Forming process and device of polylactic acid composite material

Abstract

The invention discloses a molding process and device of a polylactic acid composite material, and relates to the technical field of polylactic acid composite materials. The method specifically comprises a multi-stage temperature control and dynamic pressure maintaining crystallization stage which specifically comprises the following steps: a high-temperature crystallization stage: maintaining the temperature of a mold at 100-120 DEG C, and applying first-stage pressure maintaining pressure for 10-60 seconds; in a medium-temperature shaping period, the temperature of the mold is reduced to 80-95 DEG C; and a low-temperature cooling period. According to the preparation method, sufficient activity is provided for a PLA molecular chain segment in a high-temperature environment in the first-stage heat preservation stage, crystal nucleuses are rapidly formed and start to grow under the action of a nucleating agent, the crystallization process in the second-stage heat preservation stage continues to be carried out, but the movement ability of the molecular chain is weakened, and the crystallization rate is slowed down after reaching a peak value; the main effect is to stabilize the formed crystal structure and prevent the product from excessive shrinkage, the molecular chain is quickly frozen at the three-stage stage, the crystallization process is terminated, and the heat resistance of the product is improved.

Description

Technical Field

[0001] This invention relates to the field of polylactic acid composite materials technology, and more particularly to the molding process and apparatus for polylactic acid composite materials. Background Technology

[0002] Polylactic acid (PLA) is a biodegradable polyester derived from renewable resources such as corn and cassava. It has excellent biocompatibility, processability and mechanical properties, and is considered one of the most promising alternatives to traditional petroleum-based plastics.

[0003] In the prior art, such as the Chinese patent announcement number CN117962255A, a molding process and apparatus for polylactic acid composite materials are disclosed, including the following steps: Step 1: Prepare polylactic acid composite material masterbatch, which includes 80-85% starch, limestone and hydrated magnesium silicate, 10% polylactic acid base material, and 5-10% additives. The masterbatch is prepared by high-temperature stirring, room-temperature drying and dispersion, extrusion granulation and drying; Step 2: Inject into a temperature-controlled mold. The temperature-controlled mold is heated to the crystallization temperature of the polylactic acid composite material before and during injection. After injection, it is rapidly cooled to complete the plasticization of the product and demolding; Step 3: Repeat steps 1 and 2 according to production needs. The upper and lower molds of the polylactic acid composite material molding process apparatus are respectively equipped with cooling systems to cool the molds.

[0004] The aforementioned patent has the following shortcomings: it directly performs rapid cooling, and single-stage rapid cooling can lead to low crystallinity or no crystallization, which results in poor heat resistance of the product. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a molding process and apparatus for polylactic acid composite materials.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: Molding process of polylactic acid composite materials This includes a multi-stage temperature-controlled and dynamic pressure-holding crystallization stage, which specifically involves: S1: High-temperature crystallization period: Maintain the mold temperature at 100-120℃ and apply the first level of holding pressure for 10-60 seconds; S2: Medium temperature setting period: Reduce the mold temperature to 80-95℃ and apply a second-level holding pressure lower than the first-level holding pressure for 20-50 seconds; S3: Low-temperature cooling period: Cool the mold temperature to 30-50℃, release the holding pressure, and allow the product to set.

[0007] Preferably, in step S1, the holding pressure is 40-70 MPa, and in step S2, the holding pressure is 20-50 MPa.

[0008] A molding apparatus for polylactic acid composite materials includes a worktable, a lower die fixed to the top outer wall of the worktable, a gantry frame fixed to the top of the worktable by bolts, an upper punch that cooperates with the lower die being connected to the bottom of the gantry frame by a lifting assembly, and an injection port provided on one side of the top of the upper punch.

[0009] Based on the aforementioned scheme: temperature control channels are provided on the inner walls of both the lower die and the upper die. All temperature control channels are connected to form a passage through multiple pipes 1 and 2. A flow guide box 1 and a flow guide box 2 are fixed at both ends of the passage. A semiconductor cooler is fixed on the opposite side of the flow guide box 1 and the flow guide box 2. A storage component is connected to the other side of the flow guide box 1 and the flow guide box 2 through a pipe 3. A pump is installed on one of the pipes 3.

[0010] A better option among the aforementioned solutions is that the storage component stores a fluid heat exchange medium.

[0011] As a further aspect of the present invention: the storage component includes a storage box, heat-conducting pipes and a box cover. The box cover is fixed to the top of the storage box by bolts. Multiple heat-conducting pipes are fixedly embedded in the inner wall of the box cover. Energy storage phase change material is placed inside the heat-conducting pipes. The energy storage phase change material of one storage component is cold energy storage, and the energy storage phase change material of the other storage component is thermal energy storage.

[0012] Meanwhile, the heat pipe contains energy storage phase change material, and the energy storage phase change material of one of the storage components is cold energy storage, while the energy storage phase change material of the other storage component is thermal energy storage.

[0013] As a preferred embodiment of the present invention: the lifting assembly includes a guide rod and a telescopic device. The guide rod is fixed to the top outer wall of the upper punch by bolts and is slidably connected to the inner wall of the gantry frame. The telescopic device is fixed to the top outer wall of the telescopic device by bolts, and the telescopic end of the telescopic device is fixed to the top outer wall of the upper punch by bolts.

[0014] Meanwhile, the bottom inner wall of the lower die is fitted with a release plate, which is slidably connected to the lower die via a push rod.

[0015] As a preferred embodiment of the present invention: the outer wall of the top rod is movably fitted with a lifting block, the inner wall of the top rod is provided with a plurality of annular grooves, the inner wall of the lifting block is slidably connected with a limiting post that is movably limited by the limiting post, and the inner wall of the lifting block is threadedly connected with an adjusting bolt, and a spring is provided on the opposite side of the adjusting bolt and the limiting post.

[0016] The beneficial effects of this invention are as follows: 1. In the first stage of heat preservation, the high-temperature environment provides sufficient mobility for PLA molecular chain segments, which rapidly form crystal nuclei and begin to grow under the action of nucleating agents. In the second stage of heat preservation, the crystallization process continues, but the mobility of molecular chains is weakened, and the crystallization rate slows down after reaching its peak. Its main function is to stabilize the formed crystal structure and prevent the product from shrinking excessively. In the third stage, the molecular chains are rapidly frozen, the crystallization process is terminated, and the heat resistance of the product is improved.

[0017] 2. This invention uses a fluid heat exchange medium as a medium and a semiconductor cooler as a heating / cooling source, thereby enabling preheating of the lower die and upper punch before injection to prevent the molten product from solidifying rapidly and improve product quality. On the other hand, it enables rapid cooling at different stages, increasing the overall molding efficiency.

[0018] 3. In this invention, by setting the flow channel of the fluid heat exchange medium to a bidirectional circulation type, the heat carried away during cooling can be heated and stored by a semiconductor refrigerator, and the cold energy carried away during preheating can also be cooled and stored by a semiconductor refrigerator, thereby realizing the energy recovery function, ensuring the heating / cooling rate while also achieving a certain energy-saving effect.

[0019] 4. The present invention, by setting up an energy storage phase change material, can store cold / heat energy, which on the one hand increases the reliability of the entire energy cycle, and on the other hand prevents the loss of cold / heat energy caused by the high temperature difference between the fluid heat exchange medium in the storage component and the room temperature.

[0020] 5. The present invention, by setting up components such as demolding templates and ejector pins, can demold the molded product on the one hand, increasing molding efficiency, and on the other hand, can loosen the product by vibration during demolding and lifting, thereby preventing the product from being cracked or damaged during demolding and increasing product quality. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of the molding device for polylactic acid composite materials proposed in this invention; Figure 2 This is a schematic diagram of the cooling / heating section of the molding device for polylactic acid composite materials proposed in this invention; Figure 3 This is a schematic cross-sectional view of the lower die and upper punch of the molding device for polylactic acid composite materials proposed in this invention. Figure 4 This is a schematic diagram of the semiconductor cooler structure of the molding apparatus for polylactic acid composite materials proposed in this invention; Figure 5 This is a schematic diagram of the storage component structure of the molding device for polylactic acid composite materials proposed in this invention; Figure 6 This is a schematic diagram of the lifting component structure of the polylactic acid composite material molding device proposed in this invention; Figure 7 This is a schematic diagram of the demolding section of the molding device for polylactic acid composite materials proposed in this invention; Figure 8 The molding apparatus for polylactic acid composite materials proposed in this invention Figure 7 Enlarged structural diagram of section A.

[0022] In the diagram: 1. Workbench; 2. Lower die; 3. Upper punch; 4. Gantry frame; 5. Lifting assembly; 6. Pipeline 1; 7. Pipeline 2; 8. Flow guide box 1; 9. Pump; 10. Semiconductor cooler; 11. Storage assembly; 12. Pipeline 3; 13. Temperature control channel; 14. Flow guide box 2; 15. Storage tank; 16. Heat pipe; 17. Tank cover; 18. Guide rod; 19. Expansion joint; 20. Release plate; 21. Push rod; 22. Annular groove; 23. Lifting block; 24. Limiting post; 25. Spring; 26. Adjusting bolt. Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0024] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0025] Example 1: Molding process of polylactic acid composite material, which adopts injection molding, includes a multi-stage temperature control and dynamic pressure holding crystallization stage, specifically as follows: S1: High-temperature crystallization period: Maintain the mold temperature at 120℃ and apply the first level of holding pressure for 60 seconds; S2: Medium temperature setting period: Reduce the mold temperature to 95°C and apply a second-level holding pressure lower than the first-level holding pressure for 50 seconds; S3: Low-temperature cooling period: Cool the mold temperature to 50℃, release the holding pressure, and allow the product to set.

[0026] In step S1, the holding pressure is 70 MPa, and in step S2, the holding pressure is 50 MPa.

[0027] Example 2: Molding process of polylactic acid composite material, which adopts injection molding, including a multi-stage temperature control and dynamic pressure holding crystallization stage, specifically as follows: S1: High-temperature crystallization period: Maintain the mold temperature at 110℃ and apply the first level of holding pressure for 35 seconds; S2: Medium temperature setting period: Reduce the mold temperature to 85°C and apply a second-level holding pressure lower than the first-level holding pressure for 35 seconds; S3: Low temperature cooling period: Cool the mold temperature to 40℃, release the holding pressure, and allow the product to set.

[0028] In step S1, the holding pressure is 55 MPa, and in step S2, the holding pressure is 35 MPa.

[0029] Example 3: Molding process of polylactic acid composite material, which adopts injection molding, including a multi-stage temperature control and dynamic pressure holding crystallization stage, specifically as follows: S1: High-temperature crystallization period: Maintain the mold temperature at 100℃ and apply the first level of holding pressure for 10 seconds; S2: Medium-temperature setting period: Reduce the mold temperature to 80°C and apply a second-level holding pressure lower than the first-level holding pressure for 20 seconds; S3: Low temperature cooling period: Cool the mold temperature to 30℃, release the holding pressure, and allow the product to set.

[0030] In step S1, the holding pressure is 40 MPa, and in step S2, the holding pressure is 20 MPa.

[0031] In the first stage of heat preservation, the high-temperature environment provides sufficient mobility for PLA molecular chain segments, allowing crystal nuclei to form rapidly and begin to grow under the action of nucleating agents. In the second stage of heat preservation, the crystallization process continues, but the mobility of molecular chains is weakened, and the crystallization rate slows down after reaching its peak. Its main function is to stabilize the formed crystal structure and prevent excessive shrinkage of the product. In the third stage, the molecular chains are rapidly frozen, terminating the crystallization process and improving the heat resistance of the product.

[0032] Example 4: Molding apparatus for polylactic acid composite materials, such as Figures 1-8 As shown: It is used in the molding process of polylactic acid composite material in Examples 1-3. It includes a workbench 1, a lower die 2 fixed on the top outer wall of the workbench 1, a gantry frame 4 fixed to the top of the workbench 1 by bolts, and an upper punch 3 that cooperates with the lower die 2 is connected to the bottom of the gantry frame 4 by a lifting assembly 5. An injection port is provided on one side of the top of the upper punch 3.

[0033] Temperature-controlled flow channels 13 are provided on the inner walls of both the lower concave mold 2 and the upper convex mold 3. All temperature-controlled flow channels 13 are connected to form a passage through multiple pipes 1 6 and 2 7. At both ends of the passage, flow guide boxes 1 8 and 2 14 are fixed respectively. A semiconductor cooler 10 is fixed on the opposite side of flow guide boxes 1 8 and 2 14. The other side of flow guide boxes 1 8 and 2 14 is connected to a storage component 11 through a pipe 3 12. A pump 9 is installed on one of the pipes 3 12. The storage component 11 stores a fluid heat exchange medium.

[0034] In use, the device lowers the upper punch 3 via the lifting assembly 5, causing the lower die 2 and the upper punch 3 to engage. Then, driven by the pump 9, the fluid heat exchange medium in one of the storage components 11 is extracted. After being heated by the heating surface of the semiconductor cooler 10 via the flow guide box 8 or the storage component 11, it is transported to the flow channel between the lower die 2 and the upper punch 3, preheating both components. The preheated fluid heat exchange medium is then cooled by the cooling surface of the semiconductor cooler 10 via the storage component 11 or the flow guide box 8 before entering the other storage component 11. After the mold 3 is preheated, the molten raw material can be injected into the cavity of the lower die 2 and the upper punch 3 through the injection port. Under the three-stage heat preservation state, the pump 9 can be started in reverse to allow the cooling fluid heat exchange medium in the storage component 11 to pass through the storage component 11 or the flow guide box 18 and be cooled by the cooling surface of the semiconductor cooler 10 before entering the flow channel of the lower die 2 and the upper punch 3 to cool the lower die 2 and the upper punch 3. At the same time, the fluid heat exchange medium after absorbing heat from the lower die 2 and the upper punch 3 passes through the flow guide box 18 or the storage component 11 and is heated by the heating surface of the semiconductor cooler 10 before entering the storage component 11 for storage.

[0035] This device uses a fluid heat exchange medium and a semiconductor cooler 10 as a heating / cooling source. On the one hand, it can preheat the lower die 2 and the upper die 3 before injection to prevent the molten product from solidifying rapidly and increase product quality. On the other hand, it can rapidly cool down at different stages to increase the overall molding efficiency.

[0036] In addition, by setting the flow channel of the fluid heat exchange medium to a bidirectional circulation type, the heat carried away during cooling can be heated and stored by the semiconductor cooler 10, and the cold energy carried away during preheating can also be cooled and stored by the semiconductor cooler 10, thereby realizing the energy recovery function, ensuring the heating / cooling rate while also achieving a certain energy-saving effect.

[0037] The storage component 11 includes a storage box 15, heat pipes 16, and a box cover 17. The box cover 17 is fixed to the top of the storage box 15 by bolts. Multiple heat pipes 16 are fixedly embedded in the inner wall of the box cover 17. Energy storage phase change material is placed inside the heat pipes 16. The energy storage phase change material of one of the storage components 11 is cold energy storage, and the energy storage phase change material of the other storage component 11 is thermal energy storage.

[0038] This device, by incorporating energy storage phase change material, can store cold / heat energy. On the one hand, this increases the reliability of the entire energy cycle, and on the other hand, it prevents the loss of cold / heat energy caused by the high temperature difference between the fluid heat exchange medium in the storage component 11 and the room temperature.

[0039] The lifting assembly 5 includes a guide rod 18 and a telescopic device 19. The guide rod 18 is fixed to the top outer wall of the upper punch 3 by bolts, and the guide rod 18 is slidably connected to the inner wall of the gantry frame 4. The telescopic device 19 is fixed to the top outer wall of the telescopic device 19 by bolts, and the telescopic end of the telescopic device 19 is fixed to the top outer wall of the upper punch 3 by bolts.

[0040] When the telescoping device 19 extends or retracts, it can drive the upper punch 3 to rise or fall.

[0041] The bottom inner wall of the lower die 2 is fitted with a stripping template 20, which is slidably connected to the lower die 2 via a push rod 21.

[0042] The outer wall of the top rod 21 is movably fitted with a lifting block 23. The inner wall of the top rod 21 is provided with multiple annular grooves 22. The inner wall of the lifting block 23 is slidably connected with a limiting post 24 that is movably limited by the limiting post 24. The inner wall of the lifting block 23 is connected with an adjusting bolt 26 by a thread. A spring 25 is provided on the opposite side of the adjusting bolt 26 and the limiting post 24.

[0043] In this embodiment, the lifting drive method of the lifting block 23 is not limited. Another telescopic device 19 can be used for lifting drive, or the lifting block 23 can be directly fixed to the upper punch 3 through a connecting rod / bracket or other structure, and the lifting block 23 can be controlled by the lifting of the upper punch 3.

[0044] After molding is completed, the lower die 2 separates from the upper punch 3. At the same time, the lifting block 23 will rise relative to the ejector pin 21. Since the product will slightly adhere to the inner wall of the lower die 2 at this time, the product will restrict the rise of the ejector plate 20. Therefore, the lifting block 23 will slide relative to the ejector pin 21. During the sliding process, the limiting post 24 and multiple annular grooves 22 will continuously cooperate and separate, generating vibration. This is used to loosen the product during demolding until the product separates from the lower die 2 or the ejector pin 21 cooperates with the bottom inner wall of the lifting block 23. Through the cooperation resistance between the limiting post 24 and the annular groove 22, the lifting block 23 rises to drive the ejector pin 21 and the ejector plate 20 to rise, thus ejecting the product out of the mold.

[0045] This device, by setting up components such as the demolding plate 20 and the ejector rod 21, can demold the molded product on the one hand, increasing the molding efficiency, and on the other hand, it can also use vibration to loosen the product during demolding and lifting, thereby preventing the product from being cracked or damaged during demolding and increasing product quality.

[0046] In this embodiment, the upper punch 3 can be driven to descend via the telescopic device 19, causing the lower die 2 and the upper punch 3 to engage with each other. Then, driven by the pump 9, the fluid heat exchange medium in one of the storage components 11 is extracted, heated by the heating surface of the semiconductor cooler 10 after passing through the guide box 8 or the storage component 11, and then transported to the flow channel of the lower die 2 and the upper punch 3 to preheat the lower die 2 and the upper punch 3. The preheated fluid heat exchange medium is then cooled by the cooling surface of the semiconductor cooler 10 after passing through the storage component 11 or the guide box 8, and then enters the other storage component 11. After the lower die 2 and the upper punch 3 are preheated, the molten raw material can be injected into the cavity of the lower die 2 and the upper punch 3 through the injection port. Under the three-stage heat preservation state, the pump 9 can be reversed to start the cooling fluid heat exchange medium in the storage component 11 again after passing through the storage component 11 or the guide box 8 and being cooled by the cooling surface of the semiconductor cooler 10 before entering the lower die 2 and the upper punch 3. Inside the flow channel of mold 3, the lower die 2 and the upper punch 3 are cooled. At the same time, the heat exchange medium of the fluid after the lower die 2 and the upper punch 3 absorb heat is heated again by the heating surface of the semiconductor cooler 10 through the flow guide box 8 or the storage component 11 and then stored in the storage component 11. After molding is completed, the lower die 2 and the upper punch 3 are separated. At the same time, the lifting block 23 will also rise relative to the ejector pin 21. Since the product will slightly adhere to the inner wall of the lower die 2 at this time, the product will restrict the rise of the ejector plate 20. Therefore, the lifting block 23 will slide relative to the ejector pin 21. During the sliding process, the limiting post 24 and multiple annular grooves 22 will also continuously cooperate and separate, generating vibration. This is used to loosen the product for demolding until the product is separated from the lower die 2 or the ejector pin 21 cooperates with the bottom inner wall of the lifting block 23. Through the cooperation resistance between the limiting post 24 and the annular groove 22, the lifting block 23 rises to drive the ejector pin 21 and the ejector plate 20 to rise, thus ejecting the product out of the mold.

[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A molding process for polylactic acid composite materials, characterized in that, This includes a multi-stage temperature-controlled and dynamic pressure-holding crystallization stage, which specifically involves: S1: High-temperature crystallization period: Maintain the mold temperature at 100-120℃ and apply the first level of holding pressure for 10-60 seconds; S2: Medium temperature setting period: Reduce the mold temperature to 80-95℃ and apply a second-level holding pressure lower than the first-level holding pressure for 20-50 seconds; S3: Low-temperature cooling period: Cool the mold temperature to 30-50℃, release the holding pressure, and allow the product to set.

2. The molding process of the polylactic acid composite material according to claim 1, characterized in that, In step S1, the holding pressure is 40-70 MPa, and in step S2, the holding pressure is 20-50 MPa.

3. A molding apparatus for polylactic acid composite materials, applied to the molding process of polylactic acid composite materials according to any one of claims 1-2, characterized in that, It includes a workbench (1), a lower die (2) is fixed on the top outer wall of the workbench (1), a gantry frame (4) is fixed on the top of the workbench (1) by bolts, and an upper punch (3) that cooperates with the lower die (2) is connected to the bottom of the gantry frame (4) by a lifting assembly (5), and an injection port is provided on one side of the top of the upper punch (3).

4. The molding apparatus for polylactic acid composite materials according to claim 3, characterized in that, Temperature control channels (13) are provided on the inner walls of the lower die (2) and the upper punch (3). All temperature control channels (13) are connected to form a passage through multiple pipes (6) and pipes (7). At both ends of the passage, flow guide box (8) and flow guide box (14) are fixed respectively. A semiconductor cooler (10) is fixed on the opposite side of flow guide box (8) and flow guide box (14). The other side of flow guide box (8) and flow guide box (14) is connected to a storage component (11) through a pipe (3) (12) respectively. A pump (9) is installed on one of the pipes (3) (12).

5. The molding apparatus for polylactic acid composite materials according to claim 4, characterized in that, The storage component (11) stores a fluid heat exchange medium.

6. The molding apparatus for polylactic acid composite materials according to claim 4, characterized in that, The storage component (11) includes a storage box (15), heat pipes (16) and a box cover (17). The box cover (17) is fixed to the top of the storage box (15) by bolts. Multiple heat pipes (16) are fixedly embedded in the inner wall of the box cover (17). Energy storage phase change material is placed inside the heat pipes (16). The energy storage phase change material of one of the storage components (11) is cold energy storage, and the energy storage phase change material of the other storage component (11) is thermal energy storage.

7. The molding apparatus for polylactic acid composite materials according to claim 6, characterized in that, The heat pipe (16) contains an energy storage phase change material, and the energy storage phase change material of one of the storage components (11) is cold energy storage, while the energy storage phase change material of the other storage component (11) is thermal energy storage.

8. The molding apparatus for polylactic acid composite materials according to claim 3, characterized in that, The lifting assembly (5) includes a guide rod (18) and a telescopic device (19). The guide rod (18) is fixed to the top outer wall of the upper punch (3) by bolts, and the guide rod (18) is slidably connected to the inner wall of the gantry frame (4). The telescopic device (19) is fixed to the top outer wall of the telescopic device (19) by bolts, and the telescopic end of the telescopic device (19) is fixed to the top outer wall of the upper punch (3) by bolts.

9. The molding apparatus for polylactic acid composite materials according to claim 3, characterized in that, The bottom inner wall of the lower die (2) is fitted with a stripper plate (20), which is slidably connected to the lower die (2) via a push rod (21).

10. The molding apparatus for polylactic acid composite materials according to claim 9, characterized in that, The outer wall of the top rod (21) is movably fitted with a lifting block (23), and the inner wall of the top rod (21) is provided with multiple annular grooves (22). The inner wall of the lifting block (23) is slidably connected with a limiting post (24) that is movably limited by the limiting post (24). The inner wall of the lifting block (23) is connected with an adjusting bolt (26) by a thread. A spring (25) is provided on the opposite side of the adjusting bolt (26) and the limiting post (24).

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