Ingredients and Functions of Ink

Ink ingredients and functions
Colorants – color, transparent/ opaque
Pigments – insoluble in water and organic solvents
Dyes – soluble, brilliant color, low fade resistance
Vehicles – fluid portion of ink, carrier of pigments
Oil – used in offset inks
Nondrying oils – news ink
Drying oils – quickset ink
Semidrying oil – environmentally friendly
Resins/ binders
Bonds pigments to one another
Two types – natural (pine tree), synthetic
Solvent – dissolves resin and provides a mean of dryin g
Additives
Drier – accelerate drying of paste inks
Plasticizer – improves gloss, adhesion, and ink film flexibility
Wax – improves rub resistance, reduces gloss
Color strength and bleach testing
Color strength (tinctorial strength)
Relative pigment amount per unit weight or volume
Bleach testing
Test of color strength – add white ink to color ink at different ratio
Problems caused by poor ink color strength
High ink consumption, poor concentration of pigments
Applications require transparent ink and opaque ink
Hiding or covering power
Factors affect ink film gloss
The substrate – coasted vs. uncoated
Gloss coated vs. matte coated
Ink film thickness
Thick vs. thin film
Dry ink film vs. wet ink film
Ink pigment dispersion and measurement
High ink consumption, poor concentration of pigments
Problems caused by poor pigment dispersion
High ink consumption, poor concentration of pigments
Factors affect drying rate of ink
Absorbency of substrates, coated vs. uncoated
Area of coverage
Relative humidity in the pressroom
Ink film thickness
Problems caused by ink drying too fast
Can cause problems with gravure and flexo
Ink viscosity and the factors affect the viscosity
The ability to resist flow
Affected by temperature and agitation
Thixotropic property of paste ink?
Viscosity decreases with shearing and agitation
Viscosity increases when shearing and agitation stopped
Ink tack and the problem caused by high ink tack on printing
The resistance of ink film splitting
Print with high tack ink on low surface strength paper
Only for paste ink
When ink tack is too high and press run is too high, the likelihood of picking is high
Printing sequence determined by ink tacks
Tackier inks go down first
Long ink and short ink
The ability to be stretched before snapping
Problem caused by ink which is too long
Come back to me
Drying of news ink, quickset ink, heatset ink, gravure ink, flexo ink and screen printing ink
Quickset ink – absorbs into substrate, quickly oxidizes to dry
Heatset ink – dries by evaporation in large drying oven
Gravure ink – fast dry by evaporation
Flexo ink
UV flexo dries by evaporation
Screen printing ink – evaporation at high temperature
Thixotropic property and paste ink setting on paper
Paste ink – very short, dries slowly (uses microwave, hot air, flash/ flame driers
Takes longer to dry
Viscosity of web offset ink and sheetfed offset ink
Sheetfed offset – quickset ink (dry by oxidation)
Web offset – heatset (set and dry by evaporation)
News ink – set and dry by absorption on uncoated paper
Web offset has lower viscosity than sheetfed ink
Paper properties required for sheetfed offset printing, web offset printing and gravure printing
Gravure papers
Coated or supercalendered
Porosity and compressability
Offset
Smoothness not critical, blanket is smooth and compressable
Sheetfed – higher moisture content
Heatset offset - lower moisture content
Tensile strength important for web offset
Blistering and causes
Heatset offset printing when coated paper is used and heavy ink coverage is applied
Paper with excessive moisture content
Common printing problems of gravure and flexo printing and remedies
Gravure
Web break from low tensile strength
Snowflaking/ missing dots
Improve with electrostatic assist ink transfer or use smoother paper
Flexo
Halo – too high pressure
Blocking – dries to slow, excessive pressure in rewind coil
Filling-in reverses and types from too much ink, too low ink viscosity and too high printing pressure
Tensile strength and surface strength
Mainly important to web offset
Low tensile strength results in web break
Conditioning paper
Corona treatment – electrostatic shock
Water-based flexo ink viscosity and pH
Water based flexo prints well on paper, but may have problem printing on plastics
Common offset printing problems
Blistering – when coated paper is used and heavy ink coverage is applied (in heatset offset printing)
Picking – low surface strength of paper, high tack of ink
Hickeys – foreign materials on blanket, doughnut shaped
Grain direction of paper on web and sheetfed offset press
Web – parallel
Sheetfed – perpendicular
Reel curl and offset curl
Reel curl – paper keeps curl shape from being in web curl
Offset curl – offset printing problems
Paper properties related to printability
Moisture content of paper
Edge and center of paper roll
Lose or absorb moisture, blistering, crack at fold
Web tension
Surface strength
Ink mileage
Coated – better ink mileage and holdout
Uncoated – Worse ink mileage, because of absorption
Storage requirements of fluid ink and paste ink
?
Basis weight, M weight, cwt, metric paper size
Basis weight – 500 sheets
M weight – 1000 sheets cWT – 100 lbs
Metric paper size – something metric
Wavy edge and tight edge of paper skid
Wavy edge – when exposed to higher humidity
Tight edge – when exposed to lower humidity
Calculate the number of sheets out

Storage of paper roll
On roll’s end
Roll numbering system
Different numbers for different sizes
Particle size of dry toner and liquid toner affect print quality
Lower particle sizes yield better quality pictures
Toner transferring onto paper
Paper is electrostatically charged, and treated
Types of inkjet ink
Dye ink
Pigment ink
Longer lasting
Coating and moisture content of paper affect the dry toner transferring
?
Fusing and fixing on a toner-based printer
When toner bonds to paper
Paper requirements for inkjet printing and electrophotography printing
Use anything
Types of inkjet paper
Most printer paper
Surface tension and surface energy requirement for printing water-based ink on plastic film
Improve wettability of water-based ink on plastic