Analysis of the Principle of high-frequency Welding of Soft Plastic Film Materials

The principle of high-frequency welding for soft plastic films is based on molecular polarization and frictional heat generation induced by high-frequency electromagnetic fields, combined with pressure to achieve fusion. The core process can be divided into the following steps:

1. High-Frequency Electromagnetic Field Induces Molecular Polarization

• High-frequency oscillation:
  The high-frequency welding equipment generates an electromagnetic field with a frequency exceeding 100 kHz (typically 27.12 MHz or 40.68 MHz) through an electronic tube self-excited oscillator.
• Molecular polarization:
  When soft plastic films (e.g., PVC, TPU, or other polar-group-containing plastics) are placed in the high-frequency electromagnetic field, the positive and negative charge centers within their molecules shift, forming dipoles. These dipoles rapidly oscillate in alignment with the alternating electromagnetic field direction (millions of times per second), causing intense relative motion between molecules.

2. Molecular Friction Generates Heat and Melting

• Dielectric loss:
  The high-speed molecular motion overcomes intermolecular forces, generating friction that converts electromagnetic energy into heat. This heat accumulates internally (not on the surface), rapidly raising the contact area’s temperature to the material’s melting point.
• Localized melting:
  Under pressure, the melted surfaces of the two plastic films interpenetrate, forming entangled molecular chains and creating a fusion zone.

3. Pressure Assistance and Cooling Solidification

• Pressure application:
  Uniform pressure is applied to the fusion zone via molds or rollers, ensuring full material contact and air expulsion to prevent bubble formation.
• Rapid cooling:
  After the electromagnetic field ceases, heat quickly dissipates into the surrounding material, allowing the fusion zone to solidify. Molecular chains reorganize during cooling, forming a robust welded joint.

Key Technical Advantages

1. Instantaneous heating & precise control:
   Heat is generated only in the electromagnetic field’s action zone, avoiding bulk material deformation (common in traditional methods like hot-plate welding) or excessive heat-affected zones.
2. Ideal for polar materials:
   Highly effective for polar-group plastics (e.g., PVC, TPU, EVA), while ultrasonic welding is better suited for non-polar materials (e.g., PP, PE).
3. Efficiency & aesthetics:
   Fast welding speed (typically 0.1–3 seconds), clean joints (no slag), and suitability for applications demanding high visual quality (e.g., blister packaging, medical products, automotive interiors).

Summary

High-frequency welding achieves rapid, precise fusion of soft plastic films through molecular polarization and friction-induced heat under a high-frequency electromagnetic field, assisted by pressure. Its core strengths lie in efficient processing of polar materials and superior weld aesthetics, making it widely applicable in scenarios requiring sealed, waterproof, or complex-shaped joints for soft plastic films.