Liquid silicone rubber is a material widely used in medical devices, kitchenware, and other fields. For product engineers, OEM manufacturers, and wholesalers, selecting the right material is important to ensuring product performance and safety. This guide will help you understand LSR materials to make better choices.
What Is Liquid Silicone Rubber(LSR) Material
Liquid silicone rubber (LSR) is a silicone material named for its low-viscosity liquid state before vulcanization. Only after curing does it transform into the soft, elastomer your commonly encounter.
From a chemical structure perspective, LSR is a high-molecular-weight polymer. Unlike rubber or plastics, it features a main molecular backbone composed of silicon and oxygen atoms, with numerous organic functional groups attached that determine its properties.
Liquid Silicone Rubber Material Manufacturing Process
The structure of LSR material requires a complex manufacturing process to achieve. Overall, it consists of the following 4 steps.
- Step 1: Silicon metal extracted from quartz sand through heating is crushed into powder, then mixed with methyl chloride and heated to produce silicone rubber gum, primarily composed of dimethylchlorosilane.
- Step 2: Dimethylchlorosilane undergoes hydrolysis and polymerization to yield silicone rubber gum, primarily composed of polysiloxane.
- Step 3: The silicone rubber gum is then placed in a kneader to disperse and depolymerize the raw rubber. Additives such as curing agents are subsequently incorporated. Typically, LSR materials use a platinum-based curing system for solidification. This process makes Component A of the LSR material.
- Step 4: Since LSR uses a two-component curing system, it is mixed with Component B—containing a crosslinking agent—heated, and fully vulcanized to form the final LSR product.
Liquid Silicone Rubber Material Properties
Excellent Flowability before Curing
The low-viscosity liquid state before curing enables LSR materials to achieve higher precision. During Liquid silicone rubber injection molding(LIM), its fluidity allows it to fill every corner of the mold, replicating details that other silicone rubber types struggle to achieve.
Whether producing ultra-thin silicone membranes for industrial metering equipment, fine silicone brush filaments, or textured surface products, LSR materials can be manufactured with precision tolerances of ±0.02–0.05 mm.
This fluidity also enables the integration of multiple components into a single part, allowing LSR to be used for producing complex components while reducing costs. Beyond monolithic production, it can also be combined with other materials through overmolding. This is how the soft silicone exterior on surgical instruments is achieved.
Suitable for Fully Automated Production
Thanks to injection molding, LSR materials can be applied to fully automated production lines with minimal manual intervention. From compounding to trimming, the entire process can be handled by machines, making LSR particularly well-suited for high-volume production with exceptional efficiency.
Once the mold is designed, you can consistently produce LSR products of stable quality without worrying about significant variations between batches.
Therefore, choosing LSR materials means your company will gain greater capability to meet urgent demands and earn a solid reputation for reliable product quality.
Wide Temperature Tolerance Range
LSR material can withstand temperatures ranging from -50°C to 200°C and remains relatively stable within this temperature range. As long as the upper limit is not exceeded, it maintains flexibility at high temperatures over extended periods without premature aging.
It can also withstand extreme temperatures up to 250°C for a short time. If you’re seeking a material that delivers stable sealing performance at high temperatures, heat-resistant LSR is a wise choice.
LSR also does well at low temperatures. While hardness may change, it maintains elasticity without becoming brittle like plastics.
If you would like to learn more about the performance of silicone at different temperatures, you can refer to Temperature and Silicone: What You Need to Know.
Chemical Compatibility
Due to its stable molecular backbone, liquid silicone rubber doesn’t react with or corrode by most chemicals. It can safely withstand long-term contact with common household substances like water, oxygen, salts, weak acids, and weak alkalis, and can be cleaned using baking soda or vinegar.
It also exhibits some tolerance to common kitchen fats and oils, though prolonged exposure to high-temperature oils may shorten its lifespan. Using LSR materials for baking utensils is a good choice, but remember to remind your customers of this point and clean them in time.
Avoid exposing LSR products to chloroform, aromatic hydrocarbons, mineral oils, or gasoline. These chemicals penetrate the microscopic gaps between LSR molecules, causing the material to swell while degrading its mechanical properties and potentially rendering it completely nonfunctional.
Additionally, never clean LSR materials with acetone, strong acids, strong alkalis, or strong oxidizing agents, as these will cause irreversible damage.
Electrical Insulation
LSR itself is an excellent material that maintains electrical insulation across a wide temperature range. Due to its relatively high volume resistivity, it effectively blocks current flow, providing reliable protection for users and equipment.
By incorporating conductive fillers such as carbon black, it can also be transformed into a conductive material. Depending on the type and quantity of added fillers, it can serve various functions, including electrostatic protection and EMI shielding.
Weather Resistance
LSR material also offers excellent weather resistance, making it a reliable choice for outdoor products. It withstands outdoor temperature changes and threats like ozone exposure. It also resists ultraviolet radiation, making it less prone to chalking, hardening, and cracking caused by UV degradation from exposure.
Ease of Cleaning
LSR material is naturally hydrophobic and non-stick, preventing stubborn stains that are difficult to clean and making its surface resistant to bacterial and mold growth. While its surface may attract dust over extended use, cleaning it is quite straightforward.
A dish sponge or cloth, water, soap, or common cleaning agents are enough to clean LSR products. Even persistent odors can be eliminated by using lemon or baking soda.
High-temperature-resistant, food-grade liquid silicone rubber products are also dishwasher-safe, making them highly convenient for customers using LSR products in bulk.
Silicone Product Maintenance Guide: How to Clean, Store, and What to Avoid contains more information about cleaning silicone.
Durability
Aside from short-term products like scar patches, LSR materials have an exceptionally long service life. With proper use and maintenance, LSR products can last up to 10 years, while high-quality LSR materials may even endure for decades.
Choosing LSR represents a long-term investment, meaning fewer replacements and sustained economic benefits over time.
Flexibility
As a type of silicone rubber, LSR also offers exceptional flexibility. Depending on the application, its hardness can be adjusted between 10 and 80 Shore A.
Most LSR materials are soft and elastic, conforming well to various gaps, making them suitable for diverse sealing applications. Even when the structure undergoes movement, the attached LSR can change shape to some extent.
Beyond softness, it also possesses strength, with some LSR materials capable of stretching to seven times their original length. After deformation under external pressure, it can return to its original shape once the external constraint is removed, and has minimal compression set.
This flexibility allows LSR products to be designed for some special shapes. Even shapes that are difficult to demold with other materials, such as inverted shapes, can be completely demolded with LSR.
High Transparency
Unlike other silicone rubbers, LSR material offers relatively high transparency, making it suitable for LED optical components and transparent products. It is also widely used in LED lighting applications such as outdoor fixtures. Unlike the TPU commonly used in transparent phone cases, LSR material is less prone to yellowing.
Disadvantages of Liquid Silicone Rubber Material
Cost
Although LSR is such an excellent material, its price is indeed significantly higher than that of rubber. Even within the silicone category, LSR made with premium raw materials and a platinum curing system is more expensive, let alone products that use superior additives and fumed silica fillers to ensure quality.
It is more akin to a high-end, high-performance material choice rather than a cheap, short-term consumable.
Unsuitable for Small-batch Production
If you only plan to produce or customize small batches of products, LSR material may not be your best choice.
LSR molds involved in product development and customization are relatively expensive. To achieve product precision, LSR mold machining requires high accuracy, which translates to higher costs. What’s more, LSR molds also need corresponding cold runner systems and temperature control systems, representing an extra expense.
The automation of LSR also makes it better suited for continuous production rather than small-batch manufacturing.
Low Mechanical Strength
When exposed to external forces, LSR is more susceptible to damage compared to materials like EPDM. Its abrasion resistance is not particularly strong, so prolonged friction causes the surface to become rough, losing non-stick characteristics.
If you have ever purchased silicone kitchenware, the seller may advise against using metal knives or forks on its surface. This is because the soft surface of LSR material is easily damaged by sharp objects, leaving scratches.
Repeated, prolonged stretching can also cause LSR to gradually accumulate latent damage until it loses elasticity, tears, or even breaks in two.
Relatively High Gas Permeability
Although LSR material is frequently used for sealing, it is important to note that it doesn’t provide an absolute barrier against gases but rather exhibits a certain degree of permeability. Gas molecules such as hydrogen, helium, oxygen, and water vapor may pass through the small interstitial spaces between LSR molecules and escape to the other side.
For medical dressings made from LSR, this permeability undoubtedly facilitates faster healing for patients, representing a distinct advantage. While this property has little impact on typical products like sealing rings, using LSR for sealing high-pressure gas cylinders may yield results that fall short of expectations.
Is Liquid Silicone Rubber Material Safe?
LSR material, as a high-purity silicone rubber frequently used in food contact and medical applications, generally ensures safety.
LSR itself is non-toxic and odorless, and highly stable. As long as it remains within its temperature tolerance range, there is no need to worry about LSR melting and releasing harmful substances.
LSR also exhibits biocompatibility. It is not only hypoallergenic and non-irritating to the body but, due to its stable chemical properties, can safely endure prolonged contact with human tissue.
The safety of LSR materials cannot be judged solely by the properties of the polymer itself. It is equally important to consider the substances added during its production process, their corresponding safety level, and usage.
Food-grade Liquid Silicone Rubber
Food-grade LSR is a material that has passed the FDA or the more stringent LFGB certification. It undergoes strict testing to ensure that heavy metal ions, D4, D5, and other harmful chemicals are suppressed to extremely low levels. What’s more, it contains no additives like BPA or PFAS that are prohibited in products intended for food contact.
During production, food-grade LSR uses a platinum curing system that generates no harmful byproducts, further ensuring safety.
You may be most concerned about whether harmful substances could migrate from food-grade LSR into food during contact, especially under high-temperature baking conditions. The answer is that this risk doesn’t exist when food-grade LSR products are used correctly.
Medical-grade Liquid Silicone Rubber
To meet medical-grade standards such as ISO 10993 or USP Class VI, medical-grade LSR must not only ensure material purity but also undergo cytotoxicity testing, irritation testing, and sensitization testing to guarantee safety.
For products like implants that involve long-term contact with the human body, medical-grade LSR must also be injection molded in a cleanroom and pass more stringent testing.
During use, they can be sterilized through many methods, including high-pressure steam sterilization and gamma irradiation. So you can confidently use them in medical applications, baby products, or other items.
Substandard or Low-quality Liquid Silicone Rubber
These products are the primary culprits behind concerns about LSR material safety. To cut costs, their manufacturers add cheaper additives or fillers, leading to silicone allergy and odors in LSR materials.
Some substandard LSR products even incorporate industrial additives to enhance performance. Therefore, when selecting safer LSR materials, pay close attention to whether they meet safety standards, if they exhibit suspiciously low prices, or if the non-stickiness exceeds the normal level.
If you are still concerned about LSR’s security, Is Silicone Toxic: Silicone Safety Guide may be helpful.
Applications of Liquid Silicone Rubber Material
Medical Equipment
For the medical industry, LSR materials that can withstand long-term high-pressure steam sterilization and are safe can be used to manufacture products such as respiratory masks and sealing gaskets. Due to its softness and ability to provide comfortable contact, it is also used in medical instruments and catheters.
LSR is also used in manufacturing precision components for pacemakers, offering reliable electrical insulation and dependable structural support.
Food Production
In food production, baking mats, sealing rings, and molds made from LSR materials have long been ubiquitous. Beyond providing reliable auxiliary processing functions, they are highly favored for maintaining flexibility and safety even at high temperatures. Their ease of cleaning is another reason many food processing plants choose them.
Aerospace Field
LSR’s ability to maintain elasticity at low temperatures is important for applications such as hatch seals. What’s more, aerospace equipment frequently faces threats from ozone and UV radiation, making LSR materials with excellent weather resistance and high resistivity ideal for use as cable protective sleeves.
Automotive Parts
LSR is used for sealing various components such as sensors due to its excellent sealing properties, high and low-temperature resistance, and ability to withstand vibration. It can function reliably in automobiles over extended periods without frequent replacement, making vehicles more appealing to consumers.
Electronics Equipment
LSR’s electrical insulation and high-temperature resistance make it the material of choice for sealing components and keypads in electronic devices. Its waterproof and weather-resistant properties also effectively protect outdoor equipment.
LED optical assemblies leverage LSR’s high transparency to transmit more light while preventing electrical leakage.
Industrial Equipment
Flexible LSR is highly suitable for pump blades used in peristaltic pumps, enabling precise control of internal fluids. It is also employed to seal industrial equipment. O-rings, valve seals, and gaskets made from LSR provide effective protection for production lines without releasing contaminants that could compromise the purity of contents.
Daily Consumer Goods
Manufacturers of baby products, kitchenware, premium goods, and outdoor equipment highly favor non-toxic and odorless LSR material. Baby pacifiers and kitchen utensils made from LSR are not only non-toxic and odorless but also heat-resistant.
For products like watch straps that come into prolonged contact with the body, LSR significantly reduces allergenic potential while offering lightweight comfort without causing excessive burden.
FAQ
High-temperature Silicone (HCR) vs. Room-temperature Silicone (RTV) vs. LSR
Like LSR, HCR requires curing under high-temperature conditions, while RTV can cure at room temperature. Their vulcanization systems also differ. LSR uses the safer platinum-curing system, HCR chooses the more economical peroxide-curing system, and RTV adopts an organotin-curing system.
LSR offers higher transparency and precision. HCR provides better cost-effectiveness and superior physical strength, making it widely used in industrial applications. RTV, valued for its ease of use, is frequently employed as a sealant.
Is Liquid Silicone Rubber Material Environmentally Friendly?
From a manufacturing perspective, the production of LSR materials inevitably consumes significant amounts of energy.
However, the extended service life of LSR materials reduces the need for disposable products and minimizes waste generation. Unlike plastics, it does not cause severe pollution when discarded and can be reused through specialized recycling chains.
Read Silicone Sustainability: Is Silicone Recyclable? to learn more.
Can LSR Material Be Overmolded with Plastic or Metal?
Silicone overmolding enables the combination of LSR with plastics and metals, allowing products to incorporate both soft and hard materials. LSR Electric toothbrushes and diving flashlights are manufactured using this process.
Beyond these two materials, overmolding can also integrate LSR with glass, ceramics, wood, magnets, PC, and other materials.
What Is the Shrinkage Rate of LSR Molding?
Depending on the type of LSR and the mold used, the molding shrinkage rate for LSR typically ranges between 2% and 4%. Professional LSR manufacturers can achieve more precise control over this shrinkage rate.
Can Liquid Silicone Rubber Materials Be Customized?
Yes. By adjusting the type of raw gum, fillers, additives, and processing methods, the hardness, color, transparency, conductivity, tear strength, and other properties of LSR materials can all be customized.
You can also customize LSR materials with flame retardancy or specific safety ratings for special requirements. However, you will need to find a manufacturer with LSR customization capabilities and meet the minimum order quantity.
Final Thoughts
Whether you’re finding high-quality LSR materials or looking to customize LSR products, partnering with a professional manufacturer is essential. Legensilico offers LSR for diverse applications—from FDA compliance to ISO 10993 certification—and can customize a more suitable LSR according to your specific needs. Contact us today!
