Polycarbonate films help in screening windows

Autoflex PC is being used as a critical component for the construction of an innovative range of electromagnetic interference shielded display windows.

Autoflex PC, a range of hardcoated polycarbonate films, manufactured in the UK by Autotype, is being used as a critical component for the construction of an innovative range of electromagnetic interference (EMI) shielded display windows.

Called EmiClare and developed and produced by Thame based Optical Filters, the display windows are unique in eliminating the problems of image distortion and low light transmission normally associated with these types of products.

EMI shielding is widely used to protect electronics equipment, by either filtering out conducted electromagnetic interference or shielding radiated electromagnetic waves.

Peter Fisher, Technical Sales Manager for Optical Filters, explains: "Electronics equipment is becoming increasingly powerful and sophisticated, leading to an increase in the levels of electromagnetic radiation being generated".

"At the same time, electronic systems are more sensitive to external interference and, in many applications, most notably in the military and aerospace sectors, have to be protected both from jamming and detection".

"Equipment that is fully enclosed is relatively simple to shield".

"Adding display windows, however, effectively creates a break in the shielding, allowing electromagnetic interference to be radiated or to penetrate the system".

To overcome this problem display windows typically incorporate a screen or mesh that effectively attenuates the electromagnetic waves.

To date, most display windows with EMI shielding have used a screen with a regular square pattern that, although effective in disrupting radiation, severely restricts light transmission; perhaps as importantly, when the window is placed over a computer display the screen and underlying image pixels can interfere to create moire effects.

The solution developed by Optical Filters uses a novel design of mesh pattern, with rectangular openings being formed in an extremely fine copper wire screen, less than 0.5mm in thickness.

This is then coated by means of a proprietary chemical blackening process before being integrated into a multilayer construction between outer layers of Autoflex PC The finished product can be produced in a wide range of sheet sizes and thicknesses and, as Peter Fisher explains, "Provides a level of light transmission that at over 80% is considerably better than competing products".

"In addition, the unique design of screen virtually eliminates moire fringing".

"Key to this construction is the use of the Autoflex PC film as its innovative hard coating gives us tough protective outer layers that are resistant to scratches, abrasions and a wide range of solvents".

"The film also has excellent optical clarity, is available in gloss and antiglare finishes and is dimensionally stable even at elevated temperatures; this is an important property as the film and mesh layers are bonded together in an autoclave using dry film adhesives, so any dimensional changes in the film during either manufacture or in subsequent use could affect the integrity of the mesh".

The use of the Autoflex PC has also enabled Optical Filters to gain a UL flammability rating for its EmiClare products which, as Peter Fisher points out, "is essential in many military and consumer applications".

The critical nature of many of these applications also means that every sheet of Autoflex PC film has to be produced to a consistently high standard, free from inclusions or other defects.

Fisher concludes: "The service and technical support that we have received from Autotype has been extremely good and has been key in ensuring that we maintain exceptionally high levels of product quality".

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