Flexographic printing is designed for printing text and graphics onto a range of substrates, such as paper, laminates, film, and foils. It’s one of the most popular printing methods, especially if your project requires the highest quality prints and color brilliance.
What is Flexo Printing Ink Transfer?
Ink transfer is the basis of successful flexographic printing. It's the amount of ink being moved through the components of the printing process and ultimately onto the substrate.
In flexographic, ink transfer is primarily controlled by three things.
- Image carrier (cylinder, sleeve, or plate)
Components of Ink Transfer
An anilox is a cylinder used to roll ink onto the carrier image. The amount of ink delivered is controlled by a pattern of small precisely sized dimples, or cells, in the anilox surface. This cell pattern is defined by three variables.
- Cell volume. The cell volume of an anilox is the total space available to hold ink in one square inch of cells on its surface. This controls the amount of ink supplied to the image carrier and the resulting ink film thickness on the substrate.
Generally, greater volumes are used for brighter, bolder work, and smaller volumes for finer high detail work.
Cell volumes are typically expressed in billion cubic microns per square inch (BCM/in2), with general guidelines of
- Solids and Heavy Line 4.0 -9.0 BCM/in2
- Text and Regular Line 1.0 – 8.0 BCM/in2
- Spot Vignette 2.0 – 3.6 BCM/in2
- Process Color 0.9 – 2.8 BCM/in2
- Engraving angle. The engraving angle is the arrangement of cells in relation to the axis of the roll.
The most common engraving angles are 30°, 45°, and 60°, with 60° being the most prevalent due to its efficient packing of cells. This provides a very uniform ink distribution.
- Cell count. Cell count is the amount of cells per inch the anilox has when measured along the engraving angle.
Higher cell counts (which correspond to lower volumes) are typically more appropriate for finer detail work while lower cell counts (with higher volumes) are better for bold, and higher density work.
The industry standard for halftone printing uses an anilox cell count at least 4X the line count of the halftone. This is the minimum requirement for supporting a 2% dot. In practice, even higher cell counts may be more appropriate for rendering highlight detail.
Your optimum combination of cell count, cell volume, and cell angle varies based on substrate and ink properties.
Often the best anilox is selected by trying multiple cell patterns and seeing what gives the desired result. To find this a banded anilox test is completed where a print sample is run with a special anilox that has multiple lanes with different cell patterns to compare their performance.
2. Image Carrier
The image carrier delivers the ink to the substrate. It has a major influence on the efficiency and the quality of the print.
Image carriers can be made from a variety of materials. The material is chosen to accommodate the specific printing variables for a given job, such as
- ink formulation
- substrate characteristics
- press speed
- operating temperature
High print quality can only be achieved when the carrier is able to pull all the ink out of the anilox and then release it completely to the substrate.
Image carrier materials need to be specially designed to do that while also standing up to the stresses of the printing process.
The substrate receives the ink and becomes the final product when printed. Flexographic printing is able to mark on a multitude of substrates, which makes it the method of choice for a wide variety of finished product requirements, including
- high strength
- specific appearance or feel
The need to get adequate color on various substrates drives many of the other print process variables, such as the image carrier and ink. These components must all be carefully calibrated to ensure optimal printing.
The most important part of the flexographic printing process is the application of ink. Are you laying down all that you can? Let us help you find out!
Editor's Note: This blog post was originally published Mar 24, 2017, and was updated on August 22, 2019 to reflect updated information and insight.