EPTFE membrane material with low dielectric loss performance, elliptical holes and island-shaped microscopic characteristics and application of ePTFE membrane material in cable

Abstract

The invention discloses an ePTFE membrane material with low dielectric loss performance, oval holes and island-shaped microscopic characteristics and application of the ePTFE membrane material in a cable, a micropore network structure of the ePTFE membrane material comprises PTFE resin fibers which are connected with one another to form an irregular island-shaped PTFE resin fiber structure, the structure is a supporting framework of the micropore network structure, and the micropore network structure is formed by the PTFE resin fibers and the irregular island-shaped PTFE resin fiber structure. The oval holes are distributed in the supporting framework and are defined by the boundaries of the island-shaped PTFE resin fiber structures. According to the mode, the unique micropore structure has an extremely low dielectric constant due to the fact that the unique micropore structure is rich in insulating air, and the ePTFE membrane material is rich in air components and high-purity PTFE resin fibers, so that the polarization degree can be remarkably weakened, and the dielectric loss of high-frequency and high-speed electric signals in the ePTFE membrane material can be greatly reduced; therefore, energy dissipation in the signal transmission process is reduced to the minimum, and high strength and low attenuation of communication signals in long-distance transmission can be ensured on the application level, so that stable and high-speed data interaction transmission between devices is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer functional materials, in particular to an ePTFE film with low dielectric loss performance and elliptical hole and island-shaped micro features and its application in cables. BACKGROUND

[0002] With the rapid development of 5G / 6G communication, AI computing center and other high-frequency high-speed application scenarios, the signal transmission frequency has gradually increased to 400GHz or even 1.6Tbps, which puts extremely strict requirements on the dielectric properties of cable insulation materials. The energy loss in high-frequency signal transmission is mainly caused by the dielectric loss of the material. Although traditional engineering plastics such as LCP (dielectric constant about 2.8-3.2), PI, PPO, etc. have certain applications, their dielectric constants are mostly higher than 2.6, and the dielectric loss factor is generally above 0.01, which is difficult to meet the demand for ultra-low signal attenuation in the terahertz frequency band in the future. In addition, although the existing foamed cable has certain low dielectric properties, it lacks mechanical strength and is easily damaged by external impact, and is prone to aging failure in complex environments, which seriously restricts its reliable application in high-end communication cables.

[0003] At present, in order to achieve a lower dielectric constant, the industry generally introduces air voids into the insulation layer by foaming or filling processes. However, the void structure formed by traditional foaming processes is often unevenly distributed, randomly shaped, and poorly controllable in size, making it difficult to simultaneously achieve stable low dielectric properties and good mechanical support. For example, although ordinary ePTFE films have micro-porous structures, their pore morphology lacks directional design, which cannot effectively suppress polarization loss under high-frequency electric fields, and it is also difficult to ensure the dimensional stability and flexibility during wrapping. Therefore, the development of a new type of insulation material that is rich in gas in a controllable micro-porous structure, has excellent dielectric properties and reliable mechanical strength, has become a key technical bottleneck for promoting the development of high-frequency communication cables.

[0004] In view of the above problems, although some research attempts to optimize material properties by using multi-layer composite or chemical modification, etc., the contradiction between "high porosity to achieve ultra-low dielectric constant" and "high strength support structure to ensure mechanical reliability" has not been fundamentally solved. The market urgently needs a new generation of high-frequency insulation material that can be innovated through material microstructure, while maintaining low dielectric loss, good forming processability and environmental adaptability, to support the demand for high-speed, low-latency, high-stable signal transmission in future communication systems. SUMMARY

[0005] The technical problem solved by the present application is to provide an ePTFE film material with low dielectric loss performance and island-shaped micro features, which has a micro-porous network structure, and the micro-porous network structure comprises:

[0006] To solve the above technical problems, the present application adopts one technical solution: providing an ePTFE film material with low dielectric loss performance and island-shaped micro features, which has a micro-porous network structure, and the micro-porous network structure comprises: PTFE resin fibers, which are connected to each other to form an irregular island-shaped PTFE resin fiber structure, the structure being a support framework of the micro-porous network structure, and the characteristic size being 20 nanometers to 100 micrometers; and an elliptical hole, which is scattered in the support framework and surrounded by the boundary of the island-shaped PTFE resin fiber structure, the major axis length of the elliptical hole being 50 nanometers to 50 micrometers, the minor axis length being 50 nanometers to 50 micrometers, and the width of the PTFE resin fiber constituting the boundary of the elliptical hole being 20 nanometers to 50 micrometers; The elliptical hole and the island-shaped PTFE resin fiber structure together form a three-dimensional special-shaped hole channel, which is rich in air, and the PTFE resin fiber has high purity, and through the synergistic effect of the air-rich hole component and the high-purity PTFE resin fiber, the polarization degree is reduced and the dielectric loss of high-frequency high-speed electrical signals in the ePTFE film material is reduced, so that the dielectric constant Dk of the ePTFE film material is between 1.3 and 2.9, and the loss tangent Df is between 0.00005 and 0.001.

[0007] Through the synergistic effect of the island-shaped fiber framework and the elliptical hole of a specific size, a stable micro-porous network structure is constructed, the unification of ultra-high porosity and mechanical stability of the material is realized, and the material has good mechanical strength and processing performance while maintaining extremely low dielectric constant and loss factor.

[0008] In a preferred embodiment of the present application, the island-shaped PTFE resin fiber structure contains irregular secondary micro-porous channels inside, and the gap of the secondary micro-porous channels is 10 nanometers to 30 micrometers. The addition of secondary micro-porous channels inside the island-shaped PTFE resin fiber structure further reduces the overall dielectric constant of the material, enhances the flexibility and gas permeability of the material, and at the same time maintains the structural integrity.

[0009] In a preferred embodiment of the present application, the thickness of the ePTFE film is 0.01 mm to 0.35 mm, and the apparent density is 0.02 g / cm3 to 2 g / cm3.

[0010] By specifying the range of physical parameters of the film material for different application scenarios, the material can meet the needs of ultra-thin applications and provide sufficient mechanical support, and the dielectric properties of the material can be accurately controlled by adjusting the density.

[0011] In a preferred embodiment of the present application, the porosity of the microporous network structure is 25% to 95%. By controlling the porosity in this high range, it is intended to maximize the filling of air in the microporous structure, thereby substantially reducing the overall dielectric constant of the material, while ensuring that the film material maintains the necessary mechanical strength and structural integrity.

[0012] In a preferred embodiment of the present application, the width of the PTFE resin fibers constituting the boundary of the elliptical hole is 20 nm to 50 microns. By controlling the fiber width in this nanometer to micron range, it is intended to form sufficiently fine fibers to build a high-porosity structure, while ensuring that the fibers themselves have sufficient mechanical strength to constitute a stable three-dimensional network support skeleton.

[0013] To solve the above technical problems, another technical solution adopted by the present application is to provide a preparation method of an ePTFE film with low dielectric loss performance and elliptical hole and island-shaped micro features, comprising the following steps: S1: material preparation and mixing: mix and stir PTFE resin powder and aviation kerosene in a predetermined ratio in a constant temperature environment to form a paste-like material; S2: aging: allow the paste-like material to stand and age in a constant temperature environment; S3: preforming: sequentially push and extrude the aged paste-like material to first form a cylindrical blank, and then push and extrude it into a thin diameter cylindrical disc; S4: calendering and secondary aging: calender the thin diameter cylindrical disc under constant temperature conditions to form a narrow strip disc, and allow the narrow strip disc to stand still under constant temperature; S5: two-way film stretching: unwind the narrow strip disc after secondary aging, and simultaneously stretch it in the axial and width directions under constant pressure and temperature conditions to cause the PTFE material to expand and form a microporous film with the elliptical hole and island-shaped PTFE resin fiber structure; S6: heat setting and cooling: heat set the wide-width film after two-way stretching in a constant pressure and temperature oven, and then cool it in a constant pressure and temperature oven; S7: post-processing: edge cutting and winding of the cooled film to obtain the ePTFE film.

[0014] Through precisely controlled process steps and parameters, the ePTFE film material with specific microstructure can be prepared. The directional formation of the elliptical hole and island-shaped structure is realized, the consistency and repeatability of product performance are ensured, the process controllability is strong, and the process is suitable for large-scale production.

[0015] To solve the above technical problems, another technical solution adopted by the present application is to provide an application of an ePTFE film material with low dielectric loss performance and elliptical hole and island-shaped microstructure in a cable. The ePTFE film material is cut into wrapping tape, which is used to wrap the cable conductor to form the insulating layer of the cable. The use of the ePTFE film material with ultra-low dielectric loss significantly reduces signal transmission attenuation and improves communication quality, and its good flexibility facilitates processing and installation.

[0016] In a preferred embodiment of the present application, the width of the wrapping tape is 2.5 mm to 30 mm, and the continuous length is more than 600 m, which ensures continuous and efficient wrapping process, reduces joints, and improves the efficiency and quality consistency of cable production.

[0017] In a preferred embodiment of the present application, the cable is an aviation cable, a robot cable, a radio frequency coaxial cable, a data cable, a radiation detection device cable or a medical cable. For the needs of different cable types, a high-performance insulation solution is provided to meet the stringent requirements of signal integrity for high-end applications such as radio frequency communication, data transmission and medical equipment.

[0018] The present application has the following advantages: the unique "island-shaped PTFE resin fiber structure" and "elliptical hole" constitute a microporous network, high porosity and air-filled pores, which makes the overall dielectric constant of the material extremely low and the loss factor extremely small, essentially solving the problem of high-frequency signal transmission attenuation; the interconnected island-shaped structure as a solid support framework gives the film excellent mechanical strength, tear resistance and dimensional stability, overcoming the inherent defects of poor mechanical properties of traditional porous materials.

[0019] The preparation method provided by the present application can accurately and repeatedly construct the required elliptical hole and island-shaped fiber structure through the core step of "bidirectional stretching film formation". By controlling the stretching conditions, heat setting temperature and other parameters, the size, shape and porosity of the micropores can be effectively controlled, thereby realizing accurate control of the final performance of the product and ensuring the uniformity and stability of the product performance, laying a solid foundation for large-scale industrial production.

[0020] The ePTFE film material is made into a wrapping tape for application to a cable insulation layer. The low dielectric loss characteristics of the film material can be directly converted into lower signal insertion loss and higher transmission rate, significantly improving the communication quality and efficiency of 5G / 6G, AI computing center and other scenarios. The inherent low friction coefficient and flexibility of the material make the wrapping process faster and more efficient, while reducing damage to the conductor. The low density characteristics help to achieve the lightweight of the cable, especially suitable for aerospace and other fields. The material has stable dielectric properties in a wide temperature range of-80℃ to 250℃, is resistant to chemical corrosion, and can meet the stringent requirements of reliability and durability for various high-end application scenarios such as RF coaxial cables, data cables, medical cables and the like. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Figure 1 is a scanning electron microscope image of the ePTFE film material with low dielectric loss performance and elliptical hole and island-shaped micro features prepared in Example 1 of the present application, magnified 5000 times; Figure 2 is a scanning electron microscope image of the ePTFE film material with low dielectric loss performance and elliptical hole and island-shaped micro features prepared in Example 1 of the present application, magnified 20000 times; Figure 3 is a scanning electron microscope image of the ePTFE film material with low dielectric loss performance and elliptical hole and island-shaped micro features prepared in Example 2 of the present application, magnified 8000 times; Figure 4 is a scanning electron microscope image of the ePTFE film material with low dielectric loss performance and elliptical hole and island-shaped micro features prepared in Example 2 of the present application, magnified 20000 times; Figure 5 is a scanning electron microscope image of the ePTFE film material with low dielectric loss performance and elliptical hole and island-shaped micro features prepared in Example 3 of the present application, magnified 3000 times; Figure 6 is a scanning electron microscope image of the ePTFE film material with low dielectric loss performance and elliptical hole and island-shaped micro features prepared in Example 3 of the present application, magnified 5000 times; Figure 7 is a structural schematic diagram of the wrapping tape being wound to a tray. DETAILED DESCRIPTION

[0022] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will be clearly and completely described the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative labor are within the scope of protection of the present application.

[0024] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0025] In the description of the present application, it should be noted that the terms "front", "back" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship when the product of the present application is usually placed, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0026] In the description of the present application, it should also be noted that, unless otherwise explicitly specified and limited, the terms "arrangement", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0027] In the present application, unless otherwise explicitly specified and limited, the first feature above or below the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the first feature above, above and above the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature below, below and below the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0028] Embodiments of the present application include: Embodiment 1: A method for preparing an ePTFE membrane material with low dielectric loss performance and elliptical hole and island-shaped micro features, comprising the following steps: S1: Preparation and mixing: In a constant temperature environment of 25°C, accurately weigh the PTFE resin powder with a specific molecular weight and aviation kerosene (as a lubricant) according to a mass ratio of 100:18. Put the mixture into a blender and stir at a constant speed for 30 minutes until a paste-like material with uniform composition and no dry powder particles is formed.

[0029] S2: Curing: Transfer the paste-like material obtained in step S1 to a constant temperature curing room (temperature maintained at 25°C) and store for 24 hours to allow the internal components of the material to fully diffuse and homogenize.

[0030] S3: Preforming: Put the cured paste-like material into a plunger extruder. Under the set extrusion pressure, the material is first extruded into a larger diameter cylindrical blank (e.g., about 50 mm in diameter) through a mold. Then, the blank is extruded again through a smaller aperture mold to form a dense fine diameter cylindrical disc material with a diameter of about 10 mm for subsequent calendering.

[0031] S4: Calendering and secondary curing: Send the fine diameter cylindrical disc material obtained in step S3 to a constant temperature (e.g., 30°C) calendering machine. By rolling through one or several pairs of calendering rollers, the cylindrical disc material is calendered into a narrow strip disc material with uniform thickness (e.g., about 1.5 mm thick). Then, the narrow strip disc material is again stored at 30°C for 12 hours to complete the secondary curing to eliminate the internal stress generated by calendering.

[0032] S5: Two-way stretching to form a film: Install the secondary cured narrow strip disc material onto the unwinding device of a two-way stretching machine. Under constant environmental temperature (e.g., a specific temperature about 20-50°C below the PTFE melting point) and tension control, simultaneously perform synchronous two-way stretching in the longitudinal and transverse directions. The key parameters of this embodiment are: the longitudinal stretching ratio is set to 3:1 and the transverse stretching ratio is set to 8:1. During this process, the PTFE matrix undergoes plastic deformation and fiberization, and the film blank with island-shaped fibers and elliptical hole microstructure is formed.

[0033] S6: Heat setting and cooling: Guide the wide-width film blank obtained after two-way stretching in step S5 into a constant pressure and temperature tunnel oven. The heat setting temperature is set to 320°C. The film material passes through this high temperature zone under tension, allowing the PTFE molecular chain segments to move, rearrange and crystallize, thereby fixing the microstructure formed by stretching and obtaining dimensional stability. Then, the film material is slowly cooled to room temperature (e.g., below 60°C) in the cooling section of the oven while maintaining tension.

[0034] S7: Post-treatment The width of the cooled and shaped ePTFE web is detected on-line, and the two sides of the web are trimmed using sharp blades to make the width conform to the specifications. The final ePTFE web is obtained.

[0035] The thickness of the web obtained in this example is 0.08 mm, the density is 0.5 g / cm3, and the porosity is about 80%. As Figures 1-2 Scanning electron microscope observation shows that the island-shaped PTFE fiber structure has moderate size and good connection (size about 0.5-20 μm), and the elliptical holes are uniformly distributed (major axis about 1-15 μm, minor axis about 0.5-8 μm). The dielectric constant Dk can be as low as 1.3, and the loss tangent Df is about 0.0002. This web achieves a good balance between low dielectric loss, mechanical strength and processing performance, and is suitable for the insulation layer of most high-frequency high-speed communication cables.

[0036] Example 2: A method for preparing an ePTFE web having low dielectric loss performance and island-shaped microstructure with elliptical holes, comprising the following steps: S1: Preparation and mixing: As in Example 1, mix and stir the PTFE resin powder and aviation kerosene at a mass ratio of 100:18 in a constant temperature environment of 25°C to form a uniform paste material.

[0037] S2: Curing: The paste material is cured at 25°C for 24 hours.

[0038] S3: Preforming: As in Example 1, use a plunger extruder to extrude the paste material into a thin cylindrical disc material with a diameter of about 10 mm.

[0039] S4: Calendering and secondary curing: As in Example 1, calender the cylindrical disc material into a narrow strip material with a thickness of about 1.5 mm, and then stand still at a constant temperature of 30°C for 12 hours.

[0040] S5: Film formation by two-way stretching: The narrow strip material after secondary curing is unwound and fed into a two-way stretching machine. As in Example 1, under similar constant temperature and pressure conditions, the longitudinal stretching ratio is increased to 4:1, and the transverse stretching ratio is increased to 10:1. The stretching temperature is fine-tuned to facilitate molecular chain orientation and hole expansion under higher stress. Higher stretching ratio makes the PTFE nodes be pulled apart more fully, the fiber bundles become more elongated, the size of the formed elliptical holes becomes larger, and the porosity increases significantly.

[0041] S6: Heat setting and cooling The stretched membrane material was heat-set. To partially retain the loose structure formed by high stretching while ensuring basic dimensional stability, a relatively low heat-setting temperature of 300°C was chosen. It was then slowly cooled to room temperature. The lower heat-setting temperature suppressed some thermal shrinkage of the fiber network, thus better preserving the high porosity and macroporous structure formed by high stretching.

[0042] S7: Post-processing involves trimming the edges of the membrane material and rewinding it to obtain the final ePTFE membrane material.

[0043] The membrane material obtained in this embodiment has a thickness of 0.12 mm, a density of 0.15 g / cm³, and a porosity of approximately 92%, according to the test results.

[0044] like Figure 3 The scanning electron microscope image (×8000) of the ePTFE membrane material shown exhibits typical high porosity characteristics in its microstructure. The island-shaped PTFE fiber structure is even finer (approximately 0.2-10 μm in size), and the size of the elliptical pores enclosed by it is significantly increased (major axis approximately 5-30 μm, minor axis approximately 2-15 μm); as shown... Figure 4 The scanning electron microscope image (×20000) of the ePTFE membrane material shown shows that the island-shaped structure is composed of a rich network of secondary micropores formed by interwoven nanofibers. This multi-level microporous network is the structural basis for achieving ultra-low dielectric properties.

[0045] Based on its unique microstructure, this material exhibits exceptional dielectric properties: its dielectric constant Dk can be reduced to 1.5, and its loss tangent Df is approximately 0.00008. This film material possesses extremely low dielectric loss characteristics, making it suitable for ultra-high frequency communication cables (such as 5G / 6G millimeter waves and internal interconnects of AI computing centers) where signal attenuation requirements are most stringent.

[0046] Example 3: A method for preparing an ePTFE membrane material with low dielectric loss, featuring elliptical pores and island-shaped microstructures, comprising the following steps: Steps S1-S4 are the same as in Example 1.

[0047] S5: Biaxial stretching for film formation: The narrow strip material after secondary curing is unwound and biaxially stretched. Under constant temperature and pressure conditions similar to Example 1, the longitudinal stretch ratio is controlled at 2.5:1 and the transverse stretch ratio is controlled at 6:1. The smaller stretch ratio allows the PTFE matrix to be moderately stretched, resulting in thicker fibers, denser nodes (island structures), smaller elliptical pore size, and moderate porosity.

[0048] S6: heat setting and cooling: heat setting the stretched film. In order to obtain excellent dimensional stability and higher mechanical strength, the heat setting temperature is increased to 340℃, followed by slow cooling to room temperature. Higher heat setting temperature makes PTFE molecular chain movement more sufficient, the fiber network under tension occurs more significant thermal shrinkage and crystallization, the structure becomes more dense and stable, mechanical strength (such as tensile strength) is significantly improved, but the porosity will be reduced.

[0049] S7: post-processing: edge cutting of the film, and winding to obtain the final ePTFE film.

[0050] It is detected that the film obtained in this embodiment has a thickness of 0.05 mm, a density of 1.2 g / cm³, and a porosity of about 45%. As Figures 4-5 Scanning electron microscope observation shows that the island-shaped PTFE fiber structure is more massive and closely connected (size about 1-40 μm), and the elliptical hole size is small and regular (major axis about 0.5-12 μm, minor axis about 0.3-5 μm). Its dielectric constant Dk can be reduced to 1.6, and the loss tangent Df is about 0.0007. This film has higher mechanical strength, dimensional stability and creep resistance while maintaining excellent low dielectric properties, and is suitable for cable scenarios that require frequent bending, movement or high mechanical protection requirements (such as robot joint wire harness, drag chain cable).

[0051] Embodiment 4: This embodiment describes in detail that by adjusting the preparation process parameters of embodiments 1 to 3, especially the key steps of bidirectional stretching and heat setting, low dielectric loss ePTFE films with different microstructure characteristics and performance spectrum can be prepared: a microporous network composed of unique "island-shaped PTFE resin fiber structure" and "elliptical hole".

[0052] PTFE resin fibers, which are connected to each other to form an irregular island-shaped PTFE resin fiber structure, which is a support skeleton of the microporous network structure, and the characteristic size is 20 nanometers to 100 micrometers.

[0053] and elliptical holes, which are scattered in the support skeleton and enclosed by the boundary of the island-shaped PTFE resin fiber structure, the major axis length of the elliptical hole is 50 nanometers to 50 micrometers, the minor axis length is 50 nanometers to 50 micrometers, and the width of the PTFE resin fiber constituting the boundary of the elliptical hole is 20 nanometers to 50 micrometers. The porosity of the microporous network structure is 25% to 95%. The dielectric constant Dk of the ePTFE film is between 1.3 and 2.9, and the loss tangent Df is between 0.00005 and 0.001.

[0054] By the synergistic effect of island-shaped fiber skeleton and elliptical hole of specific size, a micro-porous network structure filled with air in the stable structure is constructed, realizing the unity of ultra-high porosity and mechanical stability of the material, so that the material has good mechanical strength and processing performance while maintaining extremely low dielectric constant and loss factor.

[0055] By accurately adjusting the two-way stretching and heat setting process parameters, the microstructure can be accurately controlled to obtain a series of film materials with different properties: 1. When the medium stretching ratio (such as 3:1 in the longitudinal direction and 8:1 in the transverse direction) in Example 1 is used in combination with a standard heat setting temperature (such as 320°C), the obtained film shows a balanced structure, and the microstructure is shown in the high magnification electron micrograph in FIG. 1. The characteristics are: the island-shaped structure has moderate size, and the fiber connection is clear; the elliptical hole size is uniform, and the long axis is mainly distributed in the range of 1-15 μm; the overall porosity is moderate (about 85%). This structure makes the film maintain low dielectric constant (Dk can be as low as 1.3) while having good mechanical properties and processing performance, which is a general preferred solution suitable for most high-frequency cable insulation. Figures 1-2 2. When the high stretching ratio (such as 4:1 in the longitudinal direction and 10:1 in the transverse direction) in Example 2 is used in combination with a relatively low heat setting temperature (such as 300°C), the obtained film shows a typical high-porosity (about 80%) fibrous structure, and the microstructure is shown in the high magnification electron micrograph in FIG. 2. The characteristics are: the island-shaped structure is fully stretched, and the fiber is thin; the elliptical hole size is relatively large, and the long axis is mainly distributed in the range of 5-30 μm; the overall porosity is extremely high (can be above 80%). This structure gives the film extremely low apparent density (can be as low as about 0.15 g / cm³) and ultra-low dielectric constant (Dk can be as low as 1.5), which is very suitable for ultra-high frequency communication scenarios with the most stringent requirements for signal loss.

[0056] Figures 3-4 3. When the lower stretching ratio (such as 2.5:1 in the longitudinal direction and 6:1 in the transverse direction) in Example 3 is used in combination with a higher heat setting temperature (such as 340°C), the obtained film shows a denser structure with lower porosity, and the microstructure is shown in the high magnification electron micrograph in FIG. 3. The characteristics are: the island-shaped structure is thick and the fiber network is dense; the elliptical hole size is relatively small, and the long axis is mainly distributed in the range of 0.5-8 μm; the overall porosity is reduced (about 70%). This structure increases the apparent density of the film (can be as high as 1.2 g / cm³), and the mechanical strength, dimensional stability and creep resistance are best, while still maintaining excellent low dielectric properties (Dk can be as low as 1.6), which is suitable for occasions with stringent requirements for mechanical strength and service life, such as cables that are frequently bent or high-temperature environments.

[0057] Figures 5-6

[0058] ​​​In summary, the present application precisely regulates the core process combination of PTFE paste preparation, two-way stretching (stretching ratio, temperature) and heat setting (temperature) to directionally prepare a series of ePTFE microporous membranes. This precise control of the microstructure is directly translated into the final performance capability of the product, thereby meeting the specific needs of different application scenarios from extreme signal transmission to durability in harsh environments, fully embodying the advanced nature, flexibility and strong industrial application value of the preparation method of the present application.

[0059] Example 5: Application of ePTFE wrapping tape in high-end cables The ePTFE film material roll prepared in Examples 1-3 is used as raw material, and the wrapping tape manufacturing process is as follows: production line process preparation: including film roll 1, unwinding, using a sharp hard alloy blade to continuously cut the film into a specific tape width required by the customer, winding, inspection, and warehousing.

[0060] Through this process, wrapping tape products with a tape width range of 2.5 mm to 30 mm and a continuous length of more than 600 meters can be prepared and wound onto the tower tray 2, as shown in Figure 7 .

[0061] The wrapping tape prepared above is spirally wrapped outside the cable conductor (such as copper, silver or silver-plated copper wire) by high-speed wrapping equipment at a certain overlap rate (such as 50%), forming a uniform and tight insulation layer. According to application requirements, this insulation layer can be used alone or as part of a combined insulation.

[0062] The main performance indicators of the wrapping tape product are shown in the following table: The ePTFE wrapping tape of the present application can be widely used in the following high-end cable scenarios: Medium insulation layer of RF coaxial cable: provides a low-loss signal transmission channel for 5G / 6G base stations and millimeter wave communication.

[0063] Wrapping insulation of high-speed data cable (such as SAS, PCIe): improves the integrity and speed of data transmission within AI computing centers.

[0064] Insulation layer of radiation detection device cable: meets the requirements of high-precision instruments for signal stability and environmental resistance.

[0065] Insulation of medical device cable (such as MRI nuclear magnetic resonance equipment): has low dielectric loss and biocompatibility.

[0066] Insulation and sheath of aerospace wiring system: meets the extreme requirements of lightweight, wide temperature range, and high reliability.

[0067] Insulation layer of flexible power and control cable for AI robots: its low-friction, bend-resistant properties are perfect for frequent movement scenarios.

[0068] Insulation of high-end device power supply lines: provides high dielectric strength and heat resistance.

[0069] The present application solves the problem of high-frequency signal transmission attenuation by the unique "island-shaped PTFE resin fiber structure" and "elliptical hole" network, high porosity, and the characteristics of the pores filled with air, which make the overall dielectric constant of the material extremely low and the loss factor extremely small. The interconnected island-shaped structure serves as a solid support framework, giving the film excellent mechanical strength, tear resistance, and dimensional stability, overcoming the inherent defects of poor mechanical properties of traditional porous materials.

[0070] The preparation method provided by the present application can accurately and repeatedly construct the required elliptical holes and island-shaped fiber structure through the core step of "bidirectional stretching film formation". By controlling the stretching conditions, heat setting temperature and other parameters, the size, shape and porosity of the micropores can be effectively regulated, thereby realizing accurate control of the final performance of the product and ensuring the uniformity and stability of the product performance, laying a solid foundation for large-scale industrial production.

[0071] The ePTFE film is made into a wrapping tape for cable insulation layer, and the low dielectric loss characteristics of the film can be directly converted into lower signal insertion loss and higher transmission rate, significantly improving the communication quality and efficiency of 5G / 6G, AI power center and other scenarios. The low friction coefficient and flexibility of the material make the wrapping process faster and more efficient, while reducing damage to the conductor. Its low density characteristics help to achieve the lightweight of the cable, especially suitable for aerospace and other fields. The material has stable dielectric properties in a wide temperature range of -80℃ to 250℃, is resistant to chemical corrosion, and can meet the strict requirements of reliability and durability for various high-end application scenarios such as radio frequency coaxial cables, data cables, medical cables, etc.

[0072] The above only describes the embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation using the content of the present application specification, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. An ePTFE film material having elliptical hole and island-shaped microfeatures with low dielectric loss properties, characterized by, The ePTFE film has a microporous network structure, the microporous network structure comprises: PTFE resin fibers connected to each other to form irregular island-shaped PTFE resin fiber structures, the structures are a supporting framework of the microporous network structure, the feature size is 20 nanometers to 100 micrometers; and elliptical holes interspersed in the supporting framework, the elliptical holes are enclosed by boundaries of the island-shaped PTFE resin fiber structures, the major axis length of the elliptical holes is 50 nanometers to 50 micrometers, and the minor axis length of the elliptical holes is 50 nanometers to 50 micrometers; the elliptical holes and the island-shaped PTFE resin fiber structures jointly form a three-dimensional special-shaped hole channel, the hole channel is rich in air, the PTFE resin fibers have high purity, and through the synergistic effect of the air-rich hole channel component and the high-purity PTFE resin fibers, the degree of polarization is reduced and the dielectric loss of high-frequency high-speed electrical signals in the ePTFE film is reduced, so that the dielectric constant Dk of the ePTFE film is between 1.3 and 2.9, and the loss tangent Df is between 0.00005 and 0.

001.

2. The ePTFE film material having elliptical hole and island-shaped micro-features with low dielectric loss properties according to claim 1, characterized by, The island-shaped PTFE resin fiber structures internally comprise irregular secondary microporous hole channels, and the gap of the secondary microporous hole channels is 10 nanometers to 30 micrometers.

3. The ePTFE film material having low dielectric loss properties of elliptical hole and island-shaped micro-features according to claim 1, characterized by, The thickness of the ePTFE film is 0.01 millimeters to 0.35 millimeters, and the apparent density is 0.02 grams per cubic centimeter to 2 grams per cubic centimeter.

4. The ePTFE film material having low dielectric loss properties of elliptical hole and island-shaped micro-features according to claim 1, characterized by, The porosity of the microporous network structure is 25% to 95%.

5. The ePTFE film material of claim 1 having low dielectric loss properties, wherein the elliptical hole and island-shaped micro-features are characterized by, The width of the PTFE resin fibers constituting the boundaries of the elliptical holes is 20 nanometers to 50 micrometers.

6. The method of claim 1-5, wherein the ePTFE film having low dielectric loss properties of elliptical hole and island-shaped micro-features is prepared by the steps of: The method comprises the following steps: S1: material preparation and mixing: PTFE resin powder and aviation kerosene are mixed and stirred in a predetermined ratio in a constant temperature environment to form a paste material; S2: aging: the paste material is aged in a constant temperature environment; S3: preforming: the aged paste material is sequentially pushed to form a cylindrical blank, and then is pushed into a thin-diameter cylindrical disc material; S4: calendering and secondary aging: the thin-diameter cylindrical disc material is calendered under constant temperature conditions to form a narrow strip disc material, and the narrow strip disc material is aged under constant temperature conditions; S5: two-way film stretching: the narrow strip disc material after secondary aging is unwound, and is simultaneously stretched in the axial and width directions under constant pressure and temperature conditions, so that the PTFE material is expanded to form a microporous film having the elliptical holes and the island-shaped PTFE resin fiber structures; S6: heat setting and cooling: the wide-width film material after two-way stretching is heat set in a constant pressure and temperature oven, and then is cooled in a constant pressure and temperature oven; S7: post-processing: the cooled film material is edge cut and wound to obtain the ePTFE film.

7. Use of an ePTFE film having elliptical hole and island microfeatures with low dielectric loss properties in a cable, characterized in that, The ePTFE film of any one of claims 1 to 5 is cut to form a wrapping tape, and the wrapping tape is used to wrap a cable conductor to form an insulation layer of the cable.

8. Use of the ePTFE film with low dielectric loss properties having elliptical holes and island-shaped microfeatures according to claim 7 in cables, characterized in that, The width of the wrapping tape is 2.5 millimeters to 30 millimeters, and the continuous length is more than 600 meters.

9. Use of the ePTFE film with low dielectric loss properties having elliptical holes and island-shaped microfeatures according to claim 7 in cables, characterized in that, The cable is an aviation cable, a robot cable, a radio frequency coaxial cable, a data cable, a radiation detection device cable, or a medical cable.

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