On Sun, 03 Feb 2019 14:54:48 -0800, Jeff Liebermann wrote:
> Thanks. Now I understand. The suggestions of using double sided tape
> is closest to the solution.
Hi Jeff,
I agree.
It's a simple question - but not an easy one to answer.
I thank you for asking clarifying questions, as you forced me to prove my
words, where I realized I hadn't looked at the situation closely enough
until I snapped those photos for you.
From the photos, and from your astute queries, I realized:
1. It likely is a "tape" (and not "just" a glue), and,
2. It is all around the perimeter (which I hadn't noticed prior).
> Usually, there's a die cut pre-form in
> the shape of the bezel on the phone supplied with the replacement
> touch screen. It's basically double sided tape cut to the exact shape
> needed to attach the digitizer. As mentioned, the backing tape is
> quite thin. I couldn't find one for your LG phone.
I agree now that I've looked more closely that it's an ultra thin tape
(most likely), and not a glue, per se.
> So, that leaves the question of what manner of glue was used on the
> die cut pre-form. My original guess was some manner of rubber cement.
It _does_ seem to be a "rubbery cementy" type gooey stickiness...
> The problem is that there are a fairly large number of different types
> of rubber cement, ranging from very permanent contact cement, to the
> thin temporary rubber cement sold in art supply stores for photo and
> picture mounts. Kinda like the weird glue used on Post-It notes.
Since the goal was to find a local supply of a "typical" glue, I will try a
local art-supply store, which should have "removable" gooey rubbery cement
- thanks for that idea!
> I have some of the die cut pre-forms for an Apple 3G which I can use
> to analyze the glue. However, I don't want to, don't have the time,
> and would rather be doing something more interesting. Sorry.
Nope. Please don't go to that trouble, Jeff.
You've helped more than anyone else on this newsgroup can, simply because
you comprehend the problem set and potential solutions better than those
Snit-like folks who always prove to know even less than I do.
You're a good detective, Jeff, since you "see" the problems, in problems.
(All they saw was a credit-card solution - which was never the question.)
BTW, I had first searched the canonical archives for this question:
<
http://tinyurl.com/sci-electronics-repair>
I also first searched the Internet - and only after both came up busted,
did I ask about the glue chemistry/physics here.
That has an interesting keyword which I was unaware of:
"Rhinestone pasting adhesive"
> <
https://www.ebay.com/itm/Mobile-Phone-Screen-Adhesive-Clear-Black-Liquid-Glue-B7000-T7000-E8000-T8000/232887790775>
That one is called "Mobile Phone Screen Adhesive", which I wish they had
more information in the description about other than it ships from China
(it's one reason I've never bought from Ebay in my life).
> Tape:
> <
https://www.ebay.com/itm/2-3-5mm-Double-Sided-Adhesive-Tape-for-Mobile-Phone-Touch-Screen-Repair-25M/302902142611>
That one seems almost perfect, in that it's a 2mm, 3mm, or 5mm "Double
Sided Adhesive Tape for Mobile Phone Touch Screen Repair 25M"
It takes about a month to arrive from China, but, at _that_ price, the huge
presumed risk of Ebay disappears, since $1.60 per roll is not risking much.
Given the dimensions, the 2mm tape can be trimmed to be used on the long
sides (~1.4mm), and the 5mm tape + 3mm tape can be used on the top
(~0.9cm), with two 5mm tapes on the bottom (~1.2cm).
The beauty, as with all repair solutions, is that the tape will definitely
come in handy for _other_ repairs around the home (as long as it stores
well).
The first object is a "glue removal liquid" and the second is a "uv glue"
which is what would be needed if there were no edges - but this phone has
plenty of edges.
The rest appear to be glue removal goops, which is fine but I think simple
alcohol and/or acetone should work for removal of the existing goopy stuff.
> Again, think heavily diluted rubber cement and die cut pre-forms.
Hi Jeff,
Since you speak logically, it's impossible to disagree with you.
o If glue, it needs to be high solvent that evaporates leaving goop
o If tape, it needs to be ultra-thin, which is what I think they used
>>I repeat that it's actually shocking, to me, how _well_ this plate works
>>given that only on the perimeter has _any_ glue!
>
> That's because the various layers of the sandwich are VERY flat and
> are held together by surface tension from water vapor in the boundary
> area. It's something like what holds gauge blocks together, except
> those usually have a layer of oil in addition to water vapor.
Smooth?
Hmmm.... interesting. Very interesting.
Certainly it works. Beautifully.
That it works is very interesting, since it's so simple (glass on glass).
I agree with you Jeff that it works _beautifully_, without having to put
any of that uv-cured glue on the actual screen - where it makes sense that
there is "something" in the physics/mechanics that makes the plate bond
beautifully to the glass.
>>And yet, there are no bubbles.
>
> Yep. The glass and plastic are not sufficiently elastic and will
> therefore not stretch sufficiently to create bubbles.
o What is the property called where two objects stick together because they are both very smooth?
<
https://www.quora.com/What-is-the-property-called-where-two-objects-stick-together-because-they-are-both-very-smooth>
"It is called wringability, named after the act of joining
("wringing") two gauge blocks together"
"Wringing requires two smooth, flat surfaces with surface finishes
of 1 microinch AA or better. For gage blocks, it becomes difficult
to wring surfaces if the flatness starts to exceed 5 microinches.
The sources of the forces holding gage blocks together are thought
to come from:
1. Air pressure from the surrounding environment as the air
is squeezed out when the blocks are slid together.
2. Surface tension from oil that remains on the gage blocks or
water vapor from the air acts as a glue to hold them together.
3. When two very flat surfaces are brought into such close contact
with each other, this allows an interchange of electrons between
the atoms of the separate blocks, which creates an attractive
molecular force. (This force will remain even in a vacuum or if
no oil or water is present on the blocks.)
The last two sources are thought to be the most significant."
>>Here's where the problem arose when we swapped plates:
>>7. The plate in the center was removed easily from the left phone
>>8. But we dropped it on the floor when moving to the right phone
>>9. In subsequent cleanup, we destroyed the "stickiness" of the glue
>
> Cleaning off the old glue, and replacing it with new glue will
> probably be beyond our capabilities. You can try using a rubber
> squeegee to apply a thin layer, but I suspect you'll need some kind of
> fixture to get any manner of consistency.
The main goal will be achieved if I can find the proper temporary goopy
stuff at an art store later today or later this week.
I don't think cleaning will be difficult, simply because it must react to
solvents, and even if not, mechanical scraping seems "doable".
> It's also not worth the
> effort as a new screen will do the job for less money and effort. Try
> some solvent (not sure what type) on the existing mess and see if the
> stickiness returns.
While a new screen will work, that was never the question simply because
the goal was to understand how it worked and then to figure out a glue that
does the job.
I think we've accomplished that goal, which is both a learning and
pragmatic experience. I will know more after I visit an art supply store.
>>I've seen the videos that use a "liquid" glue which is _not_ used here.
>>This is a static sticky goopy glue (sort of what's on the back of tape).
>
> When the carrier solvent evaporates, what's left is your sticky goopy
> glue.
In this case, the liquid refractively-matched glues don't apply.
>>If we could figure out what glue they use to put on the back of typical
>>tape (like Scotch tape), that would likely be the only glue we need.
>
> It's called a PSA (pressure sensitive adhesive) and is probably an
> acrylic (or acrylate):
> <
https://www.can-dotape.com/adhesive-tape-consultant/adhesives-used-for-tape/>
>
> "Scotch Transparent Tape"
> <
https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/scotchtape.html>
> Rubber shortages during the war prompted 3M to switch to
> synthetic acrylate adhesives. Although not as strong,
> acrylate adhesives retained their clarity and actually
> aged better than rubber-based adhesives, which turned
> yellow and brittle over time. Later, acrylate adhesives
> would be mated with an acetate backing to create "invisible"
> Scotch® Magic™ Tape, the first tape that could be written
> on with pencil, pen, or marker.
>
> Basically, it's acrylic plastic dissolved in some type of solvent.
That's an interesting set of finds, which I agree with you on the analysis
of. I think the solution is simply to find that acrylic plastic in the arts
and crafts stores, which it would seem to exist most since they do more
temporary tacking than the box store stuff is designed for (I would think).
>>1. There _is_ glue on the entire perimeter
>>(Where I had thought it was only on the top & bottom.)
>
> Ok, if there is glue all over the screen, then it has to be very thin,
> not very sticky, achromatic (so the colors don't change), and very
> very very clear. That's not something you'll find at the local
> hardware store.
Ooops. I meant only on the thin perimeter is there glue.
(Long sides is about 1.5mm, top & bottom around 1cm.)
The entire "active" portion of the screen is devoid of glue.
> I don't think the layers of the sandwich will slide over each other,
> but they curl or slip from uneven temperatures.
The protective glass screen "is" itself a sandwich of at least glass on the
outside and plastic on the inside.
That protective screen is then placed on top of the phone glass, and that
is the perfect fit.
>>The question becomes:
>>o Where does one get the sticky glue that is on typical tape?
>
> First, you have to identify it. I usually start with a patent search.
> Look for "pressure sensitive adhesive tape LCD".
> <
https://patents.google.com/?q=pressure&q=sensitive&q=adhesive+tape+LCD>
>
> This one looks interesting:
> <
https://patents.google.com/patent/US20040191509A1/en?q=pressure&q=sensitive&q=adhesive+tape+LCD>
> ...examples of which include known or usual pressure-sensitive
> adhesives such as acrylic pressure-sensitive adhesives,
> silicone based pressure-sensitive adhesives, polyester
> based pressure-sensitive adhesives, rubber based
> pressure-sensitive adhesives, and polyurethane based
> pressure-sensitive adhesives. The pressure-sensitive adhesive
> can be used singly or in admixture of two or more thereof.
> So, it can be acrylic, silicone, rubber, polyurethane, or a mixture of
> the aforementioned. Not very helpful, but at least it's a start.
Thanks Jeff,
I think I can take it from here in that you've helped determine
o It's almost certainly an ultra-thin tape (originally a die-cut tape)
o A pressure-sensitive adhesive would also work
o The best source for the tape & adhesive is (apparently) overseas
o While a reasonable facsimile can likely be found in local art stores
I'll visit a few art stores today to see if I can find the glue or tape
locally (I have never bought from Ebay due to the risk but in this case at
the prices you found, the loss risk, even if real, is low).