In numerous industries, including textiles, packaging, automotive interiors, and filtration materials, nylon hot-melt yarn, thanks to its low-temperature melt bonding, high-strength bonding, and washable and aging-resistant properties, has become a key alternative to traditional stitching and chemical glues. Export demand for high-quality nylon hot-melt yarn continues to grow, particularly in global trade. Overseas customers prioritize not only product performance but also the stability and compliance of the underlying technological process. This article will begin with the core definition of nylon hot-melt yarn, analyze the key technical aspects of its entire process, and analyze its advantages and quality control logic. This article, combined with the application requirements of export scenarios, provides a comprehensive technical reference for industry practitioners and buyers.
I. Basic Understanding: What is Nylon Hot Melt Fiber? Core Characteristics Determine the Process Direction
Before delving into the process, we must first clarify the essence of nylon hot melt fiber—it is not an ordinary nylon fiber, but a “functional bonding fiber” made through raw material modification and process optimization. Its core characteristics directly determine the design logic of the technology and process.
1. Definition and Composition: The “Functional Upgrade” of Modified Nylon
Nylon Hot Melt Yarn (NHMY) uses polycaprolactam (PA6) and polyhexamethylene adipamide (PA66) as its base resins. By adding comonomers (such as adipic acid and sebacic acid), toughening agents (such as elastomers), antioxidants, UV inhibitors, and other additives, its molecular structure is adjusted to achieve melting properties “lower than the melting point of conventional nylon (180-260°C)” (the typical melting point range is 80-180°C).
Compared to ordinary nylon fiber, its core difference lies in: while ordinary nylon fiber pursues “high strength and high toughness,” nylon hot melt yarn strives for “precise melting point control, rapid melt flowability, and high bond strength after cooling”—these three key requirements are the core goals of the production process.
2. Core Characteristics: The “Guide” of Process Design
Precise Melting Point Range: Depending on the application scenario (e.g., clothing interlinings require a low melting point to avoid fabric damage, while automotive interiors require a high melting point for high and low temperature resistance), the process must maintain the melting point within a ±5°C range. Excessive deviations can lead to bond failure or fabric damage.
Melt Flowability: The melt must have an appropriate viscosity (typically 2000-5000 mPa·s). Too high a viscosity prevents penetration into fiber gaps, while too low a viscosity can easily cause “bleeding,” affecting appearance and bond strength.
Environmental Stability: The finished product must be washable (bond strength retention ≥80% after 20 washes at 50°C) and resistant to aging (no noticeable embrittlement after 1000 hours of UV irradiation). This requires strict control in raw material selection and post-processing.
II. Core Links: A Breakdown of the Full Technical Process for Nylon Hot-Melt Yarn
The production of nylon hot-melt yarn involves a “precision control + continuous production” process. From raw materials to finished product, it undergoes six key steps. Deviations in process parameters at each step can affect final product quality. The following are the key technical points and equipment requirements for each step:
Step 1: Raw Material Preparation and Pretreatment – The Foundation from “Formula” to “Qualified Raw Materials”
Raw materials are the starting point of the process and the “first line of defense” for quality. The core objective of this step is to ensure that the raw materials are dry, evenly mixed, and free of impurities to avoid problems such as yarn breakage and bubbles during the subsequent spinning process.
1.1 Formulation Design: The Core Determinant of Product Performance
Based on the application requirements of the target export market (e.g., the European and American markets have high environmental requirements and must comply with OEKO-TEX® Standard 100), the formulation should focus on adjusting the following components:
Base resin: PA6 (lower melting point, suitable for textile applications) or PA66 (higher melting point, suitable for heat-resistant applications). The melting point can be adjusted through copolymerization (e.g., copolymerization of PA6 and PA66 can lower the melting point to 120-150°C). Additives:
Tougheners (such as POE-g-MAH): Improve impact resistance after bonding, typically added at 3%-5%;
Antioxidants (such as 1010/168 blends): Prevent resin aging during high-temperature spinning, typically added at 0.2%-0.5%;
UV inhibitors (such as UV-531): For outdoor applications (such as sunshade fabrics), added at 0.3%-0.8%;
Environmentally friendly lubricants (such as erucamide): Reduce friction during spinning and prevent the release of harmful substances.
1.2 Raw Material Drying: Addressing Nylon’s Hygroscopicity
Nylon resins (especially PA6) are highly hygroscopic. If the raw material contains more than 0.1% moisture, hydrolysis will occur during high-temperature melting, leading to molecular chain breakage and affecting fiber strength and melt flowability. Therefore, rigorous drying is essential:
Equipment: Twin-screw dehumidifying dryer (temperature 80-100°C, dew point ≤ -40°C);
Parameters: Drying time 4-6 hours, moisture content controlled below 0.05%;
Note: The dried raw materials must be sealed and transported to the spinning machine hopper to prevent secondary moisture absorption.
1.3 Mixing and Homogenization: Ensure Ingredient Uniformity
Use a high-speed mixer (speed 1000-1500 rpm, temperature 60-80°C) to mix the resin and additives for 15-20 minutes to ensure uniform dispersion of the additives. Inhomogeneous mixing will result in “localized melting point deviations” in the finished product, leading to inconsistent bond strength. Step 2: Melt Spinning – The Critical Transformation from “Solid Particles” to “Nascent Fiber”
Melt spinning is the core process for converting dried raw materials into “stretchable fibers.” Its key focus is precise control of temperature, pressure, and extrusion speed to ensure stable melt flow and avoid breakage and uneven yarn thickness (the CV value for strand uniformity must be ≤2%).
2.1 Core Equipment: Screw Extruder
A single-screw extruder (diameter 30-65mm, aspect ratio L/D = 28-32) is used. The screw is divided into three sections, and the temperature of each section must be precisely set according to the resin melting point (using PA6 copolymer hot melt yarn with a melting point of 130°C as an example):
Feeding Section: 80-100°C (preheating the raw materials to prevent agglomeration);
Compression Section: 120-140°C (gradually melting the raw materials and removing air);
Metering Section: 140-160°C (complete melting, controlling melt viscosity, and ensuring stable extrusion).
2.2 Spinneret and Melt Filtration: Controlling Fiber Fineness and Purity
Spinnerets are made of stainless steel. The aperture size is selected based on the final product fineness (typically 20-150D) (e.g., 40D hot melt yarn corresponds to a spinneret aperture diameter of 0.2-0.3mm). The number of apertures is typically 36-144 (adjustable based on production requirements).
Melt Filtration: Two to three layers of filter screens (20-40μm precision) are placed before the spinneret to filter impurities and gel particles from the melt, prevent clogging of the spinneret apertures, and ensure a smooth fiber surface.
2.3 Extrusion Speed Control: Matching with Subsequent Strength
The extrusion speed is typically 10-20m/min and must be matched to the subsequent stretching speed (stretch ratio = stretch speed / extrusion speed). Extrusion speed fluctuations exceeding ±1% will result in uneven fiber thickness, affecting the final product strength.
Step 3: Cooling and Shaping – Controlling Fiber Crystallinity and Preventing Thermal Shrinkage
Synthetic fibers extruded from melt (at approximately 150-170°C) require rapid cooling and shaping to control their crystallinity (typically 20%-30%). Excessive crystallinity results in brittle fibers, while low crystallinity leads to excessive thermal shrinkage (the finished product’s thermal shrinkage must be ≤3%, otherwise deformation may occur during subsequent processing).
3.1 Cooling Method: Side Blow vs. Circular Blow
Side Blow: Suitable for fine denier yarns (20-50D), using horizontal laminar airflow (speed 0.5-1.0 m/s, air temperature 20-25°C) for uniform cooling and reduced fiber oscillation.
Circular Blow: Suitable for coarse denier yarns (50-150D), using a circular, uniform airflow (speed 1.0-1.5 m/s, air temperature 22-28°C), offering high cooling efficiency and suitable for high-volume production. 3.2 Cooling Distance: A Key Parameter
The cooling distance (the distance from the spinneret to the nozzle) is typically 10-20 cm. A distance too short will result in inadequate cooling and fiber adhesion; a distance too long will cause fiber sagging, affecting yarn uniformity.
Step 4: Stretch Orientation – Improving Fiber Strength and Dimensional Stability
Naturally spun fibers have low strength (approximately 1.0-1.5 cN/dtex). Stretch orientation is required to align the molecular chains along the fiber axis, increasing strength (the final strength must be ≥2.5 cN/dtex) while reducing elongation (controlled to 20%-30%) to prevent breakage during subsequent processing. 4.1 Stretching Equipment: Multi-Roller Stretching Machine
A 2-3-roller stretching machine is used, with stretching achieved by differential speed between the rollers. Key parameters:
Stretching Temperature: Use a temperature above the glass transition temperature but below the melting point (e.g., 50-70°C for PA6 copolymer hot-melt filament). Temperatures too low can easily cause filament breakage, while temperatures too high can cause fiber melting.
Stretching Ratio: Adjusted based on the required strength of the finished product, typically 2-5x (e.g., for 40D hot-melt filament, a 3x stretch ratio can achieve a strength of 3.0 cN/dtex).
Stretching Speed: 30-80 m/min, which must be aligned with the extrusion and winding speeds to avoid fluctuations in fiber tension. 4.2 Drawing Methods: Cold Drawing vs. Hot Drawing
Cold drawing is suitable for low-melting-point, fine-denier yarns. It requires no additional heating and relies on roller friction to generate heat, resulting in a simple process.
Hot drawing is suitable for high-melting-point, coarse-denier yarns. It requires auxiliary heating (70-90°C) with hot air or heated rollers, resulting in more uniform drawing and higher strength.
Step 5: Heat Setting – Eliminating Internal Stress and Ensuring Dimensional Stability
Stretched fibers contain internal stress (if not eliminated, they will shrink upon subsequent heating). The core goal of heat setting is to eliminate this stress, stabilize the molecular chain arrangement, and ensure dimensional stability during melt bonding (heat shrinkage ≤ 3%). 5.1 Heat Setting Equipment: Hot Air Oven or Heated Roller
Hot air oven: Temperature 80-120°C (10-20°C below the melting point of the finished product), time 10-30 seconds, hot air speed 0.8-1.2 m/s, to ensure even heating of the fiber;
Heated Roller: Temperature 90-130°C, setting is achieved through contact between the fiber and the heated roller (contact time 5-10 seconds), suitable for high-volume production.
5.2 Setting Tension Control: Key Details
Maintaining appropriate tension during setting (usually 0.1-0.3 cN/dtex). Excessive tension will cause the fiber to overstretch, resulting in increased strength but low elongation; too little tension will cause the fiber to relax and exceed the specified thermal shrinkage.
Step 6: Winding and Receiving – The Final Step from “Continuous Fiber” to “Finished Package”
Winding and receiving must ensure that the finished package is flat, tight, and free of broken ends, facilitating subsequent customer use (such as warping and weaving). It also prevents loosening and edge collapse during transportation.
6.1 Winding Equipment: Precision Winder
A fully automatic precision winder is used. Key parameters:
Winding Speed: Matches the drawing speed (30-80 m/min), with speed fluctuation ≤±0.5%;
Winding Tension: 0.05-0.2 cN/dtex, ensuring uniform package density (1.2-1.4 g/cm³);
Packaging Specifications: Adjusted according to customer requirements (e.g., diameter 200-300 mm, width 80-150 mm). Typical package weight is 5-10 kg. 6.2 Quality Inspection: A Combination of Online and Offline Methods
Online Inspection: Real-time monitoring of fiber fineness (sliver CV value ≤ 2%) using a laser diameter gauge, and tension fluctuations monitored by a tension sensor.
Offline Inspection: Samples are taken from each roll to test melting point (differential scanning calorimetry (DSC) with an accuracy of ±2°C), breaking strength (tested by an electronic strength tester, ≥2.5 cN/dtex), and melt bond strength (peel strength after hot pressing, ≥5 N/25 mm).
III. Process Advantages: Why is nylon hot-melt yarn technology superior to traditional bonding solutions?
For export, overseas customers choose nylon hot-melt yarn because they recognize the “performance + efficiency + environmental benefits” offered by its technology. Compared to traditional needle and thread sewing and chemical gluing, this process offers advantages primarily in the following four areas:
Comparison Dimensions: Nylon Hot Melt Yarn (Process in This Article) Traditional Needle and Thread Sewing Chemical Glue Bonding
Bonding Efficiency: Rapid melting at low temperatures (10-30 seconds for bonding), enabling continuous production. Relying on manual or machine sewing, this process is slow (1-5 m/min). Glue curing time is required (30-60 minutes), resulting in low efficiency.
Bond Strength: Interwoven with fibers after melting, this process is washable and resistant to aging (≥80%). Pinholes can easily break the seam, causing it to loosen after washing. Glue is susceptible to aging, resulting in a decrease in bond strength (≤50%) after high temperatures or washing.
Environmental Compliance: Solvent-free, VOC-free, and compliant with OEKO-TEX® and FDA standards. Environmentally friendly, but pinholes can affect fabric breathability. Contains solvents (such as toluene), which can easily exceed environmental standards and not meet European and American environmental requirements.
Application Flexibility: Can be made into fine denier yarn (20D), suitable for lightweight fabrics; melting point can be customized. Thick seams affect the appearance and are unsuitable for thin/elastic fabrics. They are prone to adhesive seepage, affecting the fabric’s appearance and preventing use in high-temperature environments.
For example, in the European and American textile markets, garment interlining customers are using nylon hot-melt yarn (melting point 110-130°C) to replace needle and thread sewing through “heat-press bonding.” This not only improves production efficiency (from 1m/min to 10m/min), but also avoids fabric deformation caused by pinholes, while complying with EU REACH regulations on hazardous substances—a testament to the market competitiveness enabled by technological advancements.
IV. How to Meet the Individual Needs of Different Markets?
The key is to “precisely match customer needs,” and the technical process for nylon hot-melt yarn needs to be adjusted based on the target market’s application scenarios. The following are process adaptation solutions for three typical export markets:
1. Textile and Apparel (European and American markets, such as those requiring OEKO-TEX® certification)
Process Adjustments: Use environmentally friendly additives (heavy metal-free and formaldehyde-free), control the melting point to 110-130°C (to avoid damaging lightweight fabrics like cotton and silk), and achieve a finished product fineness of 20-50D (suitable for interlining and lace bonding).
Compliance Requirements: Pass OEKO-TEX® Standard 100 testing to ensure heavy metal content (lead, cadmium) ≤ 0.1mg/kg and formaldehyde content ≤ 20mg/kg.
2. Automotive Interiors (North American market, e.g., for high and low temperature resistance requirements)
Process Adjustment: Use PA66 copolymer resin, raise the melting point to 160-180°C, add antioxidants and UV inhibitors (0.5% each), and increase the heat setting temperature to 130-150°C to ensure no embrittlement or shrinkage in temperatures between -40°C and 80°C.
Testing Standards: Meet automotive industry standards (e.g., FMVSS 302 flame retardancy test, burning rate ≤100mm/min).
3. Packaging Materials (Southeast Asian market, e.g., for low-cost requirements)
Process Adjustment: Use PA6 recycled resin (FDA food contact compliant), simplify the additive formulation (add only 0.2% antioxidant), and control the melting point to 140-160°C (suitable for bonding non-woven bags) to reduce production costs.
Performance Requirements: Breaking strength ≥ 2.0 cN/dtex, melt bond strength ≥ 3N/25mm, and meet packaging load requirements (≥5kg).
V. Innovation Directions in Nylon Hot-Melt Yarn Technology and Processes
With the increasing global market demand for “environmental protection, high performance, and functionality,” nylon hot-melt yarn technology and processes are innovating in the following three directions. These are key to enhancing the core competitiveness of export companies:
Bio-based nylon hot-melt yarn process: Bio-based PA6 (such as caprolactam extracted from castor oil) is used to replace traditional petroleum-based resins. The process requires adjustments to the drying temperature (70-90°C) and the melting temperature (reduced by 10-15°C). The final product is biodegradable (degradation rate ≥90% in 180 days under composting conditions), meeting the EU’s “carbon neutrality” goals.
Fine Denier and Functional Processing: Developing 10-20D ultra-fine denier nylon hot-melt yarn suitable for medical dressings (such as wound patch adhesives). This process requires reducing the spinneret diameter (0.1-0.2mm) and increasing the cooling air speed (1.2-1.5m/s). Furthermore, developing antibacterial hot-melt yarn (with the addition of silver ion additives, achieving an antibacterial rate ≥99%) to meet the needs of the medical and maternity markets.
Intelligent Process Upgrade: Introducing an AI control system to monitor parameters such as spinning temperature, drawing tension, and winding speed in real time (with a deviation of ≤0.3%). Through big data analysis, process parameters are optimized, reducing scrap rates from 5% to below 1%, and achieving a rapid “order-process-production” response time (delivery time for small-batch custom orders has been reduced from 7 days to 3 days).
Post time: Oct-15-2025