UK What optically clear adhesive does
Optically clear adhesive (OCA) is a transparent, pressure-sensitive adhesive supplied as a film between two release liners. It is used to bond the layers of a display stack, such as a cover glass, a touch sensor and the LCD or OLED panel, so that there is no air between them.
Removing the air is the point. Every glass-to-air surface in a display reflects around 4% of the light that hits it, and an air gap behind a cover glass adds two such surfaces. OCA has a refractive index close to that of glass, typically around 1.47 to 1.5, so light passes from one layer to the next with almost no reflection. The screen looks darker and sharper in bright light, and moisture has no gap to condense in.
OCA is the material, and optical bonding is the process. Bonding with OCA film is called dry bonding, and bonding with a liquid adhesive is called wet or liquid bonding.
OCA vs LOCA
The two main adhesives do the same job but suit different assemblies. The table compares them with an unbonded air-gap display.
| Property | OCA film | LOCA liquid | Air gap (unbonded) |
|---|---|---|---|
| Form | Pre-cut adhesive sheet | Dispensed liquid resin | Gasket or tape at the edges only |
| How it is applied | Laminated with rollers or in a vacuum | Dispensed, spread, then cured | Layers held apart by the frame |
| Curing | None, bonds under pressure | UV light, heat or moisture | Not applicable |
| Fills uneven gaps | Limited, needs flat surfaces | Yes, flows into gaps and around edges | Not applicable |
| Best suited to | Flat, small to medium displays and touch sensors | Larger, curved or uneven assemblies | Indoor displays where cost and rework matter most |
| Reflections | Internal reflections removed | Internal reflections removed | Two extra reflecting surfaces |
OCA gives a clean process with consistent thickness and no curing step. LOCA handles the uneven surfaces of larger panels and bezels, but it needs controlled dispensing to avoid bubbles and overflow.
Properties of a good optically clear adhesive
Display-grade adhesives are specified on more than stickiness. These are the properties manufacturers test for.
-
//
High transmission and low haze. The film should pass nearly all visible light and add almost no cloudiness to the image.
-
//
Matched refractive index. Close to glass, so the bonded layers behave optically like one piece.
-
//
Stability over time. Resistance to yellowing under UV and heat, and no bubbles or delamination after temperature cycling and humidity.
-
//
Thickness. Films range from tens of microns for touch sensor layers up to thicker grades that absorb small surface variations behind a cover glass.
-
//
Chemistry. Most OCAs are acrylic. Silicone grades stay flexible across a wider temperature range, which suits outdoor and vehicle displays.
How OCA bonding is done
Dry bonding with OCA is a clean-room process. One liner is peeled off and the film is laminated to the first layer, usually the cover glass or touch sensor. The second liner is removed and the assembly is laminated to the display, often in a vacuum so no air is trapped. Many lines then put the assembly in an autoclave, where heat and pressure push out any remaining micro-bubbles.
Dust is the main enemy, because any particle trapped in the bond shows as a visible spot. That is why optical bonding is done at the factory and is hard to rework in the field. Our guide to optical bonding in industrial displays compares dry and liquid bonding in more detail.
Where OCA is used
OCA is in almost every phone and tablet, where it bonds the cover glass to the touch sensor and display. In industrial displays it does the same job in harder conditions, and it is one of the main reasons a bonded screen stays readable outdoors. Our explainer on sunlight readable displays shows how bonding, brightness and glass work together. Panel PCs use it the same way: our sunlight readable panel PCs bond the touch sensor and cover glass to the display, so the whole front behaves optically as one sheet of glass.
-
//
Touch screens. Bonding a projected capacitive sensor to the cover glass and the panel, as on our PCAP touch monitors.
-
//
Sunlight readable displays. Bonded displays such as our sunlight readable monitors need less backlight power to reach the same contrast outdoors.
-
//
Vehicle and marine displays. No air gap means no condensation fogging the screen when the temperature drops.
-
//
Rugged and impact-rated screens. The bond supports the glass across its whole area, which helps it resist impact and vibration.
Quick answers on optically clear adhesive
Optically clear adhesive: common questions
Is OCA the same as glue?
Not quite. OCA is a pressure-sensitive adhesive film that bonds without curing. The liquid version, LOCA, is closer to a glue, because it is dispensed wet and then cured with UV light or heat.
What does OCA stand for on a phone screen?
Optically clear adhesive. It is the clear layer that holds the cover glass to the touch sensor and display, and replacing it is part of refurbishing a cracked screen.
Can an optically bonded display be repaired?
Sometimes, but it is difficult. The adhesive can be softened with heat and the layers separated, but the parts risk damage and re-bonding needs clean-room conditions. In practice, industrial bonded displays are usually replaced as an assembly.
Does OCA turn yellow?
Display-grade OCA is designed not to. It is tested for UV and heat ageing. Cheaper adhesives can yellow or bubble over years in sun and heat, so outdoor displays need grades specified for it.
Is OCA better than LOCA?
Neither is better overall. OCA suits flat, smaller assemblies and a clean process. LOCA suits large, curved or uneven assemblies where a film cannot fill the gap.
We supply optically bonded monitors and panel PCs with the bonding, glass and touch chosen for the site, then configure and test each display before it ships.