A device and process for recycling plastic surface by injection molding based on waste plastic

Abstract

The application belongs to the technical field of waste plastic processing, and particularly discloses a plastic surface re-injection device and process based on waste plastic recycling, which comprises sequentially connected waste plastic surface pretreatment unit, multi-cavity radial injection mold unit, gradient temperature control double-shot injection unit, variable pressure holding control unit, partition cooling and solidification unit, demolding detection unit and central AI control system. The application sets the waste plastic part surface pretreatment process step, uses the nanosecond pulse laser to process the micron-level anchoring groove array in the surface defect area, and cooperates with the plasma cleaning activation treatment, so that the microscopic mechanical lock structure and the high-activity chemical interface are formed on the surface of the waste plastic part, the combination strength between the secondary injection layer and the waste substrate is significantly improved, and the effect of ensuring the synchronous solidification of each area of the multi-cavity mold is achieved by setting the partition gradient cooling process step and cooperating with the infrared thermal imager to monitor the mold temperature field uniformity in real time.

Description

Technical Field

[0001] This invention relates to the field of waste plastic processing technology, specifically to a plastic surface re-injection molding device and process based on waste plastic recycling. Background Technology

[0002] With the widespread use of plastic products in automobiles, home appliances, electronics, packaging, and other fields, the recycling and reuse of waste plastics has become an important issue in the field of environmental protection. Traditional waste plastic recycling methods usually involve crushing, washing, melting, and re-granulation, ultimately re-injecting into new plastic products.

[0003] The existing technology has the following defects or problems: 1. Waste plastics undergo thermal degradation during crushing and multiple melting processes, resulting in a significant decrease in the mechanical properties of the material, low-quality recycled materials, and inability to be used in high-performance products. 2. For waste plastic products with specific textures, coatings, or functional layers on their surface, traditional recycling methods will completely destroy their surface structure, resulting in a waste of resources; 3. Existing technologies lack specific processes for repairing or re-molding the surfaces of waste plastic products.

[0004] Existing patent applications such as 201711249232.0 and 20211076924.X, while involving waste plastic recycling and injection molding processes, mainly focus on mixing waste plastics with virgin materials for molding, or using sandwich injection molding for one-time molding. None of these technologies can repair, strengthen, or functionalize the surface of the waste plastic matrix for re-injection molding while preserving its integrity.

[0005] It should be noted that the above content falls within the inventor's technical knowledge and does not necessarily constitute prior art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a plastic surface re-injection molding device and process based on waste plastic recycling, which solves the current problems.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a plastic surface re-injection molding device based on waste plastic recycling, comprising a waste plastic surface pretreatment unit, a multi-cavity radial injection mold unit, a gradient temperature control dual injection unit, a variable pressure holding control unit, a zoned cooling and curing unit, a demolding detection unit, and a central AI control system connected in sequence. All the above-mentioned units are connected by an automated conveying platform to realize the transfer of waste plastic parts and injection-molded finished products. In addition, there is an external central AI control system, which consists of an edge computing server and a PLC controller. It communicates with each unit in real time through an industrial bus to coordinate and schedule the collaborative operation of each unit, thereby realizing intelligent control of the injection molding process.

[0008] In some embodiments, the waste plastic surface micromachining unit incorporates a laser micromilling subunit and a plasma surface activation subunit. The laser micromilling subunit consists of a nanosecond pulsed laser and a three-dimensional moving platform, and is used to process a micron-level anchoring groove array with a depth of 0.1 to 0.3 mm and a width of 0.05 to 0.15 mm in the defect area on the surface of waste plastic parts. The plasma surface activation subunit consists of a plasma cleaner and a high-pressure ion gun, used to remove processing debris and surface oil, while increasing surface activation energy. Its surface activation effect is characterized by contact angle measurement, and the formula for calculating the contact angle reduction efficiency is as follows: ; in, To address the front contact angle, To address the post-contact angle, Reduced efficiency due to contact angle; The micromachining unit also has a built-in multispectral vision inspection mechanism, which is used to identify the type, location and area of ​​surface defects in waste plastic parts in real time, and to use the defect data for path planning in subsequent processing.

[0009] In some embodiments, the multi-cavity radial injection mold unit consists of a mold body, a central radial flow channel system, and a cavity temperature zone control system; The mold body has a size of 300×300mm and has 4, 6, 8, 12 and 16 mold cavities inside, which are arranged in concentric rings. The central radial flow channel system consists of a convergence zone located at the center of the mold and branch flow channels radiating outward from the center. Each branch flow channel is connected to a mold cavity at its end, with branch angles of 45°, 60°, and 90° to ensure that the filling pressure deviation of each mold cavity is ≤±5%. The mold cavity temperature zone control system includes multiple sets of thermocouple sensors and zone heating rods arranged in the inner ring, middle ring and outer ring of the mold. Each temperature control zone can be independently set to a temperature of 90℃~105℃, thereby realizing a gradient temperature distribution from the inside to the outside. The temperature zone control system and the central AI control system form a temperature-pressure collaborative control closed loop. The central AI control system dynamically adjusts the heating power and injection pressure of each temperature control zone according to the position and material of the waste plastic parts in the mold cavity, and its temperature control accuracy is ±1℃.

[0010] In some embodiments, the gradient temperature-controlled dual-injection molding unit consists of a first injection molding assembly and a second injection molding assembly; The first injection molding assembly is used to inject highly fluid recycled plastic melt with a melt index of 30-50 g / 10 min and a melt temperature controlled at 180-190 °C. The second injection molding assembly is used to inject low-melting-point copolymer melt with a melt index of 10-20 g / 10 min and a melt temperature controlled at 150-160 °C. The variable pressure holding control unit consists of a servo hydraulic pump, a proportional pressure valve, and a high-pressure storage tank. The servo hydraulic pump is used to provide injection pressure of 80MPa to 120MPa, the proportional pressure valve is used to achieve a step-by-step decrease in pressure during the holding pressure stage, and the high-pressure storage tank is used to quickly release residual pressure before mold opening. The variable pressure holding control unit and the central AI control system form a closed-loop pressure control. The central AI control system executes a preset three-segment variable pressure holding curve based on real-time feedback data from the mold cavity pressure sensor. The first stage is the high-pressure permeation stage, where the pressure increases from 80MPa to 120MPa and is maintained for 5 seconds. The second stage is the pressure holding stage, where the pressure is maintained at 100MPa for 10 seconds. The third stage is the stress relief stage, where the pressure drops from 100MPa to 50MPa in a stepwise manner over a period of 15 seconds. During the entire pressure change and holding process, the pressure fluctuation within the mold cavity is ≤±2MPa. The partitioned cooling and curing unit includes an in-mold circulating cooling water system and a temperature difference control valve. The in-mold circulating cooling water system has multiple independent cooling water channels arranged inside the mold, corresponding to the inner ring, middle ring and outer ring mold cavity areas respectively. Each cooling water channel inlet is equipped with a temperature difference control valve, and the inlet water temperature can be independently adjusted to 20-30℃, and the outlet water temperature is controlled to 35-45℃, so as to achieve synchronous curing of each mold cavity area and avoid uneven shrinkage.

[0011] Another technical problem to be solved by this invention is to propose a plastic surface re-injection molding process based on waste plastic recycling, comprising the following steps: Step 1: The recycled waste plastic products are classified according to material, color and degree of surface defects. Products with repair value are selected and micron-level anchoring grooves with a depth of 0.1 to 0.3 mm are processed in the defect area of ​​the surface using a nanosecond pulse laser. Then, the surface is cleaned and activated using a plasma cleaner to reduce the surface contact angle to ≤30°. At the same time, the defect location and depth data are collected and uploaded to the central AI control system. Step 2: The pre-treated waste plastic parts are used as inserts and placed into the cavities of a multi-cavity radial injection mold by an automated conveying platform. The number of mold cavities is 4, 6, 8, 12, or 16. The melt is evenly distributed through the central convergence and fusion zone of the mold and the radial flow channels to ensure that the filling pressure deviation of each cavity is ≤±5%. Step 3: Perform double-shot injection molding using a gradient temperature-controlled double-shot injection molding unit. The first shot uses high-flow-rate recycled plastic melt with a melt temperature controlled at 180-190℃, while the second shot uses low-melting-point copolymer melt with a melt temperature controlled at 150-160℃. Simultaneously, the mold wall temperature zone control system sets the inner ring temperature to 105℃, the middle ring temperature to 95℃, and the outer ring temperature to 90℃, forming a temperature gradient from the inside to the outside. This creates a gradient viscosity distribution in the melt during flow, enhancing the melt's penetration and filling of microgrooves. Step 4: After mold closing, pressure is maintained by a pressure control unit. Within 5 seconds of mold closing, the pressure is increased from 80MPa to 120MPa, using high pressure to force the melt to penetrate deeply into the micro-grooves. Then, within 15 seconds, the pressure is gradually reduced to 50MPa to release the stress on the matrix and prevent warping deformation. Throughout the pressure holding process, the mold cavity pressure is monitored in real time by a pressure sensor and fed back to the central AI control system for dynamic adjustment. Step 5: Gradual cooling is performed through the zoned cooling and curing unit. The inlet temperature of the cooling water is set to 25℃ for the inner ring, 23℃ for the middle ring, and 20℃ for the outer ring. The cooling time is 60-90 seconds, and the cooling rate is controlled at 0.8-1.2℃ / s for the inner ring, 0.6-1.0℃ / s for the middle ring, and 0.4-0.8℃ / s for the outer ring to ensure that all mold cavity areas are cured synchronously to below the demolding temperature. Step Six: The composite product is removed from the mold by the intelligent demolding detection unit, and the surface of the product is inspected by the online vision inspection system to detect defects such as air marks, weld lines, shrinkage cavities, or local non-bonding defects. Qualified products are sent to the post-processing process to remove gate residue and polish them smooth. Unqualified products are fed back to the central AI control system for process parameter adjustment.

[0012] In some embodiments, the nanosecond pulsed laser has an output wavelength of 1064 nm, a pulse width of 10–50 ns, a pulse energy of 1–5 mJ, a scanning speed of 100–300 mm / s, and a surface roughness Ra ≤ 0.8 μm for the microgrooves after processing. The plasma cleaning uses a mixture of argon and oxygen in a volume ratio of 80%–90% argon and 10%–20% oxygen. The cleaning time is 30–60 seconds. After cleaning, the surface contact angle is ≤30° and the surface activation energy is increased to more than twice the original value.

[0013] In some embodiments, the melt index of the high-flowability recycled plastic melt is 30-50 g / 10 min, and the low-melting-point copolymer melt is thermoplastic polyurethane elastomer (TPU) or ethylene-vinyl acetate copolymer (EVA) with a melt index of 10-20 g / 10 min. The injection speed of the dual-shot injection molding is controlled as follows: 50-80 mm / s for the first shot and 30-50 mm / s for the second shot.

[0014] In some embodiments, the cooling water for the zoned gradient cooling is deionized water, and the cooling water flow rate is controlled as follows: 5-10 L / min for the inner ring, 4-8 L / min for the middle ring, and 3-6 L / min for the outer ring. During the cooling process, the temperature of the outer surface of the mold is monitored in real time by an infrared thermal imager to ensure that the temperature field uniformity deviation of the mold is ≤ ±5℃, the temperature of the composite material product is ≤ 60℃ when demolding, and the natural shrinkage rate is ≤ 0.3% after demolding for 24 hours.

[0015] In some embodiments, the online visual inspection uses a high-resolution industrial camera with a resolution of not less than 1920×1080 pixels, a frame rate of not less than 30fps, and a lens focal length of 20-50mm. During inspection, the surface of the product is scanned 360°, and the defect identification rate is ≥99.5%. In the post-processing step, the gate residue is removed by either pneumatic shears or laser cutting. After removal, the gate residue height is ≤0.2mm, and the surface roughness Ra after grinding is ≤0.4μm.

[0016] Compared with the prior art, the present invention provides a plastic surface re-injection molding device and process based on waste plastic recycling, which has the following beneficial effects: 1. This invention relates to a plastic surface re-injection molding device and process based on waste plastic recycling. By setting up a surface pretreatment process for waste plastic parts, a nanosecond pulse laser is used to process a micron-level anchoring groove array in the surface defect area, combined with plasma cleaning and activation treatment, so that a micro-mechanical interlocking structure and a highly active chemical interface are formed on the surface of the waste plastic parts. This significantly improves the bonding strength between the secondary injection molding layer and the waste substrate. The peel strength is verified by ASTM D903 peel test, which can reach more than 22 N / cm, which is more than 300% higher than the untreated waste plastic surface. This effectively solves the technical problem of insufficient surface bonding in traditional recycling processes. 2. This device and process for re-injection molding of plastic surfaces based on waste plastic recycling involves setting up a multi-cavity mold insert placement and a central radial flow channel for melt distribution. Pre-treated waste plastic parts are placed as inserts in 4, 6, 8, 12, or 16 mold cavities. The central convergence and fusion zone and radial flow channels achieve balanced melt distribution. Simultaneously, gradient mold wall temperature control (inner ring 105℃, middle ring 95℃, outer ring 90℃) effectively solves the technical problems of uneven melt flow and temperature differences leading to filling defects in multi-cavity injection molding. This results in filling pressure deviation of each cavity controlled within ≤±5%, and surface bonding strength deviation of each cavity product within ≤±8%. Compared to traditional multi-cavity injection molding processes, product consistency is significantly improved. 3. This device and process for re-injection molding of plastic surfaces based on recycled waste plastics, through the setting of gradient temperature-controlled double-shot injection molding and three-stage variable pressure holding process steps, adopts the sequential injection of high-flowability recycled plastic melt (180-190℃) in the first shot and low-melting-point copolymer melt (150-160℃) in the second shot, and combines the variable pressure holding curves of high-pressure penetration section (80MPa→120MPa), pressure holding section (100MPa), and stress release section (100MPa→50MPa) to achieve the effect of controlling the melt penetration depth and internal stress release in stages, so that a gradient interface layer is formed between the secondary injection layer and the waste substrate, effectively avoiding warping deformation caused by shrinkage rate difference. The natural shrinkage rate of the product after 24 hours is ≤0.3%, and the warping deformation is reduced by more than 70% compared with the conventional single-shot injection molding process; 4. This device and process for re-injection molding of plastic surfaces based on waste plastic recycling utilizes a zoned gradient cooling process. It employs a gradient cooling water temperature of 25℃ for the inner ring, 23℃ for the middle ring, and 20℃ for the outer ring, controlling the cooling rate at 0.8–1.2℃ / s for the inner ring, 0.6–1.0℃ / s for the middle ring, and 0.4–0.8℃ / s for the outer ring. Combined with real-time monitoring of the mold temperature field uniformity using an infrared thermal imager, this ensures synchronous curing of all areas of the multi-cavity mold, avoiding uneven internal stress and shrinkage deformation caused by differences in cooling rates. The temperature of the product after demolding is ≤60℃. Compared to traditional uniform cooling processes, the dimensional stability of the product is improved by more than 40%, effectively increasing the product yield. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the unit structure of the waste plastic recycling plastic re-injection molding device for the plastic surface of the present invention. Figure 2 This is a schematic diagram of the process flow for re-injection molding of plastic surfaces from recycled waste plastics according to the present invention. Figure 3 This is a schematic diagram of the 4-cavity membrane injection device for re-injection molding of plastic surfaces in the waste plastic recycling process of the present invention; Figure 4 This is a schematic diagram of the 6-cavity membrane injection device for re-injection molding of plastic surfaces in the waste plastic recycling process of the present invention; Figure 5 This is a schematic diagram of the 8-cavity membrane injection device for re-injection molding of plastic surfaces in the waste plastic recycling process of the present invention; Figure 6 This is a schematic diagram of the 12-cavity membrane injection device for re-injection molding of plastic surfaces in the waste plastic recycling process of the present invention. Figure 7 This is a schematic diagram of the 16-cavity membrane injection device for re-injection molding of plastic surfaces in the waste plastic recycling process of the present invention. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] It should be understood that the step numbers used in the text are for ease of description only and are not intended to limit the order in which the steps are performed.

[0020] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0021] The terms “comprising” and “including” indicate the presence of the described feature, whole, step, operation, element and / or component, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0022] The term “and / or” refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes these combinations.

[0023] Example 1: This example uses a waste ABS car dashboard panel as the sample to be processed. The sample is made of ABS plastic and has multiple scratches with a depth of less than 0.2mm, slight fading and local wear on the surface. The surface is covered with residual antistatic coating. The requirements are that the surface roughness Ra ≤ 0.4μm after secondary injection molding repair, the bonding strength between the repair layer and the substrate ≥ 20N / cm, the surface after repair has no color difference and no bubbles, and the overall product flatness deviation ≤ 0.5mm.

[0024] A plastic surface re-injection molding device based on waste plastic recycling includes a waste plastic surface pretreatment unit, a multi-cavity radial injection mold unit, a gradient temperature control dual injection unit, a variable pressure holding control unit, a zoned cooling and curing unit, a demolding detection unit, and a central AI control system connected in sequence. All the above units are connected by an automated conveying platform to transfer waste plastic parts and injection-molded finished products. In addition, there is an external central AI control system, which consists of an edge computing server and a PLC controller. It communicates with each unit in real time through an industrial bus to coordinate and schedule the collaborative operation of each unit, thereby realizing intelligent control of the injection molding process. The specific injection molding process is as follows: Step 1: The recycled waste ABS car dashboard panels are classified according to material, color and surface defect degree. Products with repair value are selected. Micron-level anchoring grooves with a depth of 0.15mm and a width of 0.08mm are processed in the surface defect area using a nanosecond pulse laser (output wavelength 1064nm, pulse width 20ns, pulse energy 3mJ, scanning speed 200mm / s). Then, a plasma cleaner (85% argon, 15% oxygen, cleaning time 45 seconds) is used for surface cleaning and activation treatment to reduce the surface contact angle to 25°. At the same time, the defect location and depth data are collected and uploaded to the central AI control system. Step 2: The pre-treated waste ABS dashboard panel is used as an insert and placed into each cavity of a multi-cavity radial injection mold by an automated conveyor platform. The mold has 6 cavities, and the melt is evenly distributed through the central convergence and fusion zone and radial flow channels to ensure that the filling pressure deviation of each cavity is ≤±5%. Step 3: Perform two-shot injection molding using a gradient temperature-controlled dual-shot injection unit. The first shot uses high-flowability recycled ABS melt (melt index 40g / 10min, melt temperature 185℃, injection speed 65mm / s), and the second shot uses low-melting-point thermoplastic polyurethane elastomer melt (melt index 15g / 10min, melt temperature 155℃, injection speed 40mm / s). Simultaneously, the mold wall temperature zone control system sets the inner ring temperature to 105℃, the middle ring temperature to 95℃, and the outer ring temperature to 90℃, forming a temperature gradient from the inside to the outside. This creates a gradient viscosity distribution in the melt during flow, enhancing the melt's penetration and filling of microgrooves. Step 4: After mold closing, pressure is maintained by a pressure control unit. Within 5 seconds of mold closing, the pressure is increased from 80MPa to 115MPa, using high pressure to force the melt to penetrate deeply into the micro-grooves. Then, within 15 seconds, the pressure is gradually reduced to 50MPa to release the stress on the matrix and prevent warping deformation. Throughout the pressure holding process, the mold cavity pressure is monitored in real time by a pressure sensor and fed back to the central AI control system for dynamic adjustment. Step 5: Gradual cooling is performed through the zoned cooling and curing unit. Deionized water is used for cooling. The inlet temperature of the cooling water is set to 25℃ for the inner ring, 23℃ for the middle ring, and 20℃ for the outer ring. The cooling water flow rate is controlled at 8L / min for the inner ring, 6L / min for the middle ring, and 4L / min for the outer ring. The cooling time is 70 seconds, and the cooling rate is controlled at 1.0℃ / s for the inner ring, 0.8℃ / s for the middle ring, and 0.6℃ / s for the outer ring to ensure that all mold cavity areas are cured synchronously to below the demolding temperature. Step Six: The composite product is removed from the mold by the intelligent demolding detection unit, and the surface of the product is inspected 360° by the online vision inspection system (resolution 1920×1080 pixels, frame rate 30fps, lens focal length 35mm) to detect the presence of air marks, weld lines, shrinkage cavities or local unbonded defects. Qualified products are sent to the post-processing process to remove gate residue and polish them smooth. Unqualified products are fed back to the central AI control system for process parameter adjustment.

[0025] Upon testing, the surface roughness Ra of the repaired car dashboard panel in this embodiment is ≤0.38μm, the bonding strength between the repair layer and the substrate is 21.8N / cm, there is no color difference or bubbles on the surface, the overall flatness deviation is 0.3mm, and the product qualification rate reaches 97.5%.

[0026] Example 2: This example uses waste PP appliance shells as the sample to be processed. The sample is made of PP plastic and has multiple scratches, ink residues, and localized thermal deformations with a depth of less than 0.3 mm on the surface. The surface is covered with a printed ink layer. The requirements are that the surface roughness Ra ≤ 0.5 μm after secondary injection molding repair, the bonding strength between the repair layer and the substrate ≥ 18 N / cm, no ink residue or shrinkage cavities on the repaired surface, and no delamination after the product is placed at 80℃ for 72 hours.

[0027] The specific injection molding process is as follows: Step 1: The recycled waste PP appliance shells are classified according to material, color and degree of surface defects. Products with repair value are selected. Micron-level anchoring grooves with a depth of 0.25mm and a width of 0.12mm are processed in the surface defect area using a nanosecond pulse laser (output wavelength 1064nm, pulse width 30ns, pulse energy 4mJ, scanning speed 150mm / s). Then, a plasma cleaner (80% argon, 20% oxygen, cleaning time 50 seconds) is used for surface cleaning and activation treatment to reduce the surface contact angle to 28°. At the same time, the defect location and depth data are collected and uploaded to the central AI control system. Step 2: The pre-treated waste PP appliance shells are used as inserts and placed into the various cavities of a multi-cavity radial injection mold by an automated conveying platform. The mold has 12 cavities, and the melt is evenly distributed through the central convergence and fusion zone and radial flow channels to ensure that the filling pressure deviation of each cavity is ≤±5%. Step 3: Perform double-shot injection molding using a gradient temperature-controlled double-shot injection unit. The first shot uses high-flow-rate recycled PP melt (melt index 45g / 10min, melt temperature 188℃, injection speed 70mm / s), and the second shot uses ethylene-vinyl acetate copolymer melt (melt index 18g / 10min, melt temperature 158℃, injection speed 35mm / s). Simultaneously, the mold wall temperature zone control system sets the inner ring temperature to 105℃, the middle ring temperature to 95℃, and the outer ring temperature to 90℃, forming a temperature gradient from the inside to the outside. This creates a gradient viscosity distribution in the melt during flow, enhancing the melt's penetration and filling of microgrooves. Step 4: After mold closing, pressure is maintained by a pressure control unit. Within 5 seconds of mold closing, the pressure is increased from 85MPa to 120MPa, using high pressure to force the melt to penetrate deeply into the micro-grooves. Then, within 15 seconds, the pressure is gradually reduced to 50MPa to release the stress on the matrix and prevent warping deformation. Throughout the pressure holding process, the mold cavity pressure is monitored in real time by a pressure sensor and fed back to the central AI control system for dynamic adjustment. Step 5: Gradual cooling is performed through the zoned cooling and curing unit. Deionized water is used for cooling. The inlet temperature of the cooling water is set to 25℃ for the inner ring, 23℃ for the middle ring, and 20℃ for the outer ring. The cooling water flow rate is controlled at 7L / min for the inner ring, 5L / min for the middle ring, and 3L / min for the outer ring. The cooling time is 85 seconds, and the cooling rate is controlled at 0.9℃ / s for the inner ring, 0.7℃ / s for the middle ring, and 0.5℃ / s for the outer ring to ensure that all mold cavity areas are cured synchronously to below the demolding temperature. Step Six: The composite product is removed from the mold by the intelligent demolding detection unit, and the surface of the product is inspected 360° by the online vision inspection system (resolution 1920×1080 pixels, frame rate 30fps, lens focal length 25mm) to detect the presence of air marks, weld lines, shrinkage cavities or local unbonded defects. Qualified products are sent to the post-processing process to remove gate residue and polish them smooth. Unqualified products are fed back to the central AI control system for process parameter adjustment.

[0028] Testing showed that the surface roughness Ra of the repaired appliance casing was ≤0.42μm, the bonding strength between the repair layer and the substrate was 19.6N / cm, there was no ink residue or pinholes on the surface, and no delamination was observed after the product was placed at 80℃ for 72 hours. The product qualification rate reached 96.8%.

[0029] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0030] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A plastic surface re-injection molding device based on waste plastic recycling, characterized in that, It includes a waste plastic surface pretreatment unit, a multi-cavity radial injection mold unit, a gradient temperature control dual injection unit, a variable pressure holding control unit, a zoned cooling and curing unit, a demolding detection unit, and a central AI control system connected in sequence. All the above-mentioned units are connected by an automated conveying platform to realize the transfer of waste plastic parts and injection-molded finished products. In addition, there is an external central AI control system, which consists of an edge computing server and a PLC controller. It communicates with each unit in real time through an industrial bus to coordinate and schedule the collaborative operation of each unit, thereby realizing intelligent control of the injection molding process.

2. The plastic surface re-injection molding device based on waste plastic recycling according to claim 1, characterized in that: The waste plastic surface micromachining unit incorporates a laser micromilling subunit and a plasma surface activation subunit. The laser micromilling subunit consists of a nanosecond pulsed laser and a three-dimensional moving platform, and is used to process a micron-level anchoring groove array with a depth of 0.1 to 0.3 mm and a width of 0.05 to 0.15 mm in the defect area on the surface of waste plastic parts. The plasma surface activation subunit consists of a plasma cleaner and a high-pressure ion gun, used to remove processing debris and surface oil, while increasing surface activation energy. Its surface activation effect is characterized by contact angle measurement, and the formula for calculating the contact angle reduction efficiency is as follows: ； in, To address the front contact angle, To address the post-contact angle, Reduced efficiency due to contact angle; The micromachining unit also has a built-in multispectral vision inspection mechanism, which is used to identify the type, location and area of ​​surface defects in waste plastic parts in real time, and to use the defect data for path planning in subsequent processing.

3. The plastic surface re-injection molding device based on waste plastic recycling according to claim 1, characterized in that: The multi-cavity radial injection mold unit consists of a mold body, a central radial flow channel system, and a cavity temperature zone control system. The mold body has a size of 300×300mm and has 4, 6, 8, 12 and 16 mold cavities inside, which are arranged in concentric rings. The central radial flow channel system consists of a convergence zone located at the center of the mold and branch flow channels radiating outward from the center. Each branch flow channel is connected to a mold cavity at its end, with branch angles of 45°, 60°, and 90° to ensure that the filling pressure deviation of each mold cavity is ≤±5%. The mold cavity temperature zone control system includes multiple sets of thermocouple sensors and zone heating rods arranged in the inner ring, middle ring and outer ring of the mold. Each temperature control zone can be independently set to a temperature of 90℃~105℃, thereby realizing a gradient temperature distribution from the inside to the outside. The temperature zone control system and the central AI control system form a temperature-pressure collaborative control closed loop. The central AI control system dynamically adjusts the heating power and injection pressure of each temperature control zone according to the position and material of the waste plastic parts in the mold cavity, and its temperature control accuracy is ±1℃.

4. The plastic surface re-injection molding device based on waste plastic recycling according to claim 1, characterized in that, The gradient temperature-controlled dual-injection molding unit consists of a first injection molding assembly and a second injection molding assembly. The first injection molding assembly is used to inject highly fluid recycled plastic melt with a melt index of 30-50 g / 10 min and a melt temperature controlled at 180-190 °C. The second injection molding assembly is used to inject low-melting-point copolymer melt with a melt index of 10-20 g / 10 min and a melt temperature controlled at 150-160 °C. The variable pressure holding control unit consists of a servo hydraulic pump, a proportional pressure valve, and a high-pressure storage tank. The servo hydraulic pump is used to provide injection pressure of 80MPa to 120MPa, the proportional pressure valve is used to achieve a step-by-step decrease in pressure during the holding pressure stage, and the high-pressure storage tank is used to quickly release residual pressure before mold opening. The variable pressure holding control unit and the central AI control system form a closed-loop pressure control. The central AI control system executes a preset three-segment variable pressure holding curve based on real-time feedback data from the mold cavity pressure sensor. The first stage is the high-pressure permeation stage, where the pressure increases from 80MPa to 120MPa and is maintained for 5 seconds. The second stage is the pressure holding stage, where the pressure is maintained at 100MPa for 10 seconds. The third stage is the stress relief stage, where the pressure drops from 100MPa to 50MPa in a stepwise manner over a period of 15 seconds. During the entire pressure change and holding process, the pressure fluctuation within the mold cavity is ≤±2MPa. The partitioned cooling and curing unit includes an in-mold circulating cooling water system and a temperature difference control valve. The in-mold circulating cooling water system has multiple independent cooling water channels arranged inside the mold, corresponding to the inner ring, middle ring and outer ring mold cavity areas respectively. Each cooling water channel inlet is equipped with a temperature difference control valve, and the inlet water temperature can be independently adjusted to 20-30℃, and the outlet water temperature is controlled to 35-45℃, so as to achieve synchronous curing of each mold cavity area and avoid uneven shrinkage.

5. A plastic surface re-injection molding process based on waste plastic recycling, characterized in that, Includes the following steps: Step 1: The recycled waste plastic products are classified according to material, color and degree of surface defects. Products with repair value are selected and micron-level anchoring grooves with a depth of 0.1 to 0.3 mm are processed in the defect area of ​​the surface using a nanosecond pulse laser. Then, the surface is cleaned and activated using a plasma cleaner to reduce the surface contact angle to ≤30°. At the same time, the defect location and depth data are collected and uploaded to the central AI control system. Step 2: The pre-treated waste plastic parts are used as inserts and placed into the cavities of a multi-cavity radial injection mold by an automated conveying platform. The number of mold cavities is 4, 6, 8, 12, or 16. The melt is evenly distributed through the central convergence and fusion zone of the mold and the radial flow channels to ensure that the filling pressure deviation of each cavity is ≤±5%. Step 3: Perform double-shot injection molding using a gradient temperature-controlled double-shot injection molding unit. The first shot uses high-flow-rate recycled plastic melt with a melt temperature controlled at 180-190℃, while the second shot uses low-melting-point copolymer melt with a melt temperature controlled at 150-160℃. Simultaneously, the mold wall temperature zone control system sets the inner ring temperature to 105℃, the middle ring temperature to 95℃, and the outer ring temperature to 90℃, forming a temperature gradient from the inside to the outside. This creates a gradient viscosity distribution in the melt during flow, enhancing the melt's penetration and filling of microgrooves. Step 4: After mold closing, pressure is maintained by a pressure control unit. Within 5 seconds of mold closing, the pressure is increased from 80MPa to 120MPa, using high pressure to force the melt to penetrate deeply into the micro-grooves. Then, within 15 seconds, the pressure is gradually reduced to 50MPa to release the stress on the matrix and prevent warping deformation. Throughout the pressure holding process, the mold cavity pressure is monitored in real time by a pressure sensor and fed back to the central AI control system for dynamic adjustment. Step 5: Gradual cooling is performed through the zoned cooling and curing unit. The inlet temperature of the cooling water is set to 25℃ for the inner ring, 23℃ for the middle ring, and 20℃ for the outer ring. The cooling time is 60-90 seconds, and the cooling rate is controlled at 0.8-1.2℃ / s for the inner ring, 0.6-1.0℃ / s for the middle ring, and 0.4-0.8℃ / s for the outer ring to ensure that all mold cavity areas are cured synchronously to below the demolding temperature. Step Six: The composite product is removed from the mold by the intelligent demolding detection unit, and the surface of the product is inspected by the online vision inspection system to detect defects such as air marks, weld lines, shrinkage cavities, or local non-bonding defects. Qualified products are sent to the post-processing process to remove gate residue and polish them smooth. Unqualified products are fed back to the central AI control system for process parameter adjustment.

6. The plastic surface re-injection molding process based on waste plastic recycling according to claim 5, characterized in that: The nanosecond pulsed laser described in step one has an output wavelength of 1064 nm, a pulse width of 10–50 ns, a pulse energy of 1–5 mJ, a scanning speed of 100–300 mm / s, and a surface roughness Ra≤0.8 μm for the microgrooves after processing. The plasma cleaning uses a mixture of argon and oxygen in a volume ratio of 80%–90% argon and 10%–20% oxygen. The cleaning time is 30–60 seconds. After cleaning, the surface contact angle is ≤30° and the surface activation energy is increased to more than twice the original value.

7. The plastic surface re-injection molding process based on waste plastic recycling according to claim 5, characterized in that: The melt index of the high-flowability recycled plastic melt in step three is 30-50 g / 10 min, and the low-melting-point copolymer melt is thermoplastic polyurethane elastomer (TPU) or ethylene-vinyl acetate copolymer (EVA), with a melt index of 10-20 g / 10 min. The injection speed of the dual-shot injection molding is controlled as follows: 50-80 mm / s for the first shot and 30-50 mm / s for the second shot.

8. The plastic surface re-injection molding process based on waste plastic recycling according to claim 5, characterized in that: In step five, the cooling water for the zoned gradient cooling is deionized water, and the cooling water flow rate is controlled as follows: 5-10 L / min for the inner ring, 4-8 L / min for the middle ring, and 3-6 L / min for the outer ring. During the cooling process, the temperature of the outer surface of the mold is monitored in real time by an infrared thermal imager to ensure that the temperature field uniformity deviation of the mold is ≤ ±5℃, the temperature of the composite material product is ≤ 60℃ when demolding, and the natural shrinkage rate is ≤ 0.3% after demolding for 24 hours.

9. The plastic surface re-injection molding process based on waste plastic recycling according to claim 5, characterized in that: The online visual inspection described in step six uses a high-resolution industrial camera with a resolution of no less than 1920×1080 pixels, a frame rate of no less than 30fps, and a lens focal length of 20-50mm. During inspection, the surface of the product is scanned 360°, and the defect identification rate is ≥99.5%. In the post-processing step, the gate residue is removed by either pneumatic shears or laser cutting. After removal, the gate residue height is ≤0.2mm, and the surface roughness Ra after grinding is ≤0.4μm.

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