Chrome Plating Problems on Gravure Printing Cylinders/Rolls

A. Bill:

The peeling and blistering problem is most probably in the preparation of the copper before chrome plating. Even though it is well known that chrome is not impervious due to its micro cracking, the copper beneath it is very corrosion resistant to all kinds of commercial inks. This means that even if the ink could penetrate through the chrome cracks and reach the copper, it will not be attacked. Another possibility is an excessive thickness of chrome (more than 1-2 mils which I don't think is your case). Then the problem becomes of mechanical nature (internal stresses and their distribution through the chrome layer). Finally, have you checked the blade pressure with the machine manufacturer?

Good luck,

A. Hello Bill,

I suggest you to check following items:

Cracks going across the chrome layer due to

* thin layer thickness
* too high surface pressure
* weak plating quality
(consequence: corrosion under the chrome layer and the effect is visible as bubbles)

Insufficient adhesion of copper on the base material. (consequence: chrome bubbles off and peels off because the chrome pulls the copper off due to internal stress).
Possible causes: too much brightener, insufficient pretreatment, etc.)

I wish you a successful trouble shooting.

A. About 20 years ago I was asked to look at a chromium plated printing plate used by a well known UK printing company. Their problem was very similar to what I think is being described here, but they only had the problem with one type of green ink. I do not recall if it was water-based or not, but I do recall the pH for the ink was quite low. Examination of the failure showed it to be localised in the engraving and was similar to what would be expected by erosion corrosion caused by micro-particles in the ink. That is, where the ink, that has been squeezed into the engraving, comes into contact with the edge of the engraving, the chromium showed signs of erosion corrosion. This in turn then allowed the low pH ink to start interlamellar corrosion to occur, resulting in de-lamination of the overcoats at the interface of the over layers. I hope this may offer an insight into what is going on.

A. This corrosion of Gravure cylinders isn't uncommon. The problem usually occurs after the cylinder has been run on a press, and then stored before the next print run. After around 4~500,000 meters of printing, the Cr deposit thickness will be reduced by around 30~40%. If the copper preparation isn't thorough enough, or the Cr deposit isn't as thick as you think it is, then corrosion can occur in pits or adhesion can suffer.

In UK around three or four years ago, we had a lot of this problem. One main reason was that, printers changed from organic solvent based inks to water based. With the organic based inks the printer didn't have to be so careful about cylinder cleaning before storage. With the water based inks, cleaning is much more important.

We spent a long time working with customers and printers to improve their housekeeping and production methods. Another problem was Cr thickness. The customers thought that they were plating 10~12 microns, but in fact were only plating 8. After the cylinders had been polished they where down to 6 microns, and by the time the cylinders had been run on a press and put into storage, there was only 3~4 microns left at most. When the printers tried to run the cylinders a second time, the Cr would flake off the copper surface.

The surface area of an engraved cylinder is in reality much larger than the sum of its dimensions would suggest. So customers have to allow some extra time to deposit the thickness they think they are.

We also looked at cylinder storage at printers. New, and used cylinders must be kept dry and clean at all times. After printing they must clean and dry the cylinder thoroughly, then wrap and store the cylinder properly.

If these points are looked at, then you will be able to cure this problem.

Hope this helps.

Regards,

A. Regarding the chrome peeling:

Is the chrome peeled off from the copper or do you see after the print the steel base (or the nickel deposit?)
Where does the chrome peels off, is it on the radius in majority? If yes, the use shields in order to avoid excessive build ups and ask your printers (if they are already not doing it to cut the blade ends approx. in a 45 degrees angle and 50mm wide, if the blade oscillation is on and running about 10-15mm across the cylinder then the blade has a relaxation area.
Do you use filters in your ink, any metal particles in?
Any difference by using different inks on different units?

5-7 micron is enough to print around 1.5 - 2.2 million cylinder revolutions. Please consider that above these thicknesses you may cause a build on cell rim between the wall, that also could led to a "rip-off" during the print, especially if the angle and blade pressure as well as the impression roller pressure is too high. As low as possible from everything, as you longer you enjoy your print run.

Kind regards,
Dominik

A. Ask the supplier of the engraving and/or chrome plating to slightly polish the surface of the roll before plating it.

Regarding you high voltage maybe the contact's from the rectifier is oxidized. It's normally to use 3,5-4,5 voltage for 30 A/dm2. Also make a analyze for the trivalent chrome, iron and copper. Both these metal's can show a bad resultant by the hardness. I believe all this parameters is your's problems. Normally a chrome solutions have a hardness from 900-1100 HV depending which chrome solution who used. Regards, Anders Sundman 4th Generation Surface Engineering Consultant - Arvika, Sweden 2004 A. Dear Azizur, I think you need to correct your basics. Lower the temp to about 55-57 °C and increase anode-cathode ratio to 2:1. Also check for metallic contamination as they bring down the hardness(IRON,COPPER etc. ALL COMBINED NOT MORE THAN 15 gm/lt). Try high speed non etch baths from chem. providers say HEEF-25 they do have better hardness, throw and corrosion resistance. ALL THE BEST. Vikram Dogra Irusha India - Chandigarh, India

A. Due to the micro crack structure of the hard chrome and the fact that the solvents used in cleaning cylinders after printing attract moisture, oxidation of the copper takes place under the chrome layer.you will see this by looking at the colour of the exposed copper. I have found that a thin wipe of light oil and to wrap the cylinder in plastic solves the problem.

A. Chrome is not very resistant to corrosion, certain types of inks will attack it, but it is very hard. That's why you use it on top of your engraved rolls. Copper in turn is soft, very corrosion resistant and much more noble (galvanic potential against chrome). I think your best chances would be to find more friendly grades of inks. Also, there are special chrome baths prepared to increase the corrosion resistance. One is called microcracked or porous chrome and the other is called thin-dense chrome. It may be worth investigating their suitability for your situation.

A. What is the hard chrome bath you are using? If you are using HENE process, then try increasing sulphate content in hard chrome bath to ratio 100:1. If you are getting roughness in copper bath, then give activated carbon treatment to the copper bath.

A. Dear D. R.,

Do you plate two or more cylinders of same diameter and length? There can be difference in wall thickness of shell, contact resistance of fixtures and anode connections at different location resulting in the difference. In my view if you are plating over 8 microns and variation is maximum say 1 micron it should not matter much. Do test on non production job for thickness and hardness. Best luck!

A. You may consider TiN coating or electroless nickel plating instead of chrome. Both are more resistant to acidic environments, specially in presence of chlorides. TiN is harder than chrome but is very thin. EN is softer than chrome but may work due to it corrosion resistance. Now, if your customer really wants the best and is willing to pay, you may have the cylinder coated with a high nickel or high cobalt hard alloy. There are at least two processes for the purpose, spray-and-fuse (coating absolutely dense and adhered) and HVOF (less dense and only mechanical adhesion). Both will produce a very hard and corrosion resistant surface that will not require chrome.

A. Dear Friend,

You are maintaining the concentration of chromic acid in the correct level. That is 240 is the optimum for maximum hardness and crack. If you maintain that range 240 to 250 your deposit will have the desired characteristics at its best.

Regards

A. Please tell us more about your specific situation. What are your cylinders made of and if the base material is coated with some hard coating like chrome, also what do you think is the wear mechanism, abrasion? corrosion?

A. Dear Mr AK Viswan,

White ink is a very abrasive ink which leads pretty quick to an excessive wear of blade and chrome surface. Right choice of white ink supplier + right choice of brand and type of doctor blade gives you longer run times. Also the roughness of the polished chrome surface and its pattering plays an important role.
However, some further adjustments can be done in your pre-press as well at your press area in order to achieve major results by lower running costs.

Kind regards,
Dominik

A. Good day for all

1. Cylinder peeling off
- Method of cleaning:
(cylinder surface must be clean - to wipe with oil and to wrap with plastic)
- Method of storage:
(Must keep at dry area )
please check how long the last print, 6-12 month

- To check the mileage of cylinder print:
(The best is from 750k meters - 1.5 mil meters and sent for chrome. re chrome is cheaper compare to make new)

- To check the quality of cylinder supply from vendor:

2. White cylinder worn off (cell shallow)
- for your information white ink contains TIO2; it makes cylinder plating very fast worn off. The max for the shell life is around 1 millimeter - 1.5 millimeter and depend on your control of doctor blade pressure and machine speed. 15 days run without non stop is huge.
My advise, you should go for 2nd set of cylinders.
In my country new cylinder cost is USD 400.00 only.

All the best

A. Don't forget a regular analysis of your ink; it's very easy for a supplier to "miss" out certain lubrication additives to save cost.

A. White inks are very abrasive! Try extra Chrome! Most of the cylinder is 10 micron wall so the actual surface area is very small. And press operators crank down on the doctor blades.

A. Hi, cousin Saeed.

For most types of plating, the plating proceeds slower at lower current density; but in the case of chrome it completely stops. Chrome will not plate at all if the current density is too low. Are these troublesome cylinders bigger, or do they have more surface area than the cylinders that you successfully plate?

Regards,

A. Hi,

please consider a higher CD since after engraving your surface is increased.

Regards

True enough, David. And we could all learn from yours as well.
Luck & Regards,

A. Hi Craig. When it comes to plating, everything affects everything :-)

I am assuming that you are speaking of gravure rolls? If not, please clarify. I think you are asking if you can apply the chrome well enough and thick enough to make the properties and condition and performance of the chrome plated surface independent of the underlying copper plating layer and unaffected by it. Sorry, but I don't think that will work. Certainly the hardness and thickness of the underlying copper will affect corrosion under the chrome and cracking and other problems with the chrome.

It is very difficult to answer abstract questions because they always involve a hundred "Ifs, ands and buts", but if you can explain your individual situation, I think the readers can help you solve your problems. Good luck.

Regards,

? Hi.
To just state cylinder wear is not enough information. Firstly ASSUME your cylinders are within spec, then you can start to look at quality of ink, blade pressures/angles nip points, etc.
Sorry to be so vague, but so is the subject; we have had very similar issues here, but all can be eliminated with the correct approach.

? Hi John,

What are your chrome parameters and properties vs product of print? How is your surface quality (roughness value and pattern)?

Regards,

A. Hi,

The temperature in your pretreatment bath is too low.

Regards

A. Here is an example of classic wear, which starts on the edge of the cylinder and gradually moves in:

Normally, far too high a blade pressure, trying to achieve a clean wipe, when changing the blade and/or angle would have worked.

Garry Williams
- Liverpool, Merseyside, England
November 1, 2012