What is liquid silicone rubber used for?

Liquid silicone rubber (LSR) has become an increasingly popular material in recent years due to its many advantageous properties and wide range of applications. In this article, we will examine what exactly liquid silicone rubber is, its price, common uses, properties, and more.

What is liquid silicone rubber

Liquid silicone rubber refers to a high purity platinum-cure silicone that is processed into a liquid form. Unlike conventional rubber, liquid silicone rubber can be injection molded at room temperature without the need for heat. This allows for faster cycle times and increased productivity compared to conventional rubber molding.

Silicone itself is composed of silicon, oxygen, carbon and hydrogen. The silicone polymer chains remain flexible at low temperatures, giving silicone rubbers resilience and durability across a broad temperature range. The liquid form also allows LSR to easily take the shape of whatever container or mold it is poured into.

Key properties that make liquid silicone valuable across many industries include:

High tear strength
Flexibility and elasticity
Resistance to extreme temperatures
Electrical insulating properties
Resistance to chemicals, oils and solvents
Ability to withstand sterilization
Low compression set (retains original shape)

Liquid silicone offers versatility for producing detailed and complex part geometries. Parts can be created with tight tolerances and thin walls that would be difficult to achieve with conventional rubber molding.

Liquid silicone rubber price

The price of liquid silicone rubber varies based on the grade, purity, shore hardness, quantity ordered, and manufacturer. On average, standard injection grade LSR costs between $3 - $5 per pound. High consistency rubber (HCR) grades used for extrusion or calendering can range from $2 - $3 per pound.

Factors that affect liquid silicone rubber pricing:

Purity - Medical or food grade LSR is highest purity and most expensive
Shore hardness - Harder durometers are more expensive
Special properties - Electrically conductive, self-lubricating, and other special grades cost more
Order quantity - Bulk orders get discounted rates
Manufacturer/brand -Major suppliers include Dow, Wacker, Shin-Etsu, Momentive

For prototype and short run production, buying small quantities of liquid silicone rubber from a distributor may be most economical. For higher volume production, getting pricing directly from a major LSR manufacturer will provide the lowest cost per unit.

What are the common uses of silicone rubber?

Thanks to its unique properties, liquid silicone rubber is used across a wide range of industries and applications:

Medical:

Catheters, feeding tubes, drainage tubes
Masks, ventilators, respirators
Endoscope seals and parts
Orthodontic devices
Hearing aids
Prosthetics

Automotive:

Spark plug boots, connectors, seals
Self-lubricating parts
Airbags

Electronics:

Keyboard membranes, keypads
Electrical potting and encapsulation
Connectors, gaskets, seals

Infant Care:

Pacifiers, teether rings, bottle nipples
Baby bottle liners

Home Appliances:

Ice cube trays, bakeware
Jar sealing rings, oven door seals
Cooking utensils

Other:

Sporting goods, baby products
pv Insulators
High temperature molds
Vibration dampening

Liquid silicone can replace latex, TPE, thermoplastics, and other conventional rubbers across these applications due to its superior properties and molding capabilities. Automation and precision of LSR molding also allows silicone parts to be produced at high volumes for mass market consumer products.

What is liquid silicone used for

The two main uses of liquid silicone are liquid injection molding (LIM) and liquid silicone rubber (LSR) molding.

LIM consists of injecting liquid silicone into a mold to create detailed parts and products. LIM allows for easy filling of complex cavities and low pressure molding.

It is commonly used for:

Gaskets
Seals
Valves
Stoppers
Flexible housings

Key benefits of LIM:

Fast cycle times
No waste/low scrap rates
Excellent reproduction of fine details
Simple molds (single cavity)
Insert molding capability

LSR molding uses specialized injection molding machines to process two reactive liquid component silicones that then vulcanize inside the mold to form silicone rubber parts. LSR molding can produce high precision parts with a matte finish.

Common applications:

Seals
O-rings
Grommets
Custom rubber profiles
Milli diaphragms
Skinned parts

Benefits of LSR molding:

No secondary finishing steps
Self-releasing parts
Ideal for intricate, thin-walled parts
Excellent tear resistance
Low compression set
Capable of micro-molding

Both LIM and LSR take advantage of liquid silicone's ability to completely fill complex cavities and quickly vulcanize into cured rubber parts. This enables detailed molded silicone products across a vast range of markets.

Liquid silicone rubber products

Liquid silicone is used to produce a diverse range of products across many industries:

Medical: IV stopcocks, needle shields, tracheotomy tubes, catheters, masks, ventilator components, orthodontic devices, hearing aid eartips, etc.

Infant & Baby Care: Bottle nipples, pacifiers, teether rings, soft seals on baby products, warming pads, infant care accessories

Automotive: Spark plug boots, O-rings, gaskets, seals, self-lubricating parts, masking for coatings

Electronics: Keyboards, membranes, keypads, gaskets, adhesion/coatings, potting compounds, seals

Home Appliances: Ice cube trays, jar sealing rings, bakeware, oven door seals, kitchen tools/utensils, rice cookers, drip pans

Food Contact: Jar seals, beer tap lines, baking molds, kitchenware, bottles, food tubing

Other: Sports equipment, HV insulation, lighting, vibration dampening, prototyping

Liquid silicone can replace latex, TPE, PVC, general purpose rubber in these applications due to its resistance to extreme temperatures, durability, biocompatibility, electrical insulation, and ability to be molded into detailed parts. Automation of LSR molding also enables high volume production.

Liquid silicone chemical formula

The chemical structure of liquid silicone polymers consists of an inorganic silicone backbone chain (-Si-O-) combined with organic methyl groups attached to silicon.

The basic formula is:

R2SiO2/2

Where R represents methyl (CH3) groups.

So the overall chemical composition is -(Si(CH3)2O)n-

With n representing the number of repeating monomer units.

On average, commercial liquid silicone polymers have between 300 to 5000 monomers. So a PDMS with n=500 would have a molecular weight around 37,000 g/mol.

The polymers remain linear with the organic groups extending outwards from the inorganic backbone. This gives the unique flexible and stretchable nature of silicones.

Liquid silicone may also include vinyl (CH2=CH-) or other functional groups to facilitate cross-linking into a rubber elastomer. Fillers like silica may be added for reinforcement.

The lack of polar bonds gives silicone oils and rubbers excellent thermal stability and chemical resistance compared to other organic polymers. Overall, the liquid silicone chemistry enables versatile processing and properties.

Liquid silicone for skin

Liquid silicone has found widespread use in dermatology and personal care products due to its beneficial properties for skin:

Emollient - Spreads easily to coat skin and provide a smooth, silky feel
Occlusive - Forms a protective barrier that locks in moisture
Non-comedogenic - Does not clog pores or irritate skin
Hypoallergenic - Does not typically cause allergic reactions
UV resistance - Protects against sun damage

When applied to the skin, liquid silicone forms a flexible breathable layer that fills in cracks and crevices to give skin a smoother appearance. This helps reduce the appearance of scars and wrinkles. The water repelling effect also hydrates skin by preventing transepidermal water loss.

Liquid silicone fluids and elastomers are common in products like:

Scar gels and sheets
Anti-aging creams
Skin protectants
Hair products
Color cosmetics
Sunscreens

Medical grade liquid silicone is also used for long-term skin contact applications such as wound care. Overall, liquid silicone offers an established option for enhancing skin feel and care.

What is liquid silicone case

A liquid silicone case is a protective accessories made by placing a smartphone or other device into a mold, injecting liquid silicone to completely coat the device, then peeling it out after curing to reveal a formed-to-fit flexible case.

Liquid silicone rubber (LSR) is ideal for molding fully customized phone cases due to key properties:

Precise Molding

Liquid silicone easily fills every crevice of a mold to replicate details precisely. This ensures a perfect customized fit.

Rapid Curing

LSR cases cure rapidly at room temperature so devices can be quickly molded and turned around.

Flexibility

Silicone cases stretch and bend to absorb impacts while remaining slim.

Grip

The rubber surface provides a very secure grip compared to slippery plastics.

Heat Resistance

Silicone withstands hot electronics and high external temperatures without damage.

Customization

LSR can be easily tinted any color or swirled with color patterns. Logos can also be molded directly into the case.

With simple molds, fast processing times, and incredible precision, liquid silicone enables full customization and protection of electronic devices. Consumers can get affordable custom cases tailored specifically for their phone, tablet, or other gadgets.

Liquid silicone rubber properties

Liquid silicone rubber exhibits an exceptional combination of properties:

High Tear Strength – Excellent resistance to cuts, punctures and tearing loads
Low Compression Set – Retains original molded shape without deformation
Temperature Resistance – Withstands temperature extremes from -115°F to 500°F
Chemical Resistance – Inert to oils, solvents, water; only damaged by alkalis
Electrical Insulation – High dielectric strength; used for potting and embedding
Thermal Stability – Can be used for molding high-temperature components
Biocompatibility – Non-reactive and hypoallergenic; ideal for medical devices
Weatherability – Unaffected by UV radiation, oxygen, ozone
Low Flammability – High flash point; produces low smoke when burned

Liquid silicone's unique flexibility, durability, heat resistance and chemical inertness enable use across a wide range of demanding applications not suited for other rubbers. Automated LSR molding also allows silicone to be formed into detailed, high-precision parts.

Liquid silicone rubber molding

There are two main processing methods for molding liquid silicone into parts - Liquid Injection Molding (LIM) and Liquid Silicone Rubber (LSR) molding:

LIM consists of injecting a simple platinum-cured silicone into a mold cavity and allowing it to cure at room temperature.

It enables:

Detailed replication of mold geometry
Low-pressure injection molding
Cure times under 24 hours
Single material molding
Applications include seals, connectors, stopper, gaskets.

LSR molding uses specialized machinery to precisely meter and mix two reactive liquid component silicones that rapidly cure when combined in the mold.

Features:

Automated high-speed molding
Cure times under 2 minutes
No post-cure ovens needed
Self-releasing parts
Complex, multi-cavity molds

Liquid silicone enables silicone rubber parts to be mass produced like plastics but with far greater design freedom and material performance.

Conclusion

Liquid silicone rubber provides an exceptional material option that spans a diverse range of applications and industries. Key properties like high tear strength, flexible resilience, chemical and heat resistance, and electrical insulation make liquid silicone well-suited for medical devices, infant care products, electronics, automotive, and household items.

Automated injection molding of LSR allows the superior properties of silicone to be replicated in high volume, precise components. Tight dimensional tolerances, thin walls, and detailed geometries can be achieved. Between its versatile material properties and advanced manufacturing capabilities, expect growing usage of liquid silicone rubber across more products in the future.