Flexographic Plate Distortion

Flexographic plate distortion is a key to flexo printing and the gear teeth of your press play a role in this. In this post, we are going to cover the relation between the flexo plate distortion calculation and gear teeth.

Distortion of flexo plates is required in all flexo printing. It is not necessary at all for offset or digital printing because flexo plates have a unique third dimension – height.

The Intricate Engineering of Flexographic Printing

Flexographic printing is a marvel of modern engineering, using science to produce vibrant, high-quality images on a variety of substrates. Unlike offset printing, which deals in two dimensions—width and length—flexo printing adds a third dimension: height. This extra dimension introduces the concept of flexo distortion, a critical factor in print production.

Flexo plates are made from a flexible polymer that wraps around a printing cylinder (see green area in the above diagram).  Due to the height inherent in these plates, the outside printing edge sits above or higher than the outside edge of the cylinder as seen in the dashed blue line below.

Understanding Gear Teeth and Repeat Length

Let’s say you’re working on a job with an 8.5-inch repeat length. In the world of flexo printing, this translates to 68 gear teeth, with each gear tooth accounting for 0.125 inches of the cylinder’s circumference (68 x 0.125 = 8.5). A repeat length is essentially the length of a printed number of labels before they repeat themselves on the substrate.  For example, you could print 1, 2, or 3 labels print around the cylinder within the length of 8.5 inches that gets repeatedly printed until the job is complete. 

Why does gear teeth matter?

• Gear Teeth as Measurement Units: They serve as the fundamental units for calculating the cylinder’s circumference.
• Precision in Printing: Accurate gear teeth calculations ensure that the plate wraps perfectly around the cylinder, aligning the image seamlessly.

The Science Behind Flexographic Plate Distortion

Due to the three-dimensional nature of flexo plates, we can’t simply use the flat repeat length for our calculations. The plate wraps around the cylinder, and its thickness adds to the circumference, necessitating a distortion adjustment.

Calculating the Distortion Percentage

To achieve a perfect fit:

1. Measure the Cylinder Circumference: Multiply the number of gear teeth by the pitch (0.125 inches per tooth). For 68 teeth, that’s 8.5 inches.
2. Account for Plate Thickness: The plate wraps around the cylinder so that means the plate height comes into play twice around the cylinder, so we multiply the plate height by 2.
3. We need to account for any sticky back tape used – and again twice the height around the cylinder. Also, any mylar used in the final plate will come into play.
4. Adjust the Image Length: We need to distort the image by 95.417% in the run direction (calculation explained later). This ensures that when the plate is mounted, the outside edge measures exactly 8.5 inches. 
5. This flexo plate distortion is always applied in one direction only and that is around the cylinder (not across the cylinder).

The formula for flexo distortion

Here is a spreadsheet showing some of the variables used to calculate flexo distortion.  In this example, one would enter the Gear Teeth required (68 in this case) and the Repeat Length and Distortion Amount would automatically be calculated based on the Gear Teeth and the 4 standard variables Gear Pitch, Tape, Mylar, and Plate.

There are various flexo tools and websites that help printers with this calculation.  

The FTA, an industry organization, publishes 2 different formulas for calculating flexo distortion required for plates:

C is the cylinder radius, T is the thickness of the tape, M is the thickness of the mylar, and P is the thickness of the Plate.

Equation #2 adds the RL variable which is repeat length.  Depending on the known values, use either of these two equations.  RL is repeat length.

NOTE: The distortion percentage cannot be the same for all flexo plates.
because the percentage varies based on plate thickness, cylinder size, and repeat length. Generally, plate thickness is a fixed value.  Repeat length which determines cylinder size is different for each job – therefore, a different distortion is used for each job depending on repeat length.

Ignoring distortion or applying the incorrect distortion value means the job will not print with the correct repeat length and the plate(s) cannot be used.  In this instance, the job must be re-plated with the correct distortion applied. This is a costly endeavor and causes a setback in production. 

Bringing It All Together: The Flexo Print Process

By meticulously calculating the gear teeth and applying the correct distortion percentage, we align the flexo plate perfectly on the cylinder. This alignment is crucial for:

• Maintaining Image Integrity: Preventing unwanted stretching or compression of the printed image. Flexo distortion compensates for the plate stretching that occurs when wrapping a three-dimensional flexo plate around a cylinder, ensuring the final printed image is accurate.
• Ensuring Color Registration: Achieving accurate color overlays without misalignment.
• Optimizing Production Efficiency: Reducing waste and reprints due to miscalculations.

Expert Tips for Managing Flexographic Plate Distortion

• Use Specialized Software: Leverage prepress software designed for flexo distortion calculations.
• Consult with Plate Manufacturers: They can provide exact plate thickness measurements for precise calculations.
• Regular Equipment Calibration: Ensure that cylinders and gears are in optimal condition to maintain measurement accuracy.

The Role of Kwality Labels in Precision Printing

At Kwality Labels, precision isn’t just a goal—it’s a guarantee. Kwality Labels utilizes advanced technology and expert knowledge to perform accurate distortion calculations and gear teeth alignment, guaranteeing high-quality prints every time. Ready to transform your printing process and quality?