This technical guide includes the market characteristics, various types and production methods of Silicone Rubber, which is one of the most widely used synthetic elastomer or polymer with many applications in many different markets.
Composition and Fundamental Properties
Silicone rubber is made of a silicon-oxygen backbone (Si-O) that has organic side groups (usually methyl, vinyl, or phenyl) connected to it. This unique combination of inorganic stability and organic flexibility gives silicone rubber its own unique structure, which is semi-organic.
The main features of these materials can be described as follows:
- High Temp Resistant: These materials will work on temperatures ranging from -60 C to +260 C continuously. Certain formulations will allow for a maximum temperature range of -100 C to 300 C.
- Good Chemical and Weather Resistance: The chemical resistance of these materials includes a high degree of ozone, UV light and oxygen, along with a variety of chemicals.
- Excellent Electric Insulation: These materials have extremely low dielectric strength, but do offer excellent corona discharge resistance.
- Suitable for Medical and Food Applications: These materials are non-toxic and odourless for use in medical contact and food products.
- Good Temperature Flexibility Retention: These materials can maintain their flexibility and compression set resistance over a wide temperature range.
Classification and Types of Silicone Rubber
Silicone rubbers can be classified according to their curing method and chemical composition.
Curing Methods
High Temperature Vulcanisation (HTV): Cured by cross-linking at temperatures over 150 °C; suitable for temperatures over 300 °C.
Room Temperature Vulcanisation (RTV): Cured at room temperature (ambient). Two forms exist: One-part (RTV-1) systems have only single-component systems and two-part (RTV-2) systems have both.
Liquid Silicone Rubber (LSR): Manufactured as a low-viscosity, two-component material which has been platinum-cured for injection-moulding complex components.
Chemical Composition and Grade
Vinyl Methyl Siloxane Rubber (VMQ): This is the most widely used type and has excellent resistance to compression set.
Fluoro-silicone Rubber (FVMQ): These materials have excellent resistance to solvents, oils, and fuels, making them ideal for the aerospace and automotive markets.
Phenyl Siloxane Rubber (PMQ, PVMQ): These silicones offer better low-temperature flexibility (-120 °C) compared with other silicone grades.
Specialist Grades include: Flame-retardant (MF775), FDA-compliant, electrically conductive, and metal-detecting silicones.
Manufacturing Process Overview
Step One - Preparing The Raw Materials
Silicon should be of a very high-grade that can be obtained from the purification of Quartz or Sand Processed By Hydrolysis To Create Siloxane Bonds - The Base Building Blocks For All Silicone-Rubber Products. Additives, such as the curing agent, filler, and pigments to create a specific desired result, must then be formulated and mixed with the polyer to form the desired characteristics..
In the polymerizing stage of the Silicone Production Process, refined raw materials, particularly octamethylcyclotetrasiloxane DMC, are processed in production reactors before the appropriate temperature, time, and pressure settings are achieved so as to develop the right molecular weight and structural characteristics; therefore, a considerable stir must be conducted in order to properly and uniformly disperse the additives throughout the silicone mixture compound.
The silicone mixture will have to be introduced into a molding machine and shaped using any one of the four manufacturing options outlined below:
- Extrusion - Used for the production of items that have long uses, such as tubing and seals.
- Compression Molding - Products that require a high degree of accuracy, such as O-rings.
- Injection Molding - For the production of complex parts that will be produced in high volumes.
- Calendering - Used to produce sheets and films of silicone.
Applications
Automotive & Aerospace: Gaskets, seals, hoses, and vibration dampeners that must withstand extreme temperatures and aggressive fluids Medical Devices: Tubing, implants, surgical tools, and seals benefiting from biocompatibility and sterilization resistance Electronics Industry: EMI shielding components, conductive rubbers, keyboard contacts, and insulation for high-voltage applications Construction Sector: Sealants, adhesives, and weather-stripping that maintain flexibility and weather resistance Food Processing: FDA-approved gaskets, seals, and tubing for hygienic applications
Primer Technology for Enhanced Adhesion
Silicone primers are essential for achieving strong bonds between silicone rubber and various substrates. These primers, typically composed of silane and siloxane compounds in organic solvents, act as adhesion promoters by modifying the surface energy of inert substrates.
Application Guidelines:
- Prepare Surfaces: Prepare all Substrates; free of all Contaminants, Dry, and Clean.
- Apply Primer: Apply Primer to Surfaces With Brushing, Spraying, and Dipping In Thin Coats (1 to 10 μm).
- Dry and Cure Solvent: The solvent must be removed before bonding. This is done either by allowing the Solvent To Evaporate [10 min. to 2 hr.], and/or by Heat Treatment [100 to 150 °C] to improve adhesion;Adhesion will develop over time;
The Silicone Rubber Products must be bonded to ELASTOSIL® AUX G 3243 and the Toluene-Free G 790 Within Specified Times for Optimal Bonding Strength; and They Can Bond To Metal, Plastic, Ceramic, and Glass Surfaces Very Strongly, and, They Will Take Up To Several Days To Reach Their Maximum Adhesive Strength.
Selection Considerations
When choosing silicone rubber for a specific application, it's important to consider several factors:
- Temperature: Should be viewed as both extremes in as well as how often that particular operating temperature will occur.
- Chemicals: The types of liquids (fluids), oils, or process solvents that silicon will be using.
- Regulatory Compliance: Consider FDA, UL, or any other industry regulations.
- Physical Characteristics: This includes the minimum required hardness, tensile strength, tear strength, and elongation of silicone.
- Electrical Properties: Consider whether silicone is required to be electrically insulative, or conductively electrically conductive.
- Bonding: Determine whether it is necessary to prime the substrate you will be bonding with silicone.
Silicone continues to change based on advances in high-temperature resistant silicone, bio-compatibility, and advanced silicone formulations that can withstand the harshest of conditions (i.e., chemical resistance to many things) and therefore continue to be utilized by the industrial sector for use in new technologies as [being commercially/industrially] viable.