Plastic Extrusion: How Plastic Film is Made

Plastic Extrusion - Key Points at a Glance

• Plastic extrusion is a forming process for manufacturing plastic products such as films and sheets.
• In the plastic extrusion process, granules or powder are melted in an extruder and pressed through a die into the desired shape.
• After cooling and smoothing, the semi-finished products (films, sheets) can be further processed, for example into plastic thermoformed parts.

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What is Plastic Extrusion?

Extrusion definition: Plastic extrusion is a forming process for manufacturing plastic films. Extruding with plastic is done by forming and melting plastic granules.

What are Plastic Granules?

Plastic granules, also referred to as plastic pellets or plastic flakes, are a common starting form of plastics. They are small, granular particles made from various types of thermoplastics.

These particles typically have a uniform size and shape, making them ideal for processing in industrial manufacturing processes. In plastic extrusion, the granules or powder are pressed through a forming die to obtain the desired shape.

What is an Extruder?

The extruder ensures that the molten plastic flows into an elongated, thin form, called melt strands. After cooling and hardening, the strand is cut into small particle grains - the finished granules - which are then collected and stored in bags, big bags, or containers.

These granules are then processed either in injection molding machines or again in the extruder. For plastic films and sheets, the latter applies.

Which Materials are Suitable for Plastic Extrusion?

Manufacturers of plastic films or sheets first purchase the required granules. This depends on which plastic film is to be processed. For example, if PET film is being produced, PET granules are needed.

Virgin Material or Recyclate as Starting Material

In addition to granules made from virgin material, recyclate can also be used for the production of plastic film. With recyclate films, plastic flakes are fed into the extruder. These come from recycling, such as shredded plastic bottles or production remnants like edge strips and scrap grids.

Difference Between Granules and Flakes

• Granules: uniform grains with defined shape and size, specifically produced for extrusion.
• Flakes: irregular, thin plastic pieces created through the recycling of used products.

By choosing between virgin material and recycled material, manufacturers can influence the quality, sustainability, and costs of the plastic film.

Which Plastics Can Be Extruded?

There are various types of plastics that can be used for plastic extrusion, such as

• Polyethylene (PE)
• Polypropylene (PP)
• Polyethylene terephthalate (PET)
• Polystyrene (PS)
• Polycarbonate (PC)
• Acrylonitrile butadiene styrene copolymer (ABS)

or also bioplastics.

Selecting the Right Plastic

The choice of the right plastic depends on the desired properties of the plastic film, such as transparency, flexibility or rigidity, or resistance to external influences such as heat or cold resistance, UV resistance, etc.

Plastic Extrusion: How Does Film Production Work?

In extrusion technology with plastic and the associated film production, thermoplastics are transformed from granules into semi-finished products as films or thicker sheets. Semi-finished products describe products made from raw materials in their simplest form. In the following sections, plastic extrusion and how it works is explained in more detail.

Feeding the Raw Material

• The raw material, in the form of granules or flakes, is fed into the plastic extruder via a hopper
• Depending on the desired properties of the plastic film, additives such as dyes, stabilizers, or additives (e.g. for ESD protection or flame retardancy) can be added

Melting and Homogenizing the Plastic

• The granules are melted and homogenized in the electrically heated cylinder of the extruder.
• A screw inside the extruder ensures the conveyance of the melt flow and the mixing of the materials.

Extruder Design

• The design of the extruder varies depending on the material to be processed:
  • Horizontal dies (with or without stagnation bars) are used for viscous melts
  • Vertical dies are used for low-viscosity materials such as PET
  • Sheet systems have a completely different design as well as different cooling sections

Forming the Plastic Film

• The molten plastic leaves the extruder as a strand-shaped melt flow and is pressed into the slot die via a melt pump
• The slot die forms the melt flow into a thin layer, the preliminary stage of plastic film

Smoothing and Finishing the Film

• The formed layer is guided over a smoothing unit with temperature-controlled rollers to ensure uniform material thickness
• The material web is then brought to the target width by single or multiple groove cutting

What Happens to the Plastic Film After Plastic Extrusion?

After the cooling section, in the cooled state, the plastic film is further processed. This process can include various steps:

Printing and Finishing

The film can be printed with information, logos, or designs. Additionally, surface treatments such as lamination with other materials or the application of special coatings are possible to improve properties such as gloss, scratch resistance, or barrier effect.

Rolling or Cutting

Finally, the plastic film is usually wound onto rolls. For thicker plastic sheets, cutting is done with circular saws or guillotine shears to achieve the desired widths and lengths.

Plastic Film in Thermoforming

The resulting plastic rolls or plastic sheets are used after extrusion as starting material for the production of plastic thermoformed parts, among other things. For the production of plastic thermoformed parts in plastic thermoforming, semi-finished products are heated and drawn into a thermoforming tool. Here the semi-finished product is either unrolled from a plastic roll or placed in the machine in the form of a plastic sheet.

Initial Thickness of Plastic Films

The semi-finished product for plastic rolls has a maximum initial thickness of 3mm, although many manufacturers already set an upper limit at 2.5mm. This limit is solely due to the fact that plastic film can only be wound onto a roll to this thickness. After that, the semi-finished product becomes too inflexible for processing and is instead cut into sheets.

Application Possibilities of Plastic Film

Plastic film is a versatile material that is used in numerous industries after thermoforming. Whether as packaging, trays, or covers, thermoformed products made from plastic film combine protection, hygiene, and efficiency.

Industry Overview and Typical Applications of Plastic Thermoformed Parts

• Automotive: Thermoformed load carriers and reusable trays for small parts, film thickness usually 0.2–0.8 mm.
• Medical technology: Sterile thermoformed trays, blisters, and medical technology housings protect instruments, devices, and sensitive electronics.
• Mechanical engineering & industrial manufacturing: Machine covers, containers for chemicals, and protective covers.
• Electronics: ESD trays and transport packaging for semiconductors, circuits, or microchips.
• Consumer goods: Inlay packaging and blisters for retail and e-commerce.
• Cosmetic articles: Trays and inlays for storage and presentation of products.
• Food: Primary packaging and trays for hygienic storage and freshness preservation.
• Robotics: Robot housings for the assembly of robots.
• Aerospace & defense: Equipment trays, equipment housings for defense applications.
• Agriculture & horticulture: Planting trays, tractor covers and plant trays for agricultural and garden technology.

Plastic Extrusion with the formary Supplier Network

In most cases, plastic thermoformers purchase the required plastic film. However, there are also some suppliers in the formary network that extrude their thermoforming film themselves. This in-house extrusion offers several advantages:

• Customized solutions that are flexibly tailored to customer needs (material properties, additives, colors)
• Better control over the quality of the end product, because the film has exactly the desired properties
• Optimization of production processes and increased efficiency through deeper value creation

ℹ️ To learn about the other advantages our supplier network offers, watch the webinar on the procurement process for plastic thermoformed parts.

Conclusion: Plastic Extrusion as Essential Foundation for the Thermoforming Process

Plastic extrusion is an essential process for the production of plastic films. Thanks to their diverse properties and application areas, thermoformed parts made from plastic films are indispensable in numerous industries. Do you need thermoforming films for your industry to benefit from the properties mentioned above? Then configure your thermoformed product now.