Multi-layer co-extruded TPU calendered film: "Precise Temperature Control" and "structural strengthening" of high-frequency welding process

In the field of high-end materials processing, multilayer co-extruded TPU calendered films, with their excellent elasticity, wear resistance, weather resistance, and biocompatibility, have become core materials in industries such as sports equipment, medical protection, and smart wearables. However, the welding quality of its multilayer composite structure directly affects product performance—traditional hot-melt welding easily leads to material thermal degradation and interlayer delamination. High-frequency welding technology, through breakthroughs in two key technologies—precise temperature control and structural strengthening—has successfully resolved the contradiction between welding precision and structural stability, providing crucial support for the industrial application of TPU calendered films. I. Precise Temperature Control: Solving the "Temperature Sensitivity Paradox" of TPU Welding

The molecular chain structure of TPU materials determines their extreme sensitivity to temperature: excessively high melting temperatures can cause molecular chain breakage, leading to material embrittlement; insufficient temperatures prevent effective fusion, resulting in incomplete interlayer welding. High-frequency welding technology achieves precise temperature control through the following technical pathways:

1. Dynamic Electromagnetic Field Matching Technology

High-frequency welding utilizes the principle of electromagnetic induction, using an alternating electromagnetic field to induce resonance in the polar groups within the TPU molecules, thereby achieving heating at the molecular level. Unlike traditional heat conduction methods, this process acts directly on the material's interior, avoiding the gradient effect of heat transfer from the surface to the interior. During the process, the equipment dynamically adjusts the frequency and intensity of the electromagnetic field according to the ratio of hard to soft segments in the TPU, ensuring temperature uniformity in the welding area. For example, when welding TPU films containing rigid polyether segments, appropriately reducing the frequency can extend the heating time and prevent premature decomposition of the hard segments; while for films primarily composed of soft polyester segments, increasing the frequency achieves rapid melting, reducing the impact of thermal history on material properties.

2. Layered Temperature Control Die Design

To address the complexity of multi-layer co-extrusion structures, the die adopts a zoned temperature control design. Through independently controlled heating modules and cooling channels, differentiated temperature management is achieved for different film layers. This layered temperature control strategy not only avoids interlayer thermal stress concentration but also prevents voids or cracks at the weld interface by controlling the melt depth.

II. Structural Strengthening: Constructing a "Molecular-Level Locking" Interface for Welding

The precise temperature control of high-frequency welding lays the foundation for structural strengthening. Through the directional rearrangement of molecular chains and interface enhancement design, the welded area can achieve mechanical properties exceeding those of the base material:

1. Formation of an Interpenetrating Polymer Network

Under the influence of an electromagnetic field, the polar groups of TPU molecular chains undergo cross-linking reactions with the active groups of adjacent film layers, forming an interpenetrating polymer network. For example, in the welding of TPU/PU composite films, the urethane bonds of TPU react with the isocyanate groups of PU at high temperatures, generating a covalently bonded interface layer. This molecular-level "locking" structure enhances the tensile strength of the welded area, with peel strength significantly superior to traditional hot-melt welding.

2. Micro/Nano Structure Interface Enhancement

Through microstructure design on the mold surface, micro/nano-level roughness can be introduced into the welding interface. When molten TPU material fills these microstructures, a mechanical interlocking effect is formed, further enhancing the interlayer bonding force. For example, in the welding of TPU/non-woven composite films for medical protective clothing, the mold surface is designed with a honeycomb-like microporous array. During welding, the TPU melt penetrates into the micropores and solidifies, forming a "studded" structure, which significantly improves the tear resistance of the composite film.

III. Technological Integration: From Process Optimization to Industrial Upgrading

The "precise temperature control" and "structural strengthening" of high-frequency welding processes are not isolated technologies, but rather a systemic breakthrough achieved through synergistic innovation of equipment, materials, and processes:

1. Intelligent Equipment: Integrating infrared temperature measurement and feedback systems to correct electromagnetic field parameters in real time, ensuring minimal fluctuations in welding temperature.

2. Customized Materials: Developing TPU formulations specifically for high-frequency welding, optimizing the electromagnetic response characteristics of the material by adjusting the content of polar groups and molecular weight distribution.

3. Standardized Processes: Establishing a three-dimensional process window for welding pressure, time, and temperature to achieve stable welding of films of different thicknesses and layers.