An in-mold coating method and equipment that saves on spraying

Abstract

This invention discloses an in-mold coating method and equipment that saves on spraying. The method includes the following steps: S1, Rotational molding of a three-dimensional film: A three-dimensional film matching the surface shape of the target product is formed through rotational molding. The three-dimensional film has a multi-layer composite structure, including at least an outer decorative layer and an inner substrate layer; S2, Transfer and positioning of the three-dimensional film: The formed three-dimensional film is accurately placed and fixed in the cavity of the injection mold using a transfer device; S3, In-mold injection bonding: The mold is closed and molten plastic is injected into the cavity to fuse it with the substrate layer of the three-dimensional film. After cooling, the mold is opened; S4, Demolding of the product without damage: After the mold is opened, the product is tightly wrapped around the moving mold core. The product is separated from the core by an ejection system in conjunction with an air-assisted ejection device; S5, Recycling of waste material: The injection runner, gate, and process waste separated from the product are collected, crushed, and granulated to produce reusable granules for reuse in production. The equipment is used to perform the above method.

Description

Technical Field

[0001] This invention relates to the field of parts manufacturing technology, and in particular to an in-mold coating method and equipment for saving spraying. Background Technology

[0002] Traditional spraying processes have many drawbacks in the production of plastic products such as automotive parts. First, the spraying process is time-consuming, requiring multiple steps including surface treatment, primer spraying, and topcoat spraying, significantly impacting production efficiency. Second, the spraying process generates large amounts of volatile organic compounds (VOCs), polluting the environment and placing increasing pressure on companies due to increasingly stringent environmental regulations. Furthermore, spraying processes also suffer from quality problems such as insufficient coating adhesion and difficulty in controlling color differences.

[0003] While in-mold lamination technology exists in existing technologies, it is only suitable for products with flat or simple curved surfaces, and cannot meet the needs of products with complex three-dimensional shapes. This is mainly because traditional lamination processes struggle to achieve precise positioning of the three-dimensional film within the mold cavity, easily leading to problems such as film displacement and wrinkling during injection molding. Furthermore, existing technologies lack systematic solutions for post-injection molding demolding processes and waste recycling, resulting in low product yields and significant material waste. Summary of the Invention

[0004] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes an in-mold coating method and equipment that saves on spraying, which has the advantages of improving the processing efficiency of complex three-dimensional products, reducing environmental pollution, improving material utilization, and ensuring product quality.

[0005] In a first aspect, according to an embodiment of the present invention, an in-mold coating method for spraying is provided, comprising: S1. Rotational molding of three-dimensional film: A three-dimensional film that matches the surface shape of the target product is formed by rotational molding process. The three-dimensional film is a multi-layer composite structure, including at least an outer decorative layer and an inner substrate layer. S2. Three-dimensional film transfer and positioning: The formed three-dimensional film is accurately placed and fixed in the cavity of the injection mold through a transfer device; S3, In-mold injection molding: The mold is closed and molten plastic is injected into the cavity to fuse it with the substrate layer of the three-dimensional film. After cooling, the mold is opened. S4. Non-destructive demolding: After the mold is opened, the product is tightly wrapped around the moving mold core. The product is separated from the core by the ejection system and the air-assisted ejection device. S5. Waste material recycling: Collect, crush, and granulate the injection molding runner, gate, and process waste separated from the product to make recycled granules for reuse in production.

[0006] According to an embodiment of the present invention, an in-mold coating method for avoiding spraying has at least the following beneficial effects: This application achieves integrated molding of the decorative layer and structure of a three-dimensional product by combining three-dimensional film rotational molding and injection molding processes, replacing the traditional spraying process. In step S1, the three-dimensional film formed by rotational molding directly provides the appearance effect in its multi-layer composite structure, while the substrate layer ensures the weld strength with the injection-molded plastic, avoiding the spraying process. In step S2, a dedicated transfer device is used to achieve precise positioning of the three-dimensional film in the mold, ensuring complete adhesion between the decorative layer and the mold cavity. In step S3, the molten plastic and the substrate layer are welded together to form an unpeelable composite structure, ensuring the mechanical properties of the product. In step S4, a staged ejection combined with gas-assisted demolding is used to break the clamping force while avoiding damage to the product's appearance. In step S5, the closed-loop recycling of process waste reduces both material costs and waste emissions. The entire solution solves the problem of paint-free molding of three-dimensional products through the synergistic use of three-dimensional film molding, precise positioning, in-mold composite, non-destructive demolding, and waste material recycling technologies.

[0007] According to an embodiment of the present invention, an in-mold coating method for spraying is provided, wherein the edge of the three-dimensional film is provided with a process positioning edge with positioning holes, and the injection mold cavity is provided with a positioning groove and a positioning pin that match the process positioning edge. Mechanical positioning is achieved by the cooperation of the positioning holes and the positioning pins, and the three-dimensional film is adsorbed and fixed in the injection mold cavity by a vacuum adsorption hole provided at the bottom of the positioning groove.

[0008] According to an embodiment of the present invention, in step S2, the transfer device is a multi-degree-of-freedom robotic arm, which is connected to a contour-following clamping fixture. The robotic arm is guided to complete the gripping and precise placement by identifying the markings on the three-dimensional film and the injection mold through a vision positioning module. After the contour-following clamping fixture is introduced with positive pressure gas to expand and expand the three-dimensional film, it is then switched to negative pressure adsorption to grip and transfer.

[0009] According to an embodiment of the present invention, in step S5, a near-infrared spectral sensor is used to monitor the composition of the crushed mixed recycled material particles online. If an abnormal material is detected, a pneumatic sorting device is activated to remove the abnormal particles, thereby ensuring the quality of the recycled material particles.

[0010] According to an embodiment of the present invention, in step S5, the recycled material particles are mixed with new material in a certain proportion and then used for rotational molding of the substrate layer of the three-dimensional film or for injection molding of non-appearance structural parts.

[0011] According to an embodiment of the present invention, in a method for in-mold coating to save spraying, in step S4, the non-destructive demolding body is: firstly, the ejector rod located on the non-appearance surface structure of the product performs the first ejection to initially break the clamping force, and then the air-assisted ejection device embedded in the core blows compressed air into the gap between the product and the core to make the product demold smoothly.

[0012] Secondly, according to an embodiment of the present invention, an in-mold coating and waste-removing spraying device for performing the above-described in-mold coating and waste-removing spraying method includes: a rotational molding unit, a transfer unit, an injection molding unit, and a waste material recycling unit arranged sequentially along the processing route; The rotational molding unit is used to form a three-dimensional film; The injection molding unit is provided with a mold cavity, and the mold cavity is provided with a positioning groove, a positioning pin and a vacuum suction hole. The positioning groove can be matched and connected with the process positioning edge on the three-dimensional film, the positioning pin can be matched and connected with the positioning hole on the three-dimensional film, the vacuum suction hole is located at the bottom of the positioning groove, and the vacuum suction hole is connected to an external negative pressure device. The core of the injection molding unit is provided with an air-assisted ejection device. The transfer unit includes a multi-degree-of-freedom robotic arm and a contoured gripping fixture. The contoured gripping fixture is connected to the multi-degree-of-freedom robotic arm. The transfer unit is used to transfer the 3D film to the injection molding unit. The contoured gripping fixture is used to grasp or release the 3D film. The waste material recovery unit includes a crusher and a granulator connected in sequence. The inlet end of the crusher is connected to the discharge port of the injection molding unit, and the outlet end of the granulator is connected to the raw material inlet of the rotational molding unit and / or the injection molding unit. According to an embodiment of the present invention, an in-mold coating and spraying equipment has at least the following beneficial effects: The spraying equipment provided in this application realizes a complete closed loop of the three-dimensional coating process by constructing a four-unit collaborative production system. The rotational molding unit uses three-dimensional molding technology to generate a multi-layer composite film that matches the product surface, breaking through the limitations of planar coating. The injection molding unit ensures the precise alignment of the three-dimensional film in the complex cavity through the mechanical cooperation of the positioning groove and the process positioning edge, the insertion positioning of the positioning pin and the positioning hole, and the triple positioning and fixing of the vacuum adsorption hole. The integrated design of the gas-assisted ejection device and the core solves the problem of easy damage to the three-dimensional film after demolding. The transfer unit adopts a combination of contour clamping fixture and multi-degree-of-freedom robotic arm, and ensures that the three-dimensional film does not deform during the transfer process through shape adaptive gripping and precise motion control. The waste material recycling unit realizes the immediate recycling and reuse of waste materials through the closed-loop connection between crushing and granulation and the raw material inlet, forming a resource recycling system. The sequential layout of each unit along the processing route realizes the fully automated production process from three-dimensional film forming, precise positioning injection molding to waste material recycling.

[0013] An in-mold coating and spraying device according to an embodiment of the present invention further includes a vision positioning unit, the vision positioning unit including a first camera and a second camera, the first camera being fixed on the multi-degree-of-freedom robotic arm, the first camera being used to identify visual marks on the three-dimensional film to be grasped, and the second camera being fixed on the frame of the injection molding unit, the second camera being used to identify visual marks inside the cavity of the injection mold.

[0014] According to an embodiment of the present invention, an in-mold coating-saving spraying device further includes a near-infrared spectral sensor disposed at the outlet end of the crusher, wherein the near-infrared spectral sensor is used to monitor the material purity of the crushed material online.

[0015] According to an embodiment of the present invention, an in-mold coating and spraying device is provided, wherein the cavity and core surfaces of the injection mold are coated with a nano-scale low surface energy release coating.

[0016] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a main flowchart of an in-mold coating method for saving spraying according to an embodiment of the present invention; Figure 2 This is a flowchart of the rotational molding process according to an embodiment of the present invention; Figure 3 This is a flowchart of the transfer and positioning capture process according to an embodiment of the present invention; Figure 4 This is a flowchart of the injection molding process according to an embodiment of the present invention; Figure 5 This is a flowchart illustrating the waste material recycling process according to an embodiment of the present invention. Figure 6 This is a partial structural schematic diagram of the contour-following clamping fixture according to an embodiment of the present invention; Explanation of reference numerals in the attached figures: Support body 100; Software 200; First channel 210; Second channel 220. Detailed Implementation

[0018] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0019] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0020] In the description of the invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the number itself, while "above," "below," and "within" are understood to include the number itself. If the terms "first" and "second" are used, they are only for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0021] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0022] In existing technologies, the painting process for automotive parts suffers from low efficiency and high emissions. Traditional in-mold coating technology can only handle flat products and cannot meet the molding requirements of complex three-dimensional curved surfaces. For example, for three-dimensional parts such as automotive interior components, using flat coating can lead to incomplete adhesion between the decorative layer and the product surface, resulting in wrinkles or bubbles. After injection molding, painting is still required, which increases the number of processes and generates volatile organic compound emissions.

[0023] To address the aforementioned issues, limitations in existing technology have prompted researchers to explore the possibilities of 3D film application. The positioning methods used for planar film application cannot be directly applied to 3D structures, necessitating the development of new positioning systems. The molding process for 3D films must be compatible with the injection molding process to prevent damage to the decorative layer from high-temperature molten plastic. During the demolding stage, it is crucial to prevent damage to the appearance surface when the 3D film separates from the injection molded body. Furthermore, the recycling and reuse of process waste directly impacts production costs and environmental benefits. Analysis revealed that rotational molding can produce 3D films that match the product shape, mechanical positioning systems can solve the three-dimensional positioning problem, staged demolding technology can balance the breaking of clamping forces with appearance protection, and a closed-loop recycling system can achieve material recycling.

[0024] Therefore, embodiments of the present invention provide an in-mold coating method for spraying, and this application also provides a spraying device for performing the spraying method provided in this application.

[0025] Specifically, refer to Figures 1 to 3 The spraying method includes the following steps: S1. Rotational molding of three-dimensional film: A three-dimensional film that matches the surface shape of the target product is formed by rotational molding process. The three-dimensional film is a multi-layer composite structure, including at least an outer decorative layer and an inner substrate layer. S2. 3D film transfer and positioning: The formed 3D film is precisely placed and fixed into the cavity of the injection mold through a transfer device; S3. Close the mold and inject molten plastic into the cavity to fuse it with the substrate layer of the three-dimensional film. After cooling, open the mold. S4. Non-destructive demolding: After the mold is opened, the product is tightly wrapped on the moving mold core. The product is separated from the core by the ejection system and the air-assisted ejection device. S5. Waste material recycling: Collect, crush, and granulate injection molding runners, gates, and process waste to produce reusable granules for reuse in production.

[0026] It is understandable that 3D film rotational molding refers to using a rotating mold and heating process to uniformly adhere and shape plastic powder. Specifically, this can be achieved using multi-axis rotating equipment with temperature gradient control. This process can create a three-dimensional curved surface structure that perfectly matches the target product. Precise positioning of the transfer device refers to using a robotic arm end effector to clamp the 3D film. Specifically, this can be achieved using a six-axis robotic arm with a vision positioning system and a contouring fixture, ensuring the spatial matching of the 3D film and the mold cavity. Welding refers to the molecular chain entanglement between the molten plastic and the substrate layer. This can be achieved by controlling the injection temperature to be higher than the melting point of the substrate layer but lower than the temperature resistance threshold of the decorative layer, forming an unbreakable interface bond. Staged demolding refers to first mechanically ejecting to break the initial clamping force, and then separating with gas assistance. This can be achieved using sequentially controlled ejector rods and embedded air valves working in tandem, avoiding ejection marks remaining on the surface. Waste material recycling refers to reprocessing the plastic from non-product parts. Specifically, this can be achieved by using a twin-screw extruder to process the crushed mixture, realizing a closed-loop material cycle.

[0027] Specifically, the rotationally molded 3D film pre-loads decorative effects, and its substrate layer uses a polymer compatible with the injection molding material. During transport, a vision system identifies positioning marks on the edge of the 3D film, guiding a robotic arm to embed the film into the mold positioning structure. During the injection molding stage, molten plastic permeates to the surface of the substrate layer under pressure, and the two melt and bond to form an integral structure. During demolding, ejector pins push the product out at the reinforcing ribs or assembly structure locations, and then compressed air is blown from inside the core into the gap between the product and the mold to eliminate vacuum adhesion. The recycling system crushes the gate material and sorted waste material, and then melt-extrudes it to form uniformly sized recycled granules, which are then mixed with virgin material in proportion for the production of non-appearance parts.

[0028] Beneficially, this application directly matches the product shape through 3D film molding, eliminating subsequent finishing processes. Existing technologies using vacuum adsorption to fix planar films are prone to localized deformation of the 3D film; this solution achieves three-dimensional fixation through the synergistic effect of mechanical positioning and vacuum adsorption. Conventional demolding relies on ejector pins forcibly pushing out the film, easily creating stress marks on the surface; this solution reduces demolding resistance by breaking the clamping force in stages. Traditional waste recycling does not differentiate material purity; this solution ensures that recycled materials meet performance requirements through online monitoring, achieving one-time molding of the decorative layer on the surface of the 3D product, eliminating the need for painting processes and corresponding pollution emissions. Precise positioning of the 3D film and the injection molded body prevents displacement or wrinkling of the decorative layer, ensuring appearance quality. The staged demolding mechanism ensures a high demolding success rate while protecting the surface from mechanical damage. Closed-loop recycling of process waste reduces raw material consumption and lowers production costs. This solution effectively solves the technical obstacles of paint-free molding of 3D parts, providing a feasible solution for the green manufacturing of complex curved surface products.

[0029] In step S3, the injection molding process parameters are optimized and controlled: the injection speed adopts a multi-stage injection curve of slow-fast-slow. In the initial low-speed injection stage, the front end of the melt smoothly pushes the air in the cavity out of the venting groove to prevent trapped air from causing poor bonding between the three-dimensional film and the injection molded body or appearance defects; the melt temperature is taken at the upper limit within the material compatibility range to promote interface fusion.

[0030] Understandably, slow start-up avoids air entrapment at the melt tip, rapid filling utilizes inertia to reduce melt cooling, and slow pressure holding prevents oversaturation filling. The three-stage speed curve is implemented through the injection molding machine screw speed curve editor, effectively shortening the filling time and improving production efficiency.

[0031] According to some embodiments of this application, the edge of the three-dimensional film is provided with a process positioning edge with positioning holes, and the injection mold cavity is provided with a positioning groove and a positioning pin that match the process positioning edge. Mechanical positioning is achieved by the cooperation of the positioning holes and the positioning pins. The three-dimensional film is adsorbed and fixed in the injection mold cavity by a vacuum adsorption hole provided at the bottom of the positioning groove.

[0032] Understandably, a process positioning edge refers to a raised structure extending along the edge of the 3D film, with a width of 5-10 mm. It can be integrally molded with the 3D film body using injection molding to create a rigid positioning reference. A positioning hole is a through-hole formed on the process positioning edge, with a diameter of 3-5 mm. It can be laser-cut and used to form a clearance fit with the mold positioning pin. A positioning groove is a recessed groove structure on the surface of the mold cavity, with a depth of 2-4 mm. It can be CNC milled and used to accommodate the process positioning edge and limit its planar displacement. A positioning pin is a cylindrical structure protruding from the positioning groove, with a diameter of 2.8-4.8 mm. It can be made of cemented carbide and used to insert into the positioning hole to achieve three-dimensional spatial positioning. A vacuum adsorption hole is a micro-through-hole penetrating the surface of the mold cavity, with a diameter of 0.5-1 mm. It can be machined using electrical discharge machining and uses an external vacuum pump to generate negative pressure adsorption force.

[0033] Specifically, after the process positioning edge and the 3D film body are formed simultaneously, the 3D film is transferred to the mold cavity by a robotic arm. When the positioning pin is inserted into the positioning hole, the process positioning edge is embedded in the positioning groove, at which point the 3D film and the mold cavity form rigid contact. After the vacuum suction hole is activated, the process positioning edge is adsorbed and adhered to the bottom of the positioning groove, eliminating minor displacements caused by mold temperature changes or mechanical vibrations. When molten plastic is injected into the cavity, the fluid impact force borne by the process positioning edge is transmitted to the mold body through the positioning pin, while the vacuum suction force compensates for the fit clearance between the positioning pin and the positioning hole.

[0034] Beneficially, this application achieves three-dimensional positioning of the 3D film without adhesive by combining mechanical positioning and vacuum adsorption. The positioning accuracy can be controlled within ±0.1 mm. At the same time, the uniformly distributed adsorption force generated by vacuum adsorption can avoid local deformation of the 3D film, effectively preventing the positional shift and deformation of the 3D film during injection molding. It solves the technical problem of missing positioning reference for curved surface film application, enabling the fit between the 3D film and the mold cavity to reach more than 95%, and improving the product yield to more than 98%. Furthermore, the matching structure of the process positioning edge and the vacuum adsorption hole can adapt to any complex curved surface with a curvature radius greater than 50 mm.

[0035] Alternatively, in some other embodiments of this application, an electrostatic generator can be built into the mold cavity, and an electrostatic field can be applied through copper electrodes to make the diaphragm adhere to the surface of the cavity by electrostatic attraction. The electrostatic field strength is precisely controlled by a high-voltage power supply module to avoid diaphragm breakdown, and the adhesion can be enhanced by electrostatic adsorption.

[0036] According to some embodiments of this application, in step S2, the transfer device is a multi-degree-of-freedom robotic arm. The multi-degree-of-freedom robotic arm is connected to a contour gripping fixture. The markings on the three-dimensional film and the injection mold are identified by the vision positioning module, guiding the robotic arm to complete the gripping and precise placement. After the contour gripping fixture is introduced with positive pressure gas to expand and expand the three-dimensional film, it is switched to negative pressure adsorption to grip and transfer.

[0037] It is understandable that a multi-degree-of-freedom robotic arm refers to an automated operating device with at least five rotary joints, specifically implemented using a serial six-axis robotic arm, achieving trajectory planning in three-dimensional space through multi-axis linkage. A contour-following gripper refers to a flexible contact device that matches the outer contour of the 3D membrane, specifically implemented using a silicone airbag structure, with its internal cavity connected to a positive pressure air source and a negative pressure generator via pipelines. A visual positioning module refers to a coordinate calibration system based on image recognition, specifically implemented using an industrial camera in conjunction with QR code marking, establishing a spatial mapping relationship by extracting the center coordinates of the markings. Positive pressure gas expansion refers to introducing compressed air into the gripper to expand its volume, specifically using a pressure range of 0.2-0.5 MPa, eliminating 3D membrane wrinkles through physical expansion. Negative pressure adsorption refers to generating negative pressure through a vacuum generator to ensure tight adhesion between the gripper and the 3D membrane, specifically using a vacuum range of -80 kPa to -90 kPa, ensuring a flat membrane surface without displacement during gripping.

[0038] Specifically, the contour clamping fixture includes a support body 100 and a soft body 200 covering the outside of the support body 100. The soft body 200 is provided with a first channel 210 to allow positive pressure gas to be introduced. In addition, the soft body is also provided with a second channel 220, which is connected to a negative pressure mechanism to achieve negative pressure adsorption.

[0039] Specifically, during the transfer of the 3D membrane, an industrial camera first captures the QR code markings on the surface of the membrane, and an image processing algorithm calculates its pose data in three-dimensional space. Based on this data, the robotic arm adjusts the spatial orientation of its end effector, driving a contour-following fixture to move directly above the membrane. Before the fixture contacts the membrane, compressed air is introduced into the fixture via the pneumatic system, causing the silicone airbags to expand to a preset shape. At this point, the membrane is evenly stretched, eliminating local wrinkles. The pneumatic system then switches to negative pressure mode, and the suction holes on the airbag surface generate vacuum suction, allowing the membrane to adhere smoothly to the fixture surface. When the robotic arm carrying the membrane moves above the mold cavity, another set of industrial cameras identifies the coordinates of the mold positioning pins. A coordinate transformation algorithm calculates the matching path between the membrane's process positioning edge and the mold positioning groove, guiding the robotic arm to complete millimeter-level precision positioning.

[0040] Beneficially, compared to existing technologies, traditional transfer equipment typically uses a two-axis manipulator in conjunction with a planar suction cup, which can only achieve translational operations within a two-dimensional plane and cannot adapt to the curved surface shape of three-dimensional films. Conventional vacuum adsorption methods for direct gripping easily lead to stress concentration on the film surface, causing localized deformation in complex curved areas. Existing positioning methods mostly rely on mechanical limiting devices, which cannot correct the posture deviation of the three-dimensional film during transfer in real time. This application achieves shape preservation and precise positioning of complex curved three-dimensional films, solving the problem of film surface deformation caused by traditional planar adsorption. Staged pressure control ensures the shape integrity of the three-dimensional film during gripping, and combined with a vision-guided coordinate mapping method, effectively compensates for the impact of accumulated errors in the mechanical system on positioning accuracy. The synergistic effect of the multi-degree-of-freedom motion mechanism and the contouring fixture enables the three-dimensional film to accurately conform to the curved contour of the mold cavity, providing a reliable positioning reference for subsequent injection molding processes.

[0041] According to some embodiments of this application, in step S5, a near-infrared spectral sensor is used to monitor the composition of the crushed mixed recycled material particles online. If an abnormal material is detected, a pneumatic sorting device is activated to remove the abnormal particles, ensuring the quality of the recycled material particles.

[0042] Understandably, a near-infrared spectroscopy sensor refers to a device that uses near-infrared spectroscopy analysis technology to perform non-contact detection of material composition. Specifically, it can be implemented using sensor modules with wavelengths in the 780-2500 nanometer range. By collecting the reflectance spectrum of the material surface and comparing it with a preset database, it can identify material differences in real time. A pneumatic sorting device refers to a mechanism that uses compressed air power to sort particles. Specifically, it can be implemented using a high-pressure nozzle array combined with a valve control system. By adjusting the airflow direction and intensity, it blows abnormal particles off the conveyor belt surface to the waste bin.

[0043] Specifically, the crushed mixed recycled material particles continuously pass through the detection area of ​​a near-infrared spectral sensor during the conveying process. The sensor acquires spectral data by scanning hundreds of particles per second and compares it in real time with the pre-stored spectral characteristics of standard materials. When abnormal particles with spectral characteristics deviating from the threshold range are detected, the system immediately triggers a pneumatic sorting device. When the abnormal particles reach the sorting position, the high-pressure nozzle at the corresponding position is activated, using pulsed airflow to precisely blow them into the waste collection channel. Normal particles continue to enter the granulation process along the conveyor belt to form uniformly composed reusable particles.

[0044] Beneficially, compared to existing technologies, traditional recycled material sorting relies on manual sampling or offline laboratory analysis, which suffers from detection lag and cannot cover all materials, leading to the mixing of abnormal particles into the reprocessing stage. This solution achieves fully automated real-time sorting through the linkage control of online component monitoring and pneumatic sorting, avoiding the efficiency bottleneck of manual intervention and eliminating the blind spot risk of sampling. It can effectively prevent abnormal particles from entering the recycled material, avoiding problems such as poor substrate layer welding or decreased mechanical properties of injection molded parts caused by impurities. It also ensures that the mixing ratio of recycled and new materials is precisely controllable, thereby maintaining the product quality stability in the reprocessing process.

[0045] According to some embodiments of this application, during the demolding process, the ejector pins located on the non-appearance surface of the product first eject the product to initially break the clamping force, and then the air-assisted ejection device embedded in the core blows compressed air into the gap between the product and the core to make the product demold smoothly.

[0046] As can be understood, ejector pins are columnar ejector components located inside the mold core, with their ends not contacting the product's external surface. They can be implemented using cylindrical alloy steel rods, with a diameter ranging from 3 to 8 millimeters. The number of ejector pins is 1-3 per square decimeter, depending on the product size. Ejector pins avoid direct contact with the 3D decorative film layer by selecting a non-external surface area as the contact point.

[0047] An air-assisted ejection device refers to a gas injection mechanism integrated inside the mold core. Specifically, it can be implemented using a ring-shaped air path combined with a micro-hole array structure, with the compressed air pressure controllable within the range of 0.3-0.8 MPa. This device creates a uniform separation force field by injecting airflow into the interface between the product and the core.

[0048] Specifically, after the mold opens and the product is tightly encased in the moving mold core, the first ejection action is performed by ejector pins located on non-visual surfaces such as reinforcing ribs and mounting holes. The mechanical strength of these non-visual surfaces withstands the ejection force, creating an initial separation gap of 0.1-0.3 mm between the product and the core. Subsequently, the air-assisted ejection device blows compressed air into the separation gap through the air channel network inside the core. The airflow is distributed circumferentially along the inner surface of the product, forming a pressure gradient, allowing the product to complete a secondary demolding without mechanical contact. During this process, the ejector pins only act on non-visual areas, while the air-assisted device eliminates localized stress concentrations through hydrodynamic action.

[0049] Beneficially, this application restricts mechanical ejection to non-appearance areas through a phased demolding mechanism, while utilizing gas pressure to achieve contact demolding, fundamentally avoiding the risk of damage to the decorative layer. It effectively solves the problem of surface damage caused by mechanical contact during demolding of three-dimensional film products, ensuring the integrity of the decorative layer and the dimensional accuracy of the product while guaranteeing demolding efficiency. It is particularly suitable for the production of in-mold laminated products with complex three-dimensional structures, such as automotive grilles and home appliance panels.

[0050] According to some embodiments of this application, in step S5, the recycled material granules are mixed with the new material in a certain proportion and then used for rotational molding of the substrate layer of the three-dimensional film or for injection molding of non-appearance structural parts.

[0051] It is understandable that recycled granules refer to the regenerated particles formed from runners, gates, and process waste generated during the injection molding process through crushing and granulation. The particle size range can be 0.5-3 mm, and this can be achieved using a twin-screw extrusion granulation unit, with particle morphology adjusted by controlling the melt temperature and shear rate. This feature realizes the resource utilization of waste through physical recycling, reducing raw material consumption.

[0052] Specifically, in the waste recycling stage, process waste is crushed and granulated to form recycled particles with uniform particle size. After near-infrared spectroscopy is used to remove particles with abnormal material properties, the recycled material is uniformly mixed with virgin material in a mixer according to a preset ratio. When the mixture is conveyed to the rotational molding unit, it is preferentially used to manufacture the substrate layer of the three-dimensional film. This layer combines with the molten plastic in the subsequent injection molding process, and its internal positional characteristics can mask any color differences or impurities that may exist in the recycled material. When used for injection molding non-surface structural parts, the mixture is injected into the mold to form an internal support structure. Such parts do not have strict requirements for surface finish, but must ensure mechanical properties such as tensile strength. This requirement can be met by controlling the blending ratio of recycled material.

[0053] Beneficially, this application employs a tiered utilization strategy, directing the application of recycled materials to the substrate layer and non-appearance structural parts. This avoids the impact of material performance degradation on product appearance while achieving efficient reuse of waste materials. It solves the problems of low recycling rates of injection molding waste and the instability of recycled materials' performance, which prevents their use in appearance parts. Through this tiered and targeted utilization strategy, efficient recycling of waste materials is achieved while ensuring product appearance quality, and raw material procurement costs are reduced. By limiting the application of recycled materials to the substrate layer and non-appearance structural parts, this solution effectively isolates the impact of material performance defects on the final product, achieving a balance between resource utilization and quality assurance.

[0054] According to some embodiments of this application, this application further proposes an in-mold coating-saving spraying equipment, including a rotational molding unit, a transfer unit, an injection molding unit, and a waste material recovery unit arranged sequentially along the processing route. The rotational molding unit is used to form a three-dimensional film; the injection molding unit is provided with a mold cavity, and the mold cavity is provided with a positioning groove, a positioning pin, and a vacuum suction hole. The positioning groove can be matched and connected with the process positioning edge on the three-dimensional film, the positioning pin can be matched and connected with the positioning hole on the three-dimensional film, the vacuum suction hole is located at the bottom of the positioning groove and connected to an external negative pressure device, and the core of the injection molding unit is provided with a gas-assisted ejection device; the transfer unit includes a multi-degree-of-freedom robotic arm and a contour clamping fixture, and the contour clamping fixture is connected to the multi-degree-of-freedom robotic arm; the waste material recovery unit includes a crusher and a granulator unit connected sequentially, the inlet end of the crusher is connected to the discharge port of the injection molding unit, and the outlet end of the granulator unit is connected to the raw material inlet of the rotational molding unit or the injection molding unit.

[0055] It is understandable that the rotational molding unit refers to a technical module that uses a rotating mold and heated powdered plastic to form a three-dimensional film. Specifically, this can be achieved using a rotary heating device with a three-dimensional curved mold cavity, used to generate a three-dimensional film that matches the shape of the product surface. The contour-following clamping fixture in the transfer unit refers to a gripping device with a variable profile, specifically implemented using an inflatable silicone clamp that adapts to the shape of the three-dimensional film by changing the internal air pressure. The positioning groove in the injection molding unit refers to a groove structure set on the mold parting surface, specifically implemented using a trapezoidal groove structure with an interference fit to the edge positioning edge of the three-dimensional film, used to limit the planar displacement of the three-dimensional film. The crusher in the waste material recovery unit refers to a material crushing device, specifically implemented using a dual-shaft shearing crushing mechanism, equipped with a screen to control the crushed particle size.

[0056] Specifically, the rotational molding unit uses rotational heating to evenly adhere plastic powder to the inner wall of the mold, forming a composite three-dimensional film with a decorative layer and a substrate layer. The multi-degree-of-freedom robotic arm of the transfer unit acquires the position information of the three-dimensional film through visual positioning, drives the contour-following clamping fixture to complete the grasping action, and then transfers the three-dimensional film to the injection mold cavity. The injection molding unit achieves initial positioning by inserting positioning pins into the positioning holes of the three-dimensional film, and then the vacuum suction holes generate negative pressure to make the three-dimensional film completely adhere to the bottom surface of the positioning groove. After mold closing, molten plastic is injected into the cavity, fusing with the substrate layer of the three-dimensional film to form a composite product. During the demolding stage, the air-assisted ejection device blows compressed air into the gap between the product and the core to assist in the non-destructive separation of the product. The waste material recycling unit crushes and granulates the runner waste generated during injection molding, and then transports it through pipelines to the raw material inlet of the rotational molding or injection molding unit, forming a material recycling system.

[0057] Beneficially, this application utilizes rotational molding to generate a three-dimensional film, which, combined with an injection mold featuring multiple positioning functions, solves the problem of insufficient positioning accuracy for curved surface film application. Existing equipment lacks an integrated waste material recycling system, resulting in low waste disposal efficiency. This solution achieves immediate recycling and reuse of waste materials through a closed-loop connection between the crushing and granulation unit and the production unit. Traditional transfer devices lack shape adaptability; this solution employs an inflatable contour-following clamping fixture, avoiding the risk of deformation of the three-dimensional film during transfer, enabling continuous production of three-dimensional film-applied injection molded products, and eliminating VOC emissions from traditional spraying processes. The combined use of the multiple positioning structure and the air-assisted demolding device ensures high-quality molding of complex curved surface products. The closed-loop waste material recycling system reduces raw material consumption, ensuring waste reuse meets production requirements. The automated transfer and positioning system reduces manual intervention, improving production cycle time and product consistency.

[0058] According to some embodiments of this application, a visual positioning unit is also included. The visual positioning unit includes a first camera and a second camera. The first camera is fixed on a multi-degree-of-freedom robotic arm and is used to identify visual marks on the stereoscopic film to be grasped. The second camera is fixed on the frame of the injection molding unit and is used to identify visual marks inside the injection mold cavity. Understandably, the first camera refers to the image acquisition device integrated into the end effector of the robotic arm. Specifically, it can be implemented using an industrial-grade high-resolution camera combined with image processing algorithms. This camera dynamically captures the positions of pre-set visual markers on the surface of the 3D membrane, providing real-time feedback on the robotic arm's grasping posture deviation. The second camera refers to the image acquisition device fixedly installed at the mold station. This can be implemented using an optical sensor with 3D coordinate calibration capabilities. It is used to establish a reference coordinate system for the mold cavity, providing spatial positioning reference for the robotic arm. The visual markers refer to identifiable patterns pre-set on the edge of the 3D membrane and within the mold cavity. These can be implemented using high-contrast geometric shapes or QR codes, achieving sub-millimeter positioning accuracy through image matching algorithms.

[0059] Specifically, during the transfer of the 3D membrane, the first camera scans the visual marks on the surface of the membrane to obtain its spatial coordinates. This coordinates, combined with the robotic arm's motion trajectory, are used to correct the gripping posture in real time, eliminating gripping offsets caused by membrane deformation. Simultaneously, the second camera scans the visual marks within the mold cavity to generate mold positioning reference coordinates. These two sets of coordinate data are fused and calculated by the industrial control system to form a closed-loop positioning calibration, enabling the robotic arm to precisely embed the 3D membrane into the corresponding position within the mold cavity at a preset angle. During this process, the rigid connection design between the first camera and the robotic arm ensures real-time pose compensation during dynamic gripping, while the fixed installation of the second camera maintains the stability of the mold reference coordinates.

[0060] Beneficially, compared to existing technologies, traditional solutions typically rely on mechanical positioning pins or a single vision system for alignment, which struggles to address positioning errors caused by the flexible deformation of the 3D membrane. This solution, through a dual-camera collaborative positioning mechanism, establishes dynamic calibration and static benchmarks at the gripping end and the mold end respectively, overcoming the limitations of a single coordinate system. It is particularly suitable for the three-dimensional spatial positioning requirements of complex curved 3D membranes, effectively solving the positioning inaccuracy problem caused by visual deviations during transport, ensuring precise matching of the curved contours of the 3D membrane and the mold cavity. This solution avoids efficiency losses due to manual adjustments and prevents membrane wrinkles or tears caused by positioning deviations, significantly improving the operational stability of automated production lines.

[0061] According to some embodiments of this application, the residual material recovery unit also includes a near-infrared spectral sensor disposed at the outlet end of the crusher, which is used to monitor the material purity of the crushed material online.

[0062] It is understandable that a near-infrared spectral sensor is a detection device that uses the absorption characteristics of molecules in the 700-2500 nanometer wavelength range for compositional analysis. Specifically, it can be implemented using a Fourier transform spectrometer, identifying materials by detecting the characteristic absorption peaks of different plastic materials in the near-infrared band. This device can effectively identify material anomalies by acquiring material spectral data in real time and comparing it with preset standard spectra. The crusher outlet refers to the transition area where the material enters the conveying pipeline after crushing. This can be achieved using a combination of a vibrating screen and a screw conveyor. Setting a detection point at this location ensures that the material passes through the detection area in discrete particle form, which is beneficial for the spectral sensor to obtain accurate detection data.

[0063] Specifically, as the crushed mixed plastic granules pass through the conveying pipe, a near-infrared spectral sensor scans the continuously passing granules at a frequency of at least 50 times per second. The detection system calculates the matching degree between the real-time acquired spectral data and the pre-stored characteristic spectra of standard substrates such as polypropylene and polyethylene. When abnormal granules with spectral characteristics deviating from the threshold range are detected, the high-pressure nozzle of the pneumatic sorting device is immediately triggered, blowing the abnormal granules into the waste collection bin. This process achieves millisecond-level linkage between the detection signal and the actuator through a PLC control system, ensuring that each abnormal particle is accurately rejected before entering the granulation process.

[0064] Beneficially, this application achieves real-time monitoring of the purity of recycled materials through online full inspection, and completes the removal of abnormal particles simultaneously with the material conveying process. This avoids the risk of abnormal material mixing caused by traditional batch sampling inspection, and can effectively prevent the mixing of particles of different materials into recycled materials, which can lead to problems such as uneven melt flow and reduced interlayer bonding during injection molding. It ensures that the recycled material mixed with the new material can still meet the molding quality requirements of the rotational molding substrate layer or non-appearance parts.

[0065] According to some embodiments of this application, a nanoscale low surface energy release coating is applied to the cavity and core surfaces of an injection mold.

[0066] Understandably, nanoscale low surface energy release coatings refer to coatings with a surface energy below 20 mN / m formed through physical vapor deposition or chemical vapor deposition processes. Specifically, they can be achieved using fluorocarbon polymers or silicon-based nanocomposites. This coating reduces release resistance by lowering the adhesion between the molten plastic and the mold surface. The cavity and core surfaces refer to the molding areas in the mold that directly contact the three-dimensional film and the injection molded part. These are achieved using a mirror-finishing process with a surface roughness controlled below Ra0.2 μm to ensure the bonding strength between the coating and the mold substrate while maintaining the surface precision of the mold.

[0067] Specifically, during injection molding, when the molten plastic comes into contact with the cavity coated with the nano-coating, its surface energy decreases, leading to increased interfacial tension and reduced adhesion between the plastic and the mold. For the core, the coating weakens the bond strength between the molded part and the core after cooling and shrinkage, allowing for separation without excessive ejection force. The nanoscale thickness of the coating avoids altering the geometric accuracy of the mold surface, while simultaneously forming a physical barrier layer through its micro-nano structure to prevent mechanical seizing between the three-dimensional film substrate layer and the mold. This coating replaces traditional mold release agent spraying processes, eliminating the risk of localized sticking caused by uneven mold release agent distribution, and maintains a stable release effect without the need for repeated spraying.

[0068] Beneficially, compared with existing technologies, traditional methods rely on spraying liquid release agents onto the mold surface, which suffers from uneven coating thickness, frequent recoating, and the potential for release agent residue to contaminate the 3D decorative layer. This application achieves stable low surface energy characteristics through a permanent nano-coating, avoiding the risk of chemical migration and reducing the frequency of production interruptions and maintenance. It solves the problem of film damage caused by excessive adhesion during demolding of 3D laminated products, reduces the mechanical impact of the ejection mechanism on the product's surface, and allows injection molded parts with 3D decorative layers to completely detach from the mold, improving yield to a mass-producible level.

[0069] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0070] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. An in-mold coating method for saving spraying, characterized in that, Includes the following steps: S1. Rotational molding of three-dimensional film: A three-dimensional film that matches the surface shape of the target product is formed by rotational molding process. The three-dimensional film is a multi-layer composite structure, including at least an outer decorative layer and an inner substrate layer. S2. 3D film transfer and positioning: The formed 3D film is precisely placed and fixed in the cavity of the injection mold by a transfer device. The transfer device is a multi-degree-of-freedom robotic arm. The multi-degree-of-freedom robotic arm is connected to a contour-following gripper. The markings on the 3D film and the injection mold are identified by a vision positioning module to guide the robotic arm to complete the gripping and precise placement. After the contour-following gripper is introduced with positive pressure gas to expand and expand the 3D film, it is switched to negative pressure adsorption to grip and transfer. The three-dimensional film has a process positioning edge with positioning holes on its edge, and the injection mold cavity has a positioning groove and positioning pin that match the process positioning edge. Mechanical positioning is achieved by the cooperation of the positioning hole and the positioning pin. The three-dimensional film is adsorbed and fixed in the injection mold cavity by a vacuum adsorption hole located at the bottom of the positioning groove. S3, In-mold injection molding: The mold is closed and molten plastic is injected into the cavity to fuse it with the substrate layer of the three-dimensional film. After cooling, the mold is opened. S4. Non-destructive demolding: After the mold is opened, the product is tightly wrapped around the moving mold core. The product is separated from the core by the ejection system and the air-assisted ejection device. Specifically, the ejector rod located on the non-appearance surface of the product performs the first ejection to initially break the clamping force. Then, the air-assisted ejection device embedded in the core blows compressed air into the gap between the product and the core to make the product demold smoothly. S5. Waste material recycling: Collect, crush, and granulate the injection molding runner, gate, and process waste separated from the product to make recycled granules for reuse in production.

2. The in-mold coating method for saving spraying according to claim 1, characterized in that, In step S5, a near-infrared spectral sensor is used to monitor the composition of the crushed mixed recycled material particles online. If an abnormal material is detected, a pneumatic sorting device is activated to remove the abnormal particles, ensuring the quality of the recycled material particles.

3. The in-mold coating method for saving spraying according to claim 2, characterized in that, In step S5, the recycled material granules are mixed with the new material in a certain proportion and then used for rotational molding of the substrate layer of the three-dimensional film or for injection molding of non-appearance structural parts.

4. An in-mold coating saving spraying device, used to perform the in-mold coating saving spraying method according to any one of claims 1 to 3, characterized in that, include: The rotational molding unit, transfer unit, injection molding unit, and waste material recycling unit are arranged sequentially along the processing route. The rotational molding unit is used to form a three-dimensional film; The injection molding unit is provided with a mold cavity, and the mold cavity is provided with a positioning groove, a positioning pin and a vacuum suction hole. The positioning groove can be matched and connected with the process positioning edge on the three-dimensional film, the positioning pin can be matched and connected with the positioning hole on the three-dimensional film, the vacuum suction hole is located at the bottom of the positioning groove, and the vacuum suction hole is connected to an external negative pressure device. The core of the injection molding unit is provided with an air-assisted ejection device. The transfer unit includes a multi-degree-of-freedom robotic arm and a contoured gripping fixture. The contoured gripping fixture is connected to the multi-degree-of-freedom robotic arm. The transfer unit is used to transfer the 3D film to the injection molding unit. The contoured gripping fixture is used to grasp or release the 3D film. The waste material recovery unit includes a crusher and a granulator connected in sequence. The inlet end of the crusher is connected to the discharge port of the injection molding unit, and the outlet end of the granulator is connected to the raw material inlet of the rotational molding unit and / or the injection molding unit.

5. The in-mold coating and spraying equipment according to claim 4, characterized in that, It also includes a visual positioning unit, which includes a first camera and a second camera. The first camera is fixed on the multi-degree-of-freedom robotic arm and is used to identify visual marks on the stereoscopic film to be grasped. The second camera is fixed on the frame of the injection molding unit and is used to identify visual marks inside the injection mold cavity.

6. The in-mold coating and spraying equipment according to claim 4, characterized in that, The residual material recovery unit also includes a near-infrared spectral sensor installed at the outlet end of the crusher, which is used to monitor the material purity of the crushed material online.

7. The in-mold coating and spraying equipment according to claim 4, characterized in that, The cavity and core surfaces of the injection mold are coated with a nano-scale low surface energy release coating.

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