Thermoplastic elastomers and Liquid Silicone Rubber have similar properties and are both ideal for many types of injection molding projects. They are useful alternatives to synthetic or natural rubber. However, there are significant differences between thermoplastic characteristics and those of a thermoset.

“Thermoplastic” and “thermoset” sound related but are not interchangeable. TPE materials are thermoplastics while LSRs are thermosets. Each has different material properties and they behave inversely during the molding process. They also contrast in terms of how they react to heat. For example, TPE melts while LSR hardens.

Although each material has specific advantages and disadvantages that impact the moldability of a product, it’s vital to determine which is right for your application. Moldability is a term that defines how you can transform substances into customized designs. While both have similar characteristics at room temperature, it’s difficult to tell the difference by physical appearance alone.

What Are Thermoplastic Elastomers?

Also known as thermoplastic rubber, a thermoplastic elastomer is a blend or compound of polymers that melt and form into plastic when heated. It hardens when cooled, but its chemistry doesn’t change from one form to the next. Manufacturers shape and fabricate TPE when temperatures reach its melting point. Although it has a similar elasticity to that of cross-linked material, like LSR, its elastomeric behavior is not because of cross-linking properties.

There is no chemical bond within thermoplastic elastomers. By applying heat to the plastic pellets, they liquefy. They are then pressure-molded into various components that strengthen and retain their shape during the curing process. The seven types of TPE solutions include:

• Styrenic block copolymer
• Melt processable rubber
• Thermoplastic olefinic elastomer
• Thermoplastic polyester elastomer
• Thermoplastic vulcanisate
• Thermoplastic amide elastomer
• Thermoplastic polyurethane elastomer

In short, TPE is a class of copolymers, often made with a mix of plastic and rubber.

TPE Characteristics

Because you can melt and mold thermoplastic elastomers, you can reuse the resin thousands of times if necessary. It’s often beneficial when you need to reverse the molding process to correct product defects or want to make a new design. With the freedom to reprocess and remold an infinite number of times by re-heating, softening and re-hardening, TPE will still return to its similar or original shape.

Changing from a liquid to solid state, TPE Silicone is measured in terms of softness and hardness. You can determine the value using a Shore durometer scale. For example, soft gel TPE materials range from 20 Shore OO to 90 Shore A. As the hardness of a product increases, so does the durometer scale. It starts to reach the Shore D level when hardness values reach up to 85 Shore D, meaning the solid is very hard.

Regarding more rubbery materials, hardness ranges from 20 to 95 durometer A. A typical hardness is around 70 durometer A for thermoplastic elastomer products.

What Is TPE Plastic Injection Molding?

The injection molding process of TPE is straightforward. Thermoplastic elastomers come in the form of pellets which are added to the injection molding machine via a hopper. Either the supplier compounds the color into the pellets prior to the process or the color can be blended in by the machine. The pellets flow through a hot barrel and inject into a mold that has temperatures between 70 and 120 degrees F.

The machine can mold at low injection pressures often less than 10,000 psi and the TPE shrinks when cured. Manufacturers can also pull undercuts out from the mold without mechanical slides.

Advantages of TPE

You can discover many benefits when using thermoplastic elastomers to construct your products. For instance, they use less energy during production. Because the process avoids cross-linking, it achieves faster cycle times — as little as 20 seconds — and makes for a cost-saving process.

TPE also possesses recyclability properties where you can reprocess scrap or reject parts. The material has a good compression set and chemical resistance but not at high or low temperatures. The material can also be formulated to be non-tacky, which helps repel dirt and other contaminants. Additional advantages include:

• Abrasion resistance
• Excellent colorability
• Good electrical properties
• Heat-sealable
• High elasticity
• High fatigue resistance
• High impact strength
• Low compression set
• Low density
• Low specific gravity
• Moderate UV resistance
• Resilient to chemicals and weathering
• Strong and flexible at room temperature
• Suitable for high-volume injection molding
• Two-shot molding options
• Various surface characteristics and properties

You also have hundreds of remolding opportunities because there is no chemical change within TPEs. The mix of plastic and rubber even upholds resistance to low and high temperatures ranging from -30 to 140 degrees C.

The only drawbacks of using TPE is how it melts when exposed to high temperatures — which is a positive in some cases — and how it deforms under sustained pressure.

Uses of Thermoplastic Elastomer

You can implement TPE in a variety of industries for different applications. Depending on your requirements and environment, uses of TPEs include items such as:

• Baby bottles
• Bottle caps
• Closure liners
• Impact-resistant devices and component housing
• Seal rings
• Seals
• Soft-touch grips

A thermoplastic elastomer is an exceptional alternative to using latex, silicone, PVC or rubber — especially in medical and health applications like gloves.

What Is LSR?

Thermoplastic elastomer vs. silicone is a simple comparison when you look at how each reacts to heat as well as their specific properties. While similar in many ways, both materials are made of different components.

Liquid silicone rubber is a synthetic resin where polymers join together by a chemical bond. Heating the mixture causes polymer cross-linking which results in a chemical bond giving the substance permanent strength and shape after the curing process. When you apply heat to LSR products they harden, which is the opposite of TPE components. When you heat LSR, you can’t change its physical or chemical properties.

Another way to formulate LSR is to mix two components prior to their reaching the injection mold. One element acts as the catalyst that initiates the cross-linking progression. Conventional rubber, like natural or synthetic, undergoes chemical cross-linking during the molding process, which is called curing or vulcanization. The vulcanization process takes time to formulate, anywhere from one minute to several hours.

Silicone’s structure has alternating oxygen and silicon atoms and can come in many forms, including LSR, heat-cured rubber, and room temperature vulcanized rubber. Cured LSR is a common choice for molders because it’s easy to process.

LSR Specifications

Liquid silicone rubber forms a permanent shape and you cannot remold it, unlike TPE. It’s a durable material created through polymer cross-linking, although silicone with a low durometer, known as gels, can reach less than 10 durometer A. LSR is a cost-effective solution and is becoming a commodity among various industries. It’s often available to replace latex materials and is ideal for human contact products for medical uses.

The hardness of LSR ranges from 3 to 80 durometer A but the most common is 50 durometer A, where it has the best blend of tensile and tear strength. To receive the best sealing properties, many manufacturers create liquid silicone rubber with a hardness of 30 durometer A.

The Liquid Silicone Rubber Injection Molding Process

When forming LSR solutions through the injection molding process, the procedure requires customized molding equipment to fit your specific needs. Silicone arrives in drums with equal parts of component A and component B. Each is in separate containers to prevent the chemical reaction from starting. Component A is the catalyst and B is the crosslink.

The next step is to feed both the components into a barrel using a 1:1 ratio using metering pumps for accuracy and for minimal contamination. LSR has a consistency similar to peanut butter or honey. The A and B components mix before injecting into the mold and you can add color before it reaches the static mixer. During the transfer phase, the silicone is chilled and then inserted into the hot mold. LSR molds at low levels of injection pressures, often below 10,000 psi.

It’s imperative to make molds with tight tolerances and to use a vacuum for venting. Liquid silicone rubber parts shrink more than TPEs and you can also pull out undercuts without mechanical slides.

Advantages of LSR

The benefits of implementing LSR products within your business will exceed your expectations. When comparing TPE vs. silicone, LSR has the utmost resistance to high temperatures. You can use it at 350 to 400 degrees F without altering its shape. Over a range of extreme temperatures — whether hot or cold — the material remains stable. For example, it stays flexible and elastomeric even down to temperatures like -100 degrees F.

Because LSR is customizable, you can create thick or thin wall construction for different products. LSR has a high chemical resistance to solvents, oils and others, which is ideal for the automobile industry. For instance, gaskets and O-rings come into contact with various solvents, but by using liquid silicone material, it’s resistant to any changes.

Silicone is also impervious to UV rays, which is excellent if your solution will experience long-term exposure to the elements. It has a low compression set, which means it returns to its original shape when stretched and is a popular material for products that come in contact with the body. Being biocompatible makes it possible to form implants and other items that won’t harm a person’s skin.

Other advantages of silicone include:

• Clarity
• Dampens vibrations
• Design flexibility
• Electrical insulation
• Gas permeability
• High light transmittance
• Biocompatibility
• High tear and tensile strength
• Hydrophobic
• Hypoallergenic
• Minimal changes in the structure
• No re-molding after curing
• Odor-free and tasteless
• Resistant to radiation, UV light and bacteria

Uses for LSR

LSR is a vital material used in a variety of industries ranging from medical, auto and consumer goods to optics and electronics. Healthcare products can include items such as catheters, endoscopy and medical tubing, while the automotive market can implement LSR to form products like gaskets, O-rings, couplings and LED lenses.

Consumer goods made from silicone material can create items like earbuds, goggles and nose pads. Optics consist of professional and exterior lighting and electronic solutions can include protective sleeves. The uses of LSR are not limited to the suggested industries or items. Liquid silicone rubber has thousands of applications such as:

• Coverings
• Electronic interfaces
• Gaskets and hardware in appliances
• Medical implants
• Other auto parts exposed to chemicals and extreme heat
• Pull rings
• Soft-touch surfaces
• Stoppers
• Syringe tips
• Valve components
• Wire harnesses

Other industries LSR products can serve to include:

• Aerospace
• Appliances
• Defense
• Food
• Textile

Thermoplastic Elastomer vs. LSR Molding Processes

The primary difference between TPE and LSR molding is that liquid silicone rubber undergoes a chemical reaction involving cross-linking while thermoplastic elastomer pellets simply melt. TPE materials also form when cooled while LSR products become workable when heated.

Overmolding is also a popular technique for both processes. This is where one product is composed of two elastomeric elements or a combination of an elastomer and plastic. TPEs are easier to work with when it comes to overmolding because they bond to common plastic materials while silicone has difficulties bonding to others that aren’t silicone. However, LSR overmolding becomes stronger by applying undercuts.

The method known as silicone overmolding is when you preheat the initial shots. Everything is completed in one machine in a continuous process, whereas TPEs do not require pre-heating.

Liquid Silicone Rubber Solutions From SIMTEC Silicone Parts

Liquid silicone rubber is our exclusive focus and we have experience and knowledge in perfecting and fine-tuning the process. SIMTEC produces custom-designed and manufactured LSR parts as well as LSR multi-shot components. We create high-quality solutions using the unique material characteristics of LSR that make it ideal for a range of applications, environments and industries.

SIMTEC experts work with clients one-on-one to convert your vision into a reality. With our proficiency in LSR and LSR 2-shot and multi-shot injection molding, your possibilities are endless. Liquid silicone rubber is the ideal choice for sealing applications because it has excellent water-repellent properties, a low compression set and is thermal resistant.

We are capable of adhering to large-volume orders and we have experience in processing challenging materials, which sets us apart from other manufacturers. With SIMTEC’s consistent reputation for quality and a low parts-per-million defect rate, we provide you with the most durable products by using a streamlined procedure.

SIMTEC experts assist you with designing different products and offer prototype possibilities before committing to your design. With our fast turnaround times for reaching the market, your business can experience more productivity and success.

The benefits of choosing LSR components range from biocompatibility, thermal stability and low compression to being chemical- and UV-resistant, hypoallergenic and many more. We know every aspect of silicone and how it can benefit your company and your products.

Contact Us for a Free Estimate

To learn more about LSR solutions at SIMTEC Silicone Parts, please contact us online for more information. You can also request a free quote from a representative to gain a better understanding of the competitive pricing options we offer.