Pigments for Printing InksBy: Adesh Katariya

PigmentIndustrially, apigment is any finely divided insoluble black, white or colored solid material, a major function of which is to improve the appearance of or give color to the medium in which it is to be used.

ColourColor phenomena is the electromagnetic radiation in the wavelength range of 400 to 700 nm. When a photon enters a pigmented film following events may occur: 1. It may be absorbed by a Pigment particle 2. It may be scattered by a Pigment particle 3. It may simply pass through the film

Pigments : How they appear?Pigment must have light absorption and light-scattering properties. If absorption is very small compared with scattering, the pigment is a white pigment. The absorption is much higher than scattering over the entire visible region, and then the pigment is a black pigment. In a colored pigment, absorption is selective.

A wide variety of wavelengths (colors) encounter a pigment. This pigmentabsorbs red and green light, butreflects blue, creating the color blue.

Colour Index Generic Name

C.I. Generic Name describes a commercial product by its recognised usage class, its hue and a serial number (which simply reflects the chronological order in which related colorant types have been registered with the Colour Index)Like C.I. Red 122, C.I. Pigment Yellow 176

Quality and performance of PigmentsGoverned by :Crystal typeCrystal shape (nodular, spherical, prismatic, acicular or lamellae )Crystal size : Typical ranges for average diameter of primary particles are: Carbon black 0.01 to 0.08 m Titanium dioxide 0.22 to 0.24 m. organic 0.01 to 1.00 m; Inorganic 0.10 to 5.00 m;Crystal surface properties

Performance of pigments in Ink SystemPerformance is governed by application type, technology in use and interaction with formulating Ingredients

Parameters which have to be taken into consideration, as well modified, are physical form, dispersion property, ability to stand dispersion condition, rheological behavior, colouristic properties, heat & light fastness properties, storage properties, etc.

Pigments are classified as either organic or inorganic.Organic pigmentsare based on carbon chains and carbon rings.

Inorganic pigments, chemical compounds not based on carbon, are usually metallic salts precipitated from solutions

Inorganic v/s Organic pigmentsInorganic pigments have a much larger average particle size than organic pigments. This is the main reason why most organic pigments are considered transparent and most inorganic pigments opaque.With their larger surface area, organic pigments give much higher color strength. However, for similar reasons, their dispersibility is usually poorer.As a result of their chemical composition, inorganic pigments are stablein the presence oforganic solvents unlike many of the simpler organic pigments, which can dissolve and have high resistance to pigment bleeding and migration. With a few exceptions, inorganic pigments have higher heat stability than organic pigments. However, light fastness and weatherability vary more widely.

Cont.

ParticularsInorganic PigmentsOrganic PigmentsSourceMineralsChemically refined oilColorOften dullBrightDyeing / Coloring StrengthLowHighOpacityOpaqueTransparentLight fastnessVery goodVary from poor to goodSolubilityInsoluble in solventsHave have little degree of solubilityDegree of safetyMay be unsafeUsually safeChemical StabilityOften sensitiveUsually goodCostModerateMostly too expensive

Organic Pigments

Azo Pigments: Pigment class containing the azo group (-N=N-) in common. The synthesis of azo pigments is economically attractive.

Poly Cyclic Pigments : Pigments with condensed aromatic or heterocyclic ring systems are known as polycyclic pigments. Their chief characteristics are good light and weather-fastness and good solvent resistance. They are typically costlier than azo pigments.

Key features and characteristics of Organic PigmentsVery good stability to solvents, light, heat, and weatheringGood tinctorial strengthCost effectivenessConsistency and unique shadesCompletely non-toxicVery bright, pure, rich colorsOrganic pigments shows good color strength

Azo PigmentsMono-azo Yellow and Orange pigmentsDisazo Naphthol Naphthol AS Azo lakesBenzimidazolone Disazo condensation Metal complex

Polycyclic pigmentsPhthalocyanineQuinacridonePerylene and perinoneThioindigoAnthraquinoneDioxazineIsoindolinone and isoindolinDiketo-pyrrolo-pyrrole (DPP)TriarylcarboniumQuinophthalone

Monoazo Yellow and Orange PigmentsMonoazo yellow pigments that are obtained by a coupling a diazonium salt with acetoacetic acrylides, as coupling components, cover the spectral range between greenish and medium yellow; while coupling with 1-acrypyrazolone-5 affords reddish yellow to orange shades.All members of this family share good light fastness, combined with poor solvent and migration resistance. PY1, PY3, PY 74, PY 73 etc.

Diazo PigmentsMajor products :PY12, PY13, PY17, PY83Diazo Pigments divided into two groupsThe first and most important group includes compounds whose synthesis involves the coupling of di- and tetra-substituted diaminodiphenyls as diazonium salt with acetoacetic arylides (diarylide yellows) or pyrazolones (disazo Pyrazolones) as coupling components.

The second group, bisacetoacetic arylide pigments, are obtained by diazotization of aromatic amines, followed by coupling on to biacetoacetic arylides. The color potential of disazo pigments covers the color range from very greenish yellow to reddish yellow and orange and red.

-Naphthol Pigments-Naphthol Pigments provide colors in the range from orange to medium red.

The typical coupling reaction with -naphthol, as a coupling component, yields such wellknown pigments as Toluidine Red and Dinitroaniline Orange.

Available hues are toluidine red (PR3, PR49, PR53, PR68) and a few orange (dinitraline orange PO5, PO17, PO46)

Naphthol AS Pigments (Naphthol Reds)These pigments are obtained by substituting coupling aryl diazonium salt with arylides of 2-hydroxy-3-naphthoic acid (2- hydroxy-3-naphthoic acid anilide = Naphthol AS).

They provide a broad range of colours from yellowish and medium red to bordeux, carmine, brown, and violet; their solvent fastness and migration resistance are only marginal.

The color range is concentrated in the long wavelength end of the spectrum, including warm orange (PO24, PO38), scarlet (PR188, PR261), many reds (PR2,PR3, PR5, PR7, PR8,PR9, PR17, PR22,PR112, PR150, etc.), carmines (PR23, PR146, the many pigments listed underPR170), maroon violet (PV13, PV25, PV44), and brown (PBr1).

Azo Pigment Lakes

These pigments are formed by precipitating a monazo compound, which contains sulfo and/or carboxy groups.

The coupling component in the reaction may vary: b-naphthoic acid lakes are derived from 2-naphthol, BONA pigments lakes use 2-hydroxy-3-naphthoic acid (Beta-Oxy- Naphthoic Acid); and Naphthol AS pigment lakes contains anilides of 2-hydroxy- 3-naphthoic acid, as a coupling component.

Lakes may also be prepared from naphthalene sulfonic acids. Lake Red C is one of the commercially significant b-naphthol lakes.

Benzimidazolone pigmentsBenzimidazolone pigments feature the benzimidazolone structure, introduced as part of the coupling components.

These pigment obtained by coupling onto 5-acetoacetyl aminobenzimidazolone cover the spectrum from greenish yellow to orange; while 5-(2-hydroxy-3-naphthoylamino)-benzimidazolone as a coupling components affords products that range from medium red to carmine, maroon, bordeaux, and brown shades.

Broad range of hues, from yellow (PY120,PY151,PY154,PY175, PY180, PY181, PY194), through orange (PO36,PO37, PO60,PO62, PO72) and red (PR171,PR175,PR176, PR185, PR208) to a maroon of fair lightfastness (PV32).

Disazo Condensation These pigments can formally be viewed as resulting from the condensation of two carboxylic monoazo components with one aromatic diamine.

The resulting high molecular weight pigments show good heat stability and light fastness.

Their main markets are in the plastic field and in spin dyeing. The spectral range of disazo condensation pigments extends from greenish yellow to orange and bluish red or brown.

Available hues range from yellow (PY93, PY95, PY128, PY166), orange (PO31), red (PR144, PR166) and brown (PBr23,PBr42).

Metal Complex PigmentsAll combine a symmetrical pair of carbon (organic) compounds with a metal atom (usually nickel or copper). Included in this group are the azo-methine metal complexes. Colors range from green (PG8) to green gold (PG10,PY117,PY129), yellow (PY150,PY153, PY177, PY179), orange (PO59,PO65), and red (PR257, PR271).Those species that provide the required light fastness and weather resistance are used in automotive finishes and other industrial coatings.They are nontoxic but may (depending on the metal atom used) irritate the skin.

Phthalocyanine pigmentsPhthalocyanine pigments are derived from the phthalocyanine structure, a tetraaza-tetra-benzo-porphine.Although this basic molecule can chelate with a large variety of metals under various coordination conditions, today only the copper (II) complexes are of practical importance as pigments.

Commercial varieties include the reddish blue alpha form, as stabilized and non-stabilized pigments; the greenish blue beta modification. Bluish to yellowish shades of green pigments may be produced by introduction of chlorine or bromine atoms into the phthalocyanine molecule.

Cont..An important pigment from the family of Copper phthalocyanine is the C.I. Pigment Blue 15:3. The production steps of which is given here.

Quinacridone pigments

Highly recommended for high light fast and High resistance application.As on now major consumption in ink jet inks as well as high quality process magenta shadesDue to better transparency, the combination with pearlescent and metallic pigments creates outstanding effects that can easily be applied for coatings and inks.The available hues range from golden yellow (PO49), through reddish orange (PO48), middle red (PR209), coral (PR207), red (PV19), rose (PV19andPV42), magenta (PR122,PR202), maroon (PR206), and a dark reddish violet (PV19).

Isoindolinone and Isoindoline Pigments

Although of comparatively good light and weather fastness, solvent and migration resistance, only a few members of the isoindolinone and isoindoline families are commercially available as pigments.Chemically classified as heterocyclic pigments, they are preferably supplied for high grade inks.Colors range from yellow (PY109,PY110,PY139, PY173, PY185) to orange (PO61, PO66,PO69) and red (PR260).

Perylene Pigments

Perylene pigments are prepared by the condensation of perylenetetracarboxylic monoanhydride monoimides with primary amines. Perylene pigments are very stable thermally together with photo stability.Available colors are limited to moderately saturated scarlets (PR123,PR149, PR190), reds (PR178), dark maroons (PR190,PR179, PR224,PV29), and a very dark green (PBk31).

DioxazineThe pigment is obtained by dissolving the dye in a very hot acid, then washing and salt grinding the precipitate that results. The pigment exists in two crystal modifications, a red and a blue shade, whose hue can be modified by different methods of manufacture or grinding: both have the same color index name, are poorly distinguished by manufacturers, and are apparently confused in the lightfastness testing literaturePigment Violet 23 and 37

Anthraquinone

A small group of about 10 pigments, most of them with a long history as textile vat dyes. They made dull, weak pigments until methods of purification, careful precipitation and grinding were discovered that retained most of the dye's color brilliance. The group includes anthrapyrimidine yellow (PY108), anthraquinoid red (PR177) and my favorite, indanthrone blue (PB60).Good Re-solubility in Solvent based Inks: Use to improve resolubility

Diketo-pyrrolo-pyrrole (DPP)

A small but very important group of new synthetic organic pigments, discovered in the early 1980's and systematically developed into pigments with very good lightfastness. About six are currently offered, in the shades orange (PO71,PO73), scarlet (PR255), red (PR254) and carmine (PR264, PR274). All the pyrroles are nontoxic, extremely lightfast, semitransparent to semi-opaque, and staining.

Triarylcarbonium.Two groups of triphenylmethane pigments, obtained by laking basic dyes.

Color range is green (PG1, PG2, PG4, PG45), blue (PB1, PB2, PB9, PB10, PB14, PB18, PB19, PB56, PB61, PB62), red (PR81, PR169) or violet (PV1, PV2, PV3, PV27, PV39).

Their lightfastness ranges from poor to worthless and no paint containing these pigments or any unlaked basic dye should be used in professional quality artworks.

Quinophthalone

Quinophthalone pigmentsprepared with using of phthalic anhydride and 2-methylquinoline derivatives as starting materials and BF3 as catalyst under solvent-free and reflux conditions.These pigments are opaque in nature, fastness to weathering , Low migration nature, satisfactory HR, gloss stability and flow properties; the outstanding color strength makes it the preferred product for economic formulations.These are non-Toxic to animals by oral, so widely used for fish foods.PY 138, PY 139, PY 185

Inorganic pigmentsTitanium dioxide whiteCarbon blackIron oxideUltramarine blueChrome based pigmentsEffect Pigments ( Pearl, Metallic etc.)

Carbon black Carbon black (PBK-7) is the name of a common black pigment, traditionally produced from charring organic materials such as wood or bone. It appears black because it reflects very little light in the visible part of the spectrum, with analbedonear zero.High strength, good colour, light & weather resistant

Titanium dioxide-TiO2 (PW6) Titanium dioxide Is the naturally occurringoxideoftitanium.

The three common phases of titanium dioxide are rutile, anatase and brookite. Rutile is the most stable form of titanium dioxide. Anatase and brookite are stable at normal temperatures but slowly convert to rutile upon heating to temp. above 550 and 750 C, respectively.

Approximately 4.6 million tons of pigmentary TiO2are used annually worldwide.

High strength, high opacity, cheap, good UV resistance. Major problem: forms radicals that degrade the binder.

Manufacturing of Titanium DioxideChloride Process

Sulfate Process

Iron oxide PigmentsUsually mined although can be synthesizedNatural iron oxides are derived from hematite, which is a red iron oxide mineral; limonites, which vary from yellow to brown, such as ochers, siennas, and umbers; and magnetite, which is black iron oxide. Also can be produced synthetically by thermal decomposition of iron salts or iron compounds, precipitation of iron salts usually accompanied by oxidation, and reduction of organic compounds by ironLight and weather resistant, unreactive India is world leader in production of Iron Oxide PigmentsCannot produce clean shades

Chrome PigmentsThese pigments are chromium based pigments.Ink companies are avoiding to use these pigments due to presence of Heavy Metals.Light, weather, alkali and acid resistant; thermally stable Main products are Strontium Chromate, Lemon Chrome, Middle Chrome, Primrose Chrome, Scarlet Chrome and Zinc Chromate .

Ultramarine BlueUltramarine Blue is Synthetic Inorganic. It is a blue pigment of sodium aluminosilicate containing sulphur. It is prepared by heating kaolin, sodium carbonate, sulphur and other inexpensive ingredients together. It is heat and alkali resistant.

Effect Pigments The theory of optics as a wave and combination of Chemistry

Pearl luster pigmentsRegular reflection takes place on highly refractive parallel pigment platelets Titanium dioxide on mica

Metal effect pigmentsRegular reflection takes place

Types:Aluminium Pigments( Leafing/Non-Leafing)Vacuum Metallized PigmentsGoldbronze Pigments

Interference pigmentsThe optical effect of colored luster pigments is caused mainly due to interference of light.Iron oxide on mica

UV Fluorescent PigmentsUV Fluorescence Pigment absorbs radiation of a certain wavelength, or group of wavelengths, and re-emits photons of a different wavelength , without a delay Most of these pigments are excited by short wavelength UV light (around 254 nm).Silver-doped zinc sulfide Under Normal Light Under UV Light

Phosphorescent pigmentsThese pigment has ability to absorb light and then emitted the light of longer wavelength within several hours after excitation.When ambient darkness occurs, it becomes highly visible.Examples: copper-doped zinc sulfideCommonly called glow-in-the-darkUsed in Screen Inks for Sign Boards

IR Fluorescent (Anti-Stokes) Pigments

Coding and Marking Purposes inSecurity PrintingApplications for Offset and Solvent Based inks.Special near IR lasers or LEDs are needed for detection.Under Visible light, they appear white and in Near IR Region, they appear coloured.IR fluorescent pigments do not Stokes law, they are excited by IR energy, and either emit in the visible region or in the IR region but at a shorter wavelength.

Same Pigmented CoatingIn Visible RegionIn 980 nm IR RegionWhiteYellow

Optically Variable PigmentsPVP show angle-dependent color and lightness effects which are based on reflection, interference and absorption phenomena of visible light in pigmentary multilayer systems.

Thermochromic PigmentsThermochromic Pigments changechange their color because of the Change of TemperatureChange in the molecular structure as per temperature.Also pressure dependent pigments are usingUses in Offset and Screen Inks

Same coating haveAt 15 DCAt 30 DCWhiteOrange

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