Differences between a paper coating machine and a film coating machine

[Lachlan Young]

Hello all,

Given recent discussions elsewhere on APUG about coating machines/ scale of production etc, I was wondering just what are the absolute differences between a machine designed to put photographic emulsions on paper vis a vis one designed to put emulsions on film? Harman Technology and Innoviscoat seem to use one machine to coat both substrates, whereas we are told that the Kodak machines are quite different and could not easily be swapped between film and paper coating. Is it mostly to do with mechanical components in the feed/takeup reels - ie film bases are thinner, paper much thicker? Or is it the strength of the coated web - triacetate/polyesters strong, relatively dimensionally stable, baryta much less so? Or is it to do with the drying tunnel after coating? Or is it down to the relative speed of the machine/ number of layers the curtain coating head can deliver?

Cheers,

Lachlan

 

[Henning Serger]

Hello Lachlan,

Hello all,

Given recent discussions elsewhere on APUG about coating machines/ scale of production etc, I was wondering just what are the absolute differences between a machine designed to put photographic emulsions on paper vis a vis one designed to put emulsions on film? Harman Technology and Innoviscoat seem to use one machine to coat both substrates,

not "seem": Ilford Photo / Harman technology, InovisCoat and Foma are coating film and paper on the same coating machine.
InovisCoat is coating both colour and BW on their machine (which is a modified machine from the former Agfa plant in Leverkusen, Germany).

whereas we are told that the Kodak machines are quite different and could not easily be swapped between film and paper coating.

Kodak is using curtain coating for film, and if I remember right bead coating for paper (but I am not 100% certain).
From a pure technological point of view both methods can be used both for paper and film.

Is it mostly to do with mechanical components in the feed/takeup reels - ie film bases are thinner, paper much thicker? Or is it the strength of the coated web - triacetate/polyesters strong, relatively dimensionally stable, baryta much less so? Or is it to do with the drying tunnel after coating? Or is it down to the relative speed of the machine/ number of layers the curtain coating head can deliver?

The main differences are most probably a result of economic reasons.
The volume (in m²) of the colour paper market is much much bigger compared to the current film market (currently about 700 - 800 million m² RA-4 paper p.a.).
The paper machines are running full time 24h a day.
Switching means interruption = higher costs.

By the way, the current paper factory of Fujifilm in Europe is in Tilburg, the Netherlands. Until some years ago it was a film factory. Fuji said transferring it to paper was easy.

Best regards,
Henning

 

[Photo Engineer]

Lachlan, I explained the several differences that we observed and practiced at Kodak. No doubt you kept a reference to that and will publish it here. I did not keep a copy for that thread.

As for more differences. Well, you note that there are practically NO SW FB papers floating around? It is because wet SW FB paper is like wet tissue paper and breaks if you look at it funny! Tearoffs are very expensive due to cleanup and retension of the machine takes hours before you can coat. Film is easier to keep on track due to its stiffness, paper wanders as much but then folds upwards at the guide rollers. There are other differences such as speed and laydown due to the fact that paper has 6 layers but film can have as many as 15 layers. This relates to the size of the delivery rooms and equipment. Anyone coating B&W products exclusively will not have to deal with some of what I say due to the simpler layer count and slower coating required.

Kodak used slide coating from the mid '60s for all products, and is now using curtain coating for all products (AFAIK). Bead coating was gone except for the slow KRL test machines for single layers, but due to cost KRL kept them in use. BTW, we called the extrusion coaters because that is what they were. Technically, they extrude melted emulsion onto the film or paper.

In research, film and paper were coated on the same machine, but the coating process for both was much slower, sometimes 2 layers at a time for color which then required 7 passes for a 14 layer coating. These machines were actually 2 machines running in tandem with a coating station in the middle. I've mentioned before the "T" shaped machines with 3 coating stations as well.

Doctor blade coaters (go look it up!) ran at about 10 ft/m up to say 50 ft/min; Extrusion coaters ran at about 100 ft/min to 300 or so ft/min; Slide coaters ran at about 500 ft /min to about 2000 ft/min and Curtain coaters - well, lets just say that they were faster!

It would help if you posted the reasons for your interest in such an arcane subject!

PE

 

[Lachlan Young]

PE,

Thanks for the information above - I asked the question to confirm some suspicions I'd had about the way the machines worked. The reason for asking the question about the coating technologies was largely sparked by an interest in the history of photographic manufacturing, and while coating technology is 'arcane' it's critical to taking the product from the lab to the consumer - I have no plans to build one any time soon!

Having some involvement in intaglio gravure & letterpress printing, the damp paper handling is something I'm all too aware of, though obviously on a non-industrial scale. From reading the article by Kit Funderburk on the GEH website on the Kodak paper base textures/ formulations, it looks like they were trying to maximise the use of the cheapest possible materials without it affecting the emulsion - was this why fluorescent brighteners came along?

Doctor blades are something I've encountered too - I have a book here from the 1940s on industrial rotogravure that has an entire chapter on sharpening said blades.

Do you feel that the changes in technology were driven more by economic or engineering need? Or to put it another way, if you were designing a machine today for small scale, optimal coating of both paper & film, would a curtain coater would be the obvious choice?

Finally, Was this the link you meant? http://www.packaging-int.com/upload/image_files/suppliers/images/companies/2166/coating-methods-l.jpg

Cheers,

Lachlan

 

[winterclock]

Hi Lachlan,
What is your definition of small scale? At 2000' per minute you could go through several miles of substrate in 15 minutes. Any material handling system design, coaters included, starts with an estimate of the output you require. If you want to produce a few rolls of 120 a day you will need a much different machine and coating method than one which will produce 150 miles or so per day. Take a retail sized 100 foot roll of acetate, a doctor blade can coat it in ten minutes, an extrusion coater one minute, a curtain coater won't even be up to speed when the roll runs out. The slower machine will also be much more adaptable to different media. The high speed curtain coaters may rely on the strength of polyester substrate for keeping correct web tension at speed. So again, what is small scale? To Kodak it might be a 1000 ft/min slide coater, to Ilford it might be a 100 ft/min bead coater, to a graphic artist it might be a 10 ft/min doctor blade

 

[Photo Engineer]

Lachlan, that is the reference. I have it too for my next book, but it is a jpeg.

The cost of paper for photographic use is quite high because any impurity in the wood pulp will affect the product so that is not quite the case. As for the amount of Baryta or Titanox used, it must cover the paper fibers and present a smooth surface. It must also be designed not to crack.

A non-slide or curtain coater can become very expensive as you have to make multiple passes (up to 14 for some color products) or you must have multiple coating stations in the machine which require an operator and they are quite expensive. Many Kodak machines have multiple coating stations as I mentioned above. This is true for color and B&W and for machines with varying coating heads.

Winterclock has the right idea in expressing his figures that way for us. I have watched (under safelight) a full 5000 ft roll of paper literally vanish before my eyes as it is being "eaten" by the machine. On the other end, the takeup roll grows as fast and is then sliced and carried away in its "coffin" while a new roll is spliced in. Imagine this 24 hr/day 7 days/wk and 365 days/yr on 4 machines while 2 others sit idle for routine maintenance. Now that was high speed coating of a lot of product.

PE

 

[falotico]

Glad to hear PE is already writing his new book!

 

[Lachlan Young]

Lachlan, that is the reference. I have it too for my next book, but it is a jpeg.

The cost of paper for photographic use is quite high because any impurity in the wood pulp will affect the product so that is not quite the case. As for the amount of Baryta or Titanox used, it must cover the paper fibers and present a smooth surface. It must also be designed not to crack.

A non-slide or curtain coater can become very expensive as you have to make multiple passes (up to 14 for some color products) or you must have multiple coating stations in the machine which require an operator and they are quite expensive. Many Kodak machines have multiple coating stations as I mentioned above. This is true for color and B&W and for machines with varying coating heads.

Winterclock has the right idea in expressing his figures that way for us. I have watched (under safelight) a full 5000 ft roll of paper literally vanish before my eyes as it is being "eaten" by the machine. On the other end, the takeup roll grows as fast and is then sliced and carried away in its "coffin" while a new roll is spliced in. Imagine this 24 hr/day 7 days/wk and 365 days/yr on 4 machines while 2 others sit idle for routine maintenance. Now that was high speed coating of a lot of product.

PE

PE,

If I am reading this correctly, a multi-layer doctor-blade coater could, all things being equal, be able to produce the equivalent quality of a curtain coater but at a much lower line speed? Thus, could we say that many of the changes in coating technology were caused by a need to produce more product in a given time with a lower labour cost?

Compared to pure cotton or linen mouldmade or handmade papers, the cost of the paper is probably pretty reasonable!

Any web-fed machine going at reasonable speed is a pretty impressive sight, though for sheer eccentricity the Cossar Press may take the biscuit - it was a web-fed, flatbed letterpress printing press that swallowed newsprint at one end, printed both sides of paper, then spat out cut, folded newspapers from the side, all in a startlingly small space. They were designed and built near to where I currently live & the last surviving example is being restored close by - here's some archive footage https://www.youtube.com/watch?v=9ebBp81JTcg and some history of it http://scottishprintarchive.org/projects/cossar-project/

Cheers,

Lachlan

 

[Photo Engineer]

Lachlan, every day on my way home from high school, I passed a newspaper company that had the printer side made into picture windows that passersby could look through and see the daily news being printed up. Yes, high speed for sure.

As for doctor blade coating, it is the opposite of your way of reasoning. It takes more operators and operations for single layer coating than for slide or curtain coating. A slide coater may take one operator for everything, but a doctor blade coater may take up to 14 operators (if you take it to extremes), but usually it is the same operators (2) being used 7 times.

Now, to be sure 10 ft/min would be nice in today's market, and a curtain coater can be used as a slide coater, and a slide coater can be slowed quite a bit as I indicated above. So, this is not the entire problem.

When sales drop over 30% in one quarter there is a problem that slowdown does not fix.

PE

 

[Lachlan Young]

As for doctor blade coating, it is the opposite of your way of reasoning. It takes more operators and operations for single layer coating than for slide or curtain coating. A slide coater may take one operator for everything, but a doctor blade coater may take up to 14 operators (if you take it to extremes), but usually it is the same operators (2) being used 7 times.

Now, to be sure 10 ft/min would be nice in today's market, and a curtain coater can be used as a slide coater, and a slide coater can be slowed quite a bit as I indicated above. So, this is not the entire problem.

PE,

I was thinking in 2 directions at once without making myself clear - firstly, if coating on a v. small scale today (limted width, slower speed), would a doctor blade be a sensible option? Or would you be better with a slower, narrower curtain/slide machine? Unless I'm half asleep at the keyboard (entirely possible), you're saying the latter makes more sense, or is it a case of what you have available & what you can afford to invest in?

Secondly, I was trying to work out if the move from extrusion to slide to curtain coating was largely driven by economic considerations - ie you could coat a larger area faster & need fewer people to run the machines?

One other thing, were all the Kodak colour films multilayer coatings from the start?

Cheers,

Lachlan

 

[Photo Engineer]

This is correct " you could coat a larger area faster & need fewer people to run the machines" but you can overdo a good thing and make it too big for "planned expansion in the market" which we know never took place.

A doctor blade would be impractical from a coating quality POV. Extrusion or slide would be my choice. And, the nice thing about these methods is that you can build big but shim the hopper down to almost any width, but the experimentation to come up with a formula for these narrow widths would be expensive.

And no, Kodak made a single layer lenticular color film before the current multilayer films.

PE

 

[Lachlan Young]

This is correct " you could coat a larger area faster & need fewer people to run the machines" but you can overdo a good thing and make it too big for "planned expansion in the market" which we know never took place.

A doctor blade would be impractical from a coating quality POV. Extrusion or slide would be my choice. And, the nice thing about these methods is that you can build big but shim the hopper down to almost any width, but the experimentation to come up with a formula for these narrow widths would be expensive.

And no, Kodak made a single layer lenticular color film before the current multilayer films.

PE

Had forgotten about the lenticular Kodacolor - an interesting solution to reproducing colour.

The shimming down & multiple coating heads make a lot of sense - I suppose you could have 2 coating heads with 6 layers each, 1 at 21", 1 at 9" with the 21" shimmable to 9", thus enabling the manufacture of BW paper & film along with colour paper to 20" wide coating, & the ability to coat colour film materials in up to 12 layers at up to 9".

What's also striking is that most of the machinery is not really unique to film coating, apart from having more layers and slower line speeds.

Cheers for the information - makes it much easier to understand the relationships between coating technology and emulsion design.

Lachlan

 

[Photo Engineer]

I'm afraid there is no connection of any of this to emulsion design and IDK where you got that idea.

PE

 

[Lachlan Young]

I'm afraid there is no connection of any of this to emulsion design and IDK where you got that idea.

PE

Probably because I made a wrong connection - to rephrase it, does the type of coater have any significant impact on the design stage of the emulsion?

Cheers,

Lachlan

 

[Photo Engineer]

No, the coating machine design is not related to emulsion design.

I have coated on an extrusion coater and then went directly to slide coating with some modification in the coating formula (ie. surfactant adjustment and related changes and changes in keeping chemicals due to the longer hold time on the big machine).

PE

 

[Henning Serger]

Hi Ron,

There are other differences such as speed and laydown due to the fact that paper has 6 layers but film can have as many as 15 layers.

just as a little additional information: Fujifilm's colour films have up to 21 layers (including non-imaging interlayers; source: Interview with the Fuji CEO).

Best regards,
Henning

 

[Photo Engineer]

Yes, Fuji has extra layers for the fluorescent lighting correction.

Thanks for that correction.

PE

 

[Steve Smith]

A non-slide or curtain coater can become very expensive as you have to make multiple passes (up to 14 for some color products) or you must have multiple coating stations in the machine

Is a slide coater the type which allows several emulsions to be coated at once in layers?


Steve.

 

[Arctic amateur]

Sorry that I go a bit off-topic, but what's the reason for using RC coated paper rather than just a resin/plastic base? Is it cost? Issues with whiteness? Inadequate opacity?

 

[Photo Engineer]

Steve, a slide and a curtain coater both allow several layers to be coated at one time. I have coated up to 14 this way. Six was my usual when doing color paper.

Arctic, the paper in the RC sandwich gives it a better opacity and reflectance and a better feel. RC = /emulsions/RC/TiO2 in binder/paper/RC backing/. Without this paper, it would look like some of the cheap digital papers on the market. They are a kind of foamed plastic IIRC.

PE