OCA and LOCA for touch displays
Optically clear adhesives, OCA and LOCA, are used to bond touch glass to the display panel, eliminating the air layer between them. As a result, the display is brighter, has better contrast in sunlight, is free of air bubbles and withstands impact better.
Optical bonding technology is increasingly common in phones, tablets, automotive displays and industrial equipment. The choice between film-type OCA and liquid LOCA depends on size, construction and production volume.
Why optical bonding is needed
When there is an air gap between the glass and the LCD panel, light is reflected at each interface, reducing contrast. Optical adhesives have a refractive index of about 1.47–1.50, close to that of glass, which significantly reduces internal reflection. The adhesive layer also disperses impact forces and prevents moisture from condensing behind the glass.
OCA: film adhesive
OCA is a carrier-free acrylic adhesive film sandwiched between two release liners, with thicknesses from 25 µm to over 300 µm. Its advantages are cleanliness and uniformity, making it suitable for high-volume production of small and medium displays. The bonding process typically involves lamination, vacuum bonding and autoclaving to remove air bubbles.
LOCA: UV-curing liquid adhesive
LOCA is a liquid adhesive dispensed onto the surface, then pressed and cured with UV light. The liquid adhesive fills uneven surfaces, thick printed ink borders and curved displays, and is easy to apply to large displays.
| Criteria | OCA | LOCA |
|---|---|---|
| Material form | Pre-cut film | Liquid adhesive |
| Filling uneven surfaces | Limited | Excellent |
| Suitable sizes | Small and medium | Medium to large, curved displays |
| Equipment investment | Laminator, autoclave | Dispenser, UV lamp |
| Reworkability | Difficult | Possible with some grades |
| Light transmission | Above 99% | Above 98% |
Tips to prevent yellowing and edge lifting
- Choose an adhesive with a low yellowness index after UV and damp heat testing.
- With LOCA, pre-cure the border area to stop adhesive overflow.
- Control shrinkage to avoid mura on the LCD.
- Clean the glass and display panel surfaces in a cleanroom to prevent trapped dust particles.
If defects are found after bonding, some LOCA grades allow the layers to be separated with a cutting wire and a dedicated solvent to recover high-value LCD panels, reducing losses on large display lines.
AMS distributes OCA and LOCA adhesives from Henkel, Dymax and 3M for display assembly. Contact AMS Vietnam to receive samples and bonding trial support.
