Light-weight automobile appearance decorating part added with recycled waste and forming process of light-weight automobile appearance decorating part

Abstract

The invention provides a light-weight automobile appearance decorating part added with recycled waste and a forming process of the light-weight automobile appearance decorating part, and belongs to the technical field of automobile part manufacturing. The preparation method comprises the following steps: mixing a core layer melt containing polypropylene recycled after consumption, waste tire rubber and a styrene-ethylene-butylene-styrene block copolymer with a supercritical fluid to form a uniform dispersion; after an acrylonitrile-styrene-acrylate copolymer surface membrane is formed in a mold cavity, injecting the uniform dispersion to drive the membrane to extend and fill; and gas is induced to generate heterogeneous nucleation on the surfaces of the waste tire rubber particles through pressure relief and grow into bubbles. On the premise that the surface glossiness is not degraded, light weight and high toughness of the appearance decorating part and efficient utilization of renewable resources are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of automobile parts manufacturing, and particularly relates to a lightweight automobile appearance decoration part added with regenerated waste and a forming process thereof. BACKGROUND

[0002] In the field of automobile parts manufacturing, applying post-consumer regenerated plastics and waste rubber products to the forming process is an important technical path to realize resource recycling. The existing forming process of automobile appearance decoration parts usually adopts a sandwich injection molding process or a material blending injection molding process, which covers the surface layer material outside the core layer containing regenerated materials to balance the appearance performance and material cost of the part.

[0003] However, the existing forming process has the following phenomena in application: when the proportion of solid regenerated waste such as waste tire rubber in the core layer melt is increased, the apparent viscosity of the core layer melt increases exponentially with the increase of the content of waste tire rubber, resulting in a huge fluid dynamic resistance of the melt when filling the mold runner, causing filling difficulty or surface defects of the part. In addition, due to the difference in physical and chemical properties between the regenerated core layer and the high-performance surface layer material, the interfacial bonding strength between the core layer and the surface layer is insufficient, and the part has the risk of delamination under stress or environmental temperature fluctuation.

[0004] Based on the above phenomena, how to reduce costs while improving the forming processing performance and overall structural stability of automobile appearance decoration parts by using regenerated waste is a challenge currently faced by the industry. SUMMARY

[0005] The application overcomes the shortcomings of the prior art and provides a lightweight automobile appearance decoration part added with regenerated waste and a forming process thereof.

[0006] To achieve the above purpose, the technical solution adopted by the application is as follows: a lightweight automobile appearance decoration part added with regenerated waste and a forming process thereof, comprising the following steps:

[0007] S1: injecting a supercritical fluid into a core layer melt to form a uniform dispersion; the core layer melt comprises post-consumer recycled polypropylene, waste tire rubber and styrene-ethylene-butylene-styrene block copolymer;

[0008] S2: injecting a surface layer melt into a mold cavity to form a surface layer film on the inner wall of the mold cavity; the surface layer melt comprises acrylonitrile-styrene-acrylate copolymer;

[0009] S3: injecting the uniform dispersion into the inside of the surface layer film to drive the surface layer film to spread and fill the mold cavity;

[0010] S4: relieving pressure of the mold cavity to induce the gas dissolved in the homogeneous dispersion to nucleate and grow into bubbles on the surface of the waste tire rubber;

[0011] S5: using the expansion pressure generated by the bubble growth to drive the core layer melt to press against the surface layer film, and forming the automobile appearance decoration part after cooling and solidification.

[0012] Preferably, in step S1, the mass percentage of post-consumer recycled polypropylene is 50% to 80%, the mass percentage of waste tire rubber is 10% to 40%, and the mass percentage of styrene-ethylene-butylene-styrene block copolymer is 5% to 15%, based on the total mass of the core layer melt.

[0013] Preferably, in step S1, the supercritical fluid is nitrogen or carbon dioxide, and the injection amount is 0.2% to 1.5% of the total mass of the core layer melt.

[0014] Preferably, in step S2, the injection amount of the surface layer melt is 20% to 40% of the total mass of the part, and the wall surface temperature of the mold cavity is maintained at 40℃ to 60℃.

[0015] Preferably, in step S3, the injection speed of the homogeneous dispersion is 50mm / s to 150mm / s, and the injection pressure is 80MPa to 140MPa; before the end of the filling process, 1% to 5% of the total mass of the part of the surface layer melt is injected again to seal the gate area.

[0016] Preferably, in step S4, the pressure relief process specifically controls the holding pressure acting on the core layer melt to be in a low pressure state of 0MPa to 10MPa, and is maintained for 10s to 30s.

[0017] Preferably, in step S5, the cooling process lasts for 20s to 60s, and the wall surface temperature of the mold cavity is maintained at 40℃ to 60℃.

[0018] Preferably, in step S3, the homogeneous dispersion starts to be injected within a time interval of 0.1s to 0.5s after the termination of the surface layer melt injection action.

[0019] Preferably, the waste tire rubber is a powdery solid with a particle size of 40mesh to 120mesh.

[0020] The present application provides another technical solution: a lightweight automobile appearance decoration part with added recycled waste, which is prepared by the above molding process.

[0021] The application provides a lightweight automobile appearance decoration part with added recycled waste and a forming process thereof, which effectively overcomes the technical defects of high viscosity processing difficulty of solid waste tire rubber melt and insufficient interfacial bonding strength between the recycled core layer and the high-performance surface layer. The application couples the sandwich injection molding process with the supercritical foaming technology to realize high proportion recycling of waste tire rubber and post-consumer recycled polypropylene while ensuring that the automobile appearance decoration part has excellent surface quality, impact resistance and structural stability. The application has the following beneficial effects:

[0022] The application injects a supercritical fluid into the core melt containing post-consumer recycled polypropylene, waste tire rubber and styrene-ethylene-butylene-styrene block copolymer, uses the characteristic of supercritical fluid molecules penetrating into the gap between polymer molecular chains to increase the free volume and reduce the activation energy required for molecular chain segment transition, thereby producing a significant plasticizing effect. The plasticizing effect caused by the supercritical fluid effectively reduces the zero shear viscosity of the continuous phase matrix, weakens the fluid dynamic hindering effect and internal friction force of the solid waste tire rubber particles suspended in the melt on fluid flow. Compared with the situation that the viscosity index increases exponentially due to the solid filler in the conventional injection molding process, the application significantly reduces the maximum injection pressure required for the core melt to fill the mold cavity, ensuring the smooth molding of thin-walled complex structural parts under high filling amount of waste tire rubber.

[0023] The application uses the isotropic expansion pressure generated by bubble growth to drive the core melt to press against the inner surface of the surface film when the mold cavity is depressurized, and the expansion pressure provides a continuous driving force to force the styrene-ethylene-butylene-styrene block copolymer distributed at the interface to penetrate into the micropores of the acrylonitrile-styrene-acrylate copolymer surface layer, while driving the rigid waste tire rubber particles to embed into the inner wall of the surface film which has not yet completely solidified under the action of the expansion pressure. In this process, a firm mechanical interlocking structure and a molecular chain entanglement network are constructed at the interface between the core layer and the surface layer. Compared with the existing technology in which the interface connection only relies on the residual pressure of the melt or limited chemical compatibility, the application significantly improves the T-type peeling strength between the layers of heterogeneous materials, effectively prevents the delamination failure of the automobile appearance decoration part during use, and realizes the stable connection between the surface layer material and the recycled core layer material without chemical bonding.

[0024] The present application utilizes the rough concave-convex structure and interface defects existing on the surface of waste tire rubber particles as heterogeneous nucleation points of supercritical fluid, reduces the nucleation barrier of gas, and induces the formation of high-density and micro-sized micro-porous structure around the waste tire rubber particles. The uniform internal expansion pressure generated by the growth of these fine bubbles provides uniform internal support for the surface film during the cooling and solidification stage, effectively compensating for the volume shrinkage caused by the cooling of the polymer melt. The synergistic effect of waste tire rubber particles and supercritical fluid avoids the surface depression or corrugation defects often accompanied by conventional coarse pore plastic foaming process, so that the automobile appearance decoration part can completely retain the high gloss and appearance quality of the acrylonitrile-styrene-acrylate copolymer surface layer while realizing the lightweight of the core layer. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0026] Figure 1 A process flow diagram for forming a lightweight automobile appearance decoration part with added recycled waste. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0028] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in other manners different from those described herein, so the scope of protection of the present application is not limited by the specific embodiments disclosed below.

[0029] Unless otherwise specified, all raw materials described below may be commercially available or prepared using conventional methods in the art. Exemplary commercially available specifications are as follows: styrene monomer (99%), butadiene monomer (99.5%), acrylonitrile monomer (99%), butyl acrylate monomer (99%), divinylbenzene (crosslinking agent, 80%), n-butyllithium (initiator, 2.5M), tert-dodecyl mercaptan (molecular weight adjuster, 98%), nickel-based hydrogenation catalyst (active nickel), supercritical nitrogen (as physical foaming agent, purity 99.999%), polyolefin elastomer (melt index 0.5 g / 10 min), sodium dodecyl sulfate (emulsifier, 99%), potassium persulfate (initiator, 99.5%), and ethylbenzene (solvent, 99%).

[0030] Application Overview:

[0031] The fabrication of automotive exterior trim parts using sandwich injection molding presents challenges due to the multiphase complexity and mismatch between the multilayered structures of recycled waste. Post-consumer recycled polypropylene exhibits a significant decrease in toughness due to oxidative degradation of its molecular chains, while waste tire rubber with cross-linked structures maintains solid microparticle characteristics at molding temperatures. This increases the internal friction between polymer melt layers, leading to increased processing obstacles. Furthermore, the lack of effective molecular chain diffusion and chemical bonding at the interface results in insufficient bonding strength between the surface melt and the core melt containing solid waste, making it prone to delamination failure.

[0032] Based on this, the present invention addresses how to reduce the injection pressure during the molding process through rheological modification while ensuring a high proportion of recycled tire rubber filling, and how to improve the structural stability of the part by constructing a physical interlocking structure between the surface material and the recycled core layer using physical means. Specifically, by injecting supercritical fluid into the core layer melt to increase the free volume and reduce the melt viscosity, and by using the isotropic expansion pressure generated by the depressurization-induced bubble growth to drive the core layer components to penetrate and embed into the surface layer, the efficient utilization of recycled waste and the stable connection of the part structure are achieved without relying on a chemically compatible system.

[0033] like Figure 1 As shown, a molding process for lightweight automotive exterior trim parts incorporating recycled waste includes the following steps:

[0034] S1: Injecting supercritical fluid into the core layer melt to form a uniform dispersion;

[0035] S2: Inject the surface melt into the mold cavity to form a surface film on the inner wall of the mold cavity;

[0036] S3: Inject the uniformly dispersed material into the surface film, causing the surface film to extend and fill the mold cavity;

[0037] S4: The mold cavity is depressurized to induce the nucleation and growth of bubbles on the surface of the waste tire rubber;

[0038] S5: The inflation pressure generated by the growth of the bubbles drives the core melt to press against the surface film, and after cooling and solidification, an automobile exterior trim part is formed.

[0039] The core melt includes post-consumer recycled polypropylene, waste tire rubber, and styrene-ethylene-butylene-styrene block copolymer, and the surface melt includes acrylonitrile-styrene-acrylate copolymer.

[0040] The implementation of the above molding process relies on a dual-injection bench injection molding machine and an automobile exterior trim part mold.

[0041] The dual-injection bench injection molding machine is equipped with two independent plasticizing and injecting units, namely, a main injection bench and a secondary injection bench. The dual-injection bench injection molding machine can independently control the operating parameters of the main injection bench and the secondary injection bench, including the barrel temperature, screw speed, injection speed, and injection pressure. The main injection bench and the secondary injection bench are connected to a shared nozzle assembly through their respective flow channels. The nozzle assembly is internally provided with a flow channel switching mechanism with coaxial or split-flow structure, which can realize the alternate injection or synchronous injection of the surface melt and the core melt according to the control signal.

[0042] The automobile exterior trim part mold defines the geometry and size of the part, including the fixed mold side and the movable mold side, which form a closed mold cavity after closing. The inner surface topography of the mold cavity is directly replicated onto the surface of the part. For automobile exterior trim parts, the surface of the mold cavity is usually polished or textured to meet the appearance requirements of Class A surfaces. The automobile exterior trim part mold is internally provided with a cooling flow channel system for removing the heat of the polymer melt through circulating flow medium.

[0043] The above molding process also involves a sandwich injection molding process and a supercritical foaming technology.

[0044] The sandwich injection molding process is a multi-component injection molding method that controls the order in which two polymer melts enter the mold cavity, allowing one polymer melt (surface material) to coat the other polymer melt (core material), thereby forming a skin-core layered structure inside the part, which combines the surface properties of the surface material and the structural properties of the core material.

[0045] The supercritical foaming technology is a polymer microporous molding method that uses nitrogen or carbon dioxide in a supercritical state as a physical foaming agent. During the injection molding process, the supercritical fluid is injected into the plasticizing cylinder and dispersed in the polymer melt. When the polymer melt containing the gas is injected into the mold cavity, the phase change behavior of the gas forms a microporous structure inside the polymer melt.

[0046] The following describes each step in detail.

[0047] In step S1, the core layer melt includes post-consumer recycled polypropylene, waste tire rubber, and styrene-ethylene-butylene-styrene block copolymer. The mass percentage of post-consumer recycled polypropylene is 50% to 80%, the mass percentage of waste tire rubber is 10% to 40%, and the mass percentage of styrene-ethylene-butylene-styrene block copolymer is 5% to 15%, based on the total mass of the core layer melt.

[0048] The post-consumer recycled polypropylene is derived from a discarded automobile bumper or a discarded household appliance shell, and is processed by cleaning, crushing, and drying to form irregular flaky or granular solids. The post-consumer recycled polypropylene has a wider molecular weight distribution than virgin polypropylene, and a lower elongation at break than virgin polypropylene.

[0049] The waste tire rubber is derived from a discarded pneumatic tire, and is processed by cryogenic crushing or room temperature grinding to form black powder solids with a particle size of 40 mesh to 120 mesh. The waste tire rubber is mainly composed of a vulcanized crosslinked network of natural rubber or synthetic rubber and a carbon black reinforcing agent. The three-dimensional network structure of the waste tire rubber restricts the sliding of molecular chains, allowing the waste tire rubber to remain solid at high temperatures without melting and flowing.

[0050] The preparation of the styrene-ethylene-butylene-styrene block copolymer includes an anionic polymerization reaction stage and a hydrogenation reaction stage.

[0051] In the anionic polymerization reaction stage, using cyclohexane as the solvent and n-butyllithium as the initiator, styrene monomer, butadiene monomer, and styrene monomer are sequentially added at a temperature of 40°C to 80°C to carry out active anion block copolymerization, generating a styrene-butadiene-styrene block copolymer with a linear triblock structure.

[0052] In the hydrogenation reaction stage, the styrene-butadiene-styrene block copolymer is dissolved in a solvent, a nickel-based or titanium-based hydrogenation catalyst is added, and hydrogen gas with a pressure of 2 MPa to 5 MPa is introduced. The hydrogen gas undergoes addition reaction with the unsaturated double bonds in the polybutadiene soft segment, and the reaction conversion rate is controlled to be above 95%. The reaction product is treated by devolatilization and drying to obtain the styrene-ethylene-butylene-styrene block copolymer.

[0053] The styrene-ethylene-butylene-styrene block copolymer utilizes the polystyrene hard segments at both ends to provide physical crosslinking points, and utilizes the ethylene-butylene soft segment in the middle to provide elasticity.

[0054] The mixed post-consumer recycled polypropylene, waste tire rubber and styrene-ethylene-butylene-styrene block copolymer are fed into the sub-shooting table of the double-shooting table injection molding machine. The sub-shooting table is equipped with a plasticizing cylinder and a rotating screw. The plasticizing cylinder is provided with a temperature-controlled heating zone along the axial direction, and the temperature setting range is 190°C to 230°C. The rotating speed of the rotating screw is set to 50r / min to 120r / min.

[0055] The post-consumer recycled polypropylene, waste tire rubber and styrene-ethylene-butylene-styrene block copolymer enter the compression section of the plasticizing cylinder. Under the combined action of external heat conduction and shear friction heat, the post-consumer recycled polypropylene and the styrene-ethylene-butylene-styrene block copolymer absorb heat and change from glassy or high-elastic state to viscous flow state. The waste tire rubber particles remain in the form of solid particles, suspended in the liquid phase matrix, forming a uniform dispersion containing solid particles and completely dissolved gas. Under the action of the shear flow field, the liquid phase post-consumer recycled polypropylene acts as a continuous phase matrix, and the liquid phase styrene-ethylene-butylene-styrene block copolymer is dispersed in the continuous phase matrix or adsorbed on the surface of the waste tire rubber particles. The solid waste tire rubber particles act as a dispersed phase, which hinders the flow of the surrounding continuous phase matrix, increasing the internal friction between the polymer melt layers. The apparent viscosity of the core layer melt increases exponentially with the increase of the content of waste tire rubber, making it difficult for the core layer melt to fill the mold flow channel under normal injection pressure.

[0056] In the metering section or mixing section of the sub-shooting table, a physical blowing agent is introduced through a gas injection device. The physical blowing agent is selected from supercritical fluid of nitrogen or carbon dioxide. The gas injection device pressurizes the physical blowing agent to a supercritical state. For nitrogen, the supercritical state refers to a state with a temperature higher than -147°C and a pressure higher than 3.4MPa; for carbon dioxide, the supercritical state refers to a state with a temperature higher than 31.1°C and a pressure higher than 7.38MPa. In actual injection process, the injection pressure of the physical blowing agent is set to 10MPa to 20MPa to ensure that the physical blowing agent can overcome the melt pressure in the cylinder. The supercritical fluid is quantitatively injected into the core layer melt through the nozzle installed on the plasticizing cylinder, and the injection amount is controlled to be 0.2% to 1.5% of the total mass of the core layer melt.

[0057] The sub-shooting table screw is provided with a barrier type mixing element or a pin type mixing element downstream of the injection point. The rotating screw exerts shear division and stretching folding action on the core layer melt and the supercritical fluid, breaking the supercritical fluid into fine bubbles. In a high temperature and high pressure environment, the supercritical fluid diffuses and dissolves. Because the molecular size of the supercritical fluid is smaller than the turn radius of the polymer molecular chain segment, the supercritical fluid molecules penetrate into the molecular chain gap of the post-consumer recycled polypropylene and the styrene-ethylene-butylene-styrene block copolymer.

[0058] The supercritical fluid molecules penetrate into the polymer matrix and increase the free volume between the polymer molecular chains. The increase of free volume reduces the activation energy required for the molecular chain segment to jump, and weakens the mutual entanglement and friction between the molecular chains. This plasticizing effect reduces the zero shear viscosity of the continuous phase matrix. The reduction of the viscosity of the continuous phase matrix weakens the drag force of the continuous phase matrix on the waste tire rubber particles, offsetting the viscosity increment caused by the waste tire rubber particles. The core melt is converted into a uniform dispersion before the sub-shooting table. The uniform dispersion is macroscopically a fluid with the required fluidity to fill the thin-walled mold cavity, and maintains the uniform dispersion state of the waste tire rubber particles in the continuous phase matrix.

[0059] In step S2, the surface layer melt is selected to be acrylonitrile-styrene-acrylate copolymer. The preparation process adopts emulsion polymerization or bulk polymerization.

[0060] If emulsion polymerization is used, the preparation process includes a rubber core synthesis stage and a grafted shell synthesis stage. In the rubber core synthesis stage, water, butyl acrylate monomer, divinyl benzene crosslinking agent, sodium dodecyl sulfate emulsifier, and potassium persulfate initiator are added to the reaction kettle. Seed emulsion polymerization is carried out at a temperature of 60-80°C, and the reaction time lasts for 4-6 hours, generating a cross-linked polybutyl acrylate rubber latex. In the grafted shell synthesis stage, styrene monomer and acrylonitrile monomer are continuously added to the polybutyl acrylate rubber latex. The mass ratio of styrene monomer to acrylonitrile monomer is 70:30 to 80:20. Tertiary dodecyl mercaptan is added as a molecular weight regulator. Under the action of the initiator, in-situ graft copolymerization of styrene monomer and acrylonitrile monomer occurs on the surface of the polybutyl acrylate rubber latex particles. The reaction product is subjected to coagulation, washing, drying, and extrusion granulation processes to obtain acrylonitrile-styrene-acrylate copolymer particles with a core-shell structure.

[0061] If bulk polymerization is used, the preparation process is carried out in a series of multi-stage reactors. The raw materials include styrene monomer, acrylonitrile monomer, butyl acrylate rubber elastomer, and ethylbenzene solvent. The butyl acrylate rubber elastomer is dissolved in a mixed solution of styrene monomer, acrylonitrile monomer, and ethylbenzene solvent to form a homogeneous raw material solution. The homogeneous raw material solution is pumped into the first stage reactor and pre-polymerization is carried out at a temperature of 110-130°C. The butyl acrylate rubber elastomer undergoes phase separation to form dispersed phase particles. The dispersed phase particles enter the second stage and subsequent reactors, and continue to carry out graft copolymerization and bulk polymerization at a temperature of 130-160°C until the monomer conversion rate reaches 60-80%. The reacted melt enters a devolatilizer to remove unreacted monomers and solvents under vacuum conditions, and is cut into granules to obtain acrylonitrile-styrene-acrylate copolymer particles. In the copolymer prepared by bulk polymerization, the rubber phase is dispersed in the resin matrix in a sausage-like or island-like structure.

[0062] The acrylonitrile-styrene-acrylate copolymer particles prepared by any of the above methods are fed into the main shooting station of a twin-shooting station injection molding machine. The main shooting station is equipped with an independent plasticizing cylinder and screw. The plasticizing cylinder is provided with a temperature-controlled heating zone along the axial direction, and the temperature is set to a range of 240°C to 260°C. The rotation speed of the main shooting station screw is set to 80 r / min to 150 r / min. Under the action of screw shearing and cylinder heat conduction, the acrylonitrile-styrene-acrylate copolymer particles are transformed from a glassy state to a uniform viscous flow state melt.

[0063] The flow channel switching mechanism inside the nozzle assembly is controlled to open the main shooting station flow channel while physically blocking the secondary shooting station flow channel. The main shooting station screw moves axially forward, and the surface layer melt is injected into the mold cavity through the gate. The injection amount is controlled at 20% to 40% of the total mass of the part. The injection pressure is set to 80 MPa to 120 MPa, and the injection speed is set to 30 mm / s to 80 mm / s. The mold for the automotive exterior trim part is in a closed state, and the mold cavity wall temperature is maintained at 40°C to 60°C through the cooling channel system.

[0064] Using emulsion polymerization or continuous bulk polymerization, the dispersed phase of the acrylonitrile-styrene-acrylate copolymer is polybutyl acrylate rubber. The main chain structure of polybutyl acrylate rubber does not contain unsaturated carbon-carbon double bonds. The saturated molecular main chain has bond energy greater than the energy of ultraviolet photons, blocking the free radical oxidation reaction path induced by ultraviolet radiation, preventing polymer chain rupture and degradation. The styrene-acrylonitrile resin continuous phase provides rigid support and a surface with refractive index characteristics. This phase structure feature allows the surface skin film to maintain surface gloss and mechanical integrity during subsequent use.

[0065] The surface layer melt presents a fountain flow after entering the mold cavity, and the melt at the center of the flow front surges and spreads to the mold cavity wall. The mold cavity wall temperature is lower than the glass transition temperature of the surface layer material. The surface layer melt layer in contact with the mold wall undergoes heat transfer driven by temperature difference. As the temperature decreases, the free volume of the surface layer melt layer decreases, and the chain segment movement is hindered, resulting in a phase transition from viscous flow state to glassy state. The surface layer material after phase transition forms a high-viscosity or solid surface skin film, which closely replicates the micro-topography of the inner surface of the mold cavity. At the same time, due to the low thermal conductivity of the polymer material, the core of the surface layer melt located in the center of the flow channel and away from the mold wall has not yet cooled and still maintains a low-viscosity viscous flow state. Step S2 converts the single homogeneous surface layer melt flow into a rheological layered state, with the outer surface skin film defining the geometric boundaries of the part, and the internal molten core providing a pre-existing flow channel for the penetration and filling of the core layer melt in the subsequent S3 step.

[0066] Step S3 is a switching process of the flow channel switching mechanism in the nozzle assembly within a time interval of 0.1s to 0.5s after the termination of the step S2 skin melt injection action. The flow channel between the main injection station and the mold cavity is physically blocked, while the flow channel between the auxiliary injection station and the mold cavity is switched on. The flow channel switching action is completed immediately before the axial advancing action of the auxiliary injection screw is started.

[0067] The homogeneous dispersion prepared in step S1 is injected into the molten core of the skin film via the nozzle assembly. The injection process is set at an injection speed of 50mm / s to 150mm / s, which is greater than the injection speed of the skin melt in step S2. The injection pressure is set at 80MPa to 140MPa to overcome the flow resistance of the melt containing solid-phase particles in the flow channel. The injection amount of the homogeneous dispersion is determined by the remaining volume of the mold cavity, and is controlled at 60% to 80% of the total mass of the part.

[0068] As the homogeneous dispersion continues to be injected, the homogeneous dispersion forms a forward thrust inside the skin film. The homogeneous dispersion pushes the leading melt of the skin film to flow towards the end of the mold cavity. Before the end of the filling process, a second switching action is performed on the flow channel switching mechanism in the nozzle assembly to switch on the main injection station flow channel and inject 1% to 5% of the total mass of the skin melt to seal the gate area and completely encapsulate the core material inside the part.

[0069] In step S2, the skin material in close contact with the mold wall has undergone glass transition to form a solidified layer, while the skin material in the central region is still in a high-temperature viscous state. After the injection of the homogeneous dispersion, the viscosity gradient causes the homogeneous dispersion to preferentially enter the central region of the skin melt with the lowest viscosity. The homogeneous dispersion forms a tubular or finger-like flow channel in the central region. The solidified skin film acts as a pipeline wall to restrict the radial flow of the homogeneous dispersion, forcing the homogeneous dispersion to displace axially.

[0070] The homogeneous dispersion contains 10% to 40% of waste tire rubber. The addition of waste tire rubber increases the yield stress and viscosity of the melt. The high injection speed (50mm / s to 150mm / s) set in step S3 creates a high shear flow field with a shear rate exceeding 1000 / s in the flow channel and the mold cavity. The apparent viscosity of the polymer melt decreases with increasing shear rate, and the shear thinning effect and the plasticizing effect of the supercritical fluid are superimposed, causing the apparent viscosity of the homogeneous dispersion to decrease to below or close to the viscosity of the core of the skin melt. The low-viscosity continuous phase matrix suspends and transports solid waste tire rubber particles, preventing agglomeration or clogging of the flow channel.

[0071] During the filling process, there are velocity gradient and viscosity gradient between the skin melt and the core homogeneous dispersion. The viscosity of the core homogeneous dispersion decreases under high shear, and the skin film has formed a solidified shell with mechanical strength, and the core homogeneous dispersion is confined inside the skin film. The hydrostatic pressure generated by the core homogeneous dispersion uniformly acts on the inner surface of the skin film, driving the skin film to stretch and spread, and the rheological behavior completely confines the waste tire rubber particles inside the product, maintaining the gloss of the acrylonitrile-styrene-acrylate copolymer on the surface of the product. Step S3 changes the state in the mold cavity from a partially filled hollow film to a fully filled skin-core coated structure, and at this time the core material is in a high-pressure unfoamed state.

[0072] Step S4 immediately terminates the injection advancing action of the sub-injection station after the homogeneous dispersion in step S3 completes the volume filling of the mold cavity, and performs control mode switching processing on the sub-injection station, converting it from injection speed control mode to pressure control mode. The holding pressure of the sub-injection station is set to 0MPa to 10MPa, which is a low pressure state. The duration of maintaining the low pressure state is 10s to 30s.

[0073] Through the above pressure relief processing, the mechanical pressure acting on the core melt is cut off or reduced. The melt pressure inside the mold cavity decreases from the high pressure state in the injection stage to the set low pressure state within 0.1s to 1.0s, and the physical environment in the mold cavity is converted from a high-pressure compression environment to a low-pressure expansion environment.

[0074] Under the high-pressure environment in steps S1 and S3, the physical foaming agent is in a high solubility state in the polymer melt and is stably dissolved in the core melt in molecular form, maintaining thermodynamic equilibrium. The pressure relief processing in step S4 causes the pressure inside the mold cavity to decrease. The decrease in pressure directly leads to a decrease in the equilibrium solubility of the gas in the polymer melt. At this time, the actual concentration of the gas dissolved in the core melt is higher than the current equilibrium solubility, thereby forming a supersaturated state of gas concentration inside the homogeneous dispersion.

[0075] The supersaturation state destroys the thermodynamic stability of the homogeneous dispersion, driving the gas molecules to precipitate from the polymer matrix. The core melt is dispersed with 10% to 40% of waste tire rubber. The waste tire rubber exists in the form of solid particles, and the surface of the waste tire rubber particles has a rough concave-convex structure and interface defects. The rough concave-convex structure and interface defects reduce the Gibbs free energy barrier required for bubble nucleation. Gas molecules preferentially migrate to the solid-liquid interface of the waste tire rubber particles and gather to form heterogeneous nucleation with the waste tire rubber particles as the nucleation point. A large number of micro-bubble nuclei are generated on the surface of the waste tire rubber particles and begin to grow, converting the single-phase homogeneous dispersion into a multi-phase coexistence system containing a polymer continuous phase, a waste tire rubber dispersed phase, and a bubble dispersed phase. The generation and growth of the bubbles provide a power source for the volume expansion in the subsequent step S5.

[0076] Step S5 keeps the automobile exterior trim mold in a closed and locked state after the bubble nucleation induced in step S4. The pressure maintaining pressure of the sub-shooting table is maintained at 0 MPa to 10 MPa, and the pressure setting value continues the low pressure state in step S4, without applying a high mechanical pressure maintaining pressure for shrinkage compensation in the cooling stage. Heat exchange is performed by using the mold internal cooling channel system to maintain the mold cavity wall surface temperature at 40°C to 60°C. The cooling process lasts for 20 s to 60 s.

[0077] During the cooling process, heat is transferred from the polymer melt to the mold. The temperature of the surface skin film is lowered first below the glass transition temperature of the acrylonitrile-styrene-acrylate copolymer, and rigid solidification is completed. The temperature of the core melt is then lowered below the crystallization temperature of the post-consumer recycled polypropylene, and phase change solidification is completed. When the overall temperature of the part is lowered to the ejection temperature, the fixed mold side and the movable mold side of the mold are opened, and the solidified automobile exterior trim is ejected from the mold cavity by the ejection mechanism.

[0078] The micro-bubbles generated in the core melt continue to grow under the driving of the supersaturation degree, and the volume of the bubbles increases to produce isotropic volume expansion. At the same time, the polymer melt shrinks in volume due to the temperature reduction. In step S5, the expansion volume generated by the bubble growth is greater than or equal to the shrinkage volume generated by the polymer cooling. The internal expansion pressure generated by the bubbles is transmitted from the core center to the mold wall, pressing the surface skin film and the inner surface of the mold cavity, and the internal expansion pressure compensates for the cooling shrinkage, so that the surface of the part replicates the micro-topography of the mold cavity.

[0079] The expansion pressure acts on the interface between the core melt and the surface skin film. At this time, the inner surface of the surface skin film has not yet been completely cooled and still has a certain chain segment movement ability. Under the driving of the expansion pressure, the styrene-ethylene-butylene-styrene block copolymer in the core melt penetrates to the inner surface of the surface skin film. At the same time, the solid waste tire rubber dispersed near the interface acts as a rigid particle and embeds into the inner wall of the surface skin film under the action of the expansion pressure.

[0080] As the cooling process proceeds, the surface and core materials solidify sequentially. The penetration areas and embedding points at the interface are frozen. The styrene-ethylene-butene-styrene block copolymer utilizes ethylene-butene soft segments to connect the surface and core layers. The embedded waste tire rubber forms a microscale serrated mechanical interlocking structure at the interface, connecting the surface and core materials without chemical bonding.

[0081] In the following examples and comparative examples, the styrene-ethylene-butene-styrene block copolymers used were prepared through the following process: In the anionic polymerization stage, styrene monomer, butadiene monomer, and styrene monomer were added sequentially at 60°C using cyclohexane as a solvent and n-butyllithium as an initiator to conduct active anionic block copolymerization, generating a styrene-butadiene-styrene block copolymer with a linear triblock structure. In the hydrogenation stage, the styrene-butadiene-styrene block copolymer was dissolved in a solvent, a nickel-based hydrogenation catalyst was added, and hydrogen gas at a pressure of 3.5 MPa was introduced to carry out an addition reaction, achieving a hydrogenation conversion rate of 98%. The reaction product was devolatilized and dried to obtain the styrene-ethylene-butene-styrene block copolymer.

[0082] In the following examples and comparative examples, the acrylonitrile-styrene-acrylate copolymers used were prepared through the following process: In the rubber core synthesis stage, water, butyl acrylate monomer, divinylbenzene crosslinking agent, sodium dodecyl sulfate emulsifier, and potassium persulfate initiator were added to a reactor, and a seed emulsion polymerization reaction was carried out at a temperature of 70°C for 5 hours to generate polybutyl acrylate rubber latex with a crosslinked structure. In the graft shell synthesis stage, styrene monomer and acrylonitrile monomer were continuously added dropwise to the polybutyl acrylate rubber latex, with a mass ratio of styrene monomer to acrylonitrile monomer of 75:25. Tertiary dodecyl mercaptan was added as a molecular weight regulator. Under the action of the initiator, styrene monomer and acrylonitrile monomer underwent an in-situ graft copolymerization reaction on the surface of polybutyl acrylate rubber latex particles, and the total monomer conversion rate reached 97%. The reaction product was subjected to coagulation, washing, drying, and extrusion granulation processes to obtain the acrylonitrile-styrene-acrylate copolymer.

[0083] Example 1:

[0084] The specific process for preparing automotive exterior decorative parts in this embodiment is as follows:

[0085] S1: 80% by mass of post-consumer recycled polypropylene, 10% by mass of waste tire rubber, and 10% by mass of styrene-ethylene-butene-styrene block copolymer are mixed and fed to the secondary injection stage of a dual-injection molding machine. The temperature of the secondary injection stage's plasticizing barrel temperature control heating zone is set to 210℃, and the rotary screw speed is set to 85 r / min. Supercritical nitrogen gas at a pressure of 15 MPa and an injection volume of 0.2% by mass is injected into the mixing section of the secondary injection stage. The supercritical nitrogen gas dissolves in the core melt at the front of the nozzle of the secondary injection stage, forming a uniform dispersion.

[0086] S2: The acrylonitrile-styrene-acrylate copolymer prepared above is fed to the main injection stage of a dual-injection molding machine. The temperature of the main injection stage's plasticizing barrel is set to 250°C, and the screw speed is set to 115 r / min. The main injection stage runner is opened, the injection pressure is set to 100 MPa, and the injection speed is set to 55 mm / s. The surface melt is injected into the mold cavity. The surface melt injection volume is 30% of the total mass of the part. The mold cavity wall temperature is set to 50°C, and a surface film is formed after the surface melt contacts the wall.

[0087] S3: Within a 0.3s interval after the surface melt injection ends, the flow channel switching mechanism within the nozzle assembly is switched to physically block the flow channel between the main injection stage and the mold cavity, while opening the flow channel between the secondary injection stage and the mold cavity. The secondary injection stage screw initiates axial propulsion, injecting the uniformly dispersed material into the surface film. The injection speed is set to 100mm / s, and the injection pressure is set to 110MPa. The amount of uniformly dispersed material injected is 70% of the total mass of the part. 0.2s before the end of the filling process, the flow channel switching mechanism is switched a second time, opening the main injection stage flow channel and injecting 3% of the total mass of the part's surface melt to seal the gate area.

[0088] S4: Immediately terminate the injection process after the homogeneous dispersion has filled the mold cavity. Switch the pressure of the secondary injection unit of the dual-injection molding machine from injection speed control to pressure control. Set the holding pressure of the secondary injection unit to 5 MPa, a low-pressure state. Maintain this low-pressure state for 20 seconds. As the pressure inside the mold cavity decreases, the nitrogen dissolved in the homogeneous dispersion undergoes heterogeneous nucleation on the surface of the waste tire rubber particles and grows into bubbles.

[0089] S5: Keep the automotive exterior trim mold in a closed and locked state, maintaining the sub-injection stage pressure at 5MPa. Utilize the internal cooling channel system of the mold for heat exchange, maintaining the mold cavity wall temperature at 50℃. The cooling process lasts for 40 seconds. When the part temperature drops to the ejection temperature, open the fixed mold side and the moving mold side of the mold, and eject the part through the ejection mechanism to obtain the automotive exterior trim.

[0090] Example 2:

[0091] In this embodiment, the difference from Embodiment 1 is that the injection amount of supercritical nitrogen in step S1 is 0.8% by mass. The remaining process steps are the same as in Embodiment 1.

[0092] Example 3:

[0093] In this embodiment, the difference from Embodiment 1 is that the injection amount of supercritical nitrogen in step S1 is 1.5% by mass. The remaining process steps are the same as in Embodiment 1.

[0094] Example 4:

[0095] In this embodiment, the difference from Embodiment 1 is that in step S1, the mass percentage of waste tire rubber is 25%, and the mass percentage of post-consumer recycled polypropylene is 65%. The remaining process steps are the same as in Embodiment 1.

[0096] Example 5:

[0097] In this embodiment, the difference from Embodiment 1 is that in step S1, the mass percentage of waste tire rubber is 25%, the mass percentage of post-consumer recycled polypropylene is 65%, and the injection amount of supercritical nitrogen is 0.8% by mass. The remaining process steps are the same as in Embodiment 1.

[0098] Example 6:

[0099] In this embodiment, the difference from Embodiment 1 is that in step S1, the mass percentage of waste tire rubber is 25%, the mass percentage of post-consumer recycled polypropylene is 65%, and the injection amount of supercritical nitrogen is 1.5% by mass. The remaining process steps are the same as in Embodiment 1.

[0100] Example 7:

[0101] In this embodiment, the difference from Embodiment 1 is that in step S1, the mass percentage of waste tire rubber is 40%, and the mass percentage of post-consumer recycled polypropylene is 50%. The remaining process steps are the same as in Embodiment 1.

[0102] Example 8:

[0103] In this embodiment, the difference from Embodiment 1 is that in step S1, the mass percentage of waste tire rubber is 40%, the mass percentage of post-consumer recycled polypropylene is 50%, and the injection amount of supercritical nitrogen is 0.8% by mass. The remaining process steps are the same as in Embodiment 1.

[0104] Example 9:

[0105] In this embodiment, the difference from Embodiment 1 is that in step S1, the mass percentage of waste tire rubber is 40%, the mass percentage of post-consumer recycled polypropylene is 50%, and the injection amount of supercritical nitrogen is 1.5% by mass. The remaining process steps are the same as in Embodiment 1.

[0106] Comparative Example 1:

[0107] In this comparative example, the difference from Example 1 is that in step S1, the core layer melt is prepared by mixing 80% post-consumer recycled polypropylene with 20% polyolefin elastomer. In step S4, the holding pressure of the sub-launch stage is set to 50 MPa. The remaining process steps are the same as in Example 1.

[0108] Comparative Example 2:

[0109] In this comparative example, the difference from Example 1 is that in step S1, the core melt consists of 75% post-consumer recycled polypropylene and 25% waste tire rubber. The remaining process steps are the same as in Example 1.

[0110] Comparative Example 3:

[0111] In this comparative example, unlike Example 1, supercritical nitrogen gas is not injected into the core layer melt in step S1. The remaining process steps are the same as in Example 1.

[0112] Comparative Example 4:

[0113] In this comparative example, the difference from Example 1 is that in step S1, the core melt consists of 90% post-consumer recycled polypropylene and 10% styrene-ethylene-butene-styrene block copolymer. The remaining process steps are the same as in Example 1.

[0114] Experimental Example 1:

[0115] In this experimental example, the automotive exterior trim parts prepared in Examples 1 to 9 and Comparative Examples 1 to 4 were tested as follows:

[0116] 1. Cantilever Beam Notched Impact Strength Test: A strip specimen measuring 80mm in length, 10mm in width, and 4mm in thickness is cut from the center area of ​​the automotive exterior trim part, and a V-shaped notch is machined at the center of the specimen according to GB / T 1843 standard; the strip specimen is subjected to impact testing using a cantilever beam impact testing machine, with the pendulum impact energy set to 5.5J; the impact energy consumed per unit area is recorded as the value of the cantilever beam notched impact strength, in units of... .

[0117] 2. T-Peel Strength Test: A rectangular specimen, 150 mm long and 25 mm wide, was cut from a flat area of ​​the automotive exterior trim. The acrylonitrile-styrene-acrylate copolymer layer and the core material were pre-peeled 50 mm apart at one end along the length. Following ASTM D1876, the peeled ends of the rectangular specimen were clamped in the upper and lower fixtures of an electronic universal testing machine, and peeling was performed at a tensile speed of 50 mm / min. The average load during the peeling process was divided by the specimen width as the T-peel strength value, in units of... .

[0118] 3.60° Surface Gloss Test: Untreated automotive exterior trim parts were selected as test samples, ensuring that the test surface was free of oil and dust. According to ASTM D523 standard, five test points were randomly selected on the surface of the acrylonitrile-styrene-acrylate copolymer of the automotive exterior trim parts using a spectrophotometer, with the incident angle set at 60°. The arithmetic mean of the gloss values ​​obtained from the five test points was recorded as the 60° surface gloss value, in GU.

[0119] 4. Maximum injection pressure test: The pressure is acquired in real time during the filling of the uniform dispersion in step S3; the pressure sensor integrated inside the dual-injection stage injection molding machine is used to monitor the instantaneous pressure of the secondary injection stage screw when the uniform dispersion fills the mold cavity to 95% volume; the peak pressure fed back by the pressure sensor is recorded as the value of the maximum injection pressure, in MPa.

[0120] The results are shown in Table 1:

[0121] Table 1

[0122]

[0123] Waste tire rubber, used as a dispersed phase filler, alters the multiphase microstructure of the core melt with changes in its content, leading to a nonlinear evolution of the material's impact strength and processing pressure. Experimental data show that, under constant supercritical nitrogen injection, as the waste tire rubber content increases from 10% to 25%, the cantilever beam notched impact strength increases from 13.1... Upgraded to 20.1 When the content further increases to 40%, the impact strength drops back to 18.2. .

[0124] The increased impact strength is due to the fact that waste tire rubber particles, acting as the elastomer dispersion phase, form stress-absorbing centers within the post-consumer recycled polypropylene matrix. When the sample is subjected to impact load, the waste tire rubber particles induce numerous fine crazes in the surrounding matrix. The formation and termination of these crazes consume impact energy, preventing the unstable propagation of macroscopic cracks.

[0125] The decline in impact strength is due to the physical agglomeration of excessive waste tire rubber particles in the melt, forming macroscopic agglomerates with sizes exceeding the critical value. The weak interface regions within these macroscopic agglomerates become crack initiation sites under stress, inducing premature material fracture.

[0126] Meanwhile, the maximum injection pressure increases with the increase of waste tire rubber content. This is because waste tire rubber particles have a three-dimensional cross-linked network structure and do not melt at the injection temperature. The solid particles are suspended in the post-consumer recycled polypropylene melt, increasing the internal friction between fluid layers. As the concentration of waste tire rubber particles increases, the hydrodynamic resistance effect on the melt is enhanced, leading to an increase in apparent viscosity and increasing the axial pressure required for the auxiliary injection screw to push the melt to fill the mold cavity.

[0127] Supercritical nitrogen acts as both a plasticizer and a foaming agent in the core melt, and its injection amount directly affects the fluidity of the core melt and the interlocking depth of the interfaces. Experimental data shows that, with a waste tire rubber content of 40%, when the supercritical nitrogen injection amount increases from 0.2% to 1.5%, the maximum injection pressure decreases from 142 MPa to 94 MPa. This is because the diameter of supercritical nitrogen molecules is smaller than the radius of gyration of polymer molecular chain segments. After nitrogen molecules penetrate into the interchain gaps of post-consumer recycled polypropylene, they increase the free volume of the system. The increase in free volume lowers the activation energy required for molecular chain segment transitions, weakens the entanglement between molecular chains, and reduces the zero-shear viscosity of the matrix through a plasticizing effect, offsetting the viscosity increase caused by solid waste tire rubber particles.

[0128] Meanwhile, with a waste tire rubber content of 25%, the T-peel strength increased from 2.45 N / mm to 3.88 N / mm when the supercritical nitrogen injection rate increased from 0.2% to 0.8%. This is due to the isotropic expansion stress generated during the bubble growth process. In a closed environment with a constant mold cavity volume, the expansion stress drives the core melt to be strongly extruded towards the inner wall of the surface film. The expansion stress promotes the penetration of the styrene-ethylene-butene-styrene block copolymer at the interface into the micropores of the surface material, and forces the waste tire rubber particles near the interface to embed into the inner wall of the not-yet-fully-cured surface film, constructing a microscopic mechanical interlocking structure.

[0129] Comparing Comparative Example 3 and Example 5, the part injected with supercritical nitrogen maintained a high gloss of 95.1 GU, while the part lacking nitrogen saw its gloss drop to 78.5 GU. This is because the rough morphology and interface defects on the surface of the waste tire rubber particles provided numerous nucleation sites, lowering the Gibbs free energy barrier required for bubble nucleation. Heterogeneous nucleation of gas molecules on the surface of the waste tire rubber particles generated high-density, small-sized pores, providing stable internal support during cooling, compensating for polymer cooling shrinkage, and preventing surface depressions or ripples.

[0130] In summary, Example 5 exhibits superior overall performance compared to other examples. This is because the 25% waste tire rubber content falls within the peak range of toughening effectiveness, and the 0.8% nitrogen injection provides both sufficient viscosity reduction and moderate expansion pressure, achieving a balance between interfacial peel strength and impact resistance without degrading surface gloss.

[0131] Furthermore, in Comparative Example 2, the peel strength was only 0.42 N / mm in the absence of the styrene-ethylene-butene-styrene block copolymer. This is because the waste tire rubber particles have an inert crosslinked surface, preventing molecular diffusion with the acrylonitrile-styrene-acrylate copolymer. The styrene-ethylene-butene-styrene block copolymer has an amphiphilic structure; the hard polystyrene segments are compatible with the surface material, while the soft ethylene-butene segments are compatible with the core matrix. Driven by expansion pressure, the styrene-ethylene-butene-styrene block copolymer undergoes interlayer entanglement at the interface, connecting the surface material and the core rubber particles. The absence of the styrene-ethylene-butene-styrene block copolymer results in a lack of bonding medium in the physically interlocked structure, leading to brittle separation of the interface under stress.

[0132] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A molding process for lightweight automotive exterior decorative parts incorporating recycled waste materials, characterized in that, Includes the following steps: S1: Supercritical fluid is injected into the core melt to form a uniform dispersion; the core melt includes post-consumer recycled polypropylene, waste tire rubber and styrene-ethylene-butene-styrene block copolymer. S2: The surface melt is injected into the mold cavity to form a surface film on the inner wall of the mold cavity; the surface melt includes an acrylonitrile-styrene-acrylate copolymer; S3: Inject the uniformly dispersed material into the surface film, causing the surface film to extend and fill the mold cavity; S4: Depressurize the mold cavity to induce the gas dissolved in the uniform dispersion to nucleate and grow into bubbles on the surface of waste tire rubber; S5: The expansion pressure generated by bubble growth drives the core melt to press against the surface film, and after cooling and solidification, it forms an automotive exterior decorative part.

2. The molding process according to claim 1, characterized in that, In step S1, based on the total mass of the core melt, the mass percentage of post-consumer recycled polypropylene is 50% to 80%, the mass percentage of waste tire rubber is 10% to 40%, and the mass percentage of styrene-ethylene-butene-styrene block copolymer is 5% to 15%.

3. The molding process according to claim 2, characterized in that, In step S1, the supercritical fluid is nitrogen or carbon dioxide, and the injection amount accounts for 0.2% to 1.5% of the total mass of the core melt.

4. The molding process according to claim 1, characterized in that, In step S2, the amount of surface melt injected accounts for 20% to 40% of the total mass of the part, and the temperature of the mold cavity wall is maintained at 40°C to 60°C.

5. The molding process according to claim 1, characterized in that, In step S3, the injection speed of the uniform dispersion is 50 mm / s to 150 mm / s, and the injection pressure is 80 MPa to 140 MPa; before the end of the filling process, a second injection of surface melt accounting for 1% to 5% of the total mass of the part is performed to seal the gate area.

6. The molding process according to claim 1, characterized in that, In step S4, the pressure relief process specifically involves controlling the holding pressure acting on the core melt at a low pressure of 0 MPa to 10 MPa and maintaining it for 10 to 30 seconds.

7. The molding process according to claim 1, characterized in that, In step S5, the cooling process lasts for 20 to 60 seconds, and the temperature of the mold cavity wall is maintained at 40°C to 60°C.

8. The molding process according to claim 1, characterized in that, In step S3, the uniform dispersion is injected within a time interval of 0.1s to 0.5s after the termination of the surface melt injection action.

9. The molding process according to claim 1, characterized in that, Waste tire rubber is a powdery solid with a particle size of 40 to 120 mesh.

10. A lightweight automotive exterior trim component incorporating recycled waste materials, characterized in that, It is produced by the molding process described in any one of claims 1-9.

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