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topic 2073

Light reflecting aluminum coating on molded plastic parts


(1998)

I am looking for a process and equipment to deposit an aluminum 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 disappointing 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


(1998)

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/reflectance

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, Missouri


--

Thanks for the handy list of contact info, Ty [Ed. note, years later: unfortunately little of that contact info is accurate anymore]. But these professional organizations generally don't offer actual technical answers; 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 first :-)

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 a dust cover; rather I think it comprises part of the 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, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(1998)

Ted is right. The coating needs to have a diffuse reflection so some of the light could be reflected in whichever direction you are. Consequently, a shiny reflective 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
- Fort Collins, Colorado


Reflective Glass Beads Trial pack of four sizes & qualities

(2002)

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
elevators - Tucson, Arizona



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