Optical Liquid Silicone Rubber: Applications & Benefits

In recent years, optical liquid silicone rubber (LSR) is a material gained significant attention in the field of silicone rubber. In this article, we will delve into the properties and applications of optical LSR, shedding light on its immense potential in different fields

What is Optical Liquid Silicone Rubber?

Optical Liquid Silicone Rubber (LSR), also known as Optical Clear Liquid Silicone Rubber and Optical Grade Silicone, is a specialized type of silicone material that exhibits excellent optical properties. LSR is a transparent, high-purity silicone elastomer that is commonly used in applications requiring optical clarity, such as lenses, light guides, and optical seals

Optical LSR‘s Properties

Optical Liquid Silicone Rubber (LSR) is a highly transparent material, similar to glass, that maintains its transparency across both visible and UV spectra.

Unlike materials such as polycarbonate (PC) and acrylic, Optical Liquid Silicone does not undergo discoloration or loss of transparency with age or when exposed to heat and UV light.

One of the key advantages of Optical LSR is its scratch and crack resistance, which helps preserve its physical integrity and optical properties over time.

Optical Grade Silicone can be tailored to various hardness levels, ranging from flexible (20A) to firm (90A), providing versatility and reducing the risk of breakage. Despite its durometer of 70, Optical LSR can withstand vibrations better than plastic or glass.

Optical LSR maintains both optical and mechanical stability at temperatures up to 302°F (150°C), enabling its usage in close proximity to light sources.

The flexibility of Clear Liquid Silicone allows for the combination of a lens with a seal, reducing assembly costs, improving inventory control, and eliminating seams in the assembly.

Furthermore, Optical LSR can be mixed with colorants or phosphors to expand its lighting capabilities, enhancing its versatility in various lighting applications.

Why Optical LSR will replace plastic and glass?

Optical Materials

In the past, Glass and ceramic were materials that provided the best favorable refractive index values. Glass, in particular, is composed of Silicon (Si) and Oxygen (O) arranged in a random and low-range pattern. The atoms in glass are arranged randomly, and because of this structure, glass is transparent.

However, metals, with their organized atomic structure, are not transparent in the same manner. Although glass offers transparency, it also exhibits limitations in terms of mechanical properties and density. Its structure contributes to lower mechanical strength, and it has a relatively high density ranging between 2.3 and 6.3 g/cm3 which can be seen as a drawback.

Optically Transparent Polymers

Certain polymers possess inherent properties similar to glass, but they tend to have lower physical properties. Examples of such polymers include the thermoplastic materials Polycarbonate (PC) and Polymethyl Methacrylate (PMMA), which are typically processed using injection molding

These thermoplastic and thermoset materials offer advantages such as high-quality surfaces that replicate the mold surface, easy processability, and a wide range of available grades with diverse properties. However, they also have some disadvantages, one of which is thermal stability. Compared to glass, these materials exhibit lower thermal properties

Optically clear grades of LSR polymers offer advantages over both glass and thermoplastic and thermoset optical polymers. Optical Liquid silicone rubber (LSR) and glass share certain elements in their chemical structures. Both LSR and glass contain Silicon (Si) and Oxygen (O). However, the presence of additional radicals in its structure is what gives silicone rubbers opaque or translucent by nature.

Despite these similarities, the mechanical and physical properties of LSR surpass those of glass and carbon-based polymers. Regarding hardness, LSRs can exhibit flexibility as low as 5 Shore A or hardness comparable to glass (approximately 90 Shore A). Another advantage is its density, which ranges between 1.1 and 2.3 g/cm3, significantly lower than that of glass.

Optical Material Comparison

Optical Liquid Silicone exhibits excellent long-term stability, as it does not discolor or lose transparency over time or when exposed to heat or UV light.

Optical LSR is lighter than glass, offering the benefits of reduced weight in optical applications.

Optical LSR is not only lighter than glass and most plastics, but it also possesses remarkable scratch and crack resistant

Optical LSR demonstrates superior light transmission capabilities, retaining up to 94 percent of transmitted light. In comparison, glass experiences some light loss, retaining up to 95 percent, while PMMA retains around 93 percent, and PC ranges between 88 to 90 percent.

With a low refractive index of 1.42, Optical Liquid Silicone Rubber outperforms PC and PMMA, which have refractive indices of 1.58 and 1.49, respectively

Mold Design With Optical LSR

Optical LSR allows greater design freedom provided by optically clear liquid silicone. Its elastomeric nature reduces the need for additional components and secondary operations, resulting in lower costs for tooling and non-recurring engineering

Optical Liquid Silicone can be molded in a polished mold, eliminating the need for a secondary polishing process on individual parts. This not only saves production time but also reduces costs. Some molds can support optical surface geometry and polishing, further enhancing the efficiency of the manufacturing process.

Optically Liquid Silicone can be over-molded onto optical parts to create seals and gaskets without compromising their optical characteristics. As a thermoset material, it does not have the molded-in stresses associated with thermoplastics. This integration of mechanical and optical features becomes easier with Liquid Silicone Rubber.

Optical LSR allows for the cost-effective reproduction of aspheric, freeform, and other complex geometric optical surfaces. This enables the production of intricate optical designs with high precision.

Additionally, colorant dispersions can be added to the Liquid Silicone Rubber material, allowing for the production of tinted parts. This provides flexibility in achieving desired aesthetics or functional requirements.

Optical LSR’s Applications

Electronics and Automotive Industrial: Silicone rubber finds application in various products, including white reflectors and diffusers. In these roles, it can function as a refractive lens or utilize Total Internal Reflection (TIR) to eliminate light loss during reflection.

Imagery and Scanning: Optical Liquid Silicone Rubber (LSR) is also successfully employed in imaging and scanning applications, such as bar-code scanners, spectrometers, and particle counters

Medical applications: Optical Liquid Silicone Rubber is utilized in tubing, endoscopy components, catheters, and lenses.

Telecommunications: It is used in microlens arrays and diffractive optical elements.

Solar Collectors: These include optical lenses, light-guiding systems, and encapsulation materials

Photonics applications: Ultraviolet (UV) light is used to cure silicone rubber; the exposure of the material to an appropriate wavelength permits the generation of waveguide patterns that can be used successfully in lithography.

LEDs: Optical LSR is used in LED lighting applications to improve light diffusion, optimize light output, and enhance overall efficiency.

Optical Filters: Optical LSR is employed in the manufacturing of optical filters, which selectively transmit or block specific wavelengths of light for various applications, including photography, microscopy, and spectroscopy.

Beam Splitters: Optical LSR can be used in beam splitters, which divide a light beam into multiple paths. They find applications in optics, microscopy, and interferometry.

All Types of Lenses: Optical LSR is utilized in the production of various lenses, including camera lenses, eyewear lenses, and optical imaging lenses. It offers optical clarity, flexibility in design, and excellent light transmission properties.

When working with LSRs in optical applications, there are some important considerations to keep in mind.

Firstly, the composition of optical LSRs typically involves two parts that need to be mixed together before processing. It is crucial to ensure that the material is thoroughly blended and homogeneous to achieve consistent optical properties.

Shrinkage is another factor to consider. The shape of the component and the surface polish of the mold can influence the optical characteristics of the final product, which should be considered
Additionally, the low viscosity of LSRs can lead to the formation of flash, which refers to excess material that escapes from the mold cavity. To minimize or eliminate flashing, special design considerations and mold modifications may be necessary.

To learn more about Optical Liquid Silicone Rubber or receive a free quote, contact A1 Silicones representative today.


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