Conductive plastic film? - Page 1
Forum section: electronics / projects

author: iXod
author_rank: Frequent Contributor
timestamp: July 09, 2018, 03:15:40 pm
content: Working to eliminate a static problem on a laminating machine in a print shop. The machine unrolls plastic laminate and with heat & pressure adheres it to printed sheet labels.The combination of unrolling the laminate and blowing air to separate the sheets when feeding into the machine results in high levels of static voltage. The machine will reset when a discharge occurs at any of several points along the machine.We have installed several Keyence ion generating bars (16 nozzles each) to flood areas of the machine with negative ions to help neutralize the charge. Also copper “tinsel” (providing a path to ground) is contacting the media at several points along the path. This has helped.Our present focus is on the operator’s panel (see photo): when the operator touches the keypad and a discharge occurs the display will blank (and even fail--we’ve replaced it twice already) and the machine will halt/reset.I am looking for a conductive plastic film that I can put over the keypad and ground so as to discharge the voltage safely (3M copper tape with conductive adhesive at hand, so as to ground the film). It should be thin so as to not press multiple keys when aiming for one.Yes the solution is to eliminate the source of the charge but I think we’ve done all we can do there--any further ion generators have (and will) given diminishing returns.Looking for answers to my question re. conductive plastic film.Thanks.

author: IDEngineer
author_rank: Super Contributor
timestamp: July 09, 2018, 03:59:02 pm
content: The copper "tinsel" is interesting. BTW, laser printers solved this problem long ago with conductive plastic bristles, since the entire process relies on electrostatics they have to manage charge rather well.Sounds like you're trying to use a "shield" on the control panel to equalize the potential between the panel and the operator. Instead, how about moving the discharge to a point AWAY from the (apparently) sensitive electronics? For example, how about a conductive wristband like those used at ESD-safe workstations with its electrical connection point a nice distance away from the electronics? Those wristbands have nonzero impedance (for HV safety) but still equalize potential. If the operator put on the wristband before operating the panel, any charge difference would be equalized before they touched the panel AND no new potential could build up while they were standing there between keypresses.Just a concept to consider.Update: Here's a $6 example from Amazon:https://www.amazon.com/Rosewill-Grounding-Alligator-RTK-002-Detachable/dp/B004N8ZQKY...and a photo is attached. There are many such products on the market from a variety of suppliers.

author: iXod
author_rank: Frequent Contributor
timestamp: July 09, 2018, 04:09:09 pm
content: Thanks for your suggestion.The more I think about it the more unlikely it is to succeed. The theory of discharging the operator is sound, it's just that he ranges all around the machine (rollers and chains, etc, running all the time) and leaves the machine to fetch more paper to feed. Risk of entanglement of the ground lead and need to disconnect/reconnect means it will be problematic.Thanks again.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 09, 2018, 04:38:23 pm
content: The panel looks metal (painted, with holes in it for the various bits), but I'm willing to bet it's a shitty ground at best. Relatively extreme but best-case solution: grind off the paint around the perimeter of said panel, where it mates with the rest of the enclosure; insert EMI gasket stock.The display could stand to be grounded (RF grounded that is, and assuming the internal signals themselves are not also noisy as hell: in which case, that should be fixed first, otherwise these steps will probably make things worse before they get better!), and the keypad might not be easy to ground, but its signals can probably be filtered to ground.It's absolutely the kind of thing a technician can do, but it requires an engineer to figure outwhatto do. Preferably with many instruments and direct access to the equipment. Unfortunately this isn't something easily diagnosed remotely...Tim

author: IDEngineer
author_rank: Super Contributor
timestamp: July 09, 2018, 04:40:38 pm
content: Quote from: iXod on July 09, 2018, 04:09:09 pmThere are also conductive floormats, for the same reasons. I'd surround the machine with them so operators are always maintaining the same charge relative to the machine.

author: David Hess
author_rank: Super Contributor
timestamp: July 09, 2018, 04:41:43 pm
content: Some switches and displays are terrible in regard to ESD shielding. At best the plastic just serves as a spark gap guarantying that only the largest discharges get through while allowing small charges to remain and accumulate until they are large enough. Light pipes are particularly bad in this regard.The first thing I would try is punching out a metal shield to place over the keyboard which is held down by the existing corner screws.

author: iXod
author_rank: Frequent Contributor
timestamp: July 09, 2018, 05:40:12 pm
content: Quote from: IDEngineer on July 09, 2018, 04:40:38 pm"Conductive" floor mats don't help any more than if the operator is standing (in his shoes) on bare concrete floor. If an operator has a charge standing in his shoes, a conducting (a.k.a. ESD) floor mat does nothing more to dissipate that charge than if it weren't there.Floor mats are never used to help with an ESD issue. They are used to help with fatigue issues (standing stresses on the lower limbs and feet) and are required to *also* not insulate the operator from ground.If a floor mat is desired to cushion the operator, you don't want that mat to *insulate* the operator from ground, so they are made conductive to dissipate any charge *as measured from the bottom of his shoes*. If is body (his skin) is insulated from the bottom of his shoes due to rubber soles or such, he will hold a charge regardless the surface he is standing on, even bare metal.I think the solution is a "heel ground strap", something like this:https://www.grainger.com/product/20FX03?cm_mmc=EMT-_-OrderConf2018EnhanceControl-_-Offline-KPIRPE-_-Item&RIID=19288317&GID=723168289&mid=OrderConfirmation&rfe=b26dbbfe9791a6349cb9ac968f7c6882426fa0cbd34ab0bf5f51d0e6765ee6f6which reduces the resistance from the operator's body (skin) to the underside of the shoe, dissipating any charge to *whatever* surface he is standing on.

author: tooki
author_rank: Super Contributor
timestamp: July 09, 2018, 06:50:00 pm
content: What about using an antistatic spray like Kontakt Antistatik 100?http://www.crceurope.com/wwwcrc/tds/TKC3%20Antistat100.pdfAs I understand it, these leave a thin, slightly conductive coating that's enough to dissipate static. Would this, sprayed over the switch panels such as to make contact with the grounded metal, not do the trick? (At minimum, for $8 a can, I'd give it a shot…)

author: CopperCone
author_rank: Super Contributor
timestamp: July 09, 2018, 09:57:29 pm
content: Ok. If you want a real solution for protection, for high voltage ESD, you probably want a faraday cage shield. They sell little plastic strips with tiny wires in them that you can put ontop of a LCD screen. The edges are exposed so that you can bond them to the chassis, either through mechanical joints (like fingers that push into it), solder, conductive tape (don't recommend) or conductive epoxy.They also have screens coated with gallium arsenide, which will have a slightly green tint. They are meant for EMI protection, I don' know how well they hold up towards static discharge.Search for transparent EMI shielding on google.You can buy the strips prefabricated, with the mesh exposed on the edges. The wires are very fine, so it does not block the display too much.I say you should shield the LCD because I have seen them cause problems before when a spark is discharged near by, on a very similar display, mounted on a metal chassis.As for the keypad, a solution that might work, is to pop the keys off, fit a mesh o screen that's grounded to the chassis around the key holes, then give the keys a good coat of conductive paint, so when you touch them and depress it, you complete a circuit with chassis ground. Make it so the key touches the screen as its depressed. I don't know how well this will work though, it depends on the geometry of the keys. You might also want to use conductive epoxy ontop of the silver paint to glue something like RF fingers on the perimeter of the key, so you are not relying on contact between a grounding plate/screen and conductive paint as you depress the key, as the paint might ware away and it would be difficult to test its integrity. You can probably use thin brass for the screen and cut the form out with a exacto knife. Adding fingers to the keys would be an experiment for you.If you don't add some sort of fingers to ensure make or break contact, you might make the problem worse by making the key surface conductive since it would allow for easier charge transfer from your body.A method might be to make thin diagnol slots on the bottom of the keys that you put brass fingers on. I don't know what gauge of material or angle would work well for ergonomics, but it would be fun to make .Also what was said, to ensure that there is good contact between the panels. This means that you need to take it apart and look to see if there is paint getting in the way. Since there is a problem you should probably grind the paint off all the edges and install EMI fingers.**************Shit,its a cheap rubber keypad not something like a keyboard. That rubber shit will be difficult to modify to ensure good contact with a shield.One way to do it would be to install solder braid strips over the keys, like little blindfolds, so when you go to press a key your finger touches a copper braid first. It will look retarded. Or just put a conductive mesh that can deform over the entire thing and replace it after a while. Would look super trash though. Or you can put metal pieces through the keypad keys, but this is all begining to look like a Hannibal lecter project to me.Maybe find something pin compatible that does not look god awful and put it over the existing keypad and connect with a shielded cable?

author: David Hess
author_rank: Super Contributor
timestamp: July 09, 2018, 11:23:14 pm
content: They also make very thin metal mesh screen which can be used over displays. Tektronix used it over their oscilloscope CRTs as EMI shielding.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 09, 2018, 11:39:42 pm
content: Quote from: blueskull on July 09, 2018, 10:54:26 pmMaybe a poka-yoke solution: put a metal bar or thin table in front of the machine, so people tend to lean on it when standing there.Tim

author: jpanhalt
author_rank: Super Contributor
timestamp: July 09, 2018, 11:46:58 pm
content: How about a conductive mat at the control station(s) and conductive shoes for the operator. When flammable gases were used for anesthesia (e.g., ether and cyclopropane), that's how static was handled in the OR.

author: CopperCone
author_rank: Super Contributor
timestamp: July 10, 2018, 12:00:03 am
content: hose the operator down?