Process Calibration

Photopolymer Flexographic Printing Plates

Traditional Digital Plates (round top dots)

 

Overview

Flexography is a relief printing process.

The back exposure of the plate sets the floor thickness and subsequently the relief depth of the printing plate.

One aspect of calibrating a flexographic printing plate is finding the back exposure (Bx) time that gives a target relief depth.

A STEP TEST is the procedure used to determine a correct Bx time is determined.

You will perform a STEP TEST. This process is the same whether doing a conventional or digital photopolymer flexographic printing plate.

 

Assignment

Work with your group to determine the proper back exposure time to achieve a relief depth of:

0.018 - 0.022 in. (22 mils) for 0.067” thick plates

0.012 - 0.016 in. (15 mils) for 0.045” thick plates …if assigned

​

Assigned plate material and the exposure unit for your step test is found on Google Drive in the shared file named GC 4060 Schedule - [current term]

look on the back exposure tab in this file   

 

Plate Material Options Exposure Unit Options

 DuPont DFR .067 & .045   DuPont FAST  EC/LF

 DuPont DFM .067   Anderson & Vreeland

 Toyobo Cosmolight QS-D 1.70  (FYI 1.70 mm = 0.067 in.)

 

Materials Needed

• Digital plates Masking material  pen or marker

• Exposure units Bench Micrometer

• Thermal Processor Safety cutter

• Water Wash Processor  

 

Method   

Warm up the UV lamps on the exposure unit if not used

1. Plate material used in Godfrey Hall is sized at 25 x 30 inches.

   1. Cut your plate in half so you have a piece that is
      roughly 25 x 15 inches for the DuPont thermal plates

   2. Save/Share the other half with another group

   3. NOTE: Plates might already be pre-cut for you...if so ignore the step 2

2. Determine which is the face and which is the back of plate

3. Using a pen or marker, draw lines on the back of the plate to “STEP” the plate into 5 or 6 segments across the 25 inch or widest dimension of the plate

4. Determine a practical range of times that could bracket a back exposure result with the appropriate relief depth.

5. Write those on the back of your plate and also on this sheet.
   HINT: for these plates do not go lower than 20 seconds or more than 160 seconds for the step test.

 

1. Perform the step test as per your demo.

2. Process the plates as per your demo

   1. Note 1: Be sure to select the appropriate plate settings on the PLC of the DuPont FAST EC/LF Unit

   2. Note 2: Your widest dimension goes around the drum for this assignment

   3. Note 3: You can share the drum with another group OF THE SAME PLATE MATERIAL if the timing works out

   4. Note 4: You can share the Anderson & Vreeland washout with as many other groups who are ready and will fit on the platen.

3. Post expose and detack your plate

4. Measure your floor thickness and determine a plate relief of:

   •  0.018 - 0.022 in. (22 mils) for 0.067” thick plates

   •  0.012 - 0.016 in. (15 mils) for 0.045” thick plates…if assigned

5. If outside of this tolerance, then interpolate a correct time and make another plate or repeat step test.

 

Variables

Plate material = __________________________

Plate Caliper = __________________________

Exposure Unit = __________________________

Processor = __________________________

Results

Floor Thickness = ___________________  (use proper units)

Plate Relief = _______________________  (use proper units)

Exposure Time = ____________________  (use proper units)

 

Lab Section   MW TR

Group # _______

Group Names:

Questions

1. What does the back exposure do?
    

 

1. Why is it important to periodically measure the relief of
   a printing plate?
    

 

1. List 3 characteristics (plate or process) that can result in different exposure times to achieve the same plate relief?
   Hint: Why might other groups have different exposure times?

   1.  

   2.  

   3. 
       

2. So now you have determined the correct back exposure time for a flexographic plate to get the appropriate floor thickness, or relief depth, how might you determine the correct face exposure time for a flexographic plate?  Hint…this can be answered in one sentence or a few words.