Hydrophobically modified aluminum oxide and polytetrafluoroethylene composite film as well as preparation method and application thereof

Abstract

The invention relates to a hydrophobically modified aluminum oxide and polytetrafluoroethylene composite film as well as a preparation method and application thereof. According to the present invention, the aluminum oxide is firstly subjected to hydroxylation treatment, and then the surface of the aluminum oxide is subjected to hydrophobic treatment by using cyclosilazane, such that the Al-OH content of the prepared hydrophobic modified aluminum oxide surface is low, such that the water absorption rate of the aluminum oxide-PTFE composite film is low, and the aluminum oxide-PTFE composite film is not easily interfered by moisture, and has good electrical insulation performance. In addition, amino groups (-NH2) or imino groups (-NH-) are further introduced into the surface of the hydrophobic modified aluminum oxide and can form hydrogen-bond interaction with C-F bonds in PTFE, so that the compatibility of the hydrophobic modified aluminum oxide and the PTFE is improved, and the mechanical property of the aluminum oxide-PTFE composite film can still be kept under the condition of high addition amount of aluminum oxide.

Description

Technical Field

[0001] The present invention belongs to the technical field of polytetrafluoroethylene composite materials, and particularly relates to a hydrophobic modified alumina, a highly water-proof polytetrafluoroethylene film, a preparation method thereof and an application thereof. Background Art

[0002] With the continuous update and rapid development of current microwave communication technologies, high-frequency microwave substrates have been widely used in fields such as satellite navigation systems and 5G communication services. There is an urgent need for polymer dielectric materials with better performance and higher stability for high-frequency microwave substrates. The requirements for polymer dielectric materials are high chemical corrosion resistance, strong hydrophobicity, and excellent dielectric properties.

[0003] Among them, polytetrafluoroethylene (PTFE) is a multifunctional polymer material with excellent properties, having good chemical inertness, outstanding dielectric properties, low hydrophilicity and hygroscopicity, and high thermal stability. In particular, PTFE has an extremely low loss tangent (tan δ = 0.0003) and a reliable dielectric constant ( ε r = 2.1), and is widely used in high-frequency microwave composite substrates. However, the low inherent thermal conductivity of PTFE itself ( λ = 0.3 W / m K) severely limits the further application of PTFE in microwave composite substrates, especially in highly integrated components. This is because the low thermal conductivity of the material makes it difficult to transfer the heat generated by the increased power of electronic components in a timely manner, thereby affecting the performance, lifespan, and safety of electronic components. Therefore, a key problem to be solved is how to improve the thermal conductivity of PTFE polymers so that they can meet the requirements.

[0004] The conventional method is to use a scheme of inorganic-organic composite materials, including adding various ceramic powder fillers with high thermal conductivity to improve the thermal performance of PTFE polymers themselves, such as aluminum nitride (AlN), alumina (Al2O3), zinc oxide (ZnO), graphene nanosheets (GNP), hexagonal boron nitride (HBN), or a mixture of multiple materials above. Among them, Al2O3 is the preferred filler for PTFE composite materials due to its low dielectric constant, low cost (much cheaper than AlN or BN), high thermal conductivity (20 - 30 W·m -1 ·K -1 ), high resistivity, and low coefficient of thermal expansion.

[0005] Most of the polymer composites used in high-frequency microwave composite substrate materials have a low dielectric constant but a high dielectric loss. However, the surface of Al2O3 contains a large number of polar functional groups with adsorbed water (such as Al-OH, etc.). When used as a high-frequency substrate filler, it will cause instability of the dielectric constant and an increase in the dielectric loss, thus affecting the transmission effect of high-frequency signals. Therefore, it is necessary to modify its surface to ensure the overall hydrophobicity and mechanical properties of the PTFE composite material. At the same time, the thermal expansion coefficient (CTE) of the modified alumina-PTFE composite film is close to that of copper, which is suitable for use as a material for making high-frequency copper-clad laminates. Summary of the Invention

[0006] Aiming at the defects of the prior art, the technical problem to be solved by the present invention is to provide a preparation method and application of hydrophobic modified alumina and high waterproof polytetrafluoroethylene film.

[0007] To achieve the above technical objectives, the technical solutions adopted by the present invention are as follows: In the first aspect, a hydrophobic modified alumina is first hydroxylated and then surface modified with cyclosilazane.

[0008] Among them, the hydroxylation treatment includes: dry hydroxylation or wet hydroxylation, and the content of oxygen-containing functional groups on the surface of alumina is increased through hydroxylation.

[0009] The dry hydroxylation is plasma hydroxylation, and the surface of alumina is treated with plasma by gas.

[0010] Preferably, the gas includes one or a combination of water vapor, oxygen, ozone, and air.

[0011] Preferably, the dry hydroxylation specifically includes: putting alumina powder into a plasma device for discharge treatment; Preferably, the temperature of the discharge treatment is from room temperature to 80 °C; Preferably, the discharge power is 3 - 30 W; Preferably, the discharge treatment time is 10 - 120 min.

[0012] The wet hydroxylation is to hydroxylate the surface of alumina with sodium hydroxide solution, ammonia-hydrogen peroxide solution or piranha solution, dissolve and corrode the organic matter or metal impurities on the surface of alumina and break the surface bonds to form Al-OH groups.

[0013] Among them, the structural general formula of the cyclosilazane is: ; R1 is selected from alkyl or alkamino groups with 1 to 10 carbon atoms. Preferably, R1 is selected from -CH3 or -CH2CH2NH 2； R2 is selected from alkyl groups having 1 to 10 carbon atoms. Preferably, R2 is selected from -CH 3； R3 and R4 may be the same or different and are selected from alkyl groups having 1 to 4 carbon atoms. Preferably, R3 and R4 are the same and are selected from -CH3 or -CH2CH 3。

[0014] Preferably, the cyclic silazane is selected from: or any one of them; Furthermore, the surface modification method includes: mixing the hydroxylated alumina with the cyclic silazane; Preferably, the mixing temperature is from room temperature to 180 °C; more preferably, the mixing temperature is from room temperature to 80 °C; Preferably, the mixing time is 15 - 150 min; more preferably, the mixing time is 15 - 60 min; Preferably, a high-speed mixing and coating machine is used to mix the hydroxylated alumina with the cyclic silazane; Preferably, the rotational speed of the central rotating shaft of the high-speed mixing and coating machine during mixing is 5 - 30 m / s.

[0015] In a second aspect, the above-mentioned hydrophobic modified alumina is used in the preparation of a polytetrafluoroethylene film.

[0016] In a third aspect, a polytetrafluoroethylene composite film includes: the above-mentioned hydrophobic modified alumina and polytetrafluoroethylene; wherein, the polytetrafluoroethylene is selected from polytetrafluoroethylene powder or polytetrafluoroethylene aqueous dispersion; Preferably, the polytetrafluoroethylene is selected from polytetrafluoroethylene aqueous dispersion; more preferably, the solid content of the polytetrafluoroethylene aqueous dispersion is 40 - 80 wt%; Furthermore, the ratio of the hydrophobic modified alumina to the polytetrafluoroethylene resin is 0.2 - 0.5 (w / w); Preferably, the ratio of the hydrophobic modified alumina to the polytetrafluoroethylene resin is 0.24 - 0.42 (w / w); More preferably, the ratio of the hydrophobic modified alumina to the polytetrafluoroethylene resin is 0.36 - 0.42 (w / w); In a fourth aspect, the preparation method of the above-mentioned polytetrafluoroethylene composite film includes: mixing and drying the hydrophobic modified alumina and polytetrafluoroethylene, placing the dried product in a mold and pressing it under pressure, and then drying it again to obtain the polytetrafluoroethylene composite film.

[0017] Preferably, the drying is vacuum drying; Preferably, the temperature of the vacuum drying is 80~110°C; Preferably, the conditions for the pressure pressing are room temperature and a pressure of 10~100 MPa; more preferably, the conditions for the pressure pressing are room temperature and a pressure of 30~100 MPa.

[0018] Preferably, after the pressure pressing is completed, it is dried at 80~150°C for 10~300 min.

[0019] Fifth aspect, the application of the above-mentioned polytetrafluoroethylene composite film in the preparation of high-frequency copper clad laminates.

[0020] The beneficial effects of the present invention are as follows: First, the alumina is hydroxylated, and then the surface of the alumina is hydrophobized with cyclosilazane. Cyclosilazane is easy to undergo a ring-opening reaction with the surface hydroxyl groups of alumina, and has a better binding effect on Al-OH compared with conventional silane coupling agents. The content of Al-OH on the surface of the prepared hydrophobically modified alumina is lower, so it has a better hydrophobic effect. After preparing the alumina-PTFE composite film, the water absorption rate is lower, it is not easily interfered by moisture, the CTE is relatively lower and close to that of copper, and the electrical insulation performance is better, which can provide a clearer high-frequency signal transmission.

[0021] In addition, amino (-NH2) or imino (-NH-) is introduced on the surface of the hydrophobically modified alumina, which can form hydrogen bond interactions with the C-F bonds in PTFE, thereby increasing the compatibility between the two, and still maintaining the mechanical properties of the alumina-PTFE composite film under the condition of a high addition amount of alumina. Description of the Drawings

[0022] Figure 1 It is the infrared spectrogram of the modified alumina prepared in Example 1, 2 and Comparative Example 1, 2, where: (a) hydroxylated alumina of Comparative Example 1; (b) hydrophobically modified alumina of Comparative Example 2; (c) hydrophobically modified alumina of Example 1; (d) hydrophobically modified alumina of Example 2.

[0023] Figure 2 It is the XRD spectrogram of the alumina-PTFE composite film prepared in Example 1-1, the hydrophobically modified alumina prepared in Example 1, the alumina-PTFE composite film prepared in Comparative Example 1-1, the hydroxylated alumina prepared in Comparative Example 1, and PTFE.

[0024] Figure 3 It is the alumina-PTFE composite film with different addition amounts of hydrophobically modified alumina (Example 1-1, Example 1-2 and Example 1-3). Detailed Embodiments

[0025] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0026] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0027] If the specific experimental conditions are not specified in the examples, they are usually in accordance with the conventional conditions in the art or the conditions recommended by the reagent company; the materials, reagents, etc. used in the examples, unless otherwise specified, can be obtained through commercial channels.

[0028] Example 1 1 kg of α-alumina with 325 mesh was pulverized to 600 mesh by a knife mill, and then ultrafinely pulverized to 2000 mesh by a jet mill, with a bulk density of 40 kg / m 3 , the pulverized alumina powder was put into a low-temperature plasma device, using oxygen as the carrier gas, starting plasma discharge treatment for 30 min, the temperature was set at 40 °C, the carrier gas flow rate was 50 mL / min, the discharge power was 5 W, and then the alumina powder treated by plasma was added to a high-speed mixing and coating machine for modification. 105 g of N-methyl-aza-2,2,4-trimethylsilacyclopentane (CAS: 18387-19-4) was added to the high-speed mixing and coating machine for surface modification. The modification temperature was 65 °C, the modification time was 0.5 h, and the rotational speed of the central rotating shaft of the high-speed mixing and coating machine during the modification process was 20 m / s, obtaining hydrophobic modified alumina powder.

[0029] The hydrophobic modified alumina powder of Example 1 was fully mixed with AD916E type PTFE aqueous dispersion (Asahi Glass, Japan, solid content 60 wt%) under mechanical stirring for 2 h, and then vacuum dried at 105 °C. The dried product was ground into powder in a high-speed grinder and placed in a mold, and pressed at room temperature and a pressure of 50 MPa for 30 min, and finally dried at 120 °C for 60 min at a heating rate of 1 °C / min. After cooling, a polytetrafluoroethylene composite film was obtained.

[0030] Among them, the ratios of the hydrophobic modified alumina powder to the PTFE resin in the PTFE aqueous dispersion are 0.24, 0.36, and 0.42 (weight ratio, w / w) respectively, and the corresponding polytetrafluoroethylene composite films are denoted as: Example 1-1, Example 1-2, and Example 1-3.

[0031] Example 2 The pretreatment steps are the same as those in Example 1. Subsequently, the above-mentioned ultrafine alumina powder and 105 g of N-(2-aminoethyl)-2,2,4-trimethyl-1-aza-2-silacyclopentane (CAS: 18246-33-8) are added to a high-speed mixing and coating machine for surface modification. The modification temperature is room temperature, the modification time is 0.5 h, and the rotational speed of the central rotating shaft of the high-speed mixing and coating machine during the modification process is 20 m / s to obtain the hydrophobic modified alumina powder.

[0032] Referring to the method of Example 1 for the polytetrafluoroethylene composite film, among them, the ratios of the hydrophobic modified alumina powder to the PTFE resin in the PTFE aqueous dispersion are 0.24, 0.36, and 0.42 (weight ratio, w / w) respectively, and the corresponding polytetrafluoroethylene composite films are denoted as: Example 2-1, Example 2-2, and Example 2-3.

[0033] Comparative Example 1 1 kg of 325-mesh α-alumina is crushed to 600 mesh by a knife mill and then ultrafinely crushed to 2000 mesh by a jet mill, with a bulk density of 40 kg / m 3 . The crushed alumina powder is put into a low-temperature plasma device, using oxygen as the carrier gas, starting plasma discharge treatment for 30 min, the temperature is set at 40 °C, the carrier gas flow rate is 50 mL / min, and the discharge power is 5 W. Then the alumina powder treated by plasma is directly used for the modification of polytetrafluoroethylene. The ultrafine alumina powder and the AD916E type PTFE aqueous dispersion (Asahi Glass, Japan, solid content 60 wt%) are fully mixed under mechanical stirring for 2 h, and then vacuum dried at 105 °C. The dried product is ground into powder in a high-speed grinder and placed in a mold, and pressed at room temperature and a pressure of 50 MPa for 30 min. Finally, it is dried at 120 °C for 60 min at a heating rate of 1 °C / min, and the polytetrafluoroethylene composite film is obtained after cooling.

[0034] Among them, the ratios of the ultrafine alumina powder to the PTFE resin in the PTFE aqueous dispersion are 0.24, 0.36, and 0.42 (weight ratio, w / w) respectively, and the corresponding polytetrafluoroethylene composite films are denoted as: Comparative Example 1-1, Comparative Example 1-2, and Comparative Example 1-3.

[0035] Comparative Example 2 1 kg of α-aluminum oxide with 325 mesh was crushed to 600 mesh by a knife mill, and then ultrafinely crushed to 2000 mesh by a jet mill. The bulk density was 40 kg / m 3 , and the crushed alumina powder was put into a low-temperature plasma device. Using oxygen as the carrier gas, plasma discharge treatment was started for 30 min, the temperature was set at 40 °C, the carrier gas flow rate was 50 mL / min, and the discharge power was 5 W. Then, the alumina powder treated by plasma was added to a high-speed mixing and coating machine for modification. 105 g of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (silane coupling agent KH792) was added to the high-speed mixing and coating machine for surface modification. The modification temperature was 65 °C, the modification time was 0.5 h, and the rotational speed of the central rotating shaft of the high-speed mixing and coating machine during the modification process was 20 m / s, obtaining hydrophobic modified alumina powder.

[0036] The hydrophobic modified alumina powder of Comparative Example 2 was fully mixed with AD916E type PTFE aqueous dispersion (Asahi Glass, Japan, solid content 60 wt%) under mechanical stirring for 2 h, and then vacuum dried at 105 °C. The dried product was ground into powder in a high-speed grinder and placed in a mold, and pressed at room temperature and a pressure of 50 MPa for 30 min. Finally, it was dried at 120 °C for 60 min at a heating rate of 1 °C / min, and a polytetrafluoroethylene composite film was obtained after cooling.

[0037] Among them, the ratios of the hydrophobic modified alumina powder to the PTFE resin in the PTFE aqueous dispersion were 0.24, 0.36, and 0.42 (weight ratio, w / w) respectively, and the corresponding polytetrafluoroethylene composite films were denoted as: Comparative Example 2-1, Comparative Example 2-2, and Comparative Example 2-3.

[0038] Testing Part Attenuated total reflection (ATR) infrared spectroscopy tests were carried out on the hydrophobic modified alumina powders of Examples 1 and 2, and the hydroxylated alumina powders or hydrophobic modified alumina powders of Comparative Examples 1 and 2. The test results are as Figure 1 shown.

[0039] X-ray diffraction (XRD, Rigaku, SmartLab, Japan) analysis was carried out on the modified alumina powders, PTFE, and alumina-PTFE composite films of Example 1 and Comparative Example 1. The diffraction source was CuK α ray, λ = 0.15402 nm, the scanning speed was 10 / min, and the step size was 0.02. The test results are as Figure 2 shown.

[0040] The surface morphologies of the alumina-PTFE composite films prepared in Examples 1-1, 1-2, and 1-3 were analyzed using a scanning electron microscope (SEM, HITACHI S4800). The test results are asFigure 3 as shown

[0041] The tensile strength of the alumina-PTFE composite films prepared in Examples 1-1, 1-2, 1-3, Examples 2-1, 2-2, 2-3, Comparative Examples 1-1, 1-2, 1-3 and Comparative Examples 2-1, 2-2, 2-3 was tested using a universal testing machine (RWT 10), where the loading rate was 5 mm / min.

[0042] The coefficient of thermal expansion (CTE) of the alumina-PTFE composite films prepared in Examples 1-1, 1-2, 1-3, Examples 2-1, 2-2, 2-3, Comparative Examples 1-1, 1-2, 1-3 and Comparative Examples 2-1, 2-2, 2-3 was tested using a thermomechanical analyzer (ZRPY-1600).

[0043] The water absorption of the alumina-PTFE composite films prepared in Examples 1-1, 1-2, 1-3, Examples 2-1, 2-2, 2-3, Comparative Examples 1-1, 1-2, 1-3 and Comparative Examples 2-1, 2-2, 2-3 was tested with reference to the water absorption test method in IPC-TM-650 test standard 2.6.2.

[0044] With reference to the method for testing the dielectric constant of stripline under X-band in IPC-TM-650 test standard 2.5.5.5, the dielectric constant and loss tangent of the alumina-PTFE composite films prepared in Examples 1-1, 1-2, 1-3, Examples 2-1, 2-2, 2-3, Comparative Examples 1-1, 1-2, 1-3 and Comparative Examples 2-1, 2-2, 2-3 were tested using a vector network analyzer (Agilent, N5244A) at a frequency of 10 GHz (X-band).

[0045] The relevant test results above are listed in Table 1.

[0046] From the test results in Table 1, it can be seen that the alumina-PTFE composite film modified with cyclosilazane has a higher tensile strength, which may be related to the formation of hydrogen bonds between -NH- or -NH₂ formed after the ring-opening of cyclosilazane and the C-F bonds in PTFE, improving the mechanical properties of the composite film through intermolecular forces. At the same time, the alumina modified with cyclosilazane has lower water absorption, is not easily interfered by moisture, and has a relatively lower CTE. In the range where the addition amount of hydrophobic modified alumina powder is 36 - 42 wt%, the CTE of the corresponding modified alumina-PTFE film is about 20 - 30 ppm / °C, which is close to that of copper. Therefore, the alumina-PTFE composite film modified with cyclosilazane has a reasonable thermal expansion coefficient matching that of copper. In addition, the alumina-PTFE composite film modified with cyclosilazane has a relatively lower loss tangent, which may be related to its lower water absorption rate. During the high-frequency signal processing process, it can improve the overall efficiency, reduce the heating phenomenon, provide a clearer signal transmission, reduce signal attenuation and distortion, and is more suitable for application in high-frequency microwave communication technologies.

[0047] Table 1

[0048] For Comparative Examples 1-1, 1-2, and 1-3, unmodified alumina and PTFE were directly used to prepare composite films. Due to the poor compatibility between the two, the mechanical properties of the composite films decreased significantly. At the same time, the measured CTE was relatively high, with a large difference from the CTE of copper, indicating poor matching between the composite film and copper. Moreover, the water absorption rate of the composite film was relatively high because alumina reacted with the oxygen gas flow during the plasma hydroxylation treatment to form alumina hydroxyl groups (Al-OH) on the surface, thereby increasing the hydrophilicity of the alumina-PTFE composite film and resulting in relatively high CTE and loss tangent of the composite film.

[0049] For Comparative Examples 2-1, 2-2, and 2-3, alumina was modified with an amino-containing silane coupling agent KH792. Since the silane coupling agent contains more -Si-OR groups, it is difficult to hydrolyze completely and react completely with the aluminum hydroxyl groups (Al-OH) on the alumina surface. Moreover, -Si-OR or Si-O-Si in the silane coupling agent is prone to reverse reaction with water molecules to form Si-OH, resulting in stronger hygroscopicity of the composite film due to its higher hydrophilicity, and further leading to relatively high CTE and loss tangent of the composite film.

[0050] Regarding the content of aluminum hydroxyl groups (Al-OH) on the surface of modified alumina, semi-quantitative analysis was carried out through infrared spectroscopy characterization. From Figure 1 the infrared spectra, it can be seen that the content of aluminum hydroxyl groups (Al-OH) in the hydroxylated alumina and KH792-modified alumina of Comparative Examples 1 and 2 is relatively higher (lines a and b at 1639 and 1073 cm-1 The absorption peak intensity at this position is relatively stronger), while the content of aluminum hydroxide (Al-OH) of the alumina modified by cyclosilazane in Examples 1 and 2 is significantly lower (the absorption peak intensity of lines c and d at 1639 and 1073 cm -1 is relatively weaker), and the hydrocarbon group content is relatively higher (the absorption peak at 2971 cm of lines c and d -1 is more obvious). This confirms that the higher water absorption rate of the alumina-PTFE composite films of Examples 1-1, 1-2, 1-3, Examples 2-1, 2-2, and 2-3 is related to the surface hydroxyl content of the modified alumina. Using cyclosilazane to participate in the modification of alumina powder can better reduce the surface hydroxyl groups of the modified alumina, reduce the water absorption rate, and improve the insulation performance of the composite film.

[0051] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of them. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention. Although the specific implementation manners of the present invention have been described above, it is not a limitation to the protection scope of the present invention. Those skilled in the art should understand that based on the technical solutions of the present invention, various modifications or deformations that can be made without creative efforts by those skilled in the art are still within the protection scope of the present invention.

Claims

1. A hydrophobic modified alumina, characterized in that, First, hydroxylate alumina, and then use cyclosilazane to modify the surface of alumina; The hydroxylation treatment includes: dry hydroxylation or wet hydroxylation, and the content of oxygen-containing functional groups on the surface of alumina is increased through hydroxylation; The structural general formula of the cyclic silazane is as follows: ; Among them, R1 is selected from alkyl or alkylamino groups with 1 to 10 carbon atoms; R2 is selected from alkyl groups with 1 to 10 carbon atoms; R3 and R4 may be the same or different, and are selected from alkyl groups with 1 to 4 carbon atoms; The method of the surface modification includes: mixing the hydroxylated alumina with cyclosilazane.

2. The hydrophobic modified alumina according to claim 1, wherein The dry hydroxylation is plasma hydroxylation, and the surface of alumina is treated by plasma with gas; And / or, the wet hydroxylation is to use sodium hydroxide solution, ammonia-hydrogen peroxide solution or piranha solution to hydroxylate the surface of alumina, dissolve and corrode the organic substances or metal impurities on the surface of alumina and break the surface bonds to form Al-OH groups.

3. The hydrophobic modified alumina according to claim 2, wherein The gas includes one or a combination of water vapor, oxygen, ozone and air; And / or, the dry hydroxylation specifically includes: putting alumina powder into a plasma device for discharge treatment.

4. The hydrophobic modified alumina according to claim 1, wherein The cyclosilazane is selected from: or any one of them 5. Use of the hydrophobically modified alumina according to any one of claims 1-4, characterized in that, Application of hydrophobic modified alumina in the preparation of polytetrafluoroethylene film.

6. A polytetrafluoroethylene composite film, characterized in that, The polytetrafluoroethylene composite film includes: the hydrophobic modified alumina according to any one of claims 1-4 and polytetrafluoroethylene; Among them, the polytetrafluoroethylene is selected from polytetrafluoroethylene powder or polytetrafluoroethylene aqueous dispersion.

7. The polytetrafluoroethylene composite film according to claim 6, wherein The ratio of the hydrophobic modified alumina to the polytetrafluoroethylene resin is 0.2~0.5 (w / w).

8. The preparation method of the polytetrafluoroethylene composite film according to any one of claims 6-7, characterized in that, The preparation method includes: mixing and drying the hydrophobic modified alumina and polytetrafluoroethylene, placing the dried product in a mold and pressing it under pressure, and then drying it again to obtain the polytetrafluoroethylene composite film.

9. The preparation method of the polytetrafluoroethylene composite film according to claim 8, wherein, The drying is vacuum drying; And / or, the conditions of the pressure pressing are room temperature and a pressure of 10~100 MPa; And / or, after the pressure pressing is completed, it is dried at 80~150 °C for 10~300 min.

10. Use of the polytetrafluoroethylene composite film according to any one of claims 6-7, characterized in that, Application of the polytetrafluoroethylene composite film in the preparation of high-frequency copper clad laminate.

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