A process for the preparation of thermoplastic polyurethane elastomers

Abstract

The application provides a thermoplastic polyurethane elastomer preparation method and belongs to the technical field of thermoplastic polyurethane elastomer preparation. The steps are as follows: S1, raw material drying: thermoplastic polyurethane particles are dried in a vacuum drying box at 85-100 DEG C for 4-6h, so that the water content is less than or equal to 0.08%; S2, modified blending: 90-95 parts of the dried thermoplastic polyurethane particles, 1-5 parts of a thermoplastic polyester elastomer and various additives are mixed at a speed of 300-500 r / min for 10-15 min to obtain a uniform modified mixture; S3, graded injection molding: the temperature of the barrel is controlled in sections at 185-230 DEG C, the mold temperature is 45-60 DEG C, the temperature of the thick wall part is increased by 5-8 DEG C, the modified mixture is moved into the barrel, and graded injection molding is carried out to form a molded product; S4, slow cooling and shaping: the molded product is slowly cooled at room temperature of 25-30 DEG C for 2-3h to stabilize the size and eliminate shrinkage hazards. The preparation method realizes accurate control of the preparation process through the synergistic effect of each step.

Description

Technical Field

[0001] This invention belongs to the field of thermoplastic polyurethane elastomer preparation technology, and particularly relates to a method for preparing thermoplastic polyurethane elastomer. Background Technology

[0002] Thermoplastic polyurethane elastomers, as high-performance polymer materials, combine excellent rubber-like elasticity, outstanding wear resistance, and balanced mechanical strength, thus finding widespread application in many key fields such as the automotive industry, electronics and electrical appliances, medical devices, and precision injection molded products for daily use. However, despite its outstanding comprehensive performance, thermoplastic polyurethane materials also have some inherent processing limitations that significantly affect their molding performance in complex structural parts. Specifically, the crystallization rate of thermoplastic polyurethane melt is relatively slow, and its melt flowability at high shear rates is generally poor. In addition, its shrinkage rate after molding is relatively high compared to some other engineering plastics. These factors, when combined during injection molding, can lead to a series of serious molding defects. Especially in parts of products with complex geometries such as thick-walled sections, reinforcing rib structures, and internal corners, thermoplastic polyurethane melt is difficult to fill and compensate for shrinkage uniformly and smoothly, easily forming obvious shrinkage marks and depressions on the product surface. This also causes inconsistent dimensional stability in different areas of the product and induces overall or localized warping deformation. These molding defects not only severely damage the appearance quality and smoothness of the final product, but also directly affect its assembly accuracy with other components, as well as its long-term reliability and performance stability. Ultimately, this leads to a low product qualification rate during the production process, increasing manufacturing costs and the difficulty of quality control.

[0003] Current optimization methods all have significant limitations and shortcomings: while increasing the holding pressure or extending the holding time can control shrinkage to some extent, it can easily lead to excessive stress accumulation inside the product, causing defects such as sticking and surface cracking. Increasing mold temperature and extending cooling time significantly increases the production cycle, severely impacting overall output efficiency and making it difficult to meet the demands of large-scale, continuous production. Adding inorganic fillers to improve dimensional stability significantly weakens the inherent elasticity and toughness of thermoplastic polyurethane elastomers, reducing their mechanical properties. Using small-molecule plasticizers presents problems of easy migration and precipitation, affecting not only the long-term stability of the product but also failing to meet the stringent compliance standards in food contact and medical device fields. Furthermore, simply adjusting process parameters cannot fundamentally change the material's inherent shrinkage characteristics, thus failing to completely solve the dimensional accuracy problems caused by the material's nature. In conclusion, developing a method for preparing thermoplastic polyurethane elastomers that can effectively control shrinkage, maintain excellent material properties, and comply with relevant industry standards has become a critical challenge that urgently needs to be overcome in this technical field. Summary of the Invention

[0004] This invention overcomes the shortcomings of the prior art and provides a method for preparing thermoplastic polyurethane elastomer to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing thermoplastic polyurethane elastomer, comprising the following steps: S1. Raw material drying: Place the thermoplastic polyurethane particles in a vacuum drying oven at 85-100℃ and dry for 4-6 hours until the moisture content of the thermoplastic polyurethane particles is ≤0.08%; S2. Modified blend: By mass, take 90-95 parts of dried thermoplastic polyurethane particles, add 1-5 parts of thermoplastic polyester elastomer, 1-5 parts of hydrogenated styrene-butadiene block copolymer oil, 1.0-1.8 parts of composite crystallizing nucleating agent, 0.6-1.5 parts of molecularly compatible lubricant, and 0.2-0.5 parts of compounded antioxidant, and mix at 300-500 r / min for 10-15 min to obtain a uniform modified blend; S3, graded injection molding: The barrel temperature is controlled in sections at 185-230℃, the mold temperature is 45-60℃, and the mold temperature of the thick-walled part is increased by 5-8℃. The modified mixture is transferred into the barrel and molded into the molded product through graded injection molding. S4. Slow cooling and shaping: The molded products are slowly cooled at room temperature of 25-30℃ for 2-3 hours to stabilize the dimensions and eliminate the risk of shrinkage.

[0006] In a preferred embodiment of the present invention, in step S2, the hydrogenated styrene-butadiene block copolymer oil is formed by compounding hydrogenated styrene-butadiene block copolymer and naphthenic oil in a mass ratio of 1:1.

[0007] In a preferred embodiment of the present invention, the composite crystallizing nucleating agent is formed by compounding an aryl phosphate salt nucleating agent and a sorbitol nucleating agent in a mass ratio of 1:1.

[0008] In a preferred embodiment of the present invention, the molecularly compatible lubricant is formed by compounding ethylene-vinyl acetate wax and organosilicon lubricant at a mass ratio of 1:0.7.

[0009] In a preferred embodiment of the present invention, the compound antioxidant is formed by compounding pentaerythritol ester [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and [2,4-di-tert-butylphenyl] phosphite in a mass ratio of 1:1.

[0010] In a preferred embodiment of the present invention, step S3 employs a three-stage injection process: a first-stage pressure of 70-85 MPa, a second-stage pressure of 55-65 MPa, and a third-stage pressure of 40-50 MPa. The gradient holding pressure is 60%-70% of the first-stage injection pressure, the holding time is 12-20 seconds, and the cooling time is 25-40 seconds.

[0011] In a preferred embodiment of the present invention, in step S1, the thermoplastic polyurethane particles are polyester-type or polyether-type particles.

[0012] The present invention also provides a thermoplastic polyurethane elastomer, which is prepared according to a method for preparing a thermoplastic polyurethane elastomer, wherein the shrinkage rate of the thermoplastic polyurethane elastomer is 0.5%-1.0% and the dimensional deviation is ≤±0.15%.

[0013] This invention addresses the shortcomings of the prior art and has the following beneficial effects: 1. The preparation method of thermoplastic polyurethane elastomer of the present invention achieves precise control of the preparation process through the synergistic effect of raw material drying, modified blending, graded injection molding, and slow cooling and setting. Specifically, the material shrinkage problem is significantly improved; the shrinkage rate of the thermoplastic polyurethane material during molding is significantly reduced, by 40% to 50%, effectively eliminating shrinkage marks and dents on the surface of the product. The product has high dimensional accuracy, with deviations stably controlled within ±0.15%. While retaining the excellent elasticity, wear resistance, and mechanical strength of thermoplastic polyurethane, it significantly improves the dimensional accuracy and molding quality of the product, making it particularly suitable for fields with strict requirements for dimensional stability, such as automotive precision parts, electronic and electrical housings, and medical devices. Furthermore, the production process does not require significantly extended cycle time or sacrifice of material properties, balancing production efficiency and product quality, demonstrating good prospects for industrial application. 2. In the hydrogenated styrene-butadiene block copolymer oil-based adhesive of the present invention, the hydrogenated styrene-butadiene block copolymer and naphthenic oil are combined in a 1:1 ratio for oil-filled compounding design. Without changing the transparency and mechanical strength, it significantly reduces the melt viscosity of thermoplastic polyurethane, enhances the fluidity of thermoplastic polyurethane, reduces the internal stress of thermoplastic polyurethane, accelerates the crystallization speed of thermoplastic polyurethane, improves the sticking condition, reduces product warpage, and greatly improves processability. It is suitable for molding processes with complex structures and high fluidity requirements. 3. In the composite crystallizing nucleating agent of this invention, the aryl phosphate salt nucleating agent and the sorbitol nucleating agent are compounded in a 1:1 ratio. Its transparency is close to that of sorbitol alone, with better stability, significantly reduced haze, and high gloss, approaching the level of sorbitol alone, without white spots or whitish discoloration. Under long-term use or high-temperature conditions, its transparency is more stable, and its dispersibility is better and more uniform. Regarding rigidity and heat resistance: it is close to, and even stronger than, the flexural modulus, tensile strength, and heat distortion temperature are significantly improved. Processability: it results in faster molding speed, shorter cycle time, faster crystallization rate, shorter injection / extrusion cycle, better demolding effect, less warpage, and dimensional stability. 4. The molecularly compatible lubricant of this invention combines ethylene-vinyl acetate wax and organosilicon lubricant in a 1:0.7 ratio, achieving synergistic internal and external lubrication and comprehensively optimizing processing performance. Ethylene-vinyl acetate wax provides internal lubrication, reducing resin melt viscosity, improving mixing, extrusion / injection flowability, reducing shear heating, and lowering torque. Organosilicon provides external surface lubrication, accumulating on the product surface, reducing mold cavity adhesion, enhancing demolding effect, and lowering the product's coefficient of friction. The two complement each other to avoid the drawbacks of using only one: ethylene-vinyl acetate wax alone provides poor surface slipperiness, while organosilicon alone only offers minimal improvement in internal flow and can easily affect interfacial bonding. High-molecular-weight organosilicon migration is controllable, preventing precipitation and blooming, and is more stable than small-molecule waxes. It does not disrupt the aryl phosphate + sorbitol nucleation system and does not interfere with crystallization. The surface properties of the product are significantly improved: smooth surface, low friction, scratch and wear resistant, and delicate feel; increased gloss and reduced melt flow marks and shrinkage marks. 5. The compound antioxidant of this invention uses pentaerythritol [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and [2,4-di-tert-butylphenyl] phosphite in a 1:1 ratio. Pentaerythritol [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is the main antioxidant (hindered phenol), which can capture free radicals, inhibit thermo-oxidative aging and long-term aging after processing, providing long-term protection. It is predominantly solid and resistant to precipitation, making it suitable for long-term use. [2,4-di-tert-butylphenyl] phosphite is the secondary antioxidant (phosphite), which decomposes hydrogen peroxide, mainly ensuring processing thermal stability, inhibiting high-temperature melting degradation and yellowing, and providing significant protection during processing. Synergistic effect: 1010 captures free radicals and combines with [2,4-di-tert-butylphenyl] phosphite to decompose peroxides, taking into account both processing thermal stability and long-term aging protection, effectively inhibiting melt yellowing, molecular weight reduction, mechanical property decay, and product aging cracking. 6. The graded injection molding process of this invention, by controlling the temperature of the barrel in sections between 185-230°C and raising the mold temperature by 5-8°C for thick-walled sections, combined with three-stage injection pressure and gradient holding pressure, achieves stable filling and precise shrinkage of the melt in the complex mold cavity, preventing internal stress concentration caused by sudden pressure changes; and the slow cooling and shaping treatment at room temperature of 25-30°C for 2-3 hours further promotes the release of internal stress and the stability of the crystal structure of the product, successfully eliminating the risk of shrinkage. Detailed Implementation

[0014] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0015] Example 1 This embodiment provides a method for preparing a thermoplastic polyurethane elastomer, including the following steps: S1. Raw Material Drying: The 85A hardness polyester thermoplastic polyurethane particles are neatly placed on the tray inside the industrial vacuum drying oven. Then, the drying program is set and started, and vacuum drying is carried out continuously for 4 hours under a constant heating temperature of 90℃. This process aims to completely remove the moisture adsorbed on the surface and inside of the particles until the final moisture content of the thermoplastic polyurethane particles is strictly met and stabilized at a low moisture standard of 0.07% by precision instrument testing, so as to meet the stringent requirements of subsequent processing technology on the moisture content of raw materials.

[0016] S2. Modified Blending: Weigh and proportion according to a specific mass ratio. First, accurately weigh 90 parts of thoroughly dried thermoplastic polyurethane granules. Then, add 5 parts of thermoplastic polyester elastomer (a linear block copolymer composed of polybutylene terephthalate hard segments and polyether / polyester soft segments), 5 parts of hydrogenated styrene-butadiene block copolymer, and supplement with 1.2 parts of a composite crystallization nucleation accelerator, 0.9 parts of a molecularly compatible lubricant, and 0.3 parts of a compounded high-efficiency antioxidant stabilizer. Add all the above raw material components to a high-speed mixer, controlling the mixer speed to be within the range of 300 to 500 rpm, and continuously stir and mix for 10 to 15 minutes to ensure that the components are fully dispersed and uniformly blended, ultimately obtaining a modified blend material with uniform texture and stable performance.

[0017] S3. Staged Injection Molding: During the injection molding process, the barrel is precisely temperature-controlled to create three heating gradient zones: 195℃, 220℃, and 228℃. The overall mold temperature is stably controlled at 55℃. For specific thick-walled structural areas, localized temperature control is used to raise the temperature to 60℃ to ensure uniform material flow and full filling. In terms of injection pressure, a three-stage progressively decreasing strategy is adopted, with pressures of 75MPa, 60MPa, and 45MPa respectively, forming a gradient injection. This is followed by staged holding pressure, set at 65% of the maximum injection pressure, for 15 seconds to ensure a dense product structure and dimensional stability. Afterward, a cooling and setting stage is implemented, with a cooling time of 30 seconds, for a total molding cycle of 70 seconds. After demolding, the product needs to be slowly cooled at room temperature for up to 2.5 hours to fully release internal stress and reduce deformation. During operation, the modified mixture is pre-added to the barrel. Through the above-described staged injection molding process, a molded product with a complete structure and stable performance is ultimately formed.

[0018] S4. Slow Cooling and Shaping: After initial molding, the product needs to be slowly cooled in an indoor environment with a controlled constant temperature of 28℃ for 2.5 hours. The purpose of this step is to ensure that the product structure is fully and uniformly cured, thereby effectively stabilizing its final dimensions and completely eliminating the potential for shrinkage deformation caused by uneven cooling or insufficient stress release. After this process, the measured molding shrinkage rate of the molded product is only 0.8%, the surface is smooth and flat, without any shrinkage or dent defects, and the overall dimensional accuracy is high, with the deviation range strictly controlled within ±0.12%. Therefore, the physical and mechanical properties of the final molded product fully meet the preset standards and achieve the required quality.

[0019] In step S2 of this embodiment, to optimize the processing performance of thermoplastic polyurethane material, the hydrogenated styrene-butadiene block copolymer oil is formed by fully mixing and compounding the hydrogenated styrene-butadiene block copolymer base material with naphthenic oil at a precise mass ratio of 1:1. The core value of this special compounding scheme lies in its ability to significantly improve the processing characteristics of thermoplastic polyurethane while fully maintaining the material's original excellent transparency and mechanical strength. Specifically, it effectively and significantly reduces the melt viscosity of thermoplastic polyurethane, thereby greatly reducing the flow resistance of the melt during processing and significantly enhancing the overall fluidity of the thermoplastic polyurethane melt. This improved fluidity not only helps the melt fill the mold cavity more smoothly but also reduces the residual stress generated inside the thermoplastic polyurethane material during molding. Simultaneously, the addition of this hydrogenated styrene-butadiene block copolymer oil also promotes the regular arrangement of thermoplastic polyurethane molecular chains, thereby accelerating its crystallization speed. The combined effects of these factors result in superior processing performance: it improves the adhesion of the thermoplastic polyurethane melt to the mold, effectively reducing warping and deformation of the product after demolding due to uneven shrinkage. Ultimately, these improvements significantly enhance the overall processability and process tolerance of thermoplastic polyurethane materials, making them perfectly suited for precision injection molding or other advanced molding processes with complex structural designs and extremely high requirements for material flowability.

[0020] Furthermore, the composite nucleating agent used in this embodiment is specifically composed of an aryl phosphate salt nucleating agent and a sorbitol derivative nucleating agent, which are precisely compounded in a 1:1 mass ratio. This compound system exhibits excellent optical properties, with the final product achieving a transparency almost at the high level of using sorbitol nucleating agents alone. Simultaneously, it significantly enhances the long-term stability of the system, noticeably reducing haze and maintaining excellent surface gloss, similar to the results achieved with sorbitol alone. In practical applications, the product surface is smooth and uniform, completely eliminating defects such as white spots or localized whitening. More importantly, under long-term service or high-temperature conditions, this composite nucleating agent maintains a more stable and durable transparency, and the dispersion of its components in the matrix is ​​further optimized, resulting in a more uniform and fine distribution.

[0021] In terms of the mechanical properties and heat resistance of the material, this composite system also exhibits outstanding comprehensive advantages. It imparts rigidity and heat resistance to the material that are close to the effect of using phosphate ester nucleating agents alone, and even surpasses them in some key indicators. Specifically, the flexural modulus and tensile strength of the composite material are significantly improved, and the heat distortion temperature of the material is also significantly increased, thereby enhancing the reliability of the product under stress and heat conditions.

[0022] Furthermore, from a processing performance perspective, this composite crystallizing nucleating agent significantly improves efficiency and quality. It effectively accelerates the crystallization rate during molding, resulting in faster injection molding or extrusion and a shorter overall production cycle. Simultaneously, demolding is smoother, with minimal warpage and high dimensional stability, which contributes to improved production efficiency and the dimensional accuracy of the final product.

[0023] In this embodiment, the molecularly compatible lubrication system is formed by scientifically compounding ethylene-vinyl acetate wax (EVA wax) and a high-molecular-weight silicone lubricant at a specific mass ratio of 1:0.7. This formulation design, which combines internal and external lubrication, comprehensively and systematically optimizes the performance of the entire processing process. Specifically, EVA wax primarily performs the internal lubrication function. It can effectively penetrate into the resin melt, significantly reducing melt viscosity, thereby improving the uniformity of material dispersion during mixing and greatly enhancing melt flowability during extrusion or injection molding. In addition, it can reduce excessive heat generated by strong shearing, reduce the drive torque of processing equipment, and contribute to energy saving and extended equipment life. Meanwhile, the silicone lubricant focuses on exerting its excellent external surface lubrication effect. It tends to accumulate on the surface of the molded product, forming an extremely thin lubrication interface. This characteristic can effectively reduce melt adhesion on the mold cavity surface, thereby significantly enhancing the demolding effect and resulting in a lower surface friction coefficient for the final product.

[0024] The synergistic complementarity of these two lubricants cleverly avoids the potential application drawbacks of single lubricants: while EVA wax alone provides good internal lubrication, the surface smoothness of the product is often poor; conversely, if only silicone lubricants are used, their effect on improving the internal flowability of the melt is relatively weak, and excessive use may adversely affect the interfacial bonding strength between the multilayer structures of the material. It is worth emphasizing that the high-molecular-weight silicone used in this solution has highly controllable migration properties, making it difficult for it to randomly precipitate from the product, completely avoiding blooming. Compared to traditional easily migrating and volatile small-molecule lubricating waxes, its thermal stability and durability are superior.

[0025] This lubrication system exhibits excellent compatibility with the existing aryl phosphate and sorbitol composite nucleating agent system in the material, without compromising the effectiveness of the nucleating agent or interfering with or inhibiting the resin crystallization process. Ultimately, the overall surface properties of the product are significantly improved to the naked eye: the surface is extremely smooth, with a low coefficient of friction, enhanced scratch resistance and wear resistance, and a delicate, warm feel. Simultaneously, it helps improve the surface gloss, effectively reduces flow marks caused by uneven melt flow and sink marks caused by cooling shrinkage, resulting in a more uniform and high-end appearance.

[0026] In this embodiment, the compound antioxidant system is formed by precisely compounding pentaerythritol [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and [2,4-di-tert-butylphenyl] phosphite in a 1:1 mass ratio. In this formulation, pentaerythritol [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] serves as the primary antioxidant. Belonging to the hindered phenolic class, its core function is to efficiently capture free radicals generated during the thermo-oxidative aging process of the polymer, thereby significantly inhibiting degradation caused by thermo-oxidative action and long-term aging after processing, providing continuous and long-lasting stable protection for the material. Furthermore, this antioxidant exhibits good compatibility and partial solid-phase characteristics in the polymer matrix, with excellent resistance to migration and precipitation, making it particularly suitable for applications requiring high long-term stability. On the other hand, [2,4-di-tert-butylphenyl]phosphite acts as a co-antioxidant in this system. Belonging to the phosphite class of compounds, its main function is to decompose hydrogen peroxide generated during material processing or use, converting it into harmless stable substances, thus providing outstanding thermal stability during critical high-temperature processing stages. It effectively inhibits the molecular chain degradation of polymers in the high-temperature molten state and the resulting yellowing, thus exhibiting significant immediate protective effects during injection molding, extrusion, and other processing. The two compounds, through scientific compounding, produce a significant synergistic enhancement effect: pentaerythritol [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] blocks chain oxidation reactions by capturing free radicals, while [2,4-di-tert-butylphenyl]phosphite eliminates aging-inducing sources by decomposing hydrogen peroxide. Their complementary mechanisms of action jointly construct a multi-layered, full-cycle protective network. This synergistic effect enables the compound system to simultaneously take into account the thermal stability of the material during high-temperature processing and the anti-aging performance of the product during long-term use. This comprehensively and effectively inhibits the yellowing tendency of the polymer melt during processing, prevents the decrease in molecular weight during aging, delays the decay of mechanical properties (such as strength and toughness), and ultimately avoids problems such as surface cracking or performance failure of the product due to aging, thus improving the overall service life and reliability of the material.

[0027] In practical applications, the thermoplastic polyurethane elastomer preparation method of this embodiment successfully produces thermoplastic polyurethane elastomer products with excellent comprehensive performance through the synergistic effects of raw material drying, modified blending, staged injection molding, and slow cooling and setting. The resulting thermoplastic polyurethane elastomer not only possesses good mechanical properties, such as high tensile strength, excellent elastic recovery rate, and wear resistance, but also exhibits improved processing fluidity through the addition of hydrogenated styrene-butadiene block copolymer oil, enhanced crystallization rate and transparency through a composite crystallizing nucleating agent, optimized surface properties and processing stability through a molecularly compatible lubricating system, and ensured thermal and oxygen stability of the material during processing and long-term use. This method features precise control of process parameters, strong operability, and high production efficiency. It can stably produce thermoplastic polyurethane elastomer products with high dimensional accuracy, good surface quality, and performance meeting specific application requirements, making it suitable for the manufacturing of precision components with high material performance requirements.

[0028] Example 2 The difference between this embodiment and Embodiment 1 is that the raw material is adjusted to polyether-type thermoplastic polyurethane particles with a hardness of 50D, placed in a vacuum drying oven, and subjected to vacuum drying treatment for 4 hours under a constant heating temperature of 90°C until the final moisture content of the thermoplastic polyurethane particles reaches 0.06%.

[0029] Take 95 parts of thermoplastic polyurethane particles, 5 parts of thermoplastic polyester elastomer, 3 parts of hydrogenated styrene-butadiene block copolymer oil, 1.5 parts of composite crystallizing nucleating agent, 1.2 parts of polymeric compatibility lubricant, and 0.4 parts of compounded antioxidant. Put all the above raw material components into a high-speed mixing device, control the speed of the mixer to be within the range of 300 to 500 rpm, and continuously stir and mix for 10 to 15 minutes to ensure that each component is fully dispersed and uniformly integrated, and finally obtain a modified blend material with uniform texture and stable performance.

[0030] The barrel's interior employs precise temperature control to create three sequential heating gradients: 190℃, 215℃, and 225℃. The overall mold temperature is maintained at a stable 50℃, while specific thick-walled sections benefit from enhanced localized temperature control, raising the temperature to 55℃ to ensure uniform material flow and full filling. The injection pressure is set in three progressively decreasing stages: 80MPa, 62MPa, and 48MPa, creating a gradient injection. This is followed by staged holding pressure, set at 68% of the maximum injection pressure, for a duration of 18 seconds. The molding process involves several steps, including a 25-second cooling time for the first step, followed by a 60-second cooling phase. After demolding, the product undergoes slow cooling at room temperature for up to 3 hours to fully release internal stress and reduce deformation. During operation, the modified mixture is pre-added to the barrel, and through the above-mentioned graded injection molding process, a molded product with a complete structure and stable performance is finally formed. The molding shrinkage rate of the formed product is 1.0%, with no shrinkage defects, a dimensional deviation of ±0.1%, and excellent toughness, making it suitable for precision electronic components.

[0031] Comparative Example 1 The raw material used in this comparative example was unmodified thermoplastic polyurethane granules. In terms of molding, the most conventional and basic injection molding process was employed, without staged injection technology or a slow cooling process, resulting in a relatively simple process. The final product exhibited poor surface quality, with significant shrinkage and localized depressions. Measurements showed a molding shrinkage rate of 0.8%, and the dimensional deviation of the finished product was within ±0.4%. Due to these quality issues, the defect rate of this batch of products was relatively high.

[0032] Comparative Example 2 The main difference between this comparative experiment and Example 1 lies in the selection of nucleating agents. Specifically, only a single aryl phosphate salt nucleating agent or only a single sorbitol derivative nucleating agent was used. The composition, proportions, and preparation process of other components in the formulation remained completely consistent with Example 1. The final experimental results showed that the obtained product still exhibited slight shrinkage marks in localized areas, with a measured shrinkage rate of 1.3% and a dimensional deviation of ±0.5%. This indicates that the single nucleating agent system had a limited effect on improving the shrinkage problem and failed to achieve the expected significant optimization effect.

[0033] The table below shows the experimental results obtained from the examples and comparative examples.

[0034]

[0035] As can be seen from the table above, by comparing the experimental results of Examples 1 and 2 with those of Comparative Examples 1 and 2, it is clear that the modified formulation and optimized process used in this invention have a significant positive impact on the molding quality of thermoplastic polyurethane elastomer products. Specifically, regarding molding shrinkage, the values ​​of Example 1 (0.8%) and Comparative Example 1 (0.8%) are similar, but Example 1 completely eliminates the shrinkage defect present in Comparative Example 1, and its dimensional deviation (±0.12%) is much smaller than that of Comparative Example 1 (±0.4%). Although the molding shrinkage rate of Example 2 (1.0%) is slightly higher than that of Example 1, it also has no shrinkage defect, and its dimensional deviation (±0.1%) is more precisely controlled. Comparative Example 2, which uses a single nucleating agent, has the highest molding shrinkage rate (1.3%), and also exhibits shrinkage marks, with the largest dimensional deviation (±0.5%). This fully demonstrates that by improving processing fluidity through hydrogenated styrene-butadiene block copolymer oil, enhancing crystallization rate and stability through composite nucleating agents, optimizing surface properties and processing stability through molecularly compatible lubrication systems, ensuring thermo-oxidative stability through compounded antioxidant systems, and combining these with a synergistic preparation method involving raw material drying, modified blending, graded injection molding, and slow cooling and shaping, problems such as shrinkage, shrinkage marks, and large dimensional deviations that easily occur in unmodified thermoplastic polyurethane or when using single modification methods can be effectively solved. This significantly improves the molding quality and dimensional accuracy of the products, laying a solid foundation for their application in the field of precision component manufacturing.

[0036] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a thermoplastic polyurethane elastomer, characterized in that, Includes the following steps: S1. Raw material drying: Place the thermoplastic polyurethane particles in a vacuum drying oven at 85-100℃ and dry for 4-6 hours until the moisture content of the thermoplastic polyurethane particles is ≤0.08%; S2. Modified blend: By mass, take 90-95 parts of dried thermoplastic polyurethane particles, add 1-5 parts of thermoplastic polyester elastomer, 1-5 parts of hydrogenated styrene-butadiene block copolymer oil, 1.0-1.8 parts of composite crystallizing nucleating agent, 0.6-1.5 parts of molecularly compatible lubricant, and 0.2-0.5 parts of compounded antioxidant, and mix at 300-500 r / min for 10-15 min to obtain a uniform modified blend; S3, graded injection molding: The barrel temperature is controlled in sections at 185-230℃, the mold temperature is 45-60℃, and the mold temperature of the thick-walled part is increased by 5-8℃. The modified mixture is transferred into the barrel and molded into the molded product through graded injection molding. S4. Slow cooling and shaping: The molded products are slowly cooled at room temperature of 25-30℃ for 2-3 hours to stabilize the dimensions and eliminate the risk of shrinkage.

2. The method for preparing a thermoplastic polyurethane elastomer according to claim 1, characterized in that, In step S2, the hydrogenated styrene-butadiene block copolymer oleopolymer is formed by compounding hydrogenated styrene-butadiene block copolymer and naphthenic oil at a mass ratio of 1:

1.

3. The method for preparing a thermoplastic polyurethane elastomer according to claim 1, characterized in that, The composite crystal nucleating agent is formed by mixing an aryl phosphate nucleating agent and a sorbitol nucleating agent in a mass ratio of 1:

1.

4. The method for preparing a thermoplastic polyurethane elastomer according to claim 1, characterized in that, The molecularly compatible lubricant is formed by compounding ethylene-vinyl acetate wax and organosilicon lubricant at a mass ratio of 1:0.

7.

5. The method for preparing a thermoplastic polyurethane elastomer according to claim 1, characterized in that, The compound antioxidant is formed by compounding pentaerythritol ester [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] with [2,4-di-tert-butylphenyl] phosphite in a mass ratio of 1:

1.

6. The method for preparing a thermoplastic polyurethane elastomer according to claim 1, characterized in that, In step S3, a three-stage injection is used: the first stage pressure is 70-85 MPa, the second stage pressure is 55-65 MPa, and the third stage pressure is 40-50 MPa. The gradient holding pressure is 60%-70% of the first stage injection pressure, the holding time is 12-20 s, and the cooling time is 25-40 s.

7. The method for preparing a thermoplastic polyurethane elastomer according to claim 1, characterized in that, In step S1, the thermoplastic polyurethane particles are polyester-type or polyether-type particles.

8. A thermoplastic polyurethane elastomer, characterized in that, The thermoplastic polyurethane elastomer is prepared according to any one of claims 1-7, wherein the shrinkage rate of the thermoplastic polyurethane elastomer is 0.5%-1.0%, and the dimensional deviation is ≤±0.15%.

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