Printing Processes and Press Operations
Printing Processes and Press Operations tests how each press forms and transfers an image, and how an operator brings a job into register and colour.
What the exam tests
Expect cylinder arrangements, ink-transfer systems and press-control measurements.
Core rules
- Offset lithography uses plate, blanket and impression cylinders. The plate carries ink and fountain solution; the blanket transfers the image to paper. Ink and water must balance: too much water causes emulsification and washed-out colour; too little causes scumming in non-image areas.
- Flexography uses a relief photopolymer plate, an anilox roller to meter ink and a doctor blade to wipe the anilox. Anilox cell volume controls ink film thickness.
- Gravure uses an engraved copper cylinder; the doctor blade removes surplus ink and the substrate picks ink from cells.
- Screen printing uses a mesh, stencil and squeegee; mesh count and emulsion thickness set ink deposit.
- Make-ready includes plate mounting, ink setting, registration, pressure setting and colour approval. Registration is alignment of successive colours; colour bars and densitometers monitor ink film.
- Fountain solution is mostly water with alcohol or glycol, acid or neutral buffers, and surfactants; pH and conductivity are checked.
Worked example
A sheet shows grey scum in non-image areas and ink emulsification in the fountain tray. Reason: the balance has failed in two directions at once. Scumming suggests ink is adhering where water should protect the plate; emulsification suggests too much water is being run. Check fountain pH and conductivity, reset water feed, clean the plate, and re-establish ink-water balance before adjusting ink keys. Do not simply add ink.
Traps
Saying offset plates touch paper directly; reversing the blanket and plate roles; treating anilox volume as unrelated to colour strength; adjusting ink before checking water; confusing registration with colour correction.