What are the quality inspection steps for nylon hot-melt yarn?

What are the quality inspection steps for nylon hot-melt yarn?

In the international trade of nylon hot-melt yarn, quality stability is crucial to the success of any partnership. According to industry statistics, product returns and customs clearance delays caused by quality inspection oversights can result in an average order loss of 15%-20% for both buyers and sellers. For buyers targeting international markets such as the EU, North America, and Southeast Asia, a transparent and rigorous quality inspection system is not only a “passport” to product compliance but also the “foundation of trust” for long-term partnerships. This article will comprehensively analyze the core quality inspection steps for nylon hot-melt yarn, from raw materials to finished products, to help you understand the quality control logic behind high-quality products.

I. Source Control: Quality Inspection of Raw Materials Upon Incoming to the Factory to Avoid Risks at the Root

The quality of nylon hot-melt yarn depends primarily on the purity and stability of upstream raw materials. We implement a “three-inspection and one-verification” standard for each incoming batch of nylon chips (the main raw material) and modifying additives (such as toughening agents and antioxidants) to prevent unqualified materials from entering the production process:

Ingredient Purity Testing
High-Performance Liquid Chromatography (HPLC) and Fourier Transform Infrared Spectroscopy (FTIR) are used to test the molecular structure and impurity content of nylon chips. The requirement is that the residual caprolactam monomer content is ≤ 0.3% (in compliance with Annex XVII of the EU REACH Regulation) and the ash content is ≤ 0.05%. This prevents impurities from causing poor adhesion or discoloration during subsequent hot-melt bonding.

Key Physical Performance Testing

Melting Point Testing: Using a Differential Scanning Calorimeter (DSC), the melting point of the nylon chips is controlled within a ±2°C tolerance (the melting point of conventional hot-melt filaments is 110-130°C, adjusted based on the buyer’s application scenario) to ensure consistent melt extrusion temperature.

Melt Flow Rate (MFR) Testing: At 230°C and a load of 2.16 kg, the MFR must be stable at 8-12 g/10 min. Excessively high values ​​can lead to filament breakage; excessively low values ​​can affect extrusion efficiency and filament uniformity.

Additive Compatibility Verification

Additives such as antioxidants and UV inhibitors are tested for compatibility with the nylon substrate through accelerated aging tests (70°C, 85% humidity for 168 hours) to prevent additive precipitation that could cause blooming on the filament surface and affect downstream lamination processes.

Supplier Qualification Verification
Raw material suppliers are required to provide material reports issued by SGS or ITS, and core suppliers are audited quarterly to ensure traceability of raw material sources and consistent production standards.

II. Process Control: Inspections at all stages of production to prevent quality risks in real time

In the production process of nylon hot-melt yarn (melt extrusion → drawing → shaping → winding), even slight fluctuations in parameters such as temperature, speed, and tension can lead to product quality deviations. We employ a dual-mode approach of “fixed-point inspection + online monitoring” to achieve dynamic quality control throughout the production process:

Melt extrusion: Strictly control melt stability
Temperature monitoring: An intelligent temperature control system monitors the temperature of each screw section (feed, compression, and homogenization) in real time, with a deviation of ≤±1°C. For example, the feed section temperature must be maintained at 220-230°C, and the homogenization section temperature at 240-250°C to prevent nylon degradation due to excessively high temperatures, or incomplete melting due to excessively low temperatures.
Melt pressure monitoring: Melt pressure is recorded every 15 minutes. The normal range is 15-20 MPa. If the pressure suddenly increases, immediately check for filter blockage or raw material impurities to prevent uneven strand thickness. Wire Drawing and Forming: Ensuring the Physical Properties of the Wire

Diameter Uniformity Testing: A laser diameter gauge is used to inspect each wire inline. The diameter tolerance must be controlled within ±0.02mm (for example, if the customer customizes 40D/12F specifications, the single wire diameter deviation must not exceed 0.005mm). This prevents uneven wire diameter from causing inconsistent forces during subsequent weaving or bonding.

Stretching Ratio Control: The stretching ratio is adjusted according to product specifications (typically 3-5x). Real-time sampling testing is performed on a tensile testing machine to ensure that the wire’s breaking strength is ≥4.5cN/dtex and its elongation at break is ≤30%, meeting the mechanical requirements of various applications, such as clothing interlinings and filter materials.

Winding: Avoiding Appearance Defects in Finished Products

Tension Control: Winding tension must be maintained at a stable 5-8 cN. Excessive tension can lead to excessive stretching of the yarn; too little tension can cause looseness in the bobbin, impacting subsequent use.

Appearance Inspection: Each finished bobbin undergoes both manual and machine inspection to eliminate issues such as lint, broken ends, and oil stains. The machine uses a high-definition vision system to identify surface defects in the bobbin, while manual inspections ensure the yarn cross-section is round (shaped yarn must meet custom shape tolerances).

III. Final Inspection of Finished Products: Multi-dimensional Testing to Ensure Compliance with International Market Standards

The finished product is the final stage of quality inspection. For export nylon hot melt yarn, we perform “full-item testing + customized verification” to ensure that each batch meets the compliance requirements and application scenarios of the buyer’s market:

Final Inspection of Basic Performance

Hot Melt Adhesion Performance Test: The nylon hot melt yarn is bonded to a substrate such as polyester or cotton (temperature 120-140°C, pressure 0.3 MPa, time 10 seconds). The peel strength after bonding is tested using a peel strength tester. The requirement is ≥3N/25mm (this can be adjusted based on the buyer’s needs for different substrates) to ensure a secure bond.

Heat Shrinkage Test: After immersion in 100°C hot water for 30 minutes, the heat shrinkage must be ≤3% to prevent dimensional deformation during the high-temperature setting process.

Washability Test: According to ISO 6330, the product is washed for 5 minutes. After a second wash (40°C, using a standard detergent), the bond strength is retested, and the degradation rate must be ≤10%, meeting the durability requirements for applications requiring washing, such as clothing and home textiles.

International Compliance Testing

Hazardous Substance Screening: For the EU market, phthalates (such as DBP and DEHP) are tested using GC-MS (gas chromatography-mass spectrometry) with a requirement of ≤0.1%. Heavy metals (such as lead, cadmium, and mercury) are tested using ICP-MS (inductively coupled plasma mass spectrometry) with a requirement of ≤100 ppm, complying with RoHS 2.0 regulations.

Food Contact Compliance (for food filtration applications): Migration of nylon thermal fuses is tested in accordance with US FDA 21 CFR 177.1500 to ensure no hazardous substances are released.

Flame Retardancy (for automotive interior applications): Flame retardancy ratings must meet UL 94 standards and must meet V-2 or higher, meeting automotive safety requirements.

Batch Consistency Verification

3% of each batch of finished products is randomly sampled for full retesting. Samples are also retained (with a 12-month shelf life). If buyers raise quality concerns later, sample comparisons and test data are readily available, ensuring traceability of quality issues.

Fourth, System Assurance: Build a closed-loop quality inspection process throughout the entire process to provide buyers with peace of mind.

High-quality quality inspection is not just about “covering every step” but also about “systemic support.” We ensure the implementation of quality inspection standards through three key mechanisms:

Laboratory Accreditation

Our in-house laboratory is accredited by CNAS (China National Accreditation Service for Conformity Assessment). Our test data is mutually recognized with international organizations such as the EU CE and the US FDA, eliminating duplicate testing for buyers.

Professional Staff Training

Our quality inspection team undergoes dual training, combining theoretical assessment with practical certification, becoming familiar with international testing standards such as ISO, AATCC, and ASTM. We conduct quarterly skill upgrades to ensure standardized testing procedures.

Data Visualization and Traceability

We have established a “one-code per roll” quality traceability system. By scanning the QR code on the product label, buyers can access complete data on the roll, including raw material batches, production parameters, and test reports, ensuring transparent quality control.