How Instrumentation Affects Color on Press

March 30, 2017 by Scott Harig

In a perfect world, you should be able to put ink in the press and simply run a job. Unfortunately, every year flexo and gravure printing operations waste ink, substrate and press time trying to get color right. Although advancements in technology have made it easier to achieve color accuracy, the variables that affect color still exist.

In this three-part series, we’re sharing over two dozen reasons your color might be wrong on press. If you missed the first article – Instrumentation – check it out first.

Today we’re looking at how your standards and ink can affect final color.


1 – Using the wrong color standard.

It is easy to accidently select the wrong color standard in your software. Some systems have hundreds or thousands of color standards. Here are some tips:

  • Check to make sure the standard you select has the same characteristics as the job you’re printing.
  • Organize your standards by customer and include details like substrate, anilox, ink system, etc.
  • Enter the standard with the correct instrument settings and backing material.
  • Make sure the color standard is on the same stock as your print sample. For example, you can’t compare an uncoated Pantone Color on bleached white stock to an off white, mottled KLA white corrugated stock.

2 – Using too many colorants.

An ink batch that is formulated using too many colorants may not be capable of hitting your target color or strength. This usually causes a “chasing your tail” scenario because the ratios of colorants differ from one another. Always formulate inks with the smallest number of ingredients possible.

eXact InkKeyControl Software with eXact Scan is a manual scanning solution for press-side ink key control in offset print, increasing productivity by reducing press set-up time.

 

3 – Changing the substrate.

Is the substrate on press exactly the same as the substrate used to create the standard? Is the substrate supplier having difficulty providing a consistent material? Is the material laminated with a different material on the bottom than it was yesterday? Are you comparing a laminated structure using matte poly versus clear?

Substrate changes can make a huge difference in how your color reads on press. Consider making your substrates actual standards in your workflow, just like you would with ink drawdowns. And, before checking any colors, check your substrate to ensure it’s within tolerance before toning inks or running the job.

4 – Overlooking overprint varnish.

Overprint varnish (OPV) is often overlooked because it’s clear, but don’t let that fool you. An OPV can dramatically affect how a color shifts. Typically, an overprint varnish can cause a color to shift toward the blue side. It can also makes colors look darker and more rich.

You’ll see a drop in L value when applying varnish on most colors. If you’re not sure, take some readings with and without OPV to see the difference. If your print job requires an OPV, it’s probably best to enter your color standard with OPV since this is the final condition the customer will see. Spot OPV can also cause a problem when it’s running through the center of a color bar. Since some readings will have OPV and some will not, you’ll get erratic readings.

5 – Using a bad batch of ink.

A bad batch of ink can happen to even the best ink tech. But not noticing the issue right away can cause hours of ink toning and press waste. One way to address this is to establish a quality assurance program with your ink room to ensure the correct inks are coming to press. A common practice is to have a COA (certificate of analysis) sheet attached to batches coming to press to ensure accuracy. You should also measure and validate inks before you put them on press.

The BestMatch feature on the eXact is a predictive color tool that looks at concentration and ink thickness to see if you can get to the right color. It can also help you determine if you can achieve a closer match to a specified color by adjusting ink on press. Check out our blog Bringing Ink Back into Tolerance to learn more.

 

6 – Contamination.

This is a very common occurrence in busy pressrooms. Press operators, especially when running solvent and water-based inks, have to use additives like stabilizers, glycol, alcohol, water, etc. to maintain ink performance. Too many additives can actually ruin the ink. Another issue that’s common when everyone is rushed and production needs to get out the door is to skip the step of thoroughly cleaning press sumps and fountains when changing colors.

Once a color is contaminated, the only way to correct it may be to start over. The eXact’s Basic Compare tool can compare the ink in press to ink from a fresh container to check for contamination. A less scientific way is to drop ink from the press onto the lid from the original ink container. If you see a dramatic difference between the two, chances are your ink is contaminated.

7 – Improper drying.

Inks that don’t dry properly can cause rewetting. It may or may not affect your color, but it’s important to be aware of this. In a radical scenario, a sump of process yellow can turn completely orange or even brown if the other inks aren’t drying properly.

8 – Different opacities.

Different ink colors have different opacities. To make matters worse, ink companies use multiple ink systems and dozens of suppliers, creating endless possibilities when it comes to variance in opacity. The X-Rite eXact Advanced supports opacity readings.

You can avoid wasting time and money by taking an opacity reading. Knowing your opacity capabilities can help you set clear client expectations.

Up next…

As I mentioned in part one of this series, you’re not going to achieve consistent color if only one operator follows these steps. You must document everything and communicate it to everyone involved in the workflow.

Stay tuned for the final installment of our “Why your Color Might be Wrong on Press” series – Environmental & Press Factors – coming up soon.

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