Injection molding method of ultrahigh-strength regenerated nylon component

Abstract

The invention discloses an injection molding method of an ultrahigh-strength regenerated nylon component, which comprises the following steps: dehumidifying and drying a regenerated nylon raw material to ensure that the water content is not higher than 0.06 wt%, and keeping a constant water content state in a closed hopper; raw materials are plasticized in a screw of an injection molding machine, volatile matter is removed through vacuum devolatilization of an exhaust section, meanwhile, a chain extension reaction component is added to enable a molecular chain to be subjected to in-situ chain extension repair, and stability of a screw torque signal or a melt pressure signal serves as a repair completion criterion; in the injection molding stage, mold filling is carried out at a segmented injection speed, so that a molten material and a reinforced phase form directional orientation in the main stress direction of the component; a pressure sensor arranged in a cavity is used for collecting cavity pressure signals in real time, a pressure maintaining switching point and pressure maintaining pressure are adjusted in a closed-loop mode, and compactness is kept in the feeding stage; and cooling and shaping under the condition of mold partition temperature control to obtain the component. The method can reduce the molding defects such as shrinkage cavities and cavities, and improves the strength and consistency of the component.

Description

Technical Field

[0001] This invention belongs to the field of injection molding technology, specifically relating to an injection molding method for ultra-high strength recycled nylon components. Background Technology

[0002] Nylon materials are widely used in load-bearing components in automobiles, home appliances, and industrial equipment due to their high strength, good wear resistance, and excellent oil and chemical resistance. With increasing demands for carbon neutrality and a circular economy, the demand for recycled nylon in structural components is rapidly growing. However, recycled PA66 comes from complex sources and exhibits significant batch-to-batch variations. Common problems include: thermal-oxidative aging and hydrolytic degradation during recycling and reprocessing leading to molecular chain breakage, changes in end-group activity, and a decrease in molecular weight, causing fluctuations in melt viscosity and flowability, which in turn lead to unstable mechanical properties of the components. For reinforced systems such as glass fiber, fluctuations in matrix properties can amplify inconsistencies in interfacial bonding and fiber orientation, making it difficult to consistently meet the requirements for ultra-high strength components in terms of tensile strength, flexural strength, weld line strength, and impact performance.

[0003] On the other hand, nylon systems are extremely sensitive to moisture. When the moisture content of the raw material is too high, hydrolysis is prone to occur during the plasticizing stage, accompanied by the precipitation of volatiles, resulting in defects such as silver streaks, bubbles, and internal porosity. At the same time, if the shrinkage stage is not properly controlled, the pressure in the mold cavity will decay rapidly, easily forming shrinkage cavities, voids, and local density deficiencies, further weakening the load-bearing performance and dimensional consistency. In current injection molding production, fixed drying regimes, fixed plasticizing parameters, and empirical pressure switching points are often used for opening and closing pressure control. For fluctuating raw materials such as recycled nylon, the above methods are difficult to effectively determine and dynamically adjust the degree of molecular weight restoration and the state of shrinkage compaction. This leads to problems such as large strength fluctuations, high defect rates, warpage, and out-of-tolerance dimensional deviations in the same process under different batches of raw materials or different environmental humidity conditions. Especially in reinforced components, if the mold filling shear and flow front are unstable, it will also lead to fiber orientation dispersion and insufficient bonding in the weld line area, thus becoming a weak point in the structure. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides an injection molding method for ultra-high strength recycled nylon components, achieving significant improvements in the strength, stability, and molding quality of recycled nylon reinforced components, making it suitable for mass production of engineering structural components with high load-bearing and high reliability requirements.

[0005] The technical solution provided by this invention is as follows: A method for injection molding ultra-high strength recycled nylon components includes the following steps: S1. Raw material pretreatment: The recycled nylon raw material is dehumidified and dried to ensure that the moisture content of the raw material is not higher than 0.06 wt%. After drying, the recycled nylon raw material is transported to a closed hopper to maintain a constant moisture content. S2, In-situ reaction repair of plasticization: The recycled nylon raw material processed in step S1 is added into the screw of the injection molding machine for plasticization. During the plasticization process, devolatilization is carried out in the exhaust section of the screw. At the same time, chain extension reaction components are added to the molten recycled nylon to cause the recycled nylon molecular chains to undergo in-situ chain extension reaction. During the plasticizing process, screw torque signals or melt pressure signals are collected in real time and used as criteria for molecular weight repair completion. When the screw torque or melt pressure stabilizes within a preset range, the in-situ reaction repair is considered complete. S3, Directional Injection Molding: After the in-situ reaction repair is completed, molten recycled nylon is injected into the mold cavity. The mold is filled with segmented injection speed, so that the molten recycled nylon forms molecular chains or oriented reinforcing phases along the main force direction of the component in the mold cavity. S4, Closed-loop pressure and compensation: During the injection molding process, the cavity pressure sensor installed in the mold cavity collects the cavity pressure signal in real time, and uses the cavity pressure signal as feedback to adjust the pressure holding switching point and pressure holding of the injection molding machine in a closed loop, so that the molten recycled nylon in the cavity remains in a dense state during the shrinkage stage. S5, Cooling and Shaping: The components are cooled and shaped under temperature control in the mold zone to obtain ultra-high strength recycled nylon injection molded components.

[0006] In some embodiments, the dehumidification and drying in step S1 adopts a vacuum dehumidification and drying method, with a drying temperature of 80-95°C and a drying time of 4-10 hours.

[0007] In some embodiments, the chain extension reaction component in step S2 is a multifunctional epoxy chain extender and / or a carbodiimide chain extender stabilizer, and the amount added is 0.2 to 1.5 wt% of the mass of the recycled nylon raw material.

[0008] In some embodiments, the recycled nylon is recycled PA6 or recycled PA66. When the recycled nylon is recycled PA6, the melt temperature in the plasticizing stage of step S2 is controlled at 235-255°C. When the recycled nylon is recycled PA66, the melt temperature in the plasticizing stage of step S2 is controlled at 265-285°C.

[0009] In some embodiments, vacuum devolatilization is performed in step S2 through the screw exhaust section, with a vacuum degree of -0.06 to -0.09 MPa.

[0010] In some embodiments, the segmented injection speed in step S3 includes a high-speed filling segment and a low-speed replenishment segment. The high-speed filling segment is used to improve the orientation of molecular chains or reinforcing phases, and the low-speed replenishment segment is used to reduce uneven shearing at the end of the cavity.

[0011] In some embodiments, the mold in step S5 adopts a zoned temperature control structure, wherein the mold temperature in the gate area is 90-130°C, and the mold temperature in the area away from the gate is 60-95°C.

[0012] In some embodiments, the recycled nylon raw material also includes a reinforcing component, which is chopped glass fiber, basalt fiber or a combination thereof, with a mass fraction of 10-45 wt%, and is combined with a silane coupling agent to improve the interfacial bonding strength between the reinforcing component and the recycled nylon matrix.

[0013] In summary, the beneficial effects of this invention are: This invention achieves stable melt properties in recycled nylon before injection molding by rigorously dehumidifying and drying the raw materials before injection molding, and by combining vacuum devolatilization and chain extension reactions during the plasticizing stage to repair the molecular chains in situ. The stability of screw torque or melt pressure is used as the criterion for determining the completion of the repair. During injection molding, segmented injection speeds are employed to ensure a more consistent orientation structure between the molten material and the reinforcing phase along the main stress direction of the component. Simultaneously, a cavity pressure sensor provides real-time feedback and adjusts the holding pressure switching point and holding pressure, making the shrinkage compensation process more thorough and stable. Combined with mold zone temperature control for cooling and shaping, this effectively reduces defects such as silver streaks, bubbles, shrinkage cavities, and internal porosity, lowers component warping and dimensional fluctuations, improves the bonding strength of the weld line area, and enhances the overall mechanical property consistency. Ultimately, this results in a significant improvement in the strength, stability, and molding quality of recycled nylon-reinforced components, making them suitable for mass production of engineering structural parts with high load-bearing and high reliability requirements. Attached Figure Description

[0014] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0015] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments. The following embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0016] like Figure 1As shown, this invention provides an injection molding method for ultra-high strength recycled nylon components, using recycled PA6 (rPA6) or PA66 (rPA66) as the matrix resin. The following description uses PA66. To obtain high-strength components, a reinforcement system is employed. The reinforcement component can be selected from chopped glass fiber, basalt fiber, or a combination thereof, with a mass fraction of 10–45 wt%. A silane coupling agent of 0.2–0.8 wt% is added to improve the interfacial bonding strength between the reinforcement component and the recycled PA66 matrix.

[0017] To address potential molecular weight reduction or end-group degradation issues during the recycling and reprocessing of recycled PA66, a chain-extending reaction component is added during the plasticizing process. This component comprises a multifunctional epoxy chain extender and / or a carbodiimide chain extender stabilizer, added at an amount of 0.2–1.5 wt% of the recycled PA66 raw material. In the molten state, the chain-extending reaction component reacts in situ with the end groups of the recycled PA66 molecular chains, achieving chain extension or end-group repair, thereby improving melt viscosity stability and the consistency of the product's mechanical properties.

[0018] The technical solution of this invention can be implemented on a conventional injection molding system. The system includes at least an injection molding machine, a screw plasticizing assembly with a venting section, a vacuum devouring device, a sealed hopper, a mold, and a mold temperature control device. To achieve closed-loop control, a cavity pressure sensor is installed inside the mold cavity and communicates with the injection molding machine controller to collect cavity pressure signals and provide feedback to adjust the holding pressure switching point and holding pressure. The injection molding machine can collect screw torque signals or melt pressure signals to determine whether the in-situ chain extension repair process is complete.

[0019] Specifically, it includes the following steps: S1. Raw material pretreatment The recycled PA66 raw material is dehumidified and dried to ensure that the moisture content does not exceed 0.06 wt%. Vacuum dehumidification is preferred, with a drying temperature of 80–95°C and a drying time of 4–10 hours. After drying, the recycled PA66 raw material is directly transferred to a sealed hopper to maintain a constant moisture content, thus preventing re-hygroscopic degradation, silvering, bubbling, and fluctuations in mechanical properties.

[0020] In the reinforcement system, the reinforcing components and chain extension reaction components can be added by premixing with the recycled PA66 and then drying, or by adding them simultaneously through a metering feeding device after the main material has been dried. Regardless of the addition method, the moisture content of the recycled PA66 system before entering the screw should meet the control requirement of ≤0.06wt%.

[0021] S2, In-situ reaction repair of plasticizers The recycled PA66 raw material processed in step S1 is added to the screw of the injection molding machine for plasticization. The melt temperature during the plasticization stage is controlled at 265-285℃. During the plasticization process, devolatilization is performed in the screw exhaust section. Moisture and low-molecular-weight volatiles precipitated in the melt are removed by vacuum suction. The vacuum degree is controlled at −0.06 to −0.09 MPa.

[0022] Simultaneously, chain-extending reaction components are added to the molten recycled PA66 to induce in-situ chain extension of the recycled PA66 molecular chains. To ensure the controllability of the in-situ reaction repair, screw torque and melt pressure signals are collected in real time during plasticization and used as criteria for determining the completion of molecular weight repair: when the screw torque or melt pressure stabilizes within a preset range and remains so for a preset time T, the in-situ reaction repair is considered complete. The preset time T is preferably 30–120 seconds. By controlling the process using the above criteria, insufficient repair or over-reaction caused by setting the plasticization time solely based on experience can be avoided, improving the process consistency of different recycled batches of raw materials.

[0023] S3, Directional Injection Molding After in-situ reaction repair is completed, molten regenerated PA66 is injected into the mold cavity using a segmented injection speed, which includes a high-speed filling segment and a low-speed replenishment segment. The high-speed filling segment is used to form a high-shear and stable flow front within the cavity, causing the regenerated PA66 molecular chains and reinforcing phases to oriented along the main force direction of the component. The low-speed replenishment segment is used to reduce shear unevenness and backflow disturbance at the end of the cavity, improve the uniformity of the flow end, and reduce the risk of defects in the weld area.

[0024] In the reinforcement system, by using a reasonable segmented injection speed, the orientation consistency of the reinforcing phase can be improved while ensuring complete mold filling, thereby giving fuller play to the stiffening and modulating effect of the reinforcing phase in the main force direction.

[0025] S4, Closed-loop environmental pressure and compensation During the injection molding process, a cavity pressure sensor installed in the mold cavity collects the cavity pressure signal in real time, and uses the cavity pressure signal as feedback to perform closed-loop adjustment of the pressure holding switching point and pressure holding of the injection molding machine.

[0026] Specifically, a target curve or target pressure range for the cavity pressure can be set: when the cavity pressure reaches the set threshold, the switch from the filling stage to the holding stage is triggered; during the holding and shrinkage compensation stage, the holding pressure is dynamically corrected according to the real-time changes in the cavity pressure, so that the molten regenerated PA66 in the cavity remains in a dense state during the shrinkage compensation stage, thereby reducing defects such as shrinkage cavities, voids, internal porosity, and uneven fiber enrichment, and improving the dimensional stability and batch consistency of the parts.

[0027] S5, Cooling and Shaping The component is cooled and shaped under zoned temperature control in the mold. The mold adopts a zoned temperature control structure, with the mold temperature controlled at 90-130℃ in the gate area and 60-95℃ in the area away from the gate. The higher mold temperature in the gate area improves the fluidity and bonding quality during the welding and shrinkage compensation stages, while the lower mold temperature in the far-end area improves cooling efficiency and suppresses warpage. After cooling, the mold is opened and the part is removed, yielding an ultra-high strength recycled PA66 reinforced injection molded component.

[0028] To verify the improvement effect of the method of the present invention on mechanical properties, molding defects and consistency, Examples 1 to 3 and Comparative Examples 1 to 2 were set up. The test results of mechanical properties and molding quality of each group are shown in Tables 1 to 3.

[0029] Example 1 In this embodiment, recycled PA66 was selected as the matrix resin. 30 wt% chopped glass fiber was added to the recycled PA66 as a reinforcing component, and 0.50 wt% silane coupling agent was added to improve the interfacial bonding strength between the reinforcing component and the matrix. Simultaneously, 0.80 wt% epoxy chain extender was added as a chain-extending reaction component. The above raw materials were subjected to vacuum dehumidification and drying at 90℃ for 6 hours to control the moisture content to 0.05 wt%. After drying, the raw materials were conveyed to a closed hopper to maintain a constant moisture content. The raw materials were added to the screw of an injection molding machine for plasticization. During the plasticization stage, the melt temperature was controlled at 280℃, and vacuum devolatilization was performed at -0.08 MPa in the screw exhaust section. During plasticization, screw torque signals or melt pressure signals were collected in real time. When the signal stabilized and reached the window value for 60 seconds, the in-situ reaction repair was determined to be complete. Subsequently, segmented injection speeds were used for directional mold filling, with a first-stage injection speed of 120 mm / s and a second-stage injection speed of 40 mm / s. During the shrinkage compensation stage, cavity pressure sensors were used to collect cavity pressure signals, and the holding pressure switching point and holding pressure were adjusted in a closed loop accordingly. The mold adopted zoned temperature control, with the mold temperature in the gate area at 110℃ and the mold temperature in the area away from the gate at 80℃. After cooling and solidification, injection molded components were obtained. The mechanical properties and molding quality of the 10 obtained components were tested, and the results are shown in Tables 1 to 3.

[0030] Example 2 The raw material system, drying conditions, plasticizing temperature, vacuum devolatilization conditions, and in-situ reaction repair criteria in this embodiment are the same as in Example 1. The difference is that, to further improve the consistency of the reinforcing phase orientation, a higher high-speed mold filling speed and a lower final replenishment speed are used. The first-stage injection speed is adjusted to 150 mm / s, and the second-stage injection speed is adjusted to 35 mm / s. The remaining closed-loop shrinkage compensation and mold temperature zoning conditions are the same as in Example 1. Ten components were tested, and the results are shown in Tables 1 to 3.

[0031] Example 3 The raw material system, drying conditions, plasticizing temperature, vacuum devolatilization conditions, in-situ reaction repair criteria, and segmented injection speed in this embodiment are the same as in Example 2. The difference lies in the following: to further reduce the density fluctuation and internal defects during the shrinkage compensation stage, the closed-circuit pressure is controlled by a target cavity pressure curve smoothing method. Simultaneously, the mold zone temperature is set to 120°C in the gate area and 85°C in the area away from the gate, to improve the flow and bonding quality during the welding and shrinkage compensation stages while also considering the shaping efficiency. Ten components were tested, and the results are shown in Tables 1 to 3.

[0032] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that no chain-extending reaction component was added, i.e., no epoxy chain extender was added. All other formulations and process conditions were the same as in Example 1, including 30wt% chopped glass fiber, 0.50wt% silane coupling agent, drying conditions of 90℃×6h with a moisture content of 0.05wt%, plasticizing temperature of 280℃, vacuum devolatilization of -0.08MPa, segmented injection speed of 120mm / s→40mm / s, closed-loop cavity pressure compensation, and mold temperature partitioning of 110℃ / 80℃. Ten components were tested, and the results are shown in Tables 1 to 3.

[0033] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that, although 0.80 wt% of epoxy chain extender was added and the in-situ reaction repair was determined by maintaining a stable torque or melt pressure for 60 seconds, the segmented directional filling and cavity pressure closed-loop control were not used during the injection and shrinkage stages. Instead, a single-stage injection speed of 100 mm / s was adopted, and the holding pressure switching point and holding pressure were fixed in an open loop. The remaining formulation and pretreatment, plasticizing temperature of 280℃, vacuum devolatilization of -0.08 MPa, and mold temperature partitioning of 110℃ / 80℃ were the same as in Example 2. The 10 obtained components were tested, and the results are shown in Tables 1 to 3.

[0034] Table 1 Table 2 Table 3 Based on Tables 1-3, it can be seen that: compared with Comparative Example 1, Examples 1-3, due to the addition of chain extension reaction components and the use of screw torque or melt pressure stability to reach the window as the criterion for in-situ repair completion, make the molecular weight repair process of regenerated PA66 controllable, resulting in improved mechanical properties and a reduced standard deviation; compared with Comparative Example 2, Examples 1-3, through cavity pressure feedback closed-loop adjustment of the holding pressure switching point and holding pressure, make the cavity density more stable during the feeding stage, reduce the occurrence rate of shrinkage cavities / voids, and reduce warpage and critical dimension deviations; under the reinforced system conditions, the directional filling of the mold at segmented injection speed promotes the orientation of the reinforcing phase along the main force direction, and the coupling agent enhances the interfacial bonding strength, thereby further improving the strength and rigidity of the component.

[0035] The foregoing description illustrates and describes preferred embodiments of the present invention. As previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method of injection molding an ultrahigh-strength recycled nylon component, characterized by, The method comprises the following steps: S1, raw material pretreatment: The regenerated nylon raw material is subjected to dehumidification and drying treatment to make the water content of the raw material not higher than 0.06wt%, and the regenerated nylon raw material is transported to a closed hopper to maintain a constant water content after drying is completed; S2, in-situ reaction repair plasticization: The regenerated nylon raw material treated in step S1 is added to the screw of an injection molding machine for plasticization, and a chain extension reaction component is added to the molten regenerated nylon during the plasticization process to make the regenerated nylon molecular chain undergo in-situ chain extension reaction; In the plasticization process, the screw torque signal or the melt pressure signal is collected in real time, and it is used as a criterion for the completion of molecular weight repair, and when the screw torque or melt pressure is stable in the preset interval, it is determined that the in-situ reaction repair is completed; S3, directional mold filling injection: After the in-situ reaction repair is completed, the molten regenerated nylon is injected into the mold cavity, and segmented injection speed is used for mold filling to make the molten regenerated nylon form directional orientation of molecular chains or reinforcing phases in the component main stress direction in the cavity; S4, closed loop pressure maintaining and feeding: During the injection molding process, the cavity pressure sensor arranged in the mold cavity is used to collect the cavity pressure signal in real time, and the cavity pressure signal is used as a feedback to close loop adjust the pressure maintaining switching point and pressure of the injection molding machine, so that the molten regenerated nylon in the cavity maintains a dense state in the feeding stage; S5, cooling and setting: The component is cooled and set under the condition of mold partition temperature control to obtain a super high strength regenerated nylon injection molded component.

2. The injection molding method of ultrahigh-strength recycled nylon components according to claim 1, characterized in that, In step S1, the dehumidification and drying is performed by vacuum dehumidification, the drying temperature is 80-95℃, and the drying time is 4-10 hours.

3. The injection molding method of ultrahigh-strength recycled nylon components according to claim 1, characterized in that, In step S2, the chain extension reaction component is a multifunctional epoxy chain extender and / or a carbodiimide chain extension stabilizer, and the addition amount is 0.2-1.5wt% of the mass of the regenerated nylon raw material.

4. The injection molding method of ultrahigh-strength recycled nylon components according to claim 1, characterized in that, The regenerated nylon is regenerated PA6 or regenerated PA66, when the regenerated nylon is regenerated PA6, the melt temperature in the plasticization stage in step S2 is controlled to be 235-255℃, and when the regenerated nylon is regenerated PA66, the melt temperature in the plasticization stage in step S2 is controlled to be 265-285℃.

5. The injection molding method of ultrahigh-strength recycled nylon components according to claim 1, characterized in that, In step S2, the vacuum devolatilization treatment is performed through the screw exhaust section, and the vacuum degree is-0.06 to-0.09MPa.

6. The injection molding method of ultrahigh-strength recycled nylon components according to claim 1, characterized in that, In step S3, the segmented injection speed includes a high-speed mold filling section and a low-speed feeding section, the high-speed mold filling section is used to improve the orientation degree of the molecular chains or reinforcing phases, and the low-speed feeding section is used to reduce the shear unevenness at the end of the cavity.

7. The injection molding method of ultrahigh-strength recycled nylon components according to claim 1, characterized in that, In step S5, the mold adopts a partition temperature control structure, wherein the mold temperature of the gate area is 90-130℃, and the mold temperature of the area away from the gate is 60-95℃.

8. The injection molding method of ultrahigh-strength recycled nylon components according to claim 1, characterized in that, The regenerated nylon raw material also contains a reinforcing component, the reinforcing component is short-cut glass fiber, basalt fiber or a combination thereof, the mass fraction of the reinforcing component is 10-45wt%, and a silane coupling agent is used to improve the interfacial bonding strength between the reinforcing component and the regenerated nylon matrix.

Images