In the world of flexographic printing, accurately calculating the sheet polymer plate distortion is crucial for ensuring high-quality prints. Here’s what you need to know about this process and how to perform the calculations effectively.

Key Considerations Before Calculating Sheet Polymer Distortion

Critical Measurements Needed to Calculate Sheet Photopolymer Distortion

1. Repeat Length

• The cylinder repeat length that the plates will be mounted on.

2. Photopolymer Thickness

• The thickness of the photopolymer plates being printed.

3. Plate backing thickness

• The thickness of the polyester/Mylar backing material.  This can be obtained by consulting with your plate vendor or manufacturer.

Step-by-Step Sheet Polymer Distortion Calculations

1. Calculating the Constant

To start, you need to determine your constant based on the thickness of the photopolymer plate. Let’s use a 0.067” plate as an example. 

• Photopolymer Thickness:
  • Take the photopolymer thickness, 0.062″, and multiply by 2 (since the plate affects the diameter of the print cylinder twice, or on opposite sides of the cylinder). This equals 0.124″
• Multiply by Pi:
  • Multiply 0.124” by Pi (3.14159): 0.124×3.14159=0.38950.124 \times 3.14159 = 0.38950.124×3.14159=0.3895
  • This 0.3895 value is your K-factor for a 0.067” plate. Note: 0.39 is a common and widely accepted value in the industry.

2. Calculating the Distortion

Now, let’s calculate the distortion using a 15” repeat as an example.

• Subtract the K-factor from the Repeat:
  • Subtract the K-factor (0.3895) from the repeat (15”): 15−0.3895=14.610515 – 0.3895 = 14.610515−0.3895=14.6105
• Calculate the Distortion Percentage:
  • Divide the result by the original repeat (15”): 14.610515=0.97403 or 97.403%\frac{14.6105}{15} = 0.97403 \text{ or } 97.403\%1514.6105​=0.97403 or 97.403%

Alternative Calculation Method

You can also calculate the distortion without using the constant directly.

• Calculate the Print Diameter:
  • Divide the repeat (15”) by Pi (3.14159): 153.14159=4.7747\frac{15}{3.14159} = 4.77473.1415915​=4.7747” print diameter
• Subtract the Polymer Thickness:
  • Subtract the photopolymer thickness (0.124”) from the print diameter (4.7747): 4.7747−0.124=4.65074.7747 – 0.124 = 4.65074.7747−0.124=4.6507
• Calculate the Distortion Percentage:
  • Divide the result by the print diameter (4.7747): 4.65074.7747=0.974029 or 97.403%\frac{4.6507}{4.7747} = 0.974029 \text{ or } 97.403\%4.77474.6507​=0.974029 or 97.403%

By following these steps, you can accurately calculate the distortion for your flexographic sheet polymer plates, ensuring precise and consistent results in your printing process. Understanding and implementing these calculations will help you maintain high-quality prints and avoid common errors related to polymer distortion.

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