KB189564222: Imaging Engine - How to calculate flexo plate distortion

Description

Flexo plates become slightly larger when they are wrapped around a printing cylinder because of the soft photo-polymer stretches. To have a correct size of the printing image a shrink factor has to be applied in the direction along the printing cylinder. This is sometimes referred to as flexo distortion or dispro.

In the Imaging Engine "Image to Screened Separations" ticket and in the Automation Engine Pilot this is called "flexo distortion". Since there is a built-in assumption in Imaging Engine and other Esko prepress tools that the vertical direction is the direction along the printing cylinder and the horizontal direction is the direction across the printing cylinder, a value smaller than 100% has to be specified in the Vertical distortion control.

 But what values should be used? Can these values be calculated automatically in Automation Engine?

Plate Vendor Calculators

There are flexo plate distortion calculators provided by flexo plate vendors like DuPont and Asahi. In these plate distortion calculators, plate type and the intended print repeat length has to be specified. The tool will give you the flexo distortion value.

The tool is typically a Microsoft Excel or a Windows application. Since these calculators are endorsed by the plate vendor, you can assume that these calculators give reliable results.

This gives you the values that need to be used. But it doesn't answer the question for plate types that are not listed. 

Flexo Distortion Tables

There is also an on-line flexo plate distortion calculator available at http://www.flexoexchange.com/tools/flexo-distortion-calculator.html

This calculator uses the gear pitch, number of teeth and plate thickness as parameters and returns the flexo distortion factor.

On the same page you can find tables with results of this calculator. 

Flexo Distortion Formulas

The correct formula to use to calculate the flexo plate distortion is:

K= 2 x π x (Plate thickness - Base layer thickness)
Flexo distortion =  (print repeat length - K) / print repeat length.

e.g.  For a plate with  thickness 1.70 mm, base layer thickness 0.127mm and a circumference (vertical size) of 500mm, the flexo distortion factor becomes 98.021%.

This formula is used by the plate vendor calculator and is also the formula used in flexo distortion tables mentioned in the previous paragraph.

Automating Flexo plate Distortion Calculation in Automation Engine

Now that we know the exact formula it is easy to define a SmartName that calculates the flexo plate distortion and plugs that value into the right UI control of the Imaging Engine ticket.

The SmartName needs to have access to the following parameters to do its work:

• length of the print repeat
• thickness of the plate 
• thickness of the base layer of the plate

An example of such an implementation can be installed on your Automation Engine by importing the following ticket using the Automation Engine Pilot: ImagingEngine_with_FlexoDistortion.zip

• The SmartName MISINTEGRATION_platethickness(mm) is a conditional SmartName that returns the plate thickness in mm based on a job parameter specifying the plate type
• The SmartName MISINTEGRATION_platebasethickness(mm) is a conditional SmartName that returns the base layer thickness in mm based on a job parameter specifying the plate type
• The SmartName MISINTEGRATION_flexodistort will calculate the flexo distortion in % using the values of the previous two SmartNames and a job parameter MediaHeight, defining the print repeat length.