A wave-transparent material and a preparation method thereof

Abstract

The present application relates to a kind of wave-transparent material and its preparation method, belong to communication equipment material technical field.Foamed material layer and the skin layer covered in the foamed material layer two sides;The total thickness of wave-transparent material 28~40 mm, the thickness of the skin layer 0.1~1 mm;Wave-transparent material density is 0.03~0.20 g / cm 3 , there is bubble hole in foamed material layer, bubble hole aperture is less than 50 μm, pore wall thickness is less than 100 nm.The present application utilizes the characteristics of the above-mentioned material, and adopts green environmental protection's integrated molding die foaming technology and cryogenic finishing technology, and develops and designs integrated wideband high-transparency wave material for 600 MHz~300 GHz wideband electromagnetic wave frequency band.The developed wave-transparent material is integrally formed, and has special microstructure, which breaks through from the material itself, and fundamentally solves the technical bottleneck that current communication antenna cover is only applicable to low frequency, narrow frequency and cannot be applied to millimeter wave band.

Description

Technical Field

[0001] This invention relates to a wave-transparent material and its preparation method, belonging to the field of communication equipment materials technology. Background Technology

[0002] High-frequency 5G communication typically operates in the 30GHz–300GHz band, with wavelengths ranging from 1 to 10mm. Its drawbacks include a tendency for line-of-sight propagation and significant attenuation. Currently, the main frequency bands used in the 5G communication market are divided into two parts: the 5G-sub6 band (617 MHz–6GHz) and the 5G-mmW band (26.5GHz–40GHz). This not only requires the transparent material to have high transmittance at specific stages but also places certain demands on its transmittance performance across wide and high-frequency bands.

[0003] However, most millimeter-wave radome wave-transmitting materials currently used are sandwich composite materials, such as foam sandwich composite materials or honeycomb sandwich composite materials. The skin layer of foam sandwich composite materials is generally made of fiber-reinforced thermosetting resin material, and the core layer is generally made of thermosetting rigid foam, such as PMI foam. This structure has problems such as difficulty in recycling, difficulty in processing and molding, and low processing precision.

[0004] To address the aforementioned issues, some manufacturers have already adopted thermoplastic resins as core materials or skins to solve the environmental problems associated with these materials, as detailed in the patents below.

[0005] Patent CN103660410 discloses a radome wave-transparent sandwich material, its preparation method, and its uses. The skin is made of fiber-reinforced thermoplastic composite material, and the core layer is made of foamed polyurethane, phenolic resin, or epoxy resin. In this method, the thermoplastic resin of the skin material is polyolefin, thermoplastic polyester, or polyamide. However, the core layer foam material in this method is still thermosetting foam, which has low environmental friendliness.

[0006] Patent CN110539539 discloses a wave-transparent material for millimeter-wave radomes and its molding method. This invention uses a thermoplastic, highly flame-retardant polyethersulfone resin material, which effectively solves the material recycling problem. However, it still employs a sandwich structure, where the core material and skin are bonded together using adhesives. This structure is prone to delamination in complex environments over long periods, affecting the radome's lifespan and wave-transparent performance, and also results in higher raw material costs.

[0007] While the aforementioned patents have addressed the environmental issues of materials to some extent, they involve numerous processes, high costs, and significant structural problems due to interface issues. Prolonged use can easily lead to interface detachment, thereby improving dielectric properties and reducing lifespan. Furthermore, they primarily address the issues of high-frequency, high-transparency materials from the perspective of macroscopic structural control, without fundamentally regulating the performance of transmissive materials. Summary of the Invention

[0008] Thermoplastic polymers are highly processable and low-cost. This project utilizes the characteristics of these materials and employs green and environmentally friendly integrated molding and foaming technology as well as cryogenic finishing technology to develop and design an integrated broadband high-transmittance material with micro-nano structure for the 600MHz to 300GHz wideband electromagnetic wave band.

[0009] The first aspect of the present invention provides:

[0010] A wave-transparent material includes: a foamed material layer and skin layers covering both sides of the foamed material layer; the total thickness of the wave-transparent material is 28-40 mm, and the thickness of the skin layers is 0.1-1 mm; the density of the wave-transparent material is 0.03-0.20 g / cm³. 3 The foamed material layer contains pores with a pore diameter of <50μm and a pore wall thickness of <100nm.

[0011] In one embodiment, the skin layer is a solid layer.

[0012] In one embodiment, the microwave-transparent material is characterized by a melt index ≤15g / 10min, a dielectric constant <5, and a dielectric loss <0.05. The material is selected from general-purpose plastics, engineering plastics, or special engineering plastics, including but not limited to: polystyrene, polyethylene, polypropylene, polylactic acid, polyurethane, polymethyl methacrylate, polyvinyl chloride, polyethylene terephthalate, polycarbonate, polyimide, polyphenylene sulfide, polyetherimide, and other amorphous or semi-crystalline thermoplastic polymers and their copolymers or blends, preferably non-polar polymers.

[0013] A second aspect of the present invention provides:

[0014] A communication device comprising the aforementioned wave-transparent material.

[0015] In one embodiment, the communication device is a millimeter-wave radome.

[0016] In one embodiment, the millimeter-wave radome includes an outer housing with a wave-transparent material installed inside the housing.

[0017] A third aspect of the invention provides:

[0018] The preparation method of the wave-transparent material includes the following steps:

[0019] Step 1: Provide the raw materials for the foaming material;

[0020] Step 2: Add the raw materials from Step 1 into the foaming machine mold cavity, and attach release film to the two opposite surfaces inside the foaming machine mold cavity;

[0021] Step 3: Fill the foaming machine cavity with supercritical fluid, open the mold to release pressure, and obtain the wave-transparent material.

[0022] In one embodiment, in step 1, the raw material is prepared by a screw extruder or a vulcanizing machine.

[0023] In one embodiment, in step 1, the raw materials include: polymer, anti-aging agent and flame retardant.

[0024] In one embodiment, in step 1, the melt flow index of the raw material is ≤5 g / 10 min.

[0025] In one embodiment, in step 1, the raw material is in granular or flake form.

[0026] In one embodiment, in step 2, the release film is attached to the upper and lower surfaces of the mold cavity.

[0027] In one embodiment, in step 3, after filling with supercritical fluid, the mold cavity pressure is 8-25 MPa, the mold cavity temperature is 120-270°C, and the heat and pressure are maintained for 10-260 min; the pressure relief rate during the depressurization process is >5 MPa / s; and the foaming ratio is approximately 2-20 times.

[0028] In one embodiment, after step 3, the wave-transparent material is cut using a cold knife capable of spraying liquid nitrogen.

[0029] A fourth aspect of the present invention provides:

[0030] An apparatus for preparing a wave-transparent material, comprising:

[0031] The mold consists of an upper mold cavity and a lower mold cavity, with a chamber formed between the upper and lower mold cavities;

[0032] Gas source, used to supply supercritical gas into the chamber;

[0033] The mold is equipped with a vent.

[0034] Release films are provided on the opposing inner surfaces of the upper and lower mold cavities.

[0035] In one embodiment, the mold is further provided with a heating device for heating the cavity.

[0036] In one embodiment, the device further includes: an apparatus for cutting the wave-transparent material obtained by supercritical foaming of raw materials in the mold cavity.

[0037] In one embodiment, the cutting device is a cold knife.

[0038] In one embodiment, the structure of the cold knife includes:

[0039] CNC machine tool bearings, used to control the feed of the cold tool;

[0040] A miniature liquid nitrogen storage tank, located on the outside of the bottom of the CNC machine tool bearing, is used to store and supply liquid nitrogen;

[0041] The insulation layer, located on the outside of the liquid nitrogen miniature storage tank, is used to insulate the liquid nitrogen miniature storage tank.

[0042] The cutting head is located at the bottom end of the bearing of the CNC machine tool.

[0043] A conical metal baffle is located outside the cutter head, forming a gap between it and the cutter head for liquid nitrogen spraying.

[0044] The liquid nitrogen spray nozzle is located below the liquid nitrogen miniature storage tank, connecting the liquid nitrogen miniature storage tank to the gap.

[0045] In one embodiment, the distance of the gap is between 0.1 and 1 mm.

[0046] In one embodiment, the volume of the liquid nitrogen micro-storage tank is 1 to 50 L.

[0047] In one embodiment, the conical metal baffle is fixed to the liquid nitrogen miniature storage tank by reinforcing ribs.

[0048] A fifth aspect of the present invention provides:

[0049] The aforementioned wave-transparent materials are used in the manufacture of millimeter-wave communication equipment.

[0050] Beneficial effects

[0051] This project leverages the characteristics of thermoplastic materials and employs environmentally friendly integrated molding and foaming technology, along with cryogenic finishing technology, to develop an integrated broadband high-transparency material for the 600MHz–300GHz wideband electromagnetic wave band. The developed transparent material is integrally molded and possesses a unique microstructure, representing a breakthrough in the material itself and fundamentally solving the current technical bottleneck of communication radomes being applicable only to low-frequency, narrow-band applications and unsuitable for millimeter-wave bands. Attached Figure Description

[0052] Figure 1 This is a structural diagram of a wave-transparent material;

[0053] Figure 2 This is a diagram of a microwave-transparent material production facility;

[0054] Figure 3 This is a cross-sectional view of a cold knife;

[0055] Figure 4This is a top view of the cold blade at point A;

[0056] Figure 5 This is a top view of point B on the cold blade;

[0057] Figure 6 This is a SEM image of the liquid nitrogen quenched cross-section of Example 1;

[0058] Figure 7 This is a SEM image of the liquid nitrogen quenched cross-section of Comparative Example 3; Detailed Implementation

[0059] The wave-transparent material provided by this invention is integrally formed using a supercritical foaming method. It is suitable for millimeter-wave radomes and exhibits good wave transmission properties. Its main structure is as follows: Figure 1 As shown, it includes: a foam material layer 100 and a skin layer 101 covering both sides of the foam material layer.

[0060] More specific material parameters are: the total thickness of the wave-transparent material is 28–40 mm, and the thickness of the skin layer is 0.1–1 mm; the density of the wave-transparent material is 0.05–0.20 g / cm³. 3 The foamed material layer contains pores with a pore size of <50μm and a pore wall thickness of <100nm. The skin layer is generally solid.

[0061] Since the wavelength of millimeter waves is between 1 and 10 mm, and the pore diameter of the bubble in this invention is <50 μm and the pore wall thickness is <100 nm, the transmittance of millimeter waves can be effectively improved.

[0062] The aforementioned wave-transparent material is characterized by a melt index ≤15g / 10min, a dielectric constant <5, and a dielectric loss <0.05. The material is selected from general-purpose plastics, engineering plastics, or special engineering plastics, including but not limited to: polystyrene, polyethylene, polypropylene, polylactic acid, polyurethane, polymethyl methacrylate, polyvinyl chloride, polyethylene terephthalate, polycarbonate, polyimide, polyphenylene sulfide, polyetherimide, and other amorphous or semi-crystalline thermoplastic polymers and their copolymers or blends, preferably non-polar polymer materials.

[0063] In addition, appropriate additives, such as flame retardants and anti-aging agents, can be added to the microwave-transparent material according to the required performance.

[0064] As a flame retardant in foamed materials, halogen-free and antimony-free inorganic flame retardants are preferred. Examples of such inorganic flame retardants include metal hydroxides and hydrates of metal compounds. More specifically, examples include aluminum hydroxide; magnesium hydroxide; hydrates of magnesium oxide and nickel oxide; and hydrates of magnesium oxide and zinc oxide. Magnesium hydroxide is a suitable example. The aforementioned hydrated metal compounds may also be surface-treated. Flame retardants can be used alone or in combination of two or more.

[0065] As an anti-aging agent in foamed materials, well-known anti-aging agents can be used, such as amine-based, phenol-based, imidazole-based, and carbamate metal salt anti-aging agents.

[0066] The above materials can be prepared by:

[0067] Step 1: Provide the raw materials for the foaming material;

[0068] Step 2: Add the raw materials from Step 1 into the foaming machine mold cavity, and attach release films to the two opposite surfaces inside the foaming machine mold cavity; In this invention, setting release films at the upper and lower positions of the mold cavity can form relatively dense skins on the upper and lower surfaces of the transparent material after foaming, thereby improving the weather resistance and mechanical properties of the material to a certain extent.

[0069] Step 3: Fill the foaming machine cavity with supercritical fluid, open the mold to release pressure, and obtain the wave-transparent material.

[0070] In a typical manufacturing process, the operation method is as follows:

[0071] Step 1: After thoroughly mixing polyolefin granules (melt index ≤ 5 g / 10 min), flame retardant, and anti-aging agent, add the mixture to a sheet twin-screw extruder or flat vulcanizing machine to prepare polyolefin sheets with a thickness of 10-15 mm.

[0072] Step 2: Place the prepared polyolefin sheet into the mold cavity of a multilayer molding foaming machine (with smooth release film on both sides), fill with supercritical fluid, maintain a pressure of 8–25 MPa and a temperature of 120–270℃, and hold for 10–260 minutes. Then, quickly open the mold to release pressure (pressure release rate >5 MPa / s), thus obtaining a polyolefin microporous foam material with smooth top and bottom skins. It has a closed-cell structure, a foaming ratio of approximately 15 times, and a density of approximately 0.09 g / cm³. 3 The overall thickness is 28-40mm, with the thickness of the upper and lower leather surfaces ranging from 0.1-1mm.

[0073] Step 3: CNC machining is performed using a cold-cutting tool (the tool tip can be sprayed with liquid nitrogen) to obtain the antenna radome wave-transparent material with precise dimensions. The above process can also be used to process irregularly shaped materials.

[0074] Based on the above methods, the production apparatus provided by the present invention is as follows: Figure 2 As shown, it includes:

[0075] The mold 16 is composed of an upper mold cavity 18 and a lower mold cavity 19, and a cavity is formed between the upper mold cavity 18 and the lower mold cavity 19.

[0076] Gas source 15 is used to supply supercritical gas into the chamber;

[0077] The mold 16 is provided with an air vent 17;

[0078] Release films 20 and 21 are respectively provided on the opposing inner surfaces of the upper mold cavity 18 and the lower mold cavity 19.

[0079] In one embodiment, the mold 16 is further provided with a heating device for heating the inside of the mold cavity.

[0080] In one embodiment, the device further includes: an apparatus for cutting the wave-transparent material obtained by supercritical foaming of raw materials in the mold cavity.

[0081] In one embodiment, the cutting device is a cold knife.

[0082] In one embodiment, the structure of the cold knife includes:

[0083] CNC machine tool bearing 1, used to control the feed of the cold tool;

[0084] A liquid nitrogen miniature storage tank 3 is located on the outside of the bottom of the CNC machine tool bearing 1, and is used to store and supply liquid nitrogen;

[0085] The insulation layer 2 is located on the outside of the liquid nitrogen micro storage tank 3 and is used to insulate the liquid nitrogen micro storage tank 3.

[0086] The cutting head 5 is located at the bottom end of the bearing 1 of the CNC machine tool.

[0087] A conical metal baffle 6 is located outside the cutter head 5, forming a gap between it and the cutter head 5 for liquid nitrogen spraying.

[0088] The liquid nitrogen spray nozzle 4 is located below the liquid nitrogen miniature storage tank 3, connecting the liquid nitrogen miniature storage tank 3 to the gap.

[0089] In one embodiment, the distance of the gap is between 0.1 and 1 mm.

[0090] In one embodiment, the volume of the liquid nitrogen micro-storage tank 3 is 1 to 50 L.

[0091] In one embodiment, the conical metal baffle 6 is fixed to the liquid nitrogen micro tank 3 by reinforcing ribs 13.

[0092] Notes: 1. CNC machine tool bearing; 2. Insulation layer; 3. Liquid nitrogen miniature storage tank, volume 1-5L; 4. Liquid nitrogen spray nozzles at the bottom of the storage tank, four in total, circular, diameter 10-30mm; 5. Cutting head; 6. Conical metal baffle, fixed to the storage tank 3 by reinforcing rib 13, the distance between its opening and the cutting head 12 is 0.1-1mm, and its height is 10mm from the cutting head; 7. Liquid nitrogen centralized spray nozzle; 8. Top view of CNC machine tool bearing; 9. Top view of insulation layer; 10. Top view of storage tank A direction; 11. Top view of cutting head; 12. Top view of centralized spray nozzle; 13. Reinforcing rib of conical metal baffle; 14. Top view of storage tank B direction.

[0093] Example 1:

[0094] A polyolefin blend (melt index 2 g / 10 min) was added to a twin-screw sheet extruder at a processing temperature of 210–290 °C, with the sheet extrusion die temperature between 180–240 °C. A 10 mm thick polyolefin sheet was obtained by passing it through a three-roll cooling rack. The resulting polyolefin sheet was then placed into the mold cavity of a multilayer molding foam machine (with smooth release film applied to both sides), filled with supercritical fluid at a pressure of 13 MPa and a temperature of 163 °C, and held at this temperature and pressure for 30 min. The mold was then rapidly opened to release the pressure, yielding a polyolefin microporous foam material, which was then CNC machined using a cold knife.

[0095] Example 2:

[0096] First, preheat the polyolefin (melt index 3g / 10min) blend to 120℃. Then, add the preheated material to a preheated mold at 180-195℃, apply pressure at 14MPa and hold for 60min. Then, cool to 80℃ to demold and obtain a 10mm thick polyolefin sheet.

[0097] The prepared polyolefin sheet is placed into the mold cavity of a multilayer molding foaming machine (with smooth release film on both the top and bottom surfaces), filled with supercritical fluid, pressure of 10MPa, temperature of 163℃, and kept at the temperature and pressure for 30 minutes. Then, the mold is quickly opened and the pressure is released to obtain polyolefin microporous foam material. It is then CNC machined using a cold knife.

[0098] Comparative Example 1:

[0099] The only difference compared to Example 1 is that a smooth release membrane is not placed inside the mold cavity.

[0100] Comparative Example 2:

[0101] Compared with Comparative Example 1, the only difference is that a glass fiber reinforced polyolefin skin was later attached to the top and bottom surfaces. The skin thickness was 1 mm to ensure that the overall thickness was the same as in Example 1.

[0102] Comparative Example 3:

[0103] The difference from the formulation of the blending system in Example 1 is that it is prepared using the traditional chemical foaming agent AC.

[0104] Comparative Example 4:

[0105] The only difference compared to the process in Example 1 is that a conventional blade is used for CNC cutting.

[0106] Test method:

[0107] Measurement of cell diameter and cell wall thickness: The diameter and cell wall thickness of each cell in the sample SEM image were marked using Nano Measurer software, and then the average cell diameter and average cell wall thickness were viewed from the software analysis report.

[0108] Transmittance: using the free space method

[0109] Peel strength and compressive strength distribution were tested according to GB8808-1988 and GB8813-2008 standards.

[0110] The test results are as follows:

[0111]

[0112] A comparison of the mechanical property data of Example 1 and Comparative Example 1 shows that placing a smooth release film in the mold helps to form a smooth skin on the surface of the microwave-transparent microporous foam, thereby improving the mechanical properties of the material, such as pressure resistance, to a certain extent.

[0113] A comparison of the transmittance and mechanical properties of Example 1 and Comparative Example 2 shows that although the sandwich structure of the wave-transmitting material can significantly improve the material's performance in terms of compressive strength, it is significantly inferior to the one-piece structure in terms of peel strength and wave transmission performance due to the presence of a clear interface. In other words, the one-piece structure can better guarantee the lifespan and long-term effectiveness of the dielectric properties of the wave-transmitting material.

[0114] As can be seen from the data and SEM images of Examples 1, 2 and Comparative Example 3, the foam material obtained by using the integrated supercritical solid foaming technology developed in this project has pores of <100um and pore wall thickness of <100nm. Compared with traditional foam materials, the pore distribution is more uniform, the pore diameter is smaller, the pore wall thickness is smaller, and the mechanical properties are greatly improved. In addition, the transmittance is greater than 90% in different electromagnetic wave frequency bands, showing a good wave transmission effect, and the transmittance in the high frequency band is also better.

[0115] Based on the product flatness data from Example 1 and Comparative Example 4, the invented cold knife device has higher processing precision in the processing of microporous foam, which effectively solves the technical bottleneck of foam material application in the field of electronic communication due to processing precision issues.

Claims

1. A wave-transparent material, characterized in that, It includes: The material comprises a foamed material layer (100) and a skin layer (101) covering both sides of the foamed material layer; the total thickness of the wave-transparent material is 28-40 mm, and the thickness of the skin layer (101) is 0.1-1 mm; the density of the wave-transparent material is 0.03-0.20 g / cm³. 3 The foamed material layer (100) contains pores with a pore diameter of less than 50 μm and a pore wall thickness of less than 100 nm. The method for preparing the aforementioned wave-transparent material includes the following steps: Step 1: Provide the raw materials for the foaming material; the raw materials include: polymers, anti-aging agents, and flame retardants; the raw materials are prepared by a screw extruder or vulcanizing machine; Step 2: Add the raw materials from Step 1 into the foaming machine mold cavity, and attach release film to the two opposite surfaces inside the foaming machine mold cavity; Step 3: Fill the foaming machine cavity with supercritical fluid, open the mold to release pressure, and obtain the wave-transparent material; The microwave-transparent material is selected from polystyrene, polyethylene, polypropylene, polylactic acid, polyurethane, polymethyl methacrylate, polyvinyl chloride, polyethylene terephthalate, polycarbonate, polyimide, polyphenylene sulfide, polyetherimide, and their copolymers or blends; the microwave-transparent material has a melt index ≤15 g / 10min, a dielectric constant <5, and a dielectric loss <0.

05. Raw material melt flow index ≤ 5 g / 10 min; In step 3, after filling with supercritical fluid, the mold cavity pressure is 8~25 MPa, the mold cavity temperature is 120~270℃, and the heat and pressure are maintained for 10~260 min; the pressure relief rate during the depressurization process is >5 MPa / s; and the foaming ratio is 2~20 times.

2. The wave-transparent material according to claim 1, characterized in that, In step 1, the raw material is granular or flake-shaped; in step 2, the release film is attached to the upper and lower surfaces of the mold cavity; after step 3, the wave-transparent material is cut using a cold knife that can spray liquid nitrogen.

3. A communication device, characterized in that, It includes the wave-transparent material as described in claim 1.

4. The communication device according to claim 3, characterized in that, The communication device in question is a millimeter-wave antenna radome; The millimeter-wave antenna radome includes an outer shell, and a wave-transparent material is installed inside the shell.

5. The application of the wave-transparent material of claim 1 in the manufacture of millimeter-wave communication equipment.

Images