Registration error in printing
Registration error, or misregistration, in printing refers to the misalignment of printing plates or the improper positioning of materials. This results in colors not aligning correctly in the final print, leading to a decrease in quality. Overlapping of colors can create a rosette pattern and prevent moire patterns, but this can sometimes be caused by machine errors, worn gears in each tower, material quality issues, or improper ink viscosity adjustments.
One of the simplest ways to detect and prevent this error is to use registration marks on each printing plate. These marks, part of the printing signature, are typically crosses, circles, stars, or similar shapes that can be checked with a magnifying glass or loupe. Registration marks should be present for all colors, and therefore, each plate contains 100% of that color. The black used in registration marks is called "Registration Color" and is sometimes mistakenly used in designs instead of rich black.
Registration marks consist of a combination of circles, lines, or stars, and the color must be 100% for each plate. These marks are generally the same in offset and flexographic printing and the thinnest printable line, depending on the plate type and machine capability, is used for the line thickness in the registration mark.
Registration Error and Rosette Pattern
One of the most important goals in commercial printing is to achieve a rosette pattern and proper alignment of AM halftones. Misalignment of halftones can lead to reduced print quality, moiré patterns, waste, and a double vision effect in colors. Similarly, if a registration error occurs in any of the printing towers, the color in question will be out of registration and experience a registration error.
This often happens with yellow because yellow is very bright and difficult to see. Even if there is an error, the machine operator or quality control personnel will first focus on the other colors that are easier to see.
Different Types of Errors
While adjusting registration to improve quality is a priority for anyone involved in the production process, it's also important to understand the causes of these errors. Misalignment in registration can be due to misalignment of a plate in its mounting position, elastic or stretchy printing material, or improper machine settings for aligning the material at the machine's input or feeder. There are different names for different types of misalignment, and the reason is to identify the cause of the error and address it.
For example, "Back Stretch" occurs due to unsuitable materials under the blanket or printing cylinder; "Fit" refers to when the plate sizes in different color towers are different; and in cases where there is too much ink and it can prevent the ink from drying on time, the term "Back Sheet Flare" is used as the type and cause of the registration error.
Controlling Registration Errors
As discussed, several factors can be considered to control registration and color overlap. The most important is proper plate installation in each color tower. This is easier to manage in offset printing due to its higher precision and slower speed, but in flexographic printing, the plate is typically a gelatinous cliché, and even the wrong cliché adhesive can prevent accurate and easy registration, so more care and control are required in flexography.
Additionally, in offset printing, choosing a high-quality material with a suitable grammage and a low ink coverage is a suitable solution. Similarly, in flexographic printing, reducing TIC, using Trapping or adjusting machine speed can better control color overlap.
There are also cases where registration errors are inevitable due to the nature of the product, such as printing large cement bags or base cartons, which are typically two-color and almost always have registration errors. Before production in such cases, it is recommended to simulate the amount of registration error using professional software like Esko Deskpack. This way, if the damage is minor and tolerable, production can begin.
