A Comprehensive Analysis of POY Polyester Filament Production Process: A Precision Manufacturing Journey from Raw Materials to Finished Products

I. Core Principles of POY Polyester Filament Production The essence of POY polyester filament production is to transform polyester chips (or melt after direct esterification) through a series of physicochemical processes such as melting, spinning, cooling, drawing, and winding, so that the polymer chains are transformed from a disordered state to a partially oriented ordered structure, ultimately forming fiber products with specific linear density, strength, elongation, and other indicators. The core principle lies in balancing the orientation and crystallinity of the fiber by precisely controlling parameters such as melt temperature, spinning speed, and cooling conditions—ensuring that the fiber has a certain strength and modulus while retaining sufficient elongation, providing good processing performance for subsequent texturing (such as DTY processing) or direct application. II. Mainstream Production Process Routes: Direct Spinning and Chip Spinning. Currently, the production of POY polyester filament is mainly divided into two major process routes. Among them, the direct spinning process has become the industry mainstream due to its advantages such as short process, low energy consumption, and stable product quality, and is especially widely used by large-scale enterprises. (I) Direct Spinning Process: A Mainstream Choice for High Efficiency and Energy Saving Direct spinning refers to the direct esterification and polymerization reaction of polyester raw materials (PTA and EG) to generate polyester melt, which is then directly produced into POY filaments through a spinning system. This eliminates the need for intermediate steps such as slicing, granulation, and drying. The core process includes six major steps: "esterification polymerization — melt conveying — spinning — cooling — drawing — winding." The representative technology is the "five-reactor" direct spinning polymerization process. Esterification and Polymerization: The Core Step in Melt Preparation This step involves mixing purified terephthalic acid (PTA) and ethylene glycol (EG) in a specific molar ratio and carrying out an esterification reaction under the action of a catalyst to generate ethylene terephthalate (BHET) monomer. Subsequently, the BHET monomer is fed into a polymerization reactor for polycondensation under high temperature and vacuum conditions, gradually forming a high-molecular-weight polyester melt. The advanced "five-reactor" polymerization process, through staged reaction control, can precisely adjust the viscosity and molecular weight distribution of the melt, ensuring uniform and stable melt quality. Its technological advancement surpasses some traditional international technologies, and it achieves annual energy savings of over 37% compared to similar imported equipment, aligning with the concept of green production. Melt Conveying and Filtration: The polymerized polyester melt is conveyed to the spinning box through insulated conveying pipelines (temperature controlled at 280-290℃). During this process, it undergoes a precision filtration device to remove minute impurities and gel particles from the melt, preventing clogging of the spinneret orifices and ensuring the continuity of the spinning process and the uniformity of the fibers. Spinning: The Key Step in Converting Melt into Filaments: The purified melt enters the spinning box, where it is precisely metered by a metering pump (controlling the flow rate consistency of each filament). It is then extruded through the tiny spinneret orifices (typically 0.2-0.4mm in diameter) of the spinneret, forming a continuous stream of melt. The number and diameter distribution of orifices in the spinneret directly determine the linear density and number of filaments in POY filaments, and can be flexibly adjusted according to product specifications (such as 150D/48F, 300D/96F, etc.). Cooling and solidification: The core control of filament formation. The molten stream extruded from the spinneret is extremely hot and must immediately enter the cooling chamber. Through side-blowing or ring-blowing, the molten stream is rapidly cooled to below its glass transition temperature, solidifying to form nascent fibers. The uniformity of cooling air velocity, temperature, and pressure is a key control point—excessive air velocity can cause filament vibration and poor cohesion, while insufficient air velocity will result in uneven cooling and inconsistent fiber thickness, directly affecting the product's breaking strength and elongation stability. Drafting and Oiling: After cooling, the nascent fibers are moderately drafted through a guide disc, causing the polymer chains to partially align along the fiber axis, thus increasing fiber strength. Simultaneously, a special spinning oil is evenly sprayed onto the filament surface through an oil nozzle, providing lubrication, antistatic properties, and improved cohesion, laying the foundation for subsequent winding and processing (such as texturing and weaving). The choice of oil needs to be adjusted according to the product's intended use; for example, POY used in high-end apparel fabrics requires a low-residue, environmentally friendly oil. Winding and Forming: The drafted and oiled filaments are finally wound into POY packages of a specific weight and forming quality using a winding machine. Winding speed is one of the core parameters in POY production, typically controlled between 3000-4000 m/min. Too high a speed will result in excessive fiber orientation and insufficient elongation, while too low a speed will affect production efficiency and fiber performance. Advanced winding equipment (such as the fully automated production line from Barmag in Germany) can achieve constant tension winding, ensuring uniform package density and no hard edges, facilitating subsequent processing.

(II) Chip Spinning Process: Flexible Adaptation to Niche Needs
The chip spinning process involves first processing polyester melt into polyester chips, drying them to remove moisture, and then feeding the dried chips into a spinning machine for melting and spinning, ultimately producing POY filament. The advantages of this process are its high flexibility, adaptability to small-batch, multi-specification production needs, and relatively low equipment investment; however, the process is longer, energy consumption is higher, and the chip drying effect directly affects the spinning quality, easily leading to problems such as breakage and fuzz. Currently, it is mainly used in the production of small and medium-sized enterprises or niche specifications.

III. Key Technologies and Quality Control Points
The production of POY polyester filament is a systematic project, requiring precise technical control and full-process quality management to ensure stable product performance. Melt Quality Control: Melt viscosity is monitored in real-time using an online viscosity monitoring system, and polymerization reaction parameters such as temperature and pressure are adjusted to ensure uniform molecular weight distribution in the melt. The purity of PTA and EG raw materials is strictly controlled (≥99.9%) to prevent impurities from affecting melt quality. Precise Control of Spinning Parameters: A DCS distributed control system (some companies use imported Japanese equipment) is adopted to achieve automated and precise control of key parameters such as spinning temperature, cooling air velocity, draw ratio, and winding speed, with errors controlled within ±1%, ensuring consistency in fiber linear density, strength, elongation, and other indicators. Equipment Precision Guarantee: The spinneret undergoes precision machining and polishing to ensure consistent spinneret orifice diameter and smooth inner walls. The guide disc and winding head of the winding machine require regular maintenance to prevent mechanical wear that could cause fluctuations in filament tension. Full-process testing: Multiple testing points are set up during the production process to monitor fiber linear density deviation, breaking strength, breaking elongation, and evenness in real time. Sampling testing is conducted on finished products before they leave the factory to ensure compliance with industry standards such as GB/T 14460-2017 "Polyester Filament".

IV. Technological Advantages and Product Characteristics Advanced POY polyester filament production technology (especially direct spinning) endows the product with many core advantages: Stable performance: Through precise process control, the product's linear density deviation, strength, elongation, and other indicators fluctuate little, adapting to high-end processing needs; High added value: Differentiated products, such as flat yarns and differential shrinkage yarns, can be produced by adjusting spinning process parameters (such as spinneret shape and cooling conditions), possessing functional characteristics such as moisture absorption and wicking, warmth retention and anti-pilling, and unique luster; Energy saving and environmental protection: Direct spinning reduces energy consumption by more than 30% compared to chip spinning, with some advanced processes achieving annual energy savings of over 37%, and reducing pollutant emissions during chip granulation; Strong processing adaptability: The product has good cohesion and spinnability, and can be directly used for weaving, or processed into DTY polyester low-elasticity yarn, suitable for various applications such as high-end clothing fabrics, blankets, and carpets. V. Industry Development Trends
As the textile industry transforms towards green, intelligent, and differentiated production, the POY polyester filament production process also exhibits three major development trends:
* **Green Upgrading:** Further optimizing polymerization and spinning processes to reduce energy and water consumption; promoting environmentally friendly technologies such as solution dyeing and biodegradable polyester to reduce pollution emissions in subsequent processing stages;
* **Intelligent Transformation:** Introducing technologies such as the Industrial Internet and AI visual inspection to achieve automated monitoring and intelligent control of the entire production process, improving production efficiency and product qualification rate;
* **Differentiated Innovation:** Developing functional POY products (such as antibacterial, UV-resistant, and flame-retardant products) by developing new spinnerets and adjusting process parameters, expanding application scenarios in industrial textiles, high-end home textiles, and other fields.

Conclusion
The POY polyester filament production process is an important manifestation of technological progress in the textile industry, embodying the wisdom of precision manufacturing in every step from raw materials to finished products. With continuous iteration and upgrading of process technology, POY polyester filament has not only made breakthroughs in performance but also continuously innovated in green and intelligent aspects, providing solid support for the high-quality development of the textile industry. In the future, enterprises that master core process technologies and have full-process quality control capabilities will occupy a dominant position in industry competition, driving POY polyester filament products towards higher quality, more functions, and greater environmental friendliness.