If you want to custom silicone product used in the temperature range from -50 to 250 °C, then you have to know the silicone elastomer, especially when you need to customize the silicone seal, gasket, thermal interface materials, etc. This article will give you a deep knowledge of the silicone elastomer.
Types of Silicone Elastomer
Classified By Organic Groups
Methyl Silicone Rubber
The main chain of silicone rubber is composed of silicon-oxygen bonds, and the side groups are organic groups. Different groups result in different properties of silicone rubber.
Methyl Silicone Rubber
The most common type is methyl silicone rubber, also known as dimethyl silicone rubber, abbreviated as MQ. This type of silicone has a wide range of applications and is used in many regular products, with balanced overall performance.
Methylphenyl Silicone Rubber
If phenyl groups are added to the side groups, resulting in the coexistence of methyl and phenyl groups, it is called methyl-phenyl silicone rubber, abbreviated as PMQ. Phenyl can improve low-temperature performance. For products used outdoors in winter, choosing them makes them less likely to become hard and brittle.
Methyl Vinyl Silicone Rubber
If vinyl is added further, the combination of methyl and vinyl forms methylvinyl silicone rubber, abbreviated as VMQ. Vinyl can enhance the efficiency of vulcanization reactions. When making high-temperature products, the vulcanization speed is faster, and the cross-linking of the finished products is more thorough.
Classify By Processing Methods
Solid Silicone Elastomer
Solid silicone elastomer, also known as high-temperature vulcanized silicone rubber, is abbreviated as HTV. This kind of silicone is usually in block or granular form and has a high viscosity. During processing, high-temperature vulcanization is required. Generally, the molding process is adopted, where the rubber compound is placed in a mold and heated and pressurized to solidify and form. It is suitable for making products with complex structures and large thicknesses, such as sealing rings and industrial protective parts.
Liquid Silicone Rubber
Liquid silicone rubber, abbreviated as LSR. It is in a flowing liquid state with a small molecular weight. Injection molding for processing, similar to plastic injection molding, involves injecting liquid silicone into a mold and heating it for vulcanization. LSR has good fluidity and can replicate fine patterns. It is particularly suitable for making small and precise products, such as medical catheter joints and electronic device seals. It is highly efficient and has accurate dimensions.
Room-temperature Silicon Sulfide Elastomer
room-temperature vulcanized silicone elastomer, abbreviated as RTV. This type of silicone does not require high temperatures and can vulcanize at room temperature. It is divided into single-component and two-component types. The single-component type cures upon contact with moisture in the air when extruded and is suitable for potting and coating, such as waterproof coatings for electronic components. The two-component type requires the mixing of two rubber compounds and then vulcanization. The operation time is controllable, and it is suitable for use as a sealing material to fill gaps. If you are making products that require quick assembly, RTV can eliminate the heating step and shorten the production cycle.
In conclusion, PMQ or PVMQ is preferred. For those requiring oil resistance, consider fluorine-containing types. If the processing method is molding, HTV is more convenient. For making precision small parts, LSR is more suitable. You can conduct tests on the samples you receive first to see if the hardness and tensile strength after vulcanization meet the requirements. The processing parameters for different types of silicone rubber also vary. For instance, the vulcanization temperature of HTV is higher than that of LSR, and the surface drying time of RTV is related to humidity.
The Influence of Additives on Silicone Elastomer
Crosslinking Agent
This directly determines how the silicone cures and whether it is stable after curing. Peroxide crosslinking agents such as benzoyl peroxide (BIPB) and diisopropylbenzene peroxide (DCBP) generate active oxygen through decomposition to cross-link silicon-oxygen bonds. They have a high crosslinking density and are suitable for molded sealing rings and industrial hoses – they cure quickly, and the hardness of the finished product is sufficient. However, if it is for medical-grade pacifiers or food-grade sealed bags, platinum catalysts should be selected. Platinum catalysis is an addition reaction with no residual by-products, making the rubber compound purer and meeting the requirements of biocompatibility. For you to produce such products, choosing a platinum catalyst is equivalent to passing the compliance test in advance.
The Fillers
Adding fillers to the glue either enhances its performance or reduces the cost. Fumed silica has a large BET specific surface area and can firmly bind the silicon-oxygen bond, significantly enhancing the tear strength. Quartz powder is a non-reinforcing filler. When added, it can adjust the hardness of the rubber compound and also reduce the cost of raw materials. It is suitable for daily accessories with low strength requirements.
Stabilizers
Although silicone rubber is heat-resistant, it will gradually age over a long period of high temperatures. Adding stabilizers such as hindered phenols can capture free radicals and delay thermal oxidation. When you make seals for car engine compartments and protective covers for outdoor high-temperature equipment, stabilizers can make the products last for one or two more years and reduce after-sales maintenance.
Flame Retardants
For socket seals and circuit board protective adhesives used in electronic and electrical appliances, they must comply with flame-retardant standards. Aluminum trihydrate is an inorganic flame retardant. When added and exposed to fire, it forms an aluminum oxide barrier to prevent combustion. It also contains no halogen. If a higher flame retardant grade is required, such as for aerospace components, platinum or cerium compounds should be selected – these metal compounds can catalyze the formation of silicon-oxygen bonds to form more stable flame retardant structures with higher efficiency.
The Pigment
Silicone rubber is transparent by itself and is particularly easy to color. When you make colored teething rings for mothers and babies and colored key seals for consumer electronics, choose pigments with good dispersibility. Poor-quality pigments will aggregate, affecting the uniformity of the rubber compound and resulting in products with mottled colors. Good pigments can be evenly dispersed, maintaining the elasticity of silicone while keeping the color lasting and not fading.
In fact, the selection of additives is essentially about matching demands. For food and medical products, platinum catalysts and non-toxic fillers are preferred. When you make high-temperature weather-resistant parts, stabilizers and peroxide crosslinking agents are crucial. When you make electronic components, the right conductive or flame-retardant fillers must be selected. You can try several combinations to see the performance after vulcanization – such as tear strength, heat resistance time, and color stability- and find the formula that best suits your production line.
What are the Advantages and Properties of Silicone Elastomer?
Good Heat Resistance and Oxidation Resistance
Silicone products for high-temperature environments, such as sealing strips for ovens and protective covers for industrial heating tubes. They can withstand temperatures over 200 degrees without deforming. Winter outdoor items, such as car door seals and sealing parts for cold chain equipment, will not become hard, brittle, or crack even at minus tens of degrees Celsius – this is much better than many plastics or ordinary rubbers.
Strong Resistance to Erosion
Oxygen, ozone, and sunlight, these substances that constantly gnaw at materials, silicone rubber is not afraid at all. For outdoor products, such as sealants for solar panels and insulating sleeves for outdoor wires, silicone rubber is more suitable than ordinary rubber.
Anti-radiation Properties – Electromagnetic Radiation and Particle Radiation
It can be used as a protective layer for medical equipment or electronic components, such as the sealing parts of radiotherapy equipment and the electronic components of satellites. It can maintain stable performance and will not malfunction due to radiation.
Non-sticky
The silicone rubber hardly adheres to anything. It can be used as the inner lining of baking molds and chocolate filling machines. When demolding, there is no need to apply oil, and the products will not leave residue. It is easy to clean. As a sealing ring for kitchenware, it won’t stick to oil stains and will be clean after one wash, making it convenient for consumers to use.
Low Toxicity
Silicone rubber itself is non-toxic. This makes silicone rubber highly suitable for the production of food contact products, such as baby teething rings, food-grade sealed bags, or medical supplies, such as infusion tube seals.
Low-temperature Flexibility
The glass transition temperature of silicone rubber is low, so it won’t freeze hard in winter.
Optical Transparency
Transparent silicone rubber can be used as Windows for medical devices, transparent seals for electronic equipment, or packaging accessories for beauty products – maintaining functionality without affecting appearance and enhancing the texture of the products.
Biocompatibility
Silicone rubber is compatible with human tissues. When used in medical implants such as breast augmentation prostheses and dental impression materials, or in baby products like pacifiers, it does not cause allergies or rejection.
What are the Disadvantages of Silicone Elastomer
Difficult to Recycle
The molecular structure of silicone rubber is stable, and it is difficult to recycle. When you produce products, you need to consider environmental protection requirements.
Releasing Volatile Organic Compounds (VOCs)
Some types of silicone rubber release a small amount of VOCs during production or use, such as the smell during processing or the unpleasant odor of the finished product. This will affect the working environment of workers or the experience of consumers. You need to ensure good ventilation during production or carry out post-treatment on finished products to reduce odors.
Is it Difficult to Synthesize Silicone Elastomer, and How is It Produced?
Preparation of Chlorosilane
It requires the reaction of silica powder and chloromethane under the action of a catalyst (such as aluminum chloride) to generate basic chlorosilanes like methylchlorosilane. The reaction temperature must be kept within an appropriate range – if it is too high, by-products may pop out; if it is too low, the silicon powder and chloromethane will not react properly, and the reaction will be incomplete. The key lies in purity control: unreacted silicon powder, excess chloromethane, or by-products must be removed. For instance, a distillation column can be used to purify chlorosilane; otherwise, the remaining impurities will follow to the next step, making the hydrolyzed silanol unclean, and the final polymerized elastomer may become brittle and have an unpleasant odor. This step relies on a stable process and purification equipment; otherwise, all the previous investment will be in vain.
Hydrolysis
The purified chlorosilane is mixed with water to react and form silanols (such as methylsilanol) and hydrochloric acid. The proportion of water here must be precisely controlled – if there is too little water, the hydrolysis of chlorosilane will not be complete, and the remaining chlorosilane will clog the equipment. When there is too much water, silanol will rush to form small lumps and cannot be used for the next polymerization step. The more troublesome part is the treatment with hydrochloric acid: the hydrochloric acid produced by the reaction will corrode the reaction vessel. It is necessary to neutralize it with sodium hydroxide as soon as possible to turn it into harmless sodium chloride. Otherwise, the workshop environment will deteriorate, and the workers’ operation will not be safe.
Aggregation
Silanols cluster together under the action of catalysts (such as organoplatinum or tin) and condense to form organosilicon elastomers. The heat in this step is the most difficult to master: if too much catalyst is added, the polymerization reaction will be too fast, and there will be more residual catalyst in the elastomer. Food-grade silicone will not meet the low-toxicity requirements. The catalyst was insufficient, the polymerization was incomplete, the molecular weight of the elastomer was low, and it broke easily when pulled. The temperature also needs to be adjusted correctly – if it is too high, the silanol will randomly cluster together, form side chains, and the elastomer will become hard. It’s too low, the reaction is slow, and the production efficiency is low.
What are the Processing Methods of Silicone Elastomer?
Extrusion Molding
It is suitable for making items with uniform cross-sections, such as sealing strips, rubber hoses, and wire insulation sleeves. This method is highly efficient. One production line can produce several hundred kilograms of finished products in a day, making it particularly suitable for large-scale production if you are making outdoor sealing strips, industrial hoses, and other products with large quantities and simple shapes, choosing extrusion.
Injection Molding
It mainly focuses on precision and small parts. For instance, sealing gaskets for electronic components, catheter connectors for medical equipment, and pacifier accessories for baby and maternal products. The advantages of injection molding are dimensional stability and high repeatability, and accuracy. For products that require high precision and complex structures, such as auxiliary parts for medical implants, you can choose injection molding.
3D Printing
3D printing is suitable for making prototypes or small-batch customization. For instance, new samples in the R&D stage and personalized orders from customers. This method does not require mold opening. It only takes a few hours to make a small sample, and it is also convenient to modify the design. When you are doing research and development and want to quickly verify the structure or take small-batch custom orders, 3D printing can help you save time and mold costs. However, the efficiency and strength of 3D printing are not as good as the previous two methods. It is not cost-effective to produce large quantities.
In Which Fields Can Silicone Elastomer Be Applied?
Automotive Manufacturing Field
From the sealing gaskets in the engine compartment to the connecting parts, from spark plug protective sleeves to radiator water pipe joints, silicone can withstand high-temperature and high-pressure environments. Even when exposed to engine heat for a long time, it is not easy to harden or crack. During vehicle operation, frequent vibrations occur. Its anti-kinking and vacuum collapse characteristics make the sealing performance more stable. For example, the lens molds or reflectors in car lamps. After silicone is formed, its dimensions are precise, and it has strong weather resistance. It will not deform due to temperature differences between day and night or ultraviolet radiation, which is crucial for the long-term lighting effect of car lamps.
Electronic and Electrical Industry
Cable terminal connectors require stable insulation protection. The voltage resistance and anti-aging capabilities of silicone can reduce signal interference. The gaskets of control units or power modules must resist heat accumulation during circuit operation. Silicone will not soften or lose heat due to continuous temperature rise, maintaining the function of sealing, dust, and water vapor prevention in the control boxes of industrial equipment. These small components may seem insignificant, but they directly affect the safety of equipment operation. Choosing the right materials can reduce the frequency of later maintenance.
Medical Products
The biocompatibility of silicone is a core advantage. Devices that come into direct contact with the human body, such as catheters and infusion tubes, will not cause allergic or toxic reactions. Respiratory anesthesia masks or baby pacifiers also need soft, skin-friendly materials that can withstand repeated disinfection and cleaning. During disinfection, silicone will not deform or release harmful substances in the high-temperature and high-pressure environment. The silicone rubber coating on the outer layer of medical equipment cables not only provides insulation but also buffers mechanical pulling, thereby extending the service life of the equipment
Consumer Goods Field
The most common kitchen scenarios are silicone for cooking pot handles or baking molds, which are resistant to corrosion by edible oil and cleaning agents. They will not crack even after being rinsed at high temperatures in a dishwasher. The sealing gaskets of conveyor belts in food processing equipment can remain elastic even after long-term contact with food and grease. The sealing property of the silicone for water valves in water dispensers or water outlets in vending machines prevents water leakage and is convenient to wipe during cleaning. The surface is not prone to leaving stains. The sealing ring of swimming goggles in leisure products should fit the face tightly without leakage. The grips or mouthpieces of sports equipment should be soft, anti-slip, and resistant to sweat erosion. The silicone material should have a comfortable touch and not harden due to long-term contact with skin oils. These details can enhance the user experience.
The Aerospace Industry
The aerospace industry has extremely high requirements for material reliability. The stability of silicone at extreme temperatures can be used for internal sealing parts of aircraft or heat insulation pads for instruments. In semiconductor manufacturing workshops, equipment sealing parts need to resist the corrosion of chemical reagents. The chemical resistance of silicone enables it to handle such environments. Silicone can also work stably for sealing conveyor belts on industrial assembly lines or peripheral components of high-temperature furnaces.
Thermoplastic Elastomer(TPE) vs Silicone
Biocompatibility
Silicone is inherently friendly to the human body and can be used for medical implants, baby pacifiers, and dental impressions. It can pass strict certifications such as FDA and ISO10993. What about TPE? Most of them contain plasticizers or additives. When they come into contact with the skin, they may seep small molecules. Parents are prone to worry about “toxicity” when using them in baby and maternal products. For your products with strong compliance, silicone is a more stable choice.
Chemical Resistance
Silicone rubber is resistant to oil and solvents. The silicone rubber sealing ring used in the kitchen will not deform even after being in contact with edible oil and vinegar for half a year. The sealing parts of a car engine will not swell even when they come into contact with engine oil or coolant. TPE is delicate. When it comes into contact with grease or chemical reagents, it tends to soften or even dissolve. For outdoor or industrial products, the durability of silicone is better.
Hardness
When you make teething rings and baby teething sticks, the silicone can achieve a softness of Shore A30, so that babies won’t bite into them. TPE usually needs to be A50. It feels a bit hard when bitten, and children may not like to use it. For adult products such as massage heads, the soft and elastic feel of silicone is closer to the skin, providing a better experience.
Compression Deformation
Silicone does not deform under long-term pressure. When you use it as window and door gaskets or industrial oil seals, they remain round even after two or three years of use and will not flatten to leak air. TPE is prone to “fatigue”. If it is pressed for a long time, it will permanently deform, and the sealing effect will decline.
Costs
TPE is not without its advantages, such as fast processing and low cost. But when you make products, it depends on the demand: if it’s for medical, maternal and infant, or food contact categories, the biocompatibility and chemical resistance of silicone are essential requirements. If it is ordinary toys or commodities, TPE may play a role, but now, consumers should be carefully considered consumers more and more attention to safety silica gel non-toxic label can help you sell better.
Summary
This article covers all the information about silicone elastomers, hoping to be of help to your production and manufacturing. If you still have any other questions, you can contact us for free. We offer a wide variety of silicone products and can provide you with more free and value-added services.
FAQ
What Silicone Elastomer Products Does Legenday Sell?
Legenday sells some simple silicone products, such as silicone brushes, silicone buttons, silicone sheets, silicone tubes, silicone foam, etc. You can use them to produce more complex silicone products.
How Long is the Shelf Life of Silicone Elastomer, and What are the Storage Conditions?
Silicone elastomer shelf life is directly related to the storage method. Unopened raw materials, if well packaged and sealed, can usually be stored at room temperature for 1 to 2 years. If the purity of the raw materials is not high or the packaging leaks, the shelf life will be shortened. When storing, keep in a cool place, away from heat sources or direct sunlight.
How Do Silicone Products Ensure No Color Difference and No Yellowing?
Select raw materials with low impurities and use the premixing process to reduce color fluctuations between batches. During the vulcanization process, the temperature and time should be closely monitored. Excessive vulcanization can cause the molecular chains to break and turn yellow, while insufficient vulcanization leads to inadequate cross-linking and easy oxidation and discoloration. Adding stabilizers in post-treatment can neutralize the influence of ultraviolet rays or acids and alkalis in the environment.
