Electromagnetic shielding polypropylene foam material and preparation method thereof

Abstract

The invention relates to the field of electromagnetic shielding polypropylene materials, in particular to an electromagnetic shielding polypropylene foam material and a preparation method thereof, and the electromagnetic shielding polypropylene foam material comprises 40-80% of polypropylene; the content of the compatilizer is 5 to 10 percent; the content of the toughening agent is 4 to 10 percent; 10-30% of an electromagnetic shielding agent; 0-15% of a mineral filler; the content of the coupling agent is 0.2 to 0.6 percent; the content of the antioxidant is 0.1 to 1.0 percent; the content of the lubricating agent is 0.1 to 1.0 percent; a gas foaming agent is injected into the electromagnetic shielding polypropylene material in an injection molding mode, foam holes are formed in the material, so that an electromagnetic shielding agent dispersed in a base material is more intensively gathered in the base material in volume, and a more effective and compact conductive path is formed in the material, so that the electromagnetic shielding polypropylene foam material is obtained.

Description

Technical Field

[0001] The invention relates to the field of electromagnetic shielding polypropylene materials, and in particular to an electromagnetic shielding polypropylene foam material and a preparation method thereof. Background Art

[0002] With the continuous development of information and science and technology, more and more electronic and electrical components and electrical equipment have entered various fields of people's production and life. While bringing great convenience to people's production and life, they have also generated a large amount of electronic radiation and electromagnetic wave pollution, which not only interferes with communications and electronic systems, but also greatly harms people's health. Electromagnetic radiation pollution is called the fourth largest pollution after air pollution, water pollution, and noise pollution. Therefore, vigorously developing materials with excellent electromagnetic shielding is of great significance to people's health and life.

[0003] At present, the electromagnetic shielding materials that are being studied more are mainly ferromagnetic materials and metal good conductor materials, surface conductive shielding materials (including conductive coatings, metal spraying, metal foil and surface metal plating, etc.) and filled composite shielding materials. Filled composite shielding materials are the mainstream of the market due to their advantages such as light weight, low cost and easy processing and molding. The matrix of filled composite shielding materials mostly adopts some polymer synthetic resins with excellent electrical insulation properties, which are compounded with fillers with excellent conductive properties and other additives, and processed into various electromagnetic shielding materials by injection molding or extrusion molding. Polypropylene has good processing properties and excellent mechanical, physical and chemical properties, and is light and cheap. It is widely used in automotive interior and exterior decoration, household appliances and electronics industries. It is currently the fastest growing general thermoplastic plastic. With the rise of intelligent driving control in the automotive field, vehicle-mounted radar brackets and shells require polypropylene composite materials to meet electromagnetic shielding requirements. Therefore, the functionalization of polypropylene materials, especially the electromagnetic shielding effect, has become a new and important development direction for polymer materials.

[0004] In recent years, with the intensification of the new energy crisis, domestic and foreign researchers have unanimously agreed that lightweight materials are an important way to solve the energy crisis. Microporous foam materials, as the most intuitive product of lightweight, are widely used in the aviation industry, agriculture, automotive industry and other fields. Microporous foam materials not only reduce weight but also have excellent physical and mechanical properties, such as good dimensional stability, processing performance, mechanical properties and thermal properties. Polypropylene is a plastic with excellent comprehensive performance. After being made into a foam material, it can maintain the original high temperature resistance and corrosion resistance. By introducing a pore structure, the material is given the inherent characteristics of the foam material such as light weight, sound insulation, heat insulation, cushioning, and energy absorption. With the widespread application of polypropylene foam materials, its functional application requirements are also increasing. Traditional ordinary polypropylene foam materials have been difficult to meet the performance requirements of some applications, such as electromagnetic shielding polypropylene foam materials.

[0005] In order to achieve a better electromagnetic shielding effect, the amount of electromagnetic shielding agent added to the traditional electromagnetic shielding polypropylene material is usually about 25-40%, which greatly increases the cost of the material. At the same time, the addition of a large amount of electromagnetic shielding agent will greatly affect the mechanical properties of the material itself, thereby limiting the scope of use of the material. At the same time, the traditional micro-foamed polypropylene material, due to the low melt strength of the material, often has a poor foaming effect, and the foam cells are prone to collapse and rupture, which is also very limited in practical application.

[0006] Therefore, the technical personnel in this field urgently need to solve the problems that the electromagnetic shielding polypropylene materials in the current technology are high in cost, high in weight, poor in mechanical properties, and low in electromagnetic shielding efficiency; the polypropylene foam material has a low foaming ratio, the bubbles are easy to collapse and rupture, and the application range in electromagnetic shielding is not wide. Summary of the invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide a cross-linked network structure formed by combining an electromagnetic shielding agent and a foaming technology, thereby improving the melt index of the material, improving the foaming effect of the material, reducing the amount of electromagnetic shielding agent added to the material, improving the electromagnetic shielding performance of the material, and solving the problems of electromagnetic shielding polypropylene foam material with high cost, high weight, poor mechanical properties and low electromagnetic shielding efficiency.

[0008] To achieve the above object, the technical solution adopted by the present invention is: an electromagnetic shielding polypropylene foam material, comprising polypropylene, the content of which is 40-80%; a compatibilizer, the content of which is 5-10%; a toughening agent, the content of which is 4-10%; an electromagnetic shielding agent, the content of which is 10-30%; a mineral filler, the content of which is 0-15%; a coupling agent, the content of which is 0.2-0.6%; an antioxidant, the content of which is 0.1-1.0%; and a lubricant, the content of which is 0.1-1.0%; The polypropylene, compatibilizer, toughening agent, electromagnetic shielding agent, mineral filler, coupling agent, antioxidant and lubricant are weighed in proportion and mixed at a low speed in a mixer, and then melt-extruded by a shear screw combination of a twin-screw extruder, and the electromagnetic shielding polypropylene material is obtained by water-cooling strand pelletizing and screening and dehydration; The gas foaming agent is injected into the electromagnetic shielding polypropylene material by injection molding to obtain the electromagnetic shielding polypropylene foam material.

[0009] The above-mentioned electromagnetic shielding polypropylene foam material, the polypropylene includes at least one of homopolymer polypropylene and copolymer polypropylene, and its melt flow rate at a temperature of 230° C. and a load of 2.16 kg is 10-100 g / 10 min.

[0010] The above-mentioned electromagnetic shielding polypropylene foam material, the compatibilizer includes at least one of polypropylene grafted maleic anhydride, polypropylene grafted acrylate glycidyl ester, polyolefin elastomer grafted maleic anhydride, polyolefin elastomer grafted acrylate glycidyl ester, ABS-grafted maleic anhydride, styrene-acrylonitrile-maleic anhydride, and ethylene-butadiene-styrene ternary block copolymer grafted maleic anhydride.

[0011] The electromagnetic shielding polypropylene foam material mentioned above, the electromagnetic shielding agent includes at least one of conductive carbon black, conductive graphite, carbon nanotubes, multi-walled carbon nanotubes, carbon fibers, and graphene aerogel.

[0012] In the above-mentioned electromagnetic shielding polypropylene foam material, the toughening agent is a polyolefin elastomer or a styrene elastomer, and the polyolefin elastomer is an ethylene-octene copolymer with a melt index of 0.1-10 g / 10 min.

[0013] The above-mentioned electromagnetic shielding polypropylene foam material, the mineral filler includes at least one of talc, calcium carbonate, barium sulfate, whisker, and wollastonite; the coupling agent includes at least one of silane coupling agent and titanate coupling agent; the antioxidant includes at least one of hindered phenol, thioester, and phosphite antioxidants; the lubricant includes at least one of polyethylene wax, vinyl bisstearamide, N,N-ethylene bisstearamide, silicone oil, oleamide, ethylene bisoleamide, N,N'-ethylene bisstearamide-grafted maleic anhydride, silicone powder, and fluorine-containing lubricant.

[0014] A method for preparing the electromagnetic shielding polypropylene foam material as described in any one of the above, comprising preparing the electromagnetic shielding polypropylene material by extrusion processing and preparing the electromagnetic shielding polypropylene foam material by injection molding; The electromagnetic shielding polypropylene material obtained by extrusion processing comprises: Step 1: Weigh polypropylene, compatibilizer, toughening agent, electromagnetic shielding agent, mineral filler, coupling agent, antioxidant and lubricant according to proportion and mix them at low speed in a mixer for 10 minutes; Step 2: melt extrusion is performed by a twin-screw extruder under a medium-intensity shear screw combination, the extruded material is cooled to room temperature through a water tank, granulated by a pelletizer, and sieved and dehydrated to obtain an electromagnetic shielding polypropylene material; The electromagnetic shielding polypropylene foam material is obtained by injection molding using a supercritical fluid injection molding foaming device, comprising: Step 3: Adjust the injection molding and foaming process parameters of the supercritical fluid injection molding and foaming equipment; Step 4: Injection, injecting the melt containing the gas foaming agent into the mold cavity; Step 5: Maintain the pressure to allow the melt containing the gas foaming agent to fill the mold cavity; Step 6: Open the mold for the first time, control the mold opening distance to form a new cavity of the required thickness, so that the melt containing the gas foaming agent can be quickly decompressed, expanded and foamed; Step 7: After cooling, open the mold for the second time and take out the sample.

[0015] In the above-mentioned method for preparing the electromagnetic shielding polypropylene foam material, the supercritical fluid injection foaming equipment comprises an injection molding machine and a supercritical fluid injection device.

[0016] The preparation method of the above-mentioned electromagnetic shielding polypropylene foam material, the injection molding foaming process parameters include melt temperature, set to 200-210°C; mold temperature, set to 40-60°C; injection speed, set to 120-200mm / s; injection pressure, set to 180-250 MPa; back pressure, set to 15-25 MPa; holding pressure, set to 30-60MPa; position, set to 80-120 mm; residence time, set to 5-10 s; storage distance, set to 2-12 mm; storage speed, set to 80-120mm / s; gas foaming agent content, set to 0.5-1.0wt%.

[0017] The beneficial effects of the electromagnetic shielding polypropylene foam material of the present invention are as follows: a gas foaming agent is injected into the electromagnetic shielding polypropylene material by injection molding to form pores in the material, so that the electromagnetic shielding agent dispersed in the base material is more concentrated in the base material in terms of volume, thereby forming a more effective and dense conductive path in the material to make the electromagnetic shielding polypropylene foam material; at the same time, because its porous structure has a lower density, a weight reduction of 1-10% is achieved while ensuring material performance and product functions; compared with unfoamed injection molded parts, the amount of electromagnetic shielding polypropylene prefabricated material used is reduced, thereby reducing costs; the introduction of the pore structure can enhance the multiple reflection / scattering attenuation of electromagnetic waves inside the pores, and the substantial increase in absorption loss improves the overall shielding effectiveness of the material.

[0018] The beneficial effect of the preparation method of an electromagnetic shielding polypropylene foam material of the present invention is: this method proposes for the first time to combine two technologies together. On the one hand, the addition of electromagnetic shielding fillers can form a cross-linked network structure, thereby improving the melt index of the material and improving the foaming effect of the material; and due to the formation of pores in the material, the electromagnetic shielding fillers dispersed in the base material are more concentrated in the matrix in terms of volume, thereby forming a more effective and dense conductive path in the material, reducing the amount of electromagnetic shielding fillers added to the material and improving the electromagnetic shielding performance of the material. The internal structure of the electromagnetic shielding polypropylene foam material is a pore structure, which can absorb more than 80% of electromagnetic wave energy. The functional construction of PP foam material further broadens its application range and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the sample structure in the embodiment of the present invention. DETAILED DESCRIPTION

[0020] Invention patent CN 202211151006.X discloses an isotropic electromagnetic shielding polypropylene composite material and its preparation and application, the components include polypropylene, polyethylene, conductive carbon black, lubricant, antioxidant, filler. The composite material is composed of the following raw materials and their weight proportions: 50-70 parts of polypropylene, 18-35 parts of polyethylene, 9-15 parts of conductive carbon black, 0.1-0.3 parts of lubricant, 0.1-1 parts of antioxidant, and 0-30 parts of filler. The polypropylene composite material of the present invention has a good electromagnetic shielding effect (>30dB) and achieves an isotropic electromagnetic shielding effect.

[0021] Invention patent CN 202210224499.9 discloses a high-toughness electromagnetic shielding polypropylene composite material and its preparation method and application. The present invention uses epoxy compatibilizers and fatty acid lubricants. The epoxy groups in some compatibilizers undergo a ring-opening reaction under the acid catalysis of the fatty acid lubricant, so that the molecular chain growth of the compatibilizer undergoes a certain entanglement, forming a certain physical network in the composite material system, which can improve the dispersion stability of conductive carbon black and compatibilizer in the system, thereby improving the electromagnetic shielding performance and toughness of the material; more importantly, the present invention adds the compatibilizer to the conductive carbon black masterbatch, which can make the compatibilizer slowly released into the polypropylene composite material system during the second melting process, so that the other components in the polypropylene composite material system have sufficient time to mix evenly under the action of the lubricant, further improving the mechanical properties of the material.

[0022] Invention patent CN20181084506.8 discloses a new type of low-odor electromagnetic shielding polypropylene composite material and its preparation method, which includes the following raw materials in parts by weight: 60-90 parts of polypropylene, 5-20 parts of toughening agent, 0.1-1 parts of lubricant, 0.1-1 parts of antioxidant, 0.5-5 parts of mineral gel, 0.5-4 parts of deodorizing adsorbent, 2-20 parts of carbon fiber, 2-10 parts of magnetic particles, and 0.5-10 parts of coupling agent. The present invention adopts a composite system of carbon fiber and magnetic particles with high magnetic permeability and high electrical conductivity as an electromagnetic shielding material, so that the prepared polypropylene composite material has excellent electromagnetic shielding performance in a wider frequency range, and the introduction of carbon fiber also enhances the mechanical properties of polypropylene materials to a certain extent. The present invention adds a high-efficiency deodorizing adsorbent and magnesium aluminum silicate mineral gel to the formula system to effectively remove volatile small molecules in the polypropylene matrix. The prepared composite material also has the advantages of low odor and low VOC, which greatly expands the application field of the material.

[0023] Invention patent CN 202210613287.X discloses a high foaming ratio conductive polypropylene composite material and a preparation method thereof, which relates to the field of supercritical fluid foaming; the primary product of the composite material comprises, by mass, 60-85 parts of high-solution polypropylene, 3-5 parts of compatibilizer, 2-4 parts of carbon nanotubes, 8-20 parts of conductive carbon black, 1-2 parts of polycarboxylic acid water reducer, 1-2 parts of silica fume, 0.5-2 parts of lubricant, 0.5-1.5 parts of antioxidant and 0.2-0.5 parts of nucleating agent; the method uses a supercritical fluid foaming process to foam the primary product; the present invention adopts a compound of carbon nanotubes and conductive carbon black as the conductive filler of the polypropylene composite material, and at the same time, the surface of the carbon nanotubes is grafted by a polycarboxylic acid water reducer and then mixed and stirred with silica fume, which can effectively solve the problem of uneven dispersion of the conductive filler, thereby improving the conductive properties of the polypropylene composite material, and at the same time improving the foaming performance of the product; the final product has smaller pore size, finer pores, and a larger foaming ratio.

[0024] Invention patent CN201811126476.4 discloses a conductive foamed polypropylene material and a preparation method thereof, wherein the conductive foamed polypropylene material is made of a conductive foamed polypropylene prefabricated material and a foaming agent, wherein the amount of the foaming agent added accounts for 2-5% of the weight of the conductive foamed polypropylene material; the conductive foamed polypropylene prefabricated material is composed of the following components by weight: 54-86.8 parts of polypropylene, 8-15 parts of conductive carbon black, 0-10 parts of toughening agent, 5-20 parts of filler, 0.1-0.5 parts of antioxidant, and 0.1-0.5 parts of processing aid. The present invention applies the micro-foaming process to the conductive modified polypropylene material, the addition of conductive carbon black forms a cross-linked network structure, the formation of pores in the material, and the conductive carbon black dispersed in the base material is more concentrated in the matrix from the volume, forming a more effective and dense conductive path in the material, reducing the amount of conductive additives used in the material, effectively and significantly reducing the surface resistance of the material, improving the conductive effect of the material and reducing the material cost; the preparation process of the present invention is simple, and the prepared polypropylene material has excellent performance.

[0025] Invention patent CN 202211151006.X discloses a PP-based composite material for electromagnetic shielding and its preparation method, which is composed of the following raw materials in weight percentage: 57.2-73% PP granular resin, 3-5% compatibilizer, 18-25% conductive electromagnetic shielding agent, 4-8% foaming agent masterbatch, 1-3% toughening agent, 0.2-0.4% antioxidant, 0.6-1.0% lubricant, 0.2-0.4% light stabilizer. The present invention uses a carbon fiber and graphene aerogel compounding scheme, combined with a micro-foaming process, to prepare a polypropylene composite material with good mechanical properties and high electromagnetic shielding capability.

[0026] The parts of the above patents and prior arts that are the same as the present technical solution will not be repeated here. The present technical solution mainly aims to improve the problems existing in the prior art.

[0027] The disadvantages of current technology are that electromagnetic shielding polypropylene materials are high in cost, heavy in weight, have poor mechanical properties and low electromagnetic shielding efficiency; polypropylene foam materials have low foaming ratios, and the pores are prone to collapse and rupture, so they are not widely used in electromagnetic shielding.

[0028] This technical solution proposes for the first time to combine the two technologies together. On the one hand, the addition of electromagnetic shielding fillers can form a cross-linked network structure, thereby improving the melt index of the material and improving the foaming effect of the material; on the other hand, due to the formation of pores in the material, the electromagnetic shielding fillers dispersed in the base material are more concentrated in volume in the matrix, thereby forming a more effective and dense conductive path in the material, reducing the amount of electromagnetic shielding fillers added to the material and improving the electromagnetic shielding performance of the material.

[0029] This technical solution is an electromagnetic shielding polypropylene foam material and a preparation method thereof. First, polypropylene material, electromagnetic shielding agent and other additives are melt-blended by a twin-screw extruder to obtain an electromagnetic shielding polypropylene prefabricated material. A supercritical gas foaming method and a secondary mold opening process are used to prepare an electromagnetic shielding polypropylene foam material with a high foaming ratio. Its electromagnetic shielding efficiency is higher than that of the unfoamed sample, and the electromagnetic shielding material can be lightweight. The functional construction of PP foam material further broadens its application range and has good application prospects.

[0030] In order to achieve the purposes of good electromagnetic shielding effect, high foaming ratio, excellent mechanical properties, etc., in addition to the formula composition, the present invention will make specific modifications and requirements in the injection molding foaming process.

[0031] Example 1 An electromagnetic shielding polypropylene foam material comprises polypropylene, a compatibilizer, a toughening agent, an electromagnetic shielding agent, a mineral filler, a coupling agent, an antioxidant and a lubricant. The polypropylene, the compatibilizer, the toughening agent, the electromagnetic shielding agent, the mineral filler, the coupling agent, the antioxidant and the lubricant are weighed in proportion and mixed at a low speed in a mixer, and then melt-extruded in a screw combination sheared by a twin-screw extruder, and the electromagnetic shielding polypropylene material is obtained by water-cooling strand pelletizing and screening and dehydration.

[0032] The gas foaming agent is injected into the electromagnetic shielding polypropylene material by injection molding to obtain the electromagnetic shielding polypropylene foam material.

[0033] Polypropylene, with a content of 40-80%, includes at least one of homopolymer polypropylene and copolymer polypropylene, and has a melt flow rate of 10-100 g / 10 min at a temperature of 230° C. and a load of 2.16 kg.

[0034] The compatibilizer has a content of 5-10%, and the compatibilizer includes at least one of polypropylene grafted maleic anhydride, polypropylene grafted acrylate glycidyl ester, polyolefin elastomer grafted maleic anhydride, polyolefin elastomer grafted acrylate glycidyl ester, ABS-grafted maleic anhydride, styrene-acrylonitrile-maleic anhydride, and ethylene-butadiene-styrene ternary block copolymer grafted maleic anhydride.

[0035] The toughening agent has a content of 4-10%, and the toughening agent is a polyolefin elastomer or a styrene elastomer. The polyolefin elastomer is an ethylene-octene copolymer with a melt index of 0.1-10 g / 10 min.

[0036] The electromagnetic shielding agent has a content of 10-30%, and the electromagnetic shielding agent includes at least one of conductive carbon black, conductive graphite, carbon nanotubes, multi-walled carbon nanotubes, carbon fibers, and graphene aerogel.

[0037] The mineral filler has a content of 0-15%, and the mineral filler includes at least one of talc, calcium carbonate, barium sulfate, whisker and wollastonite.

[0038] The coupling agent has a content of 0.2-0.6%, and the coupling agent includes at least one of a silane coupling agent and a titanate coupling agent.

[0039] The antioxidant has a content of 0.1-1.0%, and the antioxidant includes at least one of hindered phenols, thioesters, and phosphites.

[0040] Lubricant, content is 0.1-1.0%, the lubricant comprises at least one of polyethylene wax, vinyl bisstearamide, N,N-ethylene bisstearamide, silicone oil, oleamide, ethylene bisoleamide, N,N'-ethylene bisstearamide-grafted maleic anhydride, silicone powder, and fluorine-containing lubricant.

[0041] Example 2 A method for preparing an electromagnetic shielding polypropylene foam material comprises extrusion processing to prepare the electromagnetic shielding polypropylene material and injection molding processing to prepare the electromagnetic shielding polypropylene foam material.

[0042] Electromagnetic shielding polypropylene materials made by extrusion processing include: Step 1: Weigh polypropylene, compatibilizer, toughening agent, electromagnetic shielding agent, mineral filler, coupling agent, antioxidant and lubricant according to proportion and mix them at low speed in a mixer for 10 minutes.

[0043] Step 2: melt extrusion is carried out through a twin-screw extruder under a medium-intensity shear screw combination, the extruded material strips are cooled to room temperature through a water trough, granulated through a pelletizer, and sieved and dehydrated to obtain an electromagnetic shielding polypropylene material.

[0044] The electromagnetic shielding polypropylene foam material is made by injection molding using supercritical fluid injection molding foaming equipment, including: Step 3: Adjust the injection molding and foaming process parameters of the supercritical fluid injection molding and foaming equipment.

[0045] Step 4: Injection: injecting the melt containing the gas foaming agent into the mold cavity.

[0046] Step 5: Maintain pressure to allow the melt containing the gas foaming agent to fill the mold cavity.

[0047] Step 6: Open the mold for the first time, control the mold opening distance to form a new cavity of the required thickness, so that the melt containing the gas foaming agent can quickly release pressure and expand and foam.

[0048] Step 7: After cooling, open the mold for the second time and eject the sample.

[0049] Example 3 An electromagnetic shielding polypropylene foam material and a preparation method thereof specifically include:

[0050] Formula: Electromagnetic shielding polypropylene material, Polypropylene: 40-80; compatibilizer: 5-10; toughening agent: 4-10; electromagnetic shielding agent: 10-30; mineral filler: 0-15; coupling agent: 0.2-0.6; antioxidant: 0.1-1.0; lubricant: 0.1-1.0.

[0051] The polypropylene is at least one of homopolypropylene and copolymer polypropylene, and has a melt flow rate of 10-100 g / 10 min at a temperature of 230° C. and a load of 2.16 kg.

[0052] The compatibilizer is at least one of PP-g-MAH, PP-g-GMA, POE-g-MAH, POE-g-GMA, ABS-g-MAH, AS-g-MAH, SEBS-g-MAH (polypropylene grafted with maleic anhydride, polypropylene grafted with glycidyl acrylate, polyolefin elastomer grafted with maleic anhydride, polyolefin elastomer grafted with glycidyl acrylate, ABS-grafted with maleic anhydride, styrene-acrylonitrile-maleic anhydride, ethylene-butadiene-styrene ternary block copolymer grafted with maleic anhydride).

[0053] The toughening agent is a polyolefin elastomer or a styrene elastomer; the polyolefin elastomer is an ethylene-octene copolymer with a melt index of 0.1-10 g / 10 min.

[0054] The electromagnetic shielding agent is at least one of conductive carbon black, conductive graphite, carbon nanotubes, multi-walled carbon nanotubes, carbon fibers, and graphene aerogel.

[0055] The mineral filler is at least one of talc, calcium carbonate, barium sulfate, whisker and wollastonite.

[0056] The coupling agent is at least one of a silane coupling agent and a titanate coupling agent.

[0057] The antioxidant is at least one of hindered phenol, thioester and phosphite antioxidants.

[0058] The lubricant is at least one of polyethylene wax, vinyl bisstearamide, N,N-ethylene bisstearamide, silicone oil, oleamide, ethylene bisoleamide, N,N'-ethylene bisstearamide-grafted maleic anhydride, silicone powder, and fluorine-containing lubricant.

[0059] Extrusion processing technology.

[0060] Polypropylene, compatibilizer, toughening agent, electromagnetic shielding agent, mineral filler, coupling agent, antioxidant and lubricant are weighed in proportion and mixed at a low speed in a mixer for 10 minutes, then melt-extruded by a twin-screw extruder under a medium-intensity shear screw combination, and the electromagnetic shielding polypropylene material is obtained by water-cooled strand pelletizing and screening and dehydration.

[0061] The temperature of each temperature zone of the extruder is: first stage: 180~195℃; second stage: 190-210℃; third stage: 200~230℃; fourth stage: 200~230℃; fifth stage: 200~230℃; sixth stage: 200~230℃; seventh stage: 200~230℃; eighth stage: 200~230℃; ninth stage: 200~230℃; tenth stage: 200~230℃; die head 200~215℃. The extruded material is cooled to room temperature through the water tank and granulated by the pelletizer. The main engine speed is set to 250~450r / min.

[0062] Injection molding process.

[0063] The gas foaming agent is one or more of carbon dioxide, nitrogen, air, pentane and oxygen.

[0064] Sample 1 was prepared using a supercritical fluid injection foaming device and a secondary mold opening foaming process. Figure 1As shown. The diameter is 223mm and the thickness is 2mm. The thickness can be adjusted to a maximum of 18mm through the first mold opening. Therefore, by adjusting the mold opening distance, foaming samples with different expansion ratios can be obtained. The supercritical fluid injection molding foaming equipment is mainly composed of an injection molding machine and a supercritical fluid injection device. The secondary mold opening injection molding foaming molding process includes five processes: injection, pressure holding (cooling), the first mold opening, cooling, and the second mold opening. The injection process injects the melt containing the gas foaming agent into the mold cavity, and the melt fills the cavity after pressure holding (cooling). The first mold opening controls the mold opening distance to form a new cavity of the required thickness, so that the melt can quickly relieve pressure and expand and foam. After cooling, the second mold opening is performed to eject the sample.

[0065] The injection molding foaming process parameters are as follows: melt temperature: 200-210℃; mold temperature: 40-60℃; injection speed: 120-200 (mm / s); injection pressure 180-250 MPa; back pressure: 15-25 MPa; holding pressure: 30-60MPa; position 80-120mm; residence time: 5-10 s; storage distance: 2-12mm; storage speed: 80-120 (mm / s); gas foaming agent content: 0.5-1.0 (wt%).

[0066] test.

[0067] Expansion ratio: actual thickness of the foamed sample / thickness of the unfoamed sample (2mm).

[0068] Electromagnetic shielding performance: Rohde & Schwarz ZVA67 vector network analyzer was used to test the waveguide method. The test frequency band is 5.38-8.17GHz (C band), the sample size is 34.9mm long and 15.8mm wide, and the thickness of the test sample is the original thickness of the sample obtained after injection molding and foaming, that is, 2mm, 4mm, 6mm, 8mm, 10mm, 12mm and 14mm respectively. Through the electromagnetic shielding performance test, the electromagnetic shielding effectiveness SE (Shielding Effectiveness) of the material can be obtained, including the total shielding effectiveness SE total, reflection loss SE ref and absorption loss SE abs, reflection coefficient R and absorption coefficient A, and the dielectric constant data can be obtained.

[0069] Example 4 70% PP M1200HS, 5% PP-g-MAH, 10% graphene aerogel, 5% POE 875L, 0.3% 1076, 0.6% silicone powder were mixed at low speed in a mixer for 10 minutes, added to the main feed port of a twin-screw extruder, and 10% continuous carbon fiber was added to the fiber port at the same time. After melt extrusion, cooling and granulation were performed to make electromagnetic shielding polypropylene material. The extrusion temperature was 190-230℃ and the screw speed was 250-350r / min. Electromagnetic shielding polypropylene foam material was prepared using supercritical fluid injection molding foaming equipment, injection molding method, and secondary mold opening foaming process. The total shielding effectiveness SE total is 34 dB.

[0070] Specific process parameters of injection molding foaming: melt temperature: 200℃; mold temperature: 40℃; injection speed: 150 (mm / s); injection pressure: 200 MPa; back pressure: 20 MPa; holding pressure: 40 MPa; position: 100 mm; residence time: 8 s; storage distance: 2-12; storage speed: 100 (mm / s); gas foaming agent N2 content: 0.8 (wt%).

[0071] Example 5 As shown in Table 1, 54.5% PP WB140HMS, 5% POE-g-MAH, 8% POE 6102, 22.5% conductive carbon black, 10% talc A60, 0.4% silane coupling agent 560, 0.2% primary antioxidant 1010, 0.4% secondary antioxidant 168, and 0.6% EBS were mixed at low speed in a mixer for 10 minutes, added to the main feed port of a twin-screw extruder, and melt-extruded and cooled to form an electromagnetic shielding polypropylene material, with an extrusion temperature of 190-210°C and a screw speed of 250-350r / min. Using supercritical fluid injection molding foaming equipment, injection molding method, and secondary mold opening foaming process, electromagnetic shielding polypropylene foam materials with different expansion ratios were prepared. Specific process parameters of injection molding foaming: melt temperature: 200℃; mold temperature: 40℃; injection speed: 150 (mm / s); injection pressure: 200 MPa; back pressure: 20 MPa; holding pressure: 40 MPa; position: 100mm; residence time: 8 s; storage distance: 2-12; storage speed: 100 (mm / s); gas foaming agent N2 content: 0.8 (wt%).

[0072] Table 1: Component composition .

[0073] Example 6 As shown in Table 2, 50% PP WB140HMS, 5% POE-g-MAH, 5% POE875, 30% conductive carbon black, 10% talcum powder A60, 0.4% silane coupling agent 560, 0.2 primary antioxidant 1010, 0.4 secondary antioxidant 168, and 0.6% EBS were mixed at low speed in a mixer for 10 minutes, added to the main feed port of a twin-screw extruder, and melt-extruded and cooled for granulation to form an electromagnetic shielding polypropylene material, with an extrusion temperature of 190-210°C and a screw speed of 250-350r / min. Using supercritical fluid injection molding foaming equipment, injection molding method, and secondary mold opening foaming process, electromagnetic shielding polypropylene foam materials with different expansion ratios were prepared. Specific process parameters of injection molding foaming: melt temperature: 200℃; mold temperature: 40℃; injection speed: 150 (mm / s); injection pressure: 200 MPa; back pressure: 20 MPa; holding pressure: 40 MPa; position: 100 mm; residence time: 8 s; storage distance: 2-12; storage speed: 100 (mm / s); gas foaming agent N2 content: 0.8 (wt%).

[0074] Table 2: Composition of each component .

[0075] From the above results, we can conclude that foaming the material can effectively adjust the electromagnetic shielding performance of the material. When the expansion ratio is low, the electromagnetic shielding efficiency of the foamed material will decrease compared with the unfoamed material. As the expansion ratio continues to increase, the electromagnetic shielding efficiency of the foamed material will increase, and even be higher than the shielding efficiency of the unfoamed material. Increasing the content of conductive fillers to improve the conductivity of the material can effectively promote the enhancement effect of the pore structure on electromagnetic shielding, so that the electromagnetic shielding efficiency of the foamed material has a significant enhancement effect at a lower expansion ratio. On the other hand, foaming the material can effectively adjust the material's absorption and reflection ability of electromagnetic waves, because the existence of the pore structure can greatly enhance the absorption loss of the foamed material to electromagnetic waves, thereby reducing the pollution of the environment caused by the secondary reflection of electromagnetic waves.

[0076] The key points of this technical solution are the amount and type of electromagnetic shielding agent; the method and process for foaming electromagnetic shielding polypropylene material; the preparation of electromagnetic shielding polypropylene material combined with the foaming process, the two influence each other to improve the electromagnetic shielding effectiveness of the material.

[0077] Foaming the material can effectively adjust the shielding performance of the material. When the content of electromagnetic shielding agent is high, foaming can improve the overall shielding effectiveness of the material. On the other hand, by adjusting the expansion ratio / cell structure, the absorption and reflection ratio of electromagnetic waves can be effectively adjusted. The existence of the cell structure can enhance the absorption loss of electromagnetic waves, thereby reducing the pollution of the environment caused by the secondary reflection of electromagnetic waves. Electromagnetic shielding polypropylene foam material has good application prospects in the preparation of lightweight electromagnetic shielding materials.

[0078] The above embodiments are only for illustrating the inventive concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. An electromagnetic shielding polypropylene foam material, characterized in that: Including polypropylene, content is 40-80%; compatibilizer, content is 5-10%; toughening agent, content is 4-10%; electromagnetic shielding agent, content is 10-30%; mineral filler, content is 0-15%; coupling agent, content is 0.2-0.6%; antioxidant, content is 0.1-1.0%; lubricant, content is 0.1-1.0%; The polypropylene, compatibilizer, toughening agent, electromagnetic shielding agent, mineral filler, coupling agent, antioxidant and lubricant are weighed in proportion and mixed at a low speed in a mixer, and then melt-extruded by a shear screw combination of a twin-screw extruder, and the electromagnetic shielding polypropylene material is obtained by water-cooling strand pelletizing and screening and dehydration; The gas foaming agent is injected into the electromagnetic shielding polypropylene material by injection molding to obtain the electromagnetic shielding polypropylene foam material.

2. The electromagnetic shielding polypropylene foam material according to claim 1, characterized in that: The polypropylene comprises at least one of homopolypropylene and copolymer polypropylene, and has a melt flow rate of 10-100 g / 10 min at a temperature of 230° C. and a load of 2.16 kg.

3. The electromagnetic shielding polypropylene foam material according to claim 1, characterized in that: The compatibilizer includes at least one of polypropylene grafted maleic anhydride, polypropylene grafted acrylate glycidyl ester, polyolefin elastomer grafted maleic anhydride, polyolefin elastomer grafted acrylate glycidyl ester, acrylonitrile-butadiene-styrene resin-grafted maleic anhydride, styrene-acrylonitrile-maleic anhydride, and ethylene-butadiene-styrene terblock copolymer grafted maleic anhydride.

4. The electromagnetic shielding polypropylene foam material according to claim 1, characterized in that: The electromagnetic shielding agent includes at least one of conductive carbon black, conductive graphite, carbon nanotubes, multi-walled carbon nanotubes, carbon fibers, and graphene aerogel.

5. The electromagnetic shielding polypropylene foam material according to claim 1, characterized in that: The toughening agent is a polyolefin elastomer or a styrene elastomer, and the polyolefin elastomer is an ethylene-octene copolymer with a melt index of 0.1-10 g / 10 min.

6. The electromagnetic shielding polypropylene foam material according to claim 1, characterized in that: The mineral filler includes at least one of talc, calcium carbonate, barium sulfate, whisker and wollastonite; the coupling agent includes at least one of silane coupling agent and titanate coupling agent; the antioxidant includes at least one of hindered phenol, thioester and phosphite antioxidants; the lubricant includes at least one of polyethylene wax, vinyl bisstearamide, N,N-ethylene bisstearamide, silicone oil, oleamide, ethylene bisoleamide, N,N'-ethylene bisstearamide-grafted maleic anhydride, silicone powder and fluorine-containing lubricant.

7. A method for preparing the electromagnetic shielding polypropylene foam material according to any one of claims 1 to 6, characterized in that: Including electromagnetic shielding polypropylene material obtained by extrusion processing and electromagnetic shielding polypropylene foam material obtained by injection molding; The electromagnetic shielding polypropylene material obtained by extrusion processing comprises: Step 1: Weigh polypropylene, compatibilizer, toughening agent, electromagnetic shielding agent, mineral filler, coupling agent, antioxidant and lubricant according to proportion and mix them at low speed in a mixer for 10 minutes; Step 2: melt extrusion is performed by a twin-screw extruder under a medium-intensity shear screw combination, the extruded material is cooled to room temperature through a water tank, granulated by a pelletizer, and sieved and dehydrated to obtain an electromagnetic shielding polypropylene material; The electromagnetic shielding polypropylene foam material is obtained by injection molding using a supercritical fluid injection molding foaming device, comprising: Step 3: Adjust the injection molding and foaming process parameters of the supercritical fluid injection molding and foaming equipment; Step 4: Injection, injecting the melt containing the gas foaming agent into the mold cavity; Step 5: Maintain the pressure to allow the melt containing the gas foaming agent to fill the mold cavity; Step 6: Open the mold for the first time, control the mold opening distance to form a new cavity of the required thickness, so that the melt containing the gas foaming agent can be quickly decompressed, expanded and foamed; Step 7: After cooling, open the mold for the second time and take out the sample.

8. The method for preparing the electromagnetic shielding polypropylene foam material according to claim 7, characterized in that: The supercritical fluid injection molding and foaming equipment comprises an injection molding machine and a supercritical fluid injection device.

9. The method for preparing the electromagnetic shielding polypropylene foam material according to claim 7, characterized in that: The injection molding foaming process parameters include melt temperature, set to 200-210°C; mold temperature, set to 40-60°C; injection speed, set to 120-200mm / s; injection pressure, set to 180-250 MPa; back pressure, set to 15-25 MPa; holding pressure, set to 30-60MPa; position, set to 80-120 mm; dwell time, set to 5-10 s; storage distance, set to 2-12mm; storage speed, set to 80-120mm / s; gas foaming agent content, set to 0.5-1.0wt%.

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