@Peter I've also heard good things about Filmguard. It might be an interesting add-on piece that could be attached at any point in the film path before the gate. Applicators could probably be made relatively simply but I'm totally guessing.
@MikeThibault I came across a post on the AMIA list (which I never check and should start) that had a link to where you could buy Filmguard. It was also pretty informative regarding cleaning film in general. I'll post that below. Here's the link to Filmguard from that post, which also shows the mechanism mentioned by @Peter.
@juanjullian I'm curious to see the wetgate system you menionted from "scanscience.com." I tried going to that site but there is nothing there. Is there a typo in your link? Thanks for starting the conversation!
Here's that AMIA post by Leo Enticknap:
You essentially have three options: hand cleaning on a bench between two rewind heads, an automated arrangement using dry web media cleaners and/or PTRs, and ultrasonic film cleaning machine.
Hand cleaning is cheapest, but the most time consuming option. It basically consists of using a lint-free cloth saturated in one of a number of proprietary film cleaning products on the market, e.g. Filmguard, Renovex or Gentech. As they are proprietary (i.e. the full list of ingredients is not published), some would argue that the use of these solutions is not a good idea in relation to the "do nothing irreversible" principle of archival conservation, because ultimately we don't know if treating films in these solutions is reversible or not. However, they are widely used and are one possible approach.
There used to be machines that automated the process of cleaning films by passing them through dry web media pads saturated in a cleaning solution. RTI made several models in the '70s and '80s that sold well to school authorities and non-theatrical distributors for cleaning the 16mm prints they had in circulation. They occasionally come up on Ebay, but as the media pads are no longer made, a solution for that will need to be improvised. I am not aware of any new models currently in production. There are people who have built their own cleaning solution consisting of motorised rewind heads (e.g. Kelmar), a media pad assembly (such as the one illustrated on the Filmguard page linked above) and/or a set of three of four PTRs.
Ultrasonic cleaners are the most effective, but most expensive solution. You're looking at six figures for a new one, and at least five for a reconditioned one. The chemical used in most of them, perchloroethane, or "perc", is acknowledged to be a totally non-invasive and thus reversible treatment (it leaves no trace on the film surface), and therefore safe for use on archival film elements. However, it also requires special handling considerations. In some jurisdictions you need a licence to have the stuff on your premises.