Pigments

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Infobox on Pigments
Example of Pigments
Pigments-1.jpg
Facts
Origin -
Stowage factor (in m3/t) -
Humidity / moisture -
Ventilation -
Risk factors See text

Description

Pigments Information
Industrial pigments are dispersed in paints to provide characteristics such as colour, hiding power, bulk, durability, and corrosion resistance. They are available in many forms and colorant types. Common colours for industrial pigments include black, blue, bronze, brown, copper, gray, green, orange, purple, red, silver, white, and yellow. Pearlescent and photoluminescent products are also available. Important specifications for industrial pigments include pH and oil absorption, the amount of oil required to make paint with a pigment. Typically, oil absorption depends upon the size of the pigment particle, the type of binder, and the pigment’s physical and chemical properties. Smaller pigment particles require greater amounts of binder in order to cover larger surface areas and wet each of pigment particle.

Industrial pigments are available in several forms. Examples include dry powders, granules, liquids, pastes, pellets, and chips. Dry powders and granules are traditional forms that are available in the widest variety of grades. Free-flowing pourable liquids and high-viscosity pastes are master batches or concentrated dispersions of organic or waterborne pigments that contain solvents or diluents. They may also contain resins, additives or surfactants. Pellets and chips do not contain solvents, but may contain additives or plasticizers. These solid industrial pigments are easy to handle and feature a high pigment-to-binder ratio. Depending on the pigment and resin type, pigment levels of between 50% and 75% are achievable.

Colorant Types
There are many colorant types for industrial pigments. Examples include barium metaborate, barium sulphate, chromium oxide, Iron Oxide, Lead carbonate, strontium chromate, zinc oxide, zinc phosphate, and zinc sulfide. Titanium dioxide or anatase titanium is the white pigment in most white paints and the primary hiding pigment in most other paints. Carbon Black, a pigment produced by the thermal decomposition of natural hydrocarbons, is available in three types: furnace, channel, and lamp black. Other colorant types for industrial pigments include organic and inorganic compounds, fluorescent and phosphorescent materials, and the synthetic products of chemical reactions and processes. Raw sienna, burnt sienna, raw umber, and burnt umber are naturally occurring and commonly available.

Industrial pigments are used in a variety of products and often contain application-specific features. Common applications for industrial pigments include adhesives, art supplies, beverages, ceramics, clothing, concrete, cosmetics, fibers, food, glass, inks, paints, paper, plastics, polymers, soap and wax. Industrial pigments are also used in medical and biomedical applications such as tissue staining. Specialized products are resistant to heat, weather conditions, and ultraviolet light (UV). Some products are water soluble or can conduct electricity. Others contain reinforcing fibers or are free from heavy metals.

Selection of a pigment for a particular application is determined by cost, and by the physical properties and attributes of the pigment itself. For example, a pigment that is used to colour glass must have very high heat stability in order to survive the manufacturing process; but, suspended in the glass vehicle, its resistance to alkali or acidic materials is not an issue. In artistic paint, heat stability is less important, while lightfastness and toxicity are greater concerns.

Biological pigments
In biology, a pigment is any coloured material of plant or animal cells. Many biological structures, such as skin, eyes, fur and hair contain pigments (such as melanin). Animal skin coloration is often achieved with specialized cells called chromatophores, which in animals such as the octopus and chameleon can be controlled to vary the animal's colour. Many conditions affect the levels or nature of pigments in plant, animal, some protista, or fungus cells. For instance, Albinism is a disorder affecting the level of melanin production in animals.

Pigments by chemical composition
Metallic and carbon

  • Cadmium pigments: cadmium yellow, cadmium red, cadmium green, cadmium orange
  • Carbon pigments: carbon black (including vine blac, lamp black), ivory black (bone char)
  • Chromium pigments: chrome yellow and chrome green
  • Cobalt pigments: cobalt violet, cobalt blue, cerulean blue, aureolin (cobalt yellow)
  • Copper pigments: Azurite, Han purple, Han blue, Egyptian blue, Malachite, Paris green, Phthalocyanine Blue BN, Phthalocyanine Green G, verdigris, viridian
  • Iron Oxide pigments: sanguine, caput mortuum, oxide red, red ochre, Venetian red, Prussian blue
  • Clay earth pigments (iron oxides): yellow ochre, raw sienna, burnt sienna, raw umber, burnt umber.
  • Lead pigments: lead white, cremnitz white, Naples yellow, Red Lead
  • Mercury pigments: vermilion
  • Titanium pigments: titanium yellow, titanium beige, titanium white, titanium black
  • Ultramarine pigments: ultramarine, ultramarine green shade
  • Zinc pigments: zinc white, zinc ferrite

The following are some of the attributes of pigments that determine their suitability for particular manufacturing processes and applications:
Lightfastness and sensitivity for damage from ultra violet light

  • Heat stability
  • Toxicity
  • Tinting strength
  • Staining
  • Dispersion
  • Opacity or transparency
  • Resistance to alkalis and acids
  • Reactions and interactions between pigments


The following table gives a good comparison among various classes of Pigments

                                                                                      Comparison of pigment families

Property BehaviourInorganic PigmentsClassical Organic PigmentsSpecialty Organic PigmentsOrganic Dyestuffs
OpacityUsually highTranslucent to transportVery transparent
Colour strengthLow to moderateConsiderably stronger than inorganic pigmentsStrongest
DispersabilityUsually good: often abrasiveAdequatePoor to goodNot required: soluble
Heat resistantUsually 500°F; some 200°C.150°C-300°C200°C-300°C250°C-350°C
Migration resistanceExcellentModerate-goodGood-outstandingVery poor-good
Light fastness (on a blue scale)6 to 82 to 66 to 82 to 7
Weather resistanceOutstanding for selectionInsuffientExcellent for selectionGood for selection


Shipment / Storage / Risk factors

Certain pigments deteriorate in contact with air due to moisture being absorbed from the atmosphere. There will be deterioration also if the material becomes wet in any other way. Pigments in paste form should not be allowed to become frozen as this will alter their physical condition.