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LCD filters

Optical and EMI filters

LCD filters are used in front of liquid crystal displays to protect the display surface and to offer antiglare properties. At Keyflex we offer a range of custom sized filters produced from Optolite and Optolite High Scratch Resistance (HSR) depending on the clients needs.
Optolite is a clear plastic with excellent optical characteristics, which ensures the viewability of the display will not be diminished. Available in a thickness ranging from 0.5mm to 8mm thick, and half-millimetre increments in between, the material can be cut to any shape or size. Print can be applied to the rear or front surface to enhance your product design. Optolite is available in a range of tinted colours as well as clear.
Optolite High Scratch Resistance is similar in all aspects to Optolite except that the material offers better scratch resistance for working environments where scratching due to frequent cleaning or inappropriate usage is a risk. Optolite HSR is 20 times more scratch resistant than acrylic whilst maintaining excellent optical transmission. In addition Optolite HSR has outstanding chemical resistance, making it suitable for use in the most demanding of applications.
Shielded Filter Windows are manufactured using Optolite or Optolite HSR and are used extensively to minimise radio frequency emissions generated by enclosed electronic equipment and to protect electronic equipment from electromagnetic interference arising from external sources.
The shielded filters operate by using a cast in highly conductive micro-fine wire mesh to attenuate EMI/RFI emissions. Different mesh thickness and sizes are available to suit a range of frequency and viewing requirements.
LCD filters can be used for liquid crystal displays, alphanumeric modules, graphic modules and custom displays. They can be printed and supplied with adhesives and gaskets for sealing or EMI filtering
Contrast enhancement filters
Optolite Clear HSR optical grade filters offer a robust, high temperature, high scratch and impact resistant material. It is especially suited to LCD’s and other display applications where these characteristics are of a particular importance.

LCD’s often suffer from a number of problems:

  • Soft front surface polariser
    – can be subject to damage from scratching, dirt, moisture, finger marks, etc.
  • Front surface reflections
    – in certain lighting conditions these may cause display reading difficulties
  • Restricted viewing angles
    – caused by LCD construction and method of operating
  • Possible Ultra Violet degradation in strong sunlight
  • Shielding from electromagnetic interference
  • Sourcing of bezels
    – not always possible or feasible with so many different LCD sizes available

Choice of Optolite Clear HSR

Keyflex offers their Optolite Clear HSR (High Scratch Resistant) filter to overcome these problems on LCD’s. It is also especially recommended in display applications requiring the characteristics mentioned below.

Optolite Clear HSR has both outstanding abrasion resistance, up to 20 times that of acrylics, and excellent impact resistance. It is also chemical resistant, being immune to the effects of virtually all common solvents. It is lightweight, approximately half that of glass, and exhibits optical properties comparable to crown glass. Its maximum continuous operating temperature is in excess of 100°C.

Optolite Clear HSR is available with selected optional cast-in non-glare finishes to overcome front surface reflections. These finishes can improve readability whilst offering advantages in that they cannot chip, peel or rub off.

OPTOLITE SHIELDED WINDOWS

Optolite™ shielded filter windows have been designed for electronic displays, combining a high level of electromagnetic shielding with excellent contrast enhancement.

They are used extensively to minimise radio frequency emissions generated by enclosed electronic equipment and to protect electronic equipment from electromagnetic interference arising from external sources.

Features:

  • Up to70dB attenuation
  • In clear HSR (High Scratch Resistance) or selected coloured band pass filters to suit most displays
  • Available flat or curved
  • Excellent impact abrasion, heat and chemical resistance for Optolite Clear HSR
  • Light weight
  • Robust construction
  • Optional blackened wire mesh to reduce mesh reflections
  • Cast-in non glare finishes to cut down front surface reflections
  • Mesh incorporated at any desired angle
  • Edge termination services available
  • Fabricated to customer requirements

Optolite™ shielded windows have a highly conductive micro-fine wire mesh which attenuates EMI/RFI emmisions. Different meshes to suit varying applications are available.

Optolite™ filters are cast in-house as a one piece filter with the mesh totally encapsulated. This approach offers customers a more cost-effective and robust solution to shielding problems, totally eliminating delamination and optical imperfections which can affect ordinary laminated windows.

Typical Applications of Optolite™ Shielded Windows

Aerospace and Defence
Radio and telecommunication
Industrial Manufacturing Equipment
Medical and Scientific Apparatus
Information Technology Equipment
Flat Panel Displays in Electronic Equipment

PROPERTIES

Shielding
Absorption of electromagnetic energy is mainly dependant on the mesh conductivity, wire diameter, weave density, electrical contact between intersecting wires, mesh material and edge terminations.

The shield effectiveness, measured by using the “Hole-in-the-Wall” technique, is typically between 60dB and 70dB from 100KHz to 1GHz and 35dB up to 10GHz for blackened stainless steel meshes.

Optical Characteristics
It is important to colour match band pass filters to the particular display characteristics. Optolite™ transmission, absorption and reflectance are dependant on the filter band pass colour, mesh density and non glare finish. Also, by casting the material as a one piece filter, the transmission is improved by reducing the number of internal reflecting surfaces from four to two compared to laminated windows.

Physical Design
Optolite™ shielded windows are supplied fabricated to customer requirements. Overall standard thicknesses are 2.5, 3, 4, 6mm. Other, non-standard thicknesses, from 1mm upwards, are also available to order together with an optional non glare finish.

Weight
For larger displays, weight can be an extremely important consideration in the design of shielded filters. Optolite™ Clear HSR and Optolite™ coloured acrylic filters weigh only half as much as glass. Additionally, an acrylic filter is up to five times as resistant to breakage as a comparable glass filter.

Mesh
Various types of mesh are offered which can be treated to produce a matt black non reflective finish. Alternatively, a standard metallic finish can be incorporated in band pass filters where the colour reduces the need for blackened mesh. Typically, the wire diameters range from .025mm to 0.5mm and the weave densities vary from 50 O.P.I. (Opening per inch) to 200 O.P.I. mesh. The mesh can be set at any angle up to 45° in more demanding applications to restrict the possibility of moiré fringes where this is important.

Edge Termination
In one piece filters, the conductive mesh is exposed along the edge of the optolite filter after it is cut to size. A silver conductive bussbar is added to the edge and then extended, if required, to the front or rear surface.

The conductive circuit from the mesh is then completed either through the bussbar or else via a conductive elastomer gasket attached to the bussbar. Other edge termination methods are also available.

Gasket
The conductive gasket consists typically of aluminium or monel wires, which are crimped for maximum pressure. The wires are oriented perpendicular to the mating surfaces and integrally bonded into a silicone elastomer. The elastomer acts either as an environmental seal or as a pressure seal. Again, other types of gaskets are also available.

Keyflex will be pleased to advise on the design and construction of Optolite™ shielded windows for specific applications.

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