Help identifying material in LCD display

Thread Starter

Aleph(0)

Joined Mar 14, 2015
597
So I'm talking abt light-guide plate from _back-light_ assembly from old Acer ccfl monitors. It's 8mm thick piece of clear plastic with _masked_ white dots. So anyhow it looks exactly like acrylic (aka Plexiglass, Perspex, Lucite) or polycarbonate (aka Lexan, Galadrielite). But since it drills with std bit w/o cracking it can't be acrylic and turnings seem too brittle 2b polycarbonate:confused:?

So anyhow if thermal (like MP > 120°C) and chemical (resistance to oxidizing agents O3 and NO2) properties are there it's perfect low cost solution for our Tutorial readers needing electrically non-conductive chassis parts cuz junked out Acer ccfl monitors are abundant and usually free to take with huge gratitude from _donors_ :)

So anyhow sry if I lost point of post:oops: Here's question: what material is light-guide panel made of?

It's times like now that I know how much I totally miss the @gophert:(! But maybe someone else can help?
 

jpanhalt

Joined Jan 18, 2008
11,087
This link describes a flame test to tell acrylic plastics from polycarbonate: http://www.tudosobreplasticos.com/en/materiais/acrilicoPolicarbonato.asp

As primitive as that test may be, I have used it for that identification as well as to tell other plastics apart. Test your chips from drilling. Probably good to use known materials for your comparison.

Although acrylic does tend to crack more -- particularly with standard 118° drill bits -- smaller bits (<0.125") may do just fine, particularly if they are a little dull. In fact, a purposely dull bit ("dubbed" off) works well and over 1/2" holes can be drilled easily with acrylics. The purpose of dubbing is to create shavings and prevent "hogging in" (where the bit pulls itself into the material). Dubbing means to grind the cutting edge of the bit so it is not an acute angle, but rather meets the drilled surface perpendicularly and gives a scraping action.

Also, PC is more chemically resistant. Chloroform melts acrylic easily and less so with PC.
 

ian field

Joined Oct 27, 2012
6,536
So I'm talking abt light-guide plate from _back-light_ assembly from old Acer ccfl monitors. It's 8mm thick piece of clear plastic with _masked_ white dots. So anyhow it looks exactly like acrylic (aka Plexiglass, Perspex, Lucite) or polycarbonate (aka Lexan, Galadrielite). But since it drills with std bit w/o cracking it can't be acrylic and turnings seem too brittle 2b polycarbonate:confused:?

So anyhow if thermal (like MP > 120°C) and chemical (resistance to oxidizing agents O3 and NO2) properties are there it's perfect low cost solution for our Tutorial readers needing electrically non-conductive chassis parts cuz junked out Acer ccfl monitors are abundant and usually free to take with huge gratitude from _donors_ :)

So anyhow sry if I lost point of post:oops: Here's question: what material is light-guide panel made of?

It's times like now that I know how much I totally miss the @gophert:(! But maybe someone else can help?
No idea about the material you mentioned - but I've been told the liquid between the glass plates is toxic.

The glass is pretty easy to crack once you take it out of all those plastic layers.
 

Thread Starter

Aleph(0)

Joined Mar 14, 2015
597
This link describes a flame test to tell acrylic plastics from polycarbonate:
Jpanhalt TNX!:cool: --- So by criteria on linked test it's definitely Acrylic! Cuz it:

◊Burns clear w/o liberation of elemental carbon (so no soot or charring).
◊Continues to burn w/o torch once it's ignited.
◊Semi-molten burning sample foams up (bubbles).
◊Smoke has nasty characteristic garlicky acrylic odor.

So even though PC is nicer material I'm still vry happy cuz I say test for acrylic is more definitive than test for PC (by which I mean acrylic combustion [garlicky propenoate odor, foaming, no charring] sound unique compared to description of PC combustion which prolly applies to other plastics than just PC). Anyhow point I'm trying 2 make is that it's nice to know for sure:)!

Although acrylic does tend to crack more -- particularly with standard 118° drill bits -- smaller bits (<0.125") may do just fine, particularly if they are a little dull. In fact, a purposely dull bit ("dubbed" off) works well and over 1/2" holes can be drilled easily with acrylics. The purpose of dubbing is to create shavings and prevent "hogging in" (where the bit pulls itself into the material). Dubbing means to grind the cutting edge of the bit so it is not an acute angle, but rather meets the drilled surface perpendicularly and gives a scraping action.
Jpanhalt Tnx for that! Cuz Acrylic will meet our application just as long as we have way drilling it w/o cracking! So it's good 2 know large holes can be cut with just modified std bit:)! Cuz I can't find special _glass cutting_ bits in sizes > 0.25".

Also, PC is more chemically resistant
Since we'll be using acrylic just for structural parts, changes to lucency won't matter, but if oxidizing gasses (O3 and NO2) have bad effect on it we can protect it with just coating of hard wax or whatever:)!

Ian Rogers tnx for reply:)! So piece I'm talking abt isn't film it's just 8mm thick plate (that had CCFLs mounted along edges) to distribute light uniformly! But tnx for link cuz I salvaged films too so maybe we can also find repurposed use for those:cool:!

I've been told the liquid between the glass plates is toxic.
Ian Field I also say it's an oxymoron (_liquid crystals_:confused:?:D)! So being serious I didn't bother with the LCD _sandwich_ but I did salvage polarizing films:)!
 
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jpanhalt

Joined Jan 18, 2008
11,087
@Aleph(0)
Just a few notes about acrylic:
1) The bubbling is characteristic. I believe it has to do with acrylic sheets being cast. If vacuum forming, it is important to let it degas first. That step is not needed with PC, and I have not seen that caution mentioned when just bending with heat.

2) Acrylic glues that are based on chloroform (and probably similar) work well, but eventually cause crazing. Similarly, exposure to oils as in some types of caulking or even prolonged stress will cause crazing. That may take years to develop. PC does not seem so prone to crazing. When I needed a safe caulking for an acrylic windshield, I got a two-part, polysulfide adhesive/caulk that had mil approval. No problems with crazing over several years. Unfortunately, it is black.

3) Finally, very large holes (e.g., 100 mm) can be done with a fly cutter and a rigid drill press or mill.
 

Thread Starter

Aleph(0)

Joined Mar 14, 2015
597
@jpanhalt huge tnx for all the info:)! So I have another question which is are there different formulations of acrylic?

Cuz now I know those light guide panels are definitely acrylic from tests and just odor when it's hot but it's way more crack resistant than like home center _plexiglass_! Cuz I can drill it with big std bits, cut it with coarse blade hole saw, bandsaw and even just sawsall w/o cracking:confused:! So I'm thinking maybe it's specially formulated to enhance optical properties with unplanned _side effect_ of reducing brittleness:)?
 

jpanhalt

Joined Jan 18, 2008
11,087
Sorry, but I really don't know much about acrylic (PMMA) except for its basic chemistry and from practical experience. A search revealed there are different grades, which probably has to do with the way it is processed, surface coatings, and/or heat treated. One source mentioned "extruded" properties versus the usual cast properties. For example, if a plastic were reheated after casting and stretched or extruded, I would expect changes in physical properties. If plasticizers are used, they were not mentioned and are often trade secrets.

Here are a few of the interesting hits I came across:

1) This link describes various aerospace grades and MIL specifications for them. The terms, "cross-linked" and "semi-crosslinked" are used, so there must be some differences:
http://www.emcoplastics.com/aerospace-grade-acrylic/

2) These two links are nice "how to" resources:
http://www.dna.caltech.edu/~nick/Working with Acrylic.pdf
https://airandspace.si.edu/rfp/exhibitions/files/j1-exhibition-guidelines/5/Acrylic Sheet Fabrication Manual--Plexiglas.pdf

3) Finally, Boedeker offers two grades, a bendable version (AC-350) and non-bendable version (AC-300). The specifications provided for each are identical, except for one. The heat deflection temperature (ASTM D648) for the bendable version is 98°C and the non-bendable is 96°C. Since you seem to like the flame test, Boedeker presents an extended table here:
https://boedeker.com/Technical-Resources/Technical-Library/Plastic-Identification

John
 

Thread Starter

Aleph(0)

Joined Mar 14, 2015
597
@jpanhalt Tnx! I'll definitely check links out ASAP:)!

One thing though! I say Boedeker shouldn't be telling ppl to use smoke odor test on fluoropolymers cuz I totally guarantee COF2 isn't any nicer to lungs than COCl2:eek:! And maybe additional health risk cuz of cardiotoxicity of fluoride ion!
But just thinking on it, maybe greater reactivity of fluoride makes COF2 too stable to react with H2O to form HF?

So anyhow thought of COCl2 always made me nervous abt overheating vinyl! Cuz even cutting PVC with power tool indoors gives me _hebejebes_! It's like my ex-bf was always telling me I have makings of class A hypochondriac if I put my mind too it:oops::rolleyes:

So anyhow being totally serious TNX again:)!
 
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Take a look at pilot point or brad point bits for drilling plastics. Dewalt has a fractional index to 1/2".

Hand Dish washing soap and a little water can be used for lubercation.

I had to drill a few 5/8" holes to mount 3/8 Acrylic to a Unistrut frame for removeable sides with big wingnuts. the largest panel was probably 3" x 7' with big handles

I ended up grinding my own bit, so you have a point in the center and it cuts around the edge and you get a round hole.
 
So I'm talking abt light-guide plate from _back-light_ assembly from old Acer ccfl monitors.
So I have another question which is are there different formulations of acrylic?
Cuz now I know those light guide panels are definitely acrylic from tests and just odor when it's hot but it's way more crack resistant than like home center _plexiglass_! Cuz I can drill it with big std bits, cut it with coarse blade hole saw, bandsaw and even just sawsall w/o cracking:confused:! So I'm thinking maybe it's specially formulated to enhance optical properties with unplanned _side effect_ of reducing brittleness:)?

Ditto for 'light guide' panels used in Dell CCFL displays:)

Best regards
HP:)
 
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