Electromagnetic shielding PBT composite material and preparation method thereof

Abstract

The invention discloses an electromagnetic shielding PBT composite material and a preparation method thereof, and belongs to the technical field of engineering plastics. The electromagnetic shielding PBT composite material is prepared from the following raw materials in parts by mass: 80 to 90 parts of PBT resin, 10 to 20 parts of stainless steel fiber, 0.2 to 1 part of antioxidant, 0.3 to 0.6 part of dispersing agent and 2 to 4 parts of low-melting-point metal alloy powder. Wherein the dispersing agent is a maleic anhydride grafted low-molecular-weight copolymer. The PBT resin and the stainless steel fibers are compounded, so that a three-dimensional conductive network structure with high conductivity and high electron transmission efficiency can be formed under a relatively low addition amount, and dyeing of the composite material is not influenced. The dispersing agent is added, so that a bridging effect is achieved, the interface bonding force between the stainless steel fibers and the PBT resin is enhanced, an internal lubricating effect is also achieved, the stainless steel fibers are protected by utilizing the lubricating effect while the melt viscosity is reduced, and the composite material with electromagnetic shielding performance and mechanical performance is obtained.

Description

Technical Field

[0001] This invention relates to the field of engineering plastics technology, and in particular to an electromagnetic shielding PBT composite material and its preparation method. Background Technology

[0002] In industrial production and daily life, electronic products are used more and more frequently. However, while electronic devices bring convenience, they also generate electromagnetic radiation during operation, which may have adverse effects on people's health. Electromagnetic interference between devices can also cause signal interception, data loss, and other problems, seriously affecting the performance and normal operation of electronic devices. One effective way to prevent electromagnetic radiation and interference is to use electromagnetic shielding materials on the surface of electronic devices. This reduces the adverse effects of electromagnetic waves and ensures that highly integrated and high-power electronic devices can operate normally without electromagnetic interference.

[0003] Electromagnetic shielding materials are functional materials that can attenuate the propagation of electromagnetic wave energy through absorption and reflection, thereby effectively suppressing electromagnetic interference and pollution. Early electromagnetic shielding materials were mostly metallic, using grounding and sealed cavities to reflect electromagnetic waves. However, metals have high density, are prone to corrosion, and are difficult to process, limiting their development in aerospace, military, and medical fields. Polymer-based electromagnetic shielding materials, on the other hand, have advantages such as low density, ease of processing, corrosion resistance, and low cost, attracting increasing attention.

[0004] However, polymers themselves generally do not have good electrical conductivity and have a weak shielding effect on electromagnetic waves. Electromagnetic shielding is usually achieved by modifying polymers by adding conductive fillers. However, conductive polymer materials prepared by simple melt blending methods are difficult to meet the shielding requirements of commercial electromagnetic shielding materials.

[0005] Furthermore, a large amount of conductive filler is often required to form an effective conductive network in the polymer matrix. However, high filler content will degrade the melt flowability of the polymer and greatly affect the processing performance of the material. Moreover, due to the large specific surface area and high surface energy of conductive fillers, they are prone to agglomeration during processing, making it difficult to achieve uniform dispersion. This results in uneven distribution of fillers in the matrix, which not only reduces the efficiency of the conductive network but also damages the mechanical properties of the conductive polymer material.

[0006] Meanwhile, conductive fillers, including carbon black, carbon nanotubes, and graphene, are all black fillers. When added in large quantities, the resulting conductive polymer material will also be black and difficult to change, thus greatly limiting the application range of the obtained conductive polymer material.

[0007] Therefore, it is of great significance to obtain a polymer-based electromagnetic shielding material with excellent performance, good processability, and good electromagnetic shielding effect. Summary of the Invention

[0008] This invention provides an electromagnetic shielding PBT composite material and its preparation method, which can solve the problems of poor electromagnetic shielding effect and difficulty in achieving both mechanical properties in existing polymer-based electromagnetic shielding materials.

[0009] In a first aspect, the present invention provides an electromagnetic shielding PBT composite material, comprising the following parts by weight of raw materials: 80-90 parts of PBT resin; 10-20 parts stainless steel fiber; Antioxidant 0.2 to 1 part; Dispersant 0.3–0.6 parts; 2-4 parts of low melting point metal alloy powder.

[0010] Preferably, the dispersant is a maleic anhydride-grafted low molecular weight copolymer.

[0011] More preferably, the maleic anhydride-grafted low molecular weight copolymer includes one or more combinations of maleic anhydride-grafted polyethylene wax, maleic anhydride-grafted polypropylene wax, and maleic anhydride-grafted acrylate wax.

[0012] Preferably, the diameter of the stainless steel fiber is 8-11 μm and the fiber length is 3-8 mm.

[0013] Preferably, the stainless steel fiber alloy type is SUS302 / 1.4310.

[0014] Preferably, the intrinsic viscosity of the PBT resin is 0.8 to 1.0 dL / g.

[0015] Preferably, the antioxidant includes one or more combinations of antioxidant 1010, antioxidant 168, antioxidant 245 and antioxidant 626.

[0016] By adopting the above technical solution, this invention selects PBT resin (polybutylene terephthalate) as the main polymer matrix material. Compared with other polymer materials, PBT resin has good fluidity and can maintain good processing performance. It can be molded into complex parts through injection molding, extrusion and other processes. In addition, PBT resin itself has good electrical insulation properties, which can provide an ideal insulating matrix for the subsequent construction of conductive shielding networks.

[0017] Adding stainless steel fibers to PBT resin, compared to traditional spherical or granular fillers, allows for easier interlocking and contact within the PBT resin matrix. This enables the formation of a three-dimensional conductive network at a much lower addition amount than traditional conductive fillers, avoiding problems such as decreased mechanical properties caused by high filler content.

[0018] Moreover, stainless steel fibers often form line contacts, which, compared to the point contacts when granular fillers form a network, result in a larger contact area, lower contact resistance, and significantly improved filler utilization efficiency. This leads to extremely high conductivity in the resulting conductive network and a substantial increase in electron transport efficiency.

[0019] Furthermore, during processing, the stainless steel fibers align along the flow direction, forming a denser network that strongly reflects incident electromagnetic waves, achieving high electromagnetic shielding effectiveness even at low addition levels. The composite materials prepared using stainless steel fibers do not affect material dyeing, thus expanding the application range of composite materials.

[0020] However, the interfacial bonding between the PBT matrix material and the stainless steel fiber is very weak. Its molecular chains are difficult to form chemical bonds or strong intermolecular forces with the surface of the stainless steel fiber. Relying solely on the mechanical anchoring effect and physical adsorption generated after the PBT resin melts, cools, and solidifies, the resulting composite material is prone to problems such as fiber floating. Moreover, during the melt blending process, high shear forces can easily shorten the brittle stainless steel fiber, resulting in a decrease in the fiber's aspect ratio and affecting its efficiency in building a conductive network in the PBT resin matrix.

[0021] To address this issue, the present invention also incorporates a dispersant, specifically a maleic anhydride-grafted low molecular weight copolymer. This dispersant introduces strongly polar maleic anhydride groups into the non-polar copolymer segments. During melt processing, the maleic anhydride groups can react with the hydroxyl groups on the surface of the stainless steel fibers. The copolymer segments can achieve good entanglement and physical compatibility with the PBT matrix, enhancing the interaction with the PBT matrix. This allows it to serve as an intermediate phase with strong covalent bonds and good physical compatibility between the stainless steel fibers and PBT resin, thereby strengthening the interfacial bonding between the stainless steel fibers and PBT resin and improving the dispersion of the stainless steel fibers in the matrix resin.

[0022] Furthermore, the improved interfacial bonding strength can enhance the adhesion of fibers in the resin during processing, which is sufficient to resist the separation tendency caused by shrinkage, thereby effectively eliminating or reducing the possible problem of fiber floating.

[0023] Furthermore, compared to general compatibilizers, the maleic anhydride-grafted low molecular weight copolymer of the present invention can also act as an internal lubricant in the melt, helping to improve the problem of increased melt viscosity caused by the introduction of stainless steel fibers during processing. Conversely, the reduced viscosity helps the stainless steel fibers to be subjected to less shear stress during melt shearing. The stainless steel fibers can not only loosen under shear force, but also disperse and slide in the melt. The lubrication effect can buffer and protect the stainless steel fibers, directly reducing the mechanical damage and breakage probability of the stainless steel fibers.

[0024] Meanwhile, low-melting-point metal alloy powder is also added to the formulation system. On the one hand, the low-melting-point metal alloy powder can also be transformed into liquid metal droplets during the melting and processing of PBT resin. It has good fluidity, can wet, encapsulate and penetrate stainless steel fibers, fill material pores, form a more stable and lower resistance conductive network, and significantly improve the electromagnetic shielding performance of the material.

[0025] On the other hand, low-melting-point metal alloy powders can work synergistically with dispersants to construct a dual-gradient interface structure of polymer compatibility layer and metal bonding layer around stainless steel fibers, thereby effectively transferring stress and improving the mechanical properties of the material.

[0026] The electromagnetic shielding material obtained by compounding the above raw materials can meet most of the electromagnetic shielding performance requirements without the need for high filler addition. Moreover, the stainless steel fibers suffer little shear damage, and the combination of dispersant and low melting point metal alloy powder can help to construct electromagnetic shielding PBT composite materials with excellent mechanical properties.

[0027] Preferably, the low-melting-point metal alloy powder includes one or more combinations of Bi-Sn alloy powder, Sn-In alloy powder, and Bi-Sn-In alloy powder.

[0028] More preferably, the low-melting-point metal alloy powder is Bi-Sn alloy powder.

[0029] Preferably, the particle size of the low-melting-point metal alloy powder is 10–30 μm.

[0030] By adopting the above technical solution, the low-melting-point metal alloy powder of the present invention, in addition to having a low melting point that meets the processing temperature requirements of PBT resin, also has extremely low viscosity and extremely high surface energy. Under the shearing action during processing, the low-melting-point metal alloy powder melts, is then extruded and spread, preferentially migrates and fills the conductive network formed by stainless steel fibers, and connects the contact points and tiny gaps between stainless steel fibers to form a more stable conductive network. This greatly reduces the contact resistance and penetration threshold of the conductive network, ensuring the formation of highly efficient and redundant conductive paths, thereby improving the electromagnetic shielding effect of the composite material.

[0031] Furthermore, the low-melting-point metal alloy powder has good wettability with stainless steel fibers, and can form a transition layer with metal bonds as the main component, resulting in a strong physicochemical bond. While wetting the fibers, it can also interpenetrate with the molten PBT resin. Specifically, since PBT resin is a crystalline polymer, it can form a three-dimensional mechanical interlocking structure with the alloy particles during the crystallization process, thereby working with the dispersant to improve the interfacial adhesion between the stainless steel fibers and the PBT resin.

[0032] Furthermore, in conjunction with the lubricating effect of the dispersant, it can effectively buffer the rigid collisions and shear impacts between stainless steel fibers and processing equipment, as well as between stainless steel fibers themselves, helping to maintain the aspect ratio of the stainless steel fibers and protecting the building blocks of the conductive network from damage.

[0033] Secondly, the present invention provides a method for preparing an electromagnetically shielded PBT composite material, which includes the following process steps: S1. Dry the PBT resin at 80-90℃ for 3-6 hours; S2. Weigh the raw materials according to the corresponding mass proportions, and then mix the other raw materials, excluding stainless steel fibers, evenly to obtain a premix; S3. The obtained premix is ​​melt-extruded at 230-250℃, stainless steel fibers are added through side feeding, and electromagnetic shielding PBT composite material is obtained after cooling and granulation.

[0034] The beneficial effects of this invention are: 1. The addition of stainless steel fibers to the electromagnetic shielding PBT composite material of the present invention can form a three-dimensional conductive network structure with high conductivity and high electron transport efficiency in the PBT resin matrix with a low addition amount, without affecting the dyeing of the composite material, thus expanding the application range of the composite material.

[0035] 2. The electromagnetic shielding PBT composite material of the present invention contains a dispersant, specifically a maleic anhydride-grafted low molecular weight copolymer. This dispersant acts as an intermediate phase with strong covalent bonds and good physical compatibility between the stainless steel fibers and PBT resin, thereby enhancing the interfacial bonding between the stainless steel fibers and PBT resin. Furthermore, it provides internal lubrication, reducing melt viscosity and buffering and protecting the stainless steel fibers, directly reducing mechanical damage and breakage.

[0036] 3. The electromagnetic shielding PBT composite material of this invention also contains low-melting-point metal alloy powder, which is compatible with the processing temperature of PBT resin. After melting, it can connect the contact points and tiny gaps between stainless steel fibers, forming a more stable conductive network. This significantly reduces the contact resistance and penetration threshold of the conductive network, ensuring the formation of highly efficient and redundant conductive pathways and improving the electromagnetic shielding effect of the composite material. It can also synergistically work with maleic anhydride-grafted low-molecular-weight copolymers, not only maintaining the integrity of the stainless steel fibers during processing but also improving the material's mechanical properties, resulting in a composite material that combines electromagnetic shielding performance with excellent mechanical properties. Detailed Implementation

[0037] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0038] Example

[0039] Example 1: An electromagnetic shielding PBT composite material was prepared according to the following method: S1. Dry the PBT resin (average intrinsic viscosity of 1.0 dL / g) at 85℃ for 5 hours; S2. Weigh the raw materials according to the corresponding mass proportions. Specifically, weigh 90 parts of dried PBT resin, 10 parts of stainless steel fiber (alloy type SUS302 / 1.4310, average fiber diameter of 10μm, average fiber length of 6mm), 0.4 parts of antioxidant, 0.3 parts of maleic anhydride grafted polyethylene wax, and 3 parts of Bi-Sn alloy powder (average particle size of 20μm). The antioxidant includes a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 0.15:0.25. Then, mix the other raw materials, excluding stainless steel fiber, evenly to obtain a premix. S3. The obtained premix is ​​melt-extruded at 230-250℃, stainless steel fibers are added through side feeding, and electromagnetic shielding PBT composite material is obtained after cooling and granulation.

[0040] Example 2: An electromagnetic shielding PBT composite material was prepared according to the following method: S1. Dry the PBT resin (average intrinsic viscosity of 1.0 dL / g) at 85℃ for 5 hours; S2. Weigh the raw materials according to the corresponding mass proportions. Specifically, weigh 85 parts of dried PBT resin, 15 parts of stainless steel fiber (alloy type SUS302 / 1.4310, average fiber diameter of 10μm, average fiber length of 6mm), 0.4 parts of antioxidant, 0.5 parts of maleic anhydride grafted polyethylene wax, and 3 parts of Bi-Sn alloy powder (average particle size of 20μm). The antioxidant includes a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 0.15:0.25. Then, mix the other raw materials, excluding stainless steel fiber, evenly to obtain a premix. S3. The obtained premix is ​​melt-extruded at 230-250℃, stainless steel fibers are added through side feeding, and electromagnetic shielding PBT composite material is obtained after cooling and granulation.

[0041] Example 3: An electromagnetic shielding PBT composite material was prepared according to the following method: S1. Dry the PBT resin (average intrinsic viscosity of 1.0 dL / g) at 85℃ for 5 hours; S2. Weigh the raw materials according to the corresponding mass proportions. Specifically, weigh 80 parts of dried PBT resin, 20 parts of stainless steel fiber (alloy type SUS302 / 1.4310, average fiber diameter of 10μm, average fiber length of 6mm), 0.4 parts of antioxidant, 0.6 parts of maleic anhydride grafted polyethylene wax, and 4 parts of Bi-Sn alloy powder (average particle size of 20μm). The antioxidant includes a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 0.15:0.25. Then, mix the other raw materials, excluding stainless steel fiber, evenly to obtain a premix. S3. The obtained premix is ​​melt-extruded at 230-250℃, stainless steel fibers are added through side feeding, and electromagnetic shielding PBT composite material is obtained after cooling and granulation.

[0042] Example 4: An electromagnetic shielding PBT composite material, which differs from Example 1 only in that an equal amount of Bi-Sn-In alloy powder is used to replace the Bi-Sn alloy powder.

[0043] Preparation Example

[0044] Preparation Example 1: An electromagnetic shielding PBT composite material, which differs from Example 1 only in that the amount of dried PBT resin added is 70 parts; and the amount of stainless steel fiber added is 30 parts.

[0045] Preparation Example 2: An electromagnetic shielding PBT composite material was prepared according to the following method: S1. Dry the PBT resin (average intrinsic viscosity of 1.0 dL / g) at 85℃ for 5 hours; S2. Weigh the raw materials according to the corresponding mass parts. Specifically, weigh 90 parts of dried PBT resin, 10 parts of conductive carbon black (average particle size of 23nm), 0.4 parts of antioxidant, 0.6 parts of maleic anhydride grafted polyethylene wax and 4 parts of Bi-Sn alloy powder (average particle size of 20μm). The antioxidant includes a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 0.15:0.25. Then, mix the other raw materials, excluding stainless steel fibers, evenly to obtain a premix. S3. The obtained premix is ​​melt-extruded at 230-250℃, stainless steel fibers are added through side feeding, and electromagnetic shielding PBT composite material is obtained after cooling and granulation.

[0046] Preparation Example 3: An electromagnetic shielding PBT composite material, which differs from Example 1 only in that the amount of Bi-Sn alloy powder added is 6 parts.

[0047] Preparation Example 4: An electromagnetic shielding PBT composite material, which differs from Example 1 only in that Bi-Sn alloy powder is not added.

[0048] Preparation Example 5: An electromagnetic shielding PBT composite material, which differs from Example 1 only in that an equal amount of polyethylene wax is used instead of maleic anhydride-grafted polyethylene wax.

[0049] Performance testing

[0050] 1. Mechanical property testing: (1) Tensile property test: The tensile strength was tested according to the relevant records in ISO 527-2019 "Determination of tensile properties of plastics". The tensile speed during the test was 5 mm / min. (2) Bending performance test: The bending strength was tested according to the relevant records in ISO 178-2019 "Determination of bending properties of plastics" at a bending speed of 2 mm / min.

[0051] 2. Electromagnetic shielding performance test: Using a vector network analyzer, the electromagnetic shielding PBT composite material samples obtained in the examples and comparative examples were tested in the X-band (8.2~12.4GHz) using the waveguide method. The sample size was 22.86mm×10.16mm×3mm.

[0052] The results of the above experiments are shown in Table 1: Table 1 Performance test results

[0053] According to Table 1, and in conjunction with Example 1 and Comparative Example 1, it can be seen that the mechanical properties and electromagnetic shielding performance of Comparative Example 1 are lower than those of Example 1. The reason is that excessive stainless steel fibers were added in Comparative Example 1, resulting in too much rigid filler in the composite material, which significantly reduced the mechanical properties. Moreover, excessive stainless steel fiber filling can damage the fiber structure of stainless steel fibers and easily cause agglomeration, which is not conducive to the formation of conductive network and leads to a decrease in electromagnetic shielding effectiveness.

[0054] Combining Example 1 and Comparative Example 2, it can be seen that the electromagnetic shielding performance of Comparative Example 2 is significantly lower than that of Example 1. The reason is that in Comparative Example 2, an equal amount of conductive carbon black was used to replace the stainless steel fiber. The introduction of a small amount of conductive carbon black has little impact on the mechanical properties of the PBT composite material, but it does not have a significant improvement effect. Moreover, the addition of a small amount of conductive carbon black cannot achieve the ideal electromagnetic shielding performance, and it is difficult to form a stable conductive network compared to stainless steel fiber.

[0055] Based on Examples 1, 3, and 4, it can be seen that the performance of Comparative Examples 3 and 4 is lower than that of Example 1. The reason is that Comparative Example 3 increased the amount of low-melting-point metal alloy powder, which significantly increased the brittleness of the composite material after curing, resulting in a significant decrease in mechanical properties. In contrast, Comparative Example 4 did not add low-melting-point metal alloy powder, which not only directly led to a decrease in the stability of the conductive network and the electromagnetic shielding effect, but also affected the interfacial bonding between PBT resin and stainless steel fiber, resulting in a decrease in the mechanical properties of the composite material.

[0056] Combining Example 1 and Comparative Example 5, it can be seen that the performance of Comparative Example 5 is lower than that of Example 1. The reason is that in Comparative Example 5, a conventional lubricant was used to replace maleic anhydride-grafted polyethylene wax. Even though it can improve the viscosity of the melt, the lack of a dispersant to bridge the interface between PBT resin and stainless steel fiber will greatly reduce the compatibility of the system. The structure of stainless steel fiber is also destroyed after shearing, which seriously affects the construction of the conductive network, resulting in a decrease in mechanical properties and electromagnetic shielding performance.

[0057] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. An electromagnetic shielding PBT composite material, characterized in that, The raw materials include the following parts by weight: 80-90 parts of PBT resin; 10-20 parts stainless steel fiber; Antioxidant 0.2 to 1 part; Dispersant 0.3–0.6 parts; 2-4 parts of low melting point metal alloy powder.

2. The electromagnetic shielding PBT composite material according to claim 1, characterized in that, The dispersant is a maleic anhydride-grafted low molecular weight copolymer.

3. The electromagnetic shielding PBT composite material according to claim 2, characterized in that, The maleic anhydride-grafted low molecular weight copolymer includes one or more combinations of maleic anhydride-grafted polyethylene wax, maleic anhydride-grafted polypropylene wax, and maleic anhydride-grafted acrylate wax.

4. The electromagnetic shielding PBT composite material according to claim 1, characterized in that, The low-melting-point metal alloy powder includes one or more combinations of Bi-Sn alloy powder, Sn-In alloy powder, and Bi-Sn-In alloy powder.

5. The electromagnetic shielding PBT composite material according to claim 1, characterized in that, The particle size of the low-melting-point metal alloy powder is 10–30 μm.

6. The electromagnetic shielding PBT composite material according to claim 1, characterized in that, The stainless steel fibers have a diameter of 8–11 μm and a length of 3–8 mm.

7. The electromagnetic shielding PBT composite material according to claim 1, characterized in that, The stainless steel fiber has an alloy type of SUS302 / 1.4310.

8. The electromagnetic shielding PBT composite material according to claim 1, characterized in that, The intrinsic viscosity of the PBT resin is 0.8 to 1.0 dL / g.

9. The electromagnetic shielding PBT composite material according to claim 1, characterized in that, The antioxidants include one or more combinations of antioxidant 1010, antioxidant 168, antioxidant 245, and antioxidant 626.

10. A method for preparing an electromagnetically shielded PBT composite material, used to prepare the electromagnetically shielded PBT composite material according to any one of claims 1 to 6, characterized in that, The process includes the following steps: S1. Dry the PBT resin at 80-90℃ for 3-6 hours; S2. Weigh the raw materials according to the corresponding mass proportions, and then mix the other raw materials, excluding stainless steel fibers, evenly to obtain a premix; S3. The obtained premix is ​​melt-extruded at 230-250℃, stainless steel fibers are added through side feeding, and electromagnetic shielding PBT composite material is obtained after cooling and granulation.

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