No Process and Chemistry Free Plates

[GJOHN]

Are no process and chemistry free plates more sensitive to calcium carbonate? If yes, what is the explanation for it?
George John
269-216-8088

 

[Alois Senefelder]

The Problems with CtP Plates

The Problems with CtP Plates

Hello fellow Lithographers,

The fundamental reason of poor press performance is ----- they are poorly "Desensitized"
I formed this conclusion over time, reading on this forum a litany of complaints about plate problems.

Basically CtP are the former "Pre-Sensitized Plates" - the difference being the Image Formation process and lack of development.

Precipitation of Calcium Compounds.

The use of low pH acidic fountain solution (especially in the USA) contributes to this problem and the subsequent deposit of abrasive PCC on blankets, destroys the "Hydrophilic" layer of the plate.

Regards, Alois

See the PDFs -- In place of the word "Ozasol" read Agfa/ Kodak/ Fuji

 

[Vinculum]

Are no process and chemistry free plates more sensitive to calcium carbonate?

I would say not. The coating is different from a regular processable plate because it is "developed" by the fountain solution rather than in a plate processor with specialised chemicals.

The non-image area is typically the same, anodised aluminium of some sort, which is desensitised by a layer of gum. Aluminium, while being a fantastic material from which to make a printing plate for numerous reasons, does not attract water very well. Lithography = water repelling an oil (ink). So if the background is not attracting water then lithography doesn't work. Hence we stick a layer of desensitising gum on the plate, usually a carbohydrate chemical that attracts and holds water very well.

If you have high calcium carbonate levels, most of which comes from the paper coating and filler, you will have serious problems long before any plate issues show up. The usual problems, like roller stripping = poor/uneven ink transfer.

 

[TheProcessIStheproduct]

We ran first gen fuji Pro-T, and yes they would blind very badly from calcium, way more than a regular thermal plate. That product would work with brand new water forms and new chemistry, but even after a couple of weeks you would get blinding and certain uncoated stocks (VIA, Superfine) you would see blinding after as few as 200 sheets. It was the weirdest thing I have ever seen... and it had the same problem with different chemistry, so everything pointed back to plates and problems ceased as soon as we switched off.

 

[GJOHN]

Hi,
That is exactly what is happening at one customer in MI, USA. The plate is blinding at 15,000 impressions. Tried 3 different founts and the same result. But the interesting thing is, this is only happening with uncoated, offset stock. No coated paper will show the same Calcium blinding. Will the offset stock behave similarly on regular, thermal, plates? Or is this common on no process, chemistry free plates and uncoated stock? Please share your experience and thoughts for the benefit of Lithographers.
George John
269-216-8088.

 

[Magdy]

Hello,
I can understand, that the first step is graining process, to make a roughness surface, secondly as an anodizing process to create the capillary cells on the surface. Thirdly is sealing process, but is about of the hydrophilic layer?
Thank you
Magdy

 

[maxon]

... the subsequent deposit of abrasive PCC on blankets, destroys the "Hydrophilic" layer of the plate

Shouldn't we understand it destroys the oleophilic layer instead ? some have referred to plate blinding already pointing to compromised coating ink receptivity.

 

[Alois Senefelder]

Definition

Definition

Maxon,

1) Plate Blinding - loss of ink receptivity of the image area, even though the image
looks intact.

2) Plate Wear - should be obvious, eroding of image area.

3) CtP image layer - composed of (Oleophilic) Cross Linked Photo Polymers, thickness of
imaging layer between 1 - 3 microns

4) Hydrophilic surface - Desensitizer functions by forming a Adsorbed Layer of gum
molecules, thickness being 1 molecule layer, which is easily abraded.


Regards, Alois

 

[Lukas Engqvist]

@Alois I doubt that the gum being abraded is an issue, since the gum is there to prevent oxidising and is washed away before printing. Your attached image does not explain how no process or chemistry free plates work, and looks to be dated for another technology age.

 

[maxon]

I agree with Lukas. Alois, no need to refresh my memory thank you although it's about 20 years since I first learned these things. Back to the topic I'm eager to see answers to George John's questions as I intend to move from n91v to lo-chem soon.

 

[Dan Roll]

If there is a lot of calcium being released into your fountain solution leading to blinding, you should be able to measure this easily. The Hatch company sells inexpensive kits for testing water hardness and these will measure the calcium content of water quite accurately. These kits are easy to use and the directions are clear enough for a plate salesman to follow. If you measure your fresh fountain solution and then measure it again when you experience blinding, you should be able to see some difference. If you don't, maybe calcium isn't the problem.
The lack of ink receptivity on many modern plate image surfaces has many explanations and is certainly a big problem for some vendors.

 

[Alois Senefelder]

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Messrs. Lukas,Maxon

The Surface Science of Offset Printing Technology

I enclose a little light bedtime reading for your enlightenment, should you require anymore please do ask.

" From knowledge to competence is a great step --- from ignorance to competence
an even greater one "

Regards, Alois