Stretch film, also known as stretch wrap, is a highly stretchable plastic film commonly used to wrap products on pallets and secure them to each other and the pallet. It ensures that products stay tightly bound during transportation and storage, preventing movement and damage.

Key Characteristics of Stretch Film:

Material

Typically made from linear low-density polyethylene (LLDPE). This material is chosen for its excellent elasticity, puncture resistance, and cling properties, which are essential for effective packaging.

Other materials that may be used in stretch films include:

• High-density polyethylene (HDPE): This material offers greater strength and stiffness than LLDPE but may have lower cling properties.
• Polypropylene (PP): PP can be used in stretch films, but it generally has lower cling and elasticity compared to LLDPE.
• Blended materials: Some stretch films may be made from blends of LLDPE, HDPE, and other polymers to achieve specific properties, such as improved cling or puncture resistance.

Elasticity

The film can stretch significantly before breaking, allowing it to tightly secure items.

Cling

The film has a natural cling property that helps it adhere to itself once wrapped, without the need for adhesives.

Factors Affecting Cling:

• Film thickness: Thinner films tend to have better cling properties due to their increased surface area.
• Temperature: Cling can be affected by temperature. Higher temperatures can reduce cling, while lower temperatures can enhance it.
• Humidity: High humidity can also affect cling, as moisture can interfere with the electrostatic attraction between the film layers.

Thickness

Available in various thicknesses, measured in microns or mils, to accommodate different load sizes and weights. There are 3 broad categories

Thin gauge      – 10 to 15 microns ( 04. To 0.6 mils)

Medium gauge – 15-20 microns (0.6-0.8 mils)

Thick gauge     – 20-30 microns (0.8-1.2 mils)

Factors Affecting Thickness Selection:

• Load weight: Heavier loads generally require thicker films.
• Product shape: Irregular or sharp-edged products may benefit from thicker films to prevent punctures.
• Storage conditions: If the products will be stored outdoors or in harsh environments, thicker films can provide better protection against the elements.
• Shipping distance: Longer shipping distances may necessitate thicker films to ensure the products remain securely wrapped during transit.

How Is Stretch Film Made?

Stretch film or Stretch wrap is primarily made from linear low-density polyethylene (LLDPE). The manufacturing process involves either the blown film extrusion or the cast film extrusion method. Here’s a detailed look at how each method works:

A. Blown Film Extrusion Process

1. Raw Material Preparation

Pellets of LLDPE are mixed with various additives to enhance properties like strength, elasticity, and cling.

2. Melting and Extrusion

The mixture is fed into an extruder where it is melted and forced through a circular die, forming a tube of molten plastic.

3. Blowing

Air is blown into the centre of the tube, causing it to expand like a balloon. This forms a bubble of plastic film.

4. Cooling

As the bubble rises, it cools and solidifies. Air rings are used to control the cooling process.

5. Flattening and Winding

The bubble collapses between rollers, forming a flat film. The film is then wound onto large rolls.

 B. Cast Film Extrusion Process

1. Raw Material Preparation

LLDPE pellets are mixed with additives similar to the blown film process.

2. Melting and Extrusion

The mixture is melted in an extruder and forced through a flat die to form a thin sheet of molten plastic.

3. Casting

The thin sheet is immediately cast onto a chilled roller (quench roll), which rapidly cools and solidifies the film.

4. Stretching

The solidified film is stretched in both the machine direction (MD) and transverse direction (TD) to enhance its strength and elasticity.

5. Winding

The film is wound onto rolls, and ready for use.

Comparison of Blown and Cast Stretch Film

• Clarity

Cast film is usually clearer than blown film.

• Strength

Blown film typically has higher puncture resistance and load-holding strength.

• Cost

Cast film is often less expensive due to the faster production process.

• Noise

Blown film tends to be noisier during application compared to cast film.

Quality Control and Testing

Throughout the manufacturing process, stretch film undergoes various quality control tests to ensure it meets specific standards for strength, puncture resistance,  cling properties and tear resistance. These tests include:

1. Tensile Strength Test

Measures the force required to stretch the film until it breaks. A sample of the stretch film is clamped between the jaws of the machine. The machine applies a force to the film, stretching it at a controlled rate. The force and elongation are recorded until the film breaks.

2. Puncture Resistance Test

Evaluates the film’s ability to withstand punctures from sharp objects. A sharp probe is pressed into the film at a controlled rate. The force required to puncture the film is recorded.

3. Cling Test

Assesses how well the film adheres to itself. A sample of the stretch film is applied to a flat surface. Weights are placed on top of the film to simulate the pressure it will experience in real-world applications. The film’s ability to cling to the surface and resist slippage is recorded.

4. Tear Resistance Test

The force required to tear the film. A notch is made in the film, and a force is applied to tear it apart which is recorded.

By employing these processes and tests, manufacturers produce high-quality stretch film that effectively secures and protects goods during transport and storage.

Types of Stretch Film

Hand Stretch Film

Designed for manual application using a handheld dispenser or simply by hand. Ideal for smaller operations.

Machine Stretch Film

Applied using a stretch wrap machine, suitable for high-volume operations.

Blown Stretch Film

Produced using the blown extrusion process, offering higher puncture resistance and load-holding strength.

Cast Stretch Film

Made using the cast extrusion process, known for its clarity and smooth release

Uses of Stretch Film

• Palletizing: Securing products on pallets for transportation.
• Bundling: Wrapping multiple small items together for easier handling.
• Protection: Shielding goods from dust, moisture, and potential damage.

 Benefits of Stretch Wrap / Stretch Film

• Cost-Effective: Reduces the need for additional packaging materials.
• Versatile: Suitable for a wide range of applications and industries.
• Efficient: Quick and easy to apply, especially with automated machines.

Stretch film is an essential tool in logistics and warehousing, ensuring product safety and integrity throughout the supply chain. Get in touch with us to learn more.