Process Calibration

Photopolymer Flexographic Printing Plates

Traditional Digital Plates (round top dots)​

 

Overview

Flexography is a relief printing process that uses a soft, resilient photopolymer printing plate. UV Light energy passes through openings in a film mask or carbon mask to expose the photopolymer. Enough energy/power needs to pass through the mask openings to fully form the image to the full height of the plate.

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Traditional digital flexo plates (with round top dots) require special attention to the minimum dots, ie the smallest halftone dot that will hold on a plate. Digital dots tend to not fully form during UV exposure because of the presence of oxygen. The best term to describe this is oxygen inhibition though you will hear it commonly call “dot sharpening” or “dot shrinking.” Because oxygen inhibits the formation of the dots, especially small highlight dots, the opening in the plate mask is enlarged so a minimum physical plate dot is held. The term used is “bump” but is actually just a dot gain curve applied to the highlights in essence “bumping” the mask open a little bit more.

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To illustrate this, a 1% file dot is “bumped” up to a 5% file dot to achieve a larger opening in the digital mask. That 5% mask opening will allow enough UV energy to pass through to form a 1, 2, or 3% physical dot on the plate. However, the actual resulting values will depend on the platemaking equipment, plate type, and then the LPI of the image.  

 

Assignment

1. You will image, expose and process your test target file on DuPont thermal plate material. Your file will not have any DGC curves applied to it.

2. You will then measure the plate on a Beta Flex to understand how minimum dots differ and determine your minimum dots.

3. You will then establish bump curves (DGC Strategy) in Esko Curve Pilot software to manage your min dots for both plate types.

4. You will RIP your file again with your bump curve applied to your test target file. Remember you do this by launching your file out of Illustrator.

5. You will confirm your bump curve was applied by checking your highlight dots when you softproof your 1-Bit TIFF.  NOTE, you might have to launch twice…one with one bump curve & again with another.

6. Remake both plates and measure according to instructions.

 

Materials

• Thermal digital plates

• Thermoflex Imager Beta Flex

• ECLF Exposure unit Bench Micrometer Test Plate

• Thermal Processor Safety plate cutter Esko Curve Pilot

 

Imaging Method

1. Be sure your 1-Bit TIFF is soft proofed in VIEWER (through Automation Engine Pilot)

2. You will share a full size plate with 7 or 8 other people (they can be your group members or others).  

3. Back exposure a plate for ___ seconds (specific to plate type)

4. Load you plate on the plate setter / plate imager

5. Layout out your 1-bit TIFF file on the CDI using the merger program.

6. Find your file on that drive and drag-n-drop to the appropriate plate ticket for your plate type and caliper

   • This will launch your file into the production queue

   • Make sure the starting position is at 30mm

   • Hit the EXPOSE! button

   • The imaging process will start (laser ablation of the mask)

7. When finished imaging, remove your plate, expose and process it

8. Once the plate is finished, continue to the BETA FLEX with YOUR GROUP and measure a plate as a group per questions on pp 7-9 then proceed to building bump curve per page 4

 

Instructions: Bump Curve Build

1. Go to the Esko PCs in middle lab to make your Bump Curves, or the PC in flexo lab area.

2. Open Esko’s Curve Pilot 16.0 software.

3. Choose File > New > Strategy (.icpro) (A bump curve is called a DGC Strategy in the software)

4. Now, build a strategy based off of LPI:

   • Click the Insert Screen Ruling button—the fourth button down that says “+LPI”.

   • Double-Click the LPI (the software automatically inserts an LPI of 100) and change it to the first LPI your plate is testing.

5. Double-click <none> and choose the appropriate pre-built bump curve.

6. Click the Insert Screen Ruling (+LPI) button three more times, and change the LPIs to match the four LPIs your plate tested.

7. Choose File > Save As… and name your DGC strategy (Dot Gain Curve) strategy as such…

   • 4060 – [semester]-[lab section]-[group #] –platetype-imager

   • Example:   4060-Spring2017-TR3-GroupA-DFR045-CDI

   • Example:   4060-Spring2017-MW2-Group5-DFM067-CDI

8. Your test target is built and in the right place! Now, you will re-RIP your Illustrator file using the bump curve you created (see note below)

   • Open your test target file in Illustrator. Rename your file by removing “raw” and replacing with “bumped”

   • Example:     GC4060Fall-[section]-[your name]-bumped

   • Choose File > Launch Workflow and RIP your individual test files. This time, you will load your group’s strategy curve in the curve options.

9. Soft Proof your 1-Bit TIFF in Automation Engine Pilot …use viewer to check that your 1% are larger than 1% to be sure that the bump curve was applied correctly.

10. Each person will remake their TestTarget plate and place it into Kodak’s TIFF Assembler program (DFM and DFR groups must pair up for plate layout and plate making).

11. Once plate is full with test targets, make another plate again.

12. As a group Measure your plates again to see how the dots are now doing on the plate.

 

How do you know which bump curve to choose?

The appropriate bump curve depends on the first consistent dot percentage to hold on your plate OR if printed, first dot to consistently print. Different LPIs typically require different bump curves. For example, if your plate’s first tone to hold is a 3% dot (as labeled), you need a bump curve to tell the RIP software to “bump up” the 1% dots (make the image mask larger), so that they will image as 3% dots in plate mask. For this example, the appropriate pre-built bump curve would be EG_FIQ_3to1,which would result in a 1% dot bumping to a 3% dot. The pre-built curve is basically a dot gain curve that focuses on the highlight dots. Someone had to build that curve in order for you to use it.