https://www.cospheric.com/P2453_solid_glass_spheres_retroreflective.htm

A paint company that doesn’t wish to remain nameless tried and gave up on using these for a highly reflective paint, because they couldn’t think of a way to orient the retroreflector to shine the reflected light outwards. One approach that almost worked is to use the different surface tension of the glass and aluminium to orient the spheres, but that gives such a slow operation that it can only be used in a very slow drying low viscosity paint formulation, so only on horizontal surfaces.

Brainstorming wanted, to think of a way to get a better highly reflective paint using these, or some other method.

Brainstorming also wanted, for how they managed to get the half-coating in the first place.

“Retroreflective Half-Shell Aluminum Coated Solid Glass Microspheres. Metallized spheres product line consists of solid, barium titanate glass microspheres with a 40 – 50 micron typical mean diameter and a tight particle size distribution. Coating: Half-shell Aluminum.”

Don’t use the paint to stick the glass beads on, use normal paint then a transparent sticky kind-of film over the top. Place the beads on the film in the desired orientation, then stick the film over the painted surface. Then a cost of clear paint over the top if required.

Spiny Norman said:

Don’t use the paint to stick the glass beads on, use normal paint then a transparent sticky kind-of film over the top. Place the beads on the film in the desired orientation, then stick the film over the painted surface. Then a cost of clear paint over the top if required.

Thanks. I’ll think about this some more.

use nanobots to paint each one

alternatively throw the glass beads on the paint whilst its still wet and the beads stick in the paint with the clear face outwards

mollwollfumble said:

https://www.cospheric.com/P2453_solid_glass_spheres_retroreflective.htm

A paint company that doesn’t wish to remain nameless tried and gave up on using these for a highly reflective paint, because they couldn’t think of a way to orient the retroreflector to shine the reflected light outwards. One approach that almost worked is to use the different surface tension of the glass and aluminium to orient the spheres, but that gives such a slow operation that it can only be used in a very slow drying low viscosity paint formulation, so only on horizontal surfaces.

Brainstorming wanted, to think of a way to get a better highly reflective paint using these, or some other method.

Brainstorming also wanted, for how they managed to get the half-coating in the first place.

“Retroreflective Half-Shell Aluminum Coated Solid Glass Microspheres. Metallized spheres product line consists of solid, barium titanate glass microspheres with a 40 – 50 micron typical mean diameter and a tight particle size distribution. Coating: Half-shell Aluminum.”

wookiemeister said:

alternatively throw the glass beads on the paint whilst its still wet and the beads stick in the paint with the clear face outwards

Start brainstorming, part 2 first.

How the heck do you coat half of microspheres with aluminium without coating the other half?

A few possibilities come to mind.

• Sit the glass beads on a hard surface and fire micron-size aluminium particles at them – sputtering, would produce a non-uniform layer.

• Sit the glass beads on a hard surface. Coat a rubber surface with ink containing aluminium, and press the rubber onto the top of the glass beads, printing the aluminium ink onto the glass beads. Then heat the result to remove the liquid component of the ink.

• Other printing methods such as using a roller or silk-screen printing.

• Fire the glass beads into a soft surface such as styrofoam so that they are half-embedded. Then coat the visible surface using vapour deposition at high temperature in a vacuum.

• Pour the glass beads onto a horizontal plate containing a liquid, chosen to have a high boiling point, low viscosity and surface tension phobic for the beads. Choose a liquid level that just covers the bottom half of the beads. Then high temperature vapour deposit a layer of aluminium on the exposed parts.

• Pour the glass beads gently onto a liquid containing aluminium. Evaporate off the liquid leaving aluminium attached to the bottom half of the spheres.

The second last of the above is probably how they actually do it. The last of the above is the only one that coats the bottom half of the spheres with aluminium. So that’s the only one that has the spheres in the correct orientation to be retroreflectors.

Then if the paint uses glass bead microspheres that do not have retroreflectors on the bottom, on top of a paint containing lots of very finely ground aluminium flakes, then wookiemeister’s method looks like the best way to solve the problem. The paint itself then provides the retroreflector, not the spheres.

mollwollfumble said:

mollwollfumble said:

https://www.cospheric.com/P2453_solid_glass_spheres_retroreflective.htm

A paint company that doesn’t wish to remain nameless tried and gave up on using these for a highly reflective paint, because they couldn’t think of a way to orient the retroreflector to shine the reflected light outwards. One approach that almost worked is to use the different surface tension of the glass and aluminium to orient the spheres, but that gives such a slow operation that it can only be used in a very slow drying low viscosity paint formulation, so only on horizontal surfaces.

Brainstorming wanted, to think of a way to get a better highly reflective paint using these, or some other method.

Brainstorming also wanted, for how they managed to get the half-coating in the first place.

“Retroreflective Half-Shell Aluminum Coated Solid Glass Microspheres. Metallized spheres product line consists of solid, barium titanate glass microspheres with a 40 – 50 micron typical mean diameter and a tight particle size distribution. Coating: Half-shell Aluminum.”

wookiemeister said:

alternatively throw the glass beads on the paint whilst its still wet and the beads stick in the paint with the clear face outwards

Start brainstorming, part 2 first.

How the heck do you coat half of microspheres with aluminium without coating the other half?

A few possibilities come to mind.

• Sit the glass beads on a hard surface and fire micron-size aluminium particles at them – sputtering, would produce a non-uniform layer.

• Sit the glass beads on a hard surface. Coat a rubber surface with ink containing aluminium, and press the rubber onto the top of the glass beads, printing the aluminium ink onto the glass beads. Then heat the result to remove the liquid component of the ink.

• Other printing methods such as using a roller or silk-screen printing.

• Fire the glass beads into a soft surface such as styrofoam so that they are half-embedded. Then coat the visible surface using vapour deposition at high temperature in a vacuum.

• Pour the glass beads onto a horizontal plate containing a liquid, chosen to have a high boiling point, low viscosity and surface tension phobic for the beads. Choose a liquid level that just covers the bottom half of the beads. Then high temperature vapour deposit a layer of aluminium on the exposed parts.

• Pour the glass beads gently onto a liquid containing aluminium. Evaporate off the liquid leaving aluminium attached to the bottom half of the spheres.

The second last of the above is probably how they actually do it. The last of the above is the only one that coats the bottom half of the spheres with aluminium. So that’s the only one that has the spheres in the correct orientation to be retroreflectors.

Then if the paint uses glass bead microspheres that do not have retroreflectors on the bottom, on top of a paint containing lots of very finely ground aluminium flakes, then wookiemeister’s method looks like the best way to solve the problem. The paint itself then provides the retroreflector, not the spheres.

Brainstorming Part 1.

• Use a thin layer of metal based paint then apply uncoated microspheres. As the paint dries it leaves a reflective back coat on the spheres. Then once the first coat has fixed the spheres in place, apply a second thin layer that is phobic to the sphere material, but sits between the spheres to give the result colour. Then if desired ass a third clear coat, although be aware that this could interfere with the reflectivity because of the different refractive index.

• Use the aluminium half-coated microspheres, but pre-corrode the aluminium layer a bit (in a hot wet salt-laden chamber) to reduce the contact angle from > 90 degrees down to < 1 degree. This speeds up the self-orientation process using surface tension.

• Use a base coat, then a second coat that contains a polymer in very low concentration that has one end that attaches firmly to aluminium and a second end that attaches firmly to the base coat. The polymer twists the half-coated microspheres into correct orientation.

• Perhaps a sphere isn’t the best shape for a retroreflector. For example, a cube corner reflector is an ideal reflecting shape. Also consider pyramids and diamond shapes. Choose a shape that combines the best retroreflecting ability with the ability to self-assemble into sheets. For example, a flat back will lay flat on a gloss base coat or its own volition. Use ray-tracing for choosing this shape, and casting in dents in metal to manufacture them.

Those are basically the only four ideas that I came up with. I did think of electrostatics, the aluminium back of the sphere at a different electrostatic charge to the front, but I couldn’t see how to make it work.

now i’ve read the question

assuming you can coat the glass spheres

throw aluminised glass beads onto the wet paint

then wipe the dry surface with a chemical that only removes the aluminium from the glass sphere (acid ?)

the exposed glass beads have their aluminium coating removed leaving only the back of the sphere in the paint left intact

so its a three step process

paint some paint that has a type of contact adhesive quality about it

throw the beads totally coated with aluminium onto the contact adhesive type paint

wait for paint top dry then wipe the painted surface with a light acid to remove the aluminium off the bead