3M's Photoguard is a coating developed to protect release prints and negatives from getting scratched and dirty. A film is treated with the material, which I understand is a polymar coating and then cured with ultraviolet light. The protection layer of it adheres to the print. I had quite a number of snipes and trailers from FILMAC that were Photogard treated and I can personally attest that the treated film certainly does stay cleaner and seems to resist scratches much better than untreated film. I also find that film so treated seems to remain much more resiliant than untreated film. It feels more supple and softer to the touch. It doesn't get that "dry", brittle feel that regular film gets after a number of years.
One side-effect, which some fellow projectionists complained about, is that Photoguarded film has a tendency to resist splice tape adhesive. You may have to take a bit of extra care rubbing the splicing tape on the film. Even without that extra bit of rubbing, I have never had a splice fail with coated film. Plus, pealing splice tape OFF a frame of film is much easier with less adhesive left clinging to the film.
At first glance, the coating seems like a miracle treatmnet -- great advantage to film protection and preservation. However I have become concerned about the long term effect it may have in increasing acidosis ("vinegar syndrome") as the coated print ages. The fact that this treatment is actually a coating that encases the film raises serious questions as to how much of the acid gases that the triacetate base material naturally releases is trapped within the molecular structure of the base. It has been demonstrated that acetate naturally exudes acid gas and if that gas is not allowed to escape, its presence excites the very same chemical reaction that produced the acid byproducts in the first place. Once the chemical reaction begins, the cycle is accelerated exponentially if the gasious biproduct is not allowed to dissipate. The gas itself then becomes a strong catalyst in the zymurgy.
Keeping triacetate film in tight cans is bad enough, but worst case scenario is a coating on the film that traps in any acid gaseous byproducts trying to escape. I hear from other collectors that coated prints that have typically been "rejuvinated" by a number of lab processes to get extra life out of them, turn vinegar and progress very fast. No amount of "airing out," or neutralizing with washes of base or alkali baths, seem to stop the process. So much chemical deterioration takes place that the film will not run through the projector. The reason given for this happening so swiftly and so irreversibly on the rejuvinated prints is that the coating that has been applied entraps the acid byproducts of the chemical reaction, causing it to cascade within the film base itself rather than gas-out into the environment (unlike untreated film where the gases can escape to the air).
(Editor.... the following is a quote of Ashwani K. Mehta, Business Manager of ScotchGuard Photo and Film Protectors as reported in the Big Reel 11-15-98)
"...the Image Permanence Institute of the Rochester Institute of Technology recently showed that the protectors do allow a film to breathe. They stated that the Photoguard film protector "does not seal the treated film. The acid generated in the film base as a result of chemical decay is able to diffuse from the degrading film even through the coating.".....If the treated film did not breathe, delamination would occur. However, no such delamination has occurred with the Photogard coating..... Our research shows that the original films coated 20 years ago, stored at room temperature, look as good as the day they were coated."