High-dielectric low-loss millimeter wave composite material and preparation method and application thereof

Abstract

The invention relates to the technical field of composite materials, and provides a high-dielectric and low-loss millimeter wave composite material and a preparation method and application thereof. The composite material comprises a polymer matrix and a functional filler dispersed in the polymer matrix, the functionalized filler comprises a core layer formed by an inorganic filler and N shell layers sequentially coating the surface of the inorganic filler, and N is greater than or equal to 2 and less than or equal to 4; the N shell layers are mesoporous silicon dioxide layers; the porosity of the mesoporous silica of the N shell layers is sequentially increased from the core layer to the outside, the porosity of the mesoporous silica of the innermost shell layer is larger than or equal to 5%, and the porosity of the mesoporous silica of the outermost shell layer is smaller than or equal to 40%; and the pore diameters of the mesoporous silica of the N shell layers are 10-30 nm. The composite material can meet the requirements of high dielectric constant and low dielectric loss at the same time, and can meet the requirements of current millimeter wave communication materials.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, specifically to a high-dielectric, low-loss millimeter-wave composite material, its preparation method, and its applications. Background Technology

[0002] With the rapid development of communication technology, the millimeter wave band (30-300 GHz) has a wide range of application prospects in fields such as 5G / 6G, autonomous driving and ultra-high-definition video transmission due to its significant advantages such as extremely wide bandwidth, narrow beamwidth and miniaturization.

[0003] Polymer dielectric materials, as the core of waveguides, transmission lines, high-frequency circuit boards, radomes, and packaging materials, must simultaneously meet the requirements of high dielectric constant (Dk) and low dielectric loss (Df). A high dielectric constant facilitates the miniaturization of communication devices, enabling the integration of more functional modules within a limited space, thus meeting the modern trend towards miniaturization and lightweighting of communication equipment. Conversely, a low loss tangent is a necessary prerequisite for achieving low-loss communication transmission, effectively reducing energy loss during signal transmission, ensuring stable signal transmission, and improving communication quality.

[0004] Polymer materials inherently have low dielectric constants. Currently, the industry primarily employs doping the polymer matrix with inorganic fillers of high dielectric constants to improve the overall dielectric constant of the composite material. However, in practice, using high dielectric constant inorganic fillers leads to significant interfacial impedance mismatch due to the large difference in dielectric constant between the filler and the polymer matrix. This results in severe interfacial electric field coupling concentration between the fillers, and the loss tangent remains higher than industry expectations, failing to meet the industry's demands for miniaturized and low-loss high-frequency communication devices. While using lower dielectric constant inorganic fillers, although the difference in dielectric constant is not significant, achieving impedance matching and thus reducing electric field coupling and maintaining low loss, these fillers cannot effectively improve the dielectric constant of the composite material, resulting in high filler doping levels and low efficiency.

[0005] Many existing technologies focus on resolving the contradiction between high dielectric constant and low loss in polymer dielectric materials. For example, Chinese patent CN111057311A discloses a thermoplastic vulcanizate-based composite material with high dielectric constant and low dielectric loss, and its preparation method. This composite material is composed of thermoplastic vulcanizate and conductive filler. The microstructure of this composite material is a sea-island structure, with the plastic phase of thermoplastic vulcanizate as the matrix and the rubber particles of thermoplastic vulcanizate as the dispersed phase. The conductive filler is selectively dispersed in the plastic phase, constructing a "filler-thermoplastic plastic-filler" microcapacitor structure in the thermoplastic vulcanizate. The presence of the rubber dispersed phase inhibits the construction of the conductive network. The formation of the microcapacitor structure in the plastic matrix of the thermoplastic vulcanizate further improves the dielectric properties of the thermoplastic vulcanizate while maintaining its low dielectric loss performance. At the same time, the dielectric constant can be increased by controlling the content of conductive filler, while maintaining the dielectric loss at a low level and also having good resilience.

[0006] For example, Chinese patent CN119286139A discloses a high-dielectric, low-loss composite material and its preparation method in the terahertz band. This method utilizes multi-sized, multi-component high-dielectric-constant inorganic fillers to significantly improve the dielectric constant. Smaller insulating materials separate the high-dielectric-constant material particles, thereby blocking electric field coupling and simultaneously solving the electric field coupling problem caused by multi-component inorganic fillers in existing technologies. Furthermore, by separately modifying the high-dielectric-constant inorganic fillers and insulating materials of different sizes, the modified high-dielectric-constant inorganic fillers repel each other, achieving a dispersion effect and improving the blocking of electric field coupling. Simultaneously, the modified insulating materials bring the modified high-dielectric-constant inorganic fillers closer together at intervals. Compared to existing technologies, this method not only increases the amount of high-dielectric-constant inorganic filler used to achieve a higher dielectric constant but also avoids agglomeration and maintains an extremely low loss tangent, thus meeting the application requirements of miniaturized and low-loss high-frequency communication devices in this field.

[0007] The aforementioned existing technologies offer technical solutions for preparing high-dielectric, low-loss composite materials from different perspectives. Their core principle is to use insulating materials to block the electric field coupling between inorganic fillers. This approach undoubtedly increases the amount of added components in the polymer matrix and places extremely high demands on the directional dispersion of the insulating material, making it difficult to implement. Furthermore, these existing technologies suffer from complex production processes, complex raw material compositions, and difficulties in controlling the production process. Significant research potential remains for the industrial-scale preparation of high-dielectric, low-loss polymer dielectric materials.

[0008] In addition, existing technologies, such as the core-double-shell nanofiller BaTiO3@TiO2@SiO2 disclosed by Wang Fan in "Design, Preparation and Energy Storage Characteristics of BaTiO3@SiO2 Filler and PVDF-based Nanocomposite Materials" (Central South University, 2023), utilize a core-double-shell nanofiller. This filler sequentially coats the surface of BaTiO3 with TiO2 and SiO2 layers, relying on the intermediate TiO2 layer with a moderate dielectric constant as a buffer layer. This creates a gradient of decreasing dielectric constant from the inside out, effectively mitigating interfacial incompatibility and local electric field concentration caused by dielectric mismatch, and significantly reducing leakage current density and dielectric loss. However, while this approach alleviates interfacial incompatibility and local electric field concentration to some extent, largely resolving the contradiction between high dielectric constant and low loss in energy storage materials, the requirements for loss are much more stringent in millimeter-wave communication materials. Therefore, this approach still cannot meet the demand for high dielectric constant and low loss in this field.

[0009] In conclusion, developing a polymer dielectric material that meets the requirements of high dielectric constant and low dielectric loss in the field of millimeter-wave communication materials remains a key technical problem that urgently needs to be solved in the current field of millimeter-wave communication materials. Summary of the Invention

[0010] The primary objective of this invention is to provide a millimeter-wave composite material that can meet the requirements of high dielectric constant and low dielectric loss in the field of millimeter-wave communication.

[0011] Another objective of this invention is to provide a method for preparing the above-mentioned high dielectric and low loss millimeter-wave composite material, so as to achieve the preparation of the above-mentioned material, and the preparation process is mature and controllable.

[0012] A third objective of this invention is to provide applications of the aforementioned high-dielectric, low-loss millimeter-wave composite material.

[0013] To achieve the above objectives, the present invention provides the following technical solution: A high-dielectric, low-loss millimeter-wave composite material includes a polymer matrix and functionalized fillers dispersed in the polymer matrix; the functionalized fillers include a core layer formed by inorganic fillers and N shell layers sequentially covering the surface of the inorganic fillers, where 2≤N≤4; all N shell layers are mesoporous silica layers; the porosity of the mesoporous silica in the N shell layers increases sequentially from the core layer outwards, and the porosity of the mesoporous silica in the innermost shell layer is ≥5%, while the porosity of the mesoporous silica in the outermost shell layer is ≤40%; the pore size of the mesoporous silica in the N shell layers is 10nm~30nm.

[0014] It should be noted that, based on the existing technology, in order to further alleviate the electric field mismatch, those skilled in the art may use more layers of coating to achieve more and more stable dielectric constants. However, this approach will undoubtedly make the preparation method more complex and the size of the entire functionalized filler will be larger. The larger size will inevitably cause more cross-sectional loss, making it difficult to meet the requirements of extremely low loss under millimeter wave conditions.

[0015] This invention achieves high dielectric constant and extremely low loss under millimeter-wave conditions by constructing a functionalized filler structure consisting of a core layer and an N-layer mesoporous silica shell.

[0016] First, the shell layer of the present invention is a multilayer shell layer prepared by mesoporous silica, and the porosity of the mesoporous silica layer increases sequentially from the inside to the outside. The larger the porosity of the mesoporous silica, the smaller its dielectric constant. Therefore, a smooth transition layer with a dielectric constant decreasing sequentially from the core layer to the surface layer is formed, which alleviates the phenomenon of interface incompatibility and local electric field concentration caused by dielectric mismatch.

[0017] Compared to existing technologies that use different materials as coating layers to achieve a transition layer with decreasing dielectric constant by selecting different materials with different dielectric constants, the transition layer formed by the same material in this invention is smoother; and there is no loss caused by cross-sectional defects due to poor compatibility of heterogeneous interfaces.

[0018] More importantly, in general, high-dielectric millimeter-wave dielectric waveguide materials have fillers dispersed within the matrix, easily forming conductive paths between them. Under the influence of electromagnetic waves, if continuous conductive paths exist within the material, electrons will move under the drive of the electric field, generating induced currents and inducing dipole relaxation losses. This invention designs mesoporous silica as a shell. The numerous pores on the shell surface divide the composite material skeleton into fragmented "insulating islands," no longer a dense continuum, thus disrupting electron migration paths. Consequently, charges cannot form long-range movements and are confined to localized polarization vibrations. Electrons cannot easily cross the pores, and the current is blocked, which effectively increases the difficulty of current formation (increasing the percolation threshold), making it more difficult for electromagnetic energy to dissipate through conductive loss paths.

[0019] The design of the multilayer mesoporous silica coating layer increases the effective penetration path of the electric field by utilizing the multilayer mesoporous structure, so that the local field energy is redistributed in multiple directions in the coating layer, rather than being concentrated and coupled to the filler core, thereby achieving extremely low electric field coupling between the filler cores.

[0020] In summary, this invention achieves electric field buffering and continuous transition from high-dielectric filler to low-dielectric matrix, while using only 2 to 4 layers of coating to achieve low current loss, providing an engineerable solution for constructing high-dielectric, low-loss polymer composite materials.

[0021] Preferably, the number of shell layers N=2 in this invention, with the first shell layer and the second shell layer arranged sequentially from the core layer outwards. The porosity of the mesoporous silica in the first shell layer is 5%~10%, and the porosity of the mesoporous silica in the second shell layer is 30%~40%.

[0022] Preferably, the number of shell layers N=3 in this invention, and the shell layers are arranged sequentially from the core layer outwards as a first shell layer, a second shell layer, and a third shell layer. The porosity of the mesoporous silica in the first shell layer is 5%~10%, the porosity of the mesoporous silica in the second shell layer is 15%~25%, and the porosity of the mesoporous silica in the third shell layer is 30%~40%.

[0023] Preferably, the number of shell layers N=4 in this invention, and the shell layers are arranged sequentially from the core layer outwards as a first shell layer, a second shell layer, a third shell layer, and a fourth shell layer. The porosity of the mesoporous silica in the first shell layer is 5%~10%, the porosity of the mesoporous silica in the second shell layer is 10%~20%, the porosity of the mesoporous silica in the third shell layer is 20%~30%, and the porosity of the mesoporous silica in the fourth shell layer is 30%~40%.

[0024] By controlling the change in mesoporous porosity gradient between multiple shell layers, the aim is to achieve a smooth transition between multiple layers and to create multiple electric field penetration paths.

[0025] Preferably, the functionalized filler further includes surface functional groups, and the surface of the inorganic filler after being sequentially coated with N shell layers is functionalized with a silane coupling agent to obtain the functionalized filler.

[0026] To ensure that the prepared functionalized filler is well dispersed in the polymer matrix, this invention modifies it with a silane coupling agent. The modification increases the oleophilicity and polarity of the functionalized filler surface, reduces the van der Waals forces between the functionalized fillers, thereby reducing the agglomeration of the functionalized filler and improving the dispersion stability of the functionalized filler in the matrix.

[0027] In addition, the shell layers of the present invention are all made of mesoporous silica layers, and the porosity of the surface mesoporous silica layer is the largest. The presence of surface mesopores can provide more attachment sites for silane coupling agents, which makes the dispersion of the entire functionalized filler in the polymer matrix better. This overcomes the problems of incompatibility between inorganic fillers and polymer matrix interfaces and the easy formation of pore defects at the interface between inorganic fillers and polymer matrix, thereby improving the dielectric properties of the overall composite material.

[0028] More preferably, the silane coupling agent of the present invention is selected from 3-(2-aminoethylamino)-propyltriethoxysilane (AEAPTMS) or γ-aminopropyltriethoxysilane (APTES).

[0029] Preferably, the inorganic filler of the present invention is selected from one or more of barium titanate, strontium titanate, and titanium dioxide. More preferably, the inorganic filler of the present invention is selected from barium titanate or strontium titanate.

[0030] Since this invention aims to construct a high-dielectric, low-loss millimeter-wave composite material, and the concept of achieving electric field reflection through the multilayer mesoporous silica layer of this invention can effectively solve the problem of electric field coupling between fillers when high-dielectric-constant fillers are in a low-dielectric-constant matrix, this invention chooses to add barium titanate (Dk=1000) or strontium titanate (Dk=200) fillers with extremely high dielectric constants to the polymer matrix in order to effectively improve the dielectric constant of the overall composite material.

[0031] Preferably, the inorganic filler of the present invention has a particle size of 8~12μm; the thickness of the N-layer shell is 0.2~0.5μm.

[0032] If the particle size of the inorganic filler is too small, it is easy to agglomerate when dispersed in the polymer matrix. If the particle size is too large, pore defects are easily generated between the interface and the polymer matrix. The coating thickness of the shell needs to ensure that it can play a corresponding role in multilayer electric field reflection, and on the other hand, it needs to occupy as small a proportion of the entire functionalized filler as possible to avoid weakening the dielectric constant of the overall material.

[0033] Preferably, the volume ratio of the functionalized filler to the polymer matrix of the present invention satisfies: 2:3 to 1.2:1.

[0034] The functionalized filler structure design of this invention can still significantly improve dielectric properties without increasing the amount of functionalized filler, thereby ensuring that its dielectric properties, loss characteristics, and mechanical properties all meet the requirements for use.

[0035] The polymer matrix of the present invention can be any non-polar thermoplastic polymer, such as polypropylene, polyethylene or polytetrafluoroethylene, etc.

[0036] This invention also provides a method for preparing the above-mentioned high-dielectric, low-loss millimeter-wave composite material, comprising the following steps: S1 sequentially coating the surface of the inorganic filler with N layers of the shell to obtain the functionalized filler; the shell is obtained by sequentially coating the surface of the inorganic filler with silica sol containing a template agent using a template method; and by adjusting the ratio of the template agent to the silica sol and the coating reaction time, mesoporous silica with different porosities is prepared; S2 dispersing the functionalized filler in the polymer matrix to prepare the composite material.

[0037] As a preferred option: In step S1: the shell layer is obtained by sequentially coating the surface of the inorganic filler with silica sol containing a template agent using a template method; and mesoporous silica with different porosities is prepared by adjusting the ratio of the template agent to the silica sol and the coating reaction time; wherein the silica sol is selected from tetraethyl orthosilicate, tetraethoxysilane or sodium silicate as the silica source, and the template agent is selected from hexadecyltrimethylammonium bromide, polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer or polyvinylpyrrolidone.

[0038] Further optimization: The specific preparation method for step S1 is as follows: Preparation of mesoporous silica sols with different porosities: Tetraethyl orthosilicate (TEOS), tetraethoxysilane (TESO), or sodium silicate (Na2SiO3) are dissolved in an appropriate amount of ethanol solvent. An appropriate amount of water and an acidic catalyst (hydrochloric acid, adjusted to pH 4-5) are added, and the mixture is stirred at room temperature for 2 hours to form a silica sol. Then, different amounts of template agents (hexadecyltrimethylammonium bromide, CTAB; or polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer, P123; or polyvinylpyrrolidone, PVP) are added. An appropriate amount of deionized water is added and the pH is adjusted to alkaline (9-10). The mixture is stirred at room temperature to form mesoporous silica sols with different porosities.

[0039] Preparation of functionalized fillers: Inorganic fillers are added to a mesoporous silica sol with a first porosity, and the mixture is stirred for a certain time. By adjusting the concentration of the silica sol and the stirring time, a mesoporous SiO2 layer is deposited on the outside of the inorganic filler, forming a mesoporous SiO2 layer with a set porosity and a thickness of 0.2~0.5 μm. The layer is then calcined in air (550℃, 2h) to remove the template agent, forming a first coating material with a first shell layer of mesoporous SiO2. The first coating material is added to a mesoporous silica sol with a second porosity, and the mixture is reacted for a certain time. By adjusting the concentration of the silica sol and the stirring time, a mesoporous SiO2 layer is deposited on the outside of the first coating material, forming a mesoporous SiO2 layer with a thickness of 0.2~0.5 μm. The layer is then calcined in air (550℃, 2h) to remove the template agent, forming a second coating material with a second shell layer of mesoporous SiO2. The third and fourth shells are formed sequentially by the above method.

[0040] As a preferred option: In step S2, the functionalized filler of the present invention is dispersed in the polymer matrix by mechanical blending.

[0041] Further preferably, in step S2, the specific method for dispersing the functionalized filler in the polymer matrix is ​​as follows (taking polypropylene matrix as an example): Weigh polypropylene masterbatch, and weigh the corresponding amount of functionalized filler according to the volume ratio of functionalized filler to polypropylene of 2:3 to 1.2:1; mechanically blend the polypropylene masterbatch and functionalized filler at a speed of 300 rpm for 5 minutes each time, in 3 batches; add the mixed raw material to a twin-screw extruder, with a twin-screw processing temperature of 220°C and a screw speed of 300 rpm; extrude the blended composite melt, water-cool and pelletize it, and dry the granulated composite masterbatch in a vacuum drying oven for 6 hours at a drying temperature of 80°C to obtain the high dielectric and low loss millimeter-wave composite material of the present invention.

[0042] Preferably, in some technical solutions, the functionalized filler also includes surface functional groups. It is necessary to coat the surface of the inorganic filler with N layers of mesoporous silica in sequence before treating it with a silane coupling agent. In this case, the inorganic filler with N shell layers prepared in step S1 is dispersed in a solution prepared with a silane coupling agent and stirred and soaked, and then dried to obtain the functionalized filler.

[0043] The specific method for further functionalizing the surface is as follows: The silane coupling agent was dissolved in toluene to form a 5 vol% solution; the second coating material was added to the solution, and the mixture was stirred at room temperature for 4 hours to functionalize its surface; subsequently, it was dried in a vacuum oven at 100°C for 6 hours to obtain the functionalized filler. Preferably, the silane coupling agent is γ-aminopropyltriethoxysilane (APTES) or 3-(2-aminoethylamino)propyltriethoxysilane (AEAPTMS).

[0044] This invention also provides applications of the aforementioned high-dielectric, low-loss millimeter-wave composite material in communication devices operating in the millimeter-wave band. Specifically, it can be used as at least one of waveguides, transmission lines, high-frequency circuit boards, radomes, or encapsulation materials.

[0045] Compared with the prior art, the present invention has the following advantages: (1) The high dielectric and low loss millimeter wave composite material provided by the present invention is to coat high dielectric inorganic filler with multilayer mesoporous silica layers with decreasing dielectric constant. By utilizing the presence of the porous silica, the functional filler formed is coated with only 2 to 4 layers, which fully disperses the electric field. Finally, after the addition of polymer matrix, the interfacial polarization effect is significantly suppressed, the dielectric loss of composite material is significantly reduced, and thus extremely low loss tangent (Dk>9, Df<0.0007 @150GHz) is achieved.

[0046] (2) The high dielectric and low loss millimeter wave composite material provided by the present invention introduces functional groups on the surface of functional fillers through silane coupling agents, so that the functional fillers can be more uniformly and stably dispersed in the polymer matrix, reducing the formation of agglomerate structures in the composite material, effectively avoiding the problem of unstable composite material performance caused by uneven filler dispersion, improving the uniformity and stability of the composite material, which is beneficial to the high dielectric and low loss dielectric performance in the millimeter wave band; and the presence of surface functional groups strengthens the interfacial compatibility between functional fillers and matrix surface, reduces interfacial porosity defects, and helps to improve the dielectric properties of the material and reduce loss.

[0047] (3) The mesoporous silica shell layer of the present invention provides more binding sites for silane coupling agents, which can more stably bind functional groups to the surface of functional fillers, so that functional fillers can be better dispersed in polymer matrix and have better interfacial compatibility with polymer matrix. Attached Figure Description

[0048] Figure 1 This is the preparation process of the high-dielectric, low-loss millimeter-wave composite material in Example 1; Figure 2 This is a finite element simulation diagram of the electric field coupling between fillers after doping with high dielectric constant fillers in Experiment Example 1. Figure 3 This is a finite element simulation diagram of the electric field coupling between fillers after doping with low dielectric constant fillers in Experiment Example 1. Figure 4 This is a finite element simulation diagram of the electric field coupling between fillers after functionalization and doping of fillers in Example 1; Figure 5 This is an SEM image of the functionalized filler from Example 1; Figure 6 This is a SEM image of the composite material from Example 1. Detailed Implementation

[0049] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0050] Example 1 This embodiment provides a method for preparing a high-dielectric, low-loss millimeter-wave composite material. The preparation method of the functionalized filler is as follows: a first shell layer and a second shell layer are sequentially coated on the surface of an inorganic filler, and the surface is modified to form a functionalized filler; wherein the inorganic filler is strontium titanate powder with a particle size of 8μm; the first shell layer is mesoporous silica with a porosity of 5% and a thickness of 0.3μm; the second shell layer is mesoporous silica with a porosity of 40% and a thickness of 0.3μm; the pore size of the mesoporous silica in the first shell layer and the second shell layer is 20nm.

[0051] The preparation process can be found in the appendix. Figure 1 Specifically, it includes the following steps: S1 is formed by sequentially coating the surface of the inorganic filler with a first shell layer and a second shell layer, and then performing surface modification to form a functionalized filler: S11 Preparation of mesoporous silica sols with different porosities: Tetraethyl orthosilicate (TEOS 10g) was dissolved in an appropriate amount of ethanol solvent (100mL), and an appropriate amount of water (5g) and acidic catalyst (hydrochloric acid, adjusted to pH 4-5) were added. The mixture was stirred at room temperature for 2h to form silica sol. Then, 0.5g and 3g of template agent (hexadecyltrimethylammonium bromide, CTAB) were added to the two silica sols respectively. Subsequently, an appropriate amount of deionized water (50mL) was added to the two sols respectively and the pH was adjusted to alkaline (9-10). The mixture was stirred at room temperature to form mesoporous silica sol with a porosity of 5% and mesoporous silica sol with a porosity of 40% respectively.

[0052] S12 covers the first shell layer: Inorganic filler was added to a mesoporous silica sol with a porosity of 5%, and the mixture was stirred for 2 hours to allow a mesoporous SiO2 layer to be deposited on the outside of the inorganic filler, forming a mesoporous SiO2 layer with a thickness of 0.3 μm. Subsequently, the mixture was calcined in air (550 °C, 2 hours) to remove the template agent, forming a first coating material with a first shell layer of mesoporous SiO2 layer and a porosity of 5%.

[0053] S13 covers the second shell: The first coating was added to a mesoporous silica sol with a porosity of 40%, and the mixture was stirred for 4.5 h to deposit a mesoporous SiO2 layer on the outside of the inorganic filler, forming a mesoporous SiO2 layer with a thickness of 0.3 μm. Subsequently, it was calcined in air (550 °C, 2 h) to remove the template agent, forming a second coating with a second shell layer of mesoporous SiO2 layer, the second shell layer of mesoporous silica layer having a porosity of 40%.

[0054] S14 Surface Modification The silane coupling agent γ-aminopropyltriethoxysilane (APTES) was dissolved in toluene to form a 5 vol% solution. The second coating material was added to the solution and stirred at room temperature for 4 h to allow the ethoxy groups in the APTES molecules to undergo a condensation reaction with the hydroxyl groups on the surface of mesoporous SiO2, thereby grafting aminopropyl functional groups onto the surface. Subsequently, the surface was dried in a vacuum oven at 100 °C for 6 h to obtain the functionalized filler.

[0055] S2 disperses the functionalized filler in the polymer matrix to form the composite material of this embodiment.

[0056] Weigh 500 g of polypropylene masterbatch, and weigh the corresponding amount of functional filler according to the volume ratio of functional filler to polypropylene of 1:1; mechanically blend the polypropylene masterbatch and functional filler at a speed of 300 rpm for 5 minutes each time, for 3 times; add the mixed raw material to a twin-screw extruder, with a twin-screw processing temperature of 220℃ and a screw speed of 300 rpm; extrude the blended composite melt, water-cool it, and pelletize it; dry the granulated composite masterbatch in a vacuum drying oven for 6 hours at a drying temperature of 80℃ to obtain the high dielectric and low loss composite material of this embodiment.

[0057] Example 2 This embodiment provides a method for preparing a high-dielectric, low-loss millimeter-wave composite material. The difference from Embodiment 1 is that the preparation method of the functionalized filler is as follows: a first shell layer, a second shell layer, and a third shell layer are sequentially coated on the surface of an inorganic filler, and surface modification is performed to form a functionalized filler. The inorganic filler is strontium titanate powder with a particle size of 8 μm. The first shell layer is mesoporous silica with a porosity of 5% and a thickness of 0.3 μm. The second shell layer is mesoporous silica with a porosity of 20% and a thickness of 0.3 μm. The third shell layer is mesoporous silica with a porosity of 40% and a thickness of 0.3 μm.

[0058] The preparation method of the mesoporous silica sol with a second shell porosity of 20% is as follows: dissolve 10g of tetraethyl orthosilicate (TEOS) in an appropriate amount of ethanol solvent (100mL), add an appropriate amount of water (5g) and an acidic catalyst (hydrochloric acid, adjusted to pH 4-5), and stir at room temperature for 2h to form a silica sol; then add 1.5g of template agent (hexadecyltrimethylammonium bromide, CTAB) to the silica sol; then add an appropriate amount of deionized water (50mL) to the sol and adjust the pH to alkaline (9-10), and stir at room temperature to form a mesoporous silica sol with a porosity of 20%.

[0059] The specific method for coating the second shell layer is as follows: the first coating material is added to a mesoporous silica sol with a porosity of 20%, and the mixture is stirred and reacted for 3.5 hours to deposit a mesoporous SiO2 layer on the outside of the inorganic filler, forming a mesoporous SiO2 layer with a thickness of 0.3 μm; then it is calcined in air (550℃, 2 hours) to remove the template agent, forming a second coating material with a second shell layer of mesoporous SiO2 layer, the porosity of which is 20%.

[0060] Example 3 This embodiment provides a method for preparing a high-dielectric, low-loss millimeter-wave composite material. The difference from Embodiment 1 is that the preparation method of the functionalized filler is as follows: a first shell layer, a second shell layer, and a third shell layer are sequentially coated on the surface of an inorganic filler, and surface modification is performed to form a functionalized filler. The inorganic filler is strontium titanate powder with a particle size of 8 μm. The first shell layer is mesoporous silica with a porosity of 5% and a thickness of 0.3 μm. The second shell layer is mesoporous silica with a porosity of 15% and a thickness of 0.3 μm. The third shell layer is mesoporous silica with a porosity of 25% and a thickness of 0.3 μm. The fourth shell layer is mesoporous silica with a porosity of 40% and a thickness of 0.3 μm.

[0061] The preparation method of the mesoporous silica sol with a second shell porosity of 15% is as follows: dissolve 10g of tetraethyl orthosilicate (TEOS) in an appropriate amount of ethanol solvent (100mL), add an appropriate amount of water (5g) and an acidic catalyst (hydrochloric acid, adjusted to pH 4-5), and stir at room temperature for 2h to form a silica sol; then add 1.25g of template agent (hexadecyltrimethylammonium bromide, CTAB) to the silica sol; then add an appropriate amount of deionized water (50mL) to the sol and adjust the pH to alkaline (9-10), and stir at room temperature to form mesoporous silica sol with a porosity of 15%.

[0062] The specific method for coating the second shell layer is as follows: the first coating material is added to a mesoporous silica sol with a porosity of 15%, and the mixture is stirred and reacted for 2.5 hours to deposit a mesoporous SiO2 layer on the outside of the inorganic filler, forming a mesoporous SiO2 layer with a thickness of 0.3 μm; then it is calcined in air (550℃, 2 hours) to remove the template agent, forming a second coating material with a second shell layer of mesoporous SiO2 layer, the porosity of which is 15%.

[0063] The preparation method of mesoporous silica sol with a third shell porosity of 25% is as follows: dissolve tetraethyl orthosilicate (TEOS 10g) in an appropriate amount of ethanol solvent (100mL), add an appropriate amount of water (5g) and an acidic catalyst (hydrochloric acid, adjusted to pH 4-5), and stir at room temperature for 2h to form silica sol; then add 2.5g of template agent (hexadecyltrimethylammonium bromide, CTAB) to the silica sol; then add an appropriate amount of deionized water (50mL) to the sol and adjust the pH to alkaline (9-10), and stir at room temperature to form mesoporous silica sol with a porosity of 25%.

[0064] The specific method for coating the third shell layer is as follows: the second coating material is added to a mesoporous silica sol with a porosity of 25%, and the mixture is stirred and reacted for 4 hours to deposit a mesoporous SiO2 layer on the outside of the inorganic filler, forming a mesoporous SiO2 layer with a thickness of 0.3 μm; then it is calcined in air (550℃, 2 hours) to remove the template agent, forming a third coating material with a third shell layer of mesoporous SiO2 layer, the porosity of which is 25%.

[0065] Example 4 This embodiment provides a method for preparing a high-dielectric, low-loss millimeter-wave composite material. The difference between this embodiment and Embodiment 1 is that the pore size of the mesoporous silica in each coating layer of the functionalized filler is 10 nm.

[0066] Example 5 This embodiment provides a method for preparing a high-dielectric, low-loss millimeter-wave composite material. The difference between this embodiment and Embodiment 1 is that the pore size of the mesoporous silica in each coating layer of the functionalized filler is 30 nm.

[0067] Example 6 This embodiment provides a method for preparing a high-dielectric, low-loss millimeter-wave composite material. The difference between this embodiment and Embodiment 1 is that the thickness of each coating layer of the functionalized filler is 0.5 μm.

[0068] Example 7 This embodiment provides a method for preparing a high dielectric and low loss millimeter wave composite material. The difference from Embodiment 1 is that in step S2, the amount of functionalized filler added satisfies the following condition: the volume ratio of functionalized filler to polypropylene is 2:3.

[0069] Example 8 This embodiment provides a method for preparing a high dielectric and low loss millimeter-wave composite material. The difference from Embodiment 1 is that in step S2, the amount of functionalized filler added satisfies the following condition: the volume ratio of functionalized filler to polypropylene is 1.2:1.

[0070] Example 9 This embodiment provides a method for preparing a high-dielectric, low-loss millimeter-wave composite material. The difference from Embodiment 1 is that in step S1, barium titanate with the same particle size and mass is used instead of strontium titanate.

[0071] Example 10 This embodiment provides a method for preparing a high-dielectric, low-loss millimeter-wave composite material. The difference from Embodiment 1 is that in step S1, titanium dioxide with the same particle size and the same mass is used instead of strontium titanate.

[0072] Example 11 This embodiment provides a method for preparing a high-dielectric, low-loss millimeter-wave composite material. The difference from Embodiment 1 is that the functionalized filler is not modified with a surface silane coupling agent, that is, the surface modification in step S14 is not performed.

[0073] Comparative Example 1 This comparative example provides a method for preparing a composite material, which differs from Example 1 in that the functionalized filler is prepared by sequentially coating the surface of the inorganic filler with two shell layers, wherein the first shell layer is a silica layer and the second shell layer is a mesoporous silica layer with a porosity of 40%, and then the surface is modified with a silane coupling agent. The thickness of the first shell layer and the second shell layer is the same as in Example 1.

[0074] The first shell layer of silica sol is prepared by dissolving tetraethyl orthosilicate (TEOS 30g) in an appropriate amount of ethanol solvent (100mL), adding an appropriate amount of water (5g) and an acidic catalyst (hydrochloric acid, adjusting the pH value to 4~5), and stirring at room temperature for 2h to form silica sol.

[0075] The specific method for coating the first shell layer is as follows: Strontium titanate is added to silica sol and stirred for 2 hours to allow SiO2 to be uniformly deposited on the surface of Strontium titanate, eventually forming a SiO2 layer with a thickness of about 0.3 μm; then it is calcined in air (600℃, 2 hours) to obtain the first coating material coated with a silica layer.

[0076] Comparative Example 2 This comparative example provides a method for preparing a composite material, which differs from Example 1 in that the functionalized filler is prepared by sequentially coating the surface of the inorganic filler with two shell layers, wherein the first shell layer is a titanium dioxide layer and the second shell layer is a silicon dioxide layer, and then surface modification is performed using a silane coupling agent. The thickness of the first shell layer and the second shell layer is the same as in Example 1.

[0077] Specifically, step S1 is as follows: S11 is configured with a first shell of titanium dioxide sol and a second shell of silica sol. Tetrabutyl titanate (TBOT 30g) was dissolved in an appropriate amount of ethanol solvent (100mL), and an appropriate amount of water (5g) and acidic catalyst (hydrochloric acid, adjusted to pH 4~5) were added. The mixture was stirred at room temperature for 2h to form titanium dioxide sol.

[0078] Tetraethyl orthosilicate (TEOS 30g) was dissolved in an appropriate amount of ethanol solvent (100mL), and an appropriate amount of water (5g) and acidic catalyst (hydrochloric acid, adjusted to pH 4~5) were added. The mixture was stirred at room temperature for 2h to form silica sol.

[0079] S12 covers the first shell layer Strontium titanate powder with a high dielectric constant was added to titanium dioxide sol and stirred for 2 hours to allow TiO2 to be uniformly deposited on the surface of the strontium titanate particles, eventually forming a TiO2 layer with a thickness of about 0.3 μm. Subsequently, it was calcined in air (600 °C, 2 hours) to obtain the first coating material with a titanium dioxide layer.

[0080] S13 encapsulates the second shell. The first coating was added to the silica sol and stirred for 2 hours to allow SiO2 to be uniformly deposited on the surface of the first coating, eventually forming a SiO2 layer with a thickness of about 0.3 μm. Then, it was calcined in air (600 °C, 2 hours) to obtain the second coating with a silica layer.

[0081] S14 Surface Modification The silane coupling agent γ-aminopropyltriethoxysilane (APTES) was dissolved in toluene to form a 5 vol% solution. The second coating material was added to the solution and stirred at room temperature for 4 h to allow the ethoxy groups in the APTES molecules to undergo a condensation reaction with the hydroxyl groups on the surface of mesoporous SiO2, thereby grafting aminopropyl functional groups onto the surface. Subsequently, the surface was dried in a vacuum oven at 100 °C for 6 h to obtain the functionalized filler.

[0082] In step S2, the amount of functionalized filler added satisfies the following condition: the volume ratio of functionalized filler to polypropylene is 2:3.

[0083] Comparative Example 3 This comparative example provides a method for preparing a composite material, which differs from Example 1 in that the functionalized filler is prepared by coating the surface of the inorganic filler with a mesoporous silica shell, followed by surface modification with a silane coupling agent. The thickness, pore size, and porosity of the mesoporous silica shell are the same as the first shell in Example 1.

[0084] In step S2, the amount of functionalized filler added satisfies the following condition: the volume ratio of functionalized filler to polypropylene is 2:3.

[0085] Comparative Example 4 This comparative example provides a method for preparing a composite material, which differs from Example 1 in that the method for preparing the functionalized filler is: the inorganic filler is not surface-coated, but is directly added to a silane coupling agent solution for surface functionalization modification.

[0086] In step S2, the amount of functionalized filler added satisfies the following condition: the volume ratio of functionalized filler to polypropylene is 2:3.

[0087] Comparative Example 5 This comparative example provides a method for preparing a composite material, which differs from Example 1 in that the method for preparing the functionalized filler is as follows: the first shell layer and the second shell layer are exchanged, that is, the porosity of the mesoporous silica in the first shell layer is 40%, and the porosity of the mesoporous silica in the second shell layer is 5%. In step S2, the amount of functionalized filler added satisfies the following condition: the volume ratio of functionalized filler to polypropylene is 2:3.

[0088] Comparative Example 6 This comparative example provides a method for preparing a composite material, which differs from Example 1 in that: the inorganic filler is not modified in any way and is directly added to the polypropylene matrix, and the amount of inorganic filler added satisfies the following: the volume ratio of inorganic filler to polypropylene is 1:3.

[0089] Experiment Example 1: Simulation Experiment Composite models were constructed using numerical simulation software for high dielectric constant fillers (Dk=200 (simulating strontium titanate), Dk=100 (simulating titanium dioxide)) dispersed in a polypropylene matrix, low dielectric constant fillers (Dk=25 (simulating magnesium titanate), Dk=4 (simulating silica)) dispersed in a polypropylene matrix, and the functionalized filler from Example 1 dispersed in a polypropylene matrix. Incident and receiving signal ports were set up, and the electric field coupling between the fillers during millimeter-wave signal transmission was simulated using the finite element method. The results are shown in the attached figures. Figure 2 Appendix Figure 3 and attached Figure 4 As shown.

[0090] Among them, the appendix Figure 2 A simulation diagram showing the electric field coupling between fillers after doping with high dielectric constant fillers is presented; from the attached diagram... Figure 2 As can be seen, when high dielectric constant inorganic fillers (strontium titanate, titanium dioxide, Dk=200, 100) are doped into polymers, the large difference in dielectric constant between the inorganic fillers and the polymer matrix leads to interfacial impedance mismatch, resulting in severe interfacial electric field coupling between the fillers, which in turn causes a high loss tangent. Appendix Figure 3 A simulation diagram showing the electric field coupling between fillers after doping with low dielectric constant fillers is presented; from the attached diagram... Figure 3As can be seen, when inorganic fillers with lower dielectric constants are doped (magnesium titanate, silicon dioxide, Dk=25, 4), the dielectric constants of the inorganic fillers and the matrix are not much different, which can achieve impedance matching, thereby weakening electric field coupling and maintaining low loss; however, the inorganic fillers with lower dielectric constants have limited effect on improving the dielectric constant of the overall composite material.

[0091] Appendix Figure 4 This diagram illustrates the electric field coupling between fillers after functionalization and doping in Embodiment 1 of the present invention. Figure 4 As can be seen, the functional filler of the present invention, after doping, interrupts the electron migration path and weakens the electric field concentration between fillers through gradient coating, mesoporous structure and stepwise impedance matching. This can improve the dielectric constant of the composite material and maintain an extremely low loss tangent, thus achieving a balance between high dielectric and low loss.

[0092] Experiment Example 2: Dielectric Property Testing The composite materials obtained in Examples 1-11 and Comparative Examples 1-6 were respectively prepared into composite sample sheets. The method for preparing the composite sample sheets was as follows: the composite material masterbatch obtained in step S2 was placed in a hot pressing mold, the plasticizing temperature was 220°C, the plasticizing time was 15 min, the hot pressing temperature was 220°C, the holding pressure was 10 MPa, the holding time was 5 min, and the cooling time was 5 min to prepare the composite sample sheet.

[0093] The composite sample sheets were polished and their dielectric properties were tested at 40 GHz, 60 GHz, 100 GHz, and 150 GHz using a vector network analyzer. The dielectric constant (Dk) and loss tangent (Df) were measured, and the test results are shown in Table 1 below. Table 1. Dielectric properties of samples from each embodiment and comparative example.

[0094] Analyzing the data in Table 1, we can see that: (1) Examples 1-11 are all coated with multiple layers of mesoporous silica with increasing porosity from the inside to the outside, which can achieve extremely high dielectric constant and extremely low dielectric loss.

[0095] (2) Comparing the data of Examples 1, 2 and 3, it can be seen that: the coating of 2 layers of mesoporous silica can achieve an extremely low loss tangent (Dk: 9.27 Df: 0.0007@100 GHz); as the coating layer increases to 3 layers, the loss tangent decreases slightly to a certain extent (Dk: 9.27 Df: 0.0006@100 GHz); as the coating layer increases to 4 layers, the loss tangent does not change, indicating that the 3-layer coating has achieved a great reduction in loss and no further coating is needed.

[0096] (3) Comparing the data of Example 1 and Comparative Example 1, it can be seen that: although the surface of Comparative Example 1 was also treated with mesoporous material, which greatly promoted the reduction of loss, its first shell layer was coated with non-mesoporous silica, which did not form multiple dispersion of current between multiple layers; it failed to better eliminate the electric field coupling channel between fillers.

[0097] (4) Comparing the data of Example 1 and Comparative Example 2, it can be seen that although Comparative Example 2 also carried out two-layer coating with decreasing dielectric constant, it did not adopt the design of mesoporous layer. Current channels still exist on the surface, and electric field coupling will still occur, resulting in increased loss.

[0098] (5) Comparing the data of Example 1 and Comparative Example 3, it can be seen that Comparative Example 3 only has a layer of mesoporous silica coating. Although its surface forms a certain degree of transition between the substrate and the filler, and the presence of the surface mesoporous layer disperses the current to a certain extent, it cannot achieve the effect of multi-layer and multi-channel dispersion, and electric field coupling still exists.

[0099] (6) Comparing the data of Example 1 and Comparative Example 4, it can be seen that Comparative Example 4 only modified the surface of the inorganic filler with silane coupling agent, which can only improve the interface compatibility and reduce interface porosity defects to a certain extent, but cannot solve the electric field coupling between high dielectric inorganic fillers well, and the loss is still very high.

[0100] (7) Comparing the data of Example 1 and Comparative Example 5, it can be seen that although Comparative Example 5 also uses two layers of mesoporous coating, the porosity between the two layers does not follow the trend of gradually increasing from the core layer to the surface layer. On the one hand, it cannot guarantee the realization of the gradient decrease of dielectric constant, and there will be an increase in loss due to the change of dielectric constant. On the other hand, the difference in pore distribution will also affect the difference in the current dispersion path.

[0101] Experiment Example 3: Scanning Electron Microscopy Experiment The functionalized filler and composite material prepared in Example 1 were subjected to SEM tests, and their SEM images at 8000x and 20000x magnification were observed. The results are shown in the appendix. Figure 5 and attached Figure 6 As shown, the attached Figure 5 The images show SEM images of the functionalized filler at 8000x magnification, and SEM images of the area shown in the figures at 20000x magnification; (Attached) Figure 6 This is a SEM image of the composite material at 8000x magnification.

[0102] From the appendix Figure 5 It can be seen that the prepared functionalized filler is a uniform particle with a uniform mesoporous layer on its surface.

[0103] From the appendix Figure 6 It can be seen that in the prepared composite material sample, the functionalized filler with gradient structure coating is uniformly distributed in the polymer matrix, which plays the expected role of blocking the coupling of polarized electric fields at the filler interface.

[0104] In summary, the high-dielectric, low-loss composite material prepared by the method of this invention can significantly reduce the loss tangent while improving the dielectric constant, providing a good foundation for its application in the field of millimeter-wave communication devices. Moreover, the preparation method of this invention is simple, easy to industrialize, and has good prospects for promotion and application.

Claims

1. A high-dielectric, low-loss millimeter-wave composite material, characterized in that, Includes a polymer matrix and functionalized fillers dispersed in the polymer matrix; The functionalized filler includes a core layer formed by inorganic filler and N shell layers sequentially covering the surface of the inorganic filler, where 2≤N≤4; All N shell layers are mesoporous silica layers; the porosity of the mesoporous silica in the N shell layers increases sequentially from the core layer outwards, with the porosity of the mesoporous silica in the innermost shell layer being ≥5% and the porosity of the mesoporous silica in the outermost shell layer being ≤40%; The pore size of the mesoporous silica in the N-layer shell is 10nm~30nm.

2. The high-dielectric, low-loss millimeter-wave composite material according to claim 1, characterized in that, N=2, and from the core layer outwards, there are a first shell layer and a second shell layer. The porosity of the mesoporous silica in the first shell layer is 5%~10%, and the porosity of the mesoporous silica in the second shell layer is 30%~40%.

3. The high-dielectric, low-loss millimeter-wave composite material according to claim 1, characterized in that, N=3, and from the core layer outwards, there are a first shell layer, a second shell layer, and a third shell layer. The porosity of the mesoporous silica in the first shell layer is 5%~10%, the porosity of the mesoporous silica in the second shell layer is 15%~25%, and the porosity of the mesoporous silica in the third shell layer is 30%~40%.

4. The high-dielectric, low-loss millimeter-wave composite material according to claim 1, characterized in that, N=4, and from the core layer outwards, there are a first shell layer, a second shell layer, a third shell layer, and a fourth shell layer. The porosity of the mesoporous silica in the first shell layer is 5%~10%, the porosity of the mesoporous silica in the second shell layer is 10%~20%, the porosity of the mesoporous silica in the third shell layer is 20%~30%, and the porosity of the mesoporous silica in the fourth shell layer is 30%~40%.

5. The high-dielectric, low-loss millimeter-wave composite material according to any one of claims 1 to 4, characterized in that, The functionalized filler also includes surface functional groups. The surface of the inorganic filler after being sequentially coated with N shell layers is functionalized with a silane coupling agent to obtain the functionalized filler.

6. The high-dielectric, low-loss millimeter-wave composite material according to claim 5, characterized in that, The inorganic filler is selected from one or more of barium titanate, strontium titanate, and titanium dioxide.

7. The high-dielectric, low-loss millimeter-wave composite material according to claim 6, characterized in that, The particle size of the inorganic filler is 8~12μm; the thickness of the N-layer shell is 0.2~0.5μm.

8. The high-dielectric, low-loss millimeter-wave composite material according to claim 7, characterized in that, The volume ratio of the functionalized filler to the polymer matrix satisfies 2:3 to 1.2:

1.

9. A method for preparing the high-dielectric, low-loss millimeter-wave composite material according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1 The functionalized filler is obtained by sequentially coating the surface of the inorganic filler with N layers of the shell layer; the shell layer is obtained by sequentially coating the surface of the inorganic filler with silica sol containing a template agent using a template method; Mesoporous silica with different porosities was prepared by adjusting the ratio of the template agent to the silica sol and the reaction time of the coating process. S2 The functionalized filler is dispersed in the polymer matrix to prepare the composite material.

10. The application of the high-dielectric, low-loss millimeter-wave composite material according to any one of claims 1 to 8, characterized in that, It is used in communication devices in the millimeter-wave band.

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