Ideally, all that is needed is to put the ink into the printing press and simply operate the production process. Unfortunately, every year, flexo and gravure printing operations waste ink, substrates, and printing time in the effort to achieve the correct colors. Although technological advancements have made color accuracy more attainable, there are still various variables that can affect color.
- Using the wrong color standard:
It is easy to accidentally select the wrong color standard in software. Some systems have hundreds or even thousands of color standards. To address this issue, pay attention to the following points:
- Check to ensure that the selected standard has the same characteristics as the job to be printed.
- Organize the standards according to the customer and note details such as the substrate, anilox roll, and ink system.
- Input standards with the correct instrument settings and backing materials.
- Ensure that the color standard is on the same substrate as the printed sample. For example, uncoated Pantone colors on bleached paper should not be compared with colors on kraft paper or off-white corrugated paper with mixed colors.
- Using too many base inks:
Ink formulations with too many base inks may not achieve the desired color or saturation, which often leads to futile situations, as each ink has a unique reflectance spectrum. It is advisable to use the minimum number of base inks to formulate an ink.
- Changing substrates:
Is the substrate on the printing press exactly the same as the one used to create the standard? Is the substrate supplier struggling to provide consistent materials? Is the underlying material different from the one used the day before? Are you comparing a laminated structure with a matte polyester to one with a transparent polyester? Changes in substrate can cause significant differences in color readings on the printing press. Substrates can be treated as actual standards in the workflow, just like ink drawdowns. Additionally, before checking any color, inspect the substrate to ensure it is within tolerance, and then adjust the ink or run the job.
- Ignoring overprint varnish (OPV):
Overprint varnish (OPV) is often overlooked because it is transparent. However, do not be deceived. OPV can cause noticeable color shifts. Typically, it causes colors to shift towards blue. Moreover, it can make colors appear darker and more intense.
In most cases of overprint varnish, the L value will decrease.
If you are uncertain, you can take readings with and without the overprint varnish to see the difference.
If your printing job requires overprint varnish, it is best to use a color standard with overprint varnish, as this is the final state the customer will see.
Spot color overprint varnish can also cause problems, especially in a color bar, because some color patches are varnished while others are not, leading to unstable readings.
- Using substandard ink batches:
Even with the best ink technology, substandard ink batches can still be produced. However, if this issue is not immediately noticed, it can lead to hours of wasted ink mixing time and press downtime. One way to address this issue is to establish a quality assurance program with the ink shop to ensure that the correct ink enters the printing press. A common practice is to attach a Certificate of Analysis (COA) to the ink batch that will enter the press to ensure accuracy. Additionally, the ink can be measured and verified before being loaded into the press.
- Contamination:
Contamination is very common in busy printing workshops. Especially when running solvent-based and water-based inks, printing operators need to use additives such as stabilizers, ethylene glycol, alcohol, and water to maintain ink performance. However, excessive additives can ruin the ink. Additionally, another common problem arises when everyone is rushing to complete production tasks and skips the step of thoroughly cleaning the ink fountain when changing colors. Once the color is contaminated, the only corrective action is to reprint. The basic comparison tool of the X-Rite Exact can check for contamination by comparing the ink in the press with the ink in a new container. Another less scientific method is to drop the press ink onto the lid of the original ink container. If a significant difference is found between the two, it is likely that the ink has been contaminated.
- Improper drying:
Improper drying of ink can lead to ink contamination. It may or may not affect the color, but this needs to be monitored. In severe cases, yellow can turn completely into orange or even brown when other inks dry improperly.
- Different opacities:
Different ink colors have varying opacities. The use of multiple ink systems and dozens of suppliers by ink companies further exacerbates these opacity differences. By measuring opacity, time and cost waste can be avoided. Understanding opacity helps set clear customer expectations.