High-toughness PTT (polytrimethylene terephthalate) resin granulation process capable of regulating and controlling crystallinity through multi-stage cooling

Abstract

The invention relates to the technical field of high polymer material forming and processing, and discloses a granulation process of high-toughness PTT (polytrimethylene terephthalate) resin capable of regulating and controlling crystallinity through multi-stage cooling, the granulation process comprises the following steps: melting, conveying and pre-treating PTT particles, quenching, carrying out gradient cooling treatment, dicing and stretching, and carrying out post-treatment to complete granulation, so as to obtain the high-toughness PTT resin. Through cooperative regulation and control of multi-section cooling, a gradient crystallization structure is constructed in PTT particles, and the surface thickness and crystallinity of the particles are controlled, so that the resin particles form a gradient structure with low crystallinity and small grain size, sufficient toughness is provided, the impact resistance and mechanical strength are excellent, the process controllability is strong, and the adaptability of raw materials and equipment is good; and the industrial large-scale production of the high-toughness PTT resin can be realized.

Description

Technical Field

[0001] This invention relates to the field of polymer material molding and processing technology, specifically to a granulation process for high-toughness PTT resin with crystallinity controlled by multi-stage cooling. Background Technology

[0002] PTT (polypropylene terephthalate), as a high-performance crystalline polymer resin, possesses excellent chemical stability, processability, and biocompatibility, making it a promising candidate for applications in textile fibers, automotive parts, flexible packaging, and engineering plastics. The mechanical properties of PTT resin are closely related to its crystallization behavior, which is influenced by its thermodynamic parameters. When the crystallinity is >40%, the brittleness of PTT resin increases dramatically, with the elongation at break dropping below 100%, resulting in insufficient flexibility and easy breakage in textile fiber products, failing to meet the high toughness requirements of textile fiber and other related fields. When the crystallinity is <20%, although it can improve the toughness of PTT to some extent, it leads to a significant decrease in tensile strength and insufficient impact resistance, making it unsuitable for applications requiring high resistance to brittle fracture. Furthermore, the crystal size and uniformity of PTT resin are crucial to its performance stability. Improper control of the crystallization process can easily result in a structural difference between an amorphous surface layer and a coarse-grained core layer, causing PTT products to crack and deform during processing due to uneven internal stress, severely impacting product yield.

[0003] In the production of PTT resin, cooling control during the granulation process is a crucial step. The cooling system directly affects the crystallinity, crystal size, and distribution of PTT by regulating the melt cooling rate, thus determining the mechanical properties of the final product. Among existing PTT granulation processes, the single quenching process is one of the most widely used mainstream technologies. Using water or liquid nitrogen as the core medium for rapid cooling, it solidifies the PTT melt from a molten state into granules. This process has advantages such as simple equipment structure, high cooling efficiency, and suitability for small to medium production capacities (≤5 tons / day). However, this process has significant drawbacks when used for PTT resin. The ultra-rapid cooling with cold water causes the surface melt of the PTT granules to solidify instantaneously, forming a 15%~20% low-crystallinity surface layer. Meanwhile, the heat in the core layer cannot be released in time, allowing the PTT molecular chains sufficient time to stack orderly in the core layer, forming coarse crystals with a size of 5~10μm. The interface between the amorphous surface layer and the coarse core layer is prone to cracking due to internal stress, resulting in a mismatch between the toughness and strength of the PTT granules, making the product susceptible to brittle fracture under stress. While a single gradient cooling process can refine PTT crystals to 5-8 μm through slow cooling, the overall crystallinity is as high as 35%-42%, far exceeding the requirements of high-toughness applications of PTT and failing to meet the flexibility requirements of textile fibers. The gas-cooled hot-die process, due to the much lower heat transfer efficiency of gas compared to water, results in a significant difference in cooling rates between the surface and interior of PTT particles, forming a reverse gradient structure of high surface crystallinity and low interior crystallinity. This causes the surface of PTT products to crack first under stress, further limiting its application range.

[0004] Furthermore, existing cooling device designs cannot precisely match the thermodynamic properties of PTT (Tg≈45℃, Tc≈160℃), resulting in low precision in PTT grain size control and poor efficiency in structure regulation during industrial production. Simultaneously, the process does not consider the synergy of cooling, pelletizing, and stretching parameters. For example, a mismatch between the cutter rotation speed and the PTT melt cooling rate leads to a large deviation in the aspect ratio of PTT particles, further exacerbating uneven crystallization. Consequently, the performance qualification rate of PTT particles produced by the existing process is only around 80%.

[0005] Therefore, developing a granulation method that does not require the addition of modifiers, optimizes crystallization behavior through process control, thereby improving the toughness and mechanical properties of PTT resin, and is suitable for industrial continuous production has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a granulation process for high-toughness PTT resin with crystallinity controlled by multi-stage cooling. Through the synergistic control of quenching and gradient cooling, the toughness and mechanical properties of resin particles are improved without the addition of modifiers.

[0007] (II) Technical Solution To achieve the above objectives, this invention discloses a granulation process for high-toughness PTT resin with multi-stage cooling to control crystallinity, comprising the following steps: Step 1, Melt transport and pretreatment: Melt PTT particles at 240~260℃, transport them to a gear pump through a melt pipeline, start the gear pump, perform pretreatment, and obtain melt strips; Step 2, rapid cooling treatment: Cool the 5%~8% ethanol aqueous solution containing 0.08wt% antioxidant 168 to 8~12℃, and perform reverse spray cooling on the melt strip prepared in step 1 through an annular spray groove to obtain the rapidly cooled melt strip. Step 3, gradient cooling: The molten strip after rapid cooling in step 2 is sequentially sent into a three-stage series temperature-controlled cooling bath for cooling treatment to obtain a gradient-cooled molten strip; Step 4, Pelletizing and Stretching: The melt strip after gradient cooling is cut using a high-speed cutting device, and the cut particles are fed into a two-roll stretching machine to obtain stretched particles; Step 5, Post-processing: The stretched particles from Step 4 are subjected to gradient drying and cooling in a warm water conveying tank to obtain high-toughness PTT resin.

[0008] As a further aspect of the present invention: during the pretreatment process in step one, the gear pump pressure is 18~20MPa and the rotation speed is 40~50r / min, controlling the melt viscosity fluctuation to ≤0.05dL / g. The melt is uniformly extruded through a heatable die guide device with a diameter of 2~3mm and a length of 10mm, controlling the melt strip diameter deviation to ≤0.1mm. The constant pressure of the gear pump can counteract the melt flow resistance and prevent the molecular chains from becoming irregularly entangled due to pressure fluctuations.

[0009] As a further aspect of the present invention: In step two, the rapid cooling treatment is carried out in an annular spray structure. During the rapid cooling process, the tank is divided into an inner ring spray zone and an outer ring guiding zone. The spray nozzles are arranged at a 45° angle to the melt strip, and the spray nozzles face the opposite direction of the melt flow to ensure that the ethanol aqueous solution and the melt strip are in counter-current contact. The flow rate of the ethanol aqueous solution at the inner ring spray nozzle of the annular spray tank is adjusted to 2.5~4.0 m / s. The different flow rates of the inner and outer rings guide the ethanol aqueous solution to form a spiral flow. After the melt strip enters the annular spray tank, it is in full contact with the counter-current ethanol aqueous solution. The cooling rate is 150~300℃ / s, the cooling time is 1200~1500ms, and the conveyor belt speed is 0.6m / s. After exiting the tank, the surface temperature of the melt strip is detected by an infrared thermometer. The surface temperature of the melt strip drops to 50~60℃, and the surface crystallinity is controlled at 10%~15%.

[0010] As a further aspect of the present invention: the ethanol-water solution containing 0.08 wt% antioxidant 168 at 8-12℃ in step two can be replaced with an aqueous solution containing 0.1 wt% antioxidant 1010 at 8-12℃. The freezing point of the ethanol-water solution is lower than that of pure water, allowing it to be adapted to lower quenching temperatures, and ethanol is easily volatile, reducing subsequent drying energy consumption.

[0011] As a further embodiment of the present invention: the annular spray groove in step two can be replaced with a double-spiral atomizing quenching tube. In the double-spiral atomizing quenching tube, there are 2 or 3 spiral guide grooves, with an angle of 20°~40°. The cross-section of the guide grooves is rectangular or trapezoidal, with a depth of 1~3mm and a width of 1~2mm. The diameter of the atomizing nozzles is 0.5~1.2mm, and the atomizing nozzles are arranged in a uniform array of 1~2 rings at the head. The annular gap spacing in the outer ring guide structure is 3~8mm, forming secondary airflow to constrain and focus the atomizing cone, preventing premature diffusion. The outlet contraction angle is 5°~15°, providing final shaping and acceleration of the atomizing cone, allowing it to more concentratedly impact the melt strip. The effective atomization length is 150~300mm, ensuring the melt strip has sufficient stroke for adequate heat exchange with the atomizing medium, matching the conveying speed to meet cooling time requirements.

[0012] As a further aspect of the present invention: In the cooling process of step three, a three-stage temperature-controlled cooling tank is arranged in series, with a volume of 50L for each stage. During the cooling process, ultrasonic vibration is used, with a frequency of 20~30kHz and a power of 500W. The ultrasonic vibration tank is installed at the bottom of each cooling unit. The temperature of the first stage tank is 40~45℃ and the residence time is 5s; the temperature of the second stage tank is 30~35℃ and the residence time is 5s; and the temperature of the third stage tank is 20~25℃ and the residence time is 5s. The temperature difference in the tank is controlled to be ≤1℃. After the treatment is completed, the core layer temperature drops steadily from 80~90℃ to 30~40℃, the core layer crystallinity is 25%~30%, and the crystal size is 2~3μm.

[0013] As a further aspect of the present invention: in step three, ultrasonic vibration can be replaced by stirring, using a paddle-type stirrer with a paddle diameter of 150 mm. The primary tank temperature is 40-45℃, stirring speed is 80 r / min, and residence time is 5 s; the secondary tank temperature is 30-35℃, stirring speed is 60 r / min, and residence time is 5 s; the tertiary tank temperature is 20-25℃, stirring speed is 50 r / min, and residence time is 5 s. The temperature difference within the tank is controlled to be ≤1℃. After treatment, the core layer temperature steadily decreases from 80-90℃ to 30-40℃, the core layer crystallinity is 25%-30%, and the crystal size is 2-3 μm. The microfluidic field generated by ultrasonic vibration can replace mechanical stirring, avoiding shear damage to the melt strips from the paddle, and improving the uniformity of core layer crystallinity.

[0014] As a further aspect of the present invention: during the cutting process in step four, the cutting speed is 2800~3200 r / min, and the aspect ratio of the particles is controlled to be 1:(0.9~1.1). High-speed cutting inhibits crystal rearrangement on the particle surface.

[0015] As a further aspect of the present invention: In step four, in a two-roll stretching machine, the roll surface temperature is set to 55~65℃, the stretching ratio is 1.5~2.0 times, the induced molecular chain orientation degree is 15%~20%, and particles with size deviation >0.5mm are screened out. The molecular chains that are slightly stretched and oriented axially under the action of the heated rolls can absorb impact energy through slippage.

[0016] As a further aspect of the present invention, the specific preparation process of the high-toughness PTT resin in step five is as follows: The stretched particles from step four are fed into a warm water conveying tank at 45~50℃ and a water flow rate of 0.6~0.8m / s. After conveying for 8~10 minutes, gradient drying is carried out. The drying process is as follows: at 60℃ and a wind speed of 1.0m / s, the temperature is maintained for 30 minutes; at 70℃ and a wind speed of 1.2m / s, the temperature is maintained for 30 minutes; and at 80℃ and a wind speed of 1.5m / s, the temperature is maintained for 60 minutes. The moisture content at the particle outlet is monitored by a moisture content detector, and the moisture content of the particles is controlled to be ≤0.08%. The particles are then cooled to room temperature by a 25℃ cooling conveyor belt to complete granulation and obtain high-toughness PTT resin.

[0017] (iii) Beneficial technical effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The granulation system in this invention consists of a melt conveying unit, a quenching unit, a gradient cooling unit, a pelletizing and stretching unit, and a post-processing unit connected in series. Molten PTT resin enters the quenching unit via a gear pump, the semi-cured melt strip after quenching enters the gradient cooling unit, the melt strip after gradient cooling enters the pelletizing and stretching unit, and the pellets after pelletizing are processed through a warm water conveying tank and a gradient dryer. Each unit is linked by conveyor belts and pipelines, and key parameters are monitored in real time by a DCS to ensure synchronization.

[0018] (2) In this invention, a composite cooling design of rapid cooling and gradient cooling is used to construct a gradient crystallization structure with "soft exterior and rigid interior" inside the PTT particles. This controls the thickness and crystallinity of the particle surface layer, resulting in a gradient structure with low crystallinity and small grain size, providing sufficient toughness and excellent impact resistance. The crystallinity of the PTT resin particle core layer is controlled at 25%~30%, the crystal size is refined to 2~3μm, and the grain boundary area is increased, which can effectively disperse impact stress. Furthermore, the transition of crystallinity between the surface layer and the core layer is smooth, with a small gradient difference, avoiding interface stress cracking and ensuring structural stability. In the rapid cooling unit, the surface layer of the high-temperature melt is rapidly cooled, and the molecular chains are "frozen" to form a surface layer with low crystallinity, rich in amorphous regions and microcrystals, giving the material initial deformation ability and high light transmittance. Subsequently, in the gradient cooling unit, the core, which still maintains a relatively high temperature, can complete full and orderly crystallization at a controlled slow cooling rate within the optimal crystallization temperature window of PTT, forming a core layer with high crystallinity and fine and uniform grains. This structure, with its gradual transition in crystallinity from the surface to the core, ingeniously achieves synergistic performance. The low-crystallinity surface layer acts as the main plastic deformation zone, absorbing impact energy, while the high-crystallinity fine-grained core layer acts as a rigid framework, dispersing stress and providing support. The gradual gradient transition effectively avoids interfacial stress concentration caused by abrupt changes in crystallinity, thus significantly improving toughness while ensuring the integrity and stability of the structure.

[0019] (3) This invention employs a high-shear pelletizing and medium-temperature stretching process to induce a slight orientation of the molecular chains, resulting in a significant increase in impact strength with only a slight increase in crystallinity. The high shear force, while cutting the melt strip, induces localized orientation and shear-induced nucleation of the molecular chains, particularly in amorphous regions and grain boundary segments. Subsequently, moderate stretching is performed in a medium-temperature region below the melting point but above the glass transition temperature, fixing and strengthening this oriented structure. This controlled slight orientation is equivalent to constructing countless microscale "fiber-like" reinforcing networks within the material. Without significantly increasing the overall crystallinity or preventing material embrittlement, the tensile strength and impact toughness of the material are simultaneously improved through the orientation strengthening mechanism, further promoting the homogenization of the crystal structure and resulting in superior and more stable mechanical properties of the final product. Furthermore, the melt delivery and cooling parameters are matched to ensure uniform cooling. The cooling water can be recycled after three-stage filtration, resulting in a high recovery rate. Furthermore, the energy consumption of gradient drying is lower than traditional processes. Combined with a universal parameter system, the overall production cost is reduced, while the overall performance is improved. The elongation at break and notched impact strength are significantly increased, and crystal size uniformity is greatly enhanced, making it suitable for PTT crystalline resins. Moreover, in the PTT resin preparation process, by modifying the cooling system of the existing granulation line, no modifier needs to be added, effectively reducing production costs and achieving excellent overall performance. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] Example 1 A granulation process for high-toughness PTT resin with controlled crystallinity through multi-stage cooling includes the following steps: Step 1: Melt PTT particles at 240℃ and transport them to a gear pump through a melt pipeline. Start the gear pump for pretreatment. The gear pump pressure is 18MPa and the speed is 40r / min. Control the melt viscosity fluctuation to ≤0.05dL / g. The melt is uniformly extruded through a 2mm diameter and 10mm long heated die guide device. Control the melt strip diameter deviation to ≤0.1mm to obtain melt strips. Step 2: Cool the 5% ethanol aqueous solution containing 0.08wt% antioxidant 168 to 8℃, and perform counter-current jet cooling on the melt strip through an annular jetting tank for quenching. In the annular jetting structure, the tank is divided into an inner ring jetting zone and an outer ring guiding zone. The jetting nozzles are arranged at a 45° angle to the melt strip and face the opposite direction of the melt flow. Adjust the flow rate of the ethanol aqueous solution in the inner ring jetting nozzle of the annular jetting tank to 2.5m / s. After the melt strip enters the annular jetting tank, the cooling rate is 150℃ / s, the cooling time is 1200ms, and the conveyor belt speed is 0.6m / s. After exiting the tank, the surface temperature of the melt strip is detected by an infrared thermometer. The surface temperature of the melt strip drops to 50℃, and the surface crystallinity is controlled at 10%, thus obtaining the quenched melt strip. Step 3: The quenched melt strip is sequentially fed into a three-stage series temperature-controlled cooling tank for cooling treatment. During the cooling process, the three-stage series temperature-controlled cooling tanks are arranged in three stages, each with a volume of 50L. During the cooling process, ultrasonic vibration is used with a frequency of 20kHz and a power of 500W. The temperatures of the three tanks are set as follows: first stage temperature 40℃, residence time 5s; second stage temperature 30℃, residence time 5s; third stage temperature 20℃, residence time 5s. The temperature difference within the tank is controlled to be ≤1℃. After the treatment, the core layer temperature drops steadily from 80℃ to 30℃, the core layer crystallinity is 25%, and the crystal size is 2μm, resulting in a gradient-cooled melt strip. Step 4: Use a high-speed cutting device to cut the gradient-cooled melt strip. During the cutting process, the cutting speed is 2800 r / min, and the particle length-to-diameter ratio is controlled at 1:0.9. The cut particles are fed into a double-roll stretching machine. In the double-roll stretching machine, the roller surface temperature is set to 55℃, the stretching ratio is 1.5 times, and the induced molecular chain orientation degree is 15%. Particles with size deviation >0.5mm are screened out to obtain stretched particles. Step 5: The stretched granules are fed into a warm water conveying tank at 45℃ and a water flow rate of 0.6m / s. After conveying for 8 minutes, gradient drying is carried out. The drying process is as follows: 60℃, wind speed 1.0m / s, heat preservation for 30 minutes; 70℃, wind speed 1.2m / s, heat preservation for 30 minutes; 80℃, wind speed 1.5m / s, heat preservation for 60 minutes. The moisture content of the granules at the outlet is monitored by a moisture content detector and controlled to be ≤0.08%. The granules are then cooled to room temperature by a 25℃ cooling conveyor belt to complete granulation and obtain high-toughness PTT resin.

[0022] Example 2 A granulation process for high-toughness PTT resin with controlled crystallinity through multi-stage cooling includes the following steps: Step 1: Melt PTT particles at 245℃ and transport them to a gear pump through a melt pipeline. Start the gear pump for pretreatment. The gear pump pressure is 19MPa and the speed is 45r / min. Control the melt viscosity fluctuation to ≤0.05dL / g. The melt is uniformly extruded through a 2.5mm diameter and 10mm long heated die guide device. Control the melt strip diameter deviation to ≤0.1mm to obtain melt strips. Step 2: Cool the 6% ethanol aqueous solution containing 0.08wt% antioxidant 168 to 10℃, and perform counter-current jet cooling on the melt strip through an annular jetting tank for quenching. In the annular jetting structure, the tank is divided into an inner ring jetting zone and an outer ring guiding zone. The jetting nozzles are arranged at a 45° angle to the melt strip and face the opposite direction of the melt flow. Adjust the flow rate of the ethanol aqueous solution in the inner ring jetting nozzle of the annular jetting tank to 3.0m / s. After the melt strip enters the annular jetting tank, the cooling rate is 200℃ / s, the cooling time is 1400ms, and the conveyor belt speed is 0.6m / s. After exiting the tank, the surface temperature of the melt strip is detected by an infrared thermometer. The surface temperature of the melt strip drops to 55℃, and the surface crystallinity is controlled at 12%, thus obtaining the quenched melt strip. Step 3: The quenched melt strip is sequentially fed into a three-stage series temperature-controlled cooling tank for cooling treatment. During the cooling process, the three-stage temperature-controlled cooling tank is arranged in series, with each stage having a volume of 50L. During the cooling process, ultrasonic vibration is used with a frequency of 24kHz and a power of 500W. The ultrasonic vibration tank is installed at the bottom of each cooling unit. The temperatures of the three stages are set as follows: Stage 1 temperature 42℃, residence time 5s; Stage 2 temperature 32℃, residence time 5s; Stage 3 temperature 22℃, residence time 5s. The temperature difference within the tank is controlled to be ≤1℃. After the treatment, the core layer temperature drops steadily from 85℃ to 35℃, the core layer crystallinity is 28%, and the crystal size is 2.6μm, resulting in a gradient-cooled melt strip. Step 4: Use a high-speed cutting device to cut the gradient-cooled melt strip. During the cutting process, the cutting speed is 3000 r / min, and the particle length-to-diameter ratio is controlled at 1:0.95. The cut particles are then fed into a double-roll stretching machine. In the double-roll stretching machine, the roller surface temperature is set to 60℃, the stretching ratio is 1.6 times, and the induced molecular chain orientation degree is 16%. Particles with size deviation >0.5mm are screened out to obtain the stretched particles. Step 5: The stretched granules are fed into a warm water conveying tank at 48℃ and a water flow rate of 0.7m / s. After conveying for 9 minutes, gradient drying is carried out. The drying process is as follows: 60℃, wind speed 1.0m / s, heat preservation for 30 minutes; 70℃, wind speed 1.2m / s, heat preservation for 30 minutes; 80℃, wind speed 1.5m / s, heat preservation for 60 minutes. The moisture content of the granules at the outlet is monitored by a moisture content detector and controlled to be ≤0.08%. The granules are then cooled to room temperature by a 25℃ cooling conveyor belt to complete granulation and obtain high-toughness PTT resin.

[0023] Example 3 A granulation process for high-toughness PTT resin with controlled crystallinity through multi-stage cooling includes the following steps: Step 1: Melt PTT particles at 255℃ and transport them to a gear pump through a melt pipeline. Start the gear pump for pretreatment. The gear pump pressure is 19MPa and the rotation speed is 48r / min. Control the melt viscosity fluctuation to ≤0.05dL / g. The melt is uniformly extruded through a 2.5mm diameter and 10mm long heated die guide device. Control the melt strip diameter deviation to ≤0.1mm to obtain melt strips. Step 2: Cool the 7% ethanol aqueous solution containing 0.08wt% antioxidant 168 to 10℃, and perform counter-current jet cooling on the melt strip through an annular jetting tank for quenching. In the annular jetting structure, the tank is divided into an inner ring jetting zone and an outer ring guiding zone. The jetting nozzles are arranged at a 45° angle to the melt strip and face the opposite direction of the melt flow. Adjust the flow rate of the ethanol aqueous solution in the inner ring jetting nozzle of the annular jetting tank to 3.5m / s. After the melt strip enters the annular jetting tank, the cooling rate is 250℃ / s, the cooling time is 1450ms, and the conveyor belt speed is 0.6m / s. After exiting the tank, the surface temperature of the melt strip is detected by an infrared thermometer. The surface temperature of the melt strip drops to 52℃, and the surface crystallinity is controlled at 14%, thus obtaining the quenched melt strip. Step 3: The quenched melt strip is sequentially fed into a three-stage series temperature-controlled cooling tank for cooling treatment. During the cooling process, the three-stage temperature-controlled cooling tank is arranged in series, with each stage having a volume of 50L. During the cooling process, ultrasonic vibration is used with a frequency of 28kHz and a power of 500W. The ultrasonic vibration tank is installed at the bottom of each cooling unit. The temperatures of the three stages are set as follows: Stage 1 temperature 44℃, residence time 5s; Stage 2 temperature 34℃, residence time 5s; Stage 3 temperature 24℃, residence time 5s. The temperature difference within the tank is controlled to be ≤1℃. After the treatment, the core layer temperature drops steadily from 85℃ to 36℃, the core layer crystallinity is 26%, and the crystal size is 2.3μm, resulting in a gradient-cooled melt strip. Step 4: Use a high-speed cutting device to cut the gradient-cooled melt strip. During the cutting process, the cutting speed is 3100 r / min, and the particle length-to-diameter ratio is controlled at 1:1.05. The cut particles are then fed into a double-roll stretching machine. In the double-roll stretching machine, the roller surface temperature is set to 62℃, the stretching ratio is 1.8 times, and the induced molecular chain orientation degree is 18%. Particles with size deviation >0.5mm are screened out to obtain the stretched particles. Step 5: The stretched granules are fed into a warm water conveying tank at 48℃ and a water flow rate of 0.75m / s. After conveying for 9 minutes, gradient drying is carried out. The drying process is as follows: 60℃, wind speed 1.0m / s, heat preservation for 30 minutes; 70℃, wind speed 1.2m / s, heat preservation for 30 minutes; 80℃, wind speed 1.5m / s, heat preservation for 60 minutes. The moisture content of the granules at the outlet is monitored by a moisture content detector and controlled to be ≤0.08%. The granules are then cooled to room temperature by a 25℃ cooling conveyor belt to complete granulation and obtain high-toughness PTT resin.

[0024] Example 4 A granulation process for high-toughness PTT resin with controlled crystallinity through multi-stage cooling includes the following steps: Step 1: Melt PTT particles at 255℃ and transport them to a gear pump through a melt pipeline. Start the gear pump for pretreatment. The gear pump pressure is 19MPa and the rotation speed is 48r / min. Control the melt viscosity fluctuation to ≤0.05dL / g. The melt is uniformly extruded through a 2.5mm diameter and 10mm long heated die guide device. Control the melt strip diameter deviation to ≤0.1mm to obtain melt strips. Step 2: Cool the aqueous solution containing 0.1 wt% antioxidant 1010 to 10°C, and then perform counter-current jet cooling on the melt strip through an annular jetting tank for quenching. In the annular jetting structure, the tank is divided into an inner ring jetting zone and an outer ring guiding zone. The jetting nozzles are arranged at a 45° angle to the melt strip and face the opposite direction of the melt flow. Adjust the flow rate of the aqueous solution in the inner ring jetting nozzle of the annular jetting tank to 3.5 m / s. After the melt strip enters the annular jetting tank, the cooling rate is 250°C / s, the cooling time is 1450 ms, and the conveyor belt speed is 0.6 m / s. After exiting the tank, the surface temperature of the melt strip is detected by an infrared thermometer. The surface temperature of the melt strip drops to 52°C, and the surface crystallinity is controlled at 14%, thus obtaining the quenched melt strip. Step 3: The quenched melt strip is sequentially fed into a three-stage series temperature-controlled cooling tank for cooling treatment. During the cooling process, the three-stage series temperature-controlled cooling tanks are arranged, with each stage having a volume of 50L. Stirring is carried out using a paddle-type stirrer with a paddle diameter of 150mm. The temperatures of the three tanks are set as follows: first tank temperature 44℃, stirring speed 80r / min, residence time 5s; second tank temperature 34℃, stirring speed 60r / min, residence time 5s; third tank temperature 24℃, stirring speed 50r / min, residence time 5s. The temperature difference within the tank is controlled to be ≤1℃. After the treatment, the core layer temperature drops steadily from 85℃ to 36℃, the core layer crystallinity is 28%, and the crystal size is 2.9μm, resulting in a gradient-cooled melt strip. Step 4: Use a high-speed cutting device to cut the gradient-cooled melt strip. During the cutting process, the cutting speed is 3100 r / min, and the particle length-to-diameter ratio is controlled at 1:1.05. The cut particles are then fed into a double-roll stretching machine. In the double-roll stretching machine, the roller surface temperature is set to 62℃, the stretching ratio is 1.8 times, and the induced molecular chain orientation degree is 18%. Particles with size deviation >0.5mm are screened out to obtain the stretched particles. Step 5: The stretched granules are fed into a warm water conveying tank at 48℃ and a water flow rate of 0.75m / s. After conveying for 9 minutes, gradient drying is carried out. The drying process is as follows: 60℃, wind speed 1.0m / s, heat preservation for 30 minutes; 70℃, wind speed 1.2m / s, heat preservation for 30 minutes; 80℃, wind speed 1.5m / s, heat preservation for 60 minutes. The moisture content of the granules at the outlet is monitored by a moisture content detector and controlled to be ≤0.08%. The granules are then cooled to room temperature by a 25℃ cooling conveyor belt to complete granulation and obtain high-toughness PTT resin.

[0025] Example 5 A granulation process for high-toughness PTT resin with controlled crystallinity through multi-stage cooling includes the following steps: Step 1: Melt PTT particles at 260℃ and transport them to a gear pump through a melt pipeline. Start the gear pump for pretreatment. The gear pump pressure is 20MPa and the rotation speed is 50r / min. Control the melt viscosity fluctuation to ≤0.05dL / g. The melt is uniformly extruded through a 3mm diameter and 10mm long heated die guide device. Control the melt strip diameter deviation to ≤0.1mm to obtain melt strips. Step 2: Cool the 8% ethanol aqueous solution containing 0.08wt% antioxidant 168 to 12℃, and perform counter-current jet cooling on the melt strip through an annular jetting tank for quenching. In the annular jetting structure, the tank is divided into an inner ring jetting zone and an outer ring guiding zone. The jetting nozzles are arranged at a 45° angle to the melt strip and face the opposite direction of the melt flow. Adjust the flow rate of the ethanol aqueous solution in the inner ring jetting nozzle of the annular jetting tank to 4.0m / s. After the melt strip enters the annular jetting tank, the cooling rate is 300℃ / s, the cooling time is 1500ms, and the conveyor belt speed is 0.6m / s. After exiting the tank, the surface temperature of the melt strip is detected by an infrared thermometer. The surface temperature of the melt strip drops to 60℃, and the surface crystallinity is controlled at 15%, thus obtaining the quenched melt strip. Step 3: The quenched melt strip is sequentially fed into a three-stage series temperature-controlled cooling tank for cooling treatment. During the cooling process, the three-stage temperature-controlled cooling tank is arranged in series, with each stage having a volume of 50L. During the cooling process, ultrasonic vibration is used with a frequency of 30kHz and a power of 500W. The ultrasonic vibration tank is installed at the bottom of each cooling unit. The temperatures of the three stages are set as follows: Stage 1 temperature 45℃, residence time 5s; Stage 2 temperature 35℃, residence time 5s; Stage 3 temperature 25℃, residence time 5s. The temperature difference within the tank is controlled to be ≤1℃. After the treatment is completed, the core layer temperature drops steadily from 90℃ to 40℃, the core layer crystallinity is 30%, and the crystal size is 3μm, resulting in a gradient-cooled melt strip. Step 4: Use a high-speed cutting device to cut the gradient-cooled melt strip. During the cutting process, the cutting speed is 3200 r / min, and the particle length-to-diameter ratio is controlled at 1:1.1. The cut particles are fed into a double-roll stretching machine. In the double-roll stretching machine, the roller surface temperature is set to 65℃, the stretching ratio is 2.0 times, and the induced molecular chain orientation degree is 20%. Particles with size deviation >0.5mm are screened out to obtain stretched particles. Step 5: The stretched granules are fed into a warm water conveying tank at 50℃ and a water flow rate of 0.8m / s. After conveying for 10 minutes, gradient drying is carried out. The drying process is as follows: 60℃, wind speed 1.0m / s, heat preservation for 30 minutes; 70℃, wind speed 1.2m / s, heat preservation for 30 minutes; 80℃, wind speed 1.5m / s, heat preservation for 60 minutes. The moisture content of the granules at the outlet is monitored by a moisture content detector and controlled to be ≤0.08%. The granules are then cooled to room temperature by a 25℃ cooling conveyor belt to complete granulation and obtain high-toughness PTT resin.

[0026] Comparative Example 1 A granulation process for PTT resin includes the following steps: Step 1: Melt PTT particles at 255℃ and transport them to a gear pump through a melt pipeline. Start the gear pump for pretreatment. The gear pump pressure is 19MPa and the rotation speed is 48r / min. Control the melt viscosity fluctuation to ≤0.05dL / g. The melt is uniformly extruded through a 2.5mm diameter and 10mm long heated die guide device. Control the melt strip diameter deviation to ≤0.1mm to obtain melt strips. Step 2: The molten strip is sequentially fed into a three-stage series temperature-controlled cooling tank for cooling. During the cooling process, the three-stage temperature-controlled cooling tank is arranged in series, with each stage having a volume of 50L. During the cooling process, ultrasonic vibration is used with a frequency of 28kHz and a power of 500W. The ultrasonic vibration tank is installed at the bottom of each cooling unit. The temperatures of the three stages are set as follows: Stage 1: 44℃, residence time 5s; Stage 2: 34℃, residence time 5s; Stage 3: 24℃, residence time 5s. The temperature difference within the tank is controlled to be ≤1℃. After the process is completed, the molten strip after gradient cooling is obtained. Step 3: Use a high-speed cutting device to cut the gradient-cooled melt strip. During the cutting process, the cutting speed is 3100 r / min, and the particle length-to-diameter ratio is controlled at 1:1.05. The cut particles are fed into a double-roll stretching machine. In the double-roll stretching machine, the roller surface temperature is set to 62℃, the stretching ratio is 1.8 times, and the induced molecular chain orientation degree is 18%. Particles with size deviation >0.5mm are screened out to obtain stretched particles. Step 4: The stretched granules are fed into a warm water conveying tank at 48℃ and a water flow rate of 0.75m / s. After conveying for 9 minutes, gradient drying is carried out. The drying process is as follows: 60℃, wind speed 1.0m / s, heat preservation for 30 minutes; 70℃, wind speed 1.2m / s, heat preservation for 30 minutes; 80℃, wind speed 1.5m / s, heat preservation for 60 minutes. The moisture content of the granules at the outlet is monitored by a moisture content meter and controlled to be ≤0.08%. The granules are then cooled to room temperature by a 25℃ cooling conveyor belt to complete granulation and obtain PTT resin.

[0027] Comparative Example 2 A granulation process for PTT resin includes the following steps: Step 1: Melt PTT particles at 255℃ and transport them to a gear pump through a melt pipeline. Start the gear pump for pretreatment. The gear pump pressure is 19MPa and the rotation speed is 48r / min. Control the melt viscosity fluctuation to ≤0.05dL / g. The melt is uniformly extruded through a 2.5mm diameter and 10mm long heated die guide device. Control the melt strip diameter deviation to ≤0.1mm to obtain melt strips. Step 2: Cool the 7% ethanol aqueous solution containing 0.08wt% antioxidant 168 to 10℃, and perform counter-current jet cooling on the melt strip through an annular jetting tank for quenching. In the annular jetting structure, the tank is divided into an inner ring jetting zone and an outer ring guiding zone. The jetting nozzles are arranged at a 45° angle to the melt strip and face the opposite direction of the melt flow. Adjust the flow rate of the ethanol aqueous solution in the inner ring jetting nozzle of the annular jetting tank to 3.5m / s. After the melt strip enters the annular jetting tank, the cooling rate is 250℃ / s, the cooling time is 1450ms, and the conveyor belt speed is 0.6m / s. After exiting the tank, the surface temperature of the melt strip is detected by an infrared thermometer. The surface temperature of the melt strip drops to 52℃, and the surface crystallinity is controlled at 14%, thus obtaining the quenched melt strip. Step 3: Use a high-speed cutting device to cut the quenched melt strip. During the cutting process, the cutting speed is 3100 r / min, and the particle length-to-diameter ratio is controlled at 1:1.05. The cut particles are then fed into a double-roll stretching machine. In the double-roll stretching machine, the roller surface temperature is set to 62℃, the stretching ratio is 1.8 times, and the induced molecular chain orientation degree is 18%. Particles with size deviation >0.5mm are screened out to obtain the stretched particles. Step 4: The stretched granules are fed into a warm water conveying tank at 48℃ and a water flow rate of 0.75m / s. After conveying for 9 minutes, gradient drying is carried out. The drying process is as follows: 60℃, wind speed 1.0m / s, heat preservation for 30 minutes; 70℃, wind speed 1.2m / s, heat preservation for 30 minutes; 80℃, wind speed 1.5m / s, heat preservation for 60 minutes. The moisture content of the granules at the outlet is monitored by a moisture content meter and controlled to be ≤0.08%. The granules are then cooled to room temperature by a 25℃ cooling conveyor belt to complete granulation and obtain PTT resin.

[0028] The PTT resins prepared in Examples 1-5 and Comparative Examples 1-2 were subjected to corresponding tests. The test methods and results are shown in Table 1. Table 1 As shown in Table 1, the PTT resins corresponding to Examples 1-5 exhibit excellent tensile strength and notched impact strength, good toughness, and superior mechanical properties. The ultrasonic vibration used in Examples 1-3 and 5 generates cavitation effects and micro-disturbances during cooling, promoting crystal nucleation and resulting in finer, more uniform crystal sizes, which improves the material's mechanical strength and toughness. The paddle stirring used in Example 4 provides less precise control over the crystal microstructure compared to ultrasonic waves, leading to a slight decrease in overall performance. In Comparative Example 1, no rapid cooling treatment was performed; the melt strip cooled slowly from the outside in simultaneously, increasing brittleness, significantly reducing notched impact strength, and decreasing toughness, thus lowering the mechanical properties of the PTT resin. In Comparative Example 2, the resin was directly cut and stretched after rapid cooling without gradient cooling, preventing the core layer heat from dissipating smoothly, resulting in incomplete core layer crystallization, high internal stress, and a significant reduction in overall performance.

[0029] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A granulation process for high-toughness PTT resin with multi-stage cooling to control crystallinity, characterized in that: Includes the following steps: Step 1, Melt transport and pretreatment: PTT particles are melted at 240~260℃ and transported to a gear pump through a melt pipeline for pretreatment to obtain melt strips; Step 2, rapid cooling treatment: Cool the 5%~8% ethanol aqueous solution containing 0.08wt% antioxidant 168 to 8~12℃, and perform reverse spray cooling on the melt strip prepared in step 1 through an annular spray groove to obtain the rapidly cooled melt strip. Step 3, gradient cooling: The molten strip after rapid cooling in step 2 is sequentially fed into a three-stage series temperature-controlled cooling bath for cooling treatment to obtain a gradient-cooled molten strip; Step 4, Pelletizing and Stretching: The melt strip after gradient cooling is cut using a high-speed cutting device, and the cut particles are fed into a two-roll stretching machine to obtain stretched particles; Step 5, Post-processing: The stretched particles from Step 4 are subjected to gradient drying and cooling in a warm water conveying tank to obtain high-toughness PTT resin.

2. The granulation process for high-toughness PTT resin with multi-stage cooling to regulate crystallinity according to claim 1, characterized in that: In step one, the gear pump pressure is 18~20MPa and the speed is 40~50r / min.

3. The granulation process for high-toughness PTT resin with multi-stage cooling to regulate crystallinity according to claim 1, characterized in that: In the pretreatment process of step one, the melt viscosity fluctuation is controlled to be ≤0.05dL / g, and the melt is uniformly extruded through a heatable die head guide device with a diameter of 2~3mm and a length of 10mm, and the diameter deviation of the melt strip is controlled to be ≤0.1mm.

4. The granulation process for high-toughness PTT resin with multi-stage cooling to regulate crystallinity according to claim 1, characterized in that: In the rapid cooling process of step two, the flow rate of the inner ring spray nozzle of the annular spray tank is adjusted to 1.5~2.0m / s, the cooling rate is 150~300℃ / s, the cooling time is 1200~1500ms, the conveyor belt speed is 0.6m / s, and the melt strip exits the tank. The surface temperature of the melt strip drops to 50~60℃, and the surface crystallinity is controlled at 10%~15%.

5. The granulation process for high-toughness PTT resin with multi-stage cooling to regulate crystallinity according to claim 1, characterized in that: In step two, the ethanol aqueous solution containing 0.08 wt% antioxidant 168 at 8-12℃ can be replaced with an aqueous solution containing 0.1 wt% antioxidant 1010 at 8-12℃.

6. The granulation process for high-toughness PTT resin with multi-stage cooling to control crystallinity according to claim 1, characterized in that: In step three, during the cooling process, three temperature-controlled cooling tanks are arranged in series, each with a volume of 50L. During the cooling process, ultrasonic vibration is used with a frequency of 20~30kHz and a power of 500W. The ultrasonic vibration tanks are installed at the bottom of each cooling unit. The temperature of the first-stage tank is 40~45℃ with a residence time of 5s, the temperature of the second-stage tank is 30~35℃ with a residence time of 5s, and the temperature of the third-stage tank is 20~25℃ with a residence time of 5s. The temperature difference within the tanks is controlled to be ≤1℃. After the treatment is completed, the core layer temperature drops steadily from 80~90℃ to 30~40℃, the core layer crystallinity is 25%~30%, and the crystal size is 2~3μm.

7. The granulation process for high-toughness PTT resin with multi-stage cooling to regulate crystallinity according to claim 6, characterized in that: In step three, ultrasonic vibration can be replaced by stirring. The stirring adopts a paddle-type stirring with a paddle diameter of 150 mm. The temperature of the first-stage tank is 40~45℃, the stirring speed is 80 r / min, and the residence time is 5 s. The temperature of the second-stage tank is 30~35℃, the stirring speed is 60 r / min, and the residence time is 5 s. The temperature of the third-stage tank is 20~25℃, the stirring speed is 50 r / min, and the residence time is 5 s. The temperature difference in the tank is controlled to be ≤1℃. After the treatment, the core layer temperature drops steadily from 80~90℃ to 30~40℃, the core layer crystallinity is 25%~30%, and the crystal size is 2~3 μm.

8. The granulation process for high-toughness PTT resin with multi-stage cooling to regulate crystallinity according to claim 1, characterized in that: During the cutting process in step four, the cutting speed is 2800~3200 r / min, and the length-to-diameter ratio of the particles is controlled to be 1:(0.9~1.1).

9. The granulation process for high-toughness PTT resin with multi-stage cooling to regulate crystallinity according to claim 1, characterized in that: In step four, the roller surface temperature is set to 55-65℃ and the stretching ratio to 1.5-2.0 times in the twin-roll stretching machine, and the molecular chain orientation is induced to be 15%-20%. Particles with a size deviation >0.5mm are screened out.

10. The granulation process for high-toughness PTT resin with multi-stage cooling to regulate crystallinity according to claim 1, characterized in that: The specific preparation process of the high-toughness PTT resin in step five is as follows: The stretched particles from step four are fed into a warm water conveying tank at 45~50℃ and a water flow rate of 0.6~0.8m / s. After conveying for 8~10 minutes, gradient drying is carried out. The drying process is as follows: at 60℃ and a wind speed of 1.0m / s, the temperature is maintained for 30 minutes; at 70℃ and a wind speed of 1.2m / s, the temperature is maintained for 30 minutes; and at 80℃ and a wind speed of 1.5m / s, the temperature is maintained for 60 minutes. The moisture content of the particles is controlled to be ≤0.08%. The particles are then cooled to room temperature by a 25℃ cooling conveyor belt to obtain the high-toughness PTT resin.

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