What is Optical Bonding Technology?

 > What is Optical Bonding Technology?


Capacitive touch screens are more and more widely used. The combination of touch screen and LCD display is connected through air bonding or optical bonding. What are the differences and advantages of these two connection methods?

1.Optical bonding for sunlight readability

2.Optical bonding has Thinner Profile

3.Optical bonding enhances stability

4.Optical bonding can Anti-Condensation

5.Enhanced Display Quality and Contrast

6.Optical Bonding Benefits for Design

7.Optical bonding steps and recommendations

Optical bonding technology involves the precise bonding of two or more optical components (such as glass, plastic, films, etc.) together using optical adhesives or bonding agents to form a unified structure. Optical bonding technology is an advanced manufacturing technique used to seamlessly connect and assemble layers of different components in displays, tablet devices, and other optoelectronic products, enhancing visual quality and user experience.

half air bonding and half optical bonding

optical bonding technology offers the following advantages:

Optical bonding for sunlight readability

Air bonding creates an air gap, and since the refractive index of air is much lower than that of the materials used for cover lenses and LCD panel modules, it hinders the propagation of light. This effect worsens in bright ambient lighting conditions, where intense light entering the touch display module can significantly affect the LCD panel’s visibility due to reflections. Optical bonding uses optical adhesives with a high transmittance (over 95%) and a refractive index of 1.5 (matching the refractive index of glass and LCD panel materials). This bonds the cover glass, touch sensor, and LCD display module together. This eliminates the issue by ensuring consistent transmittance. If you need a sunlight readable display, optical bonding with appropriate surface treatment for the cover lens is essential

air bonding structure

Air bonding Due to the existence of air gaps, the difference in refractive index from the cover lens will affect the light.

Optical bonding structure

Optical bonding uses optical glue, which has the same refractive index as the cover lens and will not affect light.

Optical bonding has Thinner Profile

When using optical adhesive for bonding touchscreens to display screens, the increase in thickness is only 25μm-50μm, compared to traditional bonding methods which add 0.1mm-0.7mm of thickness. This thinner module profile provides greater flexibility in overall device design and contributes to a sleeker product appearance.

The thickness of optical bonding is thinner

The thickness of optical bonding is thinner

Optical bonding enhances stability

Air bonding’s air layer is prone to contamination by dust and moisture in the environment, impacting device performance. Optical Clear Adhesive (OCA) fills the air gap, preventing the ingress of dust and moisture and maintaining the device’s cleanliness. Furthermore, the bonding between the cover glass and LCD panel enhances resistance to external impacts such as vibrations and shocks. Optical bonding offers greater stability and durability.

Optical bonding uses OCA or optical glue to bond the touch panel and LCD display together, and the bonding force is stronger and firmer.

Optical bonding

Optical bonding can Anti-Condensation

Optical bonding, due to the use of OCA or optical adhesive instead of an air gap, possesses anti-condensation properties. Moisture molecules within the air gap can undergo phase changes at different temperatures, leading to condensation at low temperatures, which negatively affects visibility and touch response. Optical bonding effectively addresses this issue caused by temperature variations, resulting in improved clarity. Additionally, eliminating the impact of air moisture on touch sensors and LCD panels enhances the reliability of displays in high-temperature, high-humidity environments.

Enhanced Display Quality and Contrast

The absence of gaps between the touchscreen and display module in optical bonding significantly reduces light reflection and losses compared to conventional bonding methods. This can lead to an increase in surface brightness of 8-10% in dimly lit environments and nearly 10% in sunlight. This improvement enhances viewing angles and brings out the full potential of wide-angle viewing displays, making the visual experience more vibrant. Furthermore, optical bonding can enhance the contrast of the display, which is a crucial factor influencing viewing quality.

IPS with air bonding

The IPS display has good viewing angles, but the effect is reduced with air bonding.

IPS with optical bonding

IPS displays have good viewing angles and will perform best with optical bonding.

TN with air bonding

TN displays have poor viewing angles and will get worse with air bonding.

Optical Bonding Benefits for Design

Air bonding requires double-sided tape to connect the cover lens and LCD panel module, necessitating a certain width to maintain stable bonding. For larger cover lenses, wider and more adhesive double-sided tape is needed, leading to wider product frames. In contrast, optical bonding utilizes OCA or optical adhesive to connect the cover lens and LCD panel module. As long as the touch sensor’s circuitry and LCD panel border support it, optical bonding allows for much narrower borders on touch display screens. This greatly contributes to the aesthetics of the product.

air bonding

Air bonding is bonded with double-sided tape

optical bonding

Optical bonding uses OCA to bond the entire surface.

Optical bonding steps and recommendations:

Step 1: Tear off the light release film and roll the OCA optical glue onto the product with a roller at room temperature, such as cover lens, touch screen, tft display, etc. The pressure and speed of the roller need to be kept stable during the lamination process. It is recommended that the roller pressure is 0.1~0.2Mpa and the speed is 15~30mm/s.

Step 2: After laminating the OCA heavy-duty release film to the other side of the product, put it into vacuum equipment and laminate it. It is recommended that the vacuum value is <-96Kpa and the laminating pressure is 0.05~0.2Mpa.

Step 3: Bubbles will be generated during the bonding process and need to be removed in a vacuum environment. The recommended degassing temperature is 45℃~60℃, the recommended pressure is 0.3~0.6Mpa, and the recommended time is 10~30min. The degassing time can be adjusted according to different products.

Step 4: UV curing, recommended UV light energy: high-pressure mercury lamp >3000mj/c㎡, LED cold light source 365nm>4000mj/c㎡.

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