Making your own film

[rmazzullo]

corona discharge treatment of film base

Hello all,

I was reading some material describing some methods of treating polyester with a corona discharge to enable coating the plastic with a subbing layer. Now, from reading the description of the process, it sounds a lot like what happens inside a copier, or even a laser printer, regarding how the toner is electrostatically stuck to the 'paper' and then (normally) fused to the paper to keep it permanently in place.

So...is it possible to put a piece of clear polyester in a copy machine to subject it to an electrostatic charge (corona discharge?), and then afterwards be able to coat the treated film base with a subbing layer on it manually? What about hacking a laser printer to turn off the fuser, but still allow the electrostatic charge to affect the plastic as it passes through? You might have to modify the printer so it would still operate with an empty toner cartridge.

Conversely, is the clear plastic purposely intended for use in a copy machine or a laser printer (and bought at Staples, Office Depot, etc) usable for making film, assuming it is already treated?

Thanks,

Bob Mazzullo

 

[rmazzullo]

Bob;

"Phtographic Emulsion Technique", by T. Thorne Baker. There are two editions. I have the second edition which is better than the first.

PE

Thanks, PE...

Bob Mazzullo

 

[Photo Engineer]

The corona discharge is similar to that used in a copy machine, but I don't know if that discharge is sufficient to allow the film to adhere.

Copy film may be different than the estar or acetate used for photographic film due to the fact that the copy process relies on a high temperature fusion step to facilitate adhesion of the toner to the support.

PE

 

[richard ide]

PE
In another lifetime I worked for a firm in Canada that distributed products made by Arkwright. One of them was a water clear film coated to accept aqueous based media. I am on the other side of the world at the moment, enjoying 110F weather. Perhaps it might be worth checking with them. The product was called clear inking film circa 1980.
The knowledge you are sharing is priceless.

Many thanks

 

[Photo Engineer]

Richard;

Many thanks for the hint and positive comment.

PE

 

[rmazzullo]

emulsion 'toughness' experiment

Hello PE,

Last night I tried a very simple, little experiment on two pieces of film from different manfacturers originally intended for completely different purposes.

The first piece was a piece of T-MAX 100, and the second piece was a small leftover piece of dye transfer matrix film (not Kodak).

The idea was to see what physical changes would occur to the emulsion after I placed a few drops of simmering hot water on the emulsion side of each sample.

When the hot water is placed on the dye transfer film, the emulsion becomes reticulated inside of 3 seconds, and about 10 seconds later, becomes very soft, and can be removed easily with a fingernail, paper towel, etc.

When the hot water is placed on the T-Max film (the water was brought back to simmering before placing it on the second sample) the emulsion did NOT reticulate at all, and took about 20 seconds to soften, and was only removable with more force (a pallette knife). The Kodak emulsion did not soften to the degree the non-Kodak emulsion did.

Now, put aside for a moment that the two films were originally designed for different purposes (and selected for this experiment for this reason), and may have different emulsion requirements. The results observed still indicate the Kodak emulsion was designed to be much tougher regardless.

Can you discuss how the toughness of the Kodak emulsion was achieved?

Also, the Kodak film is much much smoother. Is this a function of emulsion homogeniety, emulsion ingredients, coater design, emulsion shrinkage, etc?
Maybe a combination?

Whatever you can share is greatly appreciated.

Thanks,

Bob M.

 

[Photo Engineer]

The fundamental difference between the two films is that the Matrix film is unhardened gelatin and the Kodak film is hardened with a very efficient hardener.

PE

 

[rmazzullo]

drying finished film...

PE,

How is coated film dried? If you were to coat more than one emulsion, is there a "drying" interval between coatings to prevent one emulsion from mixing into the other? Should there be some residual moisture content in finished film to prevent the emulsion from being adversely affected?

Thanks,

Bob M.

 

[Photo Engineer]

Bob;

In present day coating at Kodak, Ilford and Fuji, all layers are coated simultaneously using a slide or curtain coater. With this method, up to 14 or more layers are coated at one time while wet. (Don't ask, its magic and also one of Kodak's biggest secrets... Muahahahaha)

At companies such as EFKE and many smaller companies, the emulsion is coated one layer at a time, with a drying step in between. This step usually includes a chiller to set the gelatin and then a heated or air temperature dryer.

PE

 

[rmazzullo]

PE,

I just did a search on slide coating, and found an example diagram and explanation, specifically mentioning photgraphic film making.

Good God Almighty. Does the person who maintains the slide coater still have all his marbles?

Thanks,

Bob M.

 

[Photo Engineer]

Bob;

You really have to see one going full blast to appreciate it. It is truly awesome, especially when there is a tearoff. I went through that in a paper coating alley at EK when it was making a full width production run. It made a mess of the whole room. Like wet sticky confetti.

PE

 

[rmazzullo]

not to go too far off the topic...

PE,

Now I understand a little bit more why films are discontinued. To allow a slide coater to do it's thing with as many layers as you mentioned, it has to coat thousands of feet of film or paper base. If you can't sell that much finished stock, perhaps the film might not get made.

>>So...does this also mean that to test color film formulations in the lab, you had to coat the film one emulsion layer at a time?<<

Here is the link that explains a slide coater in a little more detail:

http://www.webcoatingblog.com/blog/coating_applicator_slot_die_slide_curtain/index.html

You will have to scroll down the page a bit to find the section.

Thanks,

Bob M.

 

[Photo Engineer]

There is an animated version done by Agfa that shows this in color.

Basically, Kodak now uses a curtain coater which runs even faster.

In research we use an extrusion coater laying down 1 layer at a time, and this is necessary as each layer may be varied in an experimental set, but we also have both slide and curtain coaters in research to test the scale up of coating formulas just as we scale up emulsion formulas.

There is a rigid coating schedule done months in advance to make sure everything comes together at the front end of the machine at the right time.

PE

 

[rmazzullo]

PE,

What is the difference between a coating formula and an emulsion formula? I was under the impression once you created your emulsion, you would then coat the very same emulsion. Am I misinterpreting your meaning?

Thanks,

Bob M.

 

[Photo Engineer]

Bob;

The emulsion formula contains Silver Nitrate, a halide salt like Sodium Bromide, gelatin, metal salts like Rhodium Chloride and a host of other things.

The coating formula contains the emulsion at a fixed weight, and then you add keeping ingredients, surfactants, hardeners, antifoggants, antioxidants and other items such as water and gelatin. And this is just for B&W.

Color coating formulas contain all of the above, plus dispersions of couplers (which are separate formulas themselves and there may be several in each layer), scavengers, dyes for adjusting speed and sharpness, and dye stabilzers.

All in all, there are literally hundreds if not thousands of ingredients that can be incorporated into any given coating. In a color negative film where there are up to 14 layers, it can take up to a week or more to prepare one set of 10 variations each one being 100 feet long. It is delivered to the coating room by a line of people pushing carts with flashing lights on them walking/pushing down the dark hall to the coating machine.

So, an emulsion formula is just the initial step in a process like a painter who grinds his pigment, mixes it with oil, mixes pigments, preps his canvas and then he sits down to paint.

And finally, when everything is ready and at the front end of the coating machine, there is a long prep while things are degassed and filtered to remove grunge (if any).

The final 'melt' is now ready to be placed in a water jacket and these 'melts' are maintained at a constant temperature while being drawn off from the bottom with stirring into the pumps for delivery to the coating machine. And this system is as complex as the making apparatus. However, it is just as confidential as emulsion making equipment.

In my lab, I go through quite a bit of this type of work making an emulsion and then prepping it for coating. The video that is posted is a very shortened and simplistic view of the entire process.

PE

 

[AgX]

emulsion formula vs coating formula

PE, I am still puzzled:

When there is the `complete´ emulsion formula, called “coating formula”, and this for color coatings even means adding couplers! to a basic “emulsion formula”, what is the idea of speaking of a “emulsion formula” concerning a color film anyhow?
I thought in designing a color film the dye forming capacties are such an integral part of the design concept that one would not distinguish between the `BW emulsion´ and the same with couplers added.

Concerning BW films though, I got the point.

 

[Photo Engineer]

AgX;

Simply put, you don't often use a B&W emulsion for a color material. They are usually totally different.

For example, a color paper may use 3 different chloride emulsions in it, none of which were ever used for a B&W paper which all used chlorobromide emulsions. The same is true for films.

And so, you have a B&W emulsion formula and a B&W coating formula and you have as many as 6 light sensitive layers or more in a given color product, each one with up to 3 emulsion formulas and each layer with a coating formula for an astounding mix of formulas that are combined to yield a coating.

I have been trying to explain how complex a coating is, but no one has seemed to appreciate how many nested operations there are and how many nested formulas there are in any given final product.

It is like a + b = c and c + d = e and e + f = g ...... Until finally you have the final film or paper.

Oh, and in B&W production materials, don't forget overcoats and in color don't forget interlayers. All of these are critical to making the final product function properly.

PE

 

[rmazzullo]

PE,

I think that until now, I didn't realize that the emulsion formula is only part of the puzzle. Another piece being the coating formula. With this information, it now becomes clearer how the "subassemblies" combine to make the final product. At this time, we are only discussing one "subassembly" (the emulsion itself).

Thanks,

Bob M.

 

[AgX]

Dear PE,
I appreciate your attempt to show us the complexity of designing, producing and keeping reproducible what can be called a working and stable photographic product. There just seemed to happened an uncertainty concerning definitions, of what I was not sure whether there was something behind I did not understand. In replying I referred to `BW emulsion´ which I just meant to be an emulsion without couplers. To you it means an emulsion especially designed for B&W materials.

Please go on with your reports about emulsion designing/making!
Even if there will be further misunderstandings. Which surely will come up.

bye (have to go to bed)

 

[Photo Engineer]

I have referred to 'emulsion formual' in the sense of B&W only. I have not considered color. Traditional color, on average, takes a different emulsion formula and coating formula than B&W.

The big difference comes in that for testing purposes or simple experiments, B&W emulsion formulas can be mixed with color formulas to yield a workable test bed for color. So, there is an intermediate ground here and I don't want to overlook it.

That is where Ilfochrome comes in. It is in a hazy intermediate area taking less modification of everything to get to a color material and is why I've said that if color production ceases, Ilfochrome (dye bleach) materials may be our only route to color.

PE

 

[rmazzullo]

temperature of film or paper base during coating

Hello PE,

During emulsion coating, what temperature should the film / paper base be at during the actual coating procedure?

Can the base be chilled just enough to 'set' the emulsion, but not so much that another emulsion coated right on top of it a few moments later wouldn't adhere?

I was thinking about how the slide coater operates, and came up with this derivative idea (I will post drawings tomorrow to clarify the concept):

If the base can be chilled between emulsion coats as described above, and a second emulsion coat will adhere to the first properly, then it might be possible to create a 'seesaw' type of coater, with 2 emulsion troughs on a pivot. In one direction, the first trough is pushed down to the film base during coating (and the second trough is up off of the base, and going in the opposite direction, the second trough is pushed down to the substrate depositing the second emulsion, while the first is up off of the base. I did work out a possible gravity / spring valving arrangement to keep one emulsion from leaking while the other is coating. Keeping the two troughs heated is assumed.

The purpose is to be able to coat 2 different emulsions manually, with minimal time in between. Potentially, you could mount two double coaters on a rotary type of table, to move use one double coater as described, then swing it 180 degrees out of the way while the second double coater swings into place. Or, conversely, you could mount the film platen on a rotary table, and have the double coaters stationary.

Also, you could automate or mechanize something like this without too much trouble.

All this, of course, depends on to what degree, if any at all, the platen under the film base can be chilled during coating, and whether or not the first emulsion coat will be damaged when coating the second.

Your thoughts are appreciated.

Thanks,

Bob M.

 

[Photo Engineer]

Bob;

The film is usuallly coated between 90F and 115F, depending on formula. I use about 100F for all of mine.

After coating, chilling is done at 40F to set the gelatin. At this point it has generally been found that the emulsion is too tender for putting on an overcoat, and so it is generally dried before overcoating.

With hand coatings, it might be possible to use spray coating or a specially designed coating blade that we used at Kodak. It still was and probably would be a chancy proposition unless one were to become extremely skilled.

When we hand coated color multilayers, we coated 1 layer per day with dry down in between. We usually coated about 20 sheets and by the time we were done with all of the layers, with defects, we had about 5 or 6 good sheets. I was fortunate in having two of the finest hand coating technicians in the research labs, and I was no slouch myself. I would not undertake coating on a wet coating nor would they.

PE

 

[AgX]

compatibility with base

I guess my question would fit somehow:
This PanF issue made me wonder why one certain (coating) emulsion would not adhere (enough) to a certain base, given that this base would work with other emulsions and an adherent intermediate layer would have been employed.
With most hydrated fantasy I only could think of a hardening issue, though do not find it quite convincing.


Actually I intended to start practical photographic work after an interlude of about 25 years of just theorizing, but now, instead of hitting shutter releases I am hitting keys. I guess one would call this apugism...

 

[Photo Engineer]

AgX;

The ionic content of an emulsion determines how well it sticks to a non-polar support. This is true for RC and film supports, but not for Baryta. Therefore, an unwashed emulsion will generally not stick to film unless you have a thick hardened undercoat. It will stick to baryta paper though.

A washed emulsion with low ionic strength will adhere to most supports without problelms.

PE

 

[Photo Engineer]

A full formula (as far as I can make it here)

1. Emulsion formula:

a. Precipitate an emulsion by any common means using any common formula. For this argument, we will assume that there are 50 grams of silver in every Kg of the formula and 10% gelatin. This emulsion composition is after washing and any other prep which may include adding rhodium, cadmium or mercury.

b. Add preservatives to the emulsion such as Thymol or Phenol, and Tetraazaindene to keep it from growing mold, bacteria and from fogging.

c. Sulfur or Sulfur + gold sensitize emulsion.

d. Spectrally sensitize emulsion to ortho or pan sensitivity as desired (optional for contact and enlarging papers).

2. Prepare pre-melt for coating:

a. Assuming that you want to coat 250 mg of silver / square foot, and the coating machine requires 10% gelatin at 5 mil (0.005"), then you must dilute the emulsion 1:1 with gelatin + anything else you need. So assuming you wish to make 500 grams of final coatable melt, you prepare 250 grams of 10% gelatin.

b. Mix 250 grams of 1c with 250 grams of 2a and you now have 2.5 grams / kg of silver at 10% gelatin

c. Add surfactant and mix gently.

d. filter

e. degas (optional)

f. add hardner

3. Coat 2f at 0.005" which is 250 mg / ft square of silver and 500 mg / ft square foot of gelatin in the following manner.

a. Bring the coating formula to 100 F.

b. Adjust coating equipment to 100 F at the hopper

c. Adjust first dryer to 40F. / 10% RH.

d. Adjust second dryer to 100F / 10% RH.

e. Adjust third dryer to 75 F / 50% RH.

f. commence coating and drying, when dry rerun through machine to put on a gelatin overcoat containing more hardener, surfactant and antifoggant as well as some antioxidant. Use the same drying conditions but adjust coating thickness for overcoat formula.

So, this is how one uses an emulsion formula, a coating formula and coating machine setup for a B&W material.

Additional steps are needed for making color materials. I've omitted them but can add them if requested.

PE