Coating machines

[Curt]

This is part of a statement about Aristo Vario paper.

This paper is coated on the last remaining coating alley which was built especially for coating fibre based papers in the 1950s. It uses the vertical coating dunk-process and runs much slower than modern horizontal
speed-coating machines.

What are the differences between vertical and horizontal coating in the final product? Is this paper going to be similar to or better than the 1950's papers made on the same coater?

Curt

 

[AgX]

With the newer processes the emulsion physical parameters are not decicive on coating thickness in contrast to the trough coating process, to name just one issue.

But I don't see that the coating process as such would define the final product concerning paper.
(I expect curtain coating to be able to yield thinner layers than trough coating though.)

But for sure PE is the man to give a final answer.

 

[Steve Smith]

I'm not sure about this machine but it reminds me of the machine we used to have to coat printed circuit board material with photo etch resist. The board is held above a tank of liquid emulsion then lowered in. Then it is very slowly raised out at a constant speed.

This leaves a very thin, uniform coating. Unfortunately, this is on both sides so would be unsuitable for coating paper unless it was masked off with something like a removeable release liner. Also this would waste half of the emulsion.

I would also be interested to learn how this machine actually works.


Steve.

 

[olehjalmar]

Maybe you could stick two papers together and peel them apart later? No waste.

I'm not sure about this machine but it reminds me of the machine we used to have to coat printed circuit board material with photo etch resist. The board is held above a tank of liquid emulsion then lowered in. Then it is very slowly raised out at a constant speed.

This leaves a very thin, uniform coating. Unfortunately, this is on both sides so would be unsuitable for coating paper unless it was masked off with something like a removeable release liner. Also this would waste half of the emulsion.

I would also be interested to learn how this machine actually works.


Steve.

 

[palec]

A little bit out of topic, according to description if looks like the paper is rebranded Fotokemika Varycon paper made in Croatia.
http://www.fotokemika.hr/products/0/black-white-paper/varycon

 

[dancqu]

Are coated ink jet papers similarly coated? Seem to
recall reading that ink jet and silver gelatin papers
are very similar, at least when coated. Ink jet of
course minus the silver. Dan

 

[Photo Engineer]

The dunk coater with vertical rise is seen in the Dutch language video made by Kodak. It has not been used by Kodak for about the same length of time.

The coating machine does not determine the physical properties of the emulsion to any great extent. The vertical rise is a design just about forced on the builder by the use of the dunk process. Only one side is coated as long as tension is maintained on the paper. A constant thickness of coating can be achieved by use of a blade or air knife which scrapes off excess emulsion.

Ink jet and silver halide papers are not similar, but are coated in a similar fashion.

PE

 

[Curt]

Adox Fine Print Vario Classic VC FB Neutral black paper with variable contrast
on a 255g triple weight support with ultrahigh silver content.

Neutral tone fiber based paper with deep blacks and excellent greyscales.
This paper is coated on the last remaining coating alley which was built especially for coating fiber based papers in the 1950s. It uses the vertical coating dunk-process and runs much slower than modern horizontal
speed-coating machines. Thus this paper can really soak up with emulsion making it extremely silver rich. This also leads to the necessity to develop it at least 2-3 minutes in order to achieve full dmax and greyscales.

The developer and fixer are also faster exhausted, please recalculate their capacity.

As I read this description I'm to believe that the vertical process results in an "extremely silver rich" paper that is so silver rich that it requires a minimum of 2 to 3 minutes of full development to achieve the "full dmax". That's quite a statement to make if the paper is isn't any better than other fiber based papers. I was struck by the statement and is why I asked about the coating process.

Thanks,
Curt

 

[Photo Engineer]

Curt;

Firstoff, papers are limited in Dmax to about 1.8 - 2.2. This is due to the laws of physics. In addition, development rate is a function of mainly grain size and grain content, not necessarily how much is coated. And most importantly, the fact that silver rich means something good is an outright myth! Silver halide had to be coated at higher levels at one time due to the poor quality of emulsions (1900 - 1940 approx) and the poor quality of coating machines.

So there is no real substance to what they say that would make it a good emulsion. Besides, if it soaked up a lot of emulsion, it would be within the baryta undercoat and useless to you. To demonstrate this, you can coat something dyed on the surface and such that it is absorbed into the baryta. You get LOWER density if it is sucked into the baryta layer that is used to whiten the paper.

If you do the same on RC, then nothing is absorbed and the entire statement is untrue from start to finish.

PE

 

[Curt]

Thanks Ron, that makes excellent sense, I was suspicious about the claim when I first read it.

Curt

 

[AgX]

That soaking up is a bad translation from the original (seemingly by member Mirco Boedekker). Though the statement on development time and silver content remains.
Here is the original:
http://www.adox.de/ADOX_Papiere/Vario_Classic/Vario_Classic.html



PE, could you define your term `grain content´?

 

[Photo Engineer]

Grain content = AgCl vs Ag/Cl/Br vs Ag/Br. This is also in order of development rate. So an AgCl emulsion at 250 or 500 mg of silver per square foot will develop more rapidly than an Ag/Br at 250. The content (halide type) determines the rate of development or apparent development more than the weight coated on the support.

PE