Prevent inks from changing colour when drying.

[nothernlights]

We are currently running a job with a large red background ( spot color ). Our problem is whenever we get the colour close to our approved colour we find that the next day the colour lightens or appears matte.

We've used inks that are mixed in the plant and inks mixed at our ink supplier and we get the same results. As you can imagine it is very difficult matching the colour if changes when it is drying.

I've read in "Solving Sheetfed Offset Problems" that this is due to not enough oxygen for complete drying and heat generated from the drying process but would like to know what are other possible caused of the problem.

Thanks

Edited by: nothernlights on Jun 24, 2008 2:20 AM

 

[Lukew]

Re: Prevent inks from changing colour when drying.

There will always be certain PMS colours that have a colour shift as they dry, and some colours you have to allow for more dry back then other's
We have had a similar case you have , since we don't have a densitometer it gets a little tricky,, But all I can suggest is get to a set colour density you are happy with and wait for it to dry a bit then check it against the approved colour..I know this means a bit of press downtime but its better then having to reprint the whole job due to incorrect colout..
If you have a densitometer you can just take a wet reading, and use these density figures if and when you print the job again.

 

[gsmith]

Re: Prevent inks from changing colour when drying.

Are you using an Aqueous coating?
Some colors that are high in pigment, like
reds will tend to "burn out" if your inks are
not formulated to be Aqueous coatable.

Just a thought?!

G

 

[Kruto]

Re: Prevent inks from changing colour when drying.

We also are having the same problem with PMS 643. Our ink supplier tells us that PMS colors with alot of Transparent White will dry back. This is very difficult to have to guess at. Put it on wait a day, and put it back on again.

 

[jlind]

Re: Prevent inks from changing colour when drying.

Northern Lights:
What kind of paper is this color change occuring on? Matte? Gloss? Uncoated?
Is the color change caused by gloss differences wet to dry? Do you measure the dry back with a densitometer? All questions and no answers, yet. Sorry
John Lind
Cranberry Township, PA
724-776-4718

 

[keldrewett]

Re: Prevent inks from changing colour when drying.

Two causes:

1: Stock. Run the ink on 5 different coated stocks and observe the colour shift. Some stocks absorb more ink vehicle than others causing the shift.

2: METAMERIC ink. Some combinations of colours do this when combined. They also do this thing where they appear different under different lighting. Make sure you always look at the colour under the same light. Easily overcome by ink maker. (google it)

Hope this helps!!

 

[nothernlights]

Re: Prevent inks from changing colour when drying.

The inks are printed on coated paperboard stock similar to STORA's Coated Kraftback. When when it appears "glossy" or "shiny". When dry it has a dull finish. We have a densitometer and we are measuring the differences in the colour from the wet to the dry sample. Is there anything else I should be looking for?

We've printed a solid red ( different shade ) that was printed on the same paperboard stock stock withthout any problems.

Thanks.

 

[keldrewett]

Re: Prevent inks from changing colour when drying.

There is your answer.
If it is drying back dull, some of the ink is being absorbed into the stock. Run a sealer varnish under the PMS and see how that looks. Try another coated stock.

 

[PrintSlave]

Re: Prevent inks from changing colour when drying.

Another tip that works is to throw a piece of the printed piece in the microwave for about 30-45 seconds. We use this trick all the time on jobs like you describe. You'll then have a "dried back" sample.

 

[Bob Peterson]

Re: Prevent inks from changing colour when drying.

First thing I need to know is whether or not you are running a overprint varnish or aqueous coating. If this is the case your gloss back from wet to dry can be caused by too much fountain solution in the red ink. Especially if you are running an aqueous coating.

If no coating or varnish is being applied I would suspect that the vehicle or varnish portion of the ink is diving into the paper board coating. This would definitely display the gloss to dull symptoms you described. This could be confirmed by printing the inks on a variety of coated stocks and observing the out come after they have dried. Should this be the case, have your ink company reformulate the ink using a high solids varnish, rather then a quick set, as the high solids varnish will yield more hold out on the substrate and you will not need to size the sheet.

You mentioned that you also tried another red ink on this stock and did not have the problem. I would suspect that the pigment or colorants used are probably different then the problem ink. You can check with your ink supplier as to whether or not this is the case. Some red pigments like napthol red (aka: real 032 red) will have severe dry back if not coated or varnished. Have your ink company rematch the problematic red ink using a different red pigment combination i.e. (yellow and rubine in stead of warm red). This may yield a metameric match but would definitely confirm the suspicion regarding the pigment initially used.

If you would like a 3rd party evaluation please feel free to send me a message and will be happy to arrange this for you at no charge.

 

[nothernlights]

Re: Prevent inks from changing colour when drying.

Thanks for the suggestions. We are still trying to get to the bottom of the problem. Does the anti-offset powder change the colour of the inks when drying?

 

[Indexx Printing]

Change to K&E ink. They are very high pigment ink and all their Pantone colors are Bio or low solvent content. We run them and have very little dri-back problems. Watch you water settings when running it the have excellent water hold out and dry very good. Also Reds are the worst color due to the prescence of iron oxide in the pigment and have the tendancy to oxidize during the dring. K&E has shown les of this than any other ink we have run.
Todd