What is coating liquid silicone rubber?
Core Definition
Coating Liquid Silicone Rubber (LSR) is a two-part, high-purity platinum-cured silicone system that is applied in a liquid state and then cured (vulcanized) to form a solid, flexible, and durable silicone rubber coating or layer.
Think of it as a high-performance paint or dip that, once cured, turns into the same type of silicone rubber you might find in a kitchen spatula or a medical implant, but bonded to the surface of another object.
Key Characteristics and Chemistry
Liquid State: Unlike solid silicone sheets or extrusions, coating LSR starts as a low-viscosity liquid. This allows it to be processed using efficient manufacturing techniques like spraying, dipping, pouring, or injection molding.
Two-Part System (A & B Components): It is typically supplied as two separate parts:
Part A: Contains the silicone base polymers and platinum catalyst.
Part B: Contains the silicone base polymers and a crosslinker.
These two parts are precisely metered and mixed immediately before application. Once mixed, the curing process begins.
Platinum Cure (Addition Cure): This is the highest grade of curing system. It offers significant advantages:
No Byproducts: It produces no chemical byproducts during curing (unlike cheaper peroxide-cure systems), making it odorless and non-corrosive.
High Purity & Biocompatibility: This makes it ideal for medical and food contact applications.
Excellent Consistency: Shrinkage during curing is minimal, and the material properties are very consistent.
Why is it Used for Coating? (Key Properties)
When applied as a coating, LSR imparts its exceptional properties to the underlying substrate (the object being coated):
Extreme Temperature Resistance: It remains flexible and functional from as low as -60°C (-76°F) to over 200°C (392°F). It protects components from heat and cold.
Excellent Electrical Insulation: It is a superb insulator, protecting against short circuits, high voltages, and environmental moisture. This is critical in electronics.
Chemical & Environmental Resistance: It is resistant to water, ozone, UV radiation, and many chemicals, protecting components from weathering, corrosion, and oxidation.
Flexibility & Durability: It forms a flexible, tear-resistant, and abrasion-resistant layer that can absorb impacts and stress.
Biocompatibility & Hypoallergenic: Platinum-cure LSR is non-toxic, skin-safe, and approved for medical and food-grade applications. It doesn't support bacterial growth.
Sealing Properties: It can create airtight and watertight seals on complex parts.
Common Application Methods
The liquid nature of LSR allows for several coating techniques:
Spray Coating: The mixed LSR is sprayed onto a surface, often a metal or plastic part, to create a thin, uniform protective layer.
Dip Coating: An object (e.g., a tool handle, a medical instrument, or an electronic sensor) is dipped into a bath of LSR and then withdrawn, leaving a coating that conforms perfectly to the object's shape.
Overmolding / Injection Molding: This is a very common process. A rigid plastic or metal component (called an "insert") is placed into a mold. Liquid silicone is then injected into the mold, where it coats and bonds to the insert. This creates a single part with a soft, comfortable, and functional silicone exterior and a rigid interior.
Example: A rigid plastic toothbrush handle is overmolded with soft, grippy LSR.