A method for producing a polyolefin bonding sheet having low dielectric constant and low dielectric loss

Abstract

A method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss, the method comprising the following steps: soaking a porous polytetrafluoroethylene film in a sodium-naphthalene-tetrahydrofuran solution, rinsing and air-drying to obtain an activated porous polytetrafluoroethylene film; adding a silane coupling agent to ethanol to form a silane coupling agent ethanol solution, immersing the porous polytetrafluoroethylene film in the silane coupling agent ethanol solution, and drying to obtain a porous polytetrafluoroethylene film with double bonds bonded to the surface; immersing inorganic fillers in the silane coupling agent ethanol solution, and drying to obtain inorganic fillers with double bonds bonded to the surface; stirring polyolefin, inorganic fillers, a flame retardant, an antioxidant, and an initiator to form a polyolefin composite glue solution; immersing the porous polytetrafluoroethylene film with double bonds bonded to the surface in the polyolefin composite glue solution, and drying to obtain a polyolefin adhesive sheet, which has the advantages of low dielectric constant, low dielectric loss, low water absorption, and the like.

Description

Technical Field

[0001] This invention relates to the field of microwave composite dielectric substrate technology, and more specifically to a method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss. Background Technology

[0002] After more than half a century of development, microwave composite dielectric substrates have gradually become an important basic material in electronic information products. With the miniaturization, high integration, and multifunctionality of microwave devices, single-layer microwave composite dielectric substrates can no longer meet practical needs. Multilayer microwave composite dielectric substrates, composed of microwave composite dielectric substrates and bonding sheets, have gradually become a research hotspot. To achieve high signal transmission rates and low signal transmission attenuation, the microwave composite dielectric substrate and bonding sheet materials must possess low dielectric constants, low dielectric losses, and low water absorption rates.

[0003] Chinese patent CN112538184A discloses a method for preparing an adhesive sheet and its application. The method involves roller-coating a resin solution onto the upper and lower surfaces of a plasma-treated polytetrafluoroethylene (PTFE) substrate to obtain the adhesive sheet. This adhesive sheet exhibits strong bonding performance. The PTFE substrate is made by impregnating glass fiber cloth with PTFE emulsion. However, the warp and weft weave structure of the glass fiber cloth leads to differences in dielectric constant in minute areas, causing the "glass fiber effect," which severely affects the stability and reliability of high-frequency circuit signal transmission. Chinese patent CN113861865B discloses a low-dielectric-constant adhesive sheet containing hollow ceramic powder and its preparation method. The core layer of the PTFE substrate is obtained through a coating process, followed by an impregnation process to form a hydrocarbon resin layer containing hollow filler on the upper and lower surfaces of the PTFE substrate. The resulting adhesive sheet exhibits high bonding strength and uniform and stable dielectric properties, meeting the requirements of multilayer boards. However, the hollow ceramic powder has cavities and its surface is rich in polar groups such as hydroxyl groups, resulting in a high water absorption rate, which affects the transmission of high-frequency microwave signals. Therefore, in order to achieve stable and reliable transmission of high-frequency signals, it is urgent to develop a bonding sheet material with low dielectric constant, low dielectric loss and low water absorption rate to prepare multilayer microwave composite dielectric substrates to meet the requirements of high-frequency signals for stability and reliability. Summary of the Invention

[0004] The purpose of this invention is to address the problems and shortcomings of existing technologies, such as the "glass fiber effect" in glass fiber cloth reinforced adhesive sheets and the low water absorption rate of hollow ceramic powder filled adhesive sheets. This invention provides a method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss containing a porous polytetrafluoroethylene film. The resulting polyolefin adhesive sheet has advantages such as low dielectric constant, low dielectric loss, low water absorption rate, and simple processing technology. Furthermore, the preparation method described in this invention is simple and conducive to large-scale industrial production.

[0005] The technical solution adopted in this invention is: a method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss, comprising the following steps:

[0006] Step 1: Prepare a solution with a concentration of 0.3 mol•L -1 ~0.8 mol•L -1 The porous polytetrafluoroethylene film was immersed in sodium-naphthalene-tetrahydrofuran solution for 30 seconds, then rinsed with distilled water, dried and stored in the dark to obtain the activated porous polytetrafluoroethylene film.

[0007] Step 2: Add 0.5 to 1.5 parts of silane coupling agent to 50 to 70 parts of ethanol to form an ethanol solution of silane coupling agent. Immerse the activated porous polytetrafluoroethylene film in the ethanol solution of silane coupling agent, and then dry it in a drying tunnel at 90 to 120°C for 10 to 30 minutes to obtain a porous polytetrafluoroethylene film with double bonds on its surface.

[0008] Step 3: Immerse 25-50 parts of inorganic filler in an ethanol solution of silane coupling agent, stir for 60-90 min, and then dry in an oven at 90-120℃ for 2-5 h to obtain inorganic filler with double bonds on the surface.

[0009] Step 4: Add 20-45 parts of polyolefin, 25-55 parts of inorganic filler with double bonds on the surface, 10-25 parts of flame retardant, 0.5-2 parts of antioxidant, and 1-5 parts of initiator to 20-50 parts of organic solvent in sequence. Stir thoroughly for 90-150 minutes at a stirring speed of 600-1200 r / min to form a polyolefin composite adhesive.

[0010] Step 5: Impregnate the porous polytetrafluoroethylene film with double bonds on its surface with polyolefin composite adhesive, and dry it at 80-120℃ for 10-30 minutes to allow partial cross-linking reaction to occur between the porous polytetrafluoroethylene film with double bonds on its surface, the inorganic filler with double bonds on its surface, and the polyolefin resin, to obtain a polyolefin adhesive sheet.

[0011] The activated porous polytetrafluoroethylene film has a pore size of 0.02 μm to 0.5 μm and a thickness of 25 μm to 75 μm.

[0012] The inorganic filler is one or a mixture of several of the following: silicon dioxide, titanium dioxide, aluminum oxide, magnesium oxide, and perovskite ceramic powder.

[0013] The silane coupling agent is one or a mixture of several of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(2-methoxyethoxy)silane, and γ-methacryloyloxypropyltrimethoxysilane.

[0014] The polyolefin resin is one or a mixture of several of the following: polybutadiene, modified polybutadiene, polyisoprene, styrene-butadiene block copolymer, and ethylene-propylene-dicyclopentadiene copolymer.

[0015] The flame retardant is one or a mixture of several of the following: decabromodiphenyl ether, ethylenebistetrabromophthalimide, toluene diphenyl phosphate, tricresyl phosphate, and trioctyl phosphate.

[0016] The antioxidant is one or a mixture of several of the following: 4,4-bis(α,α-dimethylbenzyl)diphenylamine, pentaerythritol ester of [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and tris(2,4-di-tert-butylphenyl) phosphite.

[0017] The initiator is one or a mixture of several of the following: azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, tert-butyl peroxide, dicumyl peroxide, bis-tert-butyl peroxide, and 2,3-dimethyl-2,3-diphenylbutane.

[0018] The organic solvent is one or a mixture of two or more of cyclohexane, butanone, cyclohexanone, xylene, and ethyl acetate.

[0019] The beneficial effects of this invention are as follows: The porous polytetrafluoroethylene film selected in this invention has a pore size of 0.02 μm to 0.5 μm and a thickness of 25 μm to 75 μm. This porous film is breathable and waterproof, giving the adhesive sheet advantages such as low dielectric constant and low dielectric loss. A concentration of 0.3 mol•L is used. -1 ~0.8 mol•L -1 The surface of the porous PTFE film was activated using a sodium-naphthalene-tetrahydrofuran solution. The activated porous PTFE film exhibited active groups such as hydroxyl, carboxyl, and carbonyl groups, while its porous structure remained intact. A silane coupling agent was then used to modify the surface of the activated porous PTFE film, creating double bonds on its surface. During the impregnation and drying process, these double bonds partially crosslinked with the polyolefin resin and the inorganic filler with double bonds, resulting in a tight bond between the porous PTFE film, the polyolefin resin, and the inorganic filler. This further enhances the resulting adhesive sheet's advantages, including low dielectric constant and low dielectric loss, and its high bonding strength, which is beneficial for fabricating the sheet into microwave circuits and assembling subsequent electronic components.

[0020] The polyolefin adhesive sheet produced by this invention includes a porous polytetrafluoroethylene film as the core layer, and a polyolefin resin composite film tightly bonded to the upper and lower surfaces of the film. It has the characteristics of dielectric constant below 2.20, dielectric loss below 0.0015 and water absorption rate below 0.04%, which helps to achieve high-speed, low-delay and low-loss transmission of high-frequency signals.

[0021] The polyolefin adhesive sheet produced by this invention has a core layer of porous polytetrafluoroethylene film without glass fiber cloth, thus avoiding the "glass fiber effect" in the high-frequency signal transmission process. Then, the core layer is impregnated to obtain an upper and lower polyolefin resin composite film. This method has a simple preparation process, convenient raw material sources, and high production efficiency, which is conducive to realizing continuous industrial production.

[0022] This invention can be widely applied in fields such as communications, radar, and high-speed rail. Detailed Implementation

[0023] The present invention will now be described in detail with reference to specific embodiments.

[0024] Example 1: A method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss, comprising the following steps:

[0025] Step 1: Prepare a solution with a concentration of 0.3 mol•L -1 A porous polytetrafluoroethylene (PTFE) film with a pore size of 0.25 μm and a thickness of 50 μm was immersed in a sodium-naphthalene-tetrahydrofuran solution for 30 seconds, then rinsed with distilled water, dried, and stored in the dark to obtain an activated porous PTFE film.

[0026] Step 2: By weight, add 1 part of vinyltriethoxysilane to 60 parts of ethanol to form an ethanol solution of vinyltriethoxysilane. Immerse the activated porous polytetrafluoroethylene film in the ethanol solution of vinyltriethoxysilane, and then dry it in an oven at 110°C for 20 minutes to obtain a porous polytetrafluoroethylene film with double bonds on its surface.

[0027] Step 3: Immerse 40 parts by weight of silica filler in an ethanol solution of vinyltriethoxysilane, stir for 80 min, and then dry in an oven at 110 °C for 3.5 h to obtain silica filler with double bonds on its surface.

[0028] Step 4: By weight, add 25 parts of polybutadiene, 7.5 parts of ethylene-propylene-dicyclopentadiene copolymer, 40 parts of silica filler with double bonds on its surface, 17.5 parts of ethylene bis(tetrabromophthalimide), 1.5 parts of pentaerythritol [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 3 parts of di-tert-butyl peroxide diisopropylbenzene to 35 parts of xylene. Stir thoroughly for 120 minutes at a stirring speed of 1000 r / min to form a polyolefin composite liquid. The silica filler with double bonds on its surface has good compatibility with the polyolefin resin, allowing the silica filler to be uniformly dispersed in the polyolefin composite liquid.

[0029] Step 5: Impregnate the porous polytetrafluoroethylene film with double bonds on its surface with polyolefin composite adhesive and dry it at 105℃ for 15 minutes to allow partial cross-linking reaction to occur between the porous polytetrafluoroethylene film with double bonds on its surface, the silica filler with double bonds on its surface, and the polyolefin resin, thereby obtaining a polyolefin adhesive sheet with low dielectric constant and low dielectric loss.

[0030] Example 2: A method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss, comprising the following steps:

[0031] Step 1: Prepare a solution with a concentration of 0.55 mol•L -1 A porous polytetrafluoroethylene (PTFE) film with a pore size of 0.25 μm and a thickness of 50 μm was immersed in a sodium-naphthalene-tetrahydrofuran solution for 30 seconds, then rinsed with distilled water, dried, and stored in the dark to obtain an activated porous PTFE film.

[0032] Step 2: By weight, add 1 part of vinyltriethoxysilane to 60 parts of ethanol to form an ethanol solution of vinyltriethoxysilane. Immerse the activated porous polytetrafluoroethylene film in the ethanol solution of vinyltriethoxysilane, and then dry it in an oven at 110°C for 20 minutes to obtain a porous polytetrafluoroethylene film with double bonds on its surface.

[0033] Step 3: Immerse 40 parts by weight of silica filler in an ethanol solution of vinyltriethoxysilane, stir for 80 min, and then dry in an oven at 110 °C for 3.5 h to obtain silica filler with double bonds on its surface.

[0034] Step 4: By weight, add 25 parts of polybutadiene, 7.5 parts of ethylene-propylene-dicyclopentadiene copolymer, 40 parts of silica filler with double bonds on its surface, 17.5 parts of ethylene bis(tetrabromophthalimide), 1.5 parts of pentaerythritol [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 3 parts of di-tert-butyl peroxide diisopropylbenzene to 35 parts of xylene. Stir thoroughly for 120 minutes at a stirring speed of 1000 r / min to form a polyolefin composite liquid. The silica filler with double bonds on its surface has good compatibility with the polyolefin resin, allowing the silica filler to be uniformly dispersed in the polyolefin composite liquid.

[0035] Step 5: Impregnate the porous polytetrafluoroethylene film with double bonds on its surface with polyolefin composite adhesive and dry it at 105℃ for 15 minutes to allow partial cross-linking reaction to occur between the porous polytetrafluoroethylene film with double bonds on its surface, the silica filler with double bonds on its surface, and the polyolefin resin, thereby obtaining a polyolefin adhesive sheet with low dielectric constant and low dielectric loss.

[0036] Example 3: A method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss, comprising the following steps:

[0037] Step 1: Prepare a solution with a concentration of 0.8 mol•L -1 A porous polytetrafluoroethylene (PTFE) film with a pore size of 0.25 μm and a thickness of 50 μm was immersed in a sodium-naphthalene-tetrahydrofuran solution for 30 seconds, then rinsed with distilled water, dried, and stored in the dark to obtain an activated porous PTFE film.

[0038] Step 2: By weight, add 1 part of vinyltriethoxysilane to 60 parts of ethanol to form an ethanol solution of vinyltriethoxysilane. Immerse the activated porous polytetrafluoroethylene film in the ethanol solution of vinyltriethoxysilane, and then dry it in an oven at 110°C for 20 minutes to obtain a porous polytetrafluoroethylene film with double bonds on its surface.

[0039] Step 3: Immerse 40 parts by weight of silica filler in an ethanol solution of vinyltriethoxysilane, stir for 80 min, and then dry in an oven at 110 °C for 3.5 h to obtain silica filler with double bonds on its surface.

[0040] Step 4: By weight, add 25 parts of polybutadiene, 7.5 parts of ethylene-propylene-dicyclopentadiene copolymer, 40 parts of silica filler with double bonds on its surface, 17.5 parts of ethylene bis(tetrabromophthalimide), 1.5 parts of pentaerythritol [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 3 parts of di-tert-butyl peroxide diisopropylbenzene to 35 parts of xylene. Stir thoroughly for 120 minutes at a stirring speed of 1000 r / min to form a polyolefin composite liquid. The silica filler with double bonds on its surface has good compatibility with the polyolefin resin, allowing the silica filler to be uniformly dispersed in the polyolefin composite liquid.

[0041] Step 5: Impregnate the porous polytetrafluoroethylene film with double bonds on its surface with polyolefin composite adhesive and dry it at 105℃ for 15 minutes to allow partial cross-linking reaction to occur between the porous polytetrafluoroethylene film with double bonds on its surface, the silica filler with double bonds on its surface, and the polyolefin resin, thereby obtaining a polyolefin adhesive sheet with low dielectric constant and low dielectric loss.

[0042] Comparative Example 1

[0043] Step 1: The surface of a porous polytetrafluoroethylene film with a pore size of 0.25 μm and a thickness of 50 μm is activated by corona treatment to obtain an activated porous polytetrafluoroethylene film.

[0044] Step 2: By weight, first add 1 part of vinyltriethoxysilane to 60 parts of ethanol to form an ethanol solution of vinyltriethoxysilane. Immerse the activated porous polytetrafluoroethylene film in the ethanol solution of vinyltriethoxysilane, and then dry it in a drying tunnel at 110°C for 20 minutes to obtain a porous polytetrafluoroethylene film with double bonds on its surface.

[0045] Step 3: Immerse 40 parts by weight of silica filler in an ethanol solution of vinyltriethoxysilane, stir for 80 min, and then dry in an oven at 110 °C for 3.5 h to obtain silica filler with double bonds on its surface.

[0046] Step 4: By weight, add 25 parts of polybutadiene, 7.5 parts of ethylene-propylene-dicyclopentadiene copolymer, 40 parts of silica filler with double bonds on its surface, 17.5 parts of ethylene bis(tetrabromophthalimide), 1.5 parts of pentaerythritol [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 3 parts of di-tert-butyl peroxide diisopropylbenzene to 35 parts of xylene. Stir thoroughly for 120 minutes at a stirring speed of 1000 r / min to form a polyolefin composite adhesive. The silica filler with double bonds on its surface has good compatibility with the polyolefin resin, allowing the silica filler to be uniformly dispersed in the polyolefin composite adhesive.

[0047] Step 5: Impregnate the porous polytetrafluoroethylene film with double bonds on its surface with polyolefin composite adhesive and dry it at 105℃ for 15 minutes to allow partial cross-linking reaction to occur between the porous polytetrafluoroethylene film with double bonds on its surface, the silica filler with double bonds on its surface, and the polyolefin resin, thereby obtaining a polyolefin adhesive sheet with low dielectric constant and low dielectric loss.

[0048] Comparative Example 2

[0049] Step 1: The porous polytetrafluoroethylene film with a pore size of 0.25 μm and a thickness of 50 μm is activated by plasma treatment to obtain an activated porous polytetrafluoroethylene film.

[0050] Step 2: By weight, first add 1 part of vinyltriethoxysilane to 60 parts of ethanol to form an ethanol solution of vinyltriethoxysilane. Immerse the activated porous polytetrafluoroethylene film in the ethanol solution of vinyltriethoxysilane, and then dry it in a drying tunnel at 110°C for 20 minutes to obtain a porous polytetrafluoroethylene film with double bonds on its surface.

[0051] Step 3: Immerse 40 parts by weight of silica filler in an ethanol solution of vinyltriethoxysilane, stir for 80 min, and then dry in an oven at 110 °C for 3.5 h to obtain silica filler with double bonds on its surface.

[0052] Step 4: By weight, add 25 parts of polybutadiene, 7.5 parts of ethylene-propylene-dicyclopentadiene copolymer, 40 parts of silica filler with double bonds on its surface, 17.5 parts of ethylene bis(tetrabromophthalimide), 1.5 parts of pentaerythritol [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 3 parts of di-tert-butyl peroxide diisopropylbenzene to 35 parts of xylene. Stir thoroughly for 120 minutes at a stirring speed of 1000 r / min to form a polyolefin composite adhesive. The silica filler with double bonds on its surface has good compatibility with the polyolefin resin, allowing the silica filler to be uniformly dispersed in the polyolefin composite adhesive.

[0053] Step 5: Impregnate the porous polytetrafluoroethylene film with double bonds on its surface with polyolefin composite adhesive and dry it at 105℃ for 15 minutes to allow partial cross-linking reaction to occur between the porous polytetrafluoroethylene film with double bonds on its surface, the silica filler with double bonds on its surface, and the polyolefin resin, thereby obtaining a polyolefin adhesive sheet with low dielectric constant and low dielectric loss.

[0054] Comparative Example 3

[0055] Step 1: Prepare a solution with a concentration of 0.55 mol•L -1A 50 μm thick polytetrafluoroethylene (PTFE) film was immersed in a sodium-naphthalene-tetrahydrofuran solution for 30 seconds, then rinsed with distilled water, dried, and stored in the dark to obtain an activated PTFE film.

[0056] Step 2: By weight, first add 1 part of vinyltriethoxysilane to 60 parts of ethanol to form an ethanol solution of vinyltriethoxysilane. Immerse the activated polytetrafluoroethylene film in the ethanol solution of vinyltriethoxysilane, and then dry it in an oven at 110°C for 20 minutes to obtain a polytetrafluoroethylene film with double bonds on its surface.

[0057] Step 3: Immerse 40 parts by weight of silica filler in an ethanol solution of vinyltriethoxysilane, stir for 80 min, and then dry in an oven at 110 °C for 3.5 h to obtain silica filler with double bonds on its surface.

[0058] Step 4: By weight, add 25 parts of polybutadiene, 7.5 parts of ethylene-propylene-dicyclopentadiene copolymer, 40 parts of silica filler with double bonds on its surface, 17.5 parts of ethylene bis(tetrabromophthalimide), 1.5 parts of pentaerythritol [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 3 parts of di-tert-butyl peroxide diisopropylbenzene to 35 parts of xylene. Stir thoroughly for 120 minutes at a stirring speed of 1000 r / min to form a polyolefin composite liquid. The silica filler with double bonds on its surface has good compatibility with the polyolefin resin, allowing the silica filler to be uniformly dispersed in the polyolefin composite liquid.

[0059] Step 5: Impregnate the polytetrafluoroethylene film with double bonds on its surface with polyolefin composite adhesive, and dry it at 105℃ for 15 minutes to allow partial cross-linking reaction to occur between the polytetrafluoroethylene film with double bonds on its surface, the silica filler with double bonds on its surface, and the polyolefin resin, thereby obtaining a polyolefin adhesive sheet.

[0060] The test results for the polyolefin adhesive sheets prepared in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1:

[0061] sample Dielectric constant (10 GHz) Dielectric loss (10GHz) Water absorption rate (%) Peel strength (N / mm) Example 1 2.12 0.0012 0.029 1.02 Example 2 2.08 0.0009 0.016 1.13 Example 3 2.16 0.0014 0.036 1.08 Comparative Example 1 2.26 0.0025 0.041 0.84 Comparative Example 2 2.28 0.0029 0.042 0.88 Comparative Example 3 2.46 0.0034 0.038 0.92

[0062] As can be seen from Table 1, the porous polytetrafluoroethylene film selected in this invention has a pore size of 0.02 μm to 0.5 μm and a thickness of 25 μm to 75 μm. Then, a concentration of 0.3 mol•L... -1 ~0.8 mol•L -1The surface of the porous PTFE film is activated by a sodium-naphthalene-tetrahydrofuran solution. The activated porous PTFE film has active groups such as hydroxyl, carboxyl, and carbonyl groups on its surface. Then, a silane coupling agent is used to modify the surface of the activated porous PTFE film, creating double bonds on its surface. The porous PTFE film with double bonds on its surface improves its compatibility with organic resins and inorganic fillers, and reduces the dielectric constant and dielectric loss of the material. The polyolefin adhesive sheet prepared using this invention has a dielectric constant of less than 2.2, a dielectric loss of less than 0.0015, and a water absorption rate of less than 0.04%, meeting the requirements for low dielectric constant and low dielectric loss adhesive sheets. It exhibits high reliability in sheet processing and application, a simple preparation process, and readily available raw materials, facilitating industrial production.

Claims

1. A method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss, characterized in that, The steps are as follows: Step 1: Prepare a solution with a concentration of 0.3 mol•L -1 ~0.8 mol•L -1 The porous polytetrafluoroethylene film was immersed in sodium-naphthalene-tetrahydrofuran solution for 30 seconds, then rinsed with distilled water, dried and stored in the dark to obtain the activated porous polytetrafluoroethylene film. Step 2: Add 0.5 to 1.5 parts of silane coupling agent to 50 to 70 parts of ethanol to form an ethanol solution of silane coupling agent. Immerse the activated porous polytetrafluoroethylene film in the ethanol solution of silane coupling agent, and then dry it in a drying tunnel at 90 to 120°C for 10 to 30 minutes to obtain a porous polytetrafluoroethylene film with double bonds on its surface. Step 3: Immerse 25-50 parts of inorganic filler in an ethanol solution of silane coupling agent, stir for 60-90 min, and then dry in an oven at 90-120℃ for 2-5 h to obtain inorganic filler with double bonds on the surface. Step 4: Add 20-45 parts of polyolefin, 25-55 parts of inorganic filler with double bonds on the surface, 10-25 parts of flame retardant, 0.5-2 parts of antioxidant, and 1-5 parts of initiator to 20-50 parts of organic solvent in sequence. Stir thoroughly for 90-150 minutes at a stirring speed of 600-1200 r / min to form a polyolefin composite adhesive. Step 5: Impregnate the porous polytetrafluoroethylene film with double bonds on its surface with polyolefin composite adhesive, and dry it at 80-120℃ for 10-30 minutes to allow partial cross-linking reaction to occur between the porous polytetrafluoroethylene film with double bonds on its surface, the inorganic filler with double bonds on its surface, and the polyolefin resin to obtain a polyolefin adhesive sheet. The polyolefin resin is one or a mixture of several of the following: polybutadiene, modified polybutadiene, polyisoprene, styrene-butadiene block copolymer, and ethylene-propylene-dicyclopentadiene copolymer.

2. The method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss according to claim 1, characterized in that: The activated porous polytetrafluoroethylene film has a pore size of 0.02 μm to 0.5 μm and a thickness of 25 μm to 75 μm.

3. The method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss according to claim 1, characterized in that: The inorganic filler is one or a mixture of several of the following: silicon dioxide, titanium dioxide, aluminum oxide, magnesium oxide, and perovskite ceramic powder.

4. The method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss according to claim 1, characterized in that: The silane coupling agent is one or a mixture of several of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(2-methoxyethoxy)silane, and γ-methacryloyloxypropyltrimethoxysilane.

5. The method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss according to claim 1, characterized in that: The flame retardant is one or a mixture of several of the following: decabromodiphenyl ether, ethylenebistetrabromophthalimide, toluene diphenyl phosphate, tricresyl phosphate, and trioctyl phosphate.

6. The method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss according to claim 1, characterized in that: The antioxidant is one or a mixture of several of the following: 4,4-bis(α,α-dimethylbenzyl)diphenylamine, pentaerythritol ester of [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and tris(2,4-di-tert-butylphenyl) phosphite.

7. The method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss according to claim 1, characterized in that: The initiator is one or a mixture of several of the following: azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, tert-butyl peroxide, dicumyl peroxide, bis-tert-butyl peroxide, and 2,3-dimethyl-2,3-diphenylbutane.

8. The method for preparing a polyolefin adhesive sheet with low dielectric constant and low dielectric loss according to claim 1, characterized in that: The organic solvent is one or a mixture of two or more of cyclohexane, butanone, cyclohexanone, xylene, and ethyl acetate.