The black light absorption coatings are considered to be one of the most important parts of the modern imaging displays. The key purpose of the coatings is image enhancement, especially at the unfavorable external illuminance conditions. In the cathode display tubes (computer monitors) the black coatings are used to fill the spaces between pixels (black matrix). This allows to obtain high contrast and sharp image. Black coatings play an important role in avionics and car dashboard displays – black and non-reflecting imaging device scales offer superior data reading opportunity even in the bright ambient light conditions.

New displays based on the Organic Light Emitting Diodes (OLED displays and PLED displays) became another innovative area for the light absorption coatings application. The structure of the OLED display constitutes a set of several optically transparent layers. The Black Coating serves as a background on which luminous spots are forming a final image. The requirements for such Black Coating are very high since even a small presence of reflectance results in substantial contrast deterioration in the bright direct light conditions.

Presently, the commonly used technologies to obtain black coatings include various absorption materials like black resin, carbonic paste etc. However, this approach does not ensure obtaining optimum optical characteristics. Residual level of the reflectance of these coatings amounts to 1,0 – 1,5%, thus mapping them out from OLED display and avionics applications.

IZOVAC have developed an industrial technology and equipment to obtain integrated interference absorption coatings with superior optical characteristics. Depending on application, the coatings have reflectance average to 0,1% on the 300 mm X 400 mm substrate (Please see figure below).

The following curves are presented on the figure below:

• Curve A – the spectral characteristics of reflectance from the Black Coating;
• Curve B – the spectral characteristics with reflectance from the front uncoated side of the glass substrate.

Described interference coatings were calculated in the same way as traditional anti-reflection coatings, except that the light absorption materials (generally, metals) were used. Black Coating structure is designed individually for every case in accordance with the required optical characteristics, stability, final application etc. This is especially critical for the OLED and PLED displays, since the initial optical design for such displays should be taken into consideration during Black Coating calculations.

An important issue that needs to be considered during calculations of the low reflectance interference absorption coatings is high sensitivity of the human eye. Even a small rise of the reflectance value in certain part of the visual wavelength range (400-700 nm) may become visible resulting in the coloration of the whole coated layer. The rise of reflectance value could be caused by mistake in the design of the coating (in this case the whole surface will be tinted) or by low uniformity of layers’ thickness (in this case different areas of the coated surface will have different colors).

Traditionally, the above concerns are overcome by designing the coating with controlled rise of the reflectance in the blue area of the spectrum. The resulting coatings have a dark blue color. IZOVAC possesses and offers both technology and equipment to obtain either dark blue absorption coatings or true Black Coatings.

The advantage of proposed solution is the integration of the Black Coating into the OLED display structure. This results in superior raise on image contracts. With IZOVAC proprietary deposition technology one have an option of choosing various deposition materials and to vary electrical feature requirements of resulting coatings, thus being assured in obtaining highly uniform Black Coatings, designed for every specific application.