What are the stretching methods for stretch film?

Stretch film is a versatile packaging material used to secure, bundle, and stabilize products. Stretching methods are crucial for determining the performance, strength, and elasticity of the film. There are two main methods of stretching stretch film:

1. Machine Stretching

This method involves stretching the film using a stretch wrapper machine. It is commonly used for high-volume packaging, as it allows for uniform stretching and efficient use of the film. Machine stretching generally occurs in two stages:

Pre-stretching: In the pre-stretch section, the film is pulled or stretched over rollers before being applied to the pallet or product. This increases the film’s length and elasticity, making it stronger and more efficient in wrapping.

Application: After pre-stretching, the film is wrapped around the product or pallet, creating a tight and secure bond.

2. Blown Stretching

In the blown stretch film production process, the film is created by blowing the plastic material through a cylindrical die. This method creates a film that is biaxially stretched (both machine and transverse directions). Here’s how it works:

Extrusion: The resin (usually linear low-density polyethylene, LLDPE) is heated and extruded through a die.

Blowing: The extruded film is inflated by air pressure, stretching it both vertically and horizontally as it cools and solidifies.

3. Cast Stretching

In cast film extrusion, the resin is extruded through a flat die, creating a thin, uniform sheet. The film is then stretched using rollers:

Orientation: The film is stretched in one direction, typically the machine direction, and then cooled.

Mechanical Stretching: The film is passed through rollers or stretch units that elongate it, increasing its strength and stretchability.

4. Hand Stretching

This is a manual method where individuals use their hands to stretch the film over products. While less efficient and more labor-intensive, this method can be used in low-volume applications or in situations where machine wrapping is not available.

Manual Tensioning: The operator applies manual force to stretch the film as it is wrapped around the product.

Control: Stretching is limited by the operator’s strength and skill, which means consistency can vary.