The Core Principle of Stretch Film's Stickiness
The stickiness of stretch film (also known as stretch film) isn't achieved through traditional glue-like adhesion, but rather through the material's inherent "self-adhesion." The core principles behind this are:
1. Intermolecular forces: Stretch film typically uses linear low-density polyethylene (LLDPE) as its base material. During production through blow molding or cast film processes, the molecular chains form a micro-network structure during stretching, generating electrostatic adsorption and van der Waals forces that adhere the film layers together.
2. The Role of Additives: Tackifiers (such as polyisobutylene and EVA copolymers) are added during production. These ingredients reduce the material's surface energy, increase the contact area between films, and enhance adhesion. For example, the typical polyisobutylene addition ratio is 3%-8% (according to the Plastics Industry Handbook). Excessive amounts can lead to uneven adhesion.
Key Factors Affecting Adhesion
1. Temperature Adaptability:
- Low temperatures (e.g., below 5°C) reduce molecular mobility and weaken adhesion. High temperatures (above 40°C) may cause tackifier migration, leading to uncontrolled adhesion. The ideal operating temperature is 15-30°C.
2. Thickness and Elongation:
- Common thicknesses are 15-30 microns, with elongation rates of 300%-500%. Films that are too thin (<15μm) are prone to cracking, while films that are too thick (>30μm) are too sticky and difficult to peel (refer to ASTM D882).
3. Surface Treatment Technology:
- Some high-end stretch films undergo corona treatment to create polar groups on the surface, improving adhesion uniformity. The static charge value should be controlled within 38-52 dynes/cm (tested according to ISO 8296).
Application Scenarios and Adhesion Compatibility
1. Industrial packaging: High adhesion is required (e.g., securing warehouse pallets). High-strength stretch film with a tackifier is typically used.
2. Food packaging: Low migration is required, requiring FDA-certified non-toxic additives.
Through scientific formulation and process optimization, the adhesion of stretch film can be precisely matched to different needs. Its environmentally friendly nature (over 90% recyclability) also makes it a mainstream choice for modern packaging.