Spherical silicon dioxide, polytetrafluoroethylene film and high-frequency copper-clad laminate and preparation method thereof

Abstract

The present invention relates to the technical field of copper clad laminates, and discloses a spherical silica, a polytetrafluoroethylene film, a high-frequency copper clad laminate, and a preparation method thereof. The preparation method of the spherical silica comprises the following steps: (1) mixing a cationic surfactant with a sodium hydroxide solution; (2) mixing the obtained first solution with polytetrafluoroethylene to obtain a second solution; (3) mixing tetraethoxysilane and a modifier to obtain a mixed solution; (4) mixing the mixed solution with the second solution to obtain a mixed liquid; (5) performing solid-liquid separation on the obtained mixture and drying the obtained solid; (6) after drying the solid, performing reflux extraction on the solid. The spherical silica has low levels of adsorbed water and polar functional groups on its surface and high dispersion. The high-frequency copper clad laminate prepared by using the spherical silica as a filler has a uniform structure, a uniform and stable dielectric constant, and extremely low dielectric loss.

Description

Technical Field

[0001] The invention relates to the technical field of copper clad laminates, and in particular to spherical silicon dioxide, a polytetrafluoroethylene film, a high-frequency copper clad laminate and a preparation method thereof. Background Art

[0002] With the rapid increase in communication speeds and frequencies in the 5G / 6G communications field, the use of high-frequency bands in electronic devices and communications equipment is expanding. The 10 GHz band is gaining popularity due to its wideband, linear propagation, and high transparency. For example, in the automotive field, millimeter-wave radars used for collision avoidance require high-frequency materials in the 76-79 GHz range.

[0003] In high-frequency applications, circuit signal transmission loss increases rapidly with increasing frequency. This is primarily due to a combination of the skin effect of wires, the glass fiber effect, and the dielectric loss of the substrate material. The dielectric loss of the substrate material contributes particularly significantly to circuit signal transmission loss. Therefore, substrate materials used in high-frequency devices must not only have a stable dielectric constant but also extremely low dielectric loss.

[0004] Polymer materials used in high-frequency substrates often have low dielectric constants but high dielectric loss. However, ceramic materials often have the opposite property: high dielectric constants but low dielectric loss. To combine these properties and create high-frequency substrates with both low dielectric constants and low dielectric loss, ceramics are typically filled with polymer resins to create new composite materials, a common global approach.

[0005] Since the dielectric constant of silicon dioxide (SiO2) is small (3.7), the dielectric loss value is relatively small (0.0002@1MHZ), the expansion coefficient (0.5×10 -6 ) is low, and is currently the preferred filler for high-frequency substrate materials. In order to facilitate the uniform mixing of various resins for use as high-frequency substrate fillers, silica is synthesized into spherical shapes as much as possible. However, existing spherical silica fillers are basically limited in that the uniform particle size distribution of the resulting spherical silica is difficult to control, and the surface contains a large amount of adsorbed water and polar functional groups (such as silanol hydroxyl groups). When used as a high-frequency substrate filler, it will lead to unstable dielectric constant and increased dielectric loss, thereby affecting the transmission of high-frequency signals. Summary of the Invention

[0006] The purpose of the present invention is to overcome the problem in the prior art that when existing spherical silica is used as a filler for a high-frequency substrate, the dielectric constant becomes unstable and the dielectric loss increases, thereby affecting the transmission of high-frequency signals. The present invention provides spherical silica, a polytetrafluoroethylene film, a high-frequency copper clad laminate, and a preparation method thereof.

[0007] In order to achieve the above object, the present invention provides a method for preparing spherical silica.

[0008] The method comprises the following steps:

[0009] (1) mixing a cationic surfactant with a sodium hydroxide solution to obtain a first solution;

[0010] (2) mixing polytetrafluoroethylene with the first solution to obtain a second solution;

[0011] (3) mixing tetraethoxysilane and a modifier to obtain a mixed solution;

[0012] (4) mixing the mixed solution with the second solution at 70 to 90° C., and then stirring at 20 to 30° C. to obtain a mixture;

[0013] (5) subjecting the mixture to solid-liquid separation, and subjecting the obtained solid to vacuum freeze-drying;

[0014] (6) vacuum drying the solid obtained in step (5), then reflux extraction, and then vacuum drying to obtain spherical silica;

[0015] The modifier is selected from at least one of (3,3,3-trifluoropropyl)trimethoxysilane, (3,3,3-trifluoropropyl)triethoxysilane, 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane.

[0016] Preferably, in step (1), the cationic surfactant is cetyltrimethylammonium bromide and / or cetyltriethylammonium bromide;

[0017] Preferably, in step (1), the weight ratio of the cationic surfactant to the sodium hydroxide in the sodium hydroxide solution is 1:0.01-0.2;

[0018] Preferably, in step (1), the mass fraction of sodium hydroxide in the sodium hydroxide solution is 0.01 to 0.1%;

[0019] Preferably, in step (1), the mixing conditions include: a temperature of 80 to 100° C. and a stirring speed of 500 to 1000 rpm;

[0020] Preferably, in step (2), the mixing conditions include: a temperature of 80 to 100° C. and a stirring speed of 500 to 1000 rpm.

[0021] Preferably, in step (3), the weight ratio of the tetraethoxysilane to the modifier is 100:1-15.

[0022] Preferably, in step (6), the solvent used for reflux extraction is 95% ethanol;

[0023] Preferably, in step (6), the reflux extraction time is 5 to 7 hours.

[0024] The second aspect of the present invention provides spherical silica prepared by the method described above.

[0025] A third aspect of the present invention provides a method for preparing polytetrafluoroethylene, the method comprising the following steps:

[0026] A1. Mix spherical silica with water, disperse it ultrasonically, let it stand, remove the precipitate, and obtain a stable dispersion;

[0027] A2. Adding the dispersion to a polytetrafluoroethylene solution under stirring to obtain a slurry;

[0028] A3, coating the slurry on a mold and drying it to obtain a polytetrafluoroethylene film;

[0029] Wherein, the spherical silica is the spherical silica according to claim 5.

[0030] Preferably, the weight ratio of the spherical silica to polytetrafluoroethylene is 1:1.5-4.

[0031] Preferably, in step A2, the polytetrafluoroethylene solution is prepared according to the following process: mixing polytetrafluoroethylene with water, wherein the weight ratio of polytetrafluoroethylene to water is 1:1 to 20;

[0032] Preferably, in step A2, the stirring speed is 500-1000 rpm;

[0033] Preferably, in step A2, the dispersion is added at a rate of 50 to 70 mL / min;

[0034] Preferably, in step A3, the drying conditions include: a temperature of 110 to 130° C. and a time of 60 to 90 minutes.

[0035] A fourth aspect of the present invention provides a polytetrafluoroethylene film produced by the method described above.

[0036] A fifth aspect of the present invention provides a high-frequency copper-clad laminate, comprising the spherical silica or polytetrafluoroethylene film as described above.

[0037] The preparation method of spherical silica provided by the present invention stabilizes a metastable intermediate hydrogel in a reaction process by adding polytetrafluoroethylene; adjusts the size, crystallization speed and crystallization state of the obtained silica nuclei by changing the addition and hydrolysis speed of the precursor, so that the composition and structure of the synthesized silica are uniform and stable, and the size distribution is narrow; and the surface of the silica is modified by using a modifier, and the content of adsorbed water and polar functional groups on the surface of the prepared spherical silica is reduced through the design of the preparation steps, and the spherical silica has a high dispersion.

[0038] The method for preparing a polytetrafluoroethylene film provided by the present invention uses the highly dispersed spherical silica as a filler, so that the spherical silica can be uniformly dispersed in a polytetrafluoroethylene skeleton, thereby ensuring that the performance of the obtained polytetrafluoroethylene film is uniform and stable. In a high-frequency use environment, the polytetrafluoroethylene and spherical silica in the polytetrafluoroethylene film are difficult to undergo mutual phase conversion, so the dielectric constant is low and very stable.

[0039] The high-frequency copper-clad laminate provided by the present invention uses the above-mentioned spherical silica or polytetrafluoroethylene film as a raw material. When the high-frequency copper-clad laminate is used at high frequencies (i.e., within the millimeter wave band), when high-frequency electromagnetic waves pass through the medium, the highly dispersed spherical silica and polytetrafluoroethylene molecules will also reduce the probability of lattice collisions back and forth, so that the high-frequency copper-clad laminate has ultra-low dielectric loss, which can effectively reduce the signal loss generated by the high-frequency PCB board made of the copper-clad laminate in a high-frequency use environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The spherical silica prepared in Example 1 of the present invention;

[0041] Figure 2 The polytetrafluoroethylene film prepared in Example 1 of the present invention;

[0042] Figure 3 The high-frequency copper-clad laminate is prepared in a test example of the present invention. DETAILED DESCRIPTION

[0043] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0044] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0045] The present invention provides a method for preparing spherical silicon dioxide, which comprises the following steps:

[0046] (1) mixing a cationic surfactant with a sodium hydroxide solution to obtain a first solution;

[0047] (2) mixing polytetrafluoroethylene with the first solution to obtain a second solution;

[0048] (3) mixing tetraethoxysilane and a modifier to obtain a mixed solution;

[0049] (4) mixing the mixed solution with the second solution at 70 to 90° C., and then stirring at 20 to 30° C. to obtain a mixture;

[0050] (5) subjecting the mixture to solid-liquid separation, and subjecting the obtained solid to vacuum freeze-drying;

[0051] (6) vacuum drying the solid obtained in step (5), then reflux extraction, and then vacuum drying to obtain spherical silica;

[0052] The modifier is selected from at least one of (3,3,3-trifluoropropyl)trimethoxysilane, (3,3,3-trifluoropropyl)triethoxysilane, 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane.

[0053] In the present invention, by adding a cationic surfactant, the subsequently generated silica particles can be stably dispersed in the solvent. The present invention does not particularly limit the specific selection of the cationic surfactant, and it can be a cationic surfactant commonly used in the art. In a preferred embodiment, the cationic surfactant is hexadecyltrimethylammonium bromide and / or hexadecyltriethylammonium bromide. By selecting the above cationic surfactants, the performance of the spherical silica obtained is improved and the cost is low.

[0054] In a preferred embodiment, the modifier is (3,3,3-trifluoropropyl)trimethoxysilane and / or (3,3,3-trifluoropropyl)triethoxysilane. By selecting the above-mentioned modifier, the dielectric properties of the high-frequency copper-clad laminate made from the spherical silica are better. This may be because the surface functional group (3,3,3-trifluoropropyl) after the reaction of [(3,3,3-trifluoropropyl)trimethoxysilane and / or (3,3,3-trifluoropropyl)triethoxysilane] with the surface hydroxyl group of the oxide is easier to fuse with the PTFE resin body than the surface functional group (3-aminopropyl) after the reaction of [3-aminopropyltrimethoxysilane and / or 3-aminopropyltriethoxysilane] with the surface hydroxyl group of the oxide, thereby making the structure of the obtained PTFE film film and the high-frequency copper-clad laminate more uniform and stable, and less likely to absorb moisture from the environment.

[0055] In a preferred embodiment, in step (1), the weight ratio of the cationic surfactant to the sodium hydroxide in the sodium hydroxide solution is 1:0.01 to 0.2, specifically, for example, 1:0.01, 1:0.02, 1:0.05, 1:0.07, 1:0.09, 1:0.1, 1:0.15, 1:0.18 or 1:0.2.

[0056] In a preferred embodiment, in step (1), the mass fraction of sodium hydroxide in the sodium hydroxide solution is 0.01 to 0.1%, more preferably 0.01 to 0.02%.

[0057] In a specific embodiment, in step (1), the mixing conditions include: a temperature of 80 to 100° C. and a stirring speed of 500 to 1000 rpm.

[0058] In a specific embodiment, in step (2), the mixing conditions include: a temperature of 80 to 100° C. and a stirring speed of 500 to 1000 rpm.

[0059] In order to reduce the content of adsorbed water and polar functional groups on the surface of the prepared spherical silica and improve the dispersion, in a preferred embodiment, in step (3), the weight ratio of the tetraethoxysilane and the modifier is 100:1 to 15, specifically, for example, 100:1, 100:2, 100:5, 100:8, 100:10, 100:12 or 100:15.

[0060] In a specific embodiment, step (4) comprises: slowly dripping the mixed solution into the second solution at 70-90° C. and a stirring speed of 500-1000 rpm, then stirring at 20-30° C. and a stirring speed of 500-1000 rpm until flocculent precipitation gradually forms, and stirring for 1-3 hours to obtain a mixture. More specifically, the mixed solution is added at a rate of 10 mL / min.

[0061] The present invention does not limit the specific implementation of the solid-liquid separation in step (5), which can be a solid-liquid separation operation commonly used in the art. In a specific implementation, in step (5), the solid-liquid separation is filtration.

[0062] In a preferred embodiment, in step (6), the solvent used for reflux extraction is 95% ethanol.

[0063] In a preferred embodiment, in step (6), the reflux extraction time is 5 to 7 hours.

[0064] In a specific embodiment, step (6) comprises: heating the solid to 110-130° C. at a rate of 1-5° C. / min, vacuum drying, maintaining the set temperature for 5-6 hours, cooling to room temperature and taking out, then reflux extraction with ethanol (95%) for 5-7 hours, heating the obtained solid to 120° C. at a rate of 1-5° C. / min, vacuum drying, maintaining the set temperature for 5-6 hours, and cooling to room temperature to obtain spherical silica.

[0065] In this article, room temperature refers to 23±3°C.

[0066] The preparation method of spherical silica provided by the present invention changes the addition and hydrolysis rates of a precursor and simultaneously uses a modifier to modify the surface of the silica, so that the adsorbed water and polar functional group contents on the surface of the obtained spherical silica are very low and the dispersion is high. In this way, when the spherical silica is used as a filler for high-frequency substrates (including high-frequency copper-clad laminates and high-frequency PCBs), the obtained high-frequency substrates have a uniform structure, high peel strength, a uniform and stable dielectric constant, and extremely low dielectric loss.

[0067] The present invention also provides spherical silica prepared by the above-mentioned preparation method of spherical silica, wherein the spherical silica has a high sphericity, a low surface silanol content and is not easy to absorb water.

[0068] The present invention also provides a method for preparing a polytetrafluoroethylene film, using the above-mentioned spherical silica as a filler. The present invention is not limited to the specific preparation method of the polytetrafluoroethylene film, and the preparation steps of the polytetrafluoroethylene film filled with fillers conventional in the art can be used. In a preferred embodiment, the preparation method of the polytetrafluoroethylene film includes the following steps:

[0069] A1. Mix spherical silica with water, disperse it ultrasonically, let it stand, remove the precipitate, and obtain a stable dispersion;

[0070] A2. Adding the dispersion to a polytetrafluoroethylene solution under stirring to obtain a slurry;

[0071] A3, coating the slurry on a mold and drying it to obtain a polytetrafluoroethylene film;

[0072] Wherein, the spherical silica is the spherical silica described above.

[0073] The present invention does not limit the time of ultrasonic dispersion in step A1, as long as the spherical silica can be uniformly dispersed in water. In a specific embodiment, in step A1, the time of ultrasonic dispersion is 10 to 60 minutes.

[0074] In a preferred embodiment, the weight ratio of the spherical silica to polytetrafluoroethylene is 1:1.5-4. Within the above dosage range, the obtained polytetrafluoroethylene has better performance, so that the dielectric constant of the high-frequency copper clad laminate prepared therefrom is more stable and the dielectric loss is lower.

[0075] In a specific embodiment, in step A2, the polytetrafluoroethylene solution is prepared according to the following process: polytetrafluoroethylene is mixed with water, wherein the weight ratio of polytetrafluoroethylene to water is 1:1-20.

[0076] In a specific embodiment, in step A2, the stirring speed is 500-1000 rpm. By fully mixing the dispersion containing spherical silica and the polytetrafluoroethylene solution at the above stirring speed, the spherical silica can be more evenly dispersed in the polytetrafluoroethylene skeleton.

[0077] Furthermore, in step A2, the dispersion is added at a rate of 50 to 70 mL / min. At the above addition rate, the spherical silica and polytetrafluoroethylene are evenly mixed, and the operation time is short.

[0078] In a preferred embodiment, in step A3, the drying conditions include: a temperature of 110 to 130° C. and a time of 60 to 90 minutes.

[0079] The present invention also provides a polytetrafluoroethylene film prepared by the above-mentioned method for preparing the polytetrafluoroethylene film.

[0080] The present invention also provides a high-frequency copper-clad laminate comprising the spherical silica or polytetrafluoroethylene film described above. Because spherical silica has low levels of surface adsorbed water and polar groups and high dispersion, high-frequency copper-clad laminates made from spherical silica or polytetrafluoroethylene film filled with spherical silica exhibit a uniform and stable structure, high copper foil peel strength, a stable and low dielectric constant, and extremely low dielectric loss.

[0081] The present invention does not limit the preparation method of the high-frequency copper clad laminate, and the high-frequency copper clad laminate can be prepared according to conventional processes in the art. In a preferred embodiment, the high-frequency copper clad laminate is prepared according to the following process:

[0082] S1. Sinter the polytetrafluoroethylene film at 400-450°C for 2-10 minutes, then take it out and cool it down.

[0083] S2. Cutting the cooled polytetrafluoroethylene film into a desired size, covering the upper surface of the cut polytetrafluoroethylene film with a first electronic copper foil and the lower surface with a second electronic copper foil to obtain a sandwich-like system;

[0084] S3. Place the sandwich-like system obtained in step S2 between two mirror-finished steel plates (surface roughness less than ±2 μm) and place them flat in a vacuum hot press. Perform vacuum hot pressing at 380-400°C and 400-600 psi. After 1-2 hours, cool naturally while maintaining the pressure (cooling rate less than 10°C / min). Remove the two mirror-finished steel plates at room temperature to obtain a high-frequency copper clad laminate.

[0085] The present invention will be described in detail below by way of examples, but the scope of the present invention is not limited thereto. The experimental methods in the following examples, unless otherwise specified, are conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0086] In the following examples and comparative examples, parts are by weight.

[0087] Example 1

[0088] 1. Preparation of spherical silica

[0089] (1) dissolving 0.1 parts of sodium hydroxide in 500 parts of deionized water to obtain a sodium hydroxide solution, and uniformly mixing 1 part of a cationic surfactant, hexadecyltrimethylammonium bromide, with the sodium hydroxide solution at 80° C. with stirring (at a stirring speed of 1000 rpm) to obtain a first solution;

[0090] (2) slowly adding 1 part of polytetrafluoroethylene to the first solution under stirring at 80° C. (stirring speed: 1000 rpm) and mixing well to obtain a second solution;

[0091] (3) mixing 1 part of tetraethoxysilane and 1 / 10 part of a modifier at room temperature to obtain a mixed solution, wherein the modifier is (3,3,3-trifluoropropyl)trimethoxysilane;

[0092] (4) slowly adding the mixed solution obtained in step (3) to the second solution obtained in step (2) at 80° C. and high-speed stirring (stirring speed of 1000 rpm), and then stirring at room temperature and high-speed stirring (stirring speed of 1000 rpm) for 2 h, until a flocculent precipitate slowly forms to obtain a mixture;

[0093] (5) filtering the mixture containing the precipitate, freeze-drying the obtained solid under vacuum, and collecting the obtained solid;

[0094] (6) The solid obtained in step (5) was heated to 120°C at a rate of 5°C / min, vacuum dried, maintained at the set temperature for 6 hours, cooled to room temperature and taken out, and then reflux extracted with ethanol (95%) for 6 hours. The obtained solid was heated to 120°C at a rate of 10°C / min, vacuum dried, maintained at the set temperature for 6 hours, cooled to room temperature and taken out to obtain spherical silica ( Figure 1 ), the spherical silica is a white powdery solid particle aggregate.

[0095] 2. Preparation of polytetrafluoroethylene film

[0096] A1. Mix 1 part of the above-mentioned spherical silica with 100 parts of deionized water, and disperse them by ultrasonication for 60 minutes. After standing at room temperature for 30 minutes, remove the precipitate to obtain a stable dispersion;

[0097] A2. 1.88 parts of polytetrafluoroethylene were mixed with 10 parts of deionized water, and the mixture was slowly stirred (stirring speed 300 rpm) at room temperature for 1 hour to obtain a polytetrafluoroethylene solution; under conditions of high-speed stirring (stirring speed 1000 rpm) and room temperature, the dispersion obtained in A1 was slowly added (addition rate 60 mL / min) to the polytetrafluoroethylene solution to obtain a uniform coating slurry;

[0098] A3, the coating slurry is evenly applied on a polytetrafluoroethylene mold by drop coating, and dried at 120 ° C for 60 minutes, and then the mold is taken out and the film formed on the mold is peeled off while it is hot to obtain a polytetrafluoroethylene film film ( Figure 2 ), the polytetrafluoroethylene film is milky white and opaque and has a certain elasticity.

[0099] Example 2

[0100] 1. Preparation of spherical silica

[0101] (1) dissolving 0.1 parts of sodium hydroxide in 500 parts of deionized water to obtain a sodium hydroxide solution, and uniformly mixing 1 part of a cationic surfactant, hexadecyltriethylammonium bromide, with the sodium hydroxide solution at 80° C. and stirring (at a stirring speed of 1000 rpm) to obtain a first solution;

[0102] (2) slowly adding 1 part of polytetrafluoroethylene to the first solution under stirring at 80° C. (stirring speed: 1000 rpm) and mixing well to obtain a second solution;

[0103] (3) mixing 1 part of tetraethoxysilane and 1 / 10 part of a modifier at room temperature to obtain a mixed solution, wherein the modifier is (3,3,3-trifluoropropyl)trimethoxysilane;

[0104] (4) slowly adding the mixed solution obtained in step (3) to the second solution obtained in step (2) at 80° C. and high-speed stirring (stirring speed of 1000 rpm), and then stirring at room temperature and high-speed stirring (stirring speed of 1000 rpm) for 2 h, until a flocculent precipitate slowly forms to obtain a mixture;

[0105] (5) filtering the mixture containing the precipitate, freeze-drying the obtained solid under vacuum, and collecting the obtained solid;

[0106] (6) The solid obtained in step (5) was heated to 120°C at a rate of 5°C / min, vacuum dried, maintained at the set temperature for 6 hours, cooled to room temperature and taken out, and then reflux extracted with ethanol (95%) for 6 hours. The solid was heated to 120°C at a rate of 10°C / min, vacuum dried, maintained at the set temperature for 6 hours, cooled to room temperature and taken out to obtain spherical silica.

[0107] 2. Preparation of polytetrafluoroethylene film

[0108] A1. Mix 1 part of the above-mentioned spherical silica with 100 parts of deionized water, and disperse them by ultrasonication for 60 minutes. After standing at room temperature for 30 minutes, remove the precipitate to obtain a stable dispersion;

[0109] A2. Mix 1.88 parts of polytetrafluoroethylene with 10 parts of deionized water, and slowly stir (stirring speed 300 rpm) at room temperature for 1 hour to obtain a polytetrafluoroethylene solution; under high-speed stirring (stirring speed 1000 rpm) and room temperature conditions, slowly add the dispersion liquid in step A1 above (addition rate is 60 mL / min) to the polytetrafluoroethylene solution to obtain a uniform coating slurry;

[0110] A3. The coating slurry is evenly applied on a polytetrafluoroethylene mold by drop coating, and dried at 120° C. for 60 min. The mold is then removed and the film formed on the mold is peeled off while hot to obtain a polytetrafluoroethylene film.

[0111] Example 3

[0112] 1. Preparation of spherical silica

[0113] (1) dissolving 0.1 parts of sodium hydroxide in 500 parts of deionized water to obtain a sodium hydroxide solution, and uniformly mixing 1 part of a cationic surfactant, hexadecyltrimethylammonium bromide, with the sodium hydroxide solution at 80° C. with stirring (at a stirring speed of 1000 rpm) to obtain a first solution;

[0114] (2) slowly adding 1 part of polytetrafluoroethylene to the first solution under stirring at 80° C. (stirring speed: 1000 rpm) and mixing well to obtain a second solution;

[0115] (3) mixing 1 part of tetraethoxysilane and 1 / 10 part of a modifier at room temperature to obtain a mixed solution, wherein the modifier is (3,3,3-trifluoropropyl)triethoxysilane;

[0116] (4) slowly adding the mixed solution obtained in step (3) to the second solution obtained in step (2) at 80° C. and high-speed stirring (stirring speed of 1000 rpm), and then stirring at room temperature and high-speed stirring (stirring speed of 1000 rpm) for 2 h, until a flocculent precipitate slowly forms to obtain a mixture;

[0117] (5) filtering the mixture containing the precipitate, freeze-drying the obtained solid under vacuum, and collecting the obtained solid;

[0118] (6) The solid obtained in step (5) was heated to 120°C at a rate of 5°C / min, vacuum dried, maintained at the set temperature for 6 hours, cooled to room temperature and taken out, and then reflux extracted with ethanol (95%) for 6 hours. The solid was heated to 120°C at a rate of 10°C / min, vacuum dried, maintained at the set temperature for 6 hours, cooled to room temperature and taken out to obtain spherical silica.

[0119] 2. Preparation of polytetrafluoroethylene film

[0120] A1. Mix 1 part of the above-mentioned spherical silica with 100 parts of deionized water, and disperse them by ultrasonication for 60 minutes. After standing at room temperature for 30 minutes, remove the precipitate to obtain a stable dispersion;

[0121] A2. Mix 1.88 parts of polytetrafluoroethylene with 10 parts of deionized water, and slowly stir (stirring speed 300 rpm) at room temperature for 1 hour to obtain a polytetrafluoroethylene solution; under high-speed stirring (stirring speed 1000 rpm) and room temperature conditions, slowly add the dispersion liquid in step A1 above (addition rate is 60 mL / min) to the polytetrafluoroethylene solution to obtain a uniform coating slurry;

[0122] A3. The coating slurry is evenly applied on a polytetrafluoroethylene mold by drop coating, and dried at 120° C. for 60 min. The mold is then removed and the film formed on the mold is peeled off while hot to obtain a polytetrafluoroethylene film.

[0123] Example 4

[0124] 1. Preparation of spherical silica

[0125] (1) dissolving 0.1 parts of sodium hydroxide in 500 parts of deionized water to obtain a sodium hydroxide solution, and uniformly mixing 1 part of a cationic surfactant, hexadecyltriethylammonium bromide, with the sodium hydroxide solution at 80° C. and stirring (at a stirring speed of 1000 rpm) to obtain a first solution;

[0126] (2) slowly adding 1 part of polytetrafluoroethylene to the first solution under stirring at 80° C. (stirring speed: 1000 rpm) and mixing well to obtain a second solution;

[0127] (3) mixing 1 part of tetraethoxysilane and 1 / 10 part of a modifier at room temperature to obtain a mixed solution, wherein the modifier is (3,3,3-trifluoropropyl)triethoxysilane;

[0128] (4) slowly adding the mixed solution obtained in step (3) to the second solution obtained in step (2) at 80° C. and high-speed stirring (stirring speed of 1000 rpm), and then stirring at room temperature and high-speed stirring (stirring speed of 1000 rpm) for 2 h, until a flocculent precipitate slowly forms to obtain a mixture;

[0129] (5) filtering the mixture containing the precipitate, freeze-drying the obtained solid under vacuum, and collecting the obtained solid;

[0130] (6) The solid obtained in step (5) was heated to 120°C at a rate of 5°C / min, vacuum dried, maintained at the set temperature for 6 hours, cooled to room temperature and taken out, and then reflux extracted with ethanol (95%) for 6 hours. The solid was heated to 120°C at a rate of 10°C / min, vacuum dried, maintained at the set temperature for 6 hours, cooled to room temperature and taken out to obtain spherical silica.

[0131] 2. Preparation of polytetrafluoroethylene film

[0132] A1. Mix 1 part of the above-mentioned spherical silica with 100 parts of deionized water, and disperse them by ultrasonication for 60 minutes. After standing at room temperature for 30 minutes, remove the precipitate to obtain a stable dispersion;

[0133] A2. Mix 1.88 parts of polytetrafluoroethylene with 10 parts of deionized water, and slowly stir (stirring speed 300 rpm) at room temperature for 1 hour to obtain a polytetrafluoroethylene solution; under high-speed stirring (stirring speed 1000 rpm) and room temperature conditions, slowly add the dispersion liquid in step A1 above (addition rate is 60 mL / min) to the polytetrafluoroethylene solution to obtain a uniform coating slurry;

[0134] A3. The coating slurry is evenly applied on a polytetrafluoroethylene mold by drop coating, and dried at 120° C. for 60 min. The mold is then removed and the film formed on the mold is peeled off while hot to obtain a polytetrafluoroethylene film.

[0135] Example 5

[0136] The method described in Example 1 was followed, except that the amount of polytetrafluoroethylene was adjusted to 2.33 parts when preparing the polytetrafluoroethylene film.

[0137] That is, the weight ratio of spherical silica to polytetrafluoroethylene is 1:2.33, and the weight ratio of polytetrafluoroethylene to water is 2.33:10.

[0138] Example 6

[0139] The method described in Example 1 was followed, except that the amount of polytetrafluoroethylene was adjusted to 1.5 parts when preparing the polytetrafluoroethylene film.

[0140] That is, the weight ratio of spherical silica to polytetrafluoroethylene is 1:1.5, and the weight ratio of polytetrafluoroethylene to water is 1.5:10.

[0141] Example 7

[0142] The method described in Example 1 was followed, except that the modifier was 3-aminopropyltrimethoxysilane.

[0143] Comparative Example 1

[0144] The method described in Example 1 is different in that no modifier is added in step (3) of preparing spherical silica.

[0145] Comparative Example 2

[0146] The method described in Example 1 is different in that, in step (1) of preparing spherical silica, no cationic surfactant is added.

[0147] Comparative Example 3

[0148] The method described in Example 1 was followed, except that polytetrafluoroethylene was not added in step (2) of preparing spherical silica.

[0149] Material Testing

[0150] The polytetrafluoroethylene films prepared in the examples and comparative examples were made into high-frequency copper-clad laminates, and the preparation method thereof included the following steps: sintering the polytetrafluoroethylene film at 400°C for 3-7 minutes, taking it out and cooling it; cutting the cooled polytetrafluoroethylene film into a required size, covering the upper surface of the cut polytetrafluoroethylene film with a first electronic copper foil (1oz / 35micron) and the lower surface with a second electronic copper foil (1oz / 35micron) to obtain a sandwich-like system; the obtained sandwich-like system was placed between two mirror steel plates (surface roughness less than ±2um), and placed flat in a vacuum hot press, and vacuum hot pressed at 385°C and 460psi. After 2 hours, the system was naturally cooled while maintaining the pressure (the cooling rate was 5°C / min), and the two mirror steel plates were removed and taken out at room temperature to obtain a spherical silica-filled polytetrafluoroethylene-based high-frequency copper-clad laminate ( Figure 3 ).

[0151] The high-frequency copper clad laminate was subjected to performance testing. The test method was as follows: according to the IPC-TM-6502.5.5.5C (1998) standard, the dielectric constant and dielectric loss of the high-frequency copper clad laminates prepared in Examples 1-7 and Comparative Examples 1-3 were respectively tested under 10 GHz frequency electron wave radiation conditions; at the same time, the peel strength of the copper foil of the product was tested according to the IPC-TM-650 2.4.8C (1994) standard. The test results are shown in Table 1 below.

[0152] Table 1

[0153]

[0154] It can be seen from the results in Table 1 that the high-frequency copper clad laminates made from the polytetrafluoroethylene films of Examples 1-7 of the present invention have stable dielectric constants, low dielectric losses, and high copper foil peeling strength, and the high-frequency copper clad laminate made from the polytetrafluoroethylene film obtained in Example 1 has the best dielectric properties.

[0155] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preparing spherical silicon dioxide, characterized in that: The method comprises the following steps: (1) mixing a cationic surfactant with a sodium hydroxide solution to obtain a first solution; (2) mixing polytetrafluoroethylene with the first solution to obtain a second solution; (3) mixing tetraethoxysilane and a modifier to obtain a mixed solution; (4) mixing the mixed solution with the second solution at 70-90° C., and then stirring at 20-30° C. to obtain a mixture; (5) separating the mixture into solid and liquid, and freeze-drying the obtained solid in a vacuum manner; (6) vacuum drying the solid obtained in step (5), then reflux extraction, and then vacuum drying to obtain spherical silica; The modifier is selected from at least one of (3,3,3-trifluoropropyl)trimethoxysilane, (3,3,3-trifluoropropyl)triethoxysilane, 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane.

2. The method according to claim 1, characterized in that In step (1), the cationic surfactant is hexadecyltrimethylammonium bromide and / or hexadecyltriethylammonium bromide.

3. The method according to claim 1, characterized in that In step (1), the weight ratio of the cationic surfactant to the sodium hydroxide in the sodium hydroxide solution is 1:0.01-0.

2.

4. The method according to claim 1, wherein In step (1), the mass fraction of sodium hydroxide in the sodium hydroxide solution is 0.01 to 0.1%.

5. The method according to claim 1, wherein In step (1), the mixing conditions include: a temperature of 80-100° C. and a stirring speed of 500-1000 rpm.

6. The method according to claim 1, characterized in that In step (2), the mixing conditions include: a temperature of 80-100° C. and a stirring speed of 500-1000 rpm.

7. The method according to claim 1, characterized in that In step (3), the weight ratio of the tetraethoxysilane to the modifier is 100:1~15.

8. The method according to claim 1, characterized in that In step (6), the solvent used for reflux extraction is 95% ethanol.

9. The method according to claim 1, characterized in that In step (6), the reflux extraction time is 5 to 7 hours.

10. Spherical silica prepared by the method according to any one of claims 1 to 9.

11. A method for preparing a polytetrafluoroethylene film, characterized in that: The method comprises the following steps: A1. Mix spherical silica with water, disperse it ultrasonically, let it stand, remove the precipitate, and obtain a stable dispersion; A2. Adding the dispersion to a polytetrafluoroethylene solution under stirring to obtain a slurry; A3, coating the slurry on a mold and drying it to obtain a polytetrafluoroethylene film; Wherein, the spherical silica is the spherical silica according to claim 10.

12. The method according to claim 11, characterized in that The weight ratio of the spherical silica to polytetrafluoroethylene is 1:1.5-4.

13. The method according to claim 11, characterized in that In step A2, the polytetrafluoroethylene solution is prepared according to the following process: polytetrafluoroethylene is mixed with water, wherein the weight ratio of polytetrafluoroethylene to water is 1:1-20.

14. The method according to claim 11, characterized in that In step A2, the stirring speed is 500-1000 rpm.

15. The method according to claim 11, characterized in that In step A2, the dispersion is added at a rate of 50-70 mL / min.

16. The method according to claim 11, characterized in that In step A3, the drying conditions include: a temperature of 110-130° C. and a drying time of 60-90 min.

17. A polytetrafluoroethylene film produced by the method according to any one of claims 11 to 16.

18. A high-frequency copper-clad laminate, characterized in that: The high-frequency copper-clad laminate comprises the spherical silica according to claim 10 or the polytetrafluoroethylene film according to claim 17.

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