Polypropylene foam and method for producing the same

Abstract

The application belongs to the field of high polymer materials, and particularly relates to a kind of polypropylene foaming material and its preparation method.The polypropylene foaming material provided by the application is made of embryo material through mould pressing foaming, and the preparation raw materials of the embryo material include, in terms of weight parts, homopolymerization polypropylene 80-100 parts, adamantyl methacrylate 1-20 parts, initiator 0.01-0.5 parts, catalyst 0.01-1 parts, fluoride 0.1-10 parts, nucleating agent 0.1-0.5 parts.The application modifies the homopolymerization polypropylene through branched chain modification, while keeping good mechanics, adamantyl methacrylate and fluoride cooperatively reduce the dielectric constant of the material.The polypropylene foaming material provided by the application keeps good mechanical properties, high thermal stability, low water absorption and good processing performance while having low dielectric constant, and can be applied to the production of structural parts of 5G communication equipment.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, and particularly relates to a polypropylene foam material and its preparation method. Background Technology

[0002] The advent of 5G communication technology will place a greater reliance on new materials than ever before, primarily due to the characteristics of 5G communication technology itself. 5G communication features ultra-high-speed signal transmission and multi-user access, placing higher demands on the overall performance of existing materials. In high-frequency communication, to reduce signal transmission loss and delay, the dielectric constant of the dielectric material must be minimized, i.e., using polymeric dielectric materials with low dielectric properties. Simultaneously, the dielectric properties of the polymeric dielectric material should change as little as possible with frequency, temperature, and humidity. Furthermore, considering the practical applications of high-frequency signal transmission, the polymeric dielectric material also needs sufficient mechanical strength, high thermal stability, low water absorption, and good processing performance to support multi-layer interconnect architectures, such as 5G base station radomes, filters, and antenna elements.

[0003] Polypropylene (PP) foam materials are lightweight, cost-effective, possess excellent impact resistance, heat resistance, environmental adaptability, good degradation properties, and recyclability, and have low processing costs. They are one of the fastest-growing materials in the world in terms of production volume and can be widely used in packaging, automotive, electronic structural components, logistics and transportation, toys and sporting goods, construction, and many other fields. Developing a PP foam material suitable for 5G communication equipment, leveraging the numerous technological advantages of PP foam materials, will have broad market prospects. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a polypropylene foam material and a method for preparing the same. The polypropylene foam material provided by the present invention has good mechanical properties, high thermal stability, low water absorption and good processing performance while having a low dielectric constant, and can be used to manufacture structural components for 5G communication equipment.

[0005] This invention provides a polypropylene foam material, which is made by compression molding of a preform. The raw materials for preparing the preform, by weight, include:

[0006]

[0007] Preferably, the number average molecular weight of the homopolymer polypropylene is 5 × 10⁻⁶. 4 ~20×10 4 The melt index of the homopolymer polypropylene is 2-5 g / 10 min.

[0008] Preferably, the adamantyl methacrylate is one or more of 2-methyl-2-adamantyl methacrylate, 1-adamantyl methacrylate, 2-isopropyl-2-adamantyl methacrylate, 2-ethyl-2-adamantyl methacrylate, 3-hydroxy-1-adamantyl methacrylate and 1-methyl-1-ethyl-1-adamantyl methanol methacrylate.

[0009] Preferably, the initiator is dicumyl peroxide and / or 2,4-di-tert-butyl peroxide; the catalyst is one or more of the following: zinc 2-thiol benzothiazole, N-cyclohexyl-2-benzothiazole sulfenamide, tetramethylthiuram disulfide, tetrabutylthiuram disulfide, tetrabenzylthiuram disulfide, zinc dimethyl dithiocarbamate, zinc diethyl dithiocarbamate, zinc ethylphenyl dithiocarbamate, zinc dibenzyl dithiocarbamate, NN′-diphenylthiourea, zinc dialkyl dithiophosphate, thiomelamine, and NN′-m-phenylenebismaleimide.

[0010] Preferably, the fluoride is one or more selected from perfluoropropyl vinyl ether, perfluorocyclic ether, perfluorobutyl methyl ether, perfluorohexyl ethanol polyoxyethylene ether, perfluoroalkyl ethanol polyoxyethylene ether, perfluorobutyltetrahydrofuran, polyperfluoromethyl isopropyl ether, perfluoroethyl vinyl ether, and perfluoropolyether alcohol.

[0011] Preferably, the nucleating agent is one or more of calcium carbonate, talc, kaolin, montmorillonite, silica, diatomaceous earth, and silica fume.

[0012] This invention provides a method for preparing the polypropylene foam material described in the above technical solution, comprising the following steps:

[0013] a) Homopolymer polypropylene, adamantyl methacrylate, initiator, catalyst, fluoride and nucleating agent are melt-blended and shaped to obtain a preform;

[0014] b) The preform is molded and foamed to obtain polypropylene foam material.

[0015] Preferably, in step a), the temperature of the melt blending is 140–190°C; and the thickness of the preform is 8–20 mm.

[0016] Preferably, in step b), the specific process of compression molding foaming includes:

[0017] The preform is placed in the mold cavity of the molding foaming equipment, then supercritical gas is introduced and kept at temperature and pressure for a period of time. After that, the pressure is released and the material is shaped to obtain polypropylene foam material.

[0018] Preferably, the supercritical gas is carbon dioxide; the pressure for heat preservation and pressure holding is 8-20 MPa, the temperature is 140-170°C, and the time is 1-5 h.

[0019] Compared with existing technologies, this invention provides a polypropylene foam material and its preparation method. The polypropylene foam material provided by this invention is made from a preform through molding and foaming. By weight, the raw materials for preparing the preform include: 80-100 parts of homopolymer polypropylene, 1-20 parts of adamantyl methacrylate, 0.01-0.5 parts of initiator, 0.01-1 parts of catalyst, 0.1-10 parts of fluoride, and 0.1-0.5 parts of nucleating agent. This invention, through branching modification of homopolymer polypropylene, maintains good mechanical properties while adamantyl methacrylate and fluoride synergistically reduce the dielectric constant of the material. The polypropylene foam material provided by this invention maintains good mechanical properties, high thermal stability, low water absorption, and good processing performance while possessing a low dielectric constant, and can be applied to the production of structural components for 5G communication equipment. More specifically, the technical solution of this invention includes at least the following advantages:

[0020] (1) In this invention, adamantyl methacrylate is used as a monomer to melt graft homopolymer polypropylene under the action of initiator and catalyst, which broadens the foaming window of homopolymer polypropylene, realizes the feasibility of homopolymer polypropylene molding foaming, and at the same time maintains the good mechanical properties of homopolymer polypropylene.

[0021] (2) In this invention, a large volume rigid group adamantyl methacrylate is introduced into the molecular chain segment of homopolymer polypropylene. The introduced adamantyl methacrylate is a large volume rigid group. The large volume rigid group inside the material will destroy the regular stacking of polymer chain segments, increase the free volume, reduce the dielectric constant, and at the same time improve the thermal stability of polypropylene material.

[0022] (3) In this invention, fluoride is added. Fluoride has a high electronegativity and fluorine atoms have a strong attraction to electrons, resulting in a higher electron density and a smaller atomic radius. When an external electric field is applied to the material, the electrons are more tightly adsorbed, so it is difficult for the atomic nucleus and electron center of gravity to shift, reducing the occurrence of polarization and thus reducing the dielectric properties of the material. At the same time, fluoride has a low surface tension, which can regulate the cell structure during polypropylene foaming, promote the uniform distribution of cells, reduce cell merging and rupture, and ensure the uniformity of cell size, thereby reducing the dielectric constant of polypropylene foam material. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 This is a scanning electron microscope image of the polypropylene foam material of Example 1 provided by the present invention. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention provides a polypropylene foam material, which is made by compression molding of a preform, wherein the preform is made by melt blending of raw materials; the raw materials for preparing the preform, by weight, include:

[0027]

[0028] In the polypropylene foam material provided by the present invention, the number-average molecular weight of the homopolymer polypropylene is preferably 5 × 10⁻⁶. 4 ~20×10 4 Specifically, it can be 5×10 4 6×10 4 7×10 4 8×10 4 9×10 4 10×10 4 11×10 4 12×10 4 13×10 4 14×10 4 15×10 4 16×10 4 17×10 4 18×10 4 19×10 4 Or 20×10 4The melt index of the homopolymer polypropylene is preferably 2 to 5 g / 10 min, specifically 2 g / 10 min, 2.3 g / 10 min, 2.5 g / 10 min, 2.7 g / 10 min, 3 g / 10 min, 3.2 g / 10 min, 3.5 g / 10 min, 3.7 g / 10 min, 4 g / 10 min, 4.2 g / 10 min, 4.5 g / 10 min, 4.7 g / 10 min, or 5 g / 10 min.

[0029] In the polypropylene foam material provided by this invention, the number-average molecular weight of the polypropylene reflects the degree of polymerization and molecular chain length of the polypropylene monomers, and the number-average molecular weight is 5 × 10⁻⁶. 4 ~20×10 4 Polypropylene has strong rigidity, and after modification, it exhibits good mechanical properties in compression molding foam. The melt strength of polypropylene is related to its melt index; a lower melt index results in higher melt strength. In the compression molding foaming process, high pressure of 8–20 MPa is used. During the instantaneous depressurization process, the driving force of the cells is relatively large. If the melt strength of the substrate is low, phenomena such as cell rupture and collapse may occur. Therefore, a melt index of 2–5 g / 10 min for polypropylene raw materials is more suitable for compression molding foaming.

[0030] In the polypropylene foaming material provided by the present invention, the content of homopolymer polypropylene in the raw materials can specifically be 80 parts by weight, 81 parts by weight, 82 parts by weight, 83 parts by weight, 84 parts by weight, 85 parts by weight, 86 parts by weight, 87 parts by weight, 88 parts by weight, 89 parts by weight, 90 parts by weight, 91 parts by weight, 92 parts by weight, 93 parts by weight, 94 parts by weight, 95 parts by weight, 96 parts by weight, 97 parts by weight, 98 parts by weight, 99 parts by weight, or 100 parts by weight.

[0031] In the polypropylene foam material provided by the present invention, the adamantyl methacrylate is preferably one or more of 2-methyl-2-adamantyl methacrylate, 1-adamantyl methacrylate, 2-isopropyl-2-adamantyl methacrylate, 2-ethyl-2-adamantyl methacrylate, 3-hydroxy-1-adamantyl methacrylate and 1-methyl-1-ethyl-1-adamantyl methanol methacrylate, more preferably one or more of 2-isopropyl-2-adamantyl methacrylate, 2-ethyl-2-adamantyl methacrylate and 3-hydroxy-1-adamantyl methacrylate.

[0032] In the polypropylene foam material provided by this invention, the adamantyl methyl methacrylate monomer is introduced into the polypropylene branch chain through melt grafting modification. Homopolymer polypropylene has a short melting range, narrow foaming window, and is difficult to foam. Branching modification can broaden the melting range of polypropylene and improve its feasibility of supercritical carbon dioxide foaming. Moreover, the introduced adamantyl methyl methacrylate is a large-volume rigid group. The large-volume rigid group inside the material will destroy the regular stacking of polymer chain segments, increase the free volume, reduce the dielectric constant, and improve the thermal stability of polypropylene material.

[0033] In the polypropylene foam material provided by the present invention, the content of adamantyl methacrylate in the raw materials can specifically be 1 part by weight, 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, or 20 parts by weight.

[0034] In the polypropylene foam material provided by this invention, the initiator is preferably dicumyl peroxide and / or 2,4-di-tert-butyl peroxide. In this invention, homopolymer polypropylene undergoes chain segment cleavage under the action of the initiator, forming PP macromolecular free radicals. These macromolecular free radicals further react with the grafted monomers under the action of a catalyst.

[0035] In the polypropylene foam material provided by the present invention, the content of the initiator in the raw materials can specifically be 0.01 parts by weight, 0.03 parts by weight, 0.05 parts by weight, 0.07 parts by weight, 0.1 parts by weight, 0.12 parts by weight, 0.15 parts by weight, 0.17 parts by weight, 0.2 parts by weight, 0.23 parts by weight, 0.25 parts by weight, 0.27 parts by weight, 0.3 parts by weight, 0.32 parts by weight, 0.35 parts by weight, 0.37 parts by weight, 0.4 parts by weight, 0.42 parts by weight, 0.45 parts by weight, 0.47 parts by weight, or 0.5 parts by weight.

[0036] In the polypropylene foaming material provided by the present invention, the catalyst is preferably one or more of 2-thiol-benzothiazole zinc salt, N-cyclohexyl-2-benzothiazole sulfenamide, tetramethylthiuram disulfide, tetrabutylthiuram disulfide, tetrabenzylthiuram disulfide, zinc dimethyl dithiocarbamate, zinc diethyl dithiocarbamate, zinc ethylphenyl dithiocarbamate, zinc dibenzyl dithiocarbamate, NN′-diphenylthiourea, zinc dialkyl dithiophosphate, thiomelamine, and NN′-m-phenylenebismaleimide, more preferably one or more of 2-thiol-benzothiazole zinc salt, tetramethylthiuram disulfide, zinc dimethyl dithiocarbamate, and zinc dialkyl dithiophosphate.

[0037] In the polypropylene foam material provided by this invention, due to the low reactivity of the grafted monomers, the free radicals of PP macromolecules are prone to β-fracture reactions, resulting in side reactions in PP and a low monomer grafting rate. The catalyst preferably contains a sulfur-containing compound, which has electron-donating groups. These electron-donating groups reduce the β-fracture reactions of PP macromolecules, while the zinc salt promotes the activity of excited-state molecules of the reactants, thereby increasing the monomer grafting rate.

[0038] In the polypropylene foaming material provided by the present invention, the content of the catalyst in the raw materials can specifically be 0.01 parts by weight, 0.05 parts by weight, 0.1 parts by weight, 0.15 parts by weight, 0.2 parts by weight, 0.25 parts by weight, 0.3 parts by weight, 0.35 parts by weight, 0.4 parts by weight, 0.45 parts by weight, 0.5 parts by weight, 0.55 parts by weight, 0.6 parts by weight, 0.65 parts by weight, 0.7 parts by weight, 0.75 parts by weight, 0.8 parts by weight, 0.85 parts by weight, 0.9 parts by weight, 0.95 parts by weight, or 1 part by weight.

[0039] In the polypropylene foam material provided by the present invention, the fluoride is preferably one or more of perfluoropropyl vinyl ether, perfluorocyclic ether, perfluorobutyl methyl ether, perfluorohexyl ethanol polyoxyethylene ether, perfluoroalkyl ethanol polyoxyethylene ether, perfluorobutyltetrahydrofuran, polyperfluoromethyl isopropyl ether, perfluoroethyl vinyl ether, and perfluoropolyether alcohol, more preferably one or more of perfluoropropyl vinyl ether, perfluorocyclic ether, perfluorobutyl methyl ether, and perfluoropolyether alcohol.

[0040] In the polypropylene foam material provided by this invention, the fluoride has a high electronegativity, and the fluorine atom has a strong attraction to electrons, resulting in a higher electron density and a smaller atomic radius. When an external electric field is applied to the material, the electrons are more tightly adsorbed, making it difficult for the atomic nucleus and electron center of gravity to shift, reducing polarization and thus lowering the dielectric properties of the material. At the same time, the fluoride has a low surface tension, which can regulate the cell structure during the polypropylene foaming process, promote the uniform distribution of cells, reduce cell merging and rupture, and ensure the uniformity of cell size, thereby reducing the dielectric constant of the polypropylene foam material.

[0041] In the polypropylene foam material provided by the present invention, the content of the fluoride in the raw materials can specifically be 0.1 parts by weight, 0.5 parts by weight, 1 part by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight, 5 parts by weight, 5.5 parts by weight, 6 parts by weight, 6.5 parts by weight, 7 parts by weight, 7.5 parts by weight, 8 parts by weight, 8.5 parts by weight, 9 parts by weight, 9.5 parts by weight, or 10 parts by weight.

[0042] In the polypropylene foam material provided by this invention, the nucleating agent is preferably one or more selected from calcium carbonate, talc, kaolin, montmorillonite, silica, diatomaceous earth, and silica fume; the particle size of the nucleating agent is preferably D97≤10μm, specifically 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, or 10μm. In this invention, the nucleating agent provides nucleation sites for the polypropylene molding and foaming process, where gas accumulates, thereby forming and gradually increasing the size of the foam cells.

[0043] In the polypropylene foam material provided by the present invention, the nucleating agent in the raw materials can specifically be 0.1 parts by weight, 0.12 parts by weight, 0.15 parts by weight, 0.17 parts by weight, 0.2 parts by weight, 0.23 parts by weight, 0.25 parts by weight, 0.27 parts by weight, 0.3 parts by weight, 0.32 parts by weight, 0.35 parts by weight, 0.37 parts by weight, 0.4 parts by weight, 0.42 parts by weight, 0.45 parts by weight, 0.47 parts by weight, or 0.5 parts by weight.

[0044] The present invention also provides a method for preparing the polypropylene foam material described in the above technical solution, comprising the following steps:

[0045] a) Homopolymer polypropylene, adamantyl methacrylate, initiator, catalyst, fluoride and nucleating agent are melt-blended and shaped to obtain a preform;

[0046] b) The preform is molded and foamed to obtain polypropylene foam material.

[0047] In the preparation method proposed in this invention, in step a), the raw materials are preferably premixed uniformly before melt blending; the melt blending temperature is preferably 140-190℃, specifically 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃ or 190℃.

[0048] In the preparation method proposed in this invention, in step a), the melt blending is preferably carried out in an extruder; wherein, the length-to-diameter ratio of the extruder is preferably 20 to 50, specifically 20, 25, 30, 35, 40, 45, or 50; the main engine speed of the extruder is preferably 200 to 400 r / min, specifically 200 r / min, 230 r / min, 250 r / min, 270 r / min, 300 r / min, 320 r / min, or 350 r / min. The extruder's feeder speed is preferably 10-25 r / min, specifically 10 r / min, 12 r / min, 15 r / min, 17 r / min, 20 r / min, 23 r / min, or 25 r / min. The extruder's temperature range is preferably set to 150℃, 170℃, 180℃, 185℃, 185℃, 185℃, 185℃, 180℃, or 170℃. In this invention, during melt blending, polypropylene undergoes graft modification. The extruder's aspect ratio, main unit and feeder speeds, and processing temperature are closely related to the decomposition of polypropylene segments and the grafting rate of monomers. Excessively high processing temperatures or prolonged material residence time in the screw may lead to severe polypropylene degradation; excessively low processing temperatures prevent material melting; and insufficient material residence time in the screw cannot guarantee complete grafting reaction, resulting in a low grafting rate.

[0049] In the preparation method proposed in this invention, in step a), the shape of the molding is preferably a plate; after molding, it is preferably calendered, cooled and shaped, and cut to finally obtain a blank plate that meets the size specifications; the thickness of the blank plate is preferably 8-20mm, specifically 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, or 20mm. In this invention, when the blank is subsequently subjected to compression molding and foaming, supercritical carbon dioxide will permeate and diffuse within the blank. The thicker the blank, the longer the heat preservation and pressure holding time is required. The heat preservation and pressure holding time is proportional to the square of the blank thickness. Compression molding and foaming is an intermittent production process. If the blank is too thick, the heat preservation and pressure holding time is long and the efficiency is low. If the blank is too thin, the foamed product is prone to warping. Therefore, the above requirements are made for the thickness of the blank.

[0050] In the preparation method proposed in this invention, step b) preferably includes the following specific process of molding foaming: placing the preform into the mold cavity of the molding foaming equipment, then introducing supercritical gas and keeping it warm and pressurized for a period of time, then quickly depressurizing and shaping to obtain polypropylene foam material. Wherein, the supercritical gas is carbon dioxide; the pressure for heat preservation and pressure holding is preferably 8–20 MPa, specifically 8 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, 15 MPa, 16 MPa, 17 MPa, 18 MPa, 19 MPa, or 20 MPa; the temperature for heat preservation and pressure holding is preferably 140–170℃, specifically 140℃, 142℃, 145℃, 147℃, 150℃, 152℃, 155℃, 157℃, 160℃, 162℃, 165℃, 167℃, or 170℃; the time for heat preservation and pressure holding is preferably 1–5 hours, specifically 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours; the time for rapid depressurization is ≤2 seconds. In this invention, a holding pressure of 8–20 MPa is beneficial for the penetration and diffusion of carbon dioxide within the board, providing a suitable driving force during the instantaneous depressurization process. The polypropylene foam material obtained under a pressure of 8–20 MPa has a cell density of 10. 8 pcs / cm 3 The above refers to cells with a pore size of less than 100μm.

[0051] In this invention, the dielectric constant of the polypropylene foam material prepared by the above-mentioned raw material composition and process is preferably ≤1.25, the 10% compressive strength is preferably ≥650KPa, the Shore C hardness is preferably ≥80, and the average cell size is preferably ≤100μm.

[0052] For clarity, the following examples and comparative models will be used to provide a detailed description.

[0053] In the following embodiments and comparative examples of the present invention, a twin-screw extruder was used for melt blending and extrusion of sheets, wherein the length-to-diameter ratio of the extruder was 40, and the speeds of the main extruder and the feeder were 300 r / min and 15 r / min, respectively; the extruder temperature ranges were set as follows: 150°C, 170°C, 180°C, 185°C, 185°C, 185°C, 185°C, 185°C, 180°C, and 170°C.

[0054] Example 1

[0055] A low dielectric constant polypropylene foam material and its preparation method are described below:

[0056] (1) 90 parts by weight of homopolymer polypropylene (number average molecular weight of 15×10⁻⁶) 4The following ingredients are mixed evenly: 8 parts by weight of 2-isopropyl-2-adamantyl methacrylate (melt index 2.0 g / 10 min), 0.1 parts by weight of dicumyl peroxide, 0.3 parts by weight of 2-thiol benzothiazole zinc salt, 2 parts by weight of perfluoropropyl vinyl ether, and 0.2 parts by weight of calcium carbonate with a D97 of 8 μm. The mixture is then melt-extruded through a twin-screw extruder to form a slab, which is then calendered, cooled, and shaped before being cut into 10 mm thick sheets.

[0057] (2) Place the 10mm sheet obtained in the previous step into the mold cavity of the molding foaming equipment, then introduce supercritical carbon dioxide and maintain the temperature and pressure for a period of time. The temperature is 160℃, the pressure is 16MPa, and the holding time is 2h. After that, the pressure is quickly released within 1.0s. After shaping, a low dielectric constant polypropylene foam material is obtained (scanning electron microscopy observation results are as follows). Figure 1 (As shown).

[0058] Example 2

[0059] A low dielectric constant polypropylene foam material and its preparation method are described below:

[0060] (1) 85 parts by weight of homopolymer polypropylene (number average molecular weight of 12×10⁻⁶) 4 The following ingredients are mixed evenly: 10 parts by weight of 2-ethyl-2-adamantyl methacrylate (melt index 2.5 g / 10 min), 0.2 parts by weight of 2,4-di-tert-butyldiisopropylbenzene peroxide, 0.15 parts by weight of tetramethylthiuram disulfide, 3 parts by weight of perfluorocyclic ether, and 0.15 parts by weight of talc powder with a D97 of 9 μm. The mixture is then melt-extruded through a twin-screw extruder to form a slab. After calendering, cooling and shaping, the slab is cut into sheets with a thickness of 12 mm.

[0061] (2) Place the 12mm board obtained in the previous step into the mold cavity of the molding foaming equipment, then introduce supercritical carbon dioxide and keep it warm and pressurized for a period of time. The heat preservation temperature is 155℃, the pressure is 20MPa, and the heat preservation and pressure preservation time is 2.5h. Then, the pressure is quickly released within 1.2s. After shaping, a low dielectric constant polypropylene foam material is obtained.

[0062] Example 3

[0063] A low dielectric constant polypropylene foam material and its preparation method are described below:

[0064] (1) 95 parts by weight of homopolymer polypropylene (number average molecular weight of 9×10⁻⁶) 4The following ingredients are mixed evenly: 5 parts by weight of 3-hydroxy-1-adamantyl methacrylate (melt index 3.5 g / 10 min), 0.3 parts by weight of dicumyl peroxide, 0.5 parts by weight of zinc dimethyl dithiocarbamate, 5 parts by weight of perfluorobutyl methyl ether, and 0.5 parts by weight of kaolin with a D97 of 7 μm. The mixture is then melt-extruded through a twin-screw extruder to form a slab. After calendering, cooling and shaping, the slab is cut into 15 mm thick sheets.

[0065] (2) Place the 15mm board obtained in the previous step into the mold cavity of the molding foaming equipment, then introduce supercritical carbon dioxide and keep it warm and pressurized for a period of time. The heat preservation temperature is 165℃, the pressure is 10MPa, and the heat preservation and pressure preservation time is 4h. After that, the pressure is quickly released within 1.5s, and after shaping, a low dielectric constant polypropylene foam material is obtained.

[0066] Example 4

[0067] A low dielectric constant polypropylene foam material and its preparation method are described below:

[0068] (1) 90 parts by weight of homopolymer polypropylene (number average molecular weight of 10 × 10⁻⁶) 4 The following ingredients are mixed evenly: 10 parts by weight of 1-methyl-1-ethyl-1-adamantyl methacrylate (melt index 3.2 g / 10 min), 0.25 parts by weight of 2,4-di-tert-butyl peroxyisopropylbenzene, 0.6 parts by weight of zinc dialkyl dithiophosphate, 8 parts by weight of perfluoropolyether alcohol, and 0.1 parts by weight of silica with a D97 of 6 μm. The mixture is then melt-extruded through a twin-screw extruder to form a slab. After calendering, cooling and shaping, the slab is cut into 20 mm thick sheets.

[0069] (2) Place the 20mm board obtained in the previous step into the mold cavity of the molding foaming equipment, then introduce supercritical carbon dioxide and keep it warm and pressurized for a period of time. The heat preservation temperature is 150℃, the pressure is 12MPa, and the heat preservation and pressure preservation time is 5h. Then, the pressure is quickly released within 2.0s, and after shaping, a low dielectric constant polypropylene foam material is obtained.

[0070] Comparative Example 1

[0071] Comparative Example 1 uses copolymer polypropylene Zhenhai Refining & Chemical E02ES as the raw material for compression molding foam. The preparation process steps are as follows:

[0072] (1) 100 parts by weight of copolymer polypropylene E02ES and 0.2 parts by weight of calcium carbonate with D97 of 8μm are uniformly mixed and then melt-extruded by a twin-screw extruder to form a slab. After calendering, cooling and shaping, the slab is cut into a 12mm thick sheet.

[0073] (2) Place the 12mm board obtained in the previous step into the mold cavity of the molding foaming equipment, then introduce supercritical carbon dioxide and keep it warm and pressurized for a period of time. The heat preservation temperature is 140℃, the pressure is 12MPa, and the heat preservation and pressure preservation time is 2h. After that, the pressure is quickly released within 1.0s, and polypropylene foam material is obtained after shaping.

[0074] Performance Evaluation

[0075] The properties of the polypropylene foam materials prepared in the examples and comparative examples were tested, and the test results are shown in Table 1 below:

[0076] Table 1. Performance test data of polypropylene foam materials prepared in the examples and comparative examples.

[0077]

[0078] As can be seen from the test data in the table, the polypropylene foam material product obtained in the embodiments of the present invention has a low dielectric constant and excellent mechanical properties. Its Shore C hardness and compressive strength are significantly greater than those of the molded foam product of copolymerized polypropylene in Comparative Example 1. Furthermore, the polypropylene foam material obtained in the embodiments has a regular cell structure, uniform cell distribution, and small cell size. This good cell structure is a guarantee of the excellent overall performance of the polypropylene foam product.

[0079] The polypropylene foam material obtained by this invention can be used in the field of communication, such as 5G base station antenna covers, filters, and antenna vibrators, and can also be used in other industrial, construction, and daily life fields.

[0080] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A polypropylene foam material, characterized in that, Made from preform through molding and foaming, the raw materials for preparing the preform, by weight, include: 80-100 parts of homopolymer polypropylene; 1-20 parts of adamantyl methacrylate; Initiator 0.01~0.5 parts; Catalyst 0.01~1 part; Fluoride 0.1~10 parts; Nucleating agent 0.1~0.5 parts; The catalyst is one or more of the following: 2-thiol-benzothiazole zinc salt, N-cyclohexyl-2-benzothiazole sulfenamide, tetramethylthiuram disulfide, tetrabutylthiuram disulfide, tetrabenzylthiuram disulfide, zinc dimethyl dithiocarbamate, zinc diethyl dithiocarbamate, zinc ethylphenyl dithiocarbamate, zinc dibenzyl dithiocarbamate, NN'-diphenylthiourea, zinc dialkyl dithiophosphate, thiomelamine, and NN'-m-phenylenebismaleimide. The fluoride is one or more of perfluoropropyl vinyl ether, perfluorocyclic ether, perfluorobutyl methyl ether, perfluorohexyl ethanol polyoxyethylene ether, perfluorobutyltetrahydrofuran, polyperfluoromethyl isopropyl ether, perfluoroethyl vinyl ether, and perfluoropolyether alcohol.

2. The polypropylene foam material according to claim 1, characterized in that, The homopolymer polypropylene has a number average molecular weight of 5 × 10⁻⁶. 4 ~20×10 4 The melt index of the homopolymer polypropylene is 2~5 g / 10min.

3. The polypropylene foam material according to claim 1, characterized in that, The adamantyl methacrylate is one or more of 2-methyl-2-adamantyl methacrylate, 1-adamantyl methacrylate, 2-isopropyl-2-adamantyl methacrylate, 2-ethyl-2-adamantyl methacrylate, 3-hydroxy-1-adamantyl methacrylate and 1-methyl-1-ethyl-1-adamantyl methanol methacrylate.

4. The polypropylene foam material according to claim 1, characterized in that, The initiator is dicumyl peroxide and / or 2,4-di-tert-butyl peroxide.

5. The polypropylene foam material according to claim 1, characterized in that, The nucleating agent is one or more of calcium carbonate, talc, kaolin, montmorillonite, silica, diatomaceous earth, and silica fume.

6. A method for preparing a polypropylene foam material according to any one of claims 1 to 5, characterized in that, Includes the following steps: a) Homopolymer polypropylene, adamantyl methacrylate, initiator, catalyst, fluoride and nucleating agent are melt-blended and shaped to obtain a preform; b) The preform is molded and foamed to obtain polypropylene foam material.

7. The preparation method according to claim 6, characterized in that, In step a), the temperature of the melt blending is 140~190℃; the thickness of the blank is 8~20mm.

8. The preparation method according to claim 6, characterized in that, In step b), the specific process of compression molding foaming includes: The preform is placed in the mold cavity of the molding foaming equipment, then supercritical gas is introduced and kept at temperature and pressure for a period of time. After that, the pressure is released and the material is shaped to obtain polypropylene foam material.

9. The preparation method according to claim 8, characterized in that, The supercritical gas is carbon dioxide; the pressure for heat preservation and pressure holding is 8~20MPa, the temperature is 140~170℃, and the time is 1~5h.

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