Injection molding method of ultra-high molecular weight polyethylene

Abstract

The invention relates to an injection molding method of ultra-high molecular weight polyethylene, and relates to the technical field of macromolecules, and the injection molding method comprises the following steps: plasticizing ultra-high molecular weight polyethylene resin, and then injecting the plasticized ultra-high molecular weight polyethylene into a mold cavity of a preheated mold with a movable template; after the mold is cooled to a first preset temperature, pressure is applied to the movable mold plate, secondary cooling is conducted to a second preset temperature, the constant-temperature and constant-pressure state is maintained, and crystallization of the ultra-high molecular weight polyethylene is promoted; and continuously cooling until the ultra-high molecular weight polyethylene is completely shaped, and opening the mold to obtain the ultra-high molecular weight polyethylene product. Injection molding of the pure ultra-high molecular weight polyethylene is achieved through process optimization, damage of external auxiliaries to mechanical properties of the product is avoided fundamentally, meanwhile, the purity of the product is guaranteed, and the application boundary of the ultra-high molecular weight polyethylene product is expanded.

Description

Technical Field

[0001] This application relates to the field of polymer technology, specifically to an injection molding method for ultra-high molecular weight polyethylene. Background Technology

[0002] Ultra-high molecular weight polyethylene (UHMWPE) possesses superior properties such as wear resistance, impact resistance, self-lubrication, corrosion resistance, and low-temperature resistance. It also boasts advantages such as being hygienic and non-toxic, non-adhesive, low-absorption, and low-density. It is widely recognized as an engineering plastic with exceptionally high comprehensive performance and is extensively used in textiles, papermaking, food, chemicals, agriculture, mining, construction, medical, sports, and military industries. However, its melt viscosity is as high as 10... 8 The extremely low Pa·s results in a very low critical shear rate, making it prone to defects such as melt fracture during processing. Conventional polymer processing methods are insufficient to mold ultra-high molecular weight polyethylene products, which greatly limits its application.

[0003] In related technologies, the processing fluidity of ultra-high molecular weight polyethylene (UHMWPE) is mainly based on the addition of small molecule substances or low molecular weight polymers. For example, Chinese patent CN1191230A prepares products with high fluidity by adding liquid crystal polymers and other additives to UHMWPE, but the high price of liquid crystal polymers significantly restricts the market promotion of this technology. Chinese patent CN1244626C obtains products that can be injection molded and extruded by adding a certain amount of polypropylene and other additives and then melt-blending and granulating them at high temperature. Although this reduces the processing viscosity, the poor compatibility between polypropylene and UHMWPE leads to a significant decline in the mechanical properties of the products. Chinese patent CN106317547A introduces high-density polyethylene, long-chain branched polyethylene and other additives for high-temperature melt-blending and granulation. The product can be adapted to various molding processes such as compression molding, extrusion and injection molding. However, the addition of excessive additives not only reduces the mechanical properties of the products, but also increases the preparation cost.

[0004] The aforementioned technologies generally suffer from compromised mechanical properties due to small molecules or low molecular weight polymers, and cannot meet the specific requirements for pure ultra-high molecular weight polyethylene in medical applications (such as ultra-high molecular weight polyethylene artificial joints). Meanwhile, the market demand for pure ultra-high molecular weight polyethylene products with excellent mechanical properties continues to increase, thus necessitating a pure ultra-high molecular weight polyethylene injection molding technology to meet market demands. Summary of the Invention

[0005] To address the problem that existing flow aid modification technologies often lead to a decrease in the mechanical properties of ultra-high molecular weight polyethylene (UHMWPE) products and fail to meet the pure material injection molding requirements of medical and other applications, this application proposes an injection molding method for UHMWPE, employing the following technical solution: An injection molding method for ultra-high molecular weight polyethylene includes the following steps: Step 1: Plasticize the ultra-high molecular weight polyethylene resin, and then inject the plasticized ultra-high molecular weight polyethylene into the mold cavity of a preheated mold with a movable template. Step 2: After cooling the mold to the first preset temperature, apply pressure to the movable template, then cool it down again to the second preset temperature and maintain a constant temperature and pressure state to promote the crystallization of ultra-high molecular weight polyethylene. Step 3: Continue cooling until the ultra-high molecular weight polyethylene is fully set, then open the mold to obtain the ultra-high molecular weight polyethylene product.

[0006] By adopting the above technical solution, this application does not require the addition of any flow modifier. Utilizing the synergistic process of "plasticization-segmented cooling and pressurization-constant temperature and pressure crystallization," the problem of insufficient density of ultra-high molecular weight polyethylene (UHMWPE) caused by insufficient flow during injection is eliminated by pressurizing the movable template in the mold. Moreover, UHMWPE can fully crystallize under constant temperature and pressure conditions, which can well maintain the mechanical properties of UHMWPE. This not only solves the processing pain points of high melt viscosity and difficult filling of UHMWPE, but also achieves a dual improvement in mechanical properties and dimensional stability through crystal structure optimization, while ensuring product purity. Therefore, it is suitable for medical and other scenarios that require high purity of UHMWPE products.

[0007] Preferably, the viscosity-average molecular weight of the ultra-high molecular weight polyethylene resin is 1.0 × 10⁻⁶. 6 -1.2×10 7 g / mol.

[0008] By adopting the above technical solution, this molecular weight range balances the processing fluidity and mechanical properties of ultra-high molecular weight polyethylene. When the molecular weight is too low, the core properties of ultra-high molecular weight polyethylene, such as wear resistance and impact resistance, are insufficient; when the molecular weight is too high, the melt viscosity of ultra-high molecular weight polyethylene may exceed the processing capacity of the injection molding machine, resulting in incomplete plasticization and non-dense products. Therefore, after extensive experimental verification, the applicant has determined that the molecular weight of the ultra-high molecular weight polyethylene resin in this application is preferably as described above.

[0009] Preferably, in step 1, the plasticizing temperature and the temperature of the melt passing through the injection nozzle are both 180-290°C.

[0010] By adopting the above technical solution, when the temperature is too low, the plasticization of ultra-high molecular weight polyethylene resin is incomplete, making it difficult to obtain sufficient fluidity for injection molding; when the temperature is too high, ultra-high molecular weight polyethylene is prone to degradation, resulting in a significant decrease in the mechanical properties of ultra-high molecular weight polyethylene products; therefore, the applicant has verified through a large number of experiments that the plasticizing temperature and the temperature of the melt passing through the injection nozzle in this application are both preferably as described above.

[0011] Preferably, the plasticizing temperature and the temperature of the melt passing through the nozzle during injection molding are both 180-220°C.

[0012] By adopting the above technical solution, within the above temperature range, the folded chain crystals of ultra-high molecular weight polyethylene resin are fully melted, while some extended chain crystals are retained. This allows ultra-high molecular weight polyethylene to have a certain fluidity while reducing the high-temperature degradation of ultra-high molecular weight polyethylene. Furthermore, the retained extended chain crystals can well maintain the mechanical properties of ultra-high molecular weight polyethylene products.

[0013] Preferably, in step 1, the preheating temperature of the mold is 130-210℃.

[0014] By adopting the above technical solution, a reasonable gradient is formed between the mold temperature and the melt temperature, which can prevent the melt from cooling and solidifying rapidly after contacting the mold wall. This ensures that the melt flows fully and vents air in the mold cavity, allowing the plasticized ultra-high molecular weight polyethylene to fill the mold cavity. This reduces defects such as material shortage and weld lines, creating conditions for densification under subsequent pressure.

[0015] Preferably, in step 2, the first preset temperature is 120-160℃.

[0016] By adopting the above technical solution, within the above temperature range, ultra-high molecular weight polyethylene is in the transition range between the high elastic state and the crystalline state. The material has good plastic deformation ability. At this time, applying pressure can effectively compact the melt, increase the density of the product, and avoid internal defects caused by crystallization shrinkage.

[0017] Preferably, in step 2, the pressure applied to the movable template is 0.5-10 MPa.

[0018] By adopting the above technical solution, the low-pressure action can effectively avoid shear fracture of the high-elastic melt, while accurately expelling residual gas from the mold cavity, providing a uniform matrix structure for subsequent crystallization optimization.

[0019] Preferably, in step 2, the second preset temperature is 85-120℃, and the constant pressure after the second cooling is 2-50MPa.

[0020] By adopting the above technical solution, the temperature range is within the stable crystallization range below the melting point of ultra-high molecular weight polyethylene. At this temperature, the ultra-high molecular weight polyethylene molecular chains maintain a moderate degree of mobility, which can both get rid of the disordered entanglement of the melt state and arrange themselves in an orderly manner to form a crystal structure, so that ultra-high molecular weight polyethylene can crystallize fully.

[0021] The aforementioned constant pressure range effectively compacts the melt during the crystallization process, promoting crystal densification and orientation, thereby improving crystallinity and crystal integrity. Simultaneously, the constant pressure also promotes uniform shrinkage of the product, preventing warping after demolding. The second preset temperature and constant pressure work together to create an optimized crystallization environment, better improving the mechanical properties of ultra-high molecular weight polyethylene (UHMWPE) products and maintaining their dimensional stability.

[0022] Preferably, the duration of the constant temperature and pressure state is 10-300 min.

[0023] By adopting the above technical solution, if the isothermal and pressure time is too short, the crystallization may be incomplete, resulting in a large number of defects in the crystal structure, making it difficult to improve mechanical properties and dimensional stability; if the isothermal and pressure time is too long, it may exceed the reasonable upper limit of balancing crystallization effect and production efficiency, resulting in energy waste and decreased production efficiency. Therefore, after extensive experimental verification, the applicant believes that the maintenance time of the isothermal and pressure state in this application is as described above.

[0024] Preferably, in step 1, the antioxidant and ultra-high molecular weight polyethylene resin are blended and then plasticized together.

[0025] By adopting the above technical solutions, antioxidants can inhibit thermal oxidation reactions that may occur during plasticization and cooling, reduce molecular chain breakage and oxidation product generation, further improve the molecular weight stability of the product, and thus avoid the decline in mechanical properties caused by local oxidative degradation.

[0026] In summary, this application has the following beneficial effects: This application abandons the existing technology's reliance on small molecule substances or low molecular weight polymers as flow modifiers. Through process optimization, it achieves injection molding of pure ultra-high molecular weight polyethylene, fundamentally avoiding the damage to the mechanical properties of the product caused by external additives, while ensuring the purity of the product. This allows the prepared ultra-high molecular weight polyethylene products to be precisely matched to scenarios such as medical artificial joints, which have stringent requirements for material purity and mechanical properties, thus expanding the application boundaries of ultra-high molecular weight polyethylene products. This application constructs a full-process synergistic process of "plasticization-filling-densification-crystallization" by precisely controlling the plasticizing temperature, mold preheating temperature, segmented cooling nodes and pressure parameters. It not only solves the processing problems such as insufficient filling and melt fracture caused by the high melt viscosity and low critical shear rate of ultra-high molecular weight polyethylene, but also effectively eliminates the voids and gas residues inside the product and improves the density of the product by segmented pressurization strategy of low-pressure venting and high-pressure crystallization, laying a structural foundation for subsequent performance optimization. This application utilizes precise plasticizing temperature to retain some extended chain crystals, combined with full crystallization under constant temperature and pressure conditions. This not only maximizes the retention of the excellent core mechanical properties of ultra-high molecular weight polyethylene, such as wear resistance and impact resistance, but also achieves performance upgrades through optimization of the crystal structure. At the same time, the constant temperature and pressure process promotes uniform shrinkage of the product, effectively avoiding warping deformation after demolding and significantly improving the dimensional stability of the product. Detailed Implementation

[0027] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0028] Example 1 An injection molding method for ultra-high molecular weight polyethylene includes the following steps: Step 1: The viscosity-average molecular weight is 6.0 × 10⁻⁶. 6 g / mol of ultra-high molecular weight polyethylene resin is added to a screw injection molding machine, and the plasticizing temperature is set to 200℃ for plasticizing. Then, the plasticized ultra-high molecular weight polyethylene is injected into the mold cavity of a preheated mold with a movable template. During injection, the temperature of the melt through the nozzle is 200℃, and the preheating temperature of the mold is 180℃. Step 2: After cooling the mold to the first preset temperature of 140°C, apply a pressure of 5MPa to the movable template, then cool it down to the second preset temperature of 100°C and maintain a constant temperature and pressure of 100°C and 25MPa for 150 minutes to promote the crystallization of ultra-high molecular weight polyethylene. Step 3: Continue cooling until the ultra-high molecular weight polyethylene is fully set, then open the mold to obtain the ultra-high molecular weight polyethylene product.

[0029] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that in step 1, the mold with a movable template is replaced with a mold without a movable template for injection molding.

[0030] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that in step 2, the first cooling is not performed, and the mold is directly cooled to the second preset temperature of 100°C.

[0031] The mechanical properties and crystallinity of the ultra-high molecular weight polyethylene injection molded products prepared in Example 1 and Comparative Examples 1-2 were tested, and the specific testing methods are as follows.

[0032] Detection method: (1) Crystallinity Five to ten milligrams of ultra-high molecular weight polyethylene (UHMWPE) product were weighed and placed in a standard aluminum crucible under a dry nitrogen atmosphere. The thermal properties of the UHMWPE product were tested using a DSC8000 differential scanning calorimeter (DSC, Pekin Elmer, USA). The temperature was increased from 25°C to 200°C at a rate of 10°C / min, and the thermal property curves were recorded. The crystallinity of different samples was calculated from the enthalpy of fusion measured by DSC.

[0033] Among them, X c The crystallinity of the product; ∆H m ∆H0 represents the enthalpy of fusion calculated based on the DSC curve results; ∆H0 represents the standard enthalpy of fusion when polyethylene is fully crystallized. According to the industry standard SH / T 1826-2019 "Determination of enthalpy of fusion, crystallinity and melting temperature of plastic ultra-high molecular weight polyethylene (PE-UHMW) materials and products by differential scanning calorimetry (DSC)" (see section 10.1.3 of the original text, "Currently reported theoretical melting value of 100% crystallized polyethylene is 293.0 kJ / kg, while the previously commonly used theoretical melting value of 100% crystallization is 289.3 kJ / kg"), the standard enthalpy of fusion of polyethylene is 293 J / g.

[0034] (2) Impact strength Each sample was cut to a size of 80×10×4mm using a milling machine. 3 Given the excellent impact performance of ultra-high molecular weight polyethylene (UHMWPE) products, impact testing using conventional standard notched specimens is extremely difficult. Therefore, the unidirectional notch depth of the specimen was determined to be 8.5 mm, and other conditions remained in accordance with GB / T1043-2018 standards. A GT-7045-HMH digital impact testing machine (Gatewell Testing Instruments Co., Ltd.) was used for simply supported beam impact testing. To accurately calculate the impact strength, the width and thickness of the cross-section of each specimen were measured and recorded before and after impact. Five specimens were selected for testing in each group, and the average value was calculated. Impact strength α k Calculate using the following formula:

[0035] In the formula, A k d represents the energy absorbed by the notched sample, in J; b represents the sample width, in mm; k This represents the remaining thickness at the notch in the sample, in mm.

[0036] (3) Tensile strength Tensile strength was tested using a BHTMS-002 universal testing machine (MTS, USA) according to GB / T 1040.1-2018 standard. Each specimen was cut to size 70*15*2 mm using a milling machine, and the tensile speed was 50 mm / min. At least five samples were used for each product to obtain the average value and standard deviation.

[0037] (4) Coefficient of friction A finely machined specimen suitable for friction and wear testing was prepared, with a specimen size of 20×20×5 mm. The friction coefficient was determined using a UMT-3 multifunctional high-temperature friction and wear testing machine, with alumina (Al2O3) grinding balls selected as the grinding material. Each specimen underwent three independent repeated experiments. Before starting the experiment, the specimen surface was first cleaned with anhydrous ethanol, and the Al2O3 grinding balls were ultrasonically treated in anhydrous ethanol for 3 minutes, followed by drying in an oven for 10 minutes. The experiment was conducted under dry friction conditions, with the friction direction along the flow field direction, a load of 10 N, a frequency of 2 Hz, and a total experimental duration of 30 minutes.

[0038] The test results of Example 1 and Comparative Examples 1-2 obtained according to the above detection method are shown in Table 1 below.

[0039] Table 1 Performance test results for Example 1 and Comparative Examples 1-2

[0040] Conclusion 1: By comparing the test results of Example 1 and Comparative Examples 1-2, it can be concluded that using a mold with a movable template and a synergistic process of "segmented cooling and pressurization - constant temperature and pressure crystallization" effectively eliminates the problem of insufficient density caused by high melt viscosity and insufficient flow of ultra-high molecular weight polyethylene by applying pressure to the movable template, enabling it to be successfully injection molded. On the other hand, by first cooling to the first preset temperature and then pressurizing, and then cooling to the second preset temperature and maintaining constant temperature and pressure, a sufficient and stable crystallization environment is provided for ultra-high molecular weight polyethylene, promoting its full crystallization and thus maintaining the mechanical properties of ultra-high molecular weight polyethylene well.

[0041] Example 2 The only difference between Example 2 and Example 1 is that the viscosity-average molecular weight of the ultra-high molecular weight polyethylene resin is 1.0 × 10⁻⁶. 6 g / mol.

[0042] Example 3 The only difference between Example 3 and Example 1 is that the viscosity-average molecular weight of the ultra-high molecular weight polyethylene resin is 1.2 × 10⁻⁶. 7 g / mol.

[0043] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that the viscosity-average molecular weight of the ultra-high molecular weight polyethylene resin is 1.5 × 10⁻⁶. 7 g / mol.

[0044] Based on the above detection method, the test results of Examples 2-3 and Comparative Example 3 are shown in Table 2 below.

[0045] Table 2 Performance test results for Examples 1-3 and Comparative Example 3

[0046] Conclusion 2: A comparison of the test results from Examples 1-3 and Comparative Example 3 shows that when the molecular weight of ultra-high molecular weight polyethylene resin is 1.0 × 10⁻⁶, the desired effect is achieved. 6 -1.2×10 7 At g / mol, not only can smooth plasticization and injection molding be achieved, but the product can also maintain ideal crystallinity and exhibit excellent mechanical properties. It successfully balances the processing fluidity and mechanical properties of ultra-high molecular weight polyethylene, providing a reliable guarantee for products that have both processing feasibility, high purity and excellent mechanical properties.

[0047] Example 4 The only difference between Example 4 and Example 1 is that the plasticizing temperature and the temperature of the melt passing through the injection nozzle in step 1 are both 180°C.

[0048] Example 5 The only difference between Example 5 and Example 1 is that the plasticizing temperature and the temperature of the melt passing through the injection nozzle in step 1 are both 220°C.

[0049] Example 6 The only difference between Example 6 and Example 1 is that the plasticizing temperature and the temperature of the melt passing through the injection nozzle in step 1 are both 290°C.

[0050] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that the plasticizing temperature and the temperature of the melt passing through the injection nozzle in step 1 are both 160°C.

[0051] Comparative Example 5 The only difference between Comparative Example 5 and Example 1 is that the plasticizing temperature and the temperature of the melt passing through the injection nozzle in step 1 are both 300°C.

[0052] Based on the above detection method, the test results of Examples 4-6 and Comparative Examples 4-5 are shown in Table 3 below.

[0053] Table 3 Performance test results for Examples 1, 4-6, and Comparative Examples 4-5

[0054] Conclusion 3: A comparison of the test results from Examples 1, 4-6, and Comparative Examples 4-5 shows that when the plasticizing temperature and the temperature of the melt passing through the injection nozzle are between 180-290°C, it can ensure that the ultra-high molecular weight polyethylene resin is fully plasticized, achieving the fluidity required for injection molding and enabling smooth injection molding. Simultaneously, it effectively avoids resin degradation caused by excessively high temperatures, ensuring that the core mechanical properties of the product, such as crystallinity, impact strength, and tensile strength, remain stable. In particular, when the plasticizing temperature and the temperature of the melt passing through the injection nozzle are between 180-220°C, the folded chain crystals of the ultra-high molecular weight polyethylene resin can fully melt, while retaining some extended chain crystals. This further reduces the risk of high-temperature degradation and maintains good processing fluidity. Furthermore, the retained extended chain crystals significantly improve the mechanical properties of the product, resulting in superior crystallinity and mechanical properties.

[0055] Example 7 The only difference between Example 7 and Example 1 is that the preheating temperature of the mold in step 1 is 130°C.

[0056] Example 8 The only difference between Example 8 and Example 1 is that the preheating temperature of the mold in step 1 is 210°C.

[0057] Comparative Example 6 The only difference between Comparative Example 6 and Example 1 is that the preheating temperature of the mold in step 1 is 120°C.

[0058] Comparative Example 7 The only difference between Comparative Example 7 and Example 1 is that the preheating temperature of the mold in step 1 is 220°C.

[0059] The test results of Examples 7-8 and Comparative Examples 6-7 obtained according to the above detection method are shown in Table 4 below.

[0060] Table 4 Performance test results for Examples 1, 7-8, and Comparative Examples 6-7

[0061] Conclusion 4: By comparing the test results of Examples 1, 7-8, and Comparative Examples 6-7, it can be concluded that when the preheating temperature of the mold is between 130-210℃, a reasonable temperature gradient can be formed with the plasticized ultra-high molecular weight polyethylene melt. This effectively avoids the melt from rapidly cooling and solidifying after contacting the mold wall, ensuring that the melt flows fully in the mold cavity and vents smoothly, thus ensuring that it completely fills the mold cavity and reducing the occurrence of processing defects such as material shortage and weld lines. At the same time, it creates good conditions for the densification of the product during the subsequent segmented cooling and pressurization process, ultimately enabling the product to be successfully injection molded with uniform and stable crystallinity and excellent mechanical properties.

[0062] Example 9 The only difference between Example 9 and Example 1 is that, in step 2, the first preset temperature is 120°C.

[0063] Example 10 The only difference between Example 10 and Example 1 is that in step 2, the first preset temperature is 160°C.

[0064] Comparative Example 8 The only difference between Comparative Example 8 and Example 1 is that, in step 2, the first preset temperature is 110°C.

[0065] Comparative Example 9 The only difference between Comparative Example 9 and Example 1 is that, in step 2, the first preset temperature is 180°C.

[0066] The test results of Examples 9-10 and Comparative Examples 8-9 obtained according to the above detection method are shown in Table 5 below.

[0067] Table 5 Performance test results for Examples 1, 9-10, and Comparative Examples 8-9

[0068] Conclusion 5: By comparing the test results of Examples 1, 9-10, and Comparative Examples 8-9, it can be concluded that when the first preset temperature is between 120-160℃, ultra-high molecular weight polyethylene can be in the transition range between the high elastic state and the crystalline state, and has good plastic deformation ability. At this time, applying pressure to the movable template can effectively compact the melt, significantly improve the density of the product, and avoid internal defects caused by crystallization shrinkage, thereby preparing ultra-high molecular weight polyethylene injection molded products with uniform crystallinity and excellent mechanical properties.

[0069] Example 11 The only difference between Example 11 and Example 1 is that the pressure applied to the movable template in step 2 is 0.5 MPa.

[0070] Example 12

[0071] The only difference between Example 12 and Example 1 is that the pressure applied to the movable template in step 2 is 10 MPa.

[0072] Comparative Example 10 The only difference between Comparative Example 10 and Example 1 is that the pressure applied to the movable template in step 2 is 0.1 MPa.

[0073] Comparative Example 11 The only difference between Comparative Example 11 and Example 1 is that the pressure applied to the movable template in step 2 is 12 MPa.

[0074] The test results of Examples 11-12 and Comparative Examples 10-11 obtained according to the above detection method are shown in Table 6 below.

[0075] Table 6 Performance test results for Examples 1, 11-12 and Comparative Examples 10-11

[0076] Conclusion 6: A comparison of the test results from Examples 1 and 11-12, as well as Comparative Examples 10-11, reveals that when the pressure applied to the movable template is too low, Comparative Example 10 fails to effectively expel gas and compact the melt due to insufficient pressure, resulting in insufficient product density, increased internal voids, and a significant decrease in crystal quality and mechanical properties. Conversely, when the pressure applied to the movable template is too high, Comparative Example 11 experiences shear fracture of the highly elastic melt due to excessive pressure, leading to internal defects. This not only affects the integrity of the product molding but also damages the crystalline structure, resulting in a significant decline in mechanical properties. The preferred pressure applied in this application, 0.5-10 MPa, provides crucial support for ensuring the molding quality, density, and excellent mechanical properties of ultra-high molecular weight polyethylene products.

[0077] Example 13 The only difference between Example 13 and Example 1 is that the second preset temperature in step 2 is 85°C, and the constant pressure after the second cooling is 50MPa.

[0078] Example 14 The only difference between Example 14 and Example 1 is that the second preset temperature in step 2 is 120°C, and the constant pressure after the second cooling is 2MPa.

[0079] Comparative Example 12 The only difference between Comparative Example 12 and Example 1 is that the second preset temperature in step 2 is 70°C, and the constant pressure after the second cooling is 60 MPa.

[0080] Comparative Example 13 The only difference between Comparative Example 13 and Example 1 is that the second preset temperature in step 2 is 130°C and the constant pressure after the second cooling is 1 MPa.

[0081] The test results of Examples 13-14 and Comparative Examples 12-13 obtained according to the above detection method are shown in Table 7 below.

[0082] Table 7 Performance test results for Examples 1, 13-14 and Comparative Examples 12-13

[0083] Conclusion 7: A comparison of the test results from Examples 1, 13-14, and Comparative Examples 12-13 shows that when the second preset temperature is between 85-120℃ and the constant pressure after the second cooling is between 2-50MPa, the two factors can synergistically construct an optimized crystallization environment. The molecular chains of ultra-high molecular weight polyethylene maintain moderate mobility, allowing them to break free from disordered entanglement and arrange themselves in an orderly manner to form a crystal structure, achieving full crystallization. Simultaneously, the melt during crystallization can be effectively compacted, promoting crystal densification and orientation, improving crystallinity and crystal integrity, and resulting in uniform shrinkage of the product, effectively preventing warping after demolding. Therefore, the prepared ultra-high molecular weight polyethylene product exhibits high crystallinity, stable structure, excellent mechanical properties such as impact strength and tensile strength, and good dimensional stability.

[0084] Example 15 The only difference between Example 15 and Example 1 is that the constant temperature and pressure state in step 2 is maintained for 10 minutes.

[0085] Example 16 The only difference between Example 16 and Example 1 is that the constant temperature and pressure state in step 2 is maintained for 300 minutes.

[0086] Comparative Example 14 The only difference between Comparative Example 14 and Example 1 is that the isothermal and pressure-controlled state in step 2 is maintained for 5 minutes.

[0087] Comparative Example 15 The only difference between Comparative Example 15 and Example 1 is that the isothermal and pressure-controlled state in step 2 was maintained for 380 minutes.

[0088] Based on the above detection method, the test results of Examples 15-16 and Comparative Examples 14-15 are shown in Table 8 below.

[0089] Table 8 Performance test results for Examples 1, 15-16 and Comparative Examples 14-15

[0090] Conclusion 8: By comparing the test results of Examples 1, 15-16, and Comparative Examples 14-15, it can be concluded that when the constant temperature and pressure is maintained for 10-300 min, sufficient and reasonable crystallization time can be provided for ultra-high molecular weight polyethylene. This ensures that it crystallizes fully, forms a regular crystal structure, reduces crystal defects, and thus ensures that the product has excellent mechanical properties such as crystallinity, impact strength, and tensile strength, as well as good dimensional stability. At the same time, it can also take into account the crystallization effect and production efficiency, and avoid energy waste.

[0091] Example 17 The only difference between Example 17 and Example 1 is that the antioxidant and ultra-high molecular weight polyethylene resin are added together to a high-speed mixer for mechanical blending. The mixer speed is set to 2000 r / min, the mixing temperature is 25°C, and the mixing time is 15 min, until the materials are mixed evenly. After obtaining the mixture, the mixture is added to a screw injection molding machine for plasticizing. The antioxidant content in the mixture is 0.3wt% (0.1-0.5wt% is acceptable); The antioxidant used is a commercially available product of antioxidant 1010.

[0092] Example 18 The only difference between Example 18 and Example 17 is that the antioxidant used is a commercially available product of antioxidant 1076.

[0093] Based on the above detection method, the test results of Examples 17-18 are shown in Table 9 below.

[0094] Table 9 Performance test results for Examples 1 and 17-18

[0095] Conclusion 9: A comparison of the test results of Examples 1 and 17-18 shows that adding antioxidants to ultra-high molecular weight polyethylene resin and then blending and plasticizing it does not affect the smooth progress of injection molding, and the crystallinity of the product can be maintained at a stable level comparable to that of Example 1 without antioxidants. At the same time, antioxidants can effectively inhibit the thermal oxidation reaction that occurs during plasticization and cooling, reduce the breakage of ultra-high molecular weight polyethylene molecular chains and the generation of oxidation products, and significantly improve the stability of the molecular weight of the product, thereby avoiding the decline in mechanical properties caused by local oxidative degradation. As a result, the mechanical properties of the ultra-high molecular weight products of Examples 17-18 are better than those of Example 1.

[0096] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for injection molding ultra-high molecular weight polyethylene, characterized in that, Includes the following steps: Step 1: Plasticize the ultra-high molecular weight polyethylene resin, and then inject the plasticized ultra-high molecular weight polyethylene into the mold cavity of a preheated mold with a movable template. Step 2: After cooling the mold to the first preset temperature, apply pressure to the movable template, then cool it down again to the second preset temperature and maintain a constant temperature and pressure state to promote the crystallization of ultra-high molecular weight polyethylene. Step 3: Continue cooling until the ultra-high molecular weight polyethylene is fully set, then open the mold to obtain the ultra-high molecular weight polyethylene product.

2. The injection molding method for ultra-high molecular weight polyethylene according to claim 1, characterized in that: The viscosity-average molecular weight of the ultra-high molecular weight polyethylene resin is 1.0 × 10⁻⁶. 6 -1.2×10 7 g / mol.

3. The injection molding method for ultra-high molecular weight polyethylene according to claim 1, characterized in that: In step 1, the plasticizing temperature and the temperature of the melt passing through the injection nozzle are both 180-290℃.

4. The injection molding method for ultra-high molecular weight polyethylene according to claim 3, characterized in that: The plasticizing temperature and the temperature of the melt passing through the nozzle during injection molding are both 180-220℃.

5. The injection molding method for ultra-high molecular weight polyethylene according to claim 1, characterized in that: In step 1, the preheating temperature of the mold is 130-210℃.

6. The injection molding method for ultra-high molecular weight polyethylene according to claim 1, characterized in that: In step 2, the first preset temperature is 120-160℃.

7. The injection molding method for ultra-high molecular weight polyethylene according to claim 6, characterized in that: In step 2, the pressure applied to the movable template is 0.5-10 MPa.

8. The injection molding method for ultra-high molecular weight polyethylene according to claim 1, characterized in that: In step 2, the second preset temperature is 85-120℃, and the constant pressure after the second cooling is 2-50MPa.

9. The injection molding method for ultra-high molecular weight polyethylene according to claim 8, characterized in that: The duration of the constant temperature and pressure state is 10-300 min.

10. The injection molding method for ultra-high molecular weight polyethylene according to claim 1, characterized in that: In step 1, the antioxidant and ultra-high molecular weight polyethylene resin are blended together and then plasticized.

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