This whitepaper offers an in-depth analysis of the major challenges and solutions related to optical coatings on plastic substrates. It also offers extensive details of procedure of plastic coatings and comprehensive analysis of various aspects of optical coatings. This whitepaper contains complete information about optical coatings process with advanced technologies used to improve performance of coatings. The whitepaper also provides the complete analysis about product types, applications, and solution for each problems while coating plastic optics along with a detailed overview of the applications of optical coatings in various industries such as defense, medical, and security.

Optical Coatings are basically designed to improve the performance of an optical component for a particular angle of incidence and radiation of light such as p-polarization, s-polarization, and random polarization. The use of coating at a specific angle of polarization and incidence resulted in significant degradation with performance. Optical coatings offer a large number of functionality in vehicles and architecture industries. Optical coatings have a number of applications such as headlight lens system, rain sensors, rear view mirrors, lighting reflectors, motion detectors, and others. However, automotive and architectural coatings are a discrete application along with specific market characteristics.

Product Types of Optical Coatings

• Refractive Index

A refractive index which is also called as an index of refraction, it is basically a measure of a material’s ability to reduce light waves as they pass through. A material’s refraction index is determined by the ratio of the speed of light in a vacuum to the speed of light in the material.

• Reflective optical coatings

There are several kinds of optical coatings. The reflective optical coating is one of the popular types of coating. Such type of coating is mostly used in mirrors. In this, the highly reflective layer is placed on the product.

• Anti-reflective optical coating

Like reflective optical coatings, the anti-reflective optical coatings are also hugely available for the optical product. The key feature of anti-reflective optical coatings maximizes the light which enters an optic.

• Broadband

It refers to having a continuous spectrum of electromagnetic frequencies. Sunlight is the best example of broadband light radiation.

• Wavelength

A wavelength is a distance between the one peaks of a wave to the next wave.

• Visible Spectrum

A visible spectrum is the range of wavelengths of visible light radiation.

High-Performance coatings on plastic optics can be achieved by using appropriate design and fabrication approaches

The introduction of developed optical polymers and advancements in fabrication techniques now let designers replace high-end components of glass optical with plastic at a less price, enabling use in various applications such as industrial, medical, and defense & security. The advancements in optical coating technique for plastics have been important to this transition, facilitating the delivery of equivalent optical performance and durability even though the use of several class of substrate material.

The deposition in optical coatings on polymer substrates brings a number of challenges. Polymer optics cannot resist with the typical 250° Celsius coating temperatures used for glass. Optical coatings on plastics are more inclined to peeling, delamination, and flaking, in case it is not applied properly specifically when subjected to abrasive environmental circumstances. This can add environmental and optical performance at odds, as a rise in the number of layers to obtain the preferred spectral profile could improve stress between the coating and substrate, specifically during temperature cycling.

• Cooling down deposition

The comparatively low melting point of the most plastics needs the low-temperature deposition procedures such as Plasma-Enhanced Chemical Vapor Deposition (PECVD) or plasma ion-assisted deposition (plasma-IAD). Low temperatures such as 40°-50°C are not unusual to avoid deformation or distorting of the substrate, specifically for the softer material such as acrylic.

• Ensuring Adhesion

Adhesion of coatings to polymers is not stronger than glass. When shielded with differences in thickness variations and thermal expansion coefficients in the optic, it can assure the multiple layers which can be deposited without conceding environmental performance. Pretreatment by using low-pressure plasmas of helium (HE), nitrogen (N2), or argon (AR) has been shown to develop coating adhesion, mechanical durability, and stress compensation.

• Cleaning and Handling Plastics

Creating a high-quality optical coating from a plastic substrate is heavily depends on proper handling and cleaning of the parts before deposition. Various plastic materials scratch easily when compared to the glass without proper cleaning and handling, adhesion will be compromised. Components such as prisms, lenses, and windows are carefully cleaned ultrasonically by using surfactants and chemicals.

• All plastics are not created equal

The most complex characteristic of an optical coating on polymer substrates is the complexity and variety of the materials available. Each has unique chemistry which interacts individually with the preparation, cleaning, and deposition procedure employed, along with the stress at the optical coating substrate interface. This can restrain the performance of optical coating to pass MIL-SPEC testing. It is not guaranteed that the coating which passes through one type of plastic to pass on another plastic. The development of a layered design and deposition process need to treat with the optical specifications substrate form, environmental requirements, and others.

Conclusion

The number of optical coatings on glass can now be simulated on polymer, and with ISO and MIL-SPEC reliability. With the experienced coating vendors, it becomes possible to make a drop-in replacement for a glass component to cut cost, reduce weight, and other issues associated with splintering and cracking in the field. With the high capabilities and various plastic optics options growing significantly since the past decade.