Preparation method of composite plastic particles for anti-shielding keyboard frame and forming method of anti-shielding keyboard frame
By uniformly dispersing anti-shielding metal powder in a polycarbonate matrix and employing a low-temperature melt extrusion process, the problems of high cost of metal keyboard frames and the inability of ordinary plastic keyboard frames to provide shielding have been solved, thereby improving electromagnetic shielding performance and mechanical strength.
Patent Information
- Application Number
- CN202511359562.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-23
- Publication Date
- 2025-12-26
AI Technical Summary
In the prior art, in electronic devices, metal keyboard frames suffer from high cost, heavy weight, complex processing, and difficulty in combining with plastic components. At the same time, ordinary plastic keyboard frames cannot achieve electromagnetic shielding.
Anti-shielding keyboard frame composite plastic granules are prepared by uniformly dispersing anti-shielding metal powder, such as copper powder or aluminum powder, in a polycarbonate matrix and mixing it with compatibilizers, glass fibers and other materials, and then using a low-temperature melt extrusion process to form a continuous or semi-continuous conductive network.
It achieves excellent electromagnetic shielding performance, mechanical strength and stability of anti-shielded keyboard frames, reduces costs and simplifies the manufacturing process.
Smart Images
Figure CN121203370A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the technical field of electronic device manufacturing, and in particular to a method for preparing composite plastic granules for anti-shielding keyboard frames, and a method for molding anti-shielding keyboard frames. Background Technology
[0002] With the trend towards thinner and lighter electronic devices, especially laptops and ultra-thin keyboards, the requirements for electromagnetic shielding of their internal components are becoming increasingly stringent. As a component that is frequently used by users and transmits signals, the keyboard's casing must have good electromagnetic interference resistance to ensure stable operation of the device.
[0003] Pure metal keyboard frames are manufactured using aluminum alloys, magnesium alloys, or other alloys through stamping or die-casting processes. This approach offers excellent shielding, but it is costly, heavy, and complex to manufacture. It also hinders the design of complex overall structures. The combination of a pure metal keyboard frame and plastic components typically requires additional secondary processing, increasing assembly difficulty and cost. Ordinary plastic keyboard frames are injection molded from common engineering plastics. Ordinary plastic keyboard frames are low-cost, lightweight, offer high design flexibility, are easy to mold into complex structures, and provide insulation. However, ordinary plastic keyboard frames are non-conductive and therefore lack electromagnetic shielding capabilities, failing to meet the shielding performance requirements of modern electronic devices. Summary of the Invention
[0004] The purpose of this disclosure is to overcome the shortcomings of the prior art and to provide a method for preparing composite plastic particles for anti-shielding keyboard frames that have uniform dispersion of metal powder in a polycarbonate matrix and good anti-shielding effect, as well as a method for molding the anti-shielding keyboard frames.
[0005] The purpose of this disclosure is achieved through the following technical solution: A method for preparing composite plastic granules for anti-shielding keyboard frames includes the following steps: The polycarbonate matrix, silicon powder, glass fiber, anti-shielding metal powder, compatibilizer, toughening agent, talc, anti-dripping agent, colorant and pentaerythritol stearate lubricant are put into a mixer and mixed evenly to obtain a mixture. The mixture is fed into an extruder, and the mixture passes through the heating zone and the melting zone of the extruder in sequence for melt extrusion. The temperature of the heating zone is 200℃-260℃, and the temperature of the melting zone is 260℃-275℃. The molten material is then extruded through the die of the extruder to obtain the molten material. The molten material is cooled in a water tank to obtain shaped strips; The molded strip is cut by a pelletizer to obtain composite plastic pellets for the anti-shielding keyboard frame; The anti-shielding metal powder includes at least one of copper powder or aluminum powder, and the compatibilizer includes at least one of titanate coupling agent and silane coupling agent.
[0006] In one embodiment, the composite plastic granules for the anti-shielding keyboard frame comprise the following components by weight: 80-85 parts of polycarbonate matrix; 4-5 parts silicon powder; 4-10 parts glass fiber; 10-12 parts aluminum powder; 3-5 parts titanate coupling agent; Silane coupling agent 0.1-0.2; Toughening agent 1-5 parts; 1-2 parts talcum powder; Anti-dripping agent: 0.1-0.3 parts; Colorant: 2-2.5 parts; Pentaerythritol stearate lubricant, 0.1-0.2 parts.
[0007] In one embodiment, the heating zone includes a first feeding heating zone, a second heating heating zone, and a third heating heating zone. The temperature of the first feeding heating zone is 200℃-210℃, the temperature of the second heating heating zone is 210℃-230℃, and the temperature of the third heating heating zone is 230℃-260℃.
[0008] In one embodiment, the melting zone includes a fourth heating zone, a fifth heating zone, a sixth heating zone, a seventh heating zone, an eighth heating zone, and a ninth heating zone. The temperature of the fourth heating zone is 260℃-270℃, the temperature of the fifth heating zone is 260℃-270℃, the temperature of the sixth heating zone is 260℃-270℃, the temperature of the seventh heating zone is 260℃-270℃, the temperature of the eighth heating zone is 270℃-275℃, the temperature of the ninth heating zone is 265℃-270℃, and the die temperature of the extruder is 270℃.
[0009] In one embodiment, the glass fiber comprises a mixture of short fibers and ground fiber powder.
[0010] In one embodiment, the ratio of the short fiber to the ground fiber powder is 1:1 to 1:2.
[0011] In one embodiment, the particle size of the aluminum powder ranges from 5 μm to 50 μm.
[0012] In one embodiment, the polycarbonate matrix, silicon powder, glass fiber, anti-shielding metal powder, compatibilizer, toughening agent, talc, anti-dripping agent, colorant, and pentaerythritol stearate lubricant are added to a mixer and mixed evenly. Before obtaining the mixture, the aluminum powder is pre-coated with a silane coupling agent, including the following steps: The silane coupling agent is diluted in water and hydrolyzed to obtain a silane solution after dilution. The aluminum powder is dispersed in a high-speed mixer and preheated to 80℃-100℃; The silane coupling agent solution is evenly sprayed into the aluminum powder using a spraying device, and then continuously mixed in a high-speed mixer for 15-20 minutes at a mixing temperature of 100°C. After cooling, the material is discharged to obtain pre-coated aluminum powder.
[0013] In one embodiment, nitrogen gas is introduced into the feed inlet, melt zone, and die of the extruder.
[0014] A method for molding an anti-shielding keyboard frame includes the following steps: The plastic granules of the anti-shielding keyboard frame are obtained by the preparation method of the anti-shielding keyboard frame plastic granules described in any of the above embodiments. Plastic granules are added to an injection molding machine for hot melting to obtain a hot melt adhesive. Hot melt adhesive is injected into the mold cavity through a hot runner for injection molding and pressure holding; The hot melt adhesive in the cavity is cooled and solidified to obtain an anti-shielding keyboard frame; The anti-shielding keyboard frame is subjected to heat treatment.
[0015] Compared with the prior art, this disclosure has at least the following advantages: The above-described method for preparing composite plastic granules for anti-shielding keyboard frames involves mixing anti-shielding metal powder with raw materials before the polycarbonate melts, ensuring that the anti-shielding metal powder and compatibilizer are mixed evenly beforehand. This avoids the problem of the anti-shielding metal powder being difficult to disperse in molten, high-viscosity polycarbonate. The compatibilizer improves the compatibility between the anti-shielding metal powder and polycarbonate, resulting in uniform dispersion and good compatibility of the anti-shielding metal powder in the polycarbonate matrix. By controlling the low-temperature melt extrusion of the anti-shielding metal powder and polycarbonate matrix, the high-temperature degradation of polycarbonate and the high-temperature oxidation of the anti-shielding metal powder are effectively avoided. The anti-shielding metal powder forms a continuous or semi-continuous conductive network in the polycarbonate matrix, giving the obtained composite plastic granules excellent electromagnetic shielding performance, mechanical strength, and stability, making them suitable for molding anti-shielding keyboard frames. Attached Figure Description
[0016] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0017] Figure 1 This is a flowchart illustrating the steps of a method for preparing composite plastic granules for an anti-shielding keyboard frame, according to one embodiment. Detailed Implementation
[0018] To facilitate understanding of this disclosure, a more complete description will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the present disclosure. However, this disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure.
[0019] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.
[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.
[0021] This application provides a method for preparing composite plastic granules for anti-shielding keyboard frames, comprising the following steps: mixing polycarbonate matrix, silicon powder, glass fiber, anti-shielding metal powder, compatibilizer, toughening agent, talc, anti-dripping agent, colorant, and pentaerythritol stearate lubricant in a mixer to obtain a mixture; feeding the mixture into an extruder, wherein the mixture is sequentially passed through several heating zones and several melting zones of the extruder for melt extrusion, the temperature of the heating zones being 200℃-260℃, and the temperature of the melting zones being 260℃-275℃; then extruding the molten material through the die of the extruder to obtain a molten material; cooling the molten material in a water bath to obtain a shaped strip; cutting the shaped strip by a pelletizer to obtain composite plastic granules for anti-shielding keyboard frames; wherein the anti-shielding metal powder includes at least one of copper powder or aluminum powder, and the compatibilizer includes at least one of titanate coupling agent and silane coupling agent.
[0022] The above-mentioned method for preparing composite plastic granules for anti-shielding keyboard frames involves mixing anti-shielding metal powder with raw materials before the polycarbonate melts, ensuring that the anti-shielding metal powder and compatibilizer are mixed evenly beforehand, thus avoiding the problem of the anti-shielding metal powder being difficult to disperse in molten, high-viscosity polycarbonate. The compatibilizer improves the compatibility between the anti-shielding metal powder and polycarbonate, resulting in uniform dispersion and good compatibility of the anti-shielding metal powder in the polycarbonate matrix. By controlling the low-temperature melt extrusion of the anti-shielding metal powder and polycarbonate matrix, the high-temperature degradation of polycarbonate and the high-temperature oxidation of the anti-shielding metal powder are effectively avoided. The anti-shielding metal powder forms a continuous or semi-continuous conductive network in the polycarbonate matrix, giving the obtained composite plastic granules excellent electromagnetic shielding performance, mechanical strength, and stability for use in molding anti-shielding keyboard frames.
[0023] To better understand the technical solutions and beneficial effects of this disclosure, the following detailed description is provided in conjunction with specific embodiments: Please see Figure 1 As shown, this is a method for preparing composite plastic granules for an anti-shielding keyboard frame according to an embodiment of the present invention, comprising the following steps: S101 The polycarbonate matrix, silicon powder, glass fiber, anti-shielding metal powder, compatibilizer, toughening agent, talc, anti-dripping agent, colorant and pentaerythritol stearate lubricant are put into a mixer and mixed evenly to obtain a mixture; S103 feeds the mixture into the extruder, and the mixture passes through several heating zones and several melting zones of the extruder in sequence for melt extrusion. The temperature of the heating zones is 200℃-260℃, and the temperature of the melting zones is 260℃-275℃. The molten material is then extruded through the die of the extruder to obtain the molten material. The molten material described in S105 is cooled in a water tank to obtain a shaped strip; The molding strip described in S107 is cut by a pelletizer to obtain composite plastic pellets for use in anti-shielding keyboard frames.
[0024] The anti-shielding metal powder includes at least one of copper powder or aluminum powder, and the compatibilizer includes at least one of titanate coupling agent and silane coupling agent.
[0025] In this embodiment, the metal powder is an inorganic non-polar surface, which is prone to agglomeration and cannot form a uniform conductive network. The titanate coupling agent or silane coupling agent connects the metal powder at one end and the polycarbonate plastic matrix at the other end, thereby significantly improving the cross-sectional compatibility and adhesion between the two, preventing metal powder agglomeration, reducing interfacial energy, and making it easier for the molten plastic to wet the surface of the metal powder. During the mixing stage, aluminum powder and copper powder, as anti-shielding metal powders, need to be fully mixed with other raw materials in solid form before the polycarbonate melts. The anti-shielding metal powder exists in the form of independent particles and is uniformly dispersed by mechanical stirring to avoid uniform agglomeration due to increased viscosity after melting. It also allows the anti-shielding metal powder to be in pre-contact with the titanate coupling agent or silane coupling agent, thereby enhancing the interfacial compatibility between the metal and the polycarbonate matrix and reducing phase separation during melt blending.
[0026] Understandably, polycarbonate is a thermoplastic engineering plastic, and excessively high temperatures can cause the molecular chains of polycarbonate to break and decompose. Copper and aluminum are easily oxidized at high temperatures, forming an oxide film on the surface. This oxide film can damage the conductivity of the metal powder, leading to a decrease in shielding effectiveness. The melting temperature is below 275°C to avoid the degradation of polycarbonate caused by excessively high temperatures, as well as the oxidation problems caused by copper or aluminum powder.
[0027] The above-mentioned method for preparing composite plastic granules for anti-shielding keyboard frames involves mixing anti-shielding metal powder with raw materials before the polycarbonate melts, ensuring that the anti-shielding metal powder and compatibilizer are mixed evenly beforehand, thus avoiding the problem of the anti-shielding metal powder being difficult to disperse in molten, high-viscosity polycarbonate. The compatibilizer improves the compatibility between the anti-shielding metal powder and polycarbonate, resulting in uniform dispersion and good compatibility of the anti-shielding metal powder in the polycarbonate matrix. By controlling the low-temperature melt extrusion of the anti-shielding metal powder and polycarbonate matrix, the high-temperature degradation of polycarbonate and the high-temperature oxidation of the anti-shielding metal powder are effectively avoided. The anti-shielding metal powder forms a continuous or semi-continuous conductive network in the polycarbonate matrix, giving the obtained composite plastic granules excellent electromagnetic shielding performance, mechanical strength, and stability for use in molding anti-shielding keyboard frames.
[0028] In one embodiment, the composite plastic granules for the anti-shielding keyboard frame comprise the following components by weight: 80-85 parts of polycarbonate matrix; 4-5 parts silicon powder; 4-10 parts glass fiber; 10-15 parts aluminum powder; 3-5 parts titanate coupling agent; Silane coupling agent 0.1-0.2; Toughening agent 1-5 parts; 1-2 parts talcum powder; Anti-dripping agent: 0.1-0.3 parts; Colorant: 2-2.5 parts; Pentaerythritol stearate lubricant, 0.1-0.2 parts.
[0029] In this embodiment, polycarbonate is used to provide the overall frame, toughness, heat resistance, and mechanical strength; the addition of silicon powder improves the high and low temperature resistance of the composite plastic particles and reduces dimensional changes caused by thermal expansion and contraction; glass fiber significantly improves strength and dimensional stability, offsetting the brittleness caused by aluminum powder; toughening agents include organosilicon K210 toughening agent, toughening agent 1105A, and EMA ethylene-methyl acrylate copolymer, which improves the impact toughness of the material through the composite toughening agent system, making the keyboard frame sturdy and durable; titanate coupling agent has a good coupling effect on talc and aluminum powder, and reduces melt viscosity and improves processing fluidity; anti-dripping agent prevents melt dripping during high-temperature processing; the colorant is a black masterbatch, which is used to provide a uniform black appearance; pentaerythritol stearate, as a lubricant, can reduce melt viscosity, reduce equipment wear, and reduce shear heat generation.
[0030] Understandably, aluminum powder forms a conductive network within the polycarbonate matrix, reflecting and absorbing electromagnetic waves to provide electromagnetic shielding. When the aluminum powder content is less than 10 parts, the aluminum powder particles are dispersed in the polycarbonate matrix but isolated from each other, failing to form a continuous conductive path, thus reducing shielding effectiveness. When the aluminum powder content is greater than 12 parts, excessive rigid aluminum powder particles become numerous stress concentration points, easily leading to cracks under external impact. More titanate coupling agent is needed to coat its surface to improve compatibility, maintaining dispersibility and interfacial adhesion. An aluminum powder content of 10-12 parts ensures that the aluminum powder is dispersed within the polycarbonate matrix to form a conductive network, thereby reliably achieving the shielding function and avoiding embrittlement and compatibility problems caused by excessive aluminum powder filling.
[0031] In one embodiment, the composite plastic granules for the anti-shielding keyboard frame comprise the following components by weight: 80-85 parts polycarbonate; 4-5 parts silicon powder; 4-10 parts glass fiber; 10-12 parts aluminum powder; 3-5 parts titanate coupling agent; Silane coupling agent 0.1-0.2; Toughening agent 1-5 parts; 1-2 parts talcum powder; Anti-dripping agent: 0.1-0.3 parts; Colorant: 2-2.5 parts; Pentaerythritol stearate lubricant, 0.1-0.2 parts.
[0032] In this embodiment, copper powder has better conductivity and is added in smaller amounts compared to aluminum powder. Copper powder with a content of 2.5 to 4 parts forms a continuous or semi-continuous conductive network in the polycarbonate matrix, thereby achieving excellent electromagnetic shielding performance. At the same time, it reduces the amount of rigid metal filler and improves the impact toughness and ductility of the composite plastic particles.
[0033] In one embodiment, the glass fiber comprises a mixture of short fibers and ground fiber powder. In this embodiment, the short fibers provide core reinforcement, while the ground fiber powder is more evenly distributed in the polycarbonate matrix, effectively reducing warping and shrinkage problems caused by orientation shrinkage differences, improving the dimensional stability of the composite plastic granules, and enhancing the overall rigidity and heat distortion temperature of the composite plastic granules by forming a dense reinforcing network through the short fibers and ground fiber powder.
[0034] In one embodiment, the ratio of short fibers to ground fiber powder is 1:1 to 1:2. In this embodiment, the addition of a large amount of ground fiber powder effectively counteracts the anisotropic shrinkage caused by short fibers, making the overall shrinkage behavior more stable and avoiding unevenness caused by short fibers easily exposed on the surface, thereby improving the surface gloss.
[0035] In one embodiment, the heating zone includes a first feeding heating zone, a second heating heating zone, and a third heating heating zone. The temperature of the first feeding heating zone is 200℃-210℃, the temperature of the second heating heating zone is 210℃-230℃, and the temperature of the third heating heating zone is 230℃-260℃. In this embodiment, the first feeding heating zone is located near the feed inlet and has a lower temperature setting to prevent the polycarbonate matrix from melting and adhering too early at the feed inlet, ensuring the forward conveying of the material. In the second heating zone, the polycarbonate matrix begins to soften and partially melt, encapsulating other components. This allows the polycarbonate matrix to undergo initial mixing and wetting with glass fiber, aluminum powder, and silicon powder. At the temperature in the second heating zone, the titanate coupling agent begins to function, further coating the surface of the aluminum powder with the polycarbonate matrix in a semi-molten state. In the third heating zone, under high shear force and high temperature, the fillers such as aluminum powder and silicon powder are completely dispersed and, with the help of the coupling agent, are evenly dispersed in the polycarbonate melt, forming a homogeneous molten material. This prevents aluminum powder agglomeration and forms a conductive network.
[0036] In one embodiment, the melting zone includes a fourth heating zone, a fifth heating zone, a sixth heating zone, a seventh heating zone, an eighth heating zone, and a ninth heating zone. The temperature of the fourth heating zone is 260℃-270℃, the temperature of the fifth heating zone is 260℃-270℃, the temperature of the sixth heating zone is 260℃-270℃, the temperature of the seventh heating zone is 260℃-270℃, the temperature of the eighth heating zone is 270℃-275℃, the temperature of the ninth heating zone is 265℃-270℃, and the die temperature of the extruder is 270℃. In this embodiment, the dispersion of aluminum powder affects the electromagnetic shielding effect. By shearing at above 260°C and passing through multiple heating zones, the aluminum powder is ensured to be uniformly distributed in the molten material. The temperature is controlled below 275°C, causing the polycarbonate resin to undergo molecular chain breakage, degradation, and yellowing due to overheating. This maintains its mechanical properties and inhibits the formation of a non-conductive alumina film on the surface of the aluminum powder at high temperatures, ensuring the stability of its conductivity. The viscosity of the polycarbonate melt is sensitive to temperature. The temperature fluctuation in zones four through seven is controlled within an extremely narrow range of 10°C, ensuring the extreme stability of the viscosity of the polycarbonate matrix molten material. This results in a constant load on the extruder screw, smooth equipment operation, and stable shear force, thus ensuring good consistency in the quality of the mixed extruded molten material.
[0037] In one embodiment, the polycarbonate matrix, glass fiber, aluminum powder, compatibilizer, toughening modifier, talc, anti-dripping agent, colorant, and surface modifier are added to a mixer and mixed evenly. Before obtaining the mixture, the aluminum powder is pre-coated with a silane coupling agent, including the following steps: The silane coupling agent is diluted in water and hydrolyzed to obtain a silane solution after dilution. The aluminum powder is dispersed in a high-speed mixer and preheated to 80℃-100℃; The silane coupling agent solution is evenly sprayed into the aluminum powder using a spraying device, and then continuously mixed in a high-speed mixer for 15-20 minutes at a mixing temperature of 100°C. After cooling, the material is discharged to obtain pre-coated aluminum powder.
[0038] In this embodiment, aluminum powder and titanate coupling agent are directly mixed in a mixer. However, within a short time, the titanate coupling agent and silane coupling agent cannot fully contact the aluminum powder, and the titanate coupling agent competes with other fillers for adsorption, further affecting the modification of the aluminum powder by the titanate coupling agent. This leads to agglomeration of the aluminum powder, resulting in discontinuous conductive networks and affecting the anti-shielding performance of the composite plastic granules. Removing moisture from the aluminum powder and activating the surface activity of the metal powder makes it easier for it to react with the silane coupling agent. Spraying ensures the silicon... The silane solution, in the form of extremely fine droplets, contacts the anti-shielding metal powder, achieving uniform wetting. This allows the silane coupling agent to construct a uniform, covalently bonded organic molecular layer on the surface of the anti-shielding metal powder, improving its compatibility with the polycarbonate matrix. By pre-coating the anti-shielding metal powder with the silane coupling agent and then mixing it with the titanate coupling agent, the coating effect on the metal powder is increased, and the consumption of the titanate coupling agent is reduced. Together, the silane coupling agent and the titanate coupling agent provide a highly compatible and uniformly dispersed composite filler system for the polycarbonate matrix.
[0039] In one embodiment, the aluminum powder has a particle size range of 5 μm to 50 μm. In this embodiment, the particle size range of 5 μm to 50 μm can effectively form a continuous or semi-continuous conductive network, thereby enabling the aluminum powder to provide excellent electromagnetic shielding performance.
[0040] Furthermore, in one embodiment, the particle size of the aluminum powder ranges from 10 μm to 50 μm. In this embodiment, when the particle size of the aluminum powder is in the range of 10 μm to 50 μm, it causes less damage to the continuity of the polycarbonate matrix and has a smaller negative impact on the toughness and impact strength of the polycarbonate compared to nano-sized or extremely coarse aluminum powder.
[0041] Furthermore, in one embodiment, the aluminum powder has a particle size range of 5 μm to 10 μm. It is understood that smaller particle sizes result in a greater number of particles and a larger specific surface area within the same filling volume, increasing the probability of contact between particles and improving electromagnetic shielding. However, smaller particle sizes also lead to higher surface energy, making the aluminum powder more prone to agglomeration, necessitating further improvements in its dispersibility.
[0042] Furthermore, after pre-coating the aluminum powder with a silane coupling agent, before adding the polycarbonate matrix, glass fiber, anti-shielding metal powder, compatibilizer, toughening modifier, talc, anti-drip agent, colorant, and surface modifier into a mixer for uniform mixing, a secondary anti-shielding coating treatment of the metal powder is further included, comprising the following steps: An acrylate polymeric dispersant was added to the anti-shielding metal powder and stirred at a temperature of 60℃-80℃ for 10-15 minutes. After cooling, the material is discharged to obtain anti-shielding metal powder with secondary encapsulation treatment.
[0043] In this embodiment, the acrylate polymeric dispersant is a polymethyl methacrylate (PMMA)-based dispersant. PMMA-based dispersants have good compatibility with the polycarbonate matrix. The protective layer formed by its long molecular chains around the aluminum powder particles provides strong physical repulsion through steric hindrance, preventing agglomeration and thus achieving stable dispersion. Based on chemical bonding achieved through a silane coupling agent, a further physical steric hindrance layer is constructed to improve the dispersibility of the aluminum powder, ensuring uniform distribution of the aluminum powder in the composite plastic granules, thereby improving the long-term reliability and batch-to-batch stability of the composite plastic granules.
[0044] In one embodiment, nitrogen gas is introduced into the feed inlet, melting zone, and die of the extruder. In this embodiment, aluminum powder is oxidized to form aluminum oxide, and copper powder is oxidized to form copper oxide. The surface of the copper or aluminum powder is coated with an oxide film, causing the electromagnetic shielding effectiveness to fail. Introducing nitrogen gas prevents the copper or aluminum powder from oxidizing. The nitrogen environment also inhibits the thermal oxidative degradation of the polycarbonate molecular chains by oxygen, thereby maintaining the molecular weight and mechanical properties of the polycarbonate matrix and reducing yellowing. At the same time, the nitrogen gas flow better removes moisture and small volatile molecules from the material.
[0045] Further, the molten material is cooled in a water bath to obtain a shaped strip, including the following steps: The molten material is subjected to a first stage of water cooling in a water tank, and the temperature of the first stage of water cooling is 15℃-25℃. The molten material undergoes a second stage of water cooling at a temperature of 25°C-30°C. In this embodiment, the first stage of rapid cooling rapidly lowers the temperature of the molten material, shortening the residence time of the aluminum powder in the molten material at high temperatures, which helps to reduce the oxidation of aluminum powder in the molten material. The second stage of slow cooling reduces the internal stress caused by the large temperature difference between the inside and outside of the material strip.
[0046] This application also provides a method for molding an anti-shielding keyboard frame, comprising the following steps: The plastic granules of the anti-shielding keyboard frame are obtained by the preparation method of the anti-shielding keyboard frame plastic granules described in any of the above embodiments. Plastic granules are added to an injection molding machine for hot melting to obtain a hot melt adhesive. Hot melt adhesive is injected into the mold cavity through a hot runner for injection molding and pressure holding; The hot melt adhesive in the cavity is cooled and solidified to obtain an anti-shielding keyboard frame; The anti-shielding keyboard frame is subjected to heat treatment.
[0047] The above-described molding method for the anti-shielding keyboard frame involves injection molding of plastic granules containing anti-shielding metal powder, resulting in a keyboard frame with good structural strength and shielding performance. The hot runner injects the molten metal into the mold cavity at high speed, avoiding waste material at the gate and improving the utilization rate of the plastic granules containing the anti-shielding metal powder. A heat treatment process is added after injection molding to eliminate internal stress generated during the cooling process of the anti-shielding keyboard frame. Simultaneously, the heat treatment allows the anti-shielding metal powder to form a stable conductive path, thereby stabilizing its electromagnetic shielding effectiveness.
[0048] In one embodiment, the heating temperature in the injection molding machine is 270℃-280℃, and the mold temperature is 90℃-110℃. In this embodiment, the heating temperature of 270℃-280℃ in the injection molding machine ensures that the polycarbonate matrix is completely melted, thereby obtaining good fluidity, which facilitates filling the thin-walled keyboard frame cavity. The mold temperature slows down the cooling rate of the melt surface in the cavity, helping the melt to fill smoothly.
[0049] Furthermore, in one embodiment, the injection molding process of injecting hot melt adhesive into the mold cavity via a hot runner and holding pressure includes the following steps: Inject at the first injection speed to 60%-70% of the cavity volume; Inject at a second injection speed higher than the first injection speed to 70%-100% of the cavity volume; A third injection speed, lower than the second injection speed, is used to inject the material into the mold cavity for pressure holding. In this embodiment, the first injection speed is used to slowly break through the gate and stably fill the main body of the mold cavity. Then, a higher speed and pressure are switched to compact the remaining part. Finally, pressure is held to compensate for shrinkage, thereby forming a uniform hot melt adhesive, which helps to ensure the consistency of electromagnetic shielding effectiveness. The smooth filling and switching avoid excessive orientation of molecular chains and anti-shielding metal powder, reducing internal stress and thus reducing the risk of product warping and cracking. Furthermore, in one embodiment, after heat treatment of the anti-shielding keyboard frame, the following steps are also included: A UV coating is applied to the keyboard frame; The UV coating is then cured. In this embodiment, the UV coating can provide a variety of gloss levels, from high gloss to matte. The cured UV coating has high hardness and can effectively resist scratches, abrasion, and chemical corrosion. At the same time, the UV coating can protect the aluminum powder and prevent the surface aluminum powder from oxidizing.
[0050] Compared with the prior art, this disclosure has at least the following advantages: The above-described method for preparing composite plastic granules for anti-shielding keyboard frames involves mixing anti-shielding metal powder with raw materials before the polycarbonate melts, ensuring that the anti-shielding metal powder and compatibilizer are thoroughly mixed, thus avoiding the problem of the anti-shielding metal powder being difficult to disperse in molten, high-viscosity polycarbonate. The compatibilizer improves the compatibility between the anti-shielding metal powder and polycarbonate, resulting in uniform dispersion and good compatibility of the anti-shielding metal powder in the polycarbonate matrix. By controlling the low-temperature melt extrusion of the anti-shielding metal powder and the polycarbonate matrix, the high-temperature degradation of polycarbonate and the high-temperature oxidation of the anti-shielding metal powder are effectively avoided. The anti-shielding metal powder forms a continuous or semi-continuous conductive network in the polycarbonate matrix, giving the obtained composite plastic granules excellent electromagnetic shielding performance, mechanical strength, and stability for use in molding anti-shielding keyboard frames.
[0051] The following are some specific examples. When %, it refers to a percentage by weight. It should be noted that the following examples do not exhaustively list all possible scenarios, and unless otherwise specified, the materials used in the following examples are commercially available.
[0052] Example 1 80 kg of polycarbonate matrix, 5 kg of silicon powder, 3 kg of short fiber, 3 kg of ground fiber powder, 10 kg of aluminum powder, 3 kg of titanate coupling agent, 0.2 kg of silane coupling agent, 1 kg of toughening agent K210, 1 kg of 1105A dispersing toughening agent, 1 kg of EMA ethylene-methyl acrylate copolymer, 2 kg of talc, 0.3 kg of anti-dripping agent, 2.5 kg of black masterbatch colorant, and 0.2 kg of pentaerythritol stearate lubricant are added to a mixer and mixed evenly to obtain a mixture. The mixture is fed into an extruder, where it sequentially passes through a first feeding heating zone (200℃-210℃), a second heating zone (230℃), a third heating zone (230℃-260℃), a fourth, fifth, sixth, and seventh heating zones (260℃-270℃), an eighth heating zone (270℃-275℃), and a ninth heating zone (265℃-270℃). The mixture is then extruded through a die at 270℃ to obtain molten material. This molten material is cooled in a water bath to obtain shaped strips. The shaped strips are then cut by a pelletizer to obtain composite plastic granules for use in anti-shielding keyboard frames. Composite plastic granules for the anti-shielding keyboard frame are added to an injection molding machine for hot melting. The hot melt adhesive is then injected into the mold cavity through a hot runner for injection molding and pressure holding. After cooling and molding, heat treatment is performed to obtain the anti-shielding keyboard frame.
[0053] Example 2 80 kg of polycarbonate matrix, 5 kg of silicon powder, 3 kg of short fiber, 3 kg of ground fiber powder, 11 kg of aluminum powder, 3 kg of titanate coupling agent, 0.2 kg of silane coupling agent, 1 kg of toughening agent K210, 1 kg of 1105A dispersing toughening agent, 1 kg of EMA ethylene-methyl acrylate copolymer, 2 kg of talc, 0.3 kg of anti-dripping agent, 2.5 kg of black masterbatch colorant, and 0.2 kg of pentaerythritol stearate lubricant are added to a mixer and mixed evenly to obtain a mixture. The mixture is fed into an extruder, where it sequentially passes through a first feeding heating zone (200℃-210℃), a second heating zone (230℃), a third heating zone (230℃-260℃), a fourth, fifth, sixth, and seventh heating zones (260℃-270℃), an eighth heating zone (270℃-275℃), and a ninth heating zone (265℃-270℃). The mixture is then extruded through a die at 270℃ to obtain molten material. This molten material is cooled in a water bath to obtain shaped strips. These strips are then cut by a pelletizer to obtain composite plastic granules for use in anti-shielding keyboard frames.
[0054] Composite plastic granules for the anti-shielding keyboard frame are added to an injection molding machine for hot melting. The hot melt adhesive is then injected into the mold cavity through a hot runner for injection molding and pressure holding. After cooling and molding, heat treatment is performed to obtain the anti-shielding keyboard frame.
[0055] Example 3 80 kg of polycarbonate matrix, 5 kg of silicon powder, 3 kg of short fiber, 3 kg of ground fiber powder, 12 kg of aluminum powder, 3 kg of titanate coupling agent, 0.2 kg of silane coupling agent, 1 kg of toughening agent K210, 1 kg of 1105A dispersing toughening agent, 1 kg of EMA ethylene-methyl acrylate copolymer, 2 kg of talc, 0.3 kg of anti-dripping agent, 2.5 kg of black masterbatch colorant, and 0.2 kg of pentaerythritol stearate lubricant are added to a mixer and mixed evenly to obtain a mixture. The mixture is fed into an extruder, where it sequentially passes through a first feeding heating zone (200℃-210℃), a second heating zone (230℃), a third heating zone (230℃-260℃), a fourth, fifth, sixth, and seventh heating zones (260℃-270℃), an eighth heating zone (270℃-275℃), and a ninth heating zone (265℃-270℃). The mixture is then extruded through a die at 270℃ to obtain molten material. This molten material is cooled in a water bath to obtain shaped strips. These strips are then cut by a pelletizer to obtain composite plastic granules for use in anti-shielding keyboard frames.
[0056] Composite plastic granules for the anti-shielding keyboard frame are added to an injection molding machine for hot melting. The hot melt adhesive is then injected into the mold cavity through a hot runner for injection molding and pressure holding. After cooling and molding, heat treatment is performed to obtain the anti-shielding keyboard frame.
[0057] Example 4 80 kg of polycarbonate matrix, 5 kg of silicon powder, 3 kg of short fiber, 3 kg of ground fiber powder, 4 kg of copper powder, 3 kg of titanate coupling agent, 0.2 kg of silane coupling agent, 1 kg of toughening agent K210, 1 kg of 1105A dispersing toughening agent, 1 kg of EMA ethylene-methyl acrylate copolymer, 2 kg of talc, 0.3 kg of anti-dripping agent, 2.5 kg of black masterbatch colorant, and 0.2 kg of pentaerythritol stearate lubricant are added to a mixer and mixed evenly to obtain a mixture. The mixture is fed into an extruder, where it sequentially passes through a first feeding heating zone (200℃-210℃), a second heating zone (230℃), a third heating zone (230℃-260℃), a fourth, fifth, sixth, and seventh heating zones (260℃-270℃), an eighth heating zone (270℃-275℃), and a ninth heating zone (265℃-270℃). The mixture is then extruded through a die at 270℃ to obtain molten material. This molten material is cooled in a water bath to obtain shaped strips. These strips are then cut by a pelletizer to obtain composite plastic granules for use in anti-shielding keyboard frames.
[0058] Composite plastic granules for the anti-shielding keyboard frame are added to an injection molding machine for hot melting. The hot melt adhesive is then injected into the mold cavity through a hot runner for injection molding and pressure holding. After cooling and molding, heat treatment is performed to obtain the anti-shielding keyboard frame.
[0059] Example 5 80 kg of polycarbonate matrix, 5 kg of silicon powder, 3 kg of short fiber, 3 kg of ground fiber powder, 11 kg of aluminum powder, 3 kg of silane coupling agent, 1 kg of toughening agent K210, 1 kg of 1105A dispersing toughening agent, 1 kg of EMA ethylene-methyl acrylate copolymer, 2 kg of talc, 0.3 kg of anti-dripping agent, 2.5 kg of black masterbatch colorant, and 0.2 kg of pentaerythritol stearate lubricant are added to a mixer and mixed evenly to obtain a mixture. The mixture is fed into an extruder, where it sequentially passes through a first feeding heating zone (200℃-210℃), a second heating zone (230℃), a third heating zone (230℃-260℃), a fourth, fifth, sixth, and seventh heating zones (260℃-270℃), an eighth heating zone (270℃-275℃), and a ninth heating zone (265℃-270℃). The mixture is then extruded through a die at 270℃ to obtain molten material. This molten material is cooled in a water bath to obtain shaped strips. These strips are then cut by a pelletizer to obtain composite plastic granules for use in anti-shielding keyboard frames.
[0060] Composite plastic granules for the anti-shielding keyboard frame are added to an injection molding machine for hot melting. The hot melt adhesive is then injected into the mold cavity through a hot runner for injection molding and pressure holding. After cooling and molding, heat treatment is performed to obtain the anti-shielding keyboard frame.
[0061] Example 6 85 kg of polycarbonate matrix, 5 kg of silicon powder, 3 kg of short fiber, 3 kg of ground fiber powder, 11 kg of aluminum powder, 3 kg of silane coupling agent, 1 kg of toughening agent K210, 1 kg of 1105A dispersing toughening agent, 1 kg of EMA ethylene-methyl acrylate copolymer, 2 kg of talc, 0.3 kg of anti-dripping agent, 2.5 kg of black masterbatch colorant, and 0.2 kg of pentaerythritol stearate lubricant are added to a mixer and mixed evenly to obtain a mixture. The mixture is fed into an extruder, where it sequentially passes through a first feeding heating zone (200℃-210℃), a second heating zone (230℃), a third heating zone (230℃-260℃), a fourth, fifth, sixth, and seventh heating zones (260℃-270℃), an eighth heating zone (270℃-275℃), and a ninth heating zone (265℃-270℃). The mixture is then extruded through a die at 270℃ to obtain molten material. This molten material is cooled in a water bath to obtain shaped strips. These strips are then cut by a pelletizer to obtain composite plastic granules for use in anti-shielding keyboard frames.
[0062] Composite plastic granules for the anti-shielding keyboard frame are added to an injection molding machine for hot melting. The hot melt adhesive is then injected into the mold cavity through a hot runner for injection molding and pressure holding. After cooling and molding, heat treatment is performed to obtain the anti-shielding keyboard frame.
[0063] Comparative Example 1 80 kg of polycarbonate matrix, 5 kg of silica powder, 3 kg of short fiber, 3 kg of ground fiber powder, 1 kg of toughening agent K210, 1 kg of 1105A dispersing toughening agent, 1 kg of EMA ethylene-methyl acrylate copolymer, 2 kg of talc, 0.3 kg of anti-dripping agent, 2.5 kg of black masterbatch colorant, and 0.2 kg of pentaerythritol stearate lubricant are added to a mixer and mixed evenly to obtain a mixture. The mixture is fed into an extruder, where it sequentially passes through a first feeding heating zone (200℃-210℃), a second heating zone (230℃), a third heating zone (230℃-260℃), a fourth, fifth, sixth, and seventh heating zones (260℃-270℃), an eighth heating zone (270℃-275℃), and a ninth heating zone (265℃-270℃). The mixture is then extruded through a die at 270℃ to obtain molten material. This molten material is cooled in a water bath to obtain shaped strips. These strips are then cut by a pelletizer to obtain composite plastic granules for use in anti-shielding keyboard frames.
[0064] Composite plastic granules for the anti-shielding keyboard frame are added to an injection molding machine for hot melting. The hot melt adhesive is then injected into the mold cavity through a hot runner for injection molding and pressure holding. After cooling and molding, heat treatment is performed to obtain the anti-shielding keyboard frame.
[0065] Comparative Example 2 80 kg of polycarbonate matrix, 5 kg of silicon powder, 3 kg of short fiber, 3 kg of ground fiber powder, 11 kg of aluminum powder, 1 kg of toughening agent K210, 1 kg of 1105A dispersing toughening agent, 1 kg of EMA ethylene-methyl acrylate copolymer, 2 kg of talc, 0.3 kg of anti-dripping agent, 2.5 kg of black masterbatch colorant, and 0.2 kg of pentaerythritol stearate lubricant are added to a mixer and mixed evenly to obtain a mixture. The mixture is fed into an extruder, where it sequentially passes through a first feeding heating zone (200℃-210℃), a second heating zone (230℃), a third heating zone (230℃-260℃), a fourth, fifth, sixth, and seventh heating zones (260℃-270℃), an eighth heating zone (270℃-275℃), and a ninth heating zone (265℃-270℃). The mixture is then extruded through a die at 270℃ to obtain molten material. This molten material is cooled in a water bath to obtain shaped strips. These strips are then cut by a pelletizer to obtain composite plastic granules for use in anti-shielding keyboard frames.
[0066] Composite plastic granules for the anti-shielding keyboard frame are added to an injection molding machine for hot melting. The hot melt adhesive is then injected into the mold cavity through a hot runner for injection molding and pressure holding. After cooling and molding, heat treatment is performed to obtain the anti-shielding keyboard frame.
[0067] Table 1. Composition of composite plastic granules used for anti-shielding keyboard frames Table 2 Test results of Examples 1-6 and Comparative Examples It should be noted that the electromagnetic shielding effectiveness (SE) is tested according to the ASTM D4935-10 standard. The planar portion of the shielded keyboard frame is selected, and the perpendicular incidence of a plane electromagnetic wave is simulated using a coaxial transmission line device. The reflection, absorption, and attenuation effects of multiple reflections of the electromagnetic wave by the shielded keyboard frame are measured. The impact strength is tested according to the ASTM D256 standard. The shielded keyboard frame is made into a standard template and fixed in a fixture. A pendulum is dropped from a certain height, and the energy remaining after the pendulum breaks the template is measured to calculate the impact strength. The bending strength is tested using a three-point bending test according to the ASTM D1238 standard.
[0068] As shown in Tables 1 and 2, compared with Examples 1-6, metal powder filler is the core element that imparts electromagnetic shielding function to the anti-shielding keyboard frame in Comparative Example 1. Comparative Example 1, which does not contain metal filler, has almost no electromagnetic shielding effectiveness. Compared with Example 4, copper powder in Example 1, due to its superior conductivity, can achieve a higher shielding effect with a smaller amount added. Compared to Comparative Example 2, the absence of the coupling agent in Example 2 significantly reduces electromagnetic shielding effectiveness, impact strength, and flexural strength. The combined action of titanate and silane coupling agent significantly improves the interfacial compatibility between the inorganic filler and the organic matrix, promotes filler dispersion, and thus simultaneously enhances conductivity, mechanical strength, and processing fluidity.
[0069] Example 2 showed the best impact and flexural strength. Example 6, by increasing the polycarbonate matrix content, achieved even better mechanical properties, making it suitable for applications requiring higher strength.
[0070] The electromagnetic shielding effectiveness of Examples 1-6 is good, indicating that the anti-shielding keyboard frame made of composite plastic particles used for anti-shielding keyboard frames by injection molding has good electromagnetic shielding effectiveness.
[0071] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the disclosed patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent should be determined by the appended claims.
Claims
1. A method for preparing composite plastic granules for anti-shielding keyboard frames, characterized in that, Includes the following steps: Polycarbonate matrix, silicon powder, glass fiber, anti-shielding metal powder, compatibilizer, toughening agent, talc, anti-dripping agent, colorant and pentaerythritol stearate lubricant are put into a mixer and mixed evenly to obtain a mixture. The mixture is fed into an extruder, and the mixture passes through the heating zone and the melting zone of the extruder in sequence for melt extrusion. The temperature of the heating zone is 200℃-260℃, and the temperature of the melting zone is 260℃-275℃. The molten material is then extruded through the die of the extruder to obtain the molten material. The molten material is cooled in a water tank to obtain shaped strips; The molded strip is cut by a pelletizer to obtain composite plastic pellets for the anti-shielding keyboard frame; The anti-shielding metal powder includes at least one of copper powder or aluminum powder, and the compatibilizer includes at least one of titanate coupling agent and silane coupling agent.
2. The method for preparing composite plastic granules for anti-shielding keyboard frames according to claim 1, characterized in that, The composite plastic granules used for the anti-shielding keyboard frame comprise the following components by weight: 80-85 parts of polycarbonate matrix; 4-5 parts silicon powder; 4-10 parts glass fiber; 10-12 parts aluminum powder; 3-5 parts titanate coupling agent; Silane coupling agent 0.1-0.2; Toughening agent 1-5 parts; 1-2 parts talcum powder; Anti-dripping agent: 0.1-0.3 parts; Colorant: 2-2.5 parts; Pentaerythritol stearate lubricant, 0.1-0.2 parts.
3. The method for preparing composite plastic granules for anti-shielding keyboard frames according to claim 1, characterized in that, The heating zones include a first feeding heating zone, a second heating zone, and a third heating zone. The temperature of the first feeding heating zone is 200℃-210℃, the temperature of the second heating zone is 210℃-230℃, and the temperature of the third heating zone is 230℃-260℃.
4. The method for preparing composite plastic granules for anti-shielding keyboard frames according to claim 1, characterized in that, The melting zone includes a fourth heating zone, a fifth heating zone, a sixth heating zone, a seventh heating zone, an eighth heating zone, and a ninth heating zone. The temperature of the fourth heating zone is 260℃-270℃, the temperature of the fifth heating zone is 260℃-270℃, the temperature of the sixth heating zone is 260℃-270℃, the temperature of the seventh heating zone is 260℃-270℃, the temperature of the eighth heating zone is 270℃-275℃, and the temperature of the ninth heating zone is 265℃-270℃. The die temperature of the extruder is 270℃.
5. The method for preparing composite plastic granules for anti-shielding keyboard frames according to claim 1, characterized in that, The glass fiber comprises a mixture of short fibers and ground fiber powder.
6. The method for preparing composite plastic granules for anti-shielding keyboard frames according to claim 5, characterized in that, The ratio of the short fiber to the ground fiber powder is 1:1 to 1:
2.
7. The method for preparing composite plastic granules for anti-shielding keyboard frames according to claim 1, characterized in that, The particle size range of the aluminum powder is 5μm-50μm.
8. The method for preparing composite plastic granules for anti-shielding keyboard frames according to claim 6, characterized in that, The polycarbonate matrix, silicon powder, glass fiber, anti-shielding metal powder, compatibilizer, toughening agent, talc, anti-dripping agent, colorant, and pentaerythritol stearate lubricant are added to a mixer and mixed evenly. Before obtaining the mixture, the aluminum powder is pre-coated with a silane coupling agent, including the following steps: The silane coupling agent is diluted in water and hydrolyzed to obtain a silane solution after dilution. The aluminum powder is dispersed in a high-speed mixer and preheated to 80℃-100℃; The silane coupling agent solution is evenly sprayed into the aluminum powder using a spraying device, and then continuously mixed in a high-speed mixer for 15-20 minutes at a mixing temperature of 100°C. After cooling, the material is discharged to obtain pre-coated aluminum powder.
9. The method for preparing composite plastic granules for anti-shielding keyboard frames according to claim 1, characterized in that, Nitrogen gas is introduced into the feed inlet, melting zone, and die of the extruder.
10. A method for molding an anti-shielding keyboard frame, characterized in that, Includes the following steps: The plastic granules for the anti-shielding keyboard frame are obtained by the method for preparing composite plastic granules for the anti-shielding keyboard frame according to any one of claims 1-9; Plastic granules are added to an injection molding machine for hot melting to obtain a hot melt adhesive. Hot melt adhesive is injected into the mold cavity through a hot runner for injection molding and pressure holding; The hot melt adhesive in the cavity is cooled and solidified to obtain an anti-shielding keyboard frame; The anti-shielding keyboard frame is subjected to heat treatment.