Mr Veeramani shares his knowledge in this Column devoted exclusively to Water Based Coatings
So far we have seen the Inorganic Pigments which are extensively used in the Water Based Emulsion Paints. Now let's go over to Organic Pigments which also play a vital role in bringing out the beauty of the colours, especially in the Interior surfaces. They are sharp with their good tinctorial strength give lot of legroom to the Formulator in choosing the pigments either in Powder form or in Paste form, which are available in pre-dispersed condition making things easy for both the Formulator and the Production personnel. Some times in a Formulation both Inorganic and Organic Pigments may be present to arrive at a particular colour/shade.
They are not usually found in nature. That is the reason that a majority of these pigments are chemically synthesized. They contain carbon and come with relatively low levels of toxicity, not providing any major environmental concern. Raw materials can include coal tar and petroleum distillates that are transformed into insoluble precipitates. Traditionally organic pigments are used as mass colorants. They are popular in plastics, synthetic fibres and as surface coatings-paints and inks. In recent years, the organic pigments are used for hi-tech applications that include photo-reprographics, opto- electronic displays and optical data storage.
Natural organic pigments were used in cave paintings and for decoration from the earliest times. The ancient Britons obtained indigo from the wood plant Isatis tinctoria , and used the extract to colour their bodies. Here the insoluble blue is used as a pigment rather than as a dye. Other organic pigments found in nature include chlorophyll, the green colouring matter of leaves responsible for photosynthesis, heme, which gives blood its red colour and, when bound to proteins in haemoglobin, transports oxygen around the body. These biochemical pigments are members of the porphyrin family.
During the early 1930s synthetic organic pigments, called phthalocyanine, were developed in Britain and manufactured by Imperial Chemical Industries (ICI). Academic researchers showed those phthalocyanines are co-ordination complexes that mimic the structures of porphyries. The coordination concept, involving groups of atoms called chelates attached to a central metal, was developed beginning in 1893 by the Swiss chemist Alfred Werner and confirmed in 1911, when he collaborated in Zurich with Victor L. King, later a leading technical expert in the U.S. colorant industry. Phthalocyanine represents the only structurally novel class of synthetic colorants invented in the twentieth century. Copper phthalocyanine, known as Môn astral blue, and its congeners are used in automobile finishes, printing inks, and plastics.
Lake pigments made from the first synthetic dyes, such as mauve, were used during the 1860s for printing postage stamps and wallpaper. Red lake pigments, such as that derived from the madder dye, or after 1870 from synthetic dyes, were highly regarded by the Impressionist painters. Other synthetic organic pigments are made from azo dyes, those containing the −N=N− atomic grouping, introduced during the 1870s. The use of synthetic organic pigments in printing inks increased perhaps threefold in the last two decades of the twentieth century, as colour became the norm in newspapers, magazines, advertising, and packaging. Careful standardization of the microcrystalline form, the crystal habit, is required for pigments employed in printing inks and paints. In order to add color to synthetic polymers, the plastics and resins, pigments are mixed in bulk with other chemicals during the manufacturing process.
In Organic pigments, the molecules are made of carbon atoms along with hydrogen, nitrogen or oxygen atoms. Organic pigments are further divided into two subgroups:
Natural organic pigments:
These types of pigments are derived from animal products and plant products. The uses of these pigments are rare due to their poor light fastness property.
But, today a large number of the natural organic dyes have been replaced by the synthetic organic dyes. Therefore, today, these pigments are remembered by theirs quaint historical names. These pigments are being adopted by the modern commercial paint companies to lend romance in their traditional mixtures. And, the most important, these pigments are environment friendly.
Synthetic organic pigments
Synthetic Organic Pigments are carbon based and are often made from petroleum compounds. Most of the Synthetic Organic Pigments except Carbon Black are not stable and they will wear away at the time of using as a pigment. Under intense pressure or heat, carbon base molecules are manufactured from petroleum, acids, and other chemicals and Synthetic Organic Pigments have been formulated from these molecules.
These two subgroups of Organic Pigments have been depicted in the following table:
Why a large number of modern pigments are synthetic organic in nature?
Carbon atoms have amazing flexibility and ability to form many different structures. That is why; the entire concept of organic chemistry mainly depends on carbon's atoms. Carbon atoms are able to form different combinations with other carbon atoms or atoms of other elements or with other compounds. This facilitates it to form almost limitless molecular variations. Out of these large numbers of carbon made molecules, intense colour variations attribute will come in these synthetic organic pigments. Pigments which are formed out of these molecules are the least toxic and economically beneficial.
AZO Pigments along with other organic pigments are derived from water soluble dyes.
Synthetic Organic Pigments are mainly derived from some selective elements atoms. These are as follows:
Chromophores are responsible for the color creation phenomena of the pigment's molecules. Chromophore is a pair or group of atoms. This pair creates a complex and dynamic clouding of the electrons within the respective electron shells in single atom or more than one atom.
When coating Formulation involves the selection of one or more Organic Colour Pigments , the performance characteristics and the cost of the pigments chosen often determine, more than any other factor, the suitability of the coating for a particular purpose and its success or failure in the market. This work is intended to assist the Formulator in making this important choice, by suggesting procedures particularly suitable for use in Paint Laboratories for comparative evaluation of Pigments and by reporting the results of such an evaluation involving a broad group of Organic Colour Pigments commonly used in Architectural, Commercial and Light Duty Industrial Coatings.
Pigments: size comparison
It is an important class of organic pigments. Its linear form is particularly important for exploiting it commercially. Quinacridone pigments are very novel pigments that have When coating Formulation involves the selection of one or many diverse applications. Quinacridone pigments generally produce seven types of bright and intense colours. These colours range from deep yellow to even vibrant violet. The following is the chemical structure of Quinacridone pigment:
Features of quinacridone pigments
- Excellent bleed and heat resistance
- Bright and vibrant tones
- Outstanding light fastness
- High transparencies
- Very good tinting value along with working properties
The family of quinacridone pigments Effect pigments
Effect Pigments guarantee brilliant performances in various industries, mainly in the plastic processing, printing industry and the colour and coating industry. They open up an infinite array of colours and effects that create unlimited design possibilities. The oldest evidences that we have found about the use of Effect Pigments are the cave paintings of the ice age people. Today, a lot variety of effect pigments have come into existence By using the effect pigments, one can get access many unique effects. These effects include the visual world effect with a decorative look, flickering lights and amazing effects. These pigments bring a new feeling and give new effect to the colours with sparkle and tremulousness.
Color Index Name | Chemical Family | -------- | ----- | Pigment Red 122 | 2,9 Dimethyl Quinacridone Pigment Violet 19 | Quinacridone Pigment Red 202 2,9 | Dichloroquinacridone Pigment Red 209 1,8 | Chloro Quinacridone
Types of effect pigments
All the conventional organic or inorganic colour pigments come in this category. These pigments absorb a particular wavelength of the incoming light. These pigments don't produce any lustre, because of their irregular shapes.
Metallic Pigments comprise of very small platelets of aluminium, copper, zinc. The formation and differentiation of opaque pigments are possible due to these metallic pigments on the basis of the surface lustre.
Pearl lustre pigments
Pearl Lustre Pigments are suitable to be used in almost all of the printing inks. They are semi-transparent. These pigments are based on guanine or bismuth oxychloride, mica minerals. In these pigments, the light reflects in between the different layers of the pigments. This phenomenon makes these pigments very lustre.
Other pigments like, Pearl, Gold, Bronze and Copper have limited application in Paint Industry. They are used to manufacture the respective Water based and Oil based Paints for bringing special effects on walls, metal surfaces, house fittings etc.
Gold Pigment Bronze Pigment Copper Pigment
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