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-   -   Glass sand-blasting beads in DIY screen (https://www.hometheatershack.com/forums/diy-screen-development-testing/55345-glass-sand-blasting-beads-diy-screen.html)

electronbee 02-22-12 02:54 PM

Glass sand-blasting beads in DIY screen
 

I found this earlier today about a guy who made his own, painted screen, and he applied a layer of glass beads used in sand-blasting.

http://makeprojects.com/Project/Glas...n-Screen/685/1

Harpmaker 02-22-12 05:03 PM

Re: Glass sand-blasting beads in DIY screen
 

Quote:

electronbee wrote: (Post 500491)
I found this earlier today about a guy who made his own, painted screen, and he applied a layer of glass beads used in sand-blasting.

http://makeprojects.com/Project/Glas...n-Screen/685/1

The main problem with that tutorial is the size of glass beads used. They are listed as being 80 grit which roughly equates to 195 micron. This is WAY too large a bead to use for a projection screen for most personal HT's. In comparison, the Da-Lite High Power glass beaded screen used to use 9 micron beads (the newer version uses a bit larger). I have some 50 micron beads I got at a craft store and these are also too large to make a good screen.

To give you an idea of what a difference the size of the glass bead used makes here is a microscope photo I took of my 50 micron beads. Now take notice of the much smaller glass beads underneath the larger ones. These are from an extremely expensive reflective paint that came from overseas.

http://i180.photobucket.com/albums/x...ndbeads2-1.png

electronbee 02-23-12 01:56 PM

Re: Glass sand-blasting beads in DIY screen
 

Is the overseas paint from Australia?

Any ways, this has me interested and I have been searching for very small glass beads. I wonder where they got such small glass beads?

Harpmaker 02-23-12 02:20 PM

Re: Glass sand-blasting beads in DIY screen
 

Quote:

electronbee wrote: (Post 500795)
Is the overseas paint from Australia? I wonder if its the DIYTheater paint, like what I sent you

I believe it was from the U.K..

One of the big problems with making retroreflective screens is getting an even application of the beads (even if you can find the right size). The beads pretty much have to be applied after the final layer of paint is sprayed/rolled, but it isn't as simple a process as the page you linked to makes it sound. If the paint is too wet the beads will sink too far into the paint, if it's too dry they won't sink in deep enough and will be easy to brush off the screen as well as not performing as they should.

As for paint that has beads already in it, there is a real problem getting even coverage when rolling or spraying. Not enough paint and the results are "splotches" of varying reflectance; and the same problem occurs if too much paint is applied!

The best retroreflective screen results when a single layer of beads are put down so that 1/2 of their diameter is below the surface of the paint. In the case of commercial screens the beads are applied by electrostatic attraction, something the DIY'er can't do.

Quote:

Any ways, this has me interested and I have been searching for very small glass beads. I wonder where they got such small glass beads?
We found several sources for beads of the proper diameter, but they were fantastically expensive! They were sold by the gram! Other potential sources were only interested in selling in 25 kilo amounts!

If you want to do your own research into this look for glass beads (preferably with a refractive index of close to 2.0) in the 10 micron to 25 micron size range.

electronbee 02-23-12 03:43 PM

Re: Glass sand-blasting beads in DIY screen
 

Wow... they got the bead application down to a serious science with using electrostatic forces to pull them down. Almost sounds like a powder coating process but more refined.

electronbee 02-24-12 01:37 AM

Re: Glass sand-blasting beads in DIY screen
 

1) OK... I found a place that sell them, they are called "glass microspheres" and they sell a kilo for $79 and 2 or more kilo for $64/kg. This is for a D90 size of 8um with a mean diameter of 3.5-5.5um, index of refraction is ~1.51

Assuming these can work, this actually sounds feasible to me. However, I have no idea how many kilos I would have to buy for a 4'x8' screen. I'll have to look into how they are mixed, by weight, or by volume.

EDIT: OH SHAZZAM! You can get optional coatings: Fluorochemical and Silane. Fluorochemical aides in bringing the spheres to the surface and Silane improves their dispersion.

Glass microsphere data sheet

2) I found a company that makes a two-part reflective paint that uses glass beads. The size they use is huge, like the link I posted here first, but they state the the two-part epoxy is designed so that the beads "float" to the surface. Hrmmm... Maybe, their paint can be used with the beads that I found above?

Harpmaker 02-24-12 08:46 AM

Re: Glass sand-blasting beads in DIY screen
 

That is a great find eb! :clap: I'll check that first site more thoroughly when I have some time. The beads you listed could well work, but they aren't all that round (85%) and the mean size is between 3.5 and 5.5 micron. This is getting a bit small. Something I found out several years ago when I was looking into retroreflectivity (I believe it was in a paper by NASA) is that when glass beads get very small they become optically dispersive and actually deaden reflection. Unfortunately they didn't say at what size this happens.

It looks like you are on the right track! :T

Harpmaker 02-24-12 09:18 AM

Re: Glass sand-blasting beads in DIY screen
 

If I was going to experiment with these beads I would try the D90=18 micron size.

lastword 04-08-12 11:33 AM

Re: Glass sand-blasting beads in DIY screen
 

There is artist supply paints that have glass beads in them. Expensive.. and you don't wanna screw up.

electricly charging the paint can be as easy as applying heat.

I used an aluminum screen once and had various metals in the mix geometrically cut and used a powder coater to apply the coating and we heated the aluminum to provide the directionality desired for the screen.

It was way more expensive than just going out and buying a screen and the application process was pretty fatiguing.


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