Are color pigments and dyes different?
Are color pigments and dyes different?
Pigments are finely ground natural or synthetic particles. They are practically insoluble in the medium in which they are dispersed. They are distinct particles, which gives the medium its color and opacity.
Pigments are organic or inorganic, colored, white, or black materials. They impart color when added to paints and coatings formulations. They also add bulk or desired physical and chemical properties to the wet or dry film.
The smallest units refer to primary particles. The particles' structure and shape depend on the crystallinity of the pigment. During the pigment production process, primary particles generally aggregate and generate agglomerates.
Pigments Dispersion
During the pigment dispersion into the polymer, high shear breaks up these agglomerates. This improves the tinting strength of the paints. Pigments are thus required to resist dissolving in solvents that they may contact during application. Otherwise, problems such as bleeding and migration may occur. Pigments are resistant to light, weathering, heat, and chemicals such as acids & alkalis. This depends on the demands of the particular application.
Dye is a substance that imparts color with some degree of permanence. Polymer Soluble Dyes are soluble in the medium in which they are dispersed. This means that there are no visible particles. Hence, the transparency of the medium remains unchanged.
Dyes Dispersion
Pigment dispersion - The step-by-step process
High-quality coatings of high brilliance and color strength are characterized by:
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A perfect pigment dispersion
- Optimal pigment particle size
- Long-term stabilization of the dispersed particle in the formulation
Most organic pigments show better transparency as dispersion improves. In larger particle-size inorganic pigments, opacity is improved by good dispersion.
The dispersion process refers to the permanent breaking of agglomerates into primary particles. There are four aspects to the dispersion process:
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Deagglomeration – The breaking down of the agglomerates & aggregates by applying force. A mixture of both crushing and mechanical shearing force is applied here.
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Wetting – It occurs at the surface of a pigment when a surface-active agent sticks to the pigment's surface. It acts as a connection between the pigment and the binder. Wetting out time depends on the viscosity. Heat produced by the mechanical shearing process increases the temperature of the mixture. This thus reduces the viscosity, helping the wetting out process.
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Distribution – It demands the pigment to be equally dispersed throughout the binder system. A lower viscosity tends to lead to a more even pigment distribution.
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Stabilization – It prevents the pigments from re-agglomerating. The pigment dispersion is stabilized by dispersing agents to prevent the formation of uncontrolled flocculates. The resultant suspension is stabilized due to the adsorption of binder species or molecules at the pigment surface.
Want to know the science behind pigment dispersion? Discover more about the dispersion process.
Which are the common types of pigments?
Which are the common types of pigments?
Each pigment types have distinct properties that distinguish them from one another. Some main pigment classes include:
-
Organic pigments
- Inorganic pigments
- Functional pigments
- Special effect pigments
Organic pigments do not disperse easily and form agglomerates (clumps of pigment particles). While inorganic pigments get more easily dispersed in the resin. Functional pigments impart a desired property to the coating. They create optical effects like metallic, hammer finish, and diverse color perceptions depending on the angle. Examples of functional pigments include corrosion inhibitors and special effect pigments.
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Organic vs. inorganic pigments - Property comparison
Pigment
Properties |
Inorganic Pigments |
Organic Pigments |
Classical |
High-performance |
Color, Purity
|
Often dull |
Usually bright |
Opacity |
High |
More or less transparent |
Color strength |
Medium to Low |
Normally High |
Light Fastness
(Blue scale) |
Good to High
(7-8) |
Low to Middle
(< 7) |
Good to High (7-8) |
Weather Resistance |
Varies (depending on chemistry) |
Insufficient |
Middle to High |
Heat resistance |
In general > 500°C
Rarely < 200°C
|
150 to 220°C |
200 to 300°C |
Fastness to solvents -
Bleed resistance |
High |
Middle to Good |
Good to High |
Resistance to chemicals |
Varies (depending on chemistry) |
High (except for salts) |
High |
Price |
Low to Medium |
Medium |
High |
Commercial Products |
Inorganic pigment grades |
Organic pigment grades |
Now when the basic distinction is clear, find out in detail about these 2 types of pigments and see which one matches the best with your final application needs.
What are organic pigments?
What are organic pigments?
Organic pigments are traditionally transparent. Modern manufacturing techniques impart properties that are not associated with the chemical type. It is now possible to produce high-opacity organic pigments.
Organic pigments are relatively new. Natural dyes have been precipitated onto inorganic bases (known as lakes). They are used in artists' colors since the Middle Ages (e.g., madder lake and crimson lake). However, true organic pigments have been known since the early years of the 20th century. They divide into two sub-groups:
- One of vegetable origin, and
- Other of animal origin
Most organic pigments show better transparency as dispersion improves. While in the case of larger particle size inorganic pigments, opacity is improved by good dispersion.
Explore the range of organic pigments in detail below. Click on the specific pigment for your formulation:
Organic Red Pigments
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There are a lot of red pigments. To select the best pigment for your application, you need to know all the products available in this color and their properties.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES |
PRICE |
Beta-naphthol
|
Pigment Red 3, 4 & Pigment Orange 5
|
- Moderate heat stability
- Limited solvent resistance
- Good chemical resistance and light fastness
|
Relatively cheap pigments
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BON arylamides
|
Pigment Red 2, 5, 12, 23, 112, 146, 170 & Pigment Orange 38
|
- Good chemical stability
- Limited light fastness and solvent resistance
|
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Toner pigments
|
Pigment Red 48, 57, 60, 68
|
- Excellent heat stability
- Good solvent resistance
- Poor alkali and acid resistance
|
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Benzimidazolone
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Pigment Red 171, 175, 176, 185, 208
Pigment Violet 32 & Pigment Brown 25
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- High solvent resistance and good heat stability
|
Relatively economic when compared with other high-quality pigments.
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Disazo condensation
|
Pigment Red 144, 166, 214, 220, 221, 242
Pigment Orange 31 & Pigment Brown 23
|
- Excellent heat stability
- Good solvent resistance
|
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Quinacridone
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Pigment Red 122, 192, 202, 207, 209 & Pigment Violet 19
|
- Excellent solvent resistance, chemical stability and heat stability
- High
light fastness and bright color
|
Relatively expensive
|
Perylene
|
Pigment Red 123, 149, 178, 179, 190, 224
Pigment Violet 29 & Pigment Black 31, 32
|
- Good chemical stability
- Excellent light fastness, heat stability and solvent resistance
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Expensive, because of their good properties
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Anthraquinone
|
Pigment Red 177
|
- Good heat stability and solvent resistance
- Moderate-good light fastness
- Bright and strong color
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Expensive
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Dibromanthrone
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Pigment Red 168
|
- Excellent light fastness and solvent resistance
- Moderate-good Heat Stability
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Expensive
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Pyranthrone
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Pigment Red 216, 226 & Pigment Orange 51
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- Good solvent resistance
- Low-moderate light fastness and gives a dull shade
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Diketopyrrolo-pyrrole pigments (DPP)
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Pigment Red 254, 255, 264, 270, 272 & Pigment Orange 71, 73
|
- Excellent heat stability solvent resistance and weatherability
- Good opacity and bright color
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Often used in combination with other more economic pigments
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Organic Blue Pigments
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The blue pigment range is dominated by one chemical type - Phthalocyanine. It is considered as the ideal pigment to impart blue color in paints and coatings.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES |
APPLICATIONS |
Copper phthalocyanine |
Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16 |
- Excellent solvent resistance and heat stability
- High color strength
- Very good light fastness & weatherability
- Being one of the cheapest organic pigments on the market they provide very high tinctorial strength
|
These pigments are relatively transparent and can be used in solid, reduced, and metallic automotive coatings |
Indanthrone |
Pigment Blue 60 |
- Excellent chemical stability
- Excellent solvent resistance, light fastness and weatherability
- Good flocculation & heat stability
|
Used in high-performance paints, i.e. automotive OEM finishes, principally in metallic and pale shades |
Organic Green Pigments
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The green spectrum is dominated by
copper phthalocyanine pigments. The common method to reach green is by mixing yellows and blues, the desired brightness and economics being the two main factors determining the best approach.
Inorganic pigments play a comparatively insignificant role.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES |
Phthalocyanine green |
Pigment Green 7, 36 |
- Excellent solvent resistance, chemical stability, light fastness & weatherability
- Good heat stability & tinctorial strength
|
Organic Violet Pigments
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Violet paints are not commonly used whereas violet pigments are. They are used to add blue tones to red paints, and red tones to blue paints, without affecting the intensity of the color.
Violet pigments can also be used to turn the yellow tint of titanium dioxide into white. Dioxazine violet is the most used violet pigment in the paint industry.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES |
LIMITATIONS |
Dioxazine violet |
Pigment Violet 23, 37 |
Excellent heat stability and solvent resistance
Good light fastness |
- Possess a very small particle size which makes them vulnerable to flocculation
- Can also produce plate out in some powder coating systems
|
Dioxazine violet pigments are used in a variety of paint systems:
In metallic paints, Pigment Violet 23 is more used because of its transparency and bluer shade.
Organic Orange Pigments
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Yellow and Orange pigments can often be difficult to differentiate. Numerous orange pigments can be produced via similar chemistry to inorganic yellow chrome pigments, and arylamide, isoindoline, and isoindoline yellow organic pigments.
Others tend to possess chemistry which is associated with red pigments, ie.
- Cadmium reds and molybdate
- Beta-naphthol and BON arylamide pigments
However, the pigments listed below are orange pigments in their own right:
PIGMENT NAME |
COLOR INDEX |
PROPERTIES |
APPLICATIONS |
Pyrazolone orange |
Pigment Orange 13, 34 |
- Good solvent resistance and heat stability
- Low light fastness
- Bright
- High tinctorial strength
|
Mainly used in printing inks.
Pigment Orange 34 can also be used in industrial finishes, especially when produced in its opaque form |
Perinone orange |
Pigment Orange 43 |
- Excellent solvent resistance, high heat stability and tinctorial strength
- Good light fastness
- Bright shade
- Expensive to manufacture
|
Used in tinting systems |
Black pigments are characterized by their origin:
- Organic blacks
- Inorganic blacks: iron oxides, graphite
- Vegetable blacks: peach, charcoal, vine
- Animal blacks: bones, ivory
Organic or inorganic blacks are the most important groups, as well as carbon black which are the most common black pigment.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES & APPLICATIONS |
Carbon Black |
Pigment
Black 6, 7, 8 |
- Excellent light fastness, chemical and heat stability
- Good resistance to solvents
- Limitations include absorption, flocculation, dispersion and viscosity of the paint
- The rubber industry is the biggest user of carbon blacks by a large margin. In comparison, the paint industry is only a modest user
- The printing inks industry uses significant quantities
- Z`Finer particle blacks are used for high-quality finishes such as in automotive paints on account of their higher jetness
- Medium size blacks are used for intermediate quality paints
- Coarser pigments are used for decorative paintsa nand tinting purposes
|
Graphite |
Pigment
Black 10 |
- A soft pigment consisting of inert plate-like particles
- These lamellar plates form layers in a paint film, which prevents water from penetrating
- Good reinforcer of other pigments in anti-corrosive paints
- Confers high spreading rates owing to the slippery nature of the particles
- Limitation - It has low tinctorial strength and low color intensity
|
Aniline Black
|
Pigment
Black 1 |
- Oldest synthetic organic pigment discovered around 1860
- Has a strong tinting strength and light absorption capability
- Fastness properties are quite good
- Low scattering power
- Produces matt effects (velvety appearance) in paint because of its high binder demand
- Mostly used in some speciality coatings where very deep blacks are required
- However, its chromium content limits its application where physiological properties have to be considered
|
Anthraquinone Black |
Pigment
Black 20 |
- Moderately good light fastness
- Moderate solvent resistance
- Used in camouflage paints, as its infrared spectra satisfies various standards
|
Organic Brown Pigments
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Iron oxide is the most important brown pigment, but a few organic pigments are used for specialty applications.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES & APPLICATIONS |
Benzimidazolone |
Pigment Red 171, 175, 176, 185, 208
Pigment Violet 32
Pigment Brown 25 |
- High solvent resistance and good heat stability
- Excellent Light fastness & weatherability
- Mainly used in plastics
- Also used in metallic automotive and vehicle refinishing paints
|
Disazo condensation |
Pigment Red 144, 166, 214, 220, 221, 242
Pigment Orange 31
Pigment Brown 23 |
- Possess two azo red molecules linked to a diamine by means of carbonamide groups
- Excellent heat stability and good solvent resistance
- Color is often bright and ranges from scarlet through bluish red to violet and brown
- Used in industrial and vehicle refinishing paints and as the basis of tinting systems
|
Organic Yellow Pigments
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A large number of organic yellow pigments are available. They differ by their:
- Brightness of shade
Opacity
- Fastness requirements
- Physiological properties, and
- Economic considerations
These properties influence the choice of the pigments depending on the end application. As well as being used in yellow paints, yellow pigments are also used in oranges, greens and browns.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES & LIMITATIONS |
Arylamide |
Pigment Yellow 1, 3, 65, 73, 74, 75, 97, 111 |
- Excellent light fastness and weatherability
- Moderate tinctorial strength
- Poor heat stability and solvent resistance
- Applications limited to water-based and white spirit-based decorative paints
|
Diarylide |
CI Pigment Yellow 12,13,14,17,81,83... |
- Good resistance to heat, chemicals and solvents
- High color strength but poor light fastness
- Have limited use in paints but are used in the printing ink industry, where they are the basis of the yellow process ink
|
Benzimidazolone |
Pigment Yellow 120,151,154,175,181,194
Pigment Orange 36,60,62 |
- Excellent light fastness and weatherability
- Good chemical and solvent resistance and heat stability
- More expensive than other monoazo pigments
|
Disazo condensation pigments |
Pigment Yellow 93, 94, 95, 128, 166 |
- Excellent heat stability, chemical and solvent resistance
- Relatively difficult to manufacture and reasonably expensive
|
Organic metal complexes |
Pigment Yellow 129, 153
Pigment Orange 65, 68 |
- Have a good solvent resistance due to the introduction of a metal group into the molecule
|
Isoindolinone |
Pigment Yellow 109, 110, 173 & Pigment Orange 61 |
- Moderate tinctorial strength
- Good light fastness
- Excellent solvent resistance, heat and chemical stability
|
Isoindoline |
Pigment Yellow 139, 185 & Pigment Orange 69 |
- These pigments have good fastness properties and tinctorial strength
- Do not resist to alkalis
|
Quinophthalone |
Pigment Yellow 138 |
- Good heat stability and solvent resistance
- Excellent light fastness
|
Anthrapyrimidine |
Pigment Yellow 108 |
- Moderately good solvent resistance
- Light fastness is not ideal as this pigment darkens when exposed to light
- Expensive due to its complex nature
|
Flavanthrone |
Pigment Yellow 24 |
- Reddish yellow color and transparent
- Stronger than anthrapyrimidine
- Light fastness is excellent for bright shades
- Durable and has good heat stability
|
What are inorganic pigments?
What are inorganic pigments?
The use of inorganic pigments dates back to the early cave paintings that are 30,000 years old. Although they occur naturally, for the manufacturing of paint they usually require modification. All white pigments are inorganic and a wide range of colored pigments is also available.
Enlighten your knowledge in colored pigments given in detail below or simply click the specific pigment of your choice:
Inorganic Red Pigments
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The popular red inorganic pigments chemistries suitable for paints, coatings and inks are discussed below.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES |
PRICE |
Lead chromate |
Pigment Red 103
CI 77601 |
- Good opacity
- Excellent Light fastness & weatherability
- Low acids resistance
- Excellent bases resistance
|
These pigments are relatively cheap |
Lead Molybdate
|
Pigment Red 104
CI 77605
|
- Good opacity durability and heat stability
- Moderate alkali resistance
- Excellent solvent resistance
|
|
Cadmium red
|
Pigment Red 108
CI 77202
|
- Moderate tinctorial strength
- Good light fastness
- Bright color Excellent opacity and solvent resistance
- Bad acid stability
|
Relatively expensive
|
Red iron oxide
|
Pigment Red 101 (synthetic) & Pigment Red 102 (natural)
|
- Excellent heat stability, solvent resistance and chemical stability
- Low tinctorial strength
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Economical to use
|
Inorganic Blue Pigments
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The blue inorganic pigment range is dominated by one chemical type -
Phthalocyanine. It is considered as the ideal pigment to impart blue color in paints and coatings.
Other blue pigments include:
- Indanthrone which is used for particular high quality applications
- Ultramarine and Prussian blue are two inorganic pigments occasionally used
The printing ink industry uses some cationic toners (phospho tungsto molybdic acid, ferrocyanide and alkali blue pigments), but their poor solvent and chemical resistance coupled with poor light fastness means they have virtually no use in paint.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES |
APPLICATIONS |
Prussian blue |
Pigment Blue 27
CI 77510 / 77520
|
- Excellent solvent resistance and good heat stability
- Excellent light fastness, poor alkali stability. It gives an intense, strong color
- Because of its hygroscopic nature (approx. 4% of water), Prussian blue is difficult to wet
- This pigment is flammable. On burning, it produces HCN, NH3, CO, and CO2 gases
|
This pigment is mainly used in printing inks. It can also be used in industrial coatings and in automotive paints |
Ultramarine
|
Pigment Blue 29
CI 77007 |
- Excellent solvent resistance and heat stability
- Good alkali stability and light fastness
- Poor stability to acids
|
|
Cobalt blue |
Pigment Blue 28
CI 77346
Pigment Blue 36 & Pigment Green 50 |
- Excellent chemical and heat stability
- Good solvent resistance
|
Used in powder coatings, silicone paints and inks |
Inorganic Green Pigments
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The green inorganic pigments spectrum is dominated by copper phthalocyanine pigments. The common method to reach green is by mixing yellows and blues, the desired brightness and economics being the two main factors determining the best approach. Inorganic pigments play a comparatively insignificant role.
PIGMENT NAME |
COLOR INDEX |
STRUCTURE |
PROPERTIES |
Chrome green |
Pigment Green 15 |
Obtained by co-precipitation or dry blending of Chrome Yellow and Prussian Blue |
- These pigments have the same properties as the pigments used for their preparation
- They have a tendency to float or flood because they wet out at different rates
|
Chromium oxide green |
Pigment Green 17
CI 77288 |
Cr2O3 |
- Excellent solvent resistance, heat- & chemical stability, light fastness & weatherability
- Good opacity
- Low tinctorial strength
|
Hydrated chromium oxide |
Pigment Green 18
CI 77289 |
Cr2O(OH)4 - Similar in chemistry to chromium oxide |
- Excellent alkalis resistance, light fastness & weatherability
- Low acids resistance & heat stability
|
Black inorganic pigments are characterized by their origin:
- Organic blacks
- Inorganic blacks: iron oxides, graphite
- Vegetable blacks: peach, charcoal, vine
- Animal blacks: bones, ivory
Organic or inorganic blacks are the most important groups, as well as carbon black which are the most common black pigment.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES & APPLICATIONS |
Black Iron Oxide |
Pigment
Black 11 |
- Relatively cheap and inert pigment
- Excellent solvent- & chemical resistance and light fastness
- Excellent durability and weatherability
- Low tinctorial strength — An advantage when used as a tinter, as it allows more control
- Low oil absorption as compared to other black pigments
- Mainly used in applications where the tendency of carbon black to float cannot be tolerated (for example in grey tones in combination with titanium dioxide)
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Black Micaceous Iron Oxide |
Not listed |
- Inert
- Greyish appearance and a shiny surface
- Capacity to absorb UV radiation also protects the polymers when used as binders
- Plate-like structure prevents the passage of oxygen and moisture
- Should not be over-dispersed because the platelets can be damaged and rendered ineffective
- Used in heavy-duty coatings to protect structural steelwork
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Brown Pigments
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Iron oxide is the most important brown inorganic pigment, but a few organic pigments are used for specialty applications.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES & APPLICATIONS |
Iron Oxide Brown |
Pigment Brown
6, 7 |
- The natural form of Brown Iron Oxide is called burnt sienna or burnt umber
- Pigments are made from naturally occurring ores that are then heated, various shades depend on the impurities, especially MnO content
- Has low tinting strength but is not opaque
- Imparts a rich brown color and give excellent fastness properties
- Synthetic brown iron oxides are not used in paint formulations, as similar shades can be obtained using mixtures of cheaper pigments
- Burnt sienna and burnt umber have become well known due to their use for artists' colors. But they can be used in commercial paints
|
Metal complex brown |
Pigment
Brown 33 |
- It has a spinel structure
- Excellent light fastness and high heat stability
- Mainly used in ceramics
- Can be used in coil coatings, where its high heat stability and excellent fastness properties make it a useful pigment
|
White Pigments for Coatings and Inks
All white pigments are inorganic. The more used white pigment is Titanium Dioxide.
Titanium Dioxide became the dominant white pigment after the Second World War. White pigments are compared by their reducing power. This corresponds to the amount of white pigment needed to produce an equal depth of shade when used with a standard amount of colored pigment.
Related Read: Titanium Dioxide Pigment for Paints & Coatings - Complete Guide
PIGMENT NAME |
COLOR INDEX |
PROPERTIES & APPLICATIONS |
Titanium Dioxide |
Pigment White 6
CI 77891 |
- Exists in three crystal forms: Brookite - Not used as a pigment; Anatase - Used occasionally; Rutile - The most commonly used crystal form
- High resistance to most chemicals, organic solvents and hea
- High refractive index
- Good durability and resistance to industrial atmospheres
- But, photoreactivity reduces the light fastness of some colored pigments and nearly all organic pigments
- Has favorable physiological properties due to its inert composition
- Suitable for use in food packaging, toys, and other sensitive applications, provided that it meets purity criteria
- Can be used in all building and industry coating formulations
|
White Lead |
Pigment White 1 |
- Formula: 2PbCO3Pb(OH)2
- Reacts with acidic binders to provide tough and durable elastic films
- Reacts with sulphurous gases in industrial atmospheres and turns black
- Use of white lead is severely restricted due to concerns regarding the toxicity of lead compounds
|
Zinc Oxide |
Pigment White 4
CI 77947 |
- An amphoteric oxide
- Good white color when it has a high purity (> 99.5%)
- Hexagonal crystal structure has empty spaces due to the big difference in size between zinc and oxygen atoms resulting in semi-conductor properties
- In a binder with a low acid index, it produces zinc soaps which improve the wet out of the pigment and make the dispersion easier
- In a binder with a high acid index, it can cause severe thickening
- Improves the viscosity of the paint and reduces the sedimentation
- Excellent bases resistance
- Can be used as additional pigment with TiO2 to improve chalking resistance, or with lithopone
- Not very interesting as a white pigment, but it can be used as UV absorber, curing agent or fungicide
|
Zinc Sulphide |
Pigment White 7
CI 77975 |
- Formula: ZnS, nH2O where n=0 or 1. It can contain traces of copper. ZnO crystallizes in a hexagonal system.
- Produces a good, strong white color, good opacity and a high degree of chemical inertness
- It chalks badly
- Not used very commonly. It can be used in association with other white pigments in coil coatings
|
Lithopone |
Pigment White 5
CI 77115 |
- Co-precipitate of BaSO4 and ZnS. The mix of the two forms does not separate in the coating
- Excellent Light fastness & weatherability
- Can be degraded under UV light and lead to a grayer color.To avoid this degradation, it is possible to add nicker or iron during the preparation of lithopone, before calcination cobalt or copper
- Can be used in every type of coating
|
Antimony Oxide |
Pigment White 11
CI 77052 |
- Formula: Sb2O3, It is inert and moderately opaque
- Originally used to reduce the chalking of anatase titanium dioxide
- Has excellent light fastness and high heat stability
- Mainly used in fire-retardant paints, because its heavy gas can choke flames
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Yellow Pigments for Coatings and Inks
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|
A large number of inorganic yellow pigments are available. They differ by their:
- Brightness of shade
- Opacity
- Fastness requirements
- Physiological properties, and
- Economic considerations
These properties influence the choice of the pigments depending on the end application. As well as being used in yellow paints, yellow pigments are also used in oranges, greens and browns.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES & LIMITATIONS |
Lead chromate |
Pigment Yellow 34
CI 77600
CI 77603 |
- Yellow Lead Chromates have very bright shades and high chroma, making them ideal for full shade yellow paints
- Excellent opacity and solvent resistance
- Fading can occur because they are sensitive to alkalis and acids
- Their light fastness is usually satisfactory in full shade, but they darken on exposure to light
- Contains both lead and chromium (VI) which effectively limits their application to certain industrial finishes
- Warning labels are required on European paints using these pigments
- Disposal of waste can also be problematic and local regulations carefully followed
|
Cadmium yellow |
Pigment Yellow 37
CI 77199 |
- Gives good quality light fastness in full shades, however, when exposed to industrial atmospheres it discolors and fades
- Presents bright colors with high chroma
- Offers excellent solvent and alkali resistance and high heat stability
- Toxic in nature. Thus, in Europe, its use in nearly all coatings is prohibited for environmental reasons
|
Yellow oxides |
Pigment
Yellow 42 & 43 |
- Excellent light fastness, durability, dispersibility
- High resistance to chemicals and solvents
- High refractive index and good hiding power
- Limited heat stability - When exposed to temperatures higher than 105°C they begin to lose water, causing their shade to shift towards red. This color shift accelerates as the temperature or time of exposure increases
|
Bismuth vanadate |
Pigment Yellow 184 |
- An intense, bright yellow pigment with a greenish shade
- When combined with organic pigments, it generates very bright shades with high chroma and high covering power
- Has high opacity, light fastness, excellent heat and solvent resistance and good hiding power
- Can only be harmful at high concentrations. Low dusting grades minimize this risk
|
Extender Pigments for Coatings and Inks
- Extender pigments are added in order to reduce the cost of a paint formulation. They are also used to modify the flow (viscosity), sedimentation stability and film strength.
- Most extender pigments appear white and possess a refractive index similar to commonly used binders.
- Most of the extender pigments occur naturally and others can be produced synthetically.
- Aluminum silicate, magnesium silicate (talc), silica, calcium carbonate (synthetic and natural) and barium sulfate are some commonly used extender in paints and coatings.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES & USES |
Aluminum silicate (china clay) |
Pigment White 19 |
- Formula: Al2O3, 2SiO2, 2H2O
- Inert and has a good color
- Excellent chemical stability and light fastness
- An inexpensive flatting agent that produces a structure that improves the suspension of other pigments
- Imparts some thixotropy in paints
- Mainly used in water-borne decorative paints
|
Magnesium silicate |
Pigment White 26 |
- Formula: 3MgO.4SO2 H2O
- Inert and hydrophobic
- Does not settle in the wet paint because of its plate-like form
- Provides some resistance to humidity, improves flow behavior, and enhances the sanding properties of paint films
- Used in both water- and solvent-based decorative paints, in undercoats and industrial finishes, in coatings for building and construction, and in anti-corrosion paints
|
Silica |
Pigment White 27 |
- Formula: SiO2
- Fine particle size
- Has excellent chemical stability
- Used as a matting agent to reduce paints gloss
- Improves intercoat adhesion and the sanding properties of the paint film
|
Calcium carbonate |
Pigment White 18 |
- Formula: CaCO3
- used in water- and solvent-based paints, for interior and exterior decoration, and in many other coatings
|
Barium sulphate |
Pigment White 21, 22 |
- Formula: BaSO4
- Very inert and insoluble
- Natural barium sulphate is used in anti-corrosion paints, industrial paints and coatings for building and construction
- Synthetic barium sulphate is used in primers, undercoats, and industrial finishes
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Corrosion Inhibiting Pigments for Coatings & Inks
Corrosion is the destruction or degradation of metal by chemical attack.
Corrosion inhibiting pigments can help prevent corrosion by:
- Physically obstructing the passage of water and oxygen
- Protecting the anodic sites that have become pitted
- Providing soluble pacifying ions to protect the metal
- Producing an insoluble film to prevent active corrosion
Most of these pigments can be toxic because of lead or chrome VI they contain. Corrosion inhibiting pigments have to be selected carefully depending on the application.
PIGMENT NAME |
COLOR INDEX |
PROPERTIES & USES |
Red lead |
Pigment Red 105 |
- Formula: Pb3O4
- Reacts with the acidic groups in the resin to produce lead soaps that passivate iron and steel surfaces
- Mainly used in primers for metal protection
|
Basic lead silicochromate |
|
- Formula: PbSiO3 3PbO PbCrO4 PbO3
- Easily dispersible
- Imparts a high-quality metal protection in automotive paints and structural steel
- Finer grades find use in electrocoat paints
|
Zinc chromate |
Pigment Yellow 36 |
- Formula: ZnCrO4
- Liberates chromate ions, which passivate metal surfaces, producing a protective film at the anodes that prevents the anodic reaction
- In the past they have been used for iron, steel and aluminum protection, however their physiological properties make them unsuitable
|
Calcium, strontium and zinc molybdate |
|
- Formula:CaMoO4, SrMoO4, ZnMoO4
- These three pigments passivate the anode
- Their use has grown considerably in recent years on account of their more favorable physiological properties
|
Calcium plumbate |
Pigment Brown 10 |
- Formula:Ca2PbO4
- A powerful oxidizing agent which also reacts with the acid groups in binders and fatty acid groups such as linseed oil to produce lead and calcium soaps
- Its corrosion-inhibiting effect is a result of the pigments capacity to oxidize soluble iron compounds formed in anodic areas, which then form an insoluble film of iron compounds at the anode. This neutralizes that element of the corrosion cell and restricts any further corrosion
- Promotes adhesion in the paint film and confers toughness
|
Zinc phosphate |
Pigment White 32 |
- Formula: Zn3(PO4)2 2H2O
- Offers good durability, excellent intercoat adhesion and good flow properties in paint systems
- In industrial atmospheres, it reacts with ammonium sulphate to form complex hetero acids, which inhibit corrosion
|
Zinc dust |
Pigment Metal 6 & Pigment Black 16 |
- Formula: Zn
- Fine bluish grey powder that reacts with alkalis to produce zincates and with oils to make zinc soaps
- Corrosion resistance is generated via a sacrificial chemical reaction of the pigment rather than the steel substrate
- protects film formers in exterior coatings by absorbing UV radiation
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How to measure the performance of pigments?
Which properties to consider while selecting pigments?
Which properties to consider while selecting pigments?
Crystal structure
Pigments can be crystalline or non-crystalline (amorphous). In crystalline pigments, the atoms within each molecule are arranged in a well-structured pattern. However, in amorphous pigments, the atoms are randomly arranged. It is also possible for materials to have several different crystalline forms. This is known as polymorphism.
Color is dependent on these different structures. There exist pigments that have chemically identical entities in different crystal forms. Yet these polymorphic pigments are not suitable for use as a pigment. Examples of such polymorphic pigments include:
Techniques for influencing the desired crystal form and particle distribution are being developed. This is done by pigment manufacturers to optimize the commercial product for end applications.
Particle shape
Particle shape can influence the shade of a pigment and the properties of the paint. The following parameters determine the shape of particles:
-
chemical structure,
- crystalline structure, or
- synthesis of a pigment
The primary particles of a pigment may be nodular, spherical, prismatic, acicular, or lamellar. Primary particles are composed of single particles. The smaller these particles, the greater their surface energy. Thus, the more likely it is that they will clump together during manufacturing.
It is not practical to supply pigments in the form of primary particles as they would be more like smoke than powder. In practice, they only exist as the pigment is synthesized. When particles clump during the manufacturing process they form either aggregates or agglomerates.
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Aggregates are connected along crystal boundaries during synthesis or drying. It is difficult to separate them. Hence, pigment manufacturers attempt to avoid their formation during the pigment's production.
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Agglomerates are loose clusters of primary particles. They can break down via an efficient dispersion process. Following this process, it is still possible for particles to re-agglomerate into loosely held groups. These groups are known as flocculates. This commonly occurs when there is a rapid change of state, i.e.,
- Too rapid dilution or
- The addition of an incompatible substance
Flocculation results in a loss of tinctorial strength. However, flocculates are usually easier to separate than true agglomerates. Even normal shear such as brushing out is sufficient for their separation. This result in an uneven increase in tinctorial strength, depending on how much shear has been developing.
One point to note during brushing out is that small particles are more susceptible to flocculation than larger ones. So pigments at risk are carbon blacks and organic pigments such as phthalocyanine and dioxazine violet pigments. There are an increasing number of flocculation-stable grades being released in the market.
Particle size
Pigment particles are not usually spherical. They can have different dimensions depending on whether one measures the length, width or height. Particle size is an average diameter of primary particles. Typical ranges are:
- Carbon black - 0.01 to 0.08 µm;
- Titanium dioxide - 0.22 to 0.24 µm;
- Organics - 0.01 to 1.00 µm;
- Inorganics - 0.10 to 5.00 µm;
Extender pigments can be among the coarsest pigment particles, up to 50 µm. But other types can be exceptionally fine (e.g., the precipitated silicas).
The pigment's particle size can affect its color, hide and settling characteristics. Large particles usually settle faster than smaller ones, and smaller ones are harder to disperse. Light scattering is also often influenced by pigment size. And the distribution will also affect the colloidal stability and color.
Surface area & oil absorption
The surface area is the total area of the solid surface. The unit of the surface area is square units (m2) and is usually defined as 1 gram of pigment. Typical values for organic pigments are between 10 and 130m2. This surface area is determined by an accepted measurement technique such as the BET (Brunauer, Emmett, and Teller) method using nitrogen adsorption. This technique consists in calculating the adsorption properties of the pigment.
The surface area is closely linked to the pigment's demand for binder. Larger particles have a smaller surface area and therefore a lower demand for binder. As the size of the particle of pigment is small, the surface area becomes large. As a result, the paint needs a large amount of binder to wet each pigment particle during the dispersion process.
Oil absorption is the amount of oil that is required to "wet out" 100 grams of pigment and to make paint. Oil Absorption is expressed in number of grams of oil per 100 grams of pigment (or volume relationship from weight).
Oil absorption = Number of grams of oil/100 grams of pigment
This value varies depending on the pigment's physical nature and particle size. The amount of oil affects the time of dryness. In general, the large amount of oil causes yellowing and delay of dryness.
Hardness of the pigments
Hardness is usually based on Mohs Hardness Scale. The hardness of the pigment is measured by comparison with the ten classes of the Mohs scale.
In the absolute scale of the hardness (of Rosiwal), the abrasion resistance is measured with proofs from laboratory, and by attributing to the corindone the value 1000.
Also for the Knoop scale, the values of hardness are absolute. They depend on the depth of the signs engraved on the minerals due to a special utensil with a diamond point, with which a standard of force is applied.
Mineral
|
Mohs Scale
|
Rosiwal Scale
|
Knoop Scale
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Gold
|
0
|
-
|
-
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Talc
|
1
|
0.03
|
1
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Gypsum
|
2
|
1.25
|
32
|
Calcite
|
3
|
4.5
|
135
|
Fluorite
|
4
|
5
|
163
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Apatite
|
5
|
6.5
|
430
|
Orthoclase
|
6
|
37
|
560
|
Quartz
|
7
|
120
|
820
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Topaz
|
8
|
175
|
1340
|
Corundum
|
9
|
1000
|
1800
|
Diamond
|
10
|
140000
|
7000
|
These scales help define how hard a pigment is and if it will be easily abraded. The hardness of the pigment can affect the durability and abrasion resistance of the film. The hardness scales also allow the formulator to better define milling equipment needs and end-use. Some pigments are soft and can be damaged by milling, especially when placed in a ball mill for extended periods of time.
Another point to consider is the pigment's solubility and the effect of solvent on the pigment's hardness and structure.
Quantity of Pigment
The amount of pigment used in paint is determined by:
The paint technologist works on one of two main concepts:
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Pigment volume concentration (PVC) -
-
It fundamental concern when formulating paints with optimum durability.
There is a critical point that represents the densest packing of the pigment particles. This aligns with the degree of dispersion of the system.
For systems requiring high gloss, low PVC is required. Primers and undercoats can have much higher PVC - up to 90%.
-
Pigment to binder ratio (P:B) -
-
The P:B ratio, by weight or occasionally by volume, is a much simpler calculation.
It is often used to assist in formulating a good mill base and for balancing a formulation for gloss and opacity.
Binders used in formulations
The binder in the paint system plays a key role in terms of determining the pigment and the type of solvent in which it is dissolved.
- A common choice for a solvent is water as it is compatible with most polymers, except some toners.
- White spirit is a commonly used solvent for long oil alkyd paints. These are widely used in decorative gloss paints. A large majority of pigments are almost insoluble in white spirit. So it rarely narrows the choice of pigments.
- Industrial finishes can be based on solvents such as xylene, ketones, and esters. They are very powerful and can dissolve pigments with poor or only moderate resistance to solvents.
It is also necessary to consider whether the coating will be overcoated. For example, in the case of a car getting repaired, the pigment used on the original finish will have to be fast to overcoating.
In powder coatings, crosslinking agents can affect the pigment. Hence, the pigments must be compatible with these agents at temperatures employed during application. It is therefore evident that the type of resin and solvent used remain key factors in the choice of pigment.
Paint performance in end application
An awareness of the end use of the paint is essential, as durability and chemical resistance requirements. The maximum price that can be tolerated for improved performance depends on this knowledge.
For example, a low-quality pigment would be insufficient in an automotive finish, just as a high-quality pigment would be unnecessary for use in a gardening tool.
Paints can be classified according to the market in which they are used, such as:
- Building, architectural or decorative
- Automotive finishes, OEM (original equipment manufacturers) or VR (vehicle refinishes), and
- Industrial finishes
In the same way, pigments used in paint do not require the same properties as pigments used for ink applications.
Find suitable pigment grade for your product, analyze technical data of each product, get technical assistance or request samples.