Offset ink
Offset ink is a specialized type of printing ink formulated specifically for use in offset printing, a widely used commercial printing process where the inked image is transferred from a plate to a rubber blanket and then to the printing surface. Unlike inks used in other printing methods, offset inks must possess unique chemical and physical properties to function effectively in the offset lithographic process.
Composition and properties
Chemical composition
Offset inks typically consist of three main components:- Pigments : Provide color and opacity
- Varnish : A mixture of resins and drying oils that acts as the pigment carrier
- Additives : Including driers, waxes, and other modifiers that control ink performance
Key properties
Water resistance: The fundamental principle of offset lithography relies on the immiscibility of oil and water. Offset inks must maintain their integrity when exposed to the fountain solution used in the printing process, resisting emulsification that would compromise print quality.
Tack and viscosity: These properties must be carefully balanced to ensure proper ink transfer through the series of rollers while preventing problems such as picking or misting.
Pigment concentration: Offset inks require high pigment loading to achieve full color density with the thin ink films characteristic of offset printing.
Types of offset inks
Sheet-fed offset inks
Used for printing on individual sheets of paper, these inks are formulated to set quickly through oxidation polymerization. They typically have higher tack and viscosity than web offset inks.Web offset inks
Designed for continuous roll printing, these inks are divided into:- Heatset inks: Dry through evaporation in heated dryers
- Coldset inks: Dry through absorption into porous substrates
- UV-curable inks: Polymerize instantly when exposed to ultraviolet light
Specialty offset inks
- Metallic inks: Contain metallic pigments for special effects
- Fluorescent inks: Use daylight-fluorescent pigments
- Process colors: Cyan, magenta, yellow, and black inks used in four-color process printing
- Spot color inks: Custom-mixed inks for specific brand colors
Manufacturing process
- Varnish preparation: Resins are dissolved or dispersed in oils at elevated temperatures
- Pigment dispersion: Pigments are ground into the varnish using three-roll mills or bead mills
- Standardization: The ink is adjusted to meet color, rheological, and performance specifications
- Quality control: Testing for color accuracy, flow properties, and print performance
Environmental considerations
- Vegetable oil-based inks: Replace petroleum-based oils with soy, linseed, or other vegetable oils
- Low-VOC formulations: Reduce volatile organic compound emissions
- Waterless offset inks: Eliminate the need for fountain solutions