Cellulose Acetate vs. Polyester film base

BetterSense · Mar 3, 2009

I hope this fits here.

I was aware that film switch from nitrate to 'safety film' around the 50s. But I thought it was still made of cellulose acetate, even today. Apparently it's now Polyester or PET film? When did this transition occur, and do you think there was any difference in the look the film produced?

AgX · Mar 3, 2009

Films for pictorial still photograph typically have a TAC base.

Those with a PET base either are converted from stock intended for `industrial´use (aerial, surveilllance), or are those few where the advantages of PET have been considered. Furthermore the very situation at a manufacturer has its impact on the choice of base too.

Photo Engineer · Mar 3, 2009

Dimensional changes in film during processing hurts image size and shape, so PET film is used for graphics arts films and many LF films where dimensional shrinking or expanding can be noticable with TAC. All dye transfer materials were made on PET support.

Also, the change to safety film took place a bit before the 50s. I have seen safety film on films at least 10 years earlier or more.

PE

Michel Hardy-Vallée · Mar 3, 2009

Here's the story of film base how I know it:

Professional films were often coated on cellulose nitrate, which is the nasty, inflamable and almost unextinguishable stuff. At the same time, amateur films were coated on cellulose diacetate. Diacetate did not have the flammability problems of nitrate, but was more susceptible to turn into acetic acid ("vinagering").

There was something about nitrate that made it better than diacetate, hence the pro use, but I don't know what.

Then, cellulose triacetate was invented and it combined the lower risks of diacetate with the je-ne-sais-quoi of nitrate base.

Most 35mm and 120 films today are now coated on triacetate, except those that are coated on PET (which is even more stable).

AgX · Mar 3, 2009

The problem with finding a successor for cellulose nitrate was to find a foil that was much less flammable, had at least the same mechanical properties and (what is often neglected) was technically and economically (issue of solvents) feasible.

And to add on Michel's post above: type APS films are coated on PEN.

removed account4 · Mar 3, 2009

Michel Hardy-Vallée said:
Professional films were often coated on cellulose nitrate, which is the nasty, inflamable and almost unextinguishable stuff.

it was made with collodion / nitrocellulose ...
think "movie house fire" kind of flammable ...

Anon Ymous · Mar 4, 2009

Hello evrybody,

I read somewhere that films with PET base are prone to lightpiping. If I got it right, that's light entering from the edges of the film and scattering through, thus fogging the emulsion further in the cassete. A "cure" for that would be to load film in reduced light. Does anybody have personal experiece and/or knowledge on this?

Thanks in advance.

AgX · Mar 4, 2009

There are several things to consider concerning light piping:

-) the light transmission of the clear form of the base material

-) the reflectance of that material at its surfaces (subbing layer, air, backing layer, etc.)

-) dying of the base material

to name just a few.

Of course with designing film intended for darkroom loading some of these points need not to be considered. However they could become important when converting such film to type 135.

The general tone on type 135 films on PET base on the market at the moment is that the first 2 to 4 frames are at stake. I would add that when bulk loading by means of a daylight loader one should pay attention to the last frames as well.
Think also about the chance of a cassette with a protruding `tongue´ lying around for some time.

The best thing to do is to make a test with that very material under the worst circumstances you would expect while handling the cassette.

Photo Engineer · Mar 4, 2009

All films are subject to light piping!

This is practially eliminated by the AH base on the film and inclusion of carbon in the film itself. The carbon serves two purposes, namely reduction of light piping and reduction in static electricity.

PE

Michel Hardy-Vallée · Mar 4, 2009

jnanian said:
it was made with collodion / nitrocellulose ...
think "movie house fire" kind of flammable ...

Second language salad here: in French when something can burn, it's called "inflamable". In English it's "flammable" ...

Kirk Keyes · Mar 4, 2009

Actually, you can use both flammable and inflammable in English which makes it twice as confusing...

Chazzy · Mar 4, 2009

Michel Hardy-Vallée said:
Second language salad here: in French when something can burn, it's called "inflamable". In English it's "flammable" ...

It's the same here. "Flammable" is a later word invented by people who worried that inflammable would be misunderstood.

ntenny · Mar 4, 2009

Michel Hardy-Vallée said:
Most 35mm and 120 films today are now coated on triacetate, except those that are coated on PET (which is even more stable).

I'm just curious---does that last bit mean that, all other things being equal, negatives on a PET-base film will outlast negatives on a triacetate-base film? Or can the support already be expected to outlast the image under normal circumstances?

Thanks

-NT

Ray Rogers · Mar 4, 2009

ntenny said:
I'm just curious---does that last bit mean that, all other things being equal, negatives on a PET-base film will outlast negatives on a triacetate-base film? Or can the support already be expected to outlast the image under normal circumstances?

Thanks

-NT

No, I suspect 'dimensional stability' is what is being discussed here,
not "life expectancy".

Ray Rogers · Mar 4, 2009

Speaking of Flammable comments...

Chazzy said:
It's the same here. "Flammable" is a later word invented by people who worried that inflammable would be misunderstood.

When I was still a free thinker, I learned that there was an actual difference in meaning between those words.
Curious, I visited Mr. Wikipedia to see what he could remember, since he was a free thinker once too.
There, I found this amusing but quite offensive quote:

" The common word meaning "combustible" is inflammable.
Unless you are... concerned with the safety of children and illiterates, use inflammable. "

--------------------------------------------------------------

The full quote sounds like it could have been written by Ambrose Bierce:
The Elements of Style (by Strunk and White) says:

Flammable. An oddity, chiefly useful in saving lives. The common word meaning "combustible" is inflammable. But some people are thrown off by the in- and think inflammable means "not combustible." For this reason, trucks carrying gasoline or explosives are now marked FLAMMABLE. Unless you are operating such a truck and hence are concerned with the safety of children and illiterates, use inflammable.

Kirk Keyes · Mar 4, 2009

Just use "combustible". And that way, incombustible does mean the opposite.

AgX · Mar 5, 2009

Ray Rogers said:
No, I suspect 'dimensional stability' is what is being discussed here,
not "life expectancy".

PET, up to the reports published so far, has both, greater dimensional stability as well as greater long term (archival) stability.

So far there were cases reported of TAC based films that had lesser longevity than NC based films.

Alexander Ghaffari · Mar 6, 2009

"Inflammable means flammable? What a country!" ~Dr. Nick Riviera

I have had some problems with light piping in 35mm b&w film on a PET base...it did not have a nice remjet backing like Kodachrome.

Marco B · Mar 6, 2009

Hi all,

I just stumbled upon this link, I think you will find it interesting. Also in the light of the "How film is made" thread:

http://www.motion.kodak.com/motion/...wsletters_filmEss_04_How-film-makes-image.pdf

For the full reference including the other chapters of this document, go here:

http://www.motion.kodak.com/US/en/motion/Publications/Film_Essentials/index.htm

Marco

dwross · Mar 6, 2009

Marco,
That's a really excellent summary. Good stumbling! Thanks for passing it along.
d

CRhymer · Mar 7, 2009

I am not sure if this was mentioned, but PET is quite strong, which is good, unless one needs to tear a piece in the dark with no scissors at hand, or in a movie camera jam - not good for the works. Helen B pointed out the latter, which saved me some grief. Of course now I have some grief to spare. What ever happened to Helen B? She knew (knows) a lot.

Cheers,
Clarence

MattKing · Mar 7, 2009

I don't think Helen Bach has posted here since 2007. In case she visits anonymously from time to time, I'd just like to emphasize that I miss her contributions, and I'm sure others do too.

Matt

AgX · Mar 7, 2009

Me too.

Phormula · Mar 7, 2009

I can confirm, PET is more stable than cellulose acetate, does not break at low temperatures, can withstand temperatures up to 60°C and has a lower tendency to attract dust. It replaced celluose acetate for medical (X-ray) applications many years ago.

Besk · Mar 8, 2009

Being interested in archival properties of the B&W films that I use I only use films on a PET base.

Several of the Rollei branded 120 and 35mm films are on a PET base. (available from Freestyle in the US.) Kodak used PET for the base of the 35mm Tech Pan but not the 120 size.

Cellulose Acetate vs. Polyester film base

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