I’ve got a collection of old LCD panels that I want to turn into LED lights by salvaging their backlight. In the course of doing so, I also get some auxiliary pieces like a rigid metal frame. Another common piece that I’ve been working to salvage is the polarizer film. A sheet of polarizer film is a part of every LCD panel, interacting with the liquid crystals within to block or allow light as needed to create the picture on screen. Because it is directly on the optical path, it’s important for it to be held against the screen in a way that minimizes optical distortion.
In practice this means a very thin layer of very tough clear glue that keeps the film flat against the glass. I’ve been struggling with how to best salvage the polarizer film. While I could peel it off the glass, that leaves a layer of glue that I have yet to figure out how to remove. I worked my way from isopropyl alcohol to mineral spirits up to acetone. I found that acetone would dissolve these glues very well, but using enough to dissolve the glue also damages the film. I have yet to successfully clean off a sheet of polarizer film.
As an experiment, I want to see if I can sidestep the problem of removing the glue. Instead of trying to clean it off, keep the glue and instead transfer the polarizer film along with its glue onto something more durable and clear than the glass layers of a LCD panel. I decided to start with a sheet of acrylic I had bought for laser cutting. The pandemic cut me off from the laser cutter I had planned to use with it, so it is now fair game for use in this project.
As I did before, I left the LCD assembly in the hot Southern California summer sun to soften the glue. It didn’t take much heating, two thin layers of glass and a sheet of plastic film had very little thermal inertia. So little, in fact, that the glue solidified and cooled within a few minutes after being taken into the shade. This is disappointing, because it meant I need to move back outdoors and perform this work under the sun.
I’m still learning to work with such fragile sheets of glass, so it wasn’t a surprise when I cracked it (further) making this polarizer film project difficult. Annoying, but not a surprise.
Thankfully a LCD panel had multiple edges, so rather than give up I turned the panel 180 degrees and started peeling the other side for practice.
I was able to peel the remainder without further cracking glass, and transferred to my acrylic sheet for a quick test.
There are a lot of air bubbles in there so the result is pretty bad, but there are portions where the glue happily sucked back down to the sheet of acrylic leaving an optically clear path. If I can figure out how to increase the percentage of area that shows this clear path, I think this approach can work. This particular example, however, is pretty screwed. Any attempt to make that adhere optically clear will be continually foiled by tiny bits of broken glass.
But even though I think it’s doomed to failure, I see a learning and practicing opportunity before me so I pulled out a razor blade and started trying to remove the broken glass pieces. This is a terrible idea. I’m dealing using a sharp piece of steel to deal with with sharp pieces of glass. Not only does the blade scratch and damage the film surface, it can’t get all the little glass pieces. I have not set myself up for success with this test, but at least I managed to avoid cutting myself open in this exercise.
The results were completely unusable. That said, it actually turned out far better than I had expected. In this picture the glass shards I had removed are sitting on the keyboard beyond the polarizer film and acrylic sheet. They are several centimeters away and there’s enough clarity for us to see them. I think there is promise in this transfer approach and I intend to practice it on the next few panel salvage projects. In fact, the very next panel salvage started with the polarizer.