyl polysiloxane were pre-dispersed for 5 min, and then 18 parts by mass of the microgel prepared above were added. Then, 300 parts by mass of alumina were added in two stages, first the second peak alumina and then the first peak alumina (100 parts by mass of the first peak alumina with a D50 of 1.5 µm and 200 parts by mass of the second peak alumina with a D50 of 32 µm, the mass ratio of the first peak alumina to the second peak alumina was 33:67). Finally, 10 ppm of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex, based on the total mass of the mixture of components A and B and calculated as platinum, was added. The mixing temperature was 20 °C, the mixing speed was 200 rpm, and the mixing time was 10 min to obtain component A.

[0131] Five parts by mass of vinyl-terminated dimethyl polysiloxane pre-dispersed with vinyltrimethoxysilane are included in the total amount of vinyl-terminated dimethyl polysiloxane.

[0132] Step S4: Preparation of Component B

[0133] 85 parts by weight of vinyl-terminated dimethylpolysiloxane, 2.0 parts by weight of trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer, and 0.02 parts by weight of 1-ethynyl-1-cyclohexanol were mixed. The mixing temperature was 20°C, the mixing speed was 200 rpm, and the mixing time was 10 min to obtain component B.

[0134] The total amount of vinyl-terminated dimethyl polysiloxane in components A and B is 100 parts by mass.

[0135] Step S5: Curing and molding

[0136] Component A and component B were mixed at a mass ratio of 1:1.0, degassed under a pressure of -0.06 MPa for 5 minutes, and then molded using liquid silicone rubber injection molding. The mixture was cured at 110°C for 10 minutes to obtain a cured liquid silicone rubber system for thermal pads with a thickness of 0.3 mm. Subsequently, it was post-cured at 80°C for 0.5 hours.

[0137] Based on the composition after mixing components A and B, the molar ratio of reactive Si-H functional groups to reactive vinyl functional groups is 0.85:1 (the reactive vinyl functional groups do not include the vinyl functional groups in the 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex ligand). The mass ratio of MQ / phenyl-enriched pre-crosslinked polysiloxane microgel to vinyltrimethoxysilane-modified hexagonal boron nitride is 3:1.

[0138] Features of Example 3:

[0139] This embodiment employs mild process conditions with process parameters in the low range. In the microgel preparation process, the stirring temperature, stirring time, shear speed, shear time, reaction temperature, reaction time, xylene removal temperature, number of washes, drying temperature, and drying time are all selected at relatively low values. Similarly, in the modified boron nitride preparation process, the pH value, reflux temperature, reflux time, stirring speed, number of washes, drying temperature, and drying time are also selected at relatively low values. The mixing temperature, degassing time, curing temperature, curing time, and post-curing conditions in the curing process are also within the low range. This approach features mild reaction conditions, low energy consumption, and easy process control, making it suitable for applications requiring high process stability and precise control of curing speed in precision electronic component packaging and thin thermal pad manufacturing.

[0140] Example 4

[0141] The liquid silicone rubber system for the thermal pad in this embodiment is prepared according to the following method:

[0142] Step S1: Preparation of MQ / phenyl-enriched pre-crosslinked polysiloxane microgels

[0143] A1, 100 parts by weight of vinyl-terminated dimethylpolysiloxane, 22 parts by weight of vinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer, 15 parts by weight of trimethylsiloxysilicate, and 1.5 parts by weight of trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer were added to 90 parts by weight of xylene and stirred at 500 rpm for 40 min at 35 °C to obtain the oil phase;

[0144] A2, add 2.5 parts by weight of polyvinyl alcohol to 220 parts by weight of water, and stir mechanically at 500 rpm for 90 minutes at 95°C until completely dissolved (the system has no visible particles and the solution is clear and transparent), cool to 40°C to obtain the aqueous phase;

[0145] A3, under nitrogen protection, the oil phase was gradually added to the aqueous phase over 40 minutes, with simultaneous shearing at 8000 rpm during the addition process. After all the oil phase was added, shearing at 8000 rpm continued for 20 minutes to form droplets. Then, 60 ppm of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex (based on the total mass of the organosilicon components in step A1 and calculated as platinum) was added. The reaction was carried out at 75°C for 4 hours, and the gel content, measured by organic solvent extraction, was 28 wt%.

[0146] A4. The reaction system obtained from A3 was subjected to xylene removal at 75℃ and -0.095MPa for 3 hours, washed three times with 90wt% ethanol aqueous solution (each washing solution was 400 parts by weight relative to the microgel solid content, and the washing was performed by resuspension followed by centrifugation), and dried at 60℃ and -0.095MPa for 18 hours until the difference between two consecutive weighings was no greater than 0.5wt%, thus obtaining the microgel.

[0147] The obtained microgel had a D50 of 2.2 µm, a gel fraction of 28 wt% and a volatile content of 1.0 wt%, and a residual Si-H content of 0.15 mmol / g, as determined by organic solvent extraction. In step A1, the mass ratio of the divinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer to trimethylsiloxysilicate was 1:0.68.

[0148] Step S2: Preparation of vinyltrimethoxysilane-modified hexagonal boron nitride

[0149] B1, 100 parts by weight of hexagonal boron nitride are dispersed in a mixed solvent consisting of 800 parts by weight of ethanol and 90 parts by weight of water, and dispersed by mechanical stirring for 40 min;

[0150] B2, 50wt% acetic acid aqueous solution was added dropwise under stirring and the pH of the system was adjusted to 5.5 by real-time monitoring with a pH meter. Then, 8 parts by mass of vinyltrimethoxysilane were added, and the mixture was refluxed at 80°C in an atmospheric pressure device equipped with a reflux condenser and circulating cooling water for 6 hours (timing started after the reflux state stabilized), with a stirring speed of 800 rpm.

[0151] B3 was filtered and washed four times with ethanol (each washing solution was 300 parts by weight relative to the amount of hexagonal boron nitride fed, and the washing was carried out by resuspension followed by vacuum filtration), and dried at 110℃ and -0.095MPa for 12h until the difference between two consecutive weighings was no more than 0.5wt%, thus obtaining vinyltrimethoxysilane modified hexagonal boron nitride.

[0152] The obtained vinyltrimethoxysilane-modified hexagonal boron nitride has a surface grafting amount of 2.5 wt%, a residual free vinyltrimethoxysilane amount of 0.4 wt%, a D50 of 6 µm, a sheet thickness of 400 nm, and a lateral dimension of 12 µm.

[0153] Step S3: Prepare component A

[0154] First, 7 parts by mass of vinyltrimethoxysilane-modified hexagonal boron nitride and 20 parts by mass of vinyl-terminated dimethyl polysiloxane were pre-dispersed for 20 min, and then 22 parts by mass of the microgel prepared above were added. Then, 340 parts by mass of alumina (136 parts by mass of the first peak alumina with a D50 of 2.5 µm and 204 parts by mass of the second peak alumina with a D50 of 38 µm, the mass ratio of the first to the second peak alumina was 40:60) were added in two stages, with the second peak alumina added first and the first peak alumina added later. Finally, 40 ppm of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex (based on the total mass of the mixture of components A and B, calculated as platinum) was added. The mixing temperature was 45 °C, the mixing speed was 1200 rpm, and the mixing time was 40 min to obtain component A.

[0155] The 20 parts by mass of vinyl-terminated dimethyl polysiloxane pre-dispersed with vinyltrimethoxysilane are included in the total amount of vinyl-terminated dimethyl polysiloxane.

[0156] Step S4: Preparation of Component B

[0157] 70 parts by weight of vinyl-terminated dimethylpolysiloxane, 2.5 parts by weight of trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer, and 0.10 parts by weight of 1-ethynyl-1-cyclohexanol were mixed. The mixing temperature was 45°C, the mixing speed was 1200 rpm, and the mixing time was 40 min to obtain component B.

[0158] The total amount of vinyl-terminated dimethyl polysiloxane in components A and B is 100 parts by mass.

[0159] Step S5: Curing and molding

[0160] Component A and component B were mixed at a mass ratio of 1:1.0, degassed under a pressure of -0.095 MPa for 30 min, molded, and cured at 140℃ for 30 min to obtain a cured liquid silicone rubber system for thermal pads with a thickness of 5.0 mm. Subsequently, it was post-cured at 120℃ for 2 h.

[0161] Based on the composition after mixing components A and B, the molar ratio of reactive Si-H functional groups to reactive vinyl functional groups is 1.20:1 (the reactive vinyl functional groups do not include the vinyl functional groups in the 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex ligand). The mass ratio of MQ / phenyl-enriched pre-crosslinked polysiloxane microgel to vinyltrimethoxysilane-modified hexagonal boron nitride is 3.14:1.

[0162] Features of Example 4:

[0163] This embodiment employs enhanced process conditions with process parameters in the high-range of the given range. In the microgel preparation process, the stirring temperature, stirring time, shear speed, shear time, platinum catalyst dosage, reaction temperature, reaction time, xylene removal conditions, washing times, and drying conditions are all selected to be close to the upper end of the range. Similarly, in the modified boron nitride preparation process, the dispersion time, pH value, vinyltrimethoxysilane dosage, reflux temperature, reflux time, stirring speed, washing times, and drying conditions are also selected to be close to the upper end of the range. In the curing process, the pre-dispersion time, mixing temperature, mixing speed, mixing time, degassing time, curing temperature, curing time, and post-curing conditions are also in the high-range of the given range. Simultaneously, the molar ratio of reactive Si-H functional groups to reactive vinyl functional groups, the platinum catalyst dosage, and the inhibitor dosage are all selected to be biased towards the upper end of the range. This scheme features sufficient reaction, high crosslinking density, fast curing speed, and excellent heat resistance, making it suitable for applications in high-temperature working environments, rapid curing production lines, thick thermal pads, and heat dissipation applications in industrial power electronic equipment requiring long-term thermal stability.

[0164] Comparative Example 1: Basically the same as Example 1, except that the vinyltrimethoxysilane modification treatment is no longer performed in step S2, and the 2 parts by mass of vinyltrimethoxysilane-modified hexagonal boron nitride added in step S3 is replaced with 2 parts by mass of hexagonal boron nitride, with other conditions remaining unchanged.

[0165] Comparative Example 2: It is basically the same as Example 1, except that after all the oil phase is added in step S1 A3, it is sheared at 2500 rpm for 3 min to form droplets and reacted at 60°C for 2.0 h. The other conditions in A4 remain unchanged, and MQ / phenyl enriched pre-crosslinked polysiloxane microgel with D50 of 6.0 µm is obtained. In step S3, 8 parts by mass of the microgel are added, and the other conditions remain unchanged.

[0166] Comparative Example 3: Basically the same as Example 1, except that in step S1, after adding 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex in step S3, the reaction was carried out at 75°C for 5.0 h, and the gel fraction measured by organic solvent extraction was 50 wt%. In step S4, the other conditions remained unchanged, and MQ / phenyl enriched pre-crosslinked polysiloxane microgel with a gel fraction of 50 wt% measured by organic solvent extraction was obtained. In step S3, 8 parts by mass of the microgel were added, and the other conditions remained unchanged.

[0167] Comparative Example 4: Basically the same as Example 1, except that 0.2 parts by mass of vinyltrimethoxysilane were added in step S2 B2, and the mixture was refluxed at 70°C for 1.0 h. The other conditions in step B3 remained unchanged, and vinyltrimethoxysilane-modified hexagonal boron nitride with a surface grafting amount of 0.1 wt% was obtained. In step S3, 2 parts by mass of the modified hexagonal boron nitride were added, and the other conditions remained unchanged.

[0168] Comparative Example 5: Basically the same as Example 1, except that 160 parts by mass of alumina were added in step S3, of which 32 parts by mass of alumina were in the first peak and D50 was 0.5µm, and 128 parts by mass of alumina were in the second peak and D50 was 20µm, with other conditions remaining unchanged.

[0169] Comparative Example 6: It is basically the same as Example 1, except that 180 parts by mass of alumina are added in step S3, of which 108 parts by mass of alumina with a D50 of 0.5µm are in the first peak and 72 parts by mass of alumina with a D50 of 20µm are in the second peak, while other conditions remain unchanged.

[0170] Comparative Example 7: Basically the same as Example 1, except that the amount of trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer used in step S4 is changed to 0.65 parts by mass, so that the molar ratio of reactive Si-H functional groups to reactive vinyl functional groups after mixing components A and B is 1.30:1, and other conditions remain unchanged.

[0171] Comparative Example 8: Essentially the same as Example 1, except that MQ / phenyl-enriched pre-crosslinked polysiloxane microgel was not added in step S3, while other conditions remained unchanged. This comparative example was used to verify the synergistic effect of MQ / phenyl-enriched pre-crosslinked polysiloxane microgel and vinyltrimethoxysilane-modified hexagonal boron nitride.

[0172] Comparative Example 9: Essentially the same as Example 1, except that vinyltrimethoxysilane-modified hexagonal boron nitride was not added in step S3, and the 10 parts by mass of vinyl-terminated dimethyl polysiloxane originally used for pre-dispersion was directly incorporated into the base material of component A. Other conditions remained unchanged. This comparative example was used to verify the synergistic effect of MQ / phenyl-enriched pre-crosslinked polysiloxane microgel and vinyltrimethoxysilane-modified hexagonal boron nitride.

[0173] Comparative Example 10: This example is essentially the same as Example 1, except that in step S3, instead of pre-dispersing 2 parts by mass of vinyltrimethoxysilane-modified hexagonal boron nitride and 10 parts by mass of vinyl-terminated dimethyl polysiloxane for 12 min, 2 parts by mass of vinyltrimethoxysilane-modified hexagonal boron nitride, 8 parts by mass of MQ / phenyl-enriched pre-crosslinked polysiloxane microgel, and vinyl-terminated dimethyl polysiloxane from component A are added all at once and mixed for 25 min, with other conditions remaining unchanged. This comparative example is used to verify the synergistic effect of the pre-dispersion interface construction method and the MQ / phenyl-enriched pre-crosslinked polysiloxane microgel compound.

[0174] Performance testing:

[0175] The uncured system within 5 minutes of mixing component A and component B at a 1:0.9 ratio was evaluated for its flowability and processing window under high-filling conditions using a rotational viscometer. The acceleration and deceleration times were recorded at 25°C for 0.5, 1, 5, 10, 20, and 50 seconds. -1 Flow curves were obtained to determine the apparent viscosity and thixotropic recovery at different shear rates. Following ASTM D2196-2010 standards, the temperature was controlled at 25±0.5℃, and the samples were allowed to stand for 5 minutes. The test was repeated three times, and s was extracted. -1 Viscosity, thixotropic index, and recovery rate are key data.

[0176] The cured thermally conductive pads were evaluated for steady-state heat transfer capacity according to ASTM D5470-17. The sample was clamped between two metal test blocks, and the temperature difference between the two sides was measured under constant heat flow conditions to calculate the thermal resistance and apparent thermal conductivity. Tests were conducted at 50 kPa and 100 kPa pressures. The average test temperature was maintained at 25°C, and the sample thickness was measured. Each test was repeated three times. The thermal resistance and apparent thermal conductivity were finally calculated, and the mean ± standard deviation was taken.

[0177] Post-cured thermal pad sheets were pretreated for 24 hours at 23±2℃ and 50±5%RH. Their electrical insulation stability was evaluated according to ASTM D257-14R21E01. The guard electrode method was used to test under a 500V DC electric field for 60 seconds, and the volume resistivity was calculated based on the electrode geometry. The test was repeated three times, and the reported result was 10. 14 On the order of Ω·cm.

[0178] Cylindrical compression specimens prepared by molding with the same formulation were used to evaluate the material's ability to conform to surfaces and handle low interfacial stresses. Compression tests were conducted according to ASTM D575-91R24 at 25°C and a loading rate of 12 mm / min, and the stress-strain relationship at 10%, 20%, and 30% strain was recorded. Each test was repeated five times, and the 30% compressive stress was extracted and the differences between samples were compared.

[0179] The compressive network stability and long-term adhesion reliability of the cured thermally conductive pad were characterized by a compressive stress relaxation test. Following ISO 3384-1:2024 Method A, the sample was compressed to 25% deformation and held at a constant temperature of 100℃ for 24 hours, and the decay process of the reaction force over time was monitored. The test was repeated three times, and the residual compressive stress rate after 24 hours was calculated as the evaluation index.

[0180] Thermally conductive pad assemblies sandwiched between aluminum plates were cycled 200 times between -40℃ and 125℃ according to IEC 60068-2-14:2023, with each temperature end held for 30 minutes, to evaluate the interfacial thermal conductivity retention capability after thermal cycling. The apparent thermal conductivity was remeasured before and after cycling according to ASTM D5470-17 under a clamping pressure of 50 kPa. The test was repeated three times, and the thermal conductivity retention rate after thermal cycling was calculated.

[0181] The post-cured thermal pad sheet was evaluated for low molecular weight migration and volatilization risk according to ASTM E595-15R21 standard. After weighing, the sample was stored at 125±1℃ and below 7×10⁻⁶. -3 The sample was exposed to a vacuum of 24 Pa for 24 h, and the condensed components were collected at 25 °C. The total mass loss (TML) and condensable volatile matter (CVCM) were measured. The test was repeated three times, and TML was used as the characterization value for migration risk.

[0182] Figure 1 The images shown are FTIR overlays of samples from Example 1, Comparative Example 1, and Comparative Example 10. Fourier transform infrared spectroscopy was used to characterize the functional group structures of different samples, with a wavenumber range of 650–4000 cm⁻¹. Figure 1 As can be seen, Example 1 at 1366 cm -1 1087 cm -1 1032 cm -1 and 818 cm -1 The more coordinated absorption response observed in the characteristic range indicates a more stable synergistic relationship among the filler skeleton, silicon-oxygen segments, and interface-related structures in the system, demonstrating that Example 1 possesses good structural rationality in its basic composition design. Based on this, Figure 2 These are high-resolution B1s XPS images of samples from Example 1, Comparative Example 1, and Comparative Example 9. Figure 3 The XPS high-resolution N1s spectra of samples from Example 1, Comparative Example 1, and Comparative Example 9 are shown. X-ray photoelectron spectroscopy was used to analyze the chemical environment of B and N elements, with the B1s binding energy ranging from 186–195 eV and the N1s binding energy ranging from 394–402 eV. Example 1 showed a more concentrated main peak position and clearer peak shape in both the B1s and N1s regions, indicating a more homogeneous local chemical environment in which the boron and nitrogen-related structures are located, reflecting effective regulation of the filler surface state and interfacial interactions. This result is consistent with... Figure 1 The infrared characteristics corroborate each other, indicating that the difference in Example 1 is not only at the component level, but also forms a more stable structural basis at the molecular and interface levels.

[0183] Figure 4 These are high-resolution XPS Si2p images of samples from Example 1, Comparative Example 1, and Comparative Example 9. Figure 5 The XPS Si2p peak fitting diagram of the sample in Example 1 is shown to further verify the internal network construction of the sample from the perspective of silicon chemical state and silicon-oxygen structure composition. Figure 4 The Si2p binding energy range is 98.4–105 eV. Example 1 shows a more complete and continuous characteristic peak shape in the 101–103 eV range, indicating that its silicon-oxygen network and related interface structure are more fully formed. Figure 5 Further, it is shown that the original Si2p spectrum of Example 1 matches well with the overall fitted curve, and the peak distributions of Si-C or PDMS, Si-O-Si, and interface-related silicon-oxygen bonds are relatively clear, indicating that the material not only contains relatively complete flexible organosilicon segments, but also forms a stable silicon-oxygen connection structure and interface transition structure. Figures 2 to 5 A continuous chain of evidence can be formed, namely, Example 1 shows better synergy and uniformity in the interfacial chemical environment corresponding to key elements such as B, N, and Si, proving that the scheme can effectively construct a stable organic-inorganic composite interface, which is also an important reason why the subsequent flow, thermal conductivity and reliability performance is better than the comparative example.

[0184] After the structure and interface are validated Figure 6 The rheological flow curves of the uncured systems in Examples 1, 5, and 6 are shown below. Rheological testing was used to evaluate the flow rates of the uncured systems in the range of 0.5–50 s. -1 Viscosity variation within the shear rate range. The apparent viscosity of Example 1 at 1 s^-1 is approximately 185 Pa·s, exhibiting moderate shear thinning characteristics. This avoids both the construction difficulties caused by excessively high viscosity and the insufficient system stability caused by excessively low viscosity, indicating that it has more suitable flow characteristics in actual processing and coating / pressing. Figure 7 The thermal resistance-pressure curves of the cured thermally conductive pads for Examples 1, 5, and 6 are shown. The interfacial heat transfer performance within a pressure range of 25–200 kPa was evaluated using the ASTM D5470 method. The thermal resistance of Example 1 continuously decreases with increasing pressure, reaching a low level near 100 kPa, indicating that it can more effectively fill microscopic contact gaps and establish a continuous heat transfer path under pressure. Combined with… Figure 6 It can be seen that the relatively moderate rheological behavior in Example 1 provides conditions for interface spreading and compaction, while Figure 7 The relatively low thermal resistance directly demonstrates that the advantages of this structure and flow have been translated into effective heat transfer performance, thus proving that the solution has clear effectiveness in practical applications.

[0185] Furthermore, Figure 8The figures show the compressive stress relaxation curves of the cured thermal conductive pads in Examples 1, 7, and 8. The compressive stress relaxation test was used to evaluate the retention of residual reaction force under continuous compression conditions from 0.05 to 24 hours. Example 1 retained approximately 61.2% of its residual reaction force after 24 hours, and the attenuation trend was significantly slower than that of the comparative sample, indicating that its network structure can maintain good elastic recovery and support capacity under long-term compression conditions. Figure 9 The graph shows the thermal conductivity retention rate of the cured thermally conductive pads after thermal cycling for Examples 1, 8, and 10. The number of cycles ranged from 0 to 200. After 200 cycles, Example 1 still had a thermal conductivity retention rate of approximately 95.6%, which was significantly better than the comparative sample. This indicates that it can still maintain the internal heat transfer network and interface connection state well in alternating hot and cold environments. Figure 10 The original TML (Total Mass Loss) scatter plots with mean ± SD of the post-cured thermally conductive pad sheets from Examples 1, 8, and 10 are shown. The total mass loss test was used to evaluate the volatile and weight loss behavior of the post-cured thermally conductive pad sheets. The mean TML of Example 1 was approximately 0.46%, and the parallel sample dispersion was small, indicating that it had fewer volatile components and a more stable system composition. Figures 8 to 10 This allows for a closed-loop verification of the effectiveness of the solution. Specifically, Example 1 not only has superior initial structure and interface characteristics, but also good compressive stability, thermal cycling stability, and low volatility stability. This demonstrates that the solution can simultaneously achieve interface bonding, heat transfer efficiency, and long-term service reliability. The overall technical route has good internal consistency and practical feasibility.

[0186] Figure 11 This is a macroscopic optical photograph of the cured liquid silicone rubber system for thermal pads prepared in Example 1. The sample is a grayish-white opaque sheet with a smooth surface free of cracks or warping. The slight matte texture is due to the surface micro-roughness caused by the high filler volume fraction and the light scattering effect of the ceramic filler. This proves that the calendering process combined with vacuum degassing and segmented curing conditions effectively suppressed residual bubbles and curing shrinkage deformation, achieving large-area uniform molding.

[0187] Figure 12 This is a scanning electron microscope image of the liquid silicone rubber composite material used in the thermal pad of Example 1. Figure 12 (a) The low-magnification image shows that the bimodal alumina filler is highly densely packed in the matrix. The alumina particles of the second peak form the skeleton, while the alumina particles of the first peak fill the gaps. This reveals that the vinyltrimethoxysilane-modified hexagonal boron nitride exhibits white, bright lamellar characteristics with clear edges and an intact layered structure. Figure 12(b) High-magnification observation shows that the silicone rubber matrix is ​​tightly wrapped in a continuous thin layer between the fillers, and there is no debonding phenomenon at the interface. This proves that the bimodal particle size design achieves tight packing, the surface-modified hexagonal boron nitride maintains the intrinsic morphology while enhancing the wettability of the matrix, and the synergistic compatibilizing effect of MQ / phenyl enriched pre-crosslinked polysiloxane microgel at the interface promotes the chemical bonding and three-dimensional network coating of the filler-matrix.

[0188] Table 1 Performance of Examples and Comparative Examples

[0189]

[0190] As can be seen from the performance of the embodiments and comparative examples in Table 1, the embodiment systems, while maintaining a volume resistivity in the range of 10^14 Ω·cm, achieved higher apparent thermal conductivity, higher thermal conductivity retention after thermal cycling, and lower TML. Among them, Embodiments 2 and 4 showed the most significant advantages in thermal conductivity and reliability under high-filling and strengthening process conditions, while Embodiments 1 and 3 demonstrated process friendliness due to lower compressive stress or lower mixing viscosity. In contrast, unmodified hexagonal boron nitride, microgel particle size or gel fraction imbalance, bimodal alumina gradation imbalance, high Si-H / vinyl ratio, and absence of synergistic units or destruction of the pre-dispersion interface all resulted in decreased thermal conductivity, decreased thermal cycling retention, and increased TML. This indicates that the performance of the present invention stems from the combined effect of interface anchoring, hierarchical filling, and network constraint balance, rather than a simple change in a single variable.

[0191] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A liquid silicone rubber system for thermally conductive pads, characterized in that, The composition comprises, by weight, 100 parts vinyl-terminated dimethyl polysiloxane, 8-35 parts MQ / phenyl-enriched pre-crosslinked polysiloxane microgel, 2-12 parts vinyltrimethoxysilane-modified hexagonal boron nitride, 180-450 parts alumina, 0.5-6 parts trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer, 2-80 ppm of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex based on the total mass of the composition and in terms of platinum element, and 0.01-0.20 parts 1-ethynyl-1-cyclohexanol.

2. The liquid silicone rubber system for thermal pads as described in claim 1, characterized in that, The MQ / phenyl enriched pre-crosslinked polysiloxane microgel is prepared by pre-reaction of vinyl-terminated dimethylpolysiloxane, divinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer, trimethylsiloxysilicate, and trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer; the vinyltrimethoxysilane-modified hexagonal boron nitride is prepared by reacting hexagonal boron nitride with vinyltrimethoxysilane; the D50 of the microgel is 0.5-5.0µm, and the gel fraction measured by organic solvent extraction is 10-45wt%; the surface grafting amount of the vinyltrimethoxysilane-modified hexagonal boron nitride is 0.3-5.0wt%; the alumina exhibits a bimodal particle size distribution, including a first peak alumina and a second peak alumina, the D50 of the first peak alumina is 0.3-5µm, and the D50 of the second peak alumina is 10-60µm.

3. The liquid silicone rubber system for thermal pads as described in claim 1, characterized in that, The MQ / phenyl-enriched pre-crosslinked polysiloxane microgel was prepared by the following method: A1. 100 parts by weight of vinyl-terminated dimethylpolysiloxane, 8-30 parts by weight of vinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer, 5-25 parts by weight of trimethylsiloxysilicate, and 0.4-2.5 parts by weight of trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer are added to 40-120 parts by weight of xylene and stirred at 25-35°C for 10-40 min to obtain the oil phase. A2, add 0.5-4.0 parts by weight of polyvinyl alcohol to 100-300 parts by weight of water, stir at 80-95℃ for 30-90 minutes until completely dissolved, cool to 25-40℃ to obtain the aqueous phase; A3, under nitrogen protection, the oil phase is added to the aqueous phase. After all the oil phase has been added, the mixture is sheared at 3000-8000 rpm for 5-20 min to form droplets. Then, 10-60 ppm of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex (based on the total mass of the organosilicon components in step A1 and calculated as platinum) is added. The mixture is reacted at 55-75°C for 1-4 h, and the gel content, as measured by organic solvent extraction, is 10-45 wt%. A4. The reaction system obtained in A3 is subjected to xylene removal at 60-75℃ and -0.06 to -0.095 MPa, washed 1-3 times with 60-90wt% ethanol aqueous solution, and dried at 40-60℃ and -0.06 to -0.095 MPa for 6-18 h until the difference between two consecutive weighings is no greater than 0.5wt%, to obtain the microgel.

4. The liquid silicone rubber system for thermal pads as described in claim 3, characterized in that, The microgel meets the following requirements: D50 is 0.8-3.0µm; gel content measured by organic solvent extraction is 15-35wt%; volatile matter is not higher than 2.0wt%; residual Si-H content is 0.01-0.20mmol / g; and in step A1, the mass ratio of the divinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer to the trimethylsiloxysilicate is 0.32:1 to 2:

1.

5. The liquid silicone rubber system for thermal pads as described in claim 1, characterized in that, The vinyltrimethoxysilane-modified hexagonal boron nitride was prepared by the following method: B1, dispersing 100 parts by weight of hexagonal boron nitride in a mixed solvent consisting of 300-1000 parts by weight of ethanol and 10-120 parts by weight of water; B2, after adjusting the pH of the system to 4.0-5.5 with acetic acid, add 1-10 parts by weight of vinyltrimethoxysilane, reflux at 65-80℃ for 1-6 hours, and stir at 200-800 rpm; B3 was filtered, washed 2-4 times with ethanol, and dried at 80-110℃ and -0.06 to -0.095 MPa for 4-12 hours until the difference between two consecutive weighings was no more than 0.5 wt%, to obtain the vinyltrimethoxysilane modified hexagonal boron nitride.

6. The liquid silicone rubber system for thermal pads as described in claim 1, characterized in that, The vinyltrimethoxysilane-modified hexagonal boron nitride meets the following requirements: surface grafting amount is 0.5-3.0 wt%; residual free vinyltrimethoxysilane is not higher than 0.5 wt%; D50 is 0.5-8 µm; sheet thickness is 80-500 nm; lateral dimension is 0.5-15 µm; and the mass ratio of the MQ / phenyl enriched pre-crosslinked polysiloxane microgel to the vinyltrimethoxysilane-modified hexagonal boron nitride is 1.5:1 to 6:

1.

7. The liquid silicone rubber system for thermal pads as described in claim 1, characterized in that, The amount of the MQ / phenyl enriched pre-crosslinked polysiloxane microgel is 10-25 parts by mass, the amount of the vinyltrimethoxysilane modified hexagonal boron nitride is 3-8 parts by mass, the amount of alumina is 220-380 parts by mass, and the amount of the trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer is 0.8-3.0 parts by mass; the mass ratio of the first peak alumina to the second peak alumina is 20:80 to 50:50; the D50 of the first peak alumina is 0.5-3µm; and the D50 of the second peak alumina is 20-45µm.

8. The liquid silicone rubber system for thermal pads as described in claim 1, characterized in that, Based on the composition after mixing components A and B, the molar ratio of reactive Si-H functional groups to reactive vinyl functional groups is 0.85:1 to 1.20:1; the amount of the 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex added is 10-40 ppm based on the total mass of the composition after mixing components A and B, expressed as platinum; the amount of 1-ethynyl-1-cyclohexanol added is 0.02-0.10 parts by mass; the composition adopts a dual-phase reaction of components A and B. The product is packaged in the following manner: Component A comprises vinyl-terminated dimethyl polysiloxane, the microgel, the vinyltrimethoxysilane-modified hexagonal boron nitride, the alumina, and the 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex; Component B comprises vinyl-terminated dimethyl polysiloxane, the trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer, and the 1-ethynyl-1-cyclohexanol; the mass ratio of Component A to Component B is 1:0.9 to 1:1.

1.

9. A method for preparing a liquid silicone rubber system for thermal pads as described in any one of claims 1-8, characterized in that, Includes the following steps: S1 provides the prepared MQ / phenyl-enriched pre-crosslinked polysiloxane microgel; S2 provides a prepared vinyltrimethoxysilane-modified hexagonal boron nitride; S3, vinyl-terminated dimethyl polysiloxane, the microgel, the vinyltrimethoxysilane-modified hexagonal boron nitride, the alumina, and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane zero-valent platinum complex are mixed to obtain component A; S4, vinyl-terminated dimethylpolysiloxane, Trimethylsilane-terminated dimethylsiloxane-methylhydrosiloxane copolymer and 1-ethynyl-1-cyclohexanol were mixed to obtain component B; S5, mix component A and component B at a mass ratio of 1:0.9 to 1:1.1, degas, mold, and cure at 110-140℃ for 10-30 min to obtain the cured liquid silicone rubber system for the thermal pad.

10. The method as described in claim 9, characterized in that, In step S3, the vinyltrimethoxysilane-modified hexagonal boron nitride is first pre-dispersed with 5-20 parts by weight of vinyl-terminated dimethyl polysiloxane for 5-20 min, and then the microgel is added; in step S3, the alumina is added in two stages in the order of adding the second peak alumina first and the first peak alumina last; the mixing temperature in steps S3 and S4 is 20-45℃, the mixing speed is 200-1200 rpm, and the mixing time is 10-40 min; the degassing pressure in step S5 is -0.06 to -0.095 MPa, and the degassing time is 5-30 min; The molding method in step S5 is one of calendering, compression molding, or liquid silicone rubber injection molding; the curing conditions in step S5 are 120-135℃ for 10-25 min; the thickness of the resulting thermal pad is 0.3-5.0 mm; after step S5, there is also a post-curing step of holding at 80-120℃ for 0.5-2 h.

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