Technical Information

Under normal circumstances, you should be able to put ink into the press, run the job, and achieve color consistency. Unfortunately, flexographic and gravure operations waste ink, substrates, and press time every year trying to get the color right. Despite advancements in technology that make achieving color accuracy easier, variables that affect color still exist. In this three-part series, we will share over twenty reasons why your color may be off in print. If you missed Part 1 Instrumentation Please check it out first. We will explore how your standards and inks affect the final color.

It is easy to accidentally select the wrong color standard in software. Some systems have hundreds of color standards. For this situation, the following points should be noted:

• Check to ensure that the standard you select has the same characteristics as the job you are printing.

• Organize your standards by customer, including details such as substrate, screen ruling, ink system, etc.

• Input standards with the correct instrument settings and backing material.

• Make sure the color standard is on the same sheet of paper as the printed sample. For example, you cannot compare an uncoated Pantone color on bleached white stock to an off-white, mottled white corrugated board.

Using too many base inks may not achieve your target color or saturation, which often leads to fruitless efforts, as each ink has a different spectral composition of reflected light. An ink should be formulated with as few base inks as possible.

Is the substrate on the press exactly the same as the substrate used to create the standard? Does the substrate supplier have difficulty providing consistent material? Is the material bottom-laminated material different from yesterday? Are you comparing using matte polyethylene and clear lamination?

Changes in substrate can have a huge impact on how color reads on press. Consider making your substrate a physical standard in your workflow, just like using ink draws. Also, Check your substrate to ensure it is within tolerance before checking any colors, then adjust the ink or run the job.

Overprint varnish (OPV) is often overlooked because it is clear, but don't let that fool you. OPV can greatly affect color shifts. Typically, overprint varnish will cause the color to shift toward the blue side. It can also make the color appear darker and richer. In most color overprint varnishes, you will see a decrease in the L value. If you are unsure, take some readings with and without OPV to see what the difference is. If your print job requires OPV, it is best to use OPV to input your color standard, as this is the final condition the customer will see. Problems also arise when spot OPV goes through the center of the color bar. Since some readings will have OPV and some will not, you will get inconsistent readings.

    Even with the best ink technology, a bad batch of ink can happen. However, if this problem is not noticed immediately, it can lead to hours of ink adjustment and press waste. One way to address this is to establish a quality assurance plan with your ink room to ensure the correct ink is about to be printed. Common practice is to attach a COA (Certificate of Analysis) sheet to the batch about to be printed to ensure accuracy. You should also measure and verify the ink before putting it into production.

The BestMatch function on the eXact is a predictive color tool that looks at concentration and ink thickness to see if you can get the right color. It can also help you determine if you can achieve a closer match to the specified color by adjusting the ink on the press.

This is common in busy print shops. Press operators, especially when running solvent-based and water-based inks, must use stabilizers, glycols, alcohols, water, etc., to maintain ink performance. Too many additives will actually ruin the ink. Another common problem, when everyone is in a hurry and production needs to go out the door, is skipping the step of thoroughly cleaning the press, sump, and fountain when changing colors.

Once a color is contaminated, the only way to correct it may be to start over. The basic comparison tool on the eXact 2 can compare the ink in the press to the ink in a new container to check for contamination. A less scientific method is to drop ink from the press onto the lid of the original ink container. If you find a huge difference between the two, it is likely that your ink is contaminated.

         Improper ink drying can lead to ink duct contamination. It may or may not affect your color, but it is important to note this. In extreme cases, if other inks are not dried properly, the yellow ink sump may turn completely orange or even brown.

Different ink colors have different opacities. Worse yet, ink companies use multiple ink systems and dozens of suppliers, creating even more unknowns in terms of opacity differences. eXact 2 supports opacity readings You can avoid wasting time and money by taking opacity readings. Understanding your opacity capabilities can help you set clear customer expectations.