High Durability AR coating for Display panels

Brinell HD

 

High Durability coating process

for harsh environments

The Brinell HD process has been developed to provide a high quality, durable broadband anti-reflection (HDAR) or optical filter coatings onto glass and plastic substrate for use in harsh environments. The process utilises advanced plasma thin film deposition to allow all types of substrates and levels of surface finish to be coated to an outstanding quality. The adhesion primer layer prepares the uncoated lens for deposition of high quality dense thin films and an optional oleophobic top coat increases the resistance to chemical and mechanical damage.

Fig 1.

 

Advanced plasma deposition of AR stack

Lower temperature coating is becoming important as lens materials become more sophisticated and sensitive to processing.

Brinell HD utilises low temperature, high-powered plasma during deposition of carefully selected dielectric materials. The plasma source adds energy to the process without adding heat or thermal stress to the lens. The plasma energy added is equivalent to heating the substrate to over 400^oC; such temperatures are quite clearly not suitable for some sensitive substrates such as filter glass and plastics.

The result of the plasma process is the production of dense, smooth films, which exhibit excellent optical properties. These superior film properties, such as lower scattering, lower adsorption and higher refractive index lead to excellent transmission and clarity.

	Fig 2 Standard thin film by evaporation

 

Fig 3. Plasma assisted coating

SEM Picture (thickness approximately 200nm)

Advanced oleophobic top-coat chemistry.

The plasma assisted thin film coating exhibits a very smooth dense surface structure when compared with standard commercially available coatings (see Fig 2 & 3). This smooth film combined with advanced oleophobic top coat makes lenses and filters much easier to clean and look after without the addition of light scatter at the interface between the AR stack and top coat.

The top-coat chemistry is created by an accurately controlled vapour deposition process of per-fluorinated-polymer molecules. Unlike standard top coats these PFA-POSS molecules possess free radicals, which form covalent bonds with the top layer of the coating stack.

This highly stable reaction reduces the contact area of water and grease droplets (see Fig 6, 7 & 8). The outstanding hydrophobic and oleophobic properties make the lens easier to clean due to its rejection of water and grease.

.                                               Fig 6.      Contact angle for untreated glass

                                                Fig 7.      Contact angle of AR coated lens with standard top coat

                                                Fig 8.      Contact angle for Brinell HD oleophobic top-coat chemistry

 

 

Durability

The top-coat chemically reacts with the final layer of the AR coating stack and exhibits no clear physical interface. This ensures that the coating remains on the lens, cannot be easily removed and provides additional protection against chemicals and reduction in friction/general abrasion.

                                                                       

Fig 9.      Standard top coat contact angle after stroke test           

 Fig 10.    Brinell HD top coat contact angle after stroke test

Conductive Antireflection (AR) technology For EMI Shielding & Heating in Display

Brinell K-AR conductive antireflection technology 

for EMI shielding & heating.

High quality electronic displays are now becoming a standard requirement for many vehicles and aircraft and they need to operate well in demanding environments. High ambient light readability and electromagnetic compatibility (EMC) can be achieved only by modifying commercial 'off-the-shelf' display screens.  

To provide electromagnetic shielding components need to be surrounded by a conductive enclosure which will attenuate any unwanted electrical fields. Unfortunately this proves more of a challenge on the display area where there is a requirement for good optical transmission. A common technique for adding conductive properties to an optical substrate involve integration of fine wire meshes within a lamination of two planes of glass or plastic. These generally create moiré patterns and can seriously hinder display readability in certain conditions especially if the mesh interferes with active-matrix display.

Example of Moire' patterns 

A far better solution is the deposition of electrically conductive, thin optically transparent conductive oxide films onto the display screen. Specially selected and processed conductive films will transmit up to 80% of the visible spectrum (from 400 nm to 700 nm). The problem with both techniques is that both provide unwanted reflections which can create problems in high ambient light conditions such as aircraft cockpit or vehicle display. 

Destructive optical interference coatings

By incorporating other optical materials with different refractive indexes into a multi-layer optical design it is possible to reduce reflections and improve both transmission and clarity of a transparent conductive oxide (TCO). Reflections from the higher index TCO are cancelled out by creating corresponding reflections which are 180 degrees out of phase. This is the same method used for multi-layer AR eyeglass coatings however the challenge is the ability to control the optical thickness of the TCO to within 10nm. (10 millionths of a millimetre).

Brinell heater glass panels and EMI shielding plates are designed optically to give outstanding transmission and low spectral reflection for challenging applications by use of a complex multi-layer thin film to optically match the transparent conductive oxide. 

The resulting transmission is also extremely high and can be used in demanding applications such as vehicle display and cock-pit environments where ambient light would cause high levels of reflection.

Brinell K-AR has been tested to ensure compliance with DEF STAN 59-411, MIL-STD 461E and MIL-C-48497. Below illustrates one example of a COTS (commercial display) before modification and after modification. The top red line shows the maximum limit for electrical/electromagnetic interference allowed. In case 1 the measured signal breaches the required standard and is well above the desired value. 

                               1. Standard commercial display 

In case 2 the standard display unit is fitted with a front cover glass coated with Brinell K-AR-550-16. In this case the noise signal is suppressed well below the required standard MIL-STD 461E and also meets the lower desired level.

                               2. Standard commercial display with Brinell K-AR front plate 

Brinell BV-K-AR technology

• Resistivity from 4 Ohm/Sqr to 100 Ohm/sq

• High Clarity EMI Shielding to MIL-STD 461E

• Efficient alternative to mesh filters with outstanding optical transmission

• Optically matched for low loss lamination or air interface

• DEF STAN 59-411 and MIL-C-48497 compliant

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