In the world of resins and injection molding, there are thousands of options available. Some resins offer strength, thermal stability and chemical resistance, and yet others offer electrical resistance and ease of printing. Perusing several online databases, such as the UL Prospector (formerly IDES), MAT Web, and The British Plastics Federation, can offer a starting point, but picking the right one from the lists is a challenge. You may be searching for something strong, corrosion resistant, and easily used for injection molding. In that case, you may choose between thermoset plastics or a thermoplastic. Although the sound similar, they offer different properties that may or may not be the best choice for your new project. If you haven’t heard of either, or aren’t sure which offers what properties, we’ll take a dive into both to list what each is and where they are best used.
Thermoset Plastics for Injection Molding
Thermoset plastics contain polymers that cross-link together during the curing process to form an irreversible chemical bond. This chemical bond removes the risk of the product melting if heat is later applied. You may find it easy to remember this about thermosets if you think of the old commercial tagline, “Set it and forget it.” Thermosets are an ideal choice for products that require high-heat applications such as electronics and home appliances. Thermoset plastics are a good option for high-strength applications that can’t deform under load and also need chemical resistance due to a harsh environment. One consideration that should be noted in molding thermosets is that the components of thermoset polymers are stored in liquid form, usually in large tanks or containers. This could pose a challenge for molders not prepared for liquid components.
Pros
- Resistant to high temperatures
- Easily injection molded, which offers design flexibility for more difficult shapes
- Can be utilized for thick to thin wall applications
- Can be used for products that require smooth aesthetic appearance
- Very stable under high load applications
- Resin is a low-cost option and is cost-effective in most applications
Cons
- Due to the chemical bond, thermosets can’t be recycled by the end-consumer
- More difficult to apply a textured surface finish
- Material can’t be melted and reused
Common Use Examples
- Unsaturated polyester resins are used for the manufacture of plastics with reinforced fiberglass commonly known as polyester, and fillers for other resins
- Phenolic resins used for tool handles, some circuit boards, billiard balls, laboratory countertops, and are used as coatings and adhesives.
- Epoxy resins are used as coating materials, caulks, insulating materials, general purpose adhesives, as the binder in cement and mortars, rigid foam applications, and non-skid coatings.
What are Thermoplastics for Injection Molding?
Thermoplastics are defined as any plastic material that melts into a pliable form above a specified temperature and solidifies when cooled. They can be re-melted and re-shaped multiple times without degradation or changing their properties, and they are typically stored in the form of resin pellets prior to the injection molding process. This form makes them easier to store without the complications of liquids.
Pros
- Parts can be flexible or pliable in their end shape for the consumer
- Dimensional accuracy is good
- Good surface finish characteristics
- Materials are recyclable by the end-consumer
- Can be re-melted and molded again, which can decrease production waste
- Excellent impact resistance
- Limited chemical resistance
Cons
- Will not withstand high heat or high corrosive applications or environments
- Injection molding requires high heat and high pressure to create parts
- May not be as cost-effective as other materials if the number of parts made is large
Common Use Examples
- Acrylics are a transparent and lightweight material that is branded under the industry names of Plexiglas, Perspex, and/or Lucite. It is commonly used as a direct alternative to glass when shatter-resistance is required. One specific example of an acryclic is bullet-proof glass, which is both transparent and shatter-proof.
- Acrylonitrile butadiene styrene (ABS) is a lightweight thermoplastic with many different uses including musical instruments, outdoor equipment, children’s toys, and personal safety equipment.
- Polypropyleneis used frequently in packaging, labelling, woven into textiles, as components to laboratory equipment, speakers, automotive components and more.
- Polyester is frequently used in fabric manufacturing including clothing, blankets, household and office furniture, and many industrial uses such as conveyor belts, rope, and tire reinforcement.
- Polystyrene is used for plastic replica models, packaging materials, insulation, CD & DVD cases, disposable foam cups and cutlery.
- Cellulose acetate is used frequently in adhesives, in photography, and as a synthetic fiber material including cigarette filters and playing cards.
- Nylonis used to make fabrics, carpets, ropes, musical strings, and bridal veils. The term ‘nylons’ as in the brand Pantyhose uses nylon, which is where the name came from.
- Teflonis commonly recognized as the non-stick coating on cookware. Beyond this application, Teflon is used as a lubricant to reduce friction and wear in equipment.
Which is the Better Material to Use?
The answer to which is better is going to depend entirely on the function and design of your product. If you have a product that is used in higher temperatures, a corrosive environment, or requires high dimensional stability under loaded conditions, the thermoset plastics will probably be the better choice to make. If you have a product that requires recycling options, a flexible or pliable structure, and excellent resistance to impacts, the thermoplastics are probably going to be the better choice. If you choose the thermoplastics, you may need to dig further into your application and characteristic requirements to decide which of the types of thermoplastics would be the best choice.
Beyond the characteristics of the material, your decision could also be influenced by the manufacturing tooling or process required to achieve the end product. Some thermoplastics, such as styrene, release toxic fumes during the injection molding process. That could add additional cost from your chosen molder due to the extra safety requirements needed in manufacturing. Thermosets on the other hand don’t require special fume evacuation, and may be cheaper to injection mold overall since they are a liquid that only requires low heat and pressure to form. These can utilize less expensive molds made from various materials including aluminum, metal alloys, nickel, epoxy, silicone and fiberglass. A thermoplastic that requires higher heat and pressure may be only limited to aluminum or steel, which may add cost for material and development time to the schedule.
New engineered resins are always being developed with better properties for more uses and environments. Plastics can offer characteristics to thrive in almost any environment, but often choosing the best material for your product is a difficult one to make. You may need a partner versed in the process. SEA-LECT Plastics can aid with resin selection, turn-key assembly options, and program management to see the complete development cycle through with success. Give us a call at (425) 339-0288 or email us at mattp@sealectplastics.com. We can offer you advice on the best technology to use, the best materials to meet your product demands, and how to navigate through each development stage. At SEA-LECT Plastics, we specialize in military product applications, outdoor adventure gear, musical instruments, supporting the medical and consumer product industries. Our goal is to make your project efficient and cost-effective to manufacture, assemble, and ship no matter how complicated your concept might be.
Matthias Poischbeg was born and raised in Hamburg, Germany. Matt moved to Everett, Wash., after finishing his bachelor’s degree in business in 1995 to work for Sea-Dog Corporation, a manufacturer, and distributor of marine and rigging hardware established in 1923.
In 1999, Matt took over the reins at Sea-Lect Plastics Corporation, a sister company of Sea-Dog and a manufacturer of plastic injection molded products with an in-house tool & die shop. Matthias Poischbeg is also a contributor to Grit Daily.