Common Plastics for Thermoforming

April 8, 2014|BY: Rob Helmke

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The Thermoforming Process

The thermoforming process is really a very simple one. Thermoforming is the process of heating a material to its forming temperature and applying force to the hot sheet to push it into cavities or over a mold so the material conforms to the shape of the mold. The forces applied are any of three different methods: mechanical assist (plugs), vacuum, and form air.

Material is supplied in rolls or resin pellets. Rolls are either produced in an extrusion facility or purchased. Resin pellets are used for in-line thermoforming and for extruding roll stock. Plastic Ingenuity has its own extrusion capabilities so it has more control of the entire process. The extruded plastic sheet is fed into the thermoformer and carried into the heating area on chains.  The chains advance the sheet through the heating oven, form station, and trim station of the thermoforming machine.Thermoforming Process Diagram

When the material reaches its optimal forming temperature in the oven, it is transported to the forming station where the mold begins to close on the pliable sheet.  For most molds, plugs force the material into the mold cavities, vacuum air draws the plastic over the mold and into the cavities, and air pressure is applied to move the material into the custom mold cavities.

Once the sheet has been formed into plastic parts, it advances to the trim station where it is extracted by either a steel rule die or matched metal trim press. The remaining plastic is collected and recycled back into the process to make more plastic parts.

Plastics Used in Thermoforming

At PI, we specialize in thermoforming plastics for standard and custom sizes, generally using PET plastic. In the industry, though, six plastics lead the way for thermoforming: ABS, HIPS, HDPE, PVC, PET and PETG. See the differences with each of these thermoformable plastics to decide which one could work best for your products’ packaging:

6 types of plastics for thermoforming include ABS, HIPS and more.

ABS Plastic

A common thermoformed plastic, ABS is comprised of acrylonitrile, styrene and butadiene. ABS is known for its tough resilience to the elements, including heat; it can handle temperatures anywhere from -4 to 176 °F. This allows the plastic to be molded at high temperatures. Most commonly used for mechanical purposes, like for pipe systems, it can also be used for protective headgear, golf club heads, musical instruments, like recorders, and even for toys, like Legos. The plastic can also be used in some tattoo inks.

HIPS Plastic

HIPS plastic, or polystyrene, can be used for foamed or rigid plastic. This plastic’s clear and brittle composure makes it an ideal plastic for protective packaging, like packing peanuts, or food and drink items, like clamshell containers, bottles and disposable cutlery.  This plastic can be easy to create—and at a low cost.

HDPE Plastic

A variation of HIPS plastic, HDPE (high-density) polyethylene is a stronger thermoformed plastic comprised of petroleum. Because of its exceptional strength to density ratio, HDPE is used in a wide variety of applications, including everything from plastic bags and bottles to hula hoops to even fireworks. This plastic is also commonly used for water pipes and cable installation.

PVC Plastic

PVC—polyvinyl chloride—plastic is third most-used polymer. Created with suspension polymerization, this plastic has a strong, hard structure, making it an ideal rigid plastic that can withstand extreme temperatures and impacts. Its low cost also makes it attractive for companies. PVC is commonly used for sewage pipes, commercial signage, electric cables, flooring, faux leather clothing and more.

PET Plastic

One of the most common thermoformed plastics, PET, or polyethylene terephthalate, is commonly used for synthetic fibers and bottle production. Once molded into a shape during thermoforming, PET plastic must be dried to increase its resistance. Once finalized, products made from PET plastic have a great resistance and barriers from outside elements. This plastic is also one of the most recycled types of plastics.

PETG Plastic

PETG (polyethylene terephthalate glycol-modified) plastic is a variation of PET plastic. PETG plastic can be molded during thermoforming for blister packaging and trays.

More About Thermoforming

If you want to see how the process has changed over the years, or you just want to understand a little more about how plastic packaging manufacturers create the products you see on store shelves every day, check out the infographic below.