What is liquid silicone rubber

Liquid silicone rubber (LSR) has become an increasingly popular material in recent years due to its many useful properties and advantages over solid silicone rubber. In this article, we'll examine what exactly liquid silicone rubber is, how it differs from regular silicone rubber, its various applications and uses, composition, and more.

What is liquid silicone rubber vs silicone rubber

Silicone rubber is available in both solid and liquid forms. Solid silicone is created by mixing silicone polymers with fillers and then vulcanizing the material into a solid elastomer. This material can then be formed into sheets, extrusions, molds, and other shapes.

Liquid silicone rubber differs in that it is delivered in a viscous liquid state and then cured into rubber parts or products. The liquid form allows for injection molding, которая making it easier to produce intricate, detailed molds and parts.

Some key differences between liquid and solid silicone rubber:

Composition

LSR has a lower filler content (typically 10-20%) compared to solid silicone's high filler load (around 50% fillers). This gives it a lower initial viscosity.

Fluidity

The liquid state of LSR allows it to be easily injected into molds and cavities. Solid silicone must be formed or molded when in an uncured state.

Curing process

LSR cures very rapidly, often within seconds or minutes. Solid silicone curing takes significantly longer, from hours to days.

Part detail

The fluidity and fast curing enables LSR to produce detailed and complex parts not practical with solid silicone molding.

Automation

LSR's injection molding process lends itself to highly automated production, reducing labor costs.

What is the difference between liquid silicone and soft silicone?

Liquid silicone and soft/gel silicone generally refer to silicones with different levels of viscosity and hardness.

Liquid silicone has a very low viscosity, almost like that of water. This enables thin, easy flowing silicone. Soft silicone is thicker and may have a gel-like texture, but still retains high flexibility.

Key differences:

Viscosity - Liquid silicone has a viscosity around 100 centistokes, while soft silicone is around 500,000+ centistokes.
Flow - Liquid silicone pours and spreads thinly. Soft silicone has very low flow and deformation.
Feel/texture - Liquid silicone feels thin, while soft silicone feels thicker and may have a gummy texture.
Applications - The high flow of liquid silicone makes it suited for thin coatings. Soft silicone is often molded into pads, seals, gaskets.
Curing - Both usually addition cure with a platinum catalyst, though soft silicone may take longer to set up.

So in summary, liquid silicone has a lower viscosity and flows more easily, while soft silicone is thicker and more viscous while still flexible. Both offer useful properties.

What is liquid silicone used for

Liquid silicone's unique set of properties make it ideal for many applications:

Moldmaking - The low viscosity allows liquid silicone to capture intricate part detail that would be difficult or impossible with solid silicone moldmaking.

Medical devices - Bio-compatibility and sterilization resistance enable uses such as tubing, valves, seals, and other parts in healthcare.

Food contact - Meets FDA standards for food contact. Used for seals, valves, cookware handles, and other kitchenware components.

Electronics - Electrically insulating properties lend use for connectors, seals, potting, printed circuit boards. Withstands high temps.

Seals and gaskets - Rapid curing produces detailed, resilient seals and gaskets. Handles temperature extremes.

Automotive - Used for O-rings, seals, diaphragms that perform in harsh under-hood conditions. Improves safety and reliability.

Infant care products - Utilized in items like baby bottle nipples and pacifiers due to its durability, cleanliness, and food contact compliance.

Liquid silicone delivers high performance across many industries where its unique combination of properties are critical.

What is liquid silicone rubber used for

As a type of silicone rubber, liquid silicone rubber (LSR) is used in many of the same general applications thanks to characteristics like high temperature resistance, flexibility, and durability.

Some specific uses of liquid silicone rubber include:

Injection molding - The fast cure times allow injection molding of detailed, intricate parts and prototypes with quick turnover.

Healthcare products - Used for seals, gaskets, valves, tubes in medical devices due to bio-compatibility and sterilization resistance.

Food molds - Makes excellent detailed ice cube, chocolate, and candy molds that withstand freezing and heating.

Baking molds - Used for baking pans and molds thanks to heat resistance. Provides smooth, non-stick silicone surface. Easy release.

Seals & gaskets - Used widely for sealing and static applications, like automotive, appliances, electronic devices, lids, etc. Handles temperature swings.

Wire insulation - Insulating properties enable silicone wire and cable coating for electronics and appliances.

Vibration damping - Effective at damping vibration and shock thanks to its flexible, rubbery nature. Used for handles, sporting goods, more.

Liquid silicone rubber also sees use any place where high detail, reproducibility, and fast fabrication is needed thanks to the injection molding fabrication process.

What is liquid silicone rubber made of

Liquid silicone rubber consists of several key components that contribute to its useful properties when cured:

Silicone polymers - Specifically vinyl-substituted siloxane polymers that form the rubber matrix and provide flexibility and tear strength.

Fillers - Typically silica filler at levels around 10-20% that contribute reinforcement and hardness. Lower than solid silicone rubber.

Pigments - Pigments like carbon black can be added to obtain colored silicone parts. Does not impact physical properties.

Platinum catalyst - A platinum catalyst drives the addition cure reaction that crosslinks the polymers and transforms LSR into a rubber elastomer.

Crosslinker - Crosslinking agents containing vinyl groups. React with silicone polymer chains under platinum catalysis.

Inhibitor - Used to regulate curing and extend pot life as needed before injection into molds.

The primary components are the silicone polymers, crosslinkers, and platinum catalyst. The low viscosity polymers enable flow into molds before rapidly crosslinking into solid rubber parts and products.

Liquid silicone vs silicone

Liquid silicone and regular silicone have somewhat different properties and applications:

Viscosity

Liquid silicone has a very low viscosity, closer to that of water. Regular silicone is thick and flows poorly.

Applications

The thin, flowable nature of liquid silicone makes it suitable for lubricants, waterproof seals, conformal coatings. Regular silicone is often formed into rubber parts.

Chemistry

Liquid silicone often has vinyl or other groups to enable curing through addition reactions. Regular silicone cures via condensation reactions.

Curing

Liquid silicone typically cures rapidly once catalyzed. Regular silicone may take significantly longer to fully cure.

Strength

Regular silicone generally has higher durometer and tensile strength thanks to higher filler content. Liquid silicone is more flexible.

Cost

Liquid silicone is more specialized and costs more per volume than regular silicone grades.

In summary, while both are silicones, liquid silicone offers much greater flow and curing speed, while regular silicone provides higher strength for fabricated parts and rubbers.

What is liquid silicone case

Liquid silicone cases refer to flexible, stretchy protective cases made from liquid silicone rubber.

This material offers many advantages for phone and device covers:

Flexibility - Liquid silicone rubber has high elongation that allows it to stretch and deform easily without rupturing. It bends and flexes with devices.
Grip - Has a slight rubbery/tacky feel that provides a very secure grip of phones, reducing drops.
Thin profile - Liquid silicone can be poured very thinly, leading to slim, lightweight covers.
Customization - Can be easily injection molded into virtually any shape, style or color.
Durability - Withstands scrapes and abrasion. Resists oils, many chemicals. Won't tear easily.
Easy application - The elasticity enables quick, easy application and removal from tightly fitting devices.

Liquid silicone phone cases provide the ultimate in protection with a thin, grippy and customizable covering that adds minimal bulk to handheld electronics.

Liquid silicone rubber molding

Liquid silicone rubber is ideally suited to liquid injection molding processes thanks to its fluidity and rapid cure rates. This enables high production of detailed silicone part geometries and rapid prototyping.

There are two primary types of injection molding processes used:

Cold runner injection molding

Uses sub-cooled LSR injected through cold sprue channels into cavities
Low waste, more precise molding
Slower cycle times
More complex mold design

Hot runner injection molding

LSR flows through temperature controlled, heated sprue channels
Faster injection speeds and cycle times
Lower viscosity enables micro-molding
Simpler molds, less complex systems
Higher initial costs

Injection pressures range from 1,500-5,000 psi typically. Cure times range from seconds to minutes once in-mold. The faster curing capabilities enable very high production rates, automated processes, and lower labor costs.

Liquid silicone rubber products

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

Medical: IV tubing, catheters, seals, gaskets, masks, tubes, components

Automotive: O-rings, seals, gaskets, CV boots, hoses, mounts

Electronics: keyboards, switch membranes, cables, connectors, coatings

Infant care: Bottle nipples, pacifiers, teethers

Housewares: Cooking utensils, bakeware, small appliances

Food service: Ice cube molds, candy molds, bake molds

Sporting goods: Goggles, swim masks, grips, pads

Liquid silicone delivers high reproducibility, optimal economics, and extreme flexibility to mold intricate parts. Any application needing heat resistance, flexibility, durability, and detailed molding is a good candidate for liquid silicone rubber.

Conclusion

Liquid silicone rubber offers distinct advantages over traditional solid silicones thanks to its fluidity, rapid curing, and molding capabilities. Its unique chemistry delivers an optimal balance of biocompatibility, temperature resistance, flexibility, and economic production. Diverse medical, electronic, automotive and consumer applications benefit from liquid silicone parts and products. As injection molding processes and materials continue improving, the uses of liquid silicone rubber are sure to expand even further across many industries.