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Chapter 5

GCM 110 Chapter Notes - Chapter 5: Viscosity, Bookbinding, Offset Printing

Graphic Communications
Course Code
GCM 110
Diana Brown

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p. 135-139, p. 145-146, p.153-159, p.168-171
Printing Presses
Two types of printing processes:
Plate, impact, or pressure printing: offset litho, letterpress, flexo, gravure, screen;
prints at higher resolution and print quality than plate-less process; for long-run
Plateless, non-impact, or pressureless printing: digital printing systems;
electrophotographic printers, ion or electron deposition, magnetographic ink-jet,
thermal transfer, and dye sublimation; for short-run, variable information, or demand
printing  1) plate printing processes and 2) digital printing processes
Offset Lithography: reproduces soft, smooth transitions of color and tones, HQ
photographic images, and sometimes differences in color balances throughout a run
Letterpress/ Flexography: reproduces sharp edges with crisp line art printing, LQ
photographic images, slight embossing of type on the back of printed sheets
Gravure: reproduces strong, saturated colors, slightly ragged type
Presses: the production machines of the major printing processes
oA printing press must provide for: secure and precise mounting of the image
carrier (and, in offset litho, a blanket); means for feeding paper for printing and
delivering printed paper; accurate positioning of the paper during printing;
getting the paper through the printing units to the delivery; storing and applying
ink (and, in litho, a dampening solution) to the plate; and accurately setting
printing pressures for transfer of the inked-image to the paper
oPresses are either sheet-fed (commercial printing) or web-fed (magazines,
newspapers, catalogs, books, and other long-run work)
oPresses may be single color or multi-color (which will require separate printing
units of inking, plate, and impression mechanisms)
oPerfecting/Duplexing Press: a press that prints on both sides of the paper in one
Offset Lithography
Can be printed direct, but majority of lithographic printing uses the offset principle
Has 4 advantages: 1) the rubber blanket surface conforms to irregular printing surfaces,
resulting in the need for less pressure and makeready, and improved print quality of
text and halftones on rough-surface papers; 2) paper does not contact the printing plate
= increased plate life 3) the plate image is right reading rather than reversed reading; 4)
less ink is required for equal coverage= drying is faster, smudging/set-off reduced
Offset Presses
3 printing cylinders (plate, blanket, and impression) and inking/dampening systems
Plate contacts dampening rollers  plate contacts inking rollers  dampeners wet the
plate so non-image area repel ink  inked image from plate is transferred to rubber
blanket  paper is printed as it passes between the blanket and impression cylinders
Makeready: the work done to set up a press for printing
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oIncludes adjusting the position of wraparound plates for proper register
oThe most time-consuming operation of makeready is ink-water balance
Sheetfed presses
Commercial sheetfed printing is on 25” to 40” wide presses
Prints at 18,000+ impressions per hour
Very Large Format (VLF): larger sheetfed presses that are up to 80” wide; used for
greeting cards, gift wrapping, posters, labels, packaging, and wall coverings
Advantages: 1) a large number of sheet or format sizes can be printed on the same
press; 2) waste sheets can be used during makeready, so good paper is not spoiled while
achieving registration, color, or ink-water balance
Web offset presses
Used for long-run commercial printing
16-page web offset press displaced large sheetfed presses for books and commercial
printing, 8-page web competes with 25”-40” sheetfed market, and 32-page competes
with gravure for long-run printing
Advantages: speed; 3000 feet per minute
Disadvantage: there is a fixed cutoff (or print length)
Blanket-to-blanket press: a type of web offset press; has no impression cylinders
oBlanket cylinder of one unit acts as the impression cylinder for the other
oEach printing unit has 2 plate and 2 blanket cylinders
oPaper is printed on both sides at same time (between the 2 blanket cylinders)
oIn web printing the grain of the paper is in the direction of the travel of the paper
through the press, which is opposite to the grain direction of paper in sheetfed
Started with Gutenberg’s converted wine-press
Platen press (clamshell), flatbed cylinder
Stack type: 2-3 printing units are placed vertically in stacks
Central impression cylinder: cylinder impression cylinder with anilox rollers and reverse
angle doctor blade; for printing flexible films
Least expensive and most simple
For decoration and packaging printing
Plates are made up of rubber or polymer, ink is water-based
Invention of UV inks makes flexo comparable quality with litho
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