A wave-transmitting material with signal focusing function and preparation method thereof

Abstract

The present invention provides a wave-transmitting material with a signal focusing function and a preparation method thereof, and belongs to the field of polymer materials and communication equipment materials. The novel wave-transmitting material is made by pressing two resins whose dielectric constants differ by less than 3. During the pressing process, the two resins penetrate each other to form a dielectric constant gradient. The dielectric constant gradient value of the formed material decreases from the side of the high dielectric constant material before pressing to the side of the low dielectric constant material before pressing. The two resins whose dielectric constants differ by less than 3 constituting the material are two thermoplastic resins that can be heated and blended, each of which has a dielectric constant less than 4 and a difference between the two of which is greater than 0.5 and less than 1.8, in particular, a polyethersulfone resin and a polypropylene resin whose main chain contains a bisphenol A structure. The wave-transmitting material can be used for the production of antenna covers, and the antenna covers produced have a signal focusing function.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials and communication equipment materials, and relates to wave-transmitting materials, in particular to a method for preparing the wave-transmitting materials and the prepared wave-transmitting materials. Background Art

[0002] Wave-transmitting materials refer to dielectric materials that are conductive on both sides and have little loss and distortion when electromagnetic waves pass through. The main purpose is to manufacture various radomes, protect the antennas of radars and other electronic equipment, and prevent harmful effects from the external environment. For example, most aircraft radomes are made of fiberglass and its composite sandwich structure, and most radomes (plates) for air defense, coastal defense and other tactical missiles are made of polytetrafluoroethylene or glass fiber reinforced polytetrafluoroethylene, while the antenna window materials of strategic missiles have gone through the development process of quartz glass, punctured high silica cloth reinforced silica and three-dimensional quartz reinforced silica. In general, the smaller the dielectric loss of the material, the thinner the wall of the hood, the less energy is absorbed, and thus the greater the power transmission coefficient.

[0003] With the continuous development of communication technology, 5G base stations / micro stations, mobile phones, antennas, loT terminals, etc. have been widely used in life. Since the above facilities are generally set up in the open air, it is usually necessary to add wave-transparent plastic shells or bracket sheets to the above facilities to better protect the facilities from damage by the external environment. The main frequency bands used in the current 5G communication market are divided into two parts, 5G-sub6 band (617 MHz ~ 6 GHz) and 5G-mmW band (26.5 GHz ~ 40 GHz), which not only requires the wave-transparent material to have high wave transmittance at a specific stage, but also puts forward certain requirements and demands on its wave-transparent performance in broadband and high-frequency bands.

[0004] At present, the wave-transmitting material structure of millimeter-wave antenna covers is mostly sandwich structure composite materials, such as foam sandwich structure composite materials or honeycomb sandwich structure composite materials. The skin layer of the foam sandwich structure composite material is generally a fiber-reinforced thermosetting resin material, and the core layer is generally a thermosetting rigid foam, such as PMI foam. There are problems such as difficult recycling, difficult processing and molding, and low processing accuracy. In addition to the problems of processing and recycling, the material cannot meet the additional functions of integration such as signal focusing. In response to the processing problem, some manufacturers and institutions have provided some solutions. For example, patent CN103660410 discloses a wave-transmitting sandwich material for a antenna cover, its preparation method and use, the skin of which is made of fiber-reinforced thermoplastic composite materials, and the core layer is a foamed polyurethane, phenolic resin or epoxy resin material. The thermoplastic resin of the skin material in this method is polyolefin, thermoplastic polyester, or polyamide. Patent CN110539539 discloses a wave-transmitting material for a millimeter-wave antenna cover and a molding method thereof. The invention uses a thermoplastic highly flame-retardant polyethersulfone resin material, which can solve the problem of material recycling very well, but it still uses a sandwich structure, that is, the core material and the skin are formed by bonding with adhesives. This structure is prone to stratification in a complex environment for a long time, affecting the life and wave transmission effect of the antenna cover, and the raw material cost is relatively high. Patent CN112549666 discloses an integrated broadband high-wave-transmittance material developed and designed for the broadband electromagnetic wave band of 600MHz to 300GHz using green and environmentally friendly one-piece molding foaming technology and frozen finishing technology. The developed wave-transmitting material is one-piece molded, which has made a breakthrough in the material itself and solved the technical bottleneck that the communication antenna cover is only applicable to low-frequency and narrow frequency bands and cannot be applied to millimeter wave bands.

[0005] However, the above solutions mainly solve the problem of high-frequency and high-wave-transmittance materials from the aspect of macro-structural regulation. Even if improvements are made to the structure of the material itself, it only allows the signal to penetrate better, but cannot achieve signal focusing and amplification. Summary of the invention

[0006] In order to achieve signal focusing while ensuring the wave-transmitting performance of the material, the present invention provides a method for preparing a wave-transmitting material and the wave-transmitting material prepared therefrom.

[0007] In a first aspect, the present invention provides a wave-transmitting material having a signal focusing function.

[0008] The new wave-transmitting material is made by laminating two resins with a dielectric constant difference of less than 3. During the laminating process, the two resins penetrate each other to form a dielectric constant gradient. The dielectric constant gradient value of the formed material decreases from the side of the high dielectric constant material before laminating to the side of the low dielectric constant material before laminating.

[0009] The two resins whose dielectric constants differ by less than 3 can be thermoplastic polymers such as polyethersulfone, polypropylene, polystyrene, polyethylene, polylactic acid, polyurethane, polymethyl methacrylate, polyvinyl chloride, polyethylene terephthalate, polycarbonate, polyimide, polyphenylene sulfide, polyetherimide, and their copolymers or blends.

[0010] The two resins having a dielectric constant difference of less than 3 are particularly polyethersulfone and polypropylene, wherein the polyethersulfone is preferably a polyethersulfone having a bisphenol A structure in the main chain.

[0011] The two resins having a dielectric constant difference of less than 3 are preferably two resins having a dielectric constant difference of less than 2, and more preferably two thermoplastic resins capable of being heated and blended having a dielectric constant less than 2. In particular, the two thermoplastic resins capable of being heated and blended have dielectric constants each less than 4 and a difference between the two of greater than 0.5 and less than 1.8.

[0012] The obtained sheet material can be further treated by foaming and other processes to further reduce the dielectric constant of the obtained material.

[0013] In a second aspect, the present invention provides a method for preparing a wave-transmitting material with a signal focusing function. The method is prepared by the following steps:

[0014] Step 1, pressing a material A having a high dielectric constant and a material B having a low dielectric constant and a dielectric constant value different from that of the material A by less than 3 into sheets respectively;

[0015] Step 2, stacking the material A sheet and the material B sheet together and pressing them into sheets;

[0016] Step 3, the sheet material pressed in step 2 is made into a flat plate shape, a spherical shape, a cone shape, a rectangular cover shape, or a cube cover shape by using foaming and / or vacuum forming, mold hot pressing, or other processes.

[0017] The material A and material B are preferably thermoplastic plastics, including polyethersulfone, polypropylene, polystyrene, polyethylene, polylactic acid, thermoplastic polyurethane, etc., especially polyethersulfone, polypropylene, polyethylene, polystyrene, etc. whose dielectric constant itself is less than 3.

[0018] The pressing into sheets in step 1 can be performed by rolling the pellets into sheets after twin-screw extrusion.

[0019] The tableting described in step 1 and step 2 can be performed by roller pressing at room temperature, hot roller pressing, hot pressing on a flat plate vulcanizer, or the like.

[0020] The sheet material prepared in step 1 has a thickness between 0.01 and 100 mm, preferably between 1 mm and 20 mm.

[0021] The pressing into tablets described in step 2, such as by hot pressing, the pressing temperature is the temperature at which material A and material B can be softened and blended, which can be specifically obtained through a twin-screw extrusion test. The temperature at which the two materials are well blended by twin-screw extrusion is the preferred temperature. The "well blended" can be judged by scanning electron microscope images. The mixed material slices are observed by scanning electron microscope. If there is no obvious single-phase aggregation, it can be judged that the two materials are well blended.

[0022] The processing described in step 3 into a flat, spherical, conical, rectangular, or cube-shaped cover shape is preferably the outer surface of the cover, that is, the side that the signal first passes through from the outside to the inside, which is the side with a low dielectric constant.

[0023] In a third aspect, the present invention provides:

[0024] A communication device comprises the above-mentioned wave-transmitting material. In one embodiment, the communication device is a millimeter wave antenna cover.

[0025] The beneficial effect of the present invention is that the wave-transmitting material obtained, while ensuring low dielectric loss, adopts the method of calendering penetration to form a dielectric constant gradient inside the material, so that the incident signal can be refracted after the antenna cover made of the material, achieving the effect of signal gain amplification. In high-frequency band communication scenarios such as 5G communication, the signal strength loss is proportional to the frequency and dielectric constant of the medium. It is crucial to achieve signal gain with a simple method while reducing dielectric loss. At the same time, compared with the method of directly bonding two or more materials or other methods equivalent to direct bonding, the method provided in the present invention does not have an obvious phase interface, thereby reducing the loss of the signal when it is incident on different interfaces, thereby improving the signal strength and efficiency, and improving practicality. On the other hand, the method provided by the present invention can complete the device manufacturing with simple equipment and process, thereby reducing the production cost, and has better practicality than other methods. Among them, the preferred polyethersulfone resin with bisphenol A structure not only has a low dielectric constant and good compatibility with other thermoplastic resins, but also contains polar functional groups such as oxygen, providing sites for polar action and hydrogen bonding, and providing great convenience for further processing steps such as bonding of materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The figure shows the distribution of two polymer structural units in the wave-transmitting material of the present invention. 1 is a material structure with a high dielectric constant, and 2 is a material structure with a low dielectric constant. The dotted line in the figure represents the whole material, and the symbol density shown in 1 and 2 illustrates the distribution of the two material structures in the whole formed material.

[0027] Figure 2The figure shows the sequence of stacking two sheets before pressing, where 1 is a material with a high dielectric constant and 2 is a material with a low dielectric constant.

[0028] Figure 3 This is a diagram showing the change in dielectric constant of the wave-transmitting material from the high dielectric constant surface to the low dielectric constant surface. DETAILED DESCRIPTION

[0029] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments are helpful for those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form.

[0030] Example 1

[0031] A wave-transmitting material, composed of the following two polymer materials:

[0032] Material A is polyethersulfone with the following structure:

[0033]

[0034] Its weight average molecular weight M w =6000, the dielectric constant is 2.9 at a test frequency of 1MHz;

[0035] Material B is polypropylene PP, using the polypropylene resin of Lummus Company with the brand Novolen 1040RC, and the measured dielectric constant is 2.1 at a frequency of 1 MHz.

[0036] Material A and material B were extruded and rolled by twin screws to form 5 mm thick sheets, and then the sheet made of material A was placed on the sheet made of material B, and hot pressed by a flat vulcanizer at 10 MPa and 150°C to obtain a 7 mm thick sheet. The obtained sheet was placed in the mold cavity of a multi-layer compression foaming machine, filled with supercritical CO2 at a pressure of 10 MPa and a temperature of 165°C, and kept warm and pressurized for 20 minutes, and then the mold was quickly opened to release the pressure, and the finished wave-transmitting material was obtained.

[0037] Comparative Example 1

[0038] Compared with Example 1, the difference is that the same polyethersulfone resin as in Example 1 is directly used to make a 7 mm thick sheet, which is subjected to supercritical foaming to obtain a finished material.

[0039] Comparative Example 2

[0040] Compared with Example 1, the difference is that the same polypropylene PP resin as in Example 1 is directly used to make a 7 mm thick sheet, which is subjected to supercritical foaming to obtain a finished material.

[0041] A network analyzer was connected to the parallel plate mold, and the dielectric constants of the material sheets in Example 1, Comparative Example 1 and Comparative Example 2 were tested at different thicknesses. It was found that the dielectric constant of the material in Example 1 decreased from one side (high dielectric constant side) to the other side (low dielectric constant side). Figure 3 In comparison, the dielectric constants of the materials in Comparative Examples 1 and 2 do not change from one side to the other.

[0042] Two horn antennas were connected with a network analyzer, and the free space method was used to test the intensity of the signal after passing through the materials of Example 1, Comparative Example 1 and Comparative Example 2 at an incident angle of 30° at a frequency of 700 MHz. It was found that the signal intensity was strongest after passing through the material in Example 1, and the signal intensity after passing through the materials of Comparative Example 1 and Comparative Example 2 was 75% and 82% of the intensity after passing through the material of Example 1, respectively.

[0043] Example 2

[0044] The material obtained in Example 1 is molded by the vacuum forming method at 200°C to obtain a curved cover with a curvature radius of 1m and a low dielectric constant surface located on the convex surface, i.e., the outer surface, that is, a antenna cover with signal focusing function.

[0045] Comparative Example 3

[0046] Compared with Example 2, the material obtained in Comparative Example 1 is used to make a radome with the same curvature radius.

[0047] Comparative Example 4

[0048] Compared with Example 2, the material obtained in Comparative Example 2 is used to make a radome with the same curvature radius.

[0049] A network analyzer was used to connect the millimeter wave frequency expansion head and two horn antennas, and the free space method was used to measure the intensity of the W-band signal incident from the convex surface and received from the concave surface. The incident angle coverage when the received signal strength was 50% of the transmitted signal strength was tested at different incident angles. After testing, the radome made by the method of Example 2 had the largest incident angle coverage, and the incident angle ranges of Comparative Examples 3 and 4 were 72% and 78% of that of Example 2, respectively.

[0050] It can be seen from the examples and comparative examples that the material of the present invention can not only allow the communication signal to pass well, but also achieve effective signal focusing. The antenna cover in the embodiment can also be made by adding a shell to ensure the strength of the finished antenna cover, and similar changes also fall within the scope of protection of the present invention.

Claims

1. A wave-transmitting material with signal focusing function, characterized in that: The material is made by pressing two resins with a dielectric constant difference of less than 3. During the pressing process, the two resins penetrate each other to form a dielectric constant gradient, and the dielectric constant value of the formed material decreases from the side with a high dielectric constant before pressing to the side with a low dielectric constant before pressing. The two resins with a dielectric constant difference of less than 3 that constitute the material are two thermoplastic resins that can be heated and blended, each of which has a dielectric constant less than 4 and a difference between the two of which is greater than 0.5 and less than 1.

8.

2. The wave-transmitting material with signal focusing function according to claim 1, characterized in that: The two resins whose dielectric constants differ by less than 3 are polyethersulfone, polypropylene, polystyrene, polyethylene, polylactic acid, polyurethane, polymethyl methacrylate, polyvinyl chloride, polyethylene terephthalate, polycarbonate, polyimide, polyphenylene sulfide, polyetherimide, and two of their copolymers or blends.

3. The wave-transmitting material with signal focusing function according to claim 1, characterized in that: It is composed of polyethersulfone and polypropylene with a dielectric constant difference of less than 3.

4. The wave-transmitting material with signal focusing function according to claim 3, characterized in that: The polyethersulfone constituting the material is a polyethersulfone having a bisphenol A structure in the main chain.

5. A method for preparing a wave-transmitting material with a signal focusing function, characterized in that: This is accomplished by the following steps: Step 1, pressing a resin A with a high dielectric constant and a resin B with a low dielectric constant whose dielectric constant differs from that of the resin A by less than 3 into sheets respectively, wherein the resin A and the resin B whose dielectric constants differ by less than 3 are two thermoplastic resins capable of being heated and blended, each of which has a dielectric constant less than 4 and a difference between the two of which is greater than 0.5 and less than 1.8; Step 2, stacking the material A sheet and the material B sheet together, and pressing them into a sheet whose dielectric constant value decreases from the side with a high dielectric constant before pressing to the side with a low dielectric constant before pressing; Step 3, forming the sheet pressed in step 2 into a flat plate shape, a spherical shape, a cone shape, a rectangular cover shape, or a cube cover shape by foaming and / or vacuum forming and / or hot pressing of a mold.

6. The method for preparing a wave-transmitting material with a signal focusing function according to claim 5, characterized in that: The pressing into sheets in step 1 and step 2 is carried out by roller pressing at room temperature, hot roller pressing or hot pressing on a flat plate vulcanizer.

7. The method for preparing a wave-transmitting material with a signal focusing function according to claim 5, characterized in that: The thickness of the sheet pressed in step 1 is between 0.01 and 100 mm.

8. A communication device, characterized in that: It contains the wave-transmitting material as claimed in claim 1.

9. A communication device according to claim 8, characterized in that: The communication device is a millimeter wave antenna cover.

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