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I'm sorry, I may be slightly out of topic. I'm just an occasionnal "handyman" and I did not found any helping ressource on the web.

I'm willing to protect a touch screen and none of the usual offers satisfies me. In the screen protection market, there are usually 3 materials. The old basic one -I don't remember exactly the name of it-, the tempered glass and the TPU.

I love TPU and I feel like it really is underrated, maybe because most industries like our screens to break so often. I've always saw semi-hard TPU full shells for Iphone but when I try to find the same kind of product for my phone, I just have the choice between an ultra thin TPU protection or nothing. I would prefer a thick TPU protection to a tempered glass but a thin one is just useless.

So, sorry for the long intro, I decided that I would make my own, probably cutting it out of an Iphone case. The problem is : it will have to stick on the screen by itself, while on the Iphone I think it's fixed just by fitting around the phone. What is the material that makes screen protectors stick to a screen while keeping it removable and letting electrical signals trough ?

Thanks a lot for sharing you knowledge with me

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  • \$\begingroup\$ It's unclear what you are asking here, but it seems to be a polymer materials question not an electrical engineering one. What is quite clear is that it does not belong here. \$\endgroup\$ – Chris Stratton Mar 13 '19 at 7:53
  • \$\begingroup\$ It's about capacitive screens and materials that can be used on them. Indeed what I want to create isn't electrical but I'll need sth used in electrical engineering. My question was clear & I made a quite long intro to make it understandable. I asked this here because I saw a similar question about capacitive screens but the answers weren't useful for my own question. However, I'm not surprised to get a rude comment, as it's the tradition on stack " "exchange" ". But thks anyways, I guess I'll have to ask it to a forum where people really try to help each others, not just earn reputation pts. \$\endgroup\$ – Shane F Mar 13 '19 at 18:49
  • \$\begingroup\$ Chris wasn't being rude. On SE it's normal to migrate questions to more suitable forums. I would tend to say the question of whether TPU can be used as a screen protector is relevant to EE, but at it's heart this is a materials engineering question, and will always be handled by an engineer that designs cases(if an engineer is involved) rather than an engineer that designs electronics. From the EE perspective, the most important factors in protecting a screen without impeding capacitive sensors is specifically to keep the coating thin. \$\endgroup\$ – K H Mar 14 '19 at 4:04
  • \$\begingroup\$ This is why sacrificial glass/crystal screen protectors that dissipate a large amount of force by shattering in place of the screen or military grade soft plastic screen protectors that spread force for non sacrificial protection are the norm. I did some research on TPU and while it does appear to be a promising material, the phone cases I searched appear to be far from the best protection for overall design. They offer good shock absorption and abrasion resistance for their thickness but little rigidity or dimensional stability. \$\endgroup\$ – K H Mar 14 '19 at 4:09
  • \$\begingroup\$ If you simply want the best protection and are willing to disregard size, a mixed material case with shock absorption, rigidity and a deep bezel will be your best option and for the screen, multiple layers of glass screen protector or an inner layer of glass and an outer layer of scratch resistant/repairing shock spreading plastic(possibly TPU) would represent your best option. Which adhesive would be suitable for a DIY protector is indeed purely chemical engineering, and I doubt someone here will know offhand, but I would ask at a cell repair store about the liquid they use to \$\endgroup\$ – K H Mar 14 '19 at 4:14
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The properties of TPU and the sensitivity of your capacitive touch sensor and your desired "feel" of sensitivity will determine your maximum protector thickness. I don't know if phones have a sensitivity adjustment in software that would be relevant, and and EE or programming stack exchange answer would be suitable for that. You would have to be careful not to phrase it as a "use of consumer goods" question, which is forbidden, and you'd need some programming and phone hacking skills to get a useful answer, so you may wish to simply find a method to determine maximum thickness of your desired materials, such as simply applying normal thickness layers over each other to determine the thickness.

I've been completely satisfied with a thick, rigid bezel(far more effective than screen protector for most bend/drop situations, especially edge drop situations. For the odd time you drop your phone face down on a piece of ceramic or self-tapping wafer screw(hard object), if double thickness is not adequate for you, I would suggest an extremely thin regenerative wet install film for an inner layer, a sacrificial tempered glass protector over that to provide rigidity, and your TPU layer on top of that for abrasion resistance and shock absorption for the tempered glass. I believe this may even allow the inner screen to survive fairly hard hits on "magic" rocks and "immovable objects", like toilet ceramic or diamond, or firmly mounted pieces of hard metal. A thick TPU protector would survive hits better itself, and protect the screen better for many types of hit than a thinner protector of the same material, but is much too flexible to provide decent protection from hard point hits.

I'm pretty sure the adhesive need simply be optically clear, wetting to some degree and of course temporary and suitable to both materials.

Having decided that, an EE can only call around to chemical engineering companies and adhesive suppliers to see what might work, and in the industry that particular task would be rare for and EE as it would likely be done by a materials engineer, case designer or phone retailer/repair agent.

What adhesives have those properties, is indeed a product knowledge(shopping questions are not allowed although we typically give a few days for people to volunteer what we know offhand before inappropriate questions are migrated or deleted) or materials engineering question, which should be re-asked on the correct stack rather than migrated in this case, as this question now has an EE answer, to the degree that it is an EE question. The Engineering Beta(general engineering) stack exchange or physics stack would be the best places to ask that, as far as I know there is no chemical or materials engineering stack.

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