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Sep/12/2018

Optical Bonding

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Introduction

Optical bonding process which is the process of laminating cover glass or touchscreens to the LCD cell. Silicone gel or other adhesive, (see following figure out), to use OCA gel to insert between the cover glass and LCD to completely fill the air gap. The assembly is cured in a process that affixes the panels together while solidifying the gel.
We may need optical bonding for Protection ‐ LCDs have plastic surfaces that are not vandal or weatherproof.
To protect your display investment most LCD installations, require a cover glass or polycarbonate lens to protect the LCD.

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(Picture is from Wikipedia, the free encyclopedia, the link: https://en.wikipedia.org/wiki/File:LOCA_3_applications_industry.jpg)

Features & Principles

a. Optical bonding OCA
Optical bonding technique fills the air gap with Optical Clear Adhesive or OCA. While the optical index of OCA is designed to be very close to that of glass, light reflection at those two interfaces is minimized. Since less ambient light is bounced off the interfaces with optical bonding, the dark image remains as dark as it should be and the contrast ratio as well as the color saturation are restored back to the level when touch panel was not there. Likewise, back light of LCM experiences less reflection loss when it propagates through the interfaces with OCA, and the brightness off the touch panel is up as if the TP was not there. Optical bonding is implemented by either liquid or sheet form OCA. The high cost of both processes is mainly due to un-recoverable yield loss issue.


b. Optical bonding services
Optical bonding services plays a decisive role in the display which is installed in the highly humid, outdoor, or harsh environments due to its enhanced ruggedness and visual performance to the display. There are some factors that affect displays’ readability. The most common one is “fog”, or condensation, which forms on the inner surface of display's vandal shield. Another factor is the reflection of sunlight, which causes a mirror-image on the display. Reflection is caused by optical index mismatch between air and the glass. Both issues can be solved by using optical bonding. Not only optical improvement, using optical bounding technology with a protective cover glass can also improve scratch and damage resistance.

With touch panel attached to LCM, the display suffers not only brightness g oing down but also the deteriorating in display quality. Especially the reflection of ambient light causes the dark image being not as dark as it supposed to be.By adding the process of Optical Bonding, we can reduce the brightness loss and avoid the influence of ambient light.

Reflection appears when light propagates through media with different optical indices. The reflection energy is around 4% of incident light at each air-glass interface. As touch panel attached to LCM with air gap, two additional air-dielectric interfaces contribute to light reflection.

Optical bonding LCD benefit

1. Increased ruggedness: Bonding a sheet of glass on top of the display increases the ruggedness of the display.
2. Improved durability: A bonded display is better able to resist scratches, fluids, stains and dirt.
3. Condensation: The elimination of an air gap between the cover glass and the display means that moisture cannot penetrate and cause fogging on display’s surface. Extended temperature range and EMI filtering: The temperature range of the display can be extended by incorporating ITO heaters on the cover glass; EMI filters can be added via the same mechanism.