Thermoformable Plastic Materials

Acrylic or polymethyl methacrylate is a thermoplastic commonly found in many items that you see and use every day and it’s often used as a substitute for glass. Acrylic is easily painted and fabricated and is available in many different stocked sizes, shapes and colors. It’s generally used to manufacture products such as signs, product displays, light diffusers, fake fingernails, car light lenses, and aquariums.

Advantages – Inherent UV stability, easy to thermoform, easily to fabricate, stiffness, clarity, ability to be used as a UV stable cap layer on other substrates, ability to be rigidized with fiberglass, scuff/mar resistance

Disadvantages – Impact strength, Cost, Chemical resistance, density, ductility

Because ABS by itself is not a naturally UV stable material, it requires the introduction of a UV stabilizer into the resin mixture or requires a UV stable material to be adhered to the top of the ABS sheet. In vacuum forming (thermoforming) applications, this layer must also be thermoformable.  Acrylic and ASA are generally the materials most thermoformers choose to cap their ABS sheet with to make it UV stable. With regards to acrylic, the acrylic cap layer can be produced in a thin film typically called Korad® that is laminated on the ABS sheet. If increased scuff resistance or a deeper sheen or depth of image is required, a thicker sheet often referred to as Solarkote® can be coextruded as a cap layer in conjunction with the ABS substrate. Unfortunately, this thicker layer of thermoformable acrylic will also have a negative impact on the impact properties of the sheet as a whole and cause the sheet to become a little bit more notch sensitive. Acrylic capped ABS will provide an inexpensive layer of UV protection and will also help with scuff resistance. Korad® is available as a clear material as well as many different standard colors. Solarkote® is a thick layer of acrylic that adds more UV protection to the substrate than is offered by Korad®. Solarkote® offers more scuff resistance and also adds more sheen or a deeper, richer look to the part it is capped with. As mentioned, we can also use other materials such as ASA (Acrylonitrile Styrene Acrylic Ester) to cap ABS with to make the finished part UV stable.  Although the ASA isn’t as scuff resistant as acrylic, it is more elastic which makes it more durable in applications where the part may need to be somewhat flexible.

Some would consider ABS the workhorse of engineering grade thermoplastics. Although pricing for ABS is higher compared to some commodity materials such as Polyethylene, ABS tends to be one of the cheaper engineering grade plastics and gives decent physical properties at its price point. ABS is easy to thermoform and is readily available in stocked sheets. Thermoformed products typically made from ABS include: dashboards, instrument clusters, machine covers, tractor hoods, children’s toys, luggage, and panels for refrigerators.

Advantages – Good heat deflection temperatures, Good chemical resistance, Good impact resistance, Easy to thermoform and fabricate, Good stiffness, Can be combined with other materials to increase properties such as flame resistance and heat deflection

Disadvantages – Cost (in some cases), UV instability, Susceptible to degradation with additional heat histories, Moisture absorption, Cold weather impact performance

Many products fall into this category. Their costs range in price from very reasonable, such as Thermoplastic Polyolefin (TPO), to extremely expensive such as Polysulfone and Polyetherimide (commonly referred to as Ultem ™).   There are usually extrusion grades (typically used in thermoforming) and injection molding grades of these plastics.  These thermoplastics are chosen when one or more very specific physical requirement(s) of the plastic is required. Engineering grades of these polymers are generally found in airplane components, train components, electrical components and other applications where certain governmental regulations or ASTM specifications must be met. Some of these material (such as TPO) are fairly simple to vacuum form and can often times be thermformed over fiberglass/composite molds and some of these are very difficult to form and require sophisticated water cooled aluminum tooling, heated plugs, etc.

In some applications, Fire Retardancy is important. FR or Fire Retardant additives are available as modifiers for many different types of thermoplastics. The level of fire retardancy is usually specified by a customer and generally correlates to a specific UL 94 FR rating. Ratings can vary from UL94 5VA (highest level of fire retardancy) all the way down to UL94 HB (least fire retardant).

Some thermoplastics are limited in the amount of fire retardancy that can be obtained. Typical thermoplastics that are available in fire retardant versions are: ABS (FRABS), HIPS (FRHIPS), TPO, Polycarbonate, Acrylic/PVC blends (Kydex®) and many others. Fire retardant versions of thermoformable materials are generally more expensive than standard versions and often require minimum purchase amounts. Contact us to inquire about minimum quantities.

High Impact Polystyrene is one of the most common thermoplastics used by vacuum formers. HIPS is easy to paint and available in any color. Primary thermoformed products that HIPS is used to make: drinking cups, point of purchase displays, retail packaging, toys, CD cases, various consumer products.

Advantages – Good heat deflection temperature (180° F), Good stiffness and Easy formability

Disadvantages – Low impact resistance, Cost (compared to other commodity polymers), Low solvent and chemical resistance

Polycarbonate typically goes by the more familiar trade name of Lexan™ . Polycarbonate is available in many different stocked shapes, sizes and colors and is also available as a clear material. Polycarbonate is used in many different industries, from medical to automotive and many in between. Polycarbonate is used to make theremoformed products such as: skylights, bulletproof windows, industrial guards, eyeglasses, game housings and hockey rink partitions.
Due to some of the unique challenges with the material, many thermoformers are not willing to take on jobs that require the product be vacuum formed out of polycarbonate.
Arrowhead has extensive experience with this unique thermoplastic and is always willing to look at new vacuum forming projects where the thermoforming of polycarbonate may be required.

Advantages – eExtremely tough, Available in clear, Available in many different grades, High flexural modulus (i.e., very stiff), High heat deflection temperature

Disadvantages – Moisture absorption, Stressful on tools, Poor chemical resistance, Formability, Requires good tooling to ensure good cosmetics

Polyethylene is one of the most common inexpensive commodity plastics in use today. There are various grades of PE available, and their use depends on the product requirements. Typical grades available are:

• High Density Polyethylene: HDPE
• High Molecular Weight Polyethylene: HMWPE
• Linear Low Density Polyethylene: LLDPE
• Ultra High Molecular Weight Polyethylene: UHMWPE

PE is usually used where chemical resistance and toughness are required from the product that will be thermoformed. PE is generally used for high volume products that are price sensitive. Typical applications include: dunnage trays, milk jugs, food packaging, blister packs, gas cans, and outdoor playground equipment.

Advantages – Cost, Chemical and solvent resistance, Impact strength, Ability to be compounded with additives such as talc (for increased stiffness) to modify the material’s properties

Disadvantages – Low flex modulus (i.e., very flexible), High CLTE (i.e., moves a lot when exposed to hot or cold temperatures), Low heat deflection temperature, Formability, Longer program development times, Typically requires water cooled aluminum tooling to ensure thermoformed part consistency

PETG is generally chosen due to its availability as a clear thermoplastic. PETG is more impact resistant than Acrylic, yet not as tough as Polycarbonate. Typical products made from PETG include: electronic devices, covers, machine guards, medical braces, point of purchase displays, trays, and signs.

Advantages – Formability, Cost, Resistance to stress whitening, Stiffness, Toughness, Decent resistance to some chemicals, Available in FDA-compliant grades

Disadvantages – Density, Minimum quantities to obtain reasonable pricing (contact us for details), Susceptibility to UV degradation, Adhesive bonding, Lack of mar resistance

Polypropylene is an olefin that is similar to polyethylene. In many situations, the plastic is copolymerized with ethylene, resulting in a product called Polypropylene co-polymer. Copolymerizing helps in the thermoformability of the material and allows it to compete with some higher-end plastics such as ABS.

Polypropylene can have various fillers such as glass fibers added to it in order to modify its properties. Polypropylene is also used in the production of other plastics such as TPO (Thermoplastic Polyolefin). Some typical products made from Polypropylene include: food containers, RF capacitors, living hinges, plastic bags and chairs.

Advantages – Chemical Resistance, Stiffness (better than PE), Fatigue resistance, Cold weather impact and Relatively low cost

Disadvantages – Formability, High CLTE (moves a lot with temperature changes), Tooling costs, UV instability

TPO is becoming sought after by companies in many different industries. Part of this is due to good marketing on behalf of some of the first companies to introduce TPO to the market and much of it is due to the physical characteristics of the plastic itself. TPO is basically a blend of Polypropylene and EPDM rubber. Together, these two materials result in some interesting properties that make TPO an attractive substitute to more traditional weatherable thermoformable materials, such as acrylic capped ABS. Thermoformed products typically made from TPO include: car bumpers, rocker panels, machine covers, chemical shields, roofing membranes, engine covers, and golf car bodies.

**Arrowhead was one of the first companies in the USA to start thermoforming TPO successfully. Thus, we have many years of experience working with TPO and know how to deal with the challenges that comes along with the material. These challenges tend to scare away other thermforming companies from making parts utilizing this innovative material. Not only has Arrowhead been able to overcome the challenges that come with thermformed TPO products, but we have also been able to offer some of our customers lower cost tooling solutions as opposed to expensive aluminum tooling which other thermoformers claim is mandatory when vacuum forming TPO sheet.  

Advantages – Great chemical resistance, Good heat deflection temperature (240° F), Great cold weather impact properties, Great UV stability, Dimensionally stable (low CLTE; half that of ABS), Good stiffness, Price

Disadvantages – Difficult to thermoform, Difficult for some sheet suppliers to extrude, Aluminum tooling required for higher volume parts (although we have developed an Eco-Tool to get around this need), High minimum quantities in some cases (Contact us for details), Not stocked by distributors, Difficult to paint, Difficult to bond to