ph at 4.0 - 4.5 ?

[Green Printer]

Why must the ph be between 4.0 and 4.5?

 

[aqazi81]

I was told it should be between 4.5 - 5.5.

 

[aqazi81]

With lower pH,
Free rolling of the plates will be better.
Ink water absorption will be less.
Oxidative drying will be slower.
It will be more corrosive for the press parts.
It will attack paper coating more.

With High pH,
Free rolling of the plates will be worse.
Ink water absorption will be worse.
Oxidative drying will be quicker.
Less corrosive.
Less attack on paper coating.

 

[Green Printer]

I have heard and read these reasons for quite some time. I have never found out what is the science behind it.

 

[D Ink Man]

For the most part if you are referring to fountain solution, you can pretty much put pH on the back burner in favor of conductivity. With today's fountain solutions and the buffers that are in these formulas, ph will not have any drastic or meaningful measurement move in relation to ounces of etch and perhaps alcohol substitute per gallon of water.

I strongly suggest that you develop a running log of your tank and pan conditions. You should routinely check these conditions weekly to provide consistent lithographing. Firstly, create a titration chart. this chart should show the ph and again more importantly the conductivity as oz. per gallon are varied. The data should include raw or treated water as is along with temperature measured. Also it should include 3 crucial readings; temperature, conductivity and pH from the fountain solution tank. Periodic collection of the solution from the water pans is also suggested to ensure your press is not overly contaminated throughout the lines.

To get this started, a reliable vendor of fountain solution or ink should do the upfront work in conjunction with you to draw baselines. Once established, you the printer can maintain your healthy offset press by weekly recording the aforementioned values. Keep the data in a hand written composition notebook by your press. These easy and simple steps will go far in your understanding and maintaining the second life blood of your printing machine.

D Ink Man

 

[Alois Senefelder]

Hello fellow Lithographers,

Chemistry of Lithography ---- Fundamentals.

Fountain solutions and why the are Acidic, the safe operating pH range of 4.0 - 5.5 aids

the Adsorption of the Desensitized Film Layers on the plate, formed by the

chemical enriched F.S.

Regards, Alois

 

[gordo]

Why must the ph be between 4.0 and 4.5?

According to Heidelberg documents: consensus.
The pH wants to be between 4 and 6. The function of the acid in the fountain solution is to reduce the pH, keep the image area sensitive to ink, and keep the background area water receptive.

 

[D Ink Man]

Methinks me missed something here.

D

 

[gordo]

Methinks me missed something here.

D

Speak. What's been missed?

 

[D Ink Man]

Well, pH is dependent upon a particular fountain etch, alcohol sub and/or alcohol product brand. Some acid founts run as low as 3.3 and as high as 6.0. To try to pinpoint a range is non sensical because the pH is governed again, by a particular fount formula. There is no per se 4.0 - 4.5 standard that can be generalized as standard to be running on an offset press.

Now methinks I have messaged what methinks I have missed.

Still stand by strongly about knowing your fountain solution and maintaining it as previously replied.

May all have great holiday and holiday season.

D Ink Man

 

[Dan Roll]

it is common for people to confuse pH with strength, the best analogy I know of is to think of fountain solution pH as voltage. Knowing the voltage of a charge gives you some information about it, but not any clue to how much electricity there is. The same holds true for pH in fountain solution, the pH gives a clue as to how acidic a product is, but little or no information on how strong it may be. An example would be a very small amount of sulphuric acid in water will give a very low pH while a highly concentrated boric acid solution will have a much higher pH. The newspaper industry used alkaline pH fountain solutions for decades (pH 9 to 10) and for the last twenty years or so have moved to neutral fountain solutions (6.5 to 8) and acid fountain solutions have long histories of pH values as low as 3.5 (Rosos and Blue Chip, Red Etch, etc) and as high as 5.5 (most European acid fountain solutions). Beliefs that there is a 'correct' pH for printing are empirical and there is little that can be done to change anyones mind about the pH they are comfortable running.
To answer the threads original question I would say "no reason at all", run whatever pH product works for you and you are happy with.

 

[D Ink Man]

Excellent reply Dan Roll; certainly helps clarify the situation.

Also, i surmise that many old litho guys miss those Aggie Rosos products. Often copied, but never duplicated.

D

 

[D Ink Man]

I am now convinced that my replies are invisible to everybody but me. Ty alibryan.

D

 

[Alois Senefelder]

pH and the wider issues !

Hello fellow Lithographers,

The various contributors to this topic, give valid but but a limited view of the role pH plays in F.S.

My response widens this topic, each Constituent of F.S. serves a purpose.

Acidic F.S. Solutions. The Desensitizing Film protecting the non-image areas of the plate

is slightly acidic; however, it requires additional acid to adhere properly. The acidic

constituent added

to the F.S. enable the Desensitizing Film to be adsorbed to the non-image areas of the plate.

Regards, Alois

P.S - the reason US Newspapers used Alkaline F.S. A) they didn't know any better B) also they

used cheap "Groundwood Newsprint". In the UK and Europe we use TMP Newsprint