What is the role of film stretching?

---

Plastic film stretching is an important processing technology in the film production process, which improves the structure and physical properties of high polymeric films through directional stretching.  After the stretching process, the molecular structure will be elongated to make the film tougher, more durable and more elastic and highly improve the film transparency and glossiness.

1. Molecular orientation and mechanical enhancement

• Film stretching makes the polymer chains arranged in an orderly manner along the stretching direction to form an oriented structure.

• Strength improvement-The tensile strength and modulus in the stretching direction are significantly improved, such as the strength of BOPP film can reach 3-5 times that of unstretched.

• Toughness adjustment- Moderate film stretching balance strength and toughness, but excessive stretching may cause brittleness.

2. Thickness control and uniformity

• Film stretching reduces the thickness of the film (such as stretching from 100μm to 10-20μm), while improving thickness uniformity and reducing defects.

3. Barrier performance optimization

• The close arrangement of molecules reduces porosity and improves the barrier properties to gases (O₂, CO₂) and water vapor.

• After PET film is stretched, the oxygen permeability is reduced by 50%, which is widely used for food preservation packaging.

4. Improved optical properties

• Reduce internal scattering, improve the transparency and surface gloss, suitable for high-end packaging.

• The transmittance of BOPET film reach more than 90% after stretching.

5. Heat shrinkage characteristics

• Freeze stress after stretching, shrink when heated, which is used for bottle labels, electronic product packaging.

• PVC heat shrink film shrinkage rate can reach 70%

6. Anisotropic design

• Unidirectional stretching- strong in the longitudinal direction and weak in the transverse direction, suitable for tape substrates.

• Bidirectional stretching- Balanced longitudinal and transverse properties, used for high tear resistance packaging.

7. Surface performance regulation

• Film stretching process increases the surface roughness or polarity, and enhances printing adhesion and coating bonding, such as printable BOPP film

8. Crystallinity and temperature resistance

• Film stretching promotes crystallization and improves heat resistance

POLYSAN is professional high polymeric film factory in China, we customize different film properties to meet diverse needs by precisely controlling the stretching temperature, rate and stretching ratio. The stretching films produced by POLYSAN are widely used in packaging, electronics, medical and other fields.