What is LPI in flexo printing? | Keshenglong&Shinko Guide

What is LPI in Flexo Printing?

Understanding Line Screen Ruling (LPI) is crucial for achieving high-quality flexographic printing. Many printers struggle with achieving optimal image reproduction due to incorrect LPI settings. This article clarifies what LPI is and how it impacts your print results.

Understanding Line Screen Ruling (LPI)

LPI, or Lines Per Inch, refers to the frequency of halftone dots used to create the illusion of continuous tone in flexo printing. Instead of printing solid colors, images are broken down into tiny dots, varying in size and density to represent different shades. A higher LPI means more dots per inch, resulting in finer detail and smoother gradations. Conversely, lower LPI produces a coarser, more noticeable dot pattern.

Choosing the Right LPI for Your Flexo Printing

The ideal LPI depends on several factors:

Printing Press Capabilities: Your press's capabilities directly impact the achievable LPI. Older presses might struggle with higher LPIs, leading to poor print quality.

Substrate: The material you're printing on affects dot gain (the spreading of ink during printing). Coated substrates generally allow for higher LPIs than uncoated ones.

Ink and Anilox Roll: The viscosity of your ink and the anilox roll's volume all influence the final dot reproduction. Incorrect settings here can lead to muddiness even with a suitable LPI.

Image Resolution: Your original image's resolution should be at least twice the target LPI for optimal results. Using a low-resolution image with a high LPI will result in poor quality printing.

Common LPI Values in Flexo Printing

Common LPI values range from 85 to 175, but the optimum choice depends on the factors above. Newspaper printing might use a lower LPI, whereas high-quality packaging often utilizes higher LPIs for finer details. Experimentation and careful consideration of your specific printing parameters are key.

LPI and Image Quality: A Summary

Incorrect LPI settings can significantly impact print quality, leading to blurry images, muddy colors, and noticeable dot patterns. Selecting the appropriate LPI, in conjunction with other print parameters like ink, anilox, and substrate, is essential for achieving optimal results and meeting client expectations. Consult with your printing experts at Keshenglong&Shinko for assistance in optimizing your LPI settings.