A polyvinyl chloride electromagnetic shielding foam material and a method for preparing the same

Abstract

The present application relates to the technical field of polyvinyl chloride foam material preparation, and particularly relates to a polyvinyl chloride electromagnetic shielding foam material and a preparation method thereof, wherein polyvinyl chloride resin, diisooctyl phthalate, magnesium hydroxide, copper-plated Mxene, light calcium carbonate, a heat stabilizer, a light-proof agent and a lubricant are uniformly mixed according to a certain weight ratio, and then are mixed by using a high-temperature mixing machine, and then are subjected to mold pressing to obtain a PVC composite material forming sample; the PVC composite material forming sample is added into a barrel of a conical twin-screw extruder, is subjected to extrusion forming, is subjected to pre-stretching, and then is subjected to foaming treatment to obtain the polyvinyl chloride electromagnetic shielding foam material. After the pre-stretching process, the polyvinyl chloride electromagnetic shielding foam material is obtained, the cell morphology in the polyvinyl chloride electromagnetic shielding foam material has a certain orientation along the stretching direction, the cell size is large, the specific surface area of the cells is increased, and the electromagnetic shielding performance of the material is improved.

Description

A polyvinyl chloride electromagnetic shielding foam material and its preparation method Technical Field

[0001] This invention relates to the field of polyvinyl chloride foam material preparation technology, specifically a polyvinyl chloride electromagnetic shielding foam material and its preparation method. Background Technology

[0002] Polyvinyl chloride (PVC) is a general-purpose plastic with high mechanical properties, and its foam products also possess excellent properties such as light weight, chemical resistance, and abundant raw material sources. However, with the advancement of technology and the increasing awareness of environmental protection, traditional PVC foam materials are facing increasingly prominent challenges in terms of flame retardancy, temperature resistance, environmental friendliness, and functionality.

[0003] Patent application number 202110837965.6 discloses a flame-retardant PVC foam and its preparation method. It improves the flame-retardant rating by adding organophosphorus flame retardants. This approach not only increases costs, but the organophosphorus compounds and cationic surfactants in these flame retardants are also prone to volatilization during processing, leading to irritating odors and toxic gases. Furthermore, they produce drippings during combustion, posing a threat to the environment and human health. Patent application number 202211512401.6 discloses a polymer electromagnetic shielding composite foam with an insulating structure and its preparation method. It first prepares magnetic particle-polymer microspheres, then adds these microspheres to a chemical plating solution to coat them with conductive metal, followed by molding and foaming to obtain the polymer electromagnetic shielding composite foam. This patent uses ferromagnetic particles coated with conductive metal to improve the electromagnetic shielding performance of the material. However, ferromagnetic particles are prone to oxidation and rust in humid or corrosive environments, affecting the long-term stability and service life of the material. Under alternating electromagnetic fields, ferromagnetic particles generate eddy current losses and heat. If this heat cannot be dissipated in time, it may cause material aging and performance degradation. Patent application number 202010015985.0 discloses a polymer electromagnetic shielding composite foam with a gradient filler structure and its preparation method. Conductive metal is loaded onto hollow glass microspheres to obtain low-density conductive particles, which are then added to a polymer solution, a curing agent is added, and the mixture is ultrasonically stirred, allowed to stand at room temperature, and subsequently foamed to obtain the polymer electromagnetic shielding composite foam. Hollow glass microspheres themselves are insulating; to achieve an effective conductive network, a high content of conductive metal filler is required, leading to an increase in the density of the composite material, which is detrimental to lightweight design. Furthermore, excessive filler reduces the plasticity of the matrix, causing the material to become brittle and deteriorating mechanical properties such as compressive strength and impact toughness. Simultaneously, the inherent hydrophobicity of hollow glass microspheres, along with differences in thermal expansion coefficients and polarity between them and the polymer matrix, creates prominent interface problems, affecting the continuity of the conductive network. Furthermore, the thin walls of hollow glass microspheres make them prone to breakage during foaming and expansion, forming defects in the matrix and reducing the material's mechanical and shielding properties. As shown in Figure 4, its electromagnetic shielding effectiveness is approximately 22-38 dB, indicating a limited shielding effect. Patent application number 201910899525.6 discloses a carbon foam electromagnetic shielding material, its preparation method, and its application. The method involves mixing magnesium powder, polyvinyl chloride powder, ferrocene, and chloride salts, pressing the mixture into a column, and then placing the sample in a propagating reactor for a self-propagating high-temperature reaction to obtain carbon foam. The carbon foam is then mixed with a matrix, heated, and naturally cooled to obtain the carbon foam electromagnetic shielding material, which exhibits a shielding effectiveness between 37.5-39.0 dB, indicating a limited shielding effect.Patent application number 201310648815.6 discloses a polyvinyl chloride composite material with electromagnetic shielding function and its preparation method. The method involves mixing polyvinyl chloride, carbon black, ethylene-vinyl acetate copolymer, calcium stearate, and ferrous ferrite, then extruding the mixture using an extruder. Subsequently, the mixture is mixed evenly with a compatibilizer and thermoplastic polyurethane elastomer rubber and extruded again to obtain the final product. The electromagnetic shielding effect of the polyvinyl chloride composite material prepared by this patent is 31-35 dB, which is considered a moderate shielding effect.

[0004] Currently available PVC electromagnetic shielding materials or polymer electromagnetic shielding foam materials have limited electromagnetic shielding effects and are insufficient to meet the needs of special scenarios with high electromagnetic shielding requirements. Summary of the Invention

[0005] To address the above technical problems, this invention provides a polyvinyl chloride (PVC) electromagnetic shielding foam material and its preparation method. The flame retardancy of the PVC electromagnetic shielding foam material is improved by adding magnesium hydroxide, and its thermal and light-blocking properties are improved by adding heat stabilizers and light-blocking agents. The addition of copper-plated Mxene enhances the electromagnetic shielding capability of the PVC foam material, giving it excellent electromagnetic shielding performance. Furthermore, the pre-stretching process followed by foaming results in a certain orientation of the cell morphology along the stretching direction, larger cell size, and increased specific surface area, which further improves the material's electromagnetic shielding performance.

[0006] This invention is specifically achieved through the following technical solution: a method for preparing polyvinyl chloride electromagnetic shielding foam material according to this invention includes the following steps:

[0007] (1) According to the weight parts, 90-110 parts of polyvinyl chloride resin, 35-50 parts of diisooctyl phthalate, 1-10 parts of magnesium hydroxide, 0.5-1 parts of copper plating Mxene, 10-20 parts of light calcium carbonate, 6-12 parts of heat stabilizer, 1-3 parts of light shielding agent, and 0.5-2 parts of lubricant are mixed evenly and then kneaded in a high-temperature mixer to obtain a mixture;

[0008] (2) The mixture after mixing is molded to obtain a PVC composite material sample;

[0009] (3) The PVC composite material molding sample is added into the barrel of the conical twin-screw extruder, and after plasticizing, melting and extrusion, a PVC composite board is obtained. The PVC composite board passes through the first traction device and the second traction device in sequence. The speed of the second traction device is greater than that of the first traction device. Under the action of the second traction device and the first traction device, the PVC composite board is pre-stretched to obtain a pre-stretched extruded board.

[0010] (4) The pre-stretched extruded sheet is foamed to obtain polyvinyl chloride electromagnetic shielding foam material.

[0011] In the aforementioned method for preparing polyvinyl chloride electromagnetic shielding foam material, the stirring rate of the high-temperature mixer in step (1) is 80~120 rpm, the mixing temperature is 150~200℃, and the mixing time is 2~6 min.

[0012] The aforementioned method for preparing polyvinyl chloride electromagnetic shielding foam material includes step (2) of molding, which specifically includes: first heating the press to 180-190°C, preheating at 180-190°C for 5 minutes, placing the mixture in the mold, and pressing it under 10MPa pressure to obtain a PVC composite material sample.

[0013] In the aforementioned method for preparing polyvinyl chloride electromagnetic shielding foam material, the compression ratio of the extruder head in step (3) is 4~10, and the speed ratio of the second traction device to the first traction device is (1.1~1.9):1.

[0014] The aforementioned method for preparing polyvinyl chloride electromagnetic shielding foam material, specifically the foaming process in step (4) includes: immersing the pre-stretched extruded sheet obtained in step (3) in a foaming kettle at a temperature of 100~160℃ and a pressure of 13.8MPa, so that CO2 dissolves in the extruded sheet, and then depressurizing after 1 hour to obtain polyvinyl chloride electromagnetic shielding foam material.

[0015] In the aforementioned method for preparing polyvinyl chloride electromagnetic shielding foam material, the heat stabilizer mentioned in step (1) is a mixture of calcium / zinc stabilizer and tin heat stabilizer. The calcium / zinc stabilizer is selected from at least one of calcium ricinoleate, zinc octanoate, and zinc stearate. The tin heat stabilizer is dimethyltin isooctyl dithioacetate, and the mass ratio of calcium / zinc stabilizer to tin heat stabilizer is 4:1.

[0016] In the aforementioned method for preparing polyvinyl chloride electromagnetic shielding foam material, the light-shielding agent mentioned in step (1) is a mixture of montmorillonite and hydroxyethyl cellulose, and the mass ratio of montmorillonite to hydroxyethyl cellulose is 3:1. The lubricant is selected from at least one of polyethylene wax and oxidized polyethylene wax.

[0017] The aforementioned method for preparing polyvinyl chloride electromagnetic shielding foam material results in a polyvinyl chloride electromagnetic shielding foam material with a reflection loss of 6.9~7.8dB, an absorption loss of 67.7~73.7dB, and an electromagnetic shielding effectiveness of 74.6~81.5dB.

[0018] The present invention also provides a polyvinyl chloride electromagnetic shielding foam material prepared according to the aforementioned preparation method.

[0019] Compared with existing technologies, this invention has significant advantages and beneficial effects. Through the above technical solution, this invention achieves considerable technological advancement and practicality, and has broad application value, possessing at least the following advantages:

[0020] This invention improves the flame retardancy of polyvinyl chloride (PVC) electromagnetic shielding foam by adding magnesium hydroxide, and enhances its thermal and light stability by adding heat stabilizers and light-blocking agents. Light calcium carbonate acts as both an additive and a nucleating agent, inhibiting the transformation of amorphous to morphological regions of the polymer during PVC crystallization, thereby improving the material's dimensional stability. The addition of copper-plated Mxene enhances the electromagnetic shielding capability of the PVC foam, giving it excellent electromagnetic shielding performance. Furthermore, the pre-stretching process followed by foaming results in a certain orientation of the cell morphology along the stretching direction, larger cell size, increased specific surface area, and increased absorption loss, all contributing to improved electromagnetic shielding performance. The final PVC electromagnetic shielding foam exhibits a reflection loss of 6.9–7.8 dB, an absorption loss of 67.7–73.7 dB, and an electromagnetic shielding effectiveness of 74.6–81.5 dB, demonstrating a significant improvement in the electromagnetic shielding performance of PVC foam. Attached Figure Description

[0021] Figure 1 shows SEM images of the polyvinyl chloride electromagnetic shielding foam materials prepared in Examples 1, 2, and 3, respectively.

[0022] Figure 2 shows SEM images of the polyvinyl chloride foam materials prepared in Comparative Examples 1, 2, and 3, respectively.

[0023] Figure 3 is a comparison of the electromagnetic shielding performance of polyvinyl chloride electromagnetic shielding foam material L2 prepared in Example 2 and polyvinyl chloride foam material D2 prepared in Comparative Example 2. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0025] According to the weight percentages, the polyvinyl chloride electromagnetic shielding foam material provided by the present invention comprises 90-110 parts of polyvinyl chloride resin, 35-50 parts of diisooctyl phthalate, 1-10 parts of magnesium hydroxide, 0.5-1 parts of copper plating Mxene, 10-20 parts of light calcium carbonate, 6-12 parts of heat stabilizer, 1-3 parts of light shielding agent, and 0.5-2 parts of lubricant.

[0026] The heat stabilizer is a mixture of calcium / zinc stabilizer and tin heat stabilizer. The calcium / zinc stabilizer is selected from at least one of calcium ricinoleate, zinc octanoate, and zinc stearate. The tin heat stabilizer is dimethyltin isooctyl dithioacetate, and the mass ratio of calcium / zinc stabilizer to tin heat stabilizer is 4:1.

[0027] The light-blocking agent is a mixture of montmorillonite and hydroxyethyl cellulose, with a mass ratio of montmorillonite to hydroxyethyl cellulose of 3:1. Montmorillonite provides light protection, preventing the PVC electromagnetic shielding foam from oxidative decomposition under high temperature and strong light, improving the material's barrier properties against oxygen and water vapor, thereby enhancing its stability and maintaining its long-term light-blocking properties during use. Hydroxyethyl cellulose contains numerous free hydroxyl groups, which can form a good bond with the material, resulting in better high-temperature resistance, anti-migration properties, and superior light-blocking performance of the PVC electromagnetic shielding foam.

[0028] The lubricant is selected from at least one of polyethylene wax and oxidized polyethylene wax.

[0029] Preferably, the polyvinyl chloride electromagnetic shielding foam material comprises, by weight, 100 parts polyvinyl chloride resin, 46 parts diisooctyl phthalate, 8 parts magnesium hydroxide, 0.5 parts copper plating Mxene, 12 parts light calcium carbonate, 10 parts heat stabilizer, 2 parts light shielding agent, and 1 part lubricant.

[0030] Preferably, the polyvinyl chloride electromagnetic shielding foam material comprises, by weight, 95 parts polyvinyl chloride resin, 35 parts diisooctyl phthalate, 4 parts magnesium hydroxide, 0.7 parts copper plating Mxene, 10 parts light calcium carbonate, 6 parts heat stabilizer, 1 part light shielding agent, and 2 parts lubricant.

[0031] Preferably, the polyvinyl chloride electromagnetic shielding foam material comprises, by weight, 100 parts polyvinyl chloride resin, 50 parts diisooctyl phthalate, 6 parts magnesium hydroxide, 0.9 parts copper plating Mxene, 18 parts light calcium carbonate, 12 parts heat stabilizer, 3 parts light shielding agent, and 2 parts lubricant.

[0032] The copper-plated Mxene is prepared according to the following method, but the amounts used in the following preparation method are not considered as limitations on the present invention. The amounts of copper-plated Mxene can be increased proportionally based on the following amounts to prepare more copper-plated Mxene:

[0033] (1) Add 20 mL of 9 mol / L HCl solution to a polytetrafluoroethylene (PTFE) beaker. Under magnetic stirring, completely dissolve 1 g of LiF in the HCl solution and stir thoroughly for 12-15 min to obtain a homogeneous etching solution. Under magnetic stirring in an ice-water bath, add 1.5 g of Ti3AlC2 powder in small batches over 5 min to the obtained etching solution. After dispersing evenly, transfer the PTFE beaker to a 35°C water bath and etch for 24 h under magnetic stirring at 600 rpm. After etching, separate the solid and liquid components of the resulting mixture. Wash the solid with deionized water by centrifugation multiple times, each centrifugation time being 5 min and the speed being 3500 rpm, until the pH of the supernatant reaches 6 and there is a clay-like precipitate at the bottom of the centrifuge tube. The obtained clay-like precipitate was redispersed in water and then transferred to a single-necked flask. The single-necked flask was placed in an ice-water bath and ultrasonically exfoliated for 1 hour under N2 protection. The product after ultrasonic exfoliation was centrifuged at 8000 rpm for 20 minutes, and the supernatant was collected. The supernatant was freeze-dried to obtain solid MXene.

[0034] (2) Immerse the obtained solid Mxene in a copper plating solution at 15~25℃ for 20~30min. After immersion, perform solid-liquid separation. Wash the separated solid with deionized water 3-5 times, 2min each time. After washing, filter the solid and place it in a vacuum drying oven at 40℃ for 5h to obtain copper-plated Mxene.

[0035] The copper plating solution comprises copper sulfate, potassium sodium tartrate, sodium hydroxide, formaldehyde, and deionized water. The concentrations of copper sulfate, potassium sodium tartrate, and formaldehyde in the copper plating solution are 5 g / L, 25 g / L, 7 g / L, and 10 mL / L, respectively. The pH value of the copper plating solution is 12.8. The preparation method includes: dissolving a measured amount of copper sulfate in a certain amount of deionized water, stirring thoroughly until homogeneous, then sequentially adding measured amounts of potassium sodium tartrate, sodium hydroxide, and formaldehyde, stirring thoroughly, and finally diluting the solution with deionized water.

[0036] The aforementioned polyvinyl chloride electromagnetic shielding foam material can be prepared according to the following method:

[0037] (1) According to the weight parts, 90-110 parts of polyvinyl chloride resin (PVC), 35-50 parts of diisooctyl phthalate, 1-10 parts of magnesium hydroxide, 0.5-1 parts of copper plating Mxene, 10-20 parts of light calcium carbonate, 6-12 parts of heat stabilizer, 1-3 parts of light shielding agent, and 0.5-2 parts of lubricant are mixed evenly and then mixed in a high-temperature mixer to obtain a mixture. The stirring speed of the high-temperature mixer is 80-120 rpm, the mixing temperature is 150-200℃, and the mixing time is 2-6 min.

[0038] (2) Molding the mixture after mixing: First, heat the press to 180-190℃. After preheating at 180-190℃ for 5 minutes, place the mixture in the mold and press it for 10 minutes under 10MPa pressure to obtain a PVC composite material sample.

[0039] (3) The PVC composite material sample is added to the barrel of a conical twin-screw extruder. Under the action of the screw, it is plasticized and melted to become PVC composite material melt. After entering the extruder head, the PVC composite material melt is circumferentially split under the action of the splitting cone. The cross-sectional area of ​​the flow channel of the extruder head gradually narrows, thus exerting a certain stretching effect on the extruded melt. A heating jacket is installed on the outside of the extruder head to heat the extruder head. The compression ratio of the extruder head is 4~10. After the PVC composite material melt is extruded, it forms a PVC composite sheet. The PVC composite sheet passes through the first traction device and the second traction device in sequence. The speed of the second traction device is greater than that of the first traction device. The PVC composite sheet reaches a high elastic state through the reheating device set in the first traction device and the second traction device. The temperature of the reheating device is set to 85~90℃, which is conducive to the high elastic expansion of the PVC composite sheet. The speed ratio between the second traction device and the first traction device is (1.1~1.9):1. Due to the speed difference between the two, when the PVC composite board is heated to a high elastic state, the PVC composite board is pre-stretched under the action of the second traction device and the first traction device to obtain a pre-stretched extruded board.

[0040] (4) Immerse the pre-stretched extruded sheet in a foaming kettle at a temperature of 100~160℃ and a pressure of 13.8MPa to dissolve CO2 in the extruded sheet. After 1 hour, release the pressure to obtain the final polyvinyl chloride electromagnetic shielding foam material.

[0041] In the above preparation method, the conical twin-screw extruder, the heating jacket set on the outside of the extruder head, the first traction device, the second traction device, and the reheating device are all existing technologies, and will not be described in detail in this invention.

[0042] The present invention will be described in detail below with reference to specific embodiments. Unless otherwise specified, all conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Raw materials and reagents whose manufacturers are not specified are all commercially available products.

[0043] Example 1

[0044] A polyvinyl chloride electromagnetic shielding foam material, by weight, comprises 100 parts polyvinyl chloride resin, 46 parts diisooctyl phthalate, 8 parts magnesium hydroxide, 0.6 parts copper-plated Mxene, 12 parts light calcium carbonate, 8 parts calcium ricinoleate, 2 parts dimethyltin dithioacetate, 1.5 parts montmorillonite, 0.5 parts hydroxyethyl cellulose, and 1 part oxidized polyethylene wax. Its preparation method includes:

[0045] (1) According to the weight parts, 100 parts of polyvinyl chloride resin, 46 parts of diisooctyl phthalate, 8 parts of magnesium hydroxide, 0.6 parts of copper plating Mxene, 12 parts of light calcium carbonate, 8 parts of calcium ricinoleate, 2 parts of dimethyltin dithioacetate isooctyl ester, 1.5 parts of montmorillonite, 0.5 parts of hydroxyethyl cellulose, and 1 part of oxidized polyethylene wax are mixed and then mixed in a high-temperature mixer. The stirring speed of the high-temperature mixer is 100 rpm, the mixing temperature is 150℃, and the mixing time is 5 min.

[0046] (2) Molding the mixture after mixing: First, heat the press to 180°C. After preheating at 180°C for 5 minutes, place the mixture in the mold and press it for 10 minutes under 10MPa pressure to obtain a PVC composite material sample.

[0047] (3) The PVC composite material sample is added to the barrel of a conical twin-screw extruder. Under the action of the extruder screw, it is plasticized and melted to become PVC composite material melt. A heating jacket is installed on the outside of the extruder head to heat the extruder head. The compression ratio of the extruder head is 4. After the PVC composite material melt is extruded, it forms a PVC composite sheet. The PVC composite sheet passes through the first traction device and the second traction device in sequence. The speed of the second traction device is greater than that of the first traction device. The PVC composite sheet reaches a high elastic state through the reheating device set in the first and second traction devices. The temperature of the reheating device is set to 85℃. The speed ratio of the second traction device to the first traction device is 1.1:1. Under the action of the second traction device and the first traction device, the PVC composite sheet is pre-stretched to obtain a pre-stretched extruded sheet.

[0048] (4) The pre-stretched extruded sheet is immersed in a foaming kettle at a temperature of 120℃ and a pressure of 13.8MPa to dissolve CO2 in the extruded sheet. After 1 hour, the pressure is released to obtain the final polyvinyl chloride electromagnetic shielding foam material L1.

[0049] The reflection loss, absorption loss, and electromagnetic shielding effectiveness of the obtained polyvinyl chloride electromagnetic shielding foam material L1 were measured using a vector network analyzer (N5234A, Agilent) to be 6.9 dB, 67.7 dB, and 74.6 dB, respectively.

[0050] Example 2

[0051] A polyvinyl chloride (PVC) electromagnetic shielding foam material, by weight, comprises 95 parts polyvinyl chloride resin, 35 parts diisooctyl phthalate, 4 parts magnesium hydroxide, 0.7 parts copper-plated Mxene, 10 parts light calcium carbonate, 4.8 parts calcium ricinoleate, 1.2 parts dimethyltin dithioacetate isooctyl ester, 0.75 parts montmorillonite, 0.25 parts hydroxyethyl cellulose, and 2 parts oxidized polyethylene wax. Its preparation method includes:

[0052] (1) According to the weight parts, 95 parts of polyvinyl chloride resin, 35 parts of diisooctyl phthalate, 4 parts of magnesium hydroxide, 0.7 parts of copper plating Mxene, 10 parts of light calcium carbonate, 4.8 parts of calcium ricinoleate, 1.2 parts of dimethyltin dithioacetate isooctyl ester, 0.75 parts of montmorillonite, 0.25 parts of hydroxyethyl cellulose, and 2 parts of oxidized polyethylene wax are mixed and then mixed in a high-temperature mixer. The stirring speed of the high-temperature mixer is 120 rpm, the mixing temperature is 180℃, and the mixing time is 4 min.

[0053] (2) Molding the mixture after mixing: First, heat the press to 190°C. After preheating at 190°C for 5 minutes, place the mixture in the mold and press it for 10 minutes under 10MPa pressure to obtain a PVC composite material sample.

[0054] (3) The PVC composite material sample is added to the barrel of a conical twin-screw extruder. Under the action of the extruder screw, it is plasticized and melted to become PVC composite material melt. A heating jacket is installed on the outside of the extruder head to heat the extruder head. The compression ratio of the extruder head is 8. After the PVC composite material melt is extruded, it forms a PVC composite sheet. The PVC composite sheet passes through the first traction device and the second traction device in sequence. The speed of the second traction device is greater than that of the first traction device. The PVC composite sheet reaches a high elastic state through the reheating device set in the first and second traction devices. The temperature of the reheating device is set to 90℃. The speed ratio of the second traction device to the first traction device is 1.4:1. Under the action of the second traction device and the first traction device, the PVC composite sheet is pre-stretched to obtain a pre-stretched extruded sheet.

[0055] (4) The pre-stretched extruded sheet is immersed in a foaming kettle at a temperature of 160℃ and a pressure of 13.8MPa to dissolve CO2 in the extruded sheet. After 1 hour, the pressure is released to obtain the final polyvinyl chloride electromagnetic shielding foam material L2.

[0056] The reflection loss, absorption loss, and electromagnetic shielding effectiveness of the obtained polyvinyl chloride electromagnetic shielding foam material L2 were measured to be 7.4 dB, 68.8 dB, and 76.2 dB, respectively, using a vector network analyzer (N5234A, Agilent).

[0057] Example 3

[0058] A polyvinyl chloride (PVC) electromagnetic shielding foam material, by weight, comprises 100 parts polyvinyl chloride resin, 50 parts diisooctyl phthalate, 6 parts magnesium hydroxide, 0.9 parts copper-plated Mxene, 18 parts light calcium carbonate, 9.6 parts zinc octanoate, 2.4 parts dimethyltin dithioacetate isooctyl ester, 2.25 parts montmorillonite, 0.75 parts hydroxyethyl cellulose, and 2 parts polyethylene wax. Its preparation method includes:

[0059] (1) According to the weight parts, 100 parts of polyvinyl chloride resin, 50 parts of diisooctyl phthalate, 6 parts of magnesium hydroxide, 0.9 parts of copper plating Mxene, 18 parts of light calcium carbonate, 9.6 parts of zinc octanoate, 2.4 parts of dimethyltin dithioacetate isooctyl ester, 2.25 parts of montmorillonite, 0.75 parts of hydroxyethyl cellulose, and 2 parts of polyethylene wax are mixed and then mixed in a high-temperature mixer. The stirring speed of the high-temperature mixer is 110 rpm, the mixing temperature is 200℃, and the mixing time is 4 min.

[0060] (2) Molding the mixture after mixing: First, heat the press to 180°C. After preheating at 180°C for 5 minutes, place the mixture in the mold and press it for 10 minutes under 10MPa pressure to obtain a PVC composite material sample.

[0061] (3) The PVC composite material sample is added to the barrel of a conical twin-screw extruder. Under the action of the extruder screw, it is plasticized and melted to become PVC composite material melt. A heating jacket is installed on the outside of the extruder head to heat the extruder head. The compression ratio of the extruder head is 6. After the PVC composite material melt is extruded, it forms a PVC composite sheet. The PVC composite sheet passes through the first traction device and the second traction device in sequence. The speed of the second traction device is greater than that of the first traction device. The PVC composite sheet reaches a high elastic state through the reheating device set in the first and second traction devices. The temperature of the reheating device is set to 85℃. The speed ratio of the second traction device to the first traction device is 1.9:1. Under the action of the second traction device and the first traction device, the PVC composite sheet is pre-stretched to obtain a pre-stretched extruded sheet.

[0062] (4) The pre-stretched extruded sheet was immersed in a foaming kettle at a temperature of 140℃ and a pressure of 13.8MPa to dissolve CO2 in the extruded sheet. After 1 hour, the pressure was released to obtain the final polyvinyl chloride electromagnetic shielding foam material L3.

[0063] The reflection loss, absorption loss, and electromagnetic shielding effectiveness of the obtained polyvinyl chloride electromagnetic shielding foam material L3 were measured to be 7.8 dB, 73.7 dB, and 81.5 dB, respectively, using a vector network analyzer (N5234A, Agilent).

[0064] Comparative Example 1

[0065] According to the raw material composition and preparation method of Example 1, step (3) is omitted. The PVC composite material molding sample obtained in step (2) is directly immersed in a foaming kettle with a temperature of 120°C and a pressure of 13.8 MPa according to the process of step (4) so ​​that CO2 dissolves in the extruded board. After 1 hour, the pressure is released to obtain polyvinyl chloride foam material D1.

[0066] The reflection loss, absorption loss, and electromagnetic shielding effectiveness of the obtained polyvinyl chloride foam material D1 were measured using a vector network analyzer (N5234A, Agilent) to be 5.9 dB, 46.2 dB, and 52.1 dB, respectively.

[0067] Comparative Example 2

[0068] According to the raw material composition and preparation method of Example 2, step (3) is omitted. The PVC composite material molding sample obtained in step (2) is directly immersed in a foaming kettle with a temperature of 160°C and a pressure of 13.8 MPa according to the process of step (4) so ​​that CO2 dissolves in the extruded board. After 1 hour, the pressure is released to obtain polyvinyl chloride foam material D2.

[0069] The reflection loss, absorption loss, and electromagnetic shielding effectiveness of the obtained polyvinyl chloride foam material D2 were measured using a vector network analyzer (N5234A, Agilent) to be 6.6 dB, 51.5 dB, and 58.1 dB, respectively.

[0070] Comparative Example 3

[0071] According to the raw material composition and preparation method of Example 3, step (3) is omitted. The PVC composite material molding sample obtained in step (2) is directly immersed in a foaming kettle with a temperature of 140°C and a pressure of 13.8 MPa according to the process of step (4) so ​​that CO2 dissolves in the extruded board. After 1 hour, the pressure is released to obtain polyvinyl chloride foam material D3.

[0072] The reflection loss, absorption loss, and electromagnetic shielding effectiveness of the obtained polyvinyl chloride foam material D3 were measured using a vector network analyzer (N5234A, Agilent) to be 6.5 dB, 56.3 dB, and 62.8 dB, respectively.

[0073] Figure 1 shows SEM images of polyvinyl chloride electromagnetic shielding foam materials prepared in Examples 1, 2, and 3, respectively. As can be seen from Figure 1, after pre-stretching and then foaming, the morphology of the foam cells in the material has a certain orientation along the stretching direction, and as the stretching ratio increases from 1.1 to 1.9, the foam cells gradually become connected.

[0074] Figure 2 shows SEM images of polyvinyl chloride foam materials prepared in Comparative Examples 1, 2, and 3, respectively. As can be seen from Figure 2, the cellular size of polyvinyl chloride foam materials obtained by foaming directly without pre-stretching is not uniform, and the cellular morphology varies with the increase of the stretching ratio.

[0075] A comparison of Figures 1 and 2 shows that the cell size in the material obtained after pre-stretching and subsequent foaming is significantly increased. For example, in Figure 1b, the large cell size is approximately 1 mm, and the small cell size is approximately 100-500 μm. In contrast, in Figure 2b, the large cell size is approximately 400-500 μm, and the small cell size is approximately 50-300 μm. Furthermore, compared to the chaotic pore structure in Figure 2, the pore structure in Figure 1 exhibits a certain orientation and is more regular.

[0076] Figure 3 is a comparison of the electromagnetic shielding performance of PVC electromagnetic shielding foam material L2 prepared in Example 2 and PVC foam material D2 prepared in Comparative Example 2. As can be seen from Figure 3, under the same conditions, the electromagnetic shielding efficiency of the foam material obtained by pre-stretching and then foaming is greater than that of the foam material obtained by direct foaming without pre-stretching. The PVC electromagnetic shielding foam material obtained by pre-stretching and then foaming in Example 2 has higher reflection loss, absorption loss, and shielding effectiveness than that of Comparative Example 2. This may be because MXene forms an oriented structure in the PVC matrix after pre-stretching, increasing reflection loss. Simultaneously, the pre-stretched material forms a cell structure with a larger specific surface area, increasing absorption loss and ultimately increasing the electromagnetic shielding effectiveness of the material.

[0077] The above descriptions are merely individual embodiments of the present invention and are not intended to limit the present invention in any way. The present invention may also have other embodiments based on the above embodiments, which will not be listed hereafter. Therefore, any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention's technical solution shall still fall within the scope of the present invention's technical solution.

Claims

1. A method for preparing a polyvinyl chloride electromagnetic shielding foam material, characterized in that, The process includes the following steps: (1) Mixing 90-110 parts of polyvinyl chloride resin, 35-50 parts of diisooctyl phthalate, 1-10 parts of magnesium hydroxide, 0.5-1 parts of copper plating Mxene, 10-20 parts of light calcium carbonate, 6-12 parts of heat stabilizer, 1-3 parts of light shielding agent, and 0.5-2 parts of lubricant evenly according to the weight ratio, and then mixing them with a high-temperature mixer to obtain a mixture; (2) Molding the mixture after mixing to obtain a PVC composite material sample; (3) Adding the PVC composite material sample to the barrel of a conical twin-screw extruder, and plasticizing, melting, and extruding to obtain a PVC composite board. The PVC composite board passes through the first traction device and the second traction device in sequence. The speed of the second traction device is greater than that of the first traction device. Under the action of the second traction device and the first traction device, the PVC composite board is pre-stretched to obtain a pre-stretched extruded board; (4) Foaming the pre-stretched extruded board to obtain a polyvinyl chloride electromagnetic shielding foam material.

2. The method for preparing polyvinyl chloride electromagnetic shielding foam material as described in claim 1, characterized in that, In step (1), the stirring rate of the high-temperature mixer is 80~120 rpm, the mixing temperature is 150~200℃, and the mixing time is 2~6 min.

3. The method for preparing polyvinyl chloride electromagnetic shielding foam material as described in claim 1, characterized in that, Step (2) The molding process specifically includes: first, heating the press to 180-190℃, preheating at 180-190℃ for 5 minutes, then placing the mixture in the mold, and pressing it under 10MPa pressure to obtain a PVC composite material molded sample.

4. The method for preparing polyvinyl chloride electromagnetic shielding foam material as described in claim 1, characterized in that, In step (3), the compression ratio of the extruder head is 4~10, and the speed ratio of the second traction device to the first traction device is (1.1~1.9):

1.

5. The method for preparing polyvinyl chloride electromagnetic shielding foam material as described in claim 1, characterized in that, The foaming process described in step (4) specifically includes: immersing the pre-stretched extruded sheet obtained in step (3) in a foaming kettle with a temperature of 100~160℃ and a pressure of 13.8MPa, so that CO2 dissolves in the extruded sheet, and then depressurizes after 1 hour to obtain polyvinyl chloride electromagnetic shielding foam material.

6. The method for preparing polyvinyl chloride electromagnetic shielding foam material as described in claim 1, characterized in that, The heat stabilizer mentioned in step (1) is a mixture of calcium / zinc stabilizer and tin heat stabilizer. The calcium / zinc stabilizer is selected from at least one of calcium ricinoleate, zinc octanoate, and zinc stearate. The tin heat stabilizer is dimethyltin isooctyl dithioacetate, and the mass ratio of calcium / zinc stabilizer to tin heat stabilizer is 4:

1.

7. The method for preparing polyvinyl chloride electromagnetic shielding foam material as described in claim 1, characterized in that, The light-blocking agent mentioned in step (1) is a mixture of montmorillonite and hydroxyethyl cellulose, and the mass ratio of montmorillonite to hydroxyethyl cellulose is 3:

1. The lubricant is selected from at least one of polyethylene wax and oxidized polyethylene wax.

8. The method for preparing polyvinyl chloride electromagnetic shielding foam material as described in claim 1, characterized in that, The obtained polyvinyl chloride electromagnetic shielding foam material has a reflection loss of 6.9~7.8dB, an absorption loss of 67.7~73.7dB, and an electromagnetic shielding effectiveness of 74.6~81.5dB.

9. Polyvinyl chloride electromagnetic shielding foam material obtained by any of the preparation methods according to claims 1-7.

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