Everything You Need to Know About Liquid Silicone Rubber

A Liquid Silicone Rubber material is a two-part platinum-cured elastomer that can be injected into a mold cavity to manufacture a part. LSR is very versatile in the elastomer industry and is seen across a whole spectrum of parts from consumer products to medical devices and everything in between.

OSi Specialties are exported all over the world and different industries with quality first. Our belief is to provide our customers with more and better high value-added products. Let's create a better future together.

The operating temperature range for LSR can be between -65°C to150°C, which short peaks to 260°C.  With post cure, it offers very low compression set and can meet low outgassing down to TML < 1 percent and CVCM < 0.1percent. These polymers are translucent, which means they can be pigmented to match any color requirement. LSR also has quick cycle times and less raw material handling &#; leading to quicker delivery times and greater throughput.

To help manufacturers unleash the full potential of this material, we compiled everything you need to know about liquid silicone rubber.

Making the polymer

There are a couple of different ways to make the base polymer for an LSR. Like all elastomeric materials, there needs to a polymerization reaction to create molecular chains. Vinyl and methyl siloxane groups are polymerized to form polydimethylsiloxane chains. These chains provide strength and flexibility to the material. This process will change it from the liquid, almost watery starting components, to the more viscous basic form of the LSR. It&#;s in here that a lot of other properties can also be designed into the material, as well.

Once that main polymer gets created, the material gets reinforced normally with fumed silica. Unlike the organic materials where the filler of choice is carbon black or clays (pigmented materials), LSR materials use other silicates to reinforce the polymer chains and add tensile strength to the material.

From here, the material is split into two halves and the catalyst (platinum) and crosslinker are added to separate halves. This greatly increases the shelf life of these materials. When blended together, there&#;s a short working life of LSRs, averaging around eight hours. By splitting these halves, the material can potentially be stored for years with little worry of it curing during that time.

Types of LSR

There are many types of LSR materials. Some include:

• Medical grades

  : In the later stages, an LSR will get

  stripped of extractable

  for medical applications, which have very sensitive requirements to avoid interacting with tissues. Removing the extractables also increases the strength of the material. These grades are typically broken down to restrictive (implant less than 30 days) and unrestricted (implant greater than 30 days).  The composition of these grades are normally the same, but it is the level of biocompatibility testing that was performed on the material. Many vendors establish FDA master files to help customers get approval in their medical device.

• Self-lubricating

  : Incompatible fluids can be mixed into the components. Once the silicone cures, this material will bloom to the surface to create a slippery surface. Then, 1.5 to 3 percent of a phenyl fluid is added to the silicone depending on the rate of fluid the customer wants to bloom.

• Conductive:

  Conductive-grade carbon black is added to the LSR components. These grades have very good mechanical properties compared to metal particle filled silicones and can get down to 9 ohm-cm volume resistivity.

• Self-bonding:

  Adhesion promoters are added. This offers primerless adhesion to various substrates. The material works well on glass filled nylons, stainless steel, aluminum and polysulfones. It offers a perfect solution for composite seals to reduce assembly components or provide even better sealing between two mating components.

• Radio Opaque

  : Barium sulfate is added to allow the silicone part to be detected under X-Ray.  This works well for medical applications such as wound drains and catheters.

• FLSR

  : Fluorine is reacted to the polymer chain and can be blended typically at 60/40 ratio or a 100 percent

  fluorosilicone LSR (FLSR

  ) polymer.  The benefit is a highly resistant silicone for fuels and oils. Typically, these FLSR won&#;t meet current MIL standards for fluorosilicone. At the present time there is no FDA food grade or medical polymers.  

• Flame Retardant

  : Most LSR rubber will meet a UL 94 HB rating without any additives. Higher ratings, like V1 or VO, require additives that release water when decomposed.

• Fast Cure:

  Just like with an ethylene propylene where a terpolymer with double bonds is added, a manufacturer of LSRs can determine the level of crosslinking of the elastomer by controlling the amount of functional groups that are added as cure sites in the material. This results in higher reactivity to produce very quick cycle times for mass production of silicone parts.

The LSR manufacturing process

When a high-consistency silicone is brought into our facility, it almost always needs some sort of labor to transform it into a moldable size and shape. In most cases, all that&#;s required is the material be sized and shaped for the mold cavity &#; which is referred to as performing the material.

If you are looking for more details, kindly visit Liquid Casting Rubber.

Some materials have an extra step of adding cures to the material (which were left out to increase the shelf stability of the material). An LSR removes all of those steps. Here is a look at the LSR manufacturing process:

1. LSR A + B components typically come in a 5 gallon pail or 55 gallon drum. A process controlled pumping kit presses down on the buckets to force the material into static mixer and feed into the injection unit.

2. Then, streams of pigment can be added and controlled. In the injection, press material will be mixed together additionally with a screw and pushed forward to create a &#;shot&#; of material, or the amount needed to fill the mold.

3. After the material is injected into the mold, it will then stay clamped together to cure the LSR. Then, either an operator or a robot will remove the cured product from the mold and the cycle repeats. It is a very quick efficient process, that typically averages 30 seconds.

4. Conversely, with an organic material or high consistency silicone, the average cycle time to get a part made is around six or more minutes. Peroxide cured materials take even longer, commonly around nine minutes. LSR can lead to a significant cost savings in labor over a high consistency silicone material.

5. Secondary steps like post bake can help reduce volatilities and improve compression set. And the deflashing process removes unwanted flashing. It&#;s then cleaned to remove foreign material and packaged for shipment.

For more information on liquid silicone rubber, connect with us on Twitter or LinkedIn or contact our engineering team for assistance.

Everything You Need to Know About Liquid Silicone Rubber

In the world of manufacturing and product development, liquid silicone rubber (LSR) has emerged as a versatile material with a wide range of applications and benefits. From consumer electronics to medical devices, the use of LSR has revolutionized various industries, offering unparalleled advantages in terms of flexibility, durability, and precision.

What is Liquid Silicone Rubber?

It&#;s important first to differentiate the differences between silicon, a chemical element, and silicone, which is a synthetic polymer containing silicon. Silicon in its pure elemental form is crystalline in structure, very similar to how diamonds develop. Silicones contain equal parts oxygen and silicon in a lengthy polymer chain, along with other elements like carbon, hydrogen, and sometimes other elements as well. Since silicones consist of such a large group of different polymers, those that have properties similar to fluids are often known as liquid silicones.

Typically processed through liquid injection molding, liquid silicone rubber is a kind of dual-component silicone that is extremely pure. Though it starts as a liquid, silicone rubber can be customized to have specific characteristics. These include properties that affect its adherence and viscosity, along with the material&#;s temperature, and mechanical and chemical resistance. These properties make it durable and strong, qualities that make it useful for many types of technical components.

Properties of Liquid Silicone Rubber

Liquid silicone is highly durable while also being resistant to many environmental conditions. Additionally, it&#;s an incredibly flexible material that allows molding into complex geometries without much waste. As it enters a mold as a liquid, the silicone will fill even the most intricate hollow points within the cavity to create extraordinarily detailed products. This ability to mold into almost any shape makes it incredibly useful for the fabrication of an array of complex components.

This type of rubber has numerous advantages over other materials. Since it&#;s extremely biocompatible, it makes an excellent material for prosthetics or medical implants. Its durability and chemical resistance also make liquid silicone quite stable over time. Also, its high-performance mechanical properties allow it to work well through a wide temperature range, from -60°C to 250°C (-76°F to 482°F). Liquid silicone rubber also acts as an insulator, while its transparent color means it can be colored to exactly match different skin tones for humans, a bonus for any external prosthetic.

Applications for Liquid Silicone Rubber

Liquid silicone&#;s various material properties make it ideal for many applications. Its heat resistance makes it able to withstand both high and low temperatures without degrading. Liquid silicone rubber&#;s chemical resistance allows it to perform well under harsh conditions, while its durability means it will last longer than many other materials in an array of harsh situations. Electronic components benefit from liquid silicone&#;s insulating properties, while the material&#;s biocompatibility makes it perfect for medical applications. Additionally, because it can be molded into complex shapes, many industrial components are also made from liquid silicone.

Industries that use this type of rubber include: 

• Aerospace: Seals, gaskets, and other aircraft components that can withstand temperature extremes and other harsh conditions make the material appropriate for many aerospace applications.
• Automotive: The durability and heat resistance of liquid silicone makes it a common material for connectors, gaskets, and seals, while it&#;s also reliable in lower temperatures and deals well with vibrations.
• Consumer goods: The soft texture and ability to easily accept pigments give liquid silicone rubber an appealing feel and look for items like kitchenware and products for babies, while its durability and flexibility make it great for wearable devices that expose the material to a variety of conditions.
• Electronics: Connectors, keypads, and other parts that require electrical insulation are often made with the material due to their heat and chemical resistance, which makes them more reliable and longer lasting.
• Food and beverage: Its biocompatibility and reliability in extreme temperatures make liquid silicone a good fit for seals, molds, and packaging used in the production of food and beverages.
• Healthcare: Since it handles sterilization processes well, liquid silicone is widely used in the fabrication of prosthetics, along with medical implants and other devices used in the healthcare sector.
• Renewable energy: Wind turbines and solar panels use seals, gaskets, and other components made from the material, as liquid silicone rubber resists severe weather and other extreme environmental conditions, including extreme temperatures and ultraviolet radiation.

Advantages of Using Liquid Silicone Rubber

In summation, the usefulness of liquid silicone rubber for a plethora of applications offers many advantages over other materials.

Advantages of using this type of rubber include: 

• Being both biocompatible and chemically inert, liquid silicone rubbers don&#;t cause allergic reactions or otherwise react with fluids within human bodies.
• Combines other materials into parts by allowing manufacturers to over-mold silicones onto another substrate.
• Designs that allow the consistent molding of parts into a variety of geometries die to the elastomer&#;s lower viscosity.
• Due to its chemical resistance, it works well for gaskets, O-rings, and seals operating under unforgiving conditions, such as those found in the aerospace and automotive sectors.
• Greater efficiency and cost-effectiveness in part production due to the need for shorter molding times that allow higher output.
• High resistance to heat makes liquid silicones more durable for several industrial applications.
• Its inert nature allows liquid silicones to be sterilized without altering their chemical or physical characteristics.
• The low viscosity of liquid silicones makes them excellent for making components with complex geometries and detailed structures.
• Superior physical properties to other elastomers make it more easily moldable into complex parts.
• A wide variety of beneficial properties make the material more versatile than other elastomers.

Though these types of rubbers can prove beneficial for many applications, like any material there are limitations. Since the production of liquid silicones requires a strict regimen regarding its mixing and curing, the production of the material can result in more waste than that of other rubber types. Since it&#;s formed from a liquid, silicone rubbers take longer to cure as well, often leading to delays in production, especially regarding the fabrication of larger and more complex parts. Though liquid silicone rubber has decent elastic properties, components made from it tear more easily than those made from other materials, limiting its applications.

Contact the Experts at Manufacturer&#;s Rubber & Supply

For companies looking into making components or products using synthetic elastomers, the team at Manufacturer&#;s Rubber & Supply can help. With extensive support and expertise in all rubber products, we are here to meet your needs. Contact our expert team today to learn more.

If you want to learn more, please visit our website Silikon Oil.