Letter 14094

Vacuum metallizing  

I am trying to apply a reflective coating to acrylic by vacuum metallizing but want the thickness of the coating to allow partial transparency. During normal day time light levels it needs to be reflective but at night a light illuminates what is behind the acrylic so as to reveal the inside of my product. I have found some one to do this for me but they do not know what thickness I need to achieve this.

Thank you in advance.

Craig Bond
survey labs - New Zealand

This layer is going to be very thin. I would suspect you are going to want something between 100 and 500 Angstoms. By the time you get to 1000 Angstroms you won't be able to see through it. Unfortunately, I don't know the exact thickness.

John Davis
- Berthoud, CO, USA

The relationship between thickness and transparency is not so straightforward. Under ideal conditions where density is 100%, the metals start becoming opaque at about 100 angstroms (0.01 micron). The transparency beyond that is a function of pin-holes which are determined by the material, its surface and other process conditions. In general terms, I would say you need about 500 A or below thickness. Typical opaque reflective coatings are about 1000 to 2000 A. Ask for decreasing thickness and see which one you like.

Mandar Sunthankar
- Fort Collins, CO

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