Are you still hesitant about choosing which type of silicone rubber for your product or machine? Are you confused by the various names for silicone rubber? This article will show you the different types of silicone rubber and their application areas to help you make a better decision.
What Is Silicone Rubber
As a form of silicone, silicone rubber is a polymeric material used widely in Industrial and food manufacturing, medical, automotive, aerospace fields, etc.
Through processes of heating, mixing, molding, and curing, natural silica sand is transformed into flexible silicone rubber. It possesses excellent temperature adaptability, chemical inertness, and durability. However, different types of silicone rubber have different performance in these aspects.
Different Types of Silicone Rubber
Because there are many types of silicone rubber, in order to make it easier for you to understand and distinguish them, I classified and compared them based on the vulcanization temperature, state, organic groups in the molecular structure, and function.
Distinguished According to Vulcanization Temperature
High-temperature Vulcanized Silicone Rubber (HTV/HCR)
High-temperature vulcanized silicone rubber, also called HCR, is a type of silicone rubber whose curing process is carried out at high temperatures. The “solid silicone rubber” , “high-consistency silicone rubber” and “HCR” that you see online also refer to this type of rubber.
High-temperature vulcanized silicone rubber is often processed into solid sheets. To shape it into the desired form, it needs to be placed in a mold, heated, and extruded.
High-temperature vulcanized rubber processed in this way is less prone to damage during stretching and can return to its original shape after long-term pressure. It can withstand a temperature range of -60°C to +230°C, making it a widely used type of silicone rubber.
Because of its excellent mechanical strength and UV resistance, it is used as a material for components requiring both flexibility and high strength, such as sealing strips, conveyor belts, and wire insulation.
However, because its processing requires specialized high-pressure molding equipment and due to its shape limitations, it cannot be used for the manufacture of high-precision products.
Room Temperature Vulcanizing Silicone Rubber (RTV)
Compared to HTV, room temperature vulcanizing silicone rubber, also known as RTV, is much easier to process. With the help of a platinum catalyst, it can be cured at room temperature and can be processed into more flexible shapes than HTV.
There are two common types of RTV: RTV-1, which can be used directly, and RTV-2, which requires mixing two components to cure. RTV-1 is a major component of some sealants, while RTV-2 can be used as a dental impression material, a potting material, etc.
All types of RTV have excellent corrosion resistance and provide adhesion to a variety of material surfaces. Therefore, it is also used as a special countermeasure against highly corrosive chemicals.
Distinguish According to State
Liquid Silicone Rubber (LSR)
Liquid silicone rubber, also known as LSR, is a high-purity, highly fluid material that can be used to produce various precision parts or coatings. It is a very flexible colloid in the raw material stage, and through injection molding, material waste can be minimized.
LSR is also suitable for the production of customized products in large scale. Simply mix the two materials thoroughly, removing any air bubbles, and they can create small or complicated parts that meet specific needs.
Because liquid silicone rubber typically uses platinum salts as catalysts, it produces virtually no harmful byproducts during curing, making it a key material in many medical-grade and food-grade silicone products.
It is highly stable and durable, resisting corrosion from external factors such as salt, acid, and ultraviolet radiation, and functioning normally for a long time. What’s more, due to limitations in the use of additives and fillers, its transparency can reach a relatively high level.
When choosing materials for precision parts or for safety reasons that come into contact with food, medicine, or the human body, LSR is highly recommended. Because of its high transparency, it is also a good choice, as part of some lamp or as a safer glass alternative.
Silicone Sponge Rubber (Si Sponge/VMQ Sponge)
For better cushioning and insulation performance, silicone sponge rubber was designed as a special type of silicone rubber material.
Silicone sponge rubber is produced from other silicone materials through a foaming process. Due to its porous structure, it is very lightweight and soft, making it suitable for cushioning impacts and reducing vibrations, protecting the core structures of certain machines.
Excellent sealing properties are another major advantage of silicone sponge rubber. It is also effective for sound insulation, heat insulation, and waterproofing. Some gaskets and aerospace insulation layers are made using silicone sponge rubber.
However, due to its numerous internal pores, its tensile strength is somewhat reduced.
Distinguished According to Organic Groups
Methyl Silicone Rubber (MQ)
Methyl silicone rubber(MQ) gets its name from the fact that its molecular structure contains only methyl groups on its side chains. It is one of the most basic types of silicone rubber. Like most silicone rubbers, it has a wide range of temperature adaptability, but it is easily damaged under long-term wear and impact.
Methyl Vinyl Silicone Rubber (MVQ)
The most common type of silicone rubber you encounter frequently, perhaps the one used in food manufacturing, is methyl vinyl silicone rubber, also known as VMQ, MVQ, or VMGI.
It has good resistance to infrared and ultraviolet radiation from sunlight, provides a certain level of strength, and offers relatively high durability, but cannot be used for the transport of certain fuels and solvents, as that would cause it to swell and eventually can no longer be used.
If you don’t have any special requirements for the silicone rubber in your product, you might consider MVQ, which offers good overall performance and cost-effectiveness.
Phenyl Silicone Rubber (PVMQ)
Phenyl silicone rubber (PVMQ) has excellent low-temperature resistance compared to other silicone rubbers. Based on the proportion of phenyl groups, it can be divided into low-phenyl silicone rubber, medium-phenyl silicone rubber, and high-phenyl silicone rubber.
Low-phenyl silicone rubber can be used as a cold-resistant silicone rubber. Due to the addition of phenyl groups, the crystallization temperature of the silicone rubber decreases, allowing it to withstand temperatures as low as -100 °C and even lower while maintaining good physical properties.
Medium- and high-phenyl silicone rubbers are known for their radiation resistance. While their tolerance for low temperatures increases slightly, their resistance to high temperatures improves. Manufacturers also add additives such as cerium dioxide to them to improve their stability in high-temperature environments. Some phenyl silicone rubbers can even withstand short periods of 300°C.
Because they can withstand radiation, ozone, low temperatures, and high temperatures simultaneously, and can buffer heat transfer to a certain extent, they are important materials for the aerospace industry.
Fluoropolymer Silicone Rubber (FVMQ)
A key characteristic of fluorosilicone rubber (FVMQ) is its superior resistance to chemicals. While ordinary silicone rubber cannot be used in fuel transportation systems, fluorosilicone rubber can be used for this purpose. It remains intact and does not swell even when exposed to toluene and mineral oil.
However, due to its special processing, using fluorosilicone rubber requires a higher budget. Furthermore, while its overall temperature resistance remains largely unchanged, it performs slightly worse at high temperatures.
It can be used to make seals for automotive fuel delivery systems or in environments containing certain organic solvents or corrosive liquids, providing you with greater safety.
Silicone Rubber Designed for Special Functions
Food-grade Silicone Rubber
Food-grade silicone rubber is safer than regular silicone rubber. This safety requirement is multifaceted. Its raw materials must be of high purity and free of harmful impurities, so fumed silica is usually used. It cannot be cured using peroxides commonly used in industrial silicone rubber, as this could lead to the silicone rubber being harmful to health.
The main way to distinguish between ordinary silicone rubber and food-grade silicone rubber is to check whether it meets FDA, NSF, RoHS, and other certifications. Silicone rubber that meets these national and international food contact material standards and tests ensures that there is no risk of harmful substance transfer when it comes into contact with food.
At the same time, its tensile properties, stability, and other properties have become better. To prevent affecting the flavor of food, it should be odorless or have only a slight odor. However, because it cannot contain certain toxic additives, its physical properties have decreased.
Food-grade silicone is now widely used in baking tools, food production machinery, and catering equipment, playing an important role in daily life and food manufacturing.
Medical-grade Silicone Rubber
Compared to food-grade silicone, medical-grade silicone is safer, and its standards and regulations are stricter. High-purity raw materials, a platinum curing process that produces virtually no toxic byproducts, and ultra-clean production facilities ensure comprehensive safety for medical-grade silicone. It not only meets FDA standards but also adheres to specific standards such as USP Class VI and ISO 10993, which further define the properties that medical-grade silicone should obey.
These stringent standards guarantee biocompatibility, stability, and non-irritation during application. It seldom causes allergic reactions in humans, and medical-grade silicone products used for implantation minimize discomfort caused by foreign objects.
It also needs to meet higher levels of sterility requirements to avoid causing wounds or bacterial infections inside the body.
Medical-grade silicone rubber can be used in medical, pharmaceutical, baby products, or products where safety needs to be guaranteed. It is an expensive, high-end type of silicone rubber. You can use medical-grade silicone instead of food-grade silicone, but food-grade silicone cannot be used for medical purposes.
If you would like to learn more about medical-grade silicone, you can check out Medical Silicone: What You Need to Know.
Conductive Silicone Rubber
To supply electromagnetic interference and for other electrical applications, fillers such as Acetylene black and structural inhibitors are added to conductive silicone rubber, achieving a balance of flexibility and conductivity.
Due to its radio frequency interference shielding properties and conductivity, it is used in the manufacture of sensors, conductive components, and various displays that require both conductivity and shock resistance.
Thermally Conductive Silicone Rubber (TCSR)
Normally, silicone rubber prevents heat transfer. However, to help heat dissipation within certain mechanical structures, aluminum oxide and boron nitride are added to thermally conductive silicone rubber (TCSR) during manufacturing, effectively improving its heat conduction.
If you need to use thermally conductive silicone rubber, please also keep in mind whether the type you intend to purchase is conductive. And because of the addition of these rigid materials, their hardness is relatively higher than that of ordinary silicone rubber.
It is frequently used to fill the gap between heatsinks and CPUs, or in the manufacture of spacers.
Application of Silicone Rubber
Depending on the application area, you can choose a silicone rubber that better suits your product’s needs.
In most cases, methyl vinyl silicone rubber (VMQ) is a general-purpose choice. It’s a kind of high-temperature vulcanizing silicone rubber (HTV) suitable for various seals and general silicone products. If your product has specific requirements, consider the following options:
● In aerospace or other extreme high and low temperature environments, phenyl silicone rubber (PVMQ) performs better.
● In applications such as sealing gaskets, heat insulation layers, sound insulation layers, or waterproof materials, silicone sponge rubber has the advantage of insulating heat and reducing external impact.
● For electrical connections that require both sealing and even heat dissipation, thermally conductive silicone rubber (TCSR) is recommended.
● If you are choosing a more durable and conductive screen material or electromagnetic shielding material for your appliances, conductive silicone rubber is a suitable choice.
● If you need to use silicone rubber in pipelines or other components for transporting fuels, solvents, or corrosive chemicals, fluorosilicone rubber(FVMQ) is more durable.
● For silicone baking mats, silicone straws, and other applications that come into direct contact with food, food-grade silicone is safe.
● For baby pacifiers, menstrual cups, intravenous catheters, and pacemakers, please use standard-compliant medical-grade silicone.
● For ensuring component precision or customizing miniature silicone products, liquid silicone rubber(LSR) can do it well.
● For a convenient, readily curable potting compound or sealant, room temperature vulcanizing silicone rubber (RTV) can meet your needs.
FAQ
Are Silicone Rubber and Rubber the Same?
In fact, although both are soft and are called rubber, rubber and silicone rubber are two very different materials. Rubber is a natural or synthetic material, while silicone rubber is an elastomer obtained by processing silica. Rubber is more wear-resistant and has better mechanical properties, while silicone rubber is more resistant to high and low temperatures, corrosion, and ultraviolet radiation.
What are the forms of silicone?
Silicone exists in many forms in industrial manufacturing, and silicone rubber, mentioned in this article, is just one of them. The coating on non-stick cookware is a silicone resin. Silicone oil, frequently added to skincare products, silicone gel for scar repair, and silicone emulsions used as cleaning agents are all common forms of silicone.
What Is the Difference between Platinum-cured Silicone Rubber and Peroxide-cured Silicone Rubber?
The biggest difference lies in whether they contain harmful substances. Silicone rubber cured with peroxides is generally used in industrial manufacturing, where the focus is usually on the physical properties and price. Peroxides can cause silicone rubber to have an unpleasant odor and be unsafe for food and health. Silicone rubber produced using platinum curing systems is safer, and the catalysts used are harmless to humans.
Can Silicone Rubber Be Recycled?
Silicone rubber is a recyclable material, but it needs to be recycled through specialized silicone recycling facilities. After processes such as sorting, crushing, melting, filtering, and bleaching, silicone can be made into new products. Whats more, silicone itself does not have any highly hazardous components, so its environmental influence is minimal.
Will Silicone Rubber Melt When Heated?
The answer is that silicone rubber will not melt within the specified operating temperature range, so you don’t need to worry about it deteriorating quickly after heating, like plastic, or affecting the safety of your food and pharmaceutical production. Although some types of silicone rubber, such as high-temperature vulcanization silicone rubber, require heat to cure, once they become stable, they cannot soften or melt within the specified operating temperature range.
Final Thoughts
The above outlines the main types of silicone rubber and their corresponding applications. We hope these will help you choose the right silicone rubber material. If you would like to learn more about a specific type of silicone rubber or wish to purchase silicone rubber and its products in bulk, please visit our homepage. As a silicone manufacturer with over 20 years of experience, Legensilico offers a one-stop service for silicone products. Click to learn more!
