You may frequently encounter the processes of silicone curing and vulcanisation in the production line. Understanding the roles of these processes in silicone can help you control the quality and cost of silicone products.Therefore, in this article, we will explore the specific differences between the curing and vulcanisation processes.
What Are Silicone Curing and Vulcanisation?
In fact, when you are involved in the actual industrial production of silicone products, you will find that these two terms essentially describe the same process, which is to convert silicone polymers into elastomers through cross-linking.
Of course, the meanings of no two words are exactly the same, and there are also subtle differences between curing and vulcanisation.
Curing
The meaning scope of curing is very broad. It refers to the process of making materials hard or solid by means of heating, chemical reactions or radiation treatment. Depending on the material, most curing processes are reversible while others are irreversible.
The rubbers, plastics, coatings, adhesives and composite materials you use in various applications can all form strong bonds between molecules through curing.
Curing significantly improves the elasticity, tensile strength and durability of rubber. Curing is one of the key processes in rubber processing, which can effectively enhance the strength of the rubber itself.
High-quality cured rubber can withstand stable and long-term use even in high-temperature environments, under the influence of chemicals, or due to long-term physical friction wear.
Silicone Vulcanisation
Vulcanization traditionally refers to sulfur-based crosslinking in rubber, although the term is now often used more broadly to describe elastomer crosslinking processes. However, vulcanisation was originally a term used in the traditional rubber industry, specifically referring to the vulcanisation of natural rubber using sulfur.
Vulcanisation is an irreversible process. Once your silicone is vulcanised, it cannot be restored to its original state. Commercial silicone is typically crosslinked using peroxide or platinum-catalyzed systems rather than sulfur.
Therefore, the “vulcanised silicone” you are using actually refers to cross-linking catalyzed by peroxides or platinum. This process enables the silicone to possess better elasticity, durability, and resistance to heat and chemical substances.
Different Types of Cured and Vulcanised Silicone
In the silicone industry, you will encounter various types of vulcanised silicone, with different process conditions, curing temperatures and times. Therefore, the properties of the cured silicone also vary. The most common ones are the following three types:
Platinum-Catalyzed (Addition Cure) Vulcanisation
LSR (Liquid Silicone Rubber) is a system composed of two components. When you use it, you will find that it is like honey or water, with good fluidity. When curing the additively formed liquid silicone, a platinum catalyst is required.
Although the reaction can occur at room temperature, the industry-standard curing temperature is usually 120°C – 200°C (248°F – 392°F). Since the temperature of the mold increases, it will significantly accelerate the curing process.
Therefore, depending on the geometry of the part, the silicone curing usually takes place within 30 seconds to 5 minutes. However, this curing method requires precise temperature control.
It is usually processed by injection molding. If you adopt this method, you will find that the platinum catalyst promotes the cross-linking reaction without generating any by-products during the process.
Peroxide Cured Vulcanisation
HCR (High Consistency Rubber) is usually in a solid state or in a paste-like form, similar to clay or dough. Compared to LSR, its fluidity is extremely poor. Peroxide curing is the most common curing method for HCR, which is typically processed by extrusion, compression molding, or transfer molding for high-volume production.
Since organic peroxides are stable molecules at room temperature, the reaction usually needs to be carried out at a high temperature of 160°C – 200°C (320°F–392°F). The vulcanisation time is typically 5 – 15 minutes. Post-curing is often recommended when low volatile content, improved mechanical properties or regulatory compliance is required.
This vulcanisation method has a lower cost compared to platinum catalysis, but it may produce residual by-products. Therefore, it is not ideal for applications involving sensitive materials.
Condensation Cure vulcanisation
You can use the condensation reaction to achieve curing at room temperature. It is mainly used for RTV-1 and RTV-2 (Room Temperature Vulcanisation silicone). Although it is suitable for certain specific applications, the curing time is relatively long and may produce by-products.
When conducting condensation curing of RTV silicone, it is usually sufficient to do so at room temperature or at temperatures of 20℃-50℃(68°F–122°F). However, the process takes several hours to several days, but increasing the environmental humidity can accelerate the curing speed, because moisture participates in condensation curing.
Applications of Cured and Vulcanised Silicone
Silicone typically experiences some shrinkage during your curing process, although the amount depends on the formulation and processing conditions, but its overall shape will still remain intact. Moreover, high-quality silicone has a smaller shrinkage rate.
After the silicone is cured, its texture becomes harder, and it is less prone to deformation under force. The tensile strength also significantly increases. In addition, silicone possesses many outstanding advantages:
- Temperature resistance: Silicone can withstand extreme temperatures, typically ranging from -40℃ to 230℃.
- Durability: The cross-linked structure enhances the tear resistance and extends the service life.
- Flexibility: Even after vulcanisation, silicone still maintains high flexibility.
- Safety: Silicone is biocompatible and easy to clean, making it suitable for hygienic applications.
You can apply different types of silicone to different usage conditions based on their characteristics:
Medical Devices
Platinum cured silicone has high purity and good safety, and possesses excellent biocompatibility and low allergenicity. If your silicone products comply with FDA regulations, ISO 10993 and USP Class VI, it will be highly suitable for applications in the medical and pharmaceutical fields. The following are related products:
- Medical silicone tubes
- Injection pump pistons
- Implants
Baby Products
Platinum cured silicone is usually odorless and can be formulated to comply with both FDA and LFGB. Because the silicone remains flexible after curing and can be adjusted in hardness, your customers can ensure the safety of the baby’s use. Moreover, its smooth, durable surface is easy to clean, so it is suitable for the maternal and infant field.
Common applications include:
- Silicone teethers
- Nipples
- Silicone bibs
- Stroller grips and pads
Automotive
The peroxide cured silicone has excellent compressive set properties, is resistant to high temperatures, and can withstand harsh working conditions. You can use it in the production of the following related products:
- Gasket
- Seal
- Pipe
- Ignition cable boots
Kitchen Utensils
Platinum cured silicone has the properties of high heat resistance and non-toxicity. If your silicone product complies with food regulations, it is highly suitable for use in:
- Baking mats
- Scraper
- Spatula
- Spoon
Electronics
The insulating properties of platinum-cured silicone make it an ideal material for protecting sensitive components, and it does not yellow easily. You can use it to produce the following products:
- Keypads
- Smartwatch straps
- Lens ring
Construction
The condensation cured silicone has a low production cost and a simpler curing process, which can be carried out at a lower temperature. Therefore, it can be used as a building sealant and the construction process is good weather resistance.
FAQ
Which Curing Method Is Better, Platinum or Peroxide?
It’s difficult to determine. Since the silicone standards required by different applications vary, it’s hard to judge which fixed method is better. You just need to choose according to the requirements of the industry applications.
Can Peroxide Cured Silicone Pass FDA or LFGB?
Sure, but with conditions. Because the curing with peroxides will produce organic by-products and cause an unpleasant smell, which makes it very difficult for your peroxide-cured silicone products to pass the LFGB sensory (olfactory/taste) test and migration requirements .
However, you can achieve this by undergoing strict post-curing treatment: usually at 150–200°C for 2 to 8 hours, which can remove the residual volatile substances.
What is Catalyst Poisoning in Platinum Cured Silicone?
The main issue is that the platinum catalyst is contaminated by trace amounts of certain chemicals, losing its activity and causing the silicone to fail in the curing process.
If there are residual sticky substances that have not fully cured on the surface of your silicone or if it is completely in a liquid state, it indicates a failure in the curing process, which may affect your entire batch of goods. You can set up a dedicated platinum curing production line and isolate it from other substances to prevent this problem.
Does Platinum Cured Silicone Require Pressure for Curing?
The chemical reaction of platinum-cured silicone does not require pressure by itself, but in industrial molding, pressure is usually applied. If you use it for pouring or brushing, no pressure is needed. Just let it undergo vacuum defoaming and then flow and cure naturally.
Does Curing Method Affect the Temperature Resistance of Silicone?
Yes, the temperature resistance of silicone is mainly influenced by polymer formulation and crosslinking density. The standard range for platinum cured silicone and peroxide cured silicone is similar, typically ranging from -40°C to 230°C.
However, special formulations of platinum cured silicone can withstand high temperatures up to 260°C, while peroxide cured silicone that does not cure properly may become brittle at high temperatures. The temperature resistance range of condensation cured silicone is usually only from -40°C to 180°C.
Final Thoughts
Legensilico is a professional silicone manufacturer with 8 modern assembly lines. We are dedicated to providing you with high-quality silicone products. If you are interested in our silicone products or would like to know more about them, please feel free to contact us. We can offer a one-stop service.
