Understanding the high light transmittance, heat resistance, UV resistance and other characteristics of optical liquid silicone rubber can better meet your customers’ product requirements and differentiate from competing products.
This article also introduces the relevant applications of optical liquid silicone rubber, which can help you supply goods precisely according to industry needs.
What Is Optical Liquid Silicone Rubber?
Liquid Silicone Rubber (LSR) is a versatile silicone elastomer material that can meet your requirements for high-speed, high-precision, and design flexibility in product manufacturing.
This silicone rubber is typically produced through injection molding. Moreover, as a two-component material that is platinum-cured, it maintains excellent mechanical properties and dimensional consistency.
Optical LSR not only retains the aforementioned advantages of liquid silicone rubber, but also has superior performance. You can use this transparent, flexible thermosetting material for optical applications, which are involved in communication products, LED lighting, and various medical industries.
Key Advantages of Optical Liquid Silicone Rubber
Optical Performance
Optical performance is the most significant advantage of optical liquid silicone rubber. Optical grade LSR typically provides light transmission of up to 94%–95% in the visible spectrum.
The relatively low refractive index and relatively high Abbe number help reduce Fresnel reflection losses at the air-material interface. Additionally, the reflection loss of light on the surface of the silicone rubber material is also smaller.
The comparison of relevant optical properties of optical LSR with PC, PMMA and glass is shown in the table below. You can refer to it:
| Parameter | Optical Liquid Silicone Rubber (LSR) | Polycarbonate (PC) | Polymethyl Methacrylate (PMMA) | Glass |
| Light Transmittance | 94-95% | 88-90% | 92-93% | 95% |
| Refractive Index (nD25) | 1.41-1.42 | 1.58 | 1.49 | 1.52 |
| Abbe Number | ~50 | ~30 | ~58 | 30–60 (depending on composition) |
Heat Resistance
Depending on formulation, optical LSR has a long-term heat resistance of over 150℃ and a short-term resistance of 180℃. However, conventional polycarbonate materials generally exhibit lower long-term thermal resistance than optical LSR.
The thermal deformation temperature of the PC materials you might be using is between 130℃ and 140℃, while the long-term operating temperature of the PMMA materials is approximately 90℃.
Moreover, it has an extremely wide operating temperature range. It remains elastic even at extremely low temperatures as low as -55℃. It can be adapted to various outdoor lighting and vehicle-mounted optical applications, significantly reducing cracking failures of the product in high and low temperature environments.
Chemical Resistance and UV Resistance
High-quality optical LSR has excellent chemical resistance and UV protection properties. If you need high-quality materials with anti-yellowing, chemical corrosion resistance and UV stability, this is your option.
This LSR material resists aging and discoloration even under prolonged exposure to harsh outdoor conditions, retaining consistent high light transmittance and its inherent elasticity over time. It effectively cuts down after-sales issues stemming from aging and malfunction of outdoor optical products.
Superior Physical Properties
The optical liquid silicone rubber also has outstanding physical properties, such as crack resistance. Due to its higher flexibility, the risk of cracking is reduced. It combines optical clarity with flexibility and impact resistance, and the hardness of the optical LSR is usually between 50 Shore A and 80 Shore A.
During your customers’ usage, this LSR will not leave obvious scratches when dragged over rough surfaces, and it will not lose its optical properties during its service life. Moreover, it is lighter than glass and most other plastics, and has a low water absorption rate.
Biocompatibility
Certain medical grade optical LSR formulations can comply with USP Class VI, ISO 10993 and FDA regulations standards and are biocompatible. It can prevent bacterial growth and is conducive to sterilization treatment, allowing your customers to use it hygienically. It is relatively safe and can be used for skin contact and long-term medical purposes.
Applications of Optical Liquid Silicone Rubber
Due to its outstanding advantages, optical LSR has extensive applications and can be used in various fields such as healthcare, electronics, and automobiles. The following will provide you with detailed information about these applications, which will help you better meet customer needs.
Consumer Electronics
If you are in the consumer electronics industry, mainly using optical liquid silicone rubber to encapsulate, it can mainly protect the precise optical components.
Optical Sealing and Light Transmission Component Applications
For instance, in mobile phones and wearable devices, sealed LED lights and sensors are used. Because the high transparency of optical LSR can form a transparent protective window that covers the sensor or infrared and does not affect the functionality of your smartphone camera flash module and infrared face recognition system products.
You can also use it as hardware for virtual reality (VR) and augmented reality (AR). As a light guide or diffuser in headsets, due to its flexibility, it can create a light pipe that better suits your product design.
Applications for Imaging Equipment Components
If you are a manufacturer of projectors and cameras, you can also use optical liquid silicone rubber to make specific cover components. In particular, it is shock-resistant and suitable for making silicone lens covers for action cameras. It not only protects expensive lenses but also is not prone to cracking and has a certain service life.
Applications of LED Lighting and Light Guide Components for Displays
In the LED lighting field, apart from being used for manufacturing ordinary LED lighting, you can also utilize the high transparency, excellent flexibility and plasticity of optical LSR to create light bonding layers and light guiding tubes. They are suitable for display panels and protective glass of ultra-thin devices, as well as for guiding LED backlighting.
Automotive Industry
If you mainly produce automotive lighting equipment, optical liquid silicone rubber is an indispensable material for you.
Whether it’s the headlights, daytime running lights, interior parts, or displays, this material can be used. In the automotive field, these applications have high requirements for the material, such as high lumen output, high temperature resistance, and long service life.
Headlight Applications
In complex lens and optical guide structures, for instance, the headlights require free-form lenses to form the beam pattern and the lenses need to withstand high temperatures near the LEDs.
Due to the continuous ultraviolet radiation from the sunlight, the lenses need to remain transparent. High-quality optical LSR can achieve this. It can simplify your production process.
Moreover, LSR has sufficient durability and can withstand vibrations, stone impacts, and thermal cycles during your customers’ driving. Therefore, it can also be used as a lamp cover seal to prevent dust and moisture from entering and protect the optical components.
Interior Ambient Light Applications
The ultra-thin continuous light strips made of LSR can meet your customers’ unique styling requirements. Because they can be flexibly inserted, which is something that rigid glass materials like this are difficult to achieve.
Medical Industry
In the medical-related industry, you can promote the development of visually transparent, safe and sterilizable medical equipment by using optical liquid silicone rubber.
Endoscope and Surgical Lighting Component Applications
Endoscopes and surgical lighting components are important applications of optical LSR in the medical field. You can use it to produce optical windows, optical conduits, as well as transparent seals on medical microscopes and surgical instruments.
Such medical devices usually have the advantages of being bendable, flexible and deformable without cracking, which can reduce risks in delicate surgeries.
Moreover, LSR products that meet regulatory requirements are biocompatible and can withstand high-pressure steam and ethylene oxide. Your customers can sterilize them to ensure medical safety
Applications of Implantable and Wearable Medical Sensors
Another application is implantable or wearable medical sensors. You can use optical LSR as the transparent window or packaging material for pulse oximeters, implantable blood glucose monitors, or phototherapy devices.
Besides the advantages of low allergenicity, softness, and fitting the human body curve, it can also allow light signals to pass through smoothly while ensuring the device is sealed and waterproof.
Ophthalmic Applications
As you are still exploring new applications, if you successfully develop a reliable product, you can try to seize the market. For example, silicone ophthalmic device housings. Produce clear, safe and durable optical components for customers to enhance the quality of patient care.
FAQ
Will Molding Affect the Optical Properties of Optical LSR?
Properly controlled molding processes generally do not significantly affect the optical properties.
Because optical LSR is a thermosetting material, it does not have the problem of residual internal stress caused by cooling and freezing like PC and PMMA, which leads to the birefringence effect. But surface defects may still occur if processing conditions are not properly controlled.
What Are the Most Common Defects During Optical LSR Processing?
The most common ones are three types.
The first one is bubbles. You can find dense needle-like small bubbles or a single obvious large bubble inside the lens, which is caused by incomplete vacuum extraction, too fast curing temperature, or air being mixed in during material mixing.
There is also flash, which occurs because LSR has extremely low viscosity, insufficient mold closing force, or poor mold sealing. Surface contamination is also a common defect. At this time, you should pay attention to the contaminants on the mold surface and the dust adhering to the environment.
Is the Surface of Optical LSR More Prone to Dust Accumulation Than Conventional Silicone Rubber?
Conventional silicone rubber tends to accumulate dust due to electrostatic adsorption and the microscopic unevenness of its surface. However, some optical LSR formulas contain silicone resin, which can reduce the surface properties. Nevertheless, when exposed to non-clean environments for a long time, dust still adheres to it.
Can Optical LSR Be Bonded With Other Materials?
Sure, the optical LSR supports multi-shot injection molding. Certain self-bonding optical LSR grades can be overmolded onto engineering plastics such as PC and PBT. This can reduce the number of parts in your production and save assembly time.
Is Optical LSR a Flammable Material?
Yes. Silicone rubber exhibits relatively low smoke generation and can achieve flame-retardant ratings such as UL94 V-0 depending on formulation. If your export market has strict requirements for this, you can indicate it in the safety assessment.
What Causes Whitening and Bluish Discoloration During Optical LSR Processing?
White discoloration on the surface or inside of the optical LSR products indicates the presence of white turbidity, which is mainly related to the quality of the silicone resin raw materials.
Blue tinting of your products means a blue hue, which is associated with the formulation system of the used raw materials, like improper filler dispersion, pigment contamination. You need to be more stringent in controlling impurities to ensure the long-term optical stability of the products.
Final Thoughts
Legensilico is a professional manufacturer of silicone materials, and we can provide you with customized silicone product services. Our team is professional and can offer you high-quality LSR products. If you are interested in our silicone products or services, please feel free to contact us at any time.
