Letter 2073

Light reflecting aluminum coating on molded plastic parts

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I am looking for a process and equipment to deposit an alluminum reflective coating onto molded plastic pavement markers. I have tried outsourcing with shops that have used the vacuum vapor deposition process, but the results have been desappointing because, although the substrate molded part has a highly polished prismatic surface, the resulting finished parts don't have enough light reflectance.

Since I have no experience in the field, I don't know if it is the process itself or the way these people done it, that turned out the imperfect results.

I will appreciate any information and advise on the matter.

Thanks.

Archibaldo Hope
- Mexico DF - MEXICO

You can contact and review the following societies and associations for help:

http://www.aecnet.com I put this one in since it has to do with illuminating/reflectence

http://www.sme.org

The Aluminum Association Inc.
900 Nineteenth St NW suite 300
Washington DC 20006
202 862 5100

American Electroplaters and Surface Finishers Society
email: aesf@worldnet.att.net

American Society of Electroplated Plastics Inc.
email: namf@erols.com

Within the above groups I feel you will receive directions to help you find your answer. I would start with the last name on the list.

Good Luck
Ty

Tyrone L. caley
- Jefferson City, MO

Thanks for the handy list of contact info, Ty [Ed. note July 2005: unfortunately little of that contact info is accurate anymore]. But of the dozens of times that I've contacted professional organizations with technical questions, I don't think I recall ever getting an actual technical answer; rather they refer you to the list of consultants who advertise in their journals. So maybe Mr. Hope will talk to the consultants who advertise here and who pay the bills so his question can be posted in the first place :-)

Mr. Hope: Are you sure you have the concept -- the optics -- right? I was under the impression that retroreflectors function more like lenses than like mirrors. Don't they usually have a smooth top surface, with the sawtooth surface being on the back, not the front? I don't think the plastic in front is just a dust cover, I think it comprises a refractive element that is the whole basis of the thing. If you just aluminum coat the face of that sawtooth surface, the angle of reflection equals the angle of incidence, and I think very little light will reflect back. Then again, I'm no optics expert.

 
Ted Mooney, P.E.
Finishing.com Inc. - Brick, NJ

Ted is right. The coating needs to have a diffuse reflection so some of the light could be refleted in whichever direction you are. Consequently, a shiny refletive finish where the "angle of incidence is equal to angle of reflection" will not do. That is why metallic paints are used for street markings. These paints contain metallic powders that reflect the light back in random directions.

Mandar Sunthankar
ionEdge Corp

If I understand the original application (pavement markers), I would say that Archibaldo probably wants a retro-reflective coating. This will always send light back in the direction from which it was sent, similar to a corner-cube (three mirrors that are mutually perpendicular). A cost-effective way to do this is with glass beads inserted in the coating. The light entering the glass bead is reflected around and back out nearly anti-parallel to the incoming light.

A smooth surface will act as a mirror, where angle of reflectance equals angle of incidence and you won't see the reflected light if it's not perpendicular to the incoming ray.

Brett Cook
Otis Elevators - Tucson, AZ

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