Nylon embroidery thread is a key material in embroidery, clothing, and home decoration. The precision of its production process directly affects the color, strength, and durability of the finished product. From raw material selection to finished product packaging, the production of nylon embroidery thread requires multiple rigorous processes, integrating the core requirements of polymer materials science and textile engineering technology. The following systematically describes its typical production process.
Raw Material Pretreatment: Selection and Drying of High-Purity Nylon Chips
The basic raw material for nylon embroidery thread is high-viscosity nylon 6 or nylon 66 chips (accounting for more than 90% of the finished product mass). Its molecular weight needs to be controlled within the range of 18,000-25,000 to ensure spinnability and uniformity of subsequent dyeing. Before production, the raw material must undergo double pretreatment: first, impurities (such as metal particles and unmelted gel) are removed by a vibrating screen and magnetic separator; then, it is dried in a vacuum drum dryer at 105-120℃ for 8-12 hours, strictly controlling the moisture content to below 50ppm-a crucial step to prevent hydrolysis and chain breakage during melt spinning.
Melt Spinning: Fiber Formation under High Temperature and Pressure
Dried nylon chips are heated to 260-280℃ (Nylon 6) or 275-295℃ (Nylon 66) using a screw extruder, melting into a melt of suitable viscosity (viscosity index controlled between 2.8 and 3.5) under the action of the screw. The melt is then precisely flowed through a metering pump, filtered (pore size ≤ 5μm) to remove residual impurities, and finally extruded from a spinneret (typically 32-48 holes, pore size 0.2-0.3mm) to form nascent fibers. At this stage, precise control of melt temperature, extrusion speed, and cooling air velocity (15-25m/s) is required to ensure fiber diameter deviation ≤ ±3μm, providing a uniform initial structure for subsequent stretching.
Drawing and Orientation: Molecular Chain Directional Strengthening
The molecular chains of the nascent fibers are in a disordered coiled state, with a strength only 30%-40% of the final product. Through a multi-stage drafting process (typically including primary drafting, secondary drafting, and tension heat setting), the fibers are stretched to 3-5 times their original length using the synergistic effect of hot rollers (80-130℃) and tension rollers. During this process, the nylon molecular chains are highly oriented along the fiber axis, increasing crystallinity from 15%-20% in its initial state to 35%-45%, resulting in a final breaking strength of 4.5-6.0 cN/dtex (2-3 times that of ordinary sewing thread), while maintaining a moderate elongation (18%-25%) to meet the deformation requirements of embroidery.
Heat Setting and Winding: Dimensional Stability and Rewinding Preparation
The drafted fibers need to undergo a heat setting process (120-150℃, 20-30 seconds). This process eliminates internal stress through relaxation or tensioning, fixes the molecular chain orientation structure, and controls the boiling water shrinkage rate to within 5% (compared to 15%-20% for ordinary unset fibers). After being air-cooled, the shaped fibers are evenly wound onto paper or plastic tubes using a high-speed winding machine (linear speed 800-1200 m/min), forming a uniformly dense, non-overlapping yarn cake, providing standardized raw material units for subsequent processing.
Post-processing: Oiling, Twisting, and Dyeing
1. Oiling: A smoothing agent (such as polyether-modified silicone oil, content 0.8%-1.5%) is evenly applied to the surface of the yarn cake using an oil roller or nozzle, reducing the coefficient of friction between fibers (from 0.35 to below 0.15), decreasing thread breakage during embroidery, and improving gloss.
2. Twisting and Plying: Depending on the application (e.g., flat embroidery, towel embroidery), the monofilaments can be twisted together at a twist rate of 200-800 twists/meter (commonly 2 or 4 strands) using a twisting machine, enhancing the stiffness of the thread and the three-dimensional embroidery effect.
3. Dyeing and Fixing: For specific colors, the silk stock must undergo pretreatment (degreasing → alkali reduction → washing) followed by dyeing in a high-temperature, high-pressure dyeing machine using disperse dyes or acid dyes (pH 4.5-6.0) at 110-130℃. This is followed by reduction cleaning (removing excess dye) and fixing agent treatment (improving color fastness to grade 4-5). Finally, a softener is applied to improve the hand feel.
Quality Inspection and Packaging: Closed-Loop Quality Control Throughout the Process
Finished nylon embroidery thread must pass more than 10 rigorous tests: thread density deviation (±2%), breaking strength (≥90% of standard value), color difference (ΔE≤1.0), and fuzz index (≤3 threads/cm), etc. Qualified products are automatically counted and cut, then packaged according to specifications (e.g., 500 meters/spool, 1000 meters/roll) in moisture-proof paper tubes or plastic films, and labeled with batch number, color number, and applicable standard (e.g., FZ/T 63012-2019 "Embroidery Thread"). Finally, they are stored in an environment with a temperature of 25℃±5℃ and humidity ≤60% to ensure long-term stable performance.
In summary, the production process of nylon embroidery thread is a multi-dimensional integration of materials science, precision manufacturing, and quality control. From the molecular-level pretreatment of raw materials to the final colorfastness verification, each process requires precise parameter control to ultimately produce high-quality thread with high strength, high colorfastness, and excellent embroidery adaptability, meeting the stringent requirements of high-end apparel, handicrafts, and industrial sewing industries.