Hi black screen fans
I haven't been on here in a while for various reasons. I have however been in the lab working on some improvements to the black screen design and, trying to solve, what I believe to be, one of the biggest diy mysteries there is. Namely, how do you stick 2 pieces of material together, when one is translucent, without there being visible adhesive marks, air bubbles or the material shriveling up? It sounds like a simple task in comparison to some other DIY issues, but it isn't'. You would not believe the amount of time and expense I have invested in researching this problem.
UP until now, I have joined my layers of material together by attaching them all to a rigid flat surface. By pulling them all tight and stapling them at the back, the tension was enough to hold them all together. I was happy with this method because it worked well and the absence of an adhesive improved the overall performance. The adhesive used to bond layers in most commercial screens can reduce brightness by around 8% for every layer of adhesive. The more layers, the more brightness is lost. In the interest of disclosure, the reason I have been working on this point is because I plan to release a commercial black screen for my business. I feel it is important to state that as I no longer consider myself to be an independent view on screens. Some of you know that I started the project because I was not satisfied with the commercial offerings available. Specifically that they were all outrageously priced and deliberately misleading in their advertising. I plan on putting my money where my mouth is and releasing a genuine low cost alternative that is affordable for everyone. Well, nearly everyone anyway...
For the commercial screen, I am using a hot stamping process to bond the layers which I have found to be preferable to using adhesives. This is difficult to achieve as a diy project without buying expensive and large equipment which would be silly for a one of screen project. In the spirit of this diy thread though, I still wanted to share some of the results of my tests in case somebody has a need to use an adhesive for their diy screen. This would be in scenarios where it is not possible or desired to buy a separate rigid layer. If you want to just use the wall to attach the materials to, for example, you would probably need to use some kind of adhesive to hold the layers together with no gaps. Anyone who has tried this, will know what a nightmare it is. Firstly, a significant number of glues will melt the PVC fabric and make it shrivel up. Secondly, even glues that claim to dry clear are normally still visible through the near transparent top layer. thirdly, sticking all the layers together with no air bubbles can be like trying to thread a needle using 2 bricks in terms of difficulty. I tested over 20 different adhesives and most ending up destroying my screen materials. I did find one method that is worth sharing.
Firstly, and this is important, find a water based glue that claims to dry clear. This should not be hard as they aren't rare. what they don't tell you is that they only dry clear if the layer of glue is thinner than you could evenly spread by hand. I figured that an advantage of water based glue is that they can be diluted with water to thin the mix. I added a little water to my glue and it spread a lot easier. It kinda looked like milk:
Next, I spread it on my dark layer using a foam spreader. Note how it still looks white at this point, even when thin:
It is important to clean both layers before applying the glue. Any bits of dirt and glue will gather around them and leave white marks on the screen. once it is clean, apply the glue and material straight away without leaving enough time for dust to gather again. might be a good idea to vacuum first too.
When you lay the transparent diffuser film on top of the dark layer, all the expected problems like air bubbles and visible white glue will become obvious. But, you planned ahead so no problem. You take a wide spreader or even a credit card and flatten the materials together. You then gently push all of the excess adhesive to the edges of the material. Don't worry about the edges because you will cut them off when it is dry.
With the watered down glue, it should be relatively easy to do this:
The vacuum you create by doing this as well as the smoothing effect will leave you with perfectly flat and smooth bonding. The remaining adhesive layer will be far thinner than you could get by using a brush and it will dry clear, just like when it is applied by machine. Note what I said about dirt. I didn't clean this sample material properly and you can see the dirt marks:
BTW, another design improvement is a new reflective layer which is many times thicker than mylar and has a black backing for extra strength. Mylars mirror finish gives very directed brightness which results in a visible increase in brightness between standing in the center and watching from the sides. This reflective material has a texture which spreads the brightness more evenly to give me a wider viewing angle with the black material. For those who do not need the extra brightness this is a good idea to give better uniform brightness and wider viewing when the lights are on.
The thicker reflective layer is a lot easier to work with. trying to stick thin mylar films without getting creases was near impossible for me. If you plan on using an adhesive, I can't emphasize enough, the importance of buying a thicker reflective material.
Once dry, using this reflective material, my new dark layer which is near black gave very good results. The lift in black levels you get from a darker screen is very noticeable. With the lights on, the black level performance compared to white or grey material is, well, night and day: