What is the cause of printing color deviation? What causes the color tolerance?

Ideally, just put the ink into the press and simply operate the production. But in the effort to achieve the right color, wasted ink, printing material and printing time often occur. Although technological advances have made it easier to achieve color accuracy, there are still various variables that can affect color.

Below we describe the impact of the printing environment and the printing press on the final color.

1 - Temperature and humidity

Temperature and humidity can have a huge impact on how the ink is transferred to the substrate, especially for solvent-based inks. Some printers even use a mix of winter and summer solvents to help control the problem. Ink that transfers well will result in a deeper and fuller color. Ink that dries too quickly will feel grainy and look lighter. If the ink coverage capacity is low, the substrate can not be well covered, thus affecting the reading of the spectrophotometer. A magnifying glass can be used to observe the ink field color blocks to ensure that the ink adequately covers the substrate.

2 - pH is too high or too low

The high temperature of the printing shop will cause the evaporation of important amines in the water, so that the pH value is too low. This results in poor ink transfer, causing problems with blistering, pinholes, and lighter overall printing color.

On the other hand, too high a pH may burn the pigments in the ink, for example some oranges are not as durable as others. The volatile components of these inks may disappear from the ink in small amounts, causing a loss of color.

3 - Replace the roller

The biggest cause of color errors is probably not adjusting for the new roller or gravure roller. The new gravure cylinder will transfer more ink than the gravure cylinder that has been used for a long time. Although newly developed gravure printing operations will get very full ink results at first, after a few months their completed work will begin to fade.

Since the volume of the plate roll plays a key role in the amount of ink transferred, the ink is formulated according to the plate roll of the press and recorded in the approved job. Over time, rollers transfer less ink, so long-run jobs should be closely monitored. Consider drawing a mesh roll diagram for tracking so you can determine when to adjust it.

4 - The roller is dirty or blocked

Stains or clogging of the roller will cause the color to become very light, which is difficult for ink technicians to overcome. If there is still little effect after repeated addition of colorant, it is likely that the mesh roller is blocked. In order to quickly determine the problem, you can try to replace the roller or wash it with soda spray.

5 - viscosity

During flexo and gravure processes, viscosity can be difficult to monitor because they change quickly. Although many modern presses come with automated systems that can monitor viscosity, the monitoring system can malfunction or unexpectedly shut down. If your color becomes full quickly, it is likely that the viscosity has increased. Keep in mind that ink loses viscosity for a few seconds when it is first put into the press, which is caused by the shear action of the run cycle, because ink is a thixotropic fluid.

Once approved, it is recommended that the viscosity information be recorded.

6 - Printing pressure

Printing pressure is probably the easiest problem to solve. Observe the dot expansion and density of the color you are printing. If everything is normal, but the color is still too full, consider reducing the printing pressure. On the contrary, if the color is too light, the printing pressure can be strengthened. You may also see spots. These uneven patterns can lead to erratic readings. You can try adjusting the printing pressure, opacity, or ink connection material to eliminate inconsistencies.

7 - Network expansion and density

Primary color printing can be very tricky because it is possible for all density levels to be in the normal range, but only 1 print primary color is still too full. If the dot size is also too high, the press operator may reduce the problematic print color to obtain the correct print color overall. Density and dot expansion interact, and both can be checked using the eXact densitometer tool.

8 - Plate and blanket hardness tester

As time goes on, the hardness of the plate of the old photosensitive material may become greater. This results in poor ink transfer and too light color. In some rare cases, the transferred color may be so light that adjusting the ink is still not enough to compensate. At this time, apply the hardness tester to check the hardness of the plate. Plate suppliers can provide you with more information about the parameters.

9 - Ink scraper problem

Abrasion of the scraper can cause too much ink to flow between it and the mesh roller or gravure cylinder, resulting in very full color. In some cases, the press may still operate normally, but suddenly the density increases quickly. At this point, the ink scraper should be checked. It will probably need to be replaced.

10 - Plate liner material

As with the flexographic hardness tester itself, the adhesive liner (which is commonly known as double-sided tape) also has an impact on the performance of the flexographic. If the desired look or color cannot be obtained, consider replacing the liner material.

Different grades of plate liner material (" sticky liner ") affect printing characteristics, dot expansion and printing pressure. For example, a sticky liner with greater hardness may achieve better results on some substrates, a sticky liner with medium hardness may perform well in primary color printing, while a sticky liner with less hardness has great elasticity and a certain tolerance for printing pressure. The latter may be a good choice when there is a gear flutter problem in printing.