Anti-reflection (AR) film with moth-eye structure for in-vehicle displays application

Usage of Moth-eye type AR film for automotive displays

Films and resins that improve visibility by preventing light reflection are now the major product categories of Dexerials. The AR100 series of AR films are highly effective in reducing light reflection when applied to displays and have been adopted by manufacturers of PC monitors, tablet PCs, and automotive displays.

Optically clear resin (OCR/LOCA) is a transparent adhesive for bonding the top substrate of a display and the display module. It also reduces reflection and refraction of light at the adhesive interfaces. Dexerials has also released optical elastic resin called “SVR”.

Another optical product of Dexerials’ is the moth-eye type anti-reflection film. The surface of the eyes of nocturnal moths is aligned with uniform nanometer-sized bumps. These bumps allow light to pass through without reflection. Dexerials has succeeded in forming this moth-eye-like structure on a film using their unique imprinting technology. The newly developed “Anti-reflection film moth-eye type” has less reflectivity in a broad wavelength of light and superior transparency than sputtered AR films. When this film is applied to displays, images with higher brightness and contrast are achieved.

This moth-eye type AR film has mainly been adopted for two applications places: the Center Information Display (CID), which is installed on the dashboard of a car and displays information such as the car’s location, and the Head-Up Display (HUD), which shows information such as the car’s speed on the windshield in front of the driver.

Comparing anti-reflection films moth-eye type and OCR

The below is a diagram of a CID. The moth-eye type anti-reflection film is applied to the back of the top substrate that protects the flat-panel display (FPD).

In general, a gap between the FPD and the top substrate causes subtle blurred images due to the reflection and refraction of light on the inner surface of the top substrate. One solution is to fill the air gap with an OCR, such as Dexerials’ SVR or Hybrid SVR. However, there are cases where an OCR cannot be used for various reasons due to the design or size of the air gap. In such cases, applying the moth-eye antireflection film can have a similar to OCR effect.

The diagram below demonstrates the difference in reflection and image contrast of FPD structure of tablet PC.

First, the internal space between the touch panel and FPD is divided into three parts: the part filled with SVR (OCR), the air gap, and the part where the moth-eye type AR film is applied.

It is further divided into six areas according to the presence (right side) or absence (left side) of the anti-reflection film on the outer surface. The diagram shown below indicate the reflectance of each area. The area with anti-reflection film on the surface and SVR on the inside has the lowest reflectance, followed by the area with moth-eye film on the inner surface, which shows that it has a similar to OCR effect. On the other hand, in areas with air gap, the screen color appears whitish with visibility is reduced, indicating the importance of anti-reflection solutions.

Moth-eye type AR film and optical elastic resin (SVR) have their suitable applications. SVR is applied when the air gap between the top substrate and the display is relatively small. On the other hand, the moth-eye type anti-reflection film is suitable when the air gap is larger than 0.5 mm. Recent car navigation systems have 2.5D or 3D curved surfaces. In such cases, the moth-eye type film is suitable for the curved top substrate. 

Preventing double image (ghosting effect) in HUDs with Moth-eye type AR film

One of the automotive applications of for moth-eye type anti-reflection film head-up display (HUD) that projects information onto the driver’s side windshield. Latest HUDs use augmented reality technology to display data and instructions such as driving speed, engine rpm, and navigation information in the space in front of the driver. Recently, an increasing number of cars, especially luxury cars, are equipped with HUDs.

The HUD’s projection mechanism consists of a projector that emits images, a reflector to guide the light, and a transparent plate called a glare trap that reduces glare. The thickness of the glare trap is about 0.4 to 0.5 mm, and when light passes through it, the difference in refractive index between the glare trap and the air causes reflections on the incoming and outgoing surfaces. This results in a double image (ghosting effect) on the windshield.

By applying a moth-eye type film to the bottom of the glare trap (the incident surface of the projected light), the reflectance of the bottom surface can be reduced from ~4% to 0.3%, minimizing the ghosting phenomenon. The following figure shows an experiment to explain this phenomenon.

In recent years, digital displays in automobiles have been expanding to areas other than the dashboard. New display systems that project images of the car’s surroundings, not just side-view and rear-view mirrors, are being developed one after another. Moth-eye type AR films in automotive displays improve display visibility, thus, enhance driver safety. Overall, Dexerials’ moth-eye type film is expected to expand its automotive applications in the future.