ON-SITE FLEXO OPERATOR TRAINING

Key topics covered during this course

Concept of colour reproduction - what is the color/color perception, the difference between additive (seeing the color) and subtractive (printing the color) color perception. Spot color and process color image reproduction - how it works and what are the main parameters for quality control for operator (density, dot gain, trapping, opacity, etc.).

Concept of flexographic printing, it’s strength and weakneses in comparison to other printing methods (offset, gravure, digital printing).

Key components/consumables of flexographic printing:

• Printing ink - vital component, containing pigments/dies directly responsible for color creation. What the difference between energy curable and solvent/water-based inks, advantages and weaknesses of different ink chemisries, main applications for different kind of inks.

• Printing plates - key image reproduction media. Different plate media and plate making technologies, main plate technical parameters and their influence on printing process, KODAK vs other plates (Du Pont, ASAHI, etc.) it’s advantages and weaknesses.

• Anilox rolls - key mechanism of ink metering/dosing. Different engraving technologies, anilox specifications, key rules for perfect match of anilox vs plate. Open cell (Apex GTT) vs closed cell (HEX60, SteppedHEX) aniloxes, best kind of engraving for different inks/coatings/applications.

• Doctor blades - small, but important part of ink metering process. Metal or plastic, baisc thickness as well as lamela thickness, support blade or without there are a lot of nuances fine tuning the system to have consistent color and optimal wear of anilox roll and doctor blade.

• Sticky back - both side adhesive tape, holding plate onto plate cylinder. Key technical parameters and tape choice according different needs of printing (CMYK, Pantone, Opaque white, etc.). 

• Substrate - paper, plastic and special materials, specifics of printing onto them. Nuances of printing onto absorbent (paper) vs non-absorbent (plastic film, gloss paper) materials, surface tension level, primers, corona treatment etc. White vs transparent and special (silver, gold, colored, perlic, etc.) substrates and their effect on color reproduction.

Flexogrphic printing machines - different kind of conceptual design and design preference for different applications. Key advantages and weakneses of different kind of press designs. Level of machine control automation and it’s influence onto production quality and efficiency.

Key components of flexographic printing press:

• Roll unwinder

• Infeed/tension control unit

• Flexographic printing unit

• Drying/curing unit

• Die cutting/perforation unit

• Matrix stripping unit

• Vision inspection unit

• Longitudinal and edge slitting unit

• Outfeed control unit

• Rewinding unit

Extra decoration/printing tecjnologies for flexo machine:

• Web turnbar and delam/re-lam unit

• Lamination/cold foil unit

• Hot stamping unit

• Rotary screen unit

• Variable information printing unit

Flexo press control and parameters/tollerances operator need to control during printing:

• Color register, OK-Not OK definition

• Color matching/consistency, measurement instruments and standartisation

• Ink adhesion, Tesa tape test

• Die cutting/perforation quality

• Special converting (foiling, lamination, screen printing) quality

• Slitting/edge trimming parameters and dimensions

• Rewinded roll quality

Main defects of flexografing printing and ways to fix them (troubleshooting):

• Color density variation

• Dot gain/dot bridging/donut effect

• Ink trapping quality

• Pinholing/motling

• Bouncing/barring

• Ink spitting

• halos effect

Main defects of screen printing and ways to fix them (troubleshooting):

• Uneven ink laydown, lines in printing area

• Pinholing, dots at begining of printing area

• Printing shadow (higher density) at trailing edge of the print

• Ink scratchable

• Cloudines

Printing/press set-up (on the press):

• Tape application, plate mounting (positioning acros and 0 line, application requirements ans sequence)

• New material roll change, web splicing, web guide set-up

• Web cleaning types and set-up/maintanance, antistatic bars

• Corona unit parametrisation

• Infeed/outfeed and web tension set-up

• Printing with turnbar and specifics of web tension management

• De-lam and re-lam set-up, web tension management

• Ink metering set-up: doctor blade pressure, ductor roll se-up and troubleshooting

• Printing pressure and register set-up, speed influence and compensation during run

• Diecutting set-up, pressure limits, adjustable anvil

• Matrix removal/stripping, label shifter and de-lam/re-lam for easier matrix removal

• Different kind of edge trimming and their set-up

• Different kind of slitting

• Rewinding roll pressure set-up and tips for nice rolls