INKS MANUFACTURE

Stock inks- purchased off shelf by printers- standard requirements.
Unusual formulations- unique substrate, or end-use- special formulation.
Precise formulation: color, type of the press, substrate, end -use requirements.
Manufacture of inks- simple process- producing ink dispersion efficiently, reproducibly, and very quickly.
2 categories of inks:
Oleo-resinous systems  (letterpress, lithography)
Volatile solvent/resin systems (flexo, gravure, and most screen-printing inks)- subdivided further:
a- based on water-reducible vehicles
b- based on highly volatile and flammable solvents- requiring special building, flameproof electric for manufacture.

Manufacture of inks- following operations:
Varnish – vehicle manufacture.
Manufacture of additives.
Dispersion of pigments into vehicles using milling/mixing techniques.

Three basic operations for liquid inks:
Mixing
Milling
Filtration

Mixing

Mechanical agitation of pigment and vehicle/varnish together, till no dry pigment occurs.
In stages- first stage: introduction the pigment material into the vehicle.
Distributing the solid particles throughout the liquid.
Mixing- in batches cake mixers.
Mixers-vary in shapes and sizes, tubes holding 5-1,000 gallon batches.
Mixing speed determined by the viscosity or body of the vehicle.
Heavy paste inks- slow stirring, gradually to faster speed.
Liquid gravure inks- thousands of revolutions per minute.

Key goal- pigment wetting- put it in contact with vehicle, driving out the air pockets from around or within the agglomerates, pigment clusters.
Amount of time required: Viscosity of vehicle, Amount of predispersion
Flushed pigments- dispersed in proper vehicle (oil), easy mixing, or mixing omitted.
Inadequate mixing: inconsistent in performance, drying rate, appearance (ingredients not uniformly distributed).

Milling

Process where pigment /vehicle mixture is refined and pigment particles reduced to a size suitable for intended printing process.
Breaking down and further wetting of pigment agglomerates.
Amount of milling - depends on the nature of pigment, effectiveness of milling process.
Dispersion- breaking down the pigment agglomerates into individual particles.
Agglomerates broken up- air pockets flushed out, pigment wetting is improved.
Pigment particles tent to flocculate, reassemble into groups- dispersion must proceed to a point of stable pigment – vehicle mixture.
Paste inks, inks without volatile solvents  milled in 3 - roll mill.
3 steel rollers- revolve in opposite direction at different speeds, generating friction on the nip, friction causes the reduction of pigment particle size.

Ball mill

Large cylindrical canister containing thousands of steel or ceramic media (balls).
Rotation- cascading down- friction between the media disperses the pigment particles.
Factors affecting degree of pigment dispersion:
Milling time
Size and shape of media
Rotation speed
Advantages of ball mill: Cheap to run (during the nights), they act as a mixer as well as mill, low maintenance cost.
Disadvantages: Bulky, noisy, only 50-60% of volume can be used for batch to cascade efficiently, cannot be speed up, emptying can be difficult- (thixothropic product), can only handle low viscosity inks.

Pebble mills- mill wall is lined with nonmetallic material; steel balls replaced with ceramic or porcelain media.

Shot mill

Stationary cylinder standing on an end.
Rod with several evenly spaced propellers on it rotating at high speed inside the cylinder filled with steel shot.
Ink is pumped into the bottom – making its way upward- being caught up in the steel shot.
Whirlpool –like flow pattern between each set of blades- breaks down the pigment.
As the ink reaches the top of the cylinder: screen- ink pass, shot stays.
Shot mills efficient in pigment dispersion, difficult to clean, tendency to clog = limits popularity.

Coating of pigment with polymer- micro-encapsulation.

Filtration
Liquid inks- remove grit, dirt- pumping the ink through the bag, that traps contaminants.

INK INGREDIENTS- continue..

SOLVENTS

Dissolve oils, resins, additives.
"Like dissolves like" - solubility parameters.
Solubility parameter is a measure of cohesive energy density (CED), proportional to the energy required to vaporise 1cm3 of a liquid. CED2 = Hildebrand parameter of solubility. Includes dispersion forces, polar forces and hydrogen bonding forces involved in solvents, plasticizers and resins interactions.
Solvent must:
Dissolve the resin, does not cause pigment to bleed.
It must evaporate at acceptable rate.
Must be compatible with printing plate.
Impart the flow and adhesion properties that are desired.

Flexo, gravure- mainly alcohols, toluene, heptane, acetate (SOLVENT INKS) publication, packaging
Flexo, gravure- water (WATER-BASED INKS) no emissions of volatile organic compounds (VOC's).
Solvents with high hydroxyl content- polar- high dielectric constants.
Hydrocarbons- non-polar- low dielectric constants.
Crucial factor- volatility (speed at which it evaporates).
Not volatile- fail to dry quickly enough- smearing.
Extremely volatile- dry in cells.
Press becomes tacky, picks, tears the sheets.

ADDITIVES
Driers
Ink makes skin across the top of ink film- drying oil reacts with air oxygen.
Oxidation accelerated when catalyst (drier) is present Cobalt, Manganese compounds.
Manganese-promotes the drying through the film – through drier.
Manganese nitrate- removes fountain solution from inks.
Cobalt- promotes oxidation- top drier (Cobalt chlorine, Cobalt acetate).
Cobalt – if dries too fast- crystallization, gloss ghosting.

Plasticizers

Resins- stiff, brittle in nature.
Printed on flexible substrate- cracking, flaking off.
Flexibility – needed for some applications- toothpaste tube, bread bag.
Plasticizers- make ink softer,  more flexible, adherent to substrate.
Plasticizers- react with ink resin – polymer reduce crosslinking of polymers.
Plasticizers also: enhance gloss, improve adhesion to problematic surfaces, protect from becoming too brittle at too low temperatures –frozen food packages, prevent blocking, less discoloration at higher temperatures.
Plasticizers- have high boiling points- do not evaporate- became permanent part of ink film
Plasticizers: litho, letterpress, screen, gravure, flexo.
Phosphates, epoxy-compounds, polyesters, sulphonamides, polyglycol derivatives, phtalates,
citrates.

Waxes
 
Increse rub resistance – book jackets, playing cards, packaging products.
Improve slip and resistance to water.
Used in form of powder, or as a dispersion in oil vehicle.
Waxes move out from emulsions with the vehicle during drying, migrate to the surface- create film which not readily accept subsequent ink- crystallization.
3-5% wax maximum. Excessive wax reduces gloss, increases drying time.
Used in flexo, gravure, most letterpress, litho, screen, carbon copying, hot melt inks.
Animal waxes- bees, vegetable- carnauba.

Mineral-paraffin, polyethylene:
(-CH2- CH2-) n         1500-4000     FW

Teflon. Polytetrafluorethylene  PTFE:  2CHClF2 ---> CF2= CF2 +2HCl
Pyrolysis of chlorodifluoromethane to tetrafluoroethylene and subsequent polymerization at high pressure. Suitable for all types of printing inks, ideal for heatset inks- high temp. of drying – no use of polythylene waxes.
 
Petroleum waxes: extracted from crude petroleum- distillation of oils at 300oC and subsequent refining: C18H38 to C32H66, microcrystalline wax: C34-C43.
Petroleum waxes reduce tack of letterpress inks, slip agents.

Antiskinning agents- Antioxidants

Important for sheetfed offset, letterpress inks- prevents the ink from skinning over
React with free radicals formed during autooxidation- till antioxidant molecules are exhausted
Antioxidant incorporated into ink-delay the initiation of oxidative polymerization drying
Pyrocatechol, eugenol, guaiacol, butylated hydroxytoluene

Wetting agents

Pigment agglomerates – clusters together –air pockets form around these clusters- pigment does not disperse uniformly through the vehicle.
W. A. - Reduce the vehicle’s surface tension and help the vehicle penetrate the microscopic air pockets in  pigment agglomerates.

Defoamers for Aqueous Inks

Defoamers – surface active blends of hydrocarbon liquids, surfactants, metal soaps, hydrofobic silica, with/without silicone modification. Used during the preparation of aqueous inks to prevent foam buildup- added also during application.