Dot gain, registration, and trapping are three fundamental aspects of flexographic printing. Understanding these process variables can help packaging teams make more informed design decisions and better understand printed label outcomes.
Dot Gain
Dot gain occurs when the tiny dots of ink used to create images reproduce larger than intended during the printing process. In flexographic label printing, this can cause artwork to appear darker, more saturated, or lose fine detail compared to the original design.
Several factors can influence dot gain, such as plate characteristics, ink properties, and substrate. Dot gain may vary between materials, which is one reason a label may look different from one substrate to another.
Printers account for dot gain during prepress and press setup to reduce or eliminate any dot gain issues that will detract from the intended design.
How Dot Gain Influences Label Appearance
Customers should not expect dot gain to cause obvious changes to a finished label. However, because printing is a physical process, minor variation between a digital proof and a printed label can still occur.
Registration
Registration is the alignment of all printed colors and elements on a label. Slight registration shifts occur in almost every printing method.
In flexographic printing, each color is applied separately. Those colors must line up correctly to produce a sharp, accurate image. When registration is off, text and graphics may appear blurry, colors can look misaligned, and fine details may not look as intended.
Factors that influence registration include material movement, press speed, web tension, and substrate characteristics. Printers use established registration tolerances that help ensure a consistent result.
Why Registration Matters
Maintaining registration is a key aspect of printing a high-quality label. It is especially important for labels with fine details, small text, and specialty embellishments. During any stage of label and sleeve development, your printer might recommend design changes to better align with the printing process and registration tolerances.
Registration can be affected by normal press and material variables during production. The printer’s responsibility is to monitor and control that movement, so the finished label remains within acceptable tolerances. While slight registration shifts should not be visible, they may be when using thin outlines, borders, or drop shadow effects.
Trapping
Trapping is a prepress technique where color plates are created with intentional overlap between adjacent colors in the label design.
In flexographic printing, each color is printed separately. Even when a press is operating within acceptable registration tolerances, small movements occur as materials move through the press. Trapping acts as a safety net by creating a slight overlap between neighboring colors. This helps prevent small gaps that reveal the raw substrate as a result of minor registration movement.
How Trapping Supports Print Quality
Trapping is typically built during the prepress process and is intended to improve print quality, not change the appearance of the artwork. A prepress technician applies trapping to color separations only when the design does not allow normal registration variation to remain unnoticed.
In most cases, customers will not notice trapping on a finished label. However, depending on the colors involved, a trap may be visible as a slight darkening or overlap where two colors meet. This is less noticeable than the visible gaps trapping is designed to prevent.
Putting Flexographic Printing Fundamentals into Practice
Dot gain affects how ink reproduces, registration determines how colors align, and trapping helps prevent gaps between colors. Understanding these fundamentals of flexographic printing can help packaging teams better interpret proofs, evaluate designs, and set expectations for printed results.
At Steinhauser, we partner with you from the beginning to help your team create labels that deliver your brand promise. Packaging professionals looking to deepen their knowledge can explore educational resources and industry training offered by organizations such as the Flexographic Technical Association.