Monomer is instrumental in glass replacement

Edited by the Engineeringtalk editorial team Nov 16, 2006

A custom formulation of the thermoset monomer ADC (allyl diglycol carbonate) is rapidly growing as a replacement for glass in a number of instrument display window applications.

The use of a Fosta-Tek Optics custom formulation of the thermoset monomer ADC (allyl diglycol carbonate) is rapidly growing as a replacement for glass in a number of instrument display window and data capture system applications, the company has reported.

The combination of high optical quality, excellent chemical and gamma radiation resistance, low material cost, and ease of fabrication make cast ADC optical sheet a natural choice for an increasing range of products, including medical devices and high-end scanning systems.

"Fosta-Tek Optics' ADC cast thermosetting optical sheet has been used for display window and data capture applications for some time because of its excellent optical properties", said Danielle Provencher, ADC Co-ordinator for Fosta-Tek.

"But recently we've seen a rapid upswing in the use of this material as the preferred replacement for glass in a number of market areas, ranging from ATM displays and barcode scanners to medical and industrial instruments, navigational instruments, oscilloscopes, outdoor workstations, security sensors and touch screens".

ADC (CR-39TM) was originally developed as a replacement for glass in prescription ophthalmic lenses and currently holds over 50% of the prescription lens market, Provencher added.

With a transmission value of 92%, haze as low as 0.3-0.9%, and excellent chemical and gamma radiation resistance, it is sometimes referred to as organic glass because its optical properties are so close to those of mineral glass.

Unlike extrusion or injection moulding, the thermosetting process generates very little birefringence in ADC sheets, allowing for quality imaging.

Plus, its Abbe Value of 59 is close to that of glass (60) and higher than any other optical plastic material.

(Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain types of material, causing polarisation or a "double vision" effect.

Abbe Value is an indicator of light dispersion or chromatic aberration.) "Excellent chemical and solvent resistance make ADC especially suitable for medical and lab environments", said Provencher.

"The optical and mechanical properties of ADC sheet are unaffected by long term exposure to virtually any organic chemical, including ketones, alcohols, aliphatic and aromatic hydrocarbons, and to cleaning solvents and alkalis.

"Lower material costs and more flexible fabrication also give optical ADC sheet the edge over glass", Provencher said.

With precision laser cutting, ADC can be manufactured to specific shapes and sizes without the high costs typically associated with customising glass.

ADC materials can be cast in thicknesses from 0.030 to 0.250in and cut to sizes up to 25in square.

"One of the greatest advantages of cast resin material over its glass counterpart is the difference in relative weight", Provencher said.

"With a specific gravity of 1.3, the ADC material weighs only half as much as glass, making it an excellent option for portable devices".

Anti-glare finishes are cast directly into the window, making ADC a superior solution to a variety of lighting issues found in today's brightly lit medical environments without losing the superior resolution of the window.

A secondary thin film can be applied to the ADC material for applications requiring an anti-reflective coating to further enhance transmission.

Dyes are available in a wide range of colours, providing peak transmission values at specific nanometre ranges to optimise readability of displays.