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Chapter 9

GCM 110 Chapter Notes - Chapter 9: Letterpress Printing, Thixotropy, Rheology

Graphic Communications
Course Code
GCM 110
Diana Brown

of 2
GCM110- Pocket Pal readings
Printing Inks (PP 157-160)
Ink Properties
Colour- Colour Matching – Pigments/Dyes
Pigments: finely divided solid materials + dyes = colour
Pigment characteristics: gravity, particle size, opacity, chemical resistance,
dispersibility, and permanence
Colour matching: done by visual comparison under standard lighting conditions
using spectrophotometers
Rheology: friction between liquids
Viscosity: measure of the flow characteristics of soft or fluid inks
Letterpress and offset inks are stiff inks that are thixotropic: thick in the
can, but under certain conditions will become fluid and flowy
Body: the consistency, stiffness or softness of inks
Length: ability for an ink to flow and form filaments (fibers)
Long inks: flow well, form long filaments, but tendency to mist/fly
Short inks: butter-like, poor flow, tendency to pile on rollers and plates
Tack: the stickiness of the ink, or the force required to split ink film between two
Drying: printing inks dry in ways like absorption, selective absorption, oxidation,
polymerization, evaporation, precipitation, and curing by radiation
Job Planning
Ink and substrate relationship is critical
Letterpress inks: inks designed for printing from raised surfaces
Moderate tack and viscosity
Sheetfed letterpress inks dry by oxidation, Web letterpress inks dry by
penetration (newspaper inks), evaporation (heat-set inks), precipitation
(moisture-set inks)
Offset-Lithographic inks: inks designed for printing from flat surface that use
principle grease and water do not mix
Strong in colour value
Strongest ink
Contain more water-resistant vehicles and use special vehicles to resist
reaction with water than letterpress ink due to fountain solution of litho
Vegetable oils vehicles improve printing performance
Letterset inks: used on offset presses with raised plates and without dampening
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No pigment restriction, stronger than letterpress, not stronger than
conventional offset inks
Waterless inks: similar to letterset inks, but are formulated to resist heat effects
that can cause toning of non-image areas of water-less printing plates
Single fluid inks: developed to print using standard lithographic plates on
standard lithographic presses without the use of dampening systems
Gravure inks:
Dry through evaporation of solvent in the ink
Inks must be free of abrasive particles that can wear the engraved plate
Publication gravure solvents can cause fires and explosions
Binding/Finishing (PP 178)
- Guillotine cutters have a single knife and are used to cut labels, paper, etc
- New cutters can be set automatically using job data, instead of having the operator key
in the settings
- Trimming is done with 3 knives
- Head, foot, and face trim
Finishing workflows
- Some types of binding and trimming jobs consist of only one step, like leaflets (just
folding is needed) but some other jobs may need more than one step, for example,
books and magazines
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find more resources at oneclass.com