Self-extinguishing flame-retardant intelligent switch shell and preparation process thereof

Abstract

This invention discloses a self-extinguishing flame-retardant smart switch housing and its manufacturing process, belonging to the field of smart home electrical equipment technology. The housing consists of a weather-resistant wave-transmitting layer, a structural flame-retardant layer, and an intumescent heat-insulating layer, with a total wall thickness of 1.0~1.1 mm, layered from the outside in. The weather-resistant wave-transmitting layer uses low-dielectric weather-resistant modified ASA to ensure low-loss wireless signal transmission. The structural flame-retardant layer uses a halogen-free flame-retardant engineering plastic alloy to provide structural support and basic self-extinguishing flame-retardant performance. The intumescent heat-insulating layer uses intumescent flame-retardant silicone rubber to form a secondary flame-retardant and heat-insulating barrier. This invention is manufactured using precision injection molding, insert injection molding, and liquid silicone secondary injection molding processes, which are mature and easy to mass-produce. This invention overcomes the bottleneck of mutual constraints between flame retardancy and wave transmission of a single material, meeting the UL94 V-0 self-extinguishing flame-retardant requirements while reducing wireless signal attenuation and improving long-term service stability, making it suitable for various smart switch products with built-in wireless modules.

Description

Technical Field

[0001] This invention belongs to the field of smart home electrical equipment technology, specifically relating to a self-extinguishing flame-retardant smart switch housing and its manufacturing process. Background Technology

[0002] With the rapid popularization of the whole-house smart home industry, smart switches have become the core entry terminal of home control systems. Their functions have gradually evolved from simple on / off control to integration of scene linkage, energy consumption monitoring, and human body sensing, with the integration and power of internal components continuously improving. As the external protective structure of high-voltage circuits, the casing is a key barrier to prevent electrical fires and must meet the self-extinguishing requirements of safety standards such as GB 4706.1 and UL94. Moreover, smart switches are in a standby state for a long time, and there is a continuous temperature rise and accumulation in the confined space. The materials must maintain stable performance under long-term thermal aging and humid and hot environments, and the requirements for safety and reliability are far higher than those for ordinary electrical appliance casings.

[0003] Currently, most smart switch housings in the industry use general-purpose ABS, PC, or PC / ABS alloys as the base material, with flame retardants added for flame retardant modification. Low-to-mid-range products commonly use general-purpose ABS, which offers significant advantages in processability and cost, but its flame retardant rating is only UL94 HB, resulting in severe dripping during combustion and insufficient fire safety. Mid-to-high-end products mostly use PC or PC / ABS alloys, which offer superior heat resistance and impact resistance, but the highest flame retardant rating for unmodified systems is only V-2, failing to meet high-level safety requirements. To improve flame retardant performance, the industry generally adopts flame retardant modification schemes. Halogen-based flame retardant systems have high flame retardant efficiency, but release large amounts of toxic and corrosive fumes during combustion, failing to meet environmental and fire safety requirements. Furthermore, under long-term high temperature and humidity, flame retardants are prone to migration and precipitation, leading to whitening of the housing and performance degradation. Halogen-free flame retardant systems are the current development direction, but existing solutions have obvious shortcomings: metal hydroxides have low flame retardant efficiency, and high addition amounts will significantly degrade the mechanical properties and flowability of materials; although phosphorus-based, nitrogen-based, and intumescent flame retardants are added in lower amounts, they generally have the contradiction of "flame retardant improvement - mechanical degradation", and the problem of combustion dripping is prominent.

[0004] Meanwhile, smart switches incorporate wireless communication modules such as Wi-Fi, Bluetooth, and ZigBee, and the dielectric properties of the casing material directly affect signal transmission stability. Adding flame retardants and inorganic fillers significantly increases the material's dielectric constant and dielectric loss, leading to severe wireless signal attenuation, shortened communication distance, and decreased connection stability. Conversely, reducing the amount of flame retardant to improve wave transmission fails to meet electrical safety standards, creating an inherent and irreconcilable contradiction. Furthermore, the trend towards ultra-thin and flat casings in smart switches, with wall thickness gradually decreasing to 1.0~1.2mm and precise snap-fit ​​and assembly structures, further exacerbates the performance limitations of existing flame-retardant materials.

[0005] In summary, existing technologies have always struggled to simultaneously achieve high self-extinguishing flame retardancy, excellent wave transmission performance, good mechanical and processing properties, and long-term stability. Developing a dedicated self-extinguishing flame-retardant housing suitable for intelligent switch operating conditions is of significant practical importance. Summary of the Invention

[0006] To address the shortcomings of existing technologies, such as the difficulty in simultaneously achieving flame retardant performance and wireless wave transmission performance in intelligent switch housings, and insufficient long-term service stability, this invention adopts a functional layered decoupling design approach. Through a three-layer composite structure, different functions are separated into corresponding levels, achieving multiple objectives simultaneously, including high self-extinguishing flame retardancy, low signal loss, and long-term weather resistance and stability, without changing the conventional assembly dimensions.

[0007] In a first aspect, the present invention provides a self-extinguishing flame-retardant smart switch housing, which includes a weather-resistant wave-transmitting layer, a structural flame-retardant layer and an expansion heat-insulating layer that are integrally composited from the outside to the inside. The total wall thickness of the three layers is 1.0~1.1 mm, which is compatible with the conventional wall thickness of traditional single-material switch housings and does not change the internal assembly dimensions of existing switches.

[0008] The weather-resistant wave-transmitting layer is made of low-dielectric weather-resistant modified ASA material with a thickness of 0.2~0.3 mm. It serves three main functions: appearance protection, weather resistance and wear resistance, and low-loss wave transmission, and is the main transmission channel for wireless signals.

[0009] In a further embodiment, the weather-resistant wave-transmitting layer comprises, by mass parts:

[0010] 95-97 parts of weather-resistant ASA resin;

[0011] 0.8-1.2 parts of hindered amine light stabilizer;

[0012] 0.5-1.0 parts of benzotriazole ultraviolet absorber;

[0013] 0.3-0.5 parts of silicone-based lubricant;

[0014] Antioxidant 0.2~0.3 parts;

[0015] 1-2 parts of surface-modified hollow glass nanospheres.

[0016] Preferably, the layer has a dielectric constant of 2.7~2.9 in the 2.4GHz frequency band, a dielectric loss tangent of ≤0.005, a flame retardant rating of UL94 HB, and no open flame dripping.

[0017] The structural flame-retardant layer is a halogen-free flame-retardant engineering plastic alloy material with a thickness of 0.6~0.8 mm. It undertakes three major functions: structural support, dimensional stability, and basic self-extinguishing flame retardancy. It is the core carrier of the shell's mechanical properties and the basic flame-retardant properties.

[0018] In a further embodiment, the structural flame-retardant layer is a halogen-free flame-retardant PC / PA66 / ABS ternary alloy material, comprising, by weight:

[0019] 42-48 parts of polycarbonate;

[0020] PA66 16-20 servings;

[0021] 22-26 parts of ABS;

[0022] 2-3 parts of maleic anhydride grafted ABS compatibilizer;

[0023] 11-17 parts of a phosphorus-nitrogen-aluminum synergistic flame retardant system;

[0024] Processing aids: 0.6-1.0 parts.

[0025] As a preferred embodiment, the phosphorus-nitrogen-aluminum synergistic flame retardant system comprises 6-8 parts of resorcinol bis(diphenyl phosphate), 3-5 parts of melamine cyanurate, and 2-4 parts of nano-aluminum hydroxide. This layer achieves a UL94 V-0 flame retardant rating with a wall thickness of 1.0 mm and a glow wire ignition temperature ≥850℃.

[0026] As a preferred alternative, the structural flame-retardant layer may also be made of 30% glass fiber reinforced halogen-free flame-retardant PA66 material.

[0027] The intumescent heat insulation layer is made of halogen-free intumescent flame-retardant silicone rubber material with a thickness of 0.15~0.2mm. It performs three major functions: heat insulation and buffering, insulation protection, and secondary flame retardancy. It is a redundant guarantee layer for flame retardant performance and also blocks electromagnetic interference from internal circuits.

[0028] In a further embodiment, the intumescent thermal insulation layer is an addition-cured liquid silicone rubber system, comprising, by weight:

[0029] 70-75 parts of vinyl-terminated polydimethylsiloxane;

[0030] 3-5 parts of hydrogen-containing silicone oil;

[0031] 13-17 parts of intumescent flame retardant system;

[0032] 8-10 parts of nano aluminum hydroxide;

[0033] 0.1 to 0.2 parts of platinum complex catalyst.

[0034] As a preferred embodiment, the intumescent flame-retardant system comprises 8-10 parts ammonium polyphosphate, 3-4 parts pentaerythritol, and 2-3 parts melamine. This layer expands ≥15 times when exposed to high temperatures of 220-250℃, forming a dense, porous, heat-insulating carbon layer with a UL94 V-0 flame-retardant rating.

[0035] In a further embodiment, microstructure mechanical interlocking structures are provided between the weather-resistant wave-transparent layer and the structural flame-retardant layer, and between the structural flame-retardant layer and the inflatable thermal insulation layer, to achieve interlayer integration by combining interfacial molecular forces and avoid delamination and cracking under long-term hot and cold cycles.

[0036] Preferably, the microstructure mechanical interlocking structure is as follows: the outer surface of the structural flame-retardant layer is provided with an array of dovetail groove microstructures, with a groove depth of 0.05~0.1mm, a groove opening width of 0.08~0.12mm, a groove bottom width of 0.13~0.17mm, and a groove spacing of 0.2~0.3mm, forming a mechanical interlock with the weather-resistant wave-transparent layer, and an interlayer 90° peel bond strength ≥8MPa; the inner surface of the structural flame-retardant layer is provided with a grid-like barbed microstructure, with a depth of 0.08~0.12mm and a grid spacing of 0.25~0.35mm, forming a mechanical interlock with the expansion heat insulation layer, and an interlayer 90° peel bond strength ≥3MPa.

[0037] In a further implementation, the area on the outer shell corresponding to the internal wireless module antenna is set as a dielectric matching region. The total thickness of the three layers in this region is precisely controlled to be 1 / 4 of the equivalent wavelength in the working frequency band medium. The signal interface reflection loss is reduced through impedance matching. The thickness of the flame-retardant layer in the dielectric matching region is reduced by 0.1~0.15mm compared to the non-matching region, and the thickness of the weather-resistant wave-transmitting layer is increased accordingly. The total wall thickness remains unchanged, and the wave transmittance is further improved without reducing the flame-retardant safety redundancy.

[0038] Secondly, the present invention provides a manufacturing process for the above-mentioned self-extinguishing flame-retardant smart switch housing, specifically including the following steps:

[0039] S1 raw material pretreatment: Place the weather-resistant wave-transparent layer ASA raw material in a hot air circulating drying oven at 80~90℃ and dry for 3.5~4.5 hours, controlling the moisture content to ≤0.05%; place the structural flame-retardant layer alloy raw material in a hot air drying oven at 115~125℃ and dry for 4.5~5.5 hours, controlling the moisture content to ≤0.02%; mix the silicone rubber A and B components of the expandable heat insulation layer evenly at a 1:1 mass ratio, and remove air bubbles by vacuum degassing for 4~6 minutes.

[0040] S2 weather-resistant wave-transparent layer preform: The weather-resistant wave-transparent layer shell is formed by precision injection molding. After injection molding, the flash is removed, and the appearance and key dimensions are fully inspected. Qualified products are used as inserts for later use.

[0041] S3 structural flame retardant layer insert injection molding: The pre-formed weather-resistant and wave-transparent layer is positioned on the cavity side of the intermediate layer injection mold. After the mold is closed, the molten material of the structural flame retardant layer is injected. The melt fills the dovetail groove microstructure between the layers. After cooling and solidification, a mechanical interlock is formed, resulting in a double-layer composite part.

[0042] S4 Interface Activation Treatment: Low-temperature plasma surface activation treatment is performed on the inner surface of the double-layer composite to improve the interfacial adhesion between engineering plastics and silicone rubber.

[0043] S5 Inflatable Thermal Insulation Layer Secondary Injection Molding: The activated double-layer composite part is placed with its inner surface facing up into a secondary injection mold. Flame-retardant silicone rubber raw material is injected using a liquid silicone injection molding machine. After heating and vulcanization, a three-layer composite shell is obtained.

[0044] S6 Post-processing and Performance Testing: Manually remove gates and flash, and conduct a full visual inspection; sample products are tested for flame retardancy, interlayer bonding strength, dimensional accuracy, and wave transmission loss, and qualified products are packaged and stored.

[0045] As a preferred option, the injection molding process parameters for the weather-resistant transparent layer in step S2 are as follows: barrel temperature zone 1 195~205℃, zone 2 205~215℃, zone 3 215~225℃, nozzle 210~220℃, mold temperature 60~70℃, injection pressure 75~85MPa, holding pressure 40~50MPa, holding time 7~9s, and cooling time 20~24s.

[0046] As a preferred option, the injection molding process parameters for the structural flame-retardant layer in step S3 are as follows: barrel temperature zone 1 245~255℃, zone 2 260~270℃, zone 3 270~280℃, nozzle 265~275℃, mold temperature 80~90℃, injection pressure 85~95MPa, holding pressure 50~60MPa, holding time 9~11s, and cooling time 30~34s.

[0047] Preferably, the plasma activation treatment time in step S4 is 25~35s; the vulcanization process parameters in step S5 are: barrel temperature 125~135℃, mold temperature 100~110℃, injection pressure 35~45MPa, and vulcanization holding time 16~20s.

[0048] Compared with the prior art, the present invention has the following beneficial technical effects:

[0049] 1. This invention adopts a multi-layer structure design with functional decomposition, which allocates different functions such as wireless wave transmission, structural support, self-extinguishing flame retardancy, and heat insulation to corresponding levels. From the structural level, it breaks the inherent bottleneck of mutual restriction between flame retardancy and wave transmission performance in a single material system. Under the premise of meeting the requirements of electrical safety and flame retardancy, it effectively improves the transmission effect of wireless communication signals of the shell and ensures the wireless connection stability of the smart switch.

[0050] 2. This invention forms a multi-level flame-retardant defense line from the outside in, consisting of flame-retardant barrier, self-extinguishing main effect, and expansion heat insulation. The flame-retardant mechanisms at each level cooperate and enhance each other. Compared with a single material shell, it has a higher flame-retardant safety redundancy, can better cope with extreme fault scenarios such as circuit overload and short circuit, curb the spread of fire, and reduce the risk of electrical fires.

[0051] 3. The core flame-retardant structural layer is completely covered by the inner and outer layers, isolating it from the direct effects of external ultraviolet rays, temperature and humidity fluctuations, and corrosive media. Structurally, it avoids the performance degradation and appearance deterioration caused by the hydrolysis and migration of flame retardants. During long-term use, it can stably maintain flame-retardant performance, mechanical properties, and appearance quality, effectively extending the product's service life. Attached Figure Description

[0052] Figure 1 This is a schematic cross-sectional view of the housing of the self-extinguishing flame-retardant smart switch described in this invention.

[0053] Figure 2 for Figure 1 A partially enlarged cross-sectional schematic diagram of the dielectric matching region in area A;

[0054] Figure 3 This is a flowchart of the preparation process described in this invention.

[0055] Figure 4 This is a magnified schematic diagram of a portion of the interlayer microstructure;

[0056] The markings in the diagram are as follows: 1-weather-resistant wave-transparent layer, 2-structural flame-retardant layer, 3-expansion heat-insulating layer, 4-dovetail groove microstructure, 5-barbed microstructure, 6-dielectric matching region. Detailed Implementation

[0057] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0058] Example 1

[0059] In this embodiment, the outer shell consists of, from the outside in, a weather-resistant wave-transmitting layer, a structural flame-retardant layer, and an intumescent heat-insulating layer. The overall cross-sectional structure is as follows: Figure 1 As shown, the total wall thickness is 1.05mm; of which the weather-resistant wave-transparent layer is 0.25mm thick, the structural flame-retardant layer is 0.65mm thick, and the expansion thermal insulation layer is 0.15mm thick. Figure 4 As shown, the outer surface of the flame-retardant structural layer is provided with an array of dovetail groove microstructures, and the inner surface is provided with a grid-like barbed microstructure, which achieves integrated bonding between the layers through mechanical interlocking.

[0060] Material formulations for each layer (parts by weight):

[0061] Weather-resistant wave-transparent layer: 96 parts weather-resistant ASA resin, 1.0 part hindered amine light stabilizer, 0.8 parts benzotriazole UV absorber, 0.4 parts silicone lubricant, 0.3 parts antioxidant 1010, and 1.5 parts silane-modified hollow glass nanospheres. This layer has a dielectric constant of 2.7~2.9 in the 2.4GHz band and a dielectric loss tangent ≤0.005.

[0062] Structural flame-retardant layer: 45 parts polycarbonate, 18 parts PA66, 24 parts ABS, 2.5 parts maleic anhydride-grafted ABS compatibilizer, 7 parts resorcinol bis(diphenyl phosphate), 4 parts melamine cyanurate, 3 parts nano aluminum hydroxide, 0.3 parts antioxidant 1076, and 0.5 parts PETS lubricant. This layer, with a wall thickness of 1.0 mm, achieves a UL94 V-0 flame retardant rating and a glow wire ignition temperature ≥850℃.

[0063] Intumescent thermal insulation layer: 72 parts vinyl-terminated polydimethylsiloxane, 4 parts hydrogen-containing silicone oil, 9 parts ammonium polyphosphate, 3.5 parts pentaerythritol, 2.5 parts melamine, 9 parts nano-aluminum hydroxide, and 0.15 parts platinum complex catalyst. This layer expands ≥15 times when exposed to high temperatures of 220~250℃, and its flame retardant rating is UL94 V-0.

[0064] Preparation process flow as follows Figure 3 As shown, the specific steps are as follows:

[0065] S1 raw material pretreatment: The weather-resistant wave-transparent layer ASA raw material is dried in an 85℃ hot air circulating drying oven for 4 hours, and the moisture content is controlled to be ≤0.05%; the structural flame-retardant layer ternary alloy raw material is dried in a 120℃ hot air drying oven for 5 hours, and the moisture content is controlled to be ≤0.02%; the silicone rubber A and B components of the expandable heat insulation layer are mixed evenly in a 1:1 mass ratio and vacuum degassed for 5 minutes to remove air bubbles.

[0066] S2 Weather-resistant Transparent Layer Pre-forming: The weather-resistant transparent layer shell is formed using a precision injection molding machine. The barrel temperature is 200℃ in zone 1, 210℃ in zone 2, 220℃ in zone 3, and 215℃ in the nozzle. The mold temperature is 65℃, the injection pressure is 80MPa, the holding pressure is 45MPa, the holding time is 8s, and the cooling time is 22s. After injection molding, the flash is removed, and the appearance and key dimensions are fully inspected. Qualified products are used as inserts for later use.

[0067] S3 structural flame-retardant insert injection molding: The pre-formed weather-resistant and wave-transparent layer is positioned on the cavity side of the intermediate layer injection mold. After the mold is closed, the molten material of the structural flame-retardant layer is injected. The melt fills the dovetail groove microstructure between the layers. After cooling and solidification, a mechanical interlock is formed, resulting in a double-layer composite part. The injection molding process parameters are: barrel temperature 250℃ in zone 1, 265℃ in zone 2, 275℃ in zone 3, nozzle 270℃, mold temperature 85℃, injection pressure 90MPa, holding pressure 55MPa, holding time 10s, and cooling time 32s.

[0068] S4 Interface Activation Treatment: The inner surface of the double-layer composite is subjected to low-temperature plasma surface activation treatment for 30 seconds to improve the interfacial adhesion between engineering plastics and silicone rubber.

[0069] S5 Inflatable Thermal Insulation Layer Secondary Injection Molding: The activated double-layer composite part is placed with its inner surface facing up into a secondary injection mold. Flame-retardant silicone rubber raw material is injected using a liquid silicone injection molding machine and heated for vulcanization. The vulcanization process parameters are: barrel temperature 130℃, mold temperature 105℃, injection pressure 40MPa, and vulcanization holding time 18s, to obtain the finished three-layer composite shell.

[0070] S6 Post-processing and Performance Testing: Manually remove gates and flash, and conduct a full visual inspection; sample products are tested for flame retardancy, interlayer bonding strength, dimensional accuracy, and wave transmission loss, and qualified products are packaged and stored.

[0071] Example 2

[0072] This embodiment is a highly flame-retardant reinforced three-layer composite self-extinguishing flame-retardant smart switch housing, which increases the proportion of the flame-retardant system in the structural flame-retardant layer, making it suitable for industrial-grade smart switch scenarios with high loads and high power. Structural parameters: total wall thickness of the three layers is 1.05 mm, of which the weather-resistant wave-transparent layer is 0.25 mm thick, the structural flame-retardant layer is 0.65 mm thick, and the expansion heat insulation layer is 0.15 mm thick; the interlayer microstructure mechanical interlocking design is completely consistent with that of Embodiment 1.

[0073] Material formulations for each layer (parts by weight):

[0074] Weather-resistant wave-transparent layer: The formulation is completely consistent with that of Example 1.

[0075] Structural flame retardant layer: 43 parts polycarbonate, 17 parts PA66, 23 parts ABS, 3 parts maleic anhydride grafted ABS compatibilizer, 8 parts resorcinol bis(diphenyl phosphate), 5 parts melamine cyanurate, 4 parts nano aluminum hydroxide, 0.4 parts antioxidant 1076, and 0.6 parts PETS lubricant.

[0076] Expandable thermal insulation layer: The formula is completely consistent with that of Example 1.

[0077] Preparation process steps: completely consistent with Example 1.

[0078] Example 3

[0079] This embodiment is a high-transmittance optimized three-layer composite self-extinguishing flame-retardant smart switch housing. The dielectric properties of the weather-resistant transparent layer are optimized, and an antenna dielectric matching area is added. Figure 2 As shown, this further improves the wireless signal transmission effect. Structural parameters: The total wall thickness of the three layers is 1.05 mm, and the thickness of each layer in the non-antenna area is the same as in Example 1; the area of ​​the outer shell corresponding to the internal wireless module antenna is the dielectric matching area. In this area, the total thickness of the three layers matches 1 / 4 of the equivalent wavelength in the working frequency band medium. The thickness of the structural flame retardant layer is reduced by 0.1 mm compared to the non-matching area, and the thickness of the weather-resistant wave-transmitting layer is increased by 0.1 mm accordingly, while the total wall thickness remains unchanged at 1.05 mm. The mechanical interlocking design of the interlayer microstructure is the same as in Example 1.

[0080] Material formulations for each layer (parts by weight):

[0081] Weather-resistant translucent layer: 96.5 parts weather-resistant ASA resin, 0.9 parts hindered amine light stabilizer, 0.7 parts benzotriazole ultraviolet absorber, 0.3 parts silicone lubricant, 0.2 parts antioxidant 1010, and 1.4 parts silane-modified hollow glass nanospheres.

[0082] Structural flame retardant layer: The formulation is completely consistent with that of Example 1.

[0083] Expandable thermal insulation layer: The formula is completely consistent with that of Example 1.

[0084] The manufacturing process is basically the same as in Example 1, except that the cavity size of the mold corresponding to the antenna area is adjusted accordingly to ensure the thickness accuracy of the dielectric matching area.

[0085] Example 4

[0086] This embodiment is a high-strength three-layer composite self-extinguishing flame-retardant smart switch housing, using glass fiber reinforced PA66 as the structural flame-retardant layer, suitable for industrial-grade smart switch scenarios with higher requirements for mechanical strength and heat resistance. Structural parameters: total wall thickness of the three layers is 1.05 mm, of which the weather-resistant wave-transmitting layer is 0.2 mm thick, the structural flame-retardant layer is 0.7 mm thick, and the expansion thermal insulation layer is 0.15 mm thick; the interlayer microstructure mechanical interlocking design is consistent with that of Embodiment 1.

[0087] Material formulations for each layer (parts by weight):

[0088] Weather-resistant wave-transparent layer: The formulation is completely consistent with that of Example 1.

[0089] Structural flame-retardant layer: 67 parts PA66 resin, 30 parts alkali-free glass fiber, 9 parts melamine cyanurate, 3 parts ammonium polyphosphate, 2 parts zinc borate, 0.5 parts antioxidant 1098, and 0.5 parts calcium stearate lubricant; this layer achieves a UL94 V-0 flame retardant rating with a wall thickness of 1.0 mm.

[0090] Expandable thermal insulation layer: The formula is completely consistent with that of Example 1.

[0091] Preparation process steps: basically the same as in Example 1, only the injection molding process parameters of the structural flame retardant layer are adjusted: barrel temperature zone 1 270℃, zone 2 280℃, zone 3 290℃, nozzle 285℃, mold temperature 90℃, and other step parameters remain unchanged.

[0092] Comparative Example 1

[0093] This comparative example serves as a control group for conventional solutions in the prior art, employing the industry-leading single halogen-free flame-retardant PC shell manufacturing route to compare the comprehensive performance gains of the multi-layer composite structure of this invention. Structural parameters: A single-layer homogeneous structure with a wall thickness of 1.0 mm is adopted, essentially consistent with the total wall thickness of the embodiment. The shell shape and snap-fit ​​structure are completely identical to the embodiment, adapting to the internal assembly of intelligent switches of the same specifications.

[0094] Material formulation (parts by weight): 86 parts bisphenol A polycarbonate (weight average molecular weight 25000), 12 parts resorcinol bis(diphenyl phosphate), 0.4 parts antioxidant 1076, 0.6 parts stearate lubricant, and 1 part black masterbatch. This formulation is a typical halogen-free flame-retardant PC formulation commonly used in the industry. With a wall thickness of 1.0mm, it can achieve a UL94 V-0 flame retardant rating, making it a mainstream material for mid-to-high-end smart switch housings.

[0095] Manufacturing process: The process employs a conventional single-shot precision injection molding technique. The specific steps are as follows:

[0096] (1) Raw material pretreatment: The flame-retardant PC raw material was placed in a 120℃ hot air drying oven and dried for 4 hours, with the moisture content controlled to be ≤0.02%;

[0097] (2) Injection molding: The dried raw material is added to the precision injection molding machine. The barrel temperature is 260℃ in zone 1, 270℃ in zone 2, 280℃ in zone 3, and 275℃ in nozzle. The mold temperature is 80℃, the injection pressure is 95MPa, the holding pressure is 60MPa, the holding time is 12s, and the cooling time is 35s.

[0098] (3) Post-processing: After molding, remove the shell, remove the gate and flash, and use it after the appearance and size are inspected and qualified.

[0099] Comparative Example 2

[0100] This comparative example is a control group with a double-layer structure lacking an intumescent thermal insulation layer, used to verify the role of the intumescent thermal insulation layer in improving flame retardant safety redundancy and long-term damp heat stability.

[0101] Structural parameters: Double-layer composite structure, consisting of a weather-resistant wave-transparent layer and a structural flame-retardant layer from the outside to the inside, with a total wall thickness of 1.05 mm, consistent with the total wall thickness of Example 1; wherein the thickness of the weather-resistant wave-transparent layer is 0.25 mm and the thickness of the structural flame-retardant layer is 0.8 mm; an array-type dovetail groove microstructure mechanical interlocking is provided between the weather-resistant wave-transparent layer and the structural flame-retardant layer, and the microstructure parameters are completely consistent with those of Example 1.

[0102] Material formulation: The raw material formulations of the weather-resistant wave-transparent layer and the structural flame-retardant layer are exactly the same as those of the corresponding layers in Example 1; no expansion heat insulation layer is provided, and there is no silicone rubber-based inner layer material.

[0103] Preparation process: The inner layer-related processes are omitted from the overall process. The rest are the same as the corresponding steps in Example 1, specifically:

[0104] (1) Raw material pretreatment: Only ASA raw materials and ternary alloy raw materials were subjected to corresponding drying treatments, with parameters the same as in Example 1;

[0105] (2) Weather-resistant wave-transparent layer preforming: The process parameters are completely consistent with step S2 of Example 1;

[0106] (3) Injection molding of structural flame-retardant insert: The process parameters are completely consistent with step S3 of Example 1, resulting in a double-layer composite part;

[0107] (4) Post-processing and inspection: Remove the sprue flash, inspect the appearance and dimensions, and then perform performance testing. The plasma activation and inner layer secondary injection molding steps are omitted.

[0108] Comparative Example 3

[0109] This comparative example is a three-layer structure control group without interlayer microstructure interlocking, used to verify the effect of microstructure mechanical interlocking on improving interlayer bonding strength and long-term thermal cycling reliability.

[0110] Structural parameters: Three-layer composite structure, from the outside to the inside, consisting of a weather-resistant wave-transparent layer, a structural flame-retardant layer, and an intumescent heat-insulating layer, with a total wall thickness of 1.05mm. The thickness of each layer is exactly the same as in Example 1. The difference is that the inner and outer surfaces of the structural flame-retardant layer are smooth planes, without dovetail grooves, barbs, or other microstructure designs. The layers are bonded only by the resin fusion force of the insert injection molding and the interfacial molecular forces after plasma activation.

[0111] Material formulation: The raw material formulations for the weather-resistant wave-transparent layer, the structural flame-retardant layer, and the intumescent heat-insulating layer are exactly the same as those in Example 1.

[0112] Preparation process: The overall process flow and operation steps are completely consistent with those of Example 1, except that the cavity and core of the injection mold do not have microstructure molding features and dovetail grooves and barb structures are not processed; the other raw material pretreatment, injection parameters, activation time, vulcanization parameters, etc. are all consistent with those of Example 1.

[0113] Performance testing

[0114] After conditioning all the above samples at 23℃ and 50% relative humidity for 24 hours, performance tests were conducted. The test criteria and conditions for each performance item are as follows:

[0115] 1. Flame retardancy rating: A vertical burning test was conducted using a 1.0mm thick sample.

[0116] 2. Glow wire ignition temperature: The ignition temperature of the material is tested using the glow wire test method;

[0117] 3.2.4GHz signal attenuation: The signal transmission loss was tested using a vector network analyzer with a vertical incidence method in the 2.4GHz band;

[0118] 4. Notched impact strength of simply supported beam: The notched impact strength of the specimens in a simply supported beam was tested at room temperature of 23℃.

[0119] 5. 90° interlayer peel strength: The interlayer bonding strength was tested using a universal testing machine with a 90° peel method and a tensile rate of 50 mm / min.

[0120] 6. Double 85 damp heat aging: After aging the sample in a constant temperature and humidity chamber at 85℃ and 85%RH for 1000 hours, the flame retardancy rating was retested;

[0121] 7. UVB UV Aging: After aging the samples with a UVB fluorescent UV lamp for 1000 hours, the impact strength retention rate was calculated. The test results are shown in the table below:

[0122] Table 1 Performance test results of each embodiment and comparative example

[0123] Performance items Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Flame retardant rating (1.0mm wall thickness) V-0 V-0 V-0 V-0 V-0 V-1 V-0 ignition temperature of glowing wire 900℃ 920℃ 900℃ 910℃ 850℃ 825℃ 895℃ 2.4GHz signal attenuation 4.2dB 4.5dB 3.5dB 4.8dB 16.3dB 7.8dB 4.3dB Notched impact strength of a simply supported beam (kJ / m²) 14.8 14.2 14.6 16.2 12.5 14.5 14.6 Outer layer-middle layer bonding strength 8.2MPa 8.0MPa 8.1MPa 7.9MPa - 8.1MPa 3.2MPa Intermediate layer-inner layer bonding strength 3.5MPa 3.4MPa 3.4MPa 3.3MPa - - 1.1MPa Flame retardancy rating after 1000 hours of aging with dual 85 V-0 V-0 V-0 V-0 V-2 V-2 V-0 UVB aging 1000h impact retention rate 93.2% 92.7% 93.0% 91.5% 78.4% 85.1% 92.8%

[0124] Based on the test results, the following conclusions can be drawn:

[0125] Compared with Comparative Example 1, the wireless transmission performance of all embodiments of the present invention is significantly improved. At the same time, the glow wire has stronger resistance and better performance stability after long-term aging. This verifies the breakthrough effect of the functional layered structure on the inherent contradiction of "flame retardancy-transmission-weather resistance". It can effectively improve the wireless communication effect and service life of smart switches while meeting the requirements of electrical safety and flame retardancy.

[0126] Comparing Example 1 and Comparative Example 2, it can be seen that the addition of the expansion heat insulation layer can effectively improve the flame retardant safety redundancy, increase the temperature resistance of the glow wire, and further block the erosion of the core flame retardant layer by the humid and hot environment, and enhance the flame retardant stability during long-term service. It is an important technical feature to improve the reliability of the product under extreme working conditions.

[0127] Comparing Example 1 and Comparative Example 3, it can be seen that the interlayer microstructure mechanical interlocking can significantly improve the interlayer bonding strength, effectively avoid the risk of interlayer peeling and delamination after long-term hot and cold cycles and aging, and ensure the long-term integrity of the shell structure and the protective performance. It is a key optimization solution to improve the environmental adaptability of products.

[0128] Example 2 further enhances fire safety in extreme high-temperature scenarios by strengthening the flame-retardant system ratio, adapting to the usage requirements of high-power industrial switches; Example 3 further improves wave transmission effect without changing the overall wall thickness and flame-retardant performance by locally optimizing the dielectric matching region, adapting to product scenarios with high communication quality requirements; Example 4 uses glass fiber reinforced PA66 substrate, which has better mechanical strength and heat resistance, verifying the adaptability of the structural scheme of the present invention to different substrates.

[0129] In summary, the multi-layer composite self-extinguishing flame-retardant smart switch housing of the present invention, with the synergistic effect of each functional layer and the reinforced structure, can simultaneously achieve high self-extinguishing flame retardancy, excellent wave transmission performance and long-term service stability, and is fully adaptable to the operating conditions and safety requirements of various smart switches.

Claims

1. A self-extinguishing flame-retardant smart switch housing, characterized in that, It consists of a weather-resistant wave-transparent layer, a structural flame-retardant layer, and an intumescent heat-insulating layer, which are sequentially composited from the outside to the inside, with a total wall thickness of 1.0~1.1 mm; The weather-resistant wave-transmitting layer is made of low-dielectric weather-resistant modified ASA material with a thickness of 0.2~0.3 mm; The structural flame-retardant layer is a halogen-free flame-retardant engineering plastic alloy material with a thickness of 0.6~0.8 mm; The intumescent heat insulation layer is a halogen-free intumescent flame-retardant silicone rubber material with a thickness of 0.15~0.2 mm.

2. The self-extinguishing flame-retardant intelligent switch housing according to claim 1, characterized in that, By weight, the weather-resistant wave-transparent layer comprises 95-97 parts of weather-resistant ASA resin, 0.8-1.2 parts of hindered amine light stabilizer, 0.5-1.0 parts of benzotriazole ultraviolet absorber, 0.3-0.5 parts of silicone lubricant, 0.2-0.3 parts of antioxidant, and 1-2 parts of surface-modified nano-hollow glass microspheres.

3. The self-extinguishing flame-retardant intelligent switch housing according to claim 1, characterized in that, The structural flame-retardant layer is a halogen-free flame-retardant PC / PA66 / ABS ternary alloy material, comprising, by weight, 42-48 parts of polycarbonate, 16-20 parts of PA66, 22-26 parts of ABS, 2-3 parts of maleic anhydride-grafted ABS compatibilizer, 11-17 parts of phosphorus-nitrogen-aluminum synergistic flame-retardant system, and 0.6-1.0 parts of processing aids; The phosphorus-nitrogen-aluminum synergistic flame retardant system comprises 6-8 parts of resorcinol bis(diphenyl phosphate), 3-5 parts of melamine cyanurate, and 2-4 parts of nano aluminum hydroxide.

4. The self-extinguishing flame-retardant intelligent switch housing according to claim 1, characterized in that, The structural flame-retardant layer is made of 30% glass fiber reinforced halogen-free flame-retardant PA66 material, and its flame retardant rating reaches UL94 V-0 level with a wall thickness of 1.0 mm.

5. The self-extinguishing flame-retardant intelligent switch housing according to claim 1, characterized in that, The intumescent heat-insulating layer is an addition-type liquid silicone rubber system, comprising, by weight, 70-75 parts of vinyl-terminated polydimethylsiloxane, 3-5 parts of hydrogen-containing silicone oil, 13-17 parts of an intumescent flame-retardant system, 8-10 parts of nano-aluminum hydroxide, and 0.1-0.2 parts of a platinum complex catalyst. The intumescent flame retardant system comprises 8-10 parts of ammonium polyphosphate, 3-4 parts of pentaerythritol, and 2-3 parts of melamine.

6. The self-extinguishing flame-retardant intelligent switch housing according to claim 1, characterized in that, Microstructure mechanical interlocking structures are provided between the weather-resistant wave-transparent layer and the structural flame-retardant layer, and between the structural flame-retardant layer and the expansion heat insulation layer. The outer surface of the flame-retardant structural layer is provided with an array of dovetail groove microstructures, with a groove depth of 0.05~0.1 mm, a groove opening width of 0.08~0.12 mm, a groove bottom width of 0.13~0.17 mm, and a groove spacing of 0.2~0.3 mm, forming a mechanical interlock with the weather-resistant wave-transparent layer, and the interlayer 90° peel bond strength is ≥8MPa; The inner surface of the flame-retardant layer is provided with a grid-like barbed microstructure with a depth of 0.08~0.12 mm and a grid spacing of 0.25~0.35 mm, which forms a mechanical interlock with the expansion heat insulation layer, and the interlayer 90° peel bond strength is ≥3 MPa.

7. The self-extinguishing flame-retardant intelligent switch housing according to claim 1, characterized in that, The area of ​​the outer shell corresponding to the internal wireless module antenna is the dielectric matching region, and the total thickness of the three layers in the dielectric matching region is 1 / 4 of the equivalent wavelength in the medium of the 2.4 GHz operating frequency band; The thickness of the flame-retardant layer in the dielectric matching region is reduced by 0.1~0.15 mm compared to the non-matching region, while the thickness of the weather-resistant wave-transmitting layer increases accordingly, and the total wall thickness remains unchanged.

8. A process for the housing of a self-extinguishing flame-retardant smart switch as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1 Raw Material Pretreatment: The weather-resistant wave-transparent layer raw material and the structural flame-retardant layer raw material are respectively subjected to hot air drying treatment to control the moisture content of the weather-resistant wave-transparent layer raw material ≤0.05% and the moisture content of the structural flame-retardant layer raw material ≤0.02%; the two-component liquid silicone rubber raw material for the expansion heat insulation layer is mixed in proportion and vacuum degassed for later use. S2 Weather-resistant Wave-transparent Layer Pre-forming: The weather-resistant wave-transparent layer shell is formed by precision injection molding process. The flash is removed and the appearance and dimensions are inspected. Qualified products are used as inserts for later use. S3 structural flame retardant layer insert injection molding: The pre-formed weather-resistant and wave-transparent layer is positioned in the injection mold cavity, the structural flame retardant layer raw material is injected, the molten resin fills the interlayer microstructure, and after cooling, the weather-resistant and wave-transparent layer and the structural flame retardant layer are combined into one, resulting in a double-layer composite part. S4 Interface Activation Treatment: Low-temperature plasma surface activation treatment is performed on the inner surface of the double-layer composite to improve interface adhesion; S5 Inflatable Thermal Insulation Layer Secondary Injection Molding: The activated double-layer composite part is placed into a secondary injection mold, liquid flame-retardant silicone rubber is injected, and it is heated and vulcanized to obtain a three-layer composite shell product. S6 Post-processing and Performance Testing: Remove gates and flash, conduct full appearance inspection and sampling performance testing, and package qualified products into warehouse.

9. The preparation process according to claim 8, characterized in that, The injection molding process parameters for the weather-resistant transparent layer in step S2 are as follows: barrel temperature: zone 1 195~205℃, zone 2 205~215℃, zone 3 215~225℃, nozzle 210~220℃, mold temperature 60~70℃, injection pressure 75~85MPa, holding pressure 40~50MPa, holding time 7~9s, and cooling time 20~24s. The injection molding process parameters for the structural flame-retardant layer in step S3 are as follows: barrel temperature: zone 1 245~255℃, zone 2 260~270℃, zone 3 270~280℃, nozzle 265~275℃, mold temperature 80~90℃, injection pressure 85~95MPa, holding pressure 50~60MPa, holding time 9~11s, and cooling time 30~34s.

10. The preparation process according to claim 8, characterized in that, In step S4, the plasma activation treatment time is 25~35s; in step S5, the injection vulcanization parameters for the expanded heat insulation layer are: barrel temperature 125~135℃, mold temperature 100~110℃, injection pressure 35~45MPa, and vulcanization holding time 16~20s.

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