Optical bonding is a technique we use to laminate touch screens or cover display glass. It takes advantage of special glue and unique manufacturing technology to produce high- quality modules. The end products offer improved optical performance, durability, and many other benefits.
We also use the optical bonding technology to connect a display with transparent layers of electromagnetic protection or special coatings (for example, anti-glare, anti-reflective, hard coating, and polarizing filters).
Optical bonding is used in applications ranging from smartphones to car cockpit displays. The technology has become very popular and is frequently used in industrial, military, and medical applications – anywhere where quality, durability, and optical specification are important.
The process of optical bonding
Optical bonding can be divided into three stages:
- Preparation – decontamination of the display and touch screen surface, and selection of the most suitable adhesive depending on various parameters (for example, screen size, application environment, operating temperature)
- Glue dispensing – application of the glue precisely on the entire surface of the display.
- Bonding and curing – this is the most important stage of the entire process. The touch panel is layered onto the LCD module to prevent any gaps or bubbles from forming. We then harden the adhesive with UV light (lack of heat treatment reduces the risk of material contraction).
Advantages of optical bonding:
Reduction of light reflections improves the image quality – in air bonding, the light from an external source passes through the panel and air gap between the display and the glass, causing its refraction. Some of the light is reflected back and creates reflections on the screen.
The light generated by the backlight of an LCD module goes through the material boundaries with the different refractive index. This causes partial deflection. As a result, the display’s contrast and legibility are reduced. Optical bonding takes advantage of an adhesive that reduces the refraction effect. That’s because the refractive index of the adhesive is similar to glass.
Prevention of moisture condensation and dust protection
Prevention of moisture condensation and dust protection – moisture and dirt may penetrate into the gap between the module layers. This impacts the display readability negatively. Optical bonding introduces a glue–filled space that prevents this problem. You can be sure that the image is readable in any environment (outdoors, in production halls and warehouses, in hospitals).
Increased physical endurance – by eliminating the gap with resin, optical bonding increases the physical strength of the module. As a result, such applications can be used in public places, factories, and military environments. Optical bonding allows achieving the standard IK7 protection against mechanical impacts of 2J.
Why you need to cooperate with experienced manufacturers
Melrose will help you choose the right type of resin glue to avoid possible negative effects that stem from the lack of experience in the optical bonding technology:
Mura effect – Tensioning of the glue, which can cause mechanical stress of the TFT LCD panel, especially visible when displaying dark content and in poor lightning. Carefully selected glue and staged curing process helps to minimize stress concentration and significantly reduces the chances of the mura effect.
Shrinkage of the adhesive – High temperatures may cause the delamination of the adhesive with the top material. We use a technology that allows increasing adhesion to materials combined in the process. Our tests show that the effect doesn’t occur at 85 °C.
Yellowing – A poorly matched mixture of resin glue might become yellow under exposure to chemicals or UV radiation. This has a negative impact on the visual reception of the module. Our experts will help you choose the right mix for your application’s requirements.
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