WHAT IS AN INK ?

An ink is sticky stuff with a bunch of colored rocks in it.

An ink contains colorant, which is carried to the substrate by means of a resinous vehicle system.

BASIC COMPOSITION:
RESIN OR VARNISH
PIGMENT, DYE OR FLUSH
SOLVENT
ADDITIVES



                                        PRINTING INK

COLORANT--------------------------------------VEHICLE

Purpose:                                                            Purpose:

To provide color                                               To carry the pigment to substrate,
                                                                           hold it there, provide any desirable properties:
                                                                           e.g. light resistance, soap resistance,
                                                                           Gloss, drying mechanism, transfer properties,
                                                                           rub, setting.
COLORANTS

DYES - colored substances that are soluble in the media which they have been dissolved.

PIGMENTS – colored particulate organic and inorganic solids, which usually are insoluble, and chemically and physically unaffected by the vehicle or substrate in which they are incorporated.



PIGMENTS

INORGANIC: Chrome Yellow, Zinc Yellow, Iron Oxides, Iron Blue, Ultramarine Blue, Titanium Dioxide.
ORGANIC: Lithol Red, Lithol Rubine, Naphtol Reds, Diarylide Yellows, Phtalocyanine Blue.



PROCESS COLOR USAGE OF ORGANIC PIGMENTS

(PROCESS PRINTING: Yellow, Magenta, Cyan, Black).

75% of all Yellow organic pigments are DIARYLIDE YELLOW (PY 12).
75% of all Magenta organic pigments are LITHOL RUBINE
(PR 57).
75% of all Cyan organic pigments are PHTALO BLUE
(PB 15).
CARBON BLACK – Pigment Black 6 - Lampblack,
Pigment Black 7 – Carbon Black, Furnace Black, Gas Black.



EFFECT OF PARTICLE SIZE
Small: Excellent color strength, saturation, gloss, hiding power, dispersion, flow.
Large: Poor dispersion (plate or cylinder wear, poor ink/water balance, hickeys, printability problems), poor flow, hiding power, color strength (color fluctuation), gloss.

PIGMENTS

Pigment do not dissolve in vehicle: container of fruit gelatin with the pieces of fruit.
Dyes- do dissolve in their vehicles.
Dyes converted to pigments through several different chemical reactions.
Chemistry of pigments-complicated- derivatives of benzene, naphthalene, anthracene
Some pigments have 4-5 aromatic rings in molecule.
Chromophores - responsible for color in organic pigments:

=C=NH,  -CH=N-, -N=O, -C=C-, or –N=N-

Chromophores must be in such position in molecule - that electrons can change the energy levels when illuminated.
Molecule absorbs light energy, which promotes an electron from molecular orbital of lower energy to an orbital of higher energy content.
Pi electrons, conjugated systems.
Electrons in chromophores change energy level absorbing specific part of white light- reflecting the rest of the light - create the color.
Auxochromes- help fix the dye to substrate.

Batochromes - Shifts to longer wavelengths (-NH2, -OH, -OR). Electron delocalization incerased in the presence of these groups. Donate electron pair to extended conjugated system.
Hypsochromes- Shifts to shorter wavelengths (-NO2, -CN, -SO3, -NO)
Azo pigments- large, most important group of organic pigments.

DIAZOTIZATION:

AR-NH2 +2 HCl + NaNO2 --------->  AR-N=N+Cl- + NaCl + 2H2O

COUPLING:

AR-N=N + + Coupler + NaOH -------->  Ar-N=N-Coupler  + NaCl  + H2O    PIGMENT
 
Ar = e.g. Tobias Acid
Coupler = e.g. B-naphtol

Pigment properties
Tinctorial strength, opacity, shade, gloss, refractive index,
Durability, paricle size, specific gravity,
Hardness or texture, wettability, dispersibility,
Light, heat and chemical resistance.

Particle size
0.01- 0.005 microns  = 4. 10-7 – 2.10-7 in., Carbon blacks- smallest particle size, coarsest pigments -TiO2  - poor flow characteristics.

Specific Gravity
Inoganic > Organic

Opacity
How object scatters the light 0.2- 0.4 nm particle size maximum opacity.

Refractive index n
Measure of bending of light rays entering the pigment.
n Pigment  =  n Vehicle,  light pass through ink without bending- transparent ink film.
Inorganic - TiO2 , chrome yellows have high refractive index.

Wettability
How easy will be pigment wetted by vehicle.

Dispersibility
How easy will be pigment dispersible – separate the pigment particles, surround them by vehicle.

Texture
Hardness or softness of pigment in dry form.

Lightfastness
Chemical nature of pigment.
Protective properties of vehicle.
Time of exposure and other conditions - humidity.
Fading, darkening.

Manufacture
Petroleum chemistry.
Organic pigments 65-70 % volume of all pigments consumed in U.S.

Pigment flush
Wet filter cake “press cake” put into mixer with selected varnish and processed. Then will be wettable with the varnish.

Dried pigment
Press cake put into oven, dried, then grinding  into powder.

Chips
Pigment milled and dispersed into suitable resin (nitrocellulose, polyamide).

Carbon Blacks
Black- important-used more than others.
Stable- unaffected with light, heat, acid, solvents.
Several carbon blacks: channel black, furnace black, thermal black, lampblack.
Furnace black - the only important black pigment.
Elemental C, small % of ash, some volatile matter CO, CO2, H2O, H2.
Carbon blacks- different particle size, oil absorption, pH, volatiles content.
Structure, particle size, surface chemistry- determine their behavior.
Finer particle size, better opacity, longer the flow, higher visco, higher tack, more wetting energy.

Furnace black
Made by burning atomized mineral oil in bricklined furnaces.
Carefully controlled air supply.
Cooled, pigment collected with electronic precipitators (Bag Filters).
Volatile matter lower than in other blacks - lampblack, channel black.
Bluer undertone, higher pH (7-10) than channel black (pH = 2-5).
Less tendency to absorb driers, retard drying than do channel blacks.

Channel blacks
Burning natural gas with limited supply of air.
High color strength and gloss- rarely used- no longer manufactured in U.S.

Lampblack
Burning unsaturated residues- creosote oil byproduct from distillation of coal tar
Dull finishes.

Diarylide yellow
Widely used in many types of inks.
Highly transparent to red and green light, absorb blue effectively.
Easily ground in all types of ink mills.
Small particle size- easily dispersed –good flow properties.
High tinctorial strength.
Some diarylide yellows – for heat- resistant inks- high tinctorial strength and brilliant tones
Poor to fair lightfastness.
Less opaque, so for opaque ink- mixed with TiO2.

Hansa Yellow
Yellow 1- most commonly used Hansa yellow.
Tinctorially less strong.
Less heat resistant than diarylide.
Flow well, better lightfastness than diarylide.

Phtalocyanine blue
Most important pigment for process blue- cyan inks.
Resistant to chemicals, solvents, very lightfast.
Absorbs blue and green light- making cyan too gray.
Bronze appearance to printed ink.

Reflex or Alkali Blues
Can retard drying of oil-based systems, still very popular.
Used also as a toner for C- black inks.
High tinctorial strength, good working properties, typical for litho inks.
Tend to bleed in alcohol.

Lithol Rubine
Azo red- most commonly used azo rubine pigment.
Litho rubine- publication gravure.
Potential bleed in dampening solutions, scum.

Rhodamine
Bluer-more magenta than rubine, more expensive.
Magenta inks prepared from rubine or rhodamine or blends
Poorer lightfastness and alkali resistance than rubines.

Fluorescent pigments
Fluorescent pigments – dyes- poor lightfastness, poor flow.
Used for screen printing.
Dispersed in inert, insoluble resins that are ground to small size to produce “fluorescent pigments”.

Inorganic pigments
Formed by precipitation- settle out.
Filtration, washed from soluble salts, either flushed into varnish or dried.
Not pure chemical compounds-complex mixtures.

White pigments
TiO2 - opaque pigment.
Extensively used - Package printing , one of most widely used of all ink pigments.
Anatase- more stable,  softer texture - gravure systems.
Rutile- higher refractive index, greater opacity, more abrasive.
TiO2 – high specific gravity, size 0.2 - 0.3 micron - piling unless properly formulated.
Whitest and most opaque pigments known.
TiO2 – fairly readily ground on most ink mills.
Widely used in flexo and gravure.
TiO2 – Outstanding whitness and opacity- replaced other white pigments.

Colored Inorganic Pigments
Inexpensive, good opacity, lightfastness, can exhibit poor texture and working properties if not correctly formulated.
Cr, Pb : chrome yellow, molybdate orange, cadmium yellow, red- many good properties
Limited use of Pb = lead environmental regulations.

Iron blues
Prusian, Berlin, Bronze, Chinese blue.
Different shades- due to different manufacturing conditions.
Iron blues use decreases, phtalo blues – more economical.

Ultramarine blue
S, SiO2, china clay, carbon, soda ash. Inexpensive.

Magnetic black
Magnetic ink Character Recognition Fe3O4 ferosoferic oxide in special crystalline form. Bank checks.

Metallic pigments
Bronze: copper zinc alloys from 100% copper to 70% copper: 30% zinc.
Gold inks: bronze powders.
Silver inks- aluminum.
Coarse particles, create runnability problems.