Pigment

Pigment is a kind of white or colored fine powdery substance and is insoluble in medium such as water or oil, and can be uniformly dispersed in the medium. In this system, the pigment can be used as dispersed phase with the medium being the continuous phase. When mixed with various kinds of media (including color development agent) together, it enables the coloring of the object, and the pigment itself is not dissolved in coloring matter and can also make the object exhibit a certain color, such substances is called as pigments. Some literature also confine that the pigment should not chemically react with the coloring matter. With the progress of science and technology, this definition has been broken, because there can be certain chemical reaction occurring between some pigments and the coloring matter. As a kind of pigment, it should have appropriate color (including white), coloring strength, hiding capacity, a high degree of dispersion, light stability and vivid color.

Based on the chemical composition, it is divided into inorganic and organic pigments;
According to its color, it is classified into white, red, yellow, black and other pigments;
According to the sources, it can be divided into natural and synthetic pigments; natural pigments can be further divided into animal pigment, plant pigment and mineral pigments. Mineral pigment (inorganic) includes ocher, cinnabar, red clay, realgar and so on. Animal and plant (organisms) type include Garcinia and cochineal red; synthesis pigments also have organic and inorganic pigments, two major categories.
According to the application, it can be divided into coloring pigment, extender pigments and functional pigments. Coloring pigment is the inorganic or organic pigments that endow the media with various kinds of colors; extender pigment is a non-coloring and non-hiding pigments. In early time, it was mainly used to reduce product cost and improve the performance of coatings, plastics, rubber and other products, and thus also being called filler.

Now there are natural products and synthetic products that have processed into ultrafine-grained grade. The synthetic product has low impurity content, fine particles and can be artificially synthesized and further subject to various kinds of surface modification as needed. Owing to these advantages, it can be further used to reduce the usage amount of paint of opacity (such as titanium dioxide) and improve the product performance. Therefore, it is more suitable to call it extender (incremental) pigment. The major varieties of extender pigments are mostly processed natural minerals such as natural calcium carbonate, barite powder, talcum powder, mica powder, diatomaceous earth, quartz powder, clay and asbestos. A small number of them are synthetic products such as precipitated calcium carbonate, precipitated barium sulfate, synthetic silica; functional pigments are pigments to endow the product with particular functions. For example, the temperature-indicating paint can enable the color change of the product according to the temperature; anti-fouling pigment is able to poison and kill the aqueous creatures; luminous pigment can emit in the dark; anti-rust pigment can prevent the corrosion; pearlescent pigments exhibit pearl luster.

The differences between pigment and dye are as below: dye can be dissolved in the medium with some of them even being able to be dissolved in the dyed product and can make the dyed product being colored only after the chemical reaction between them occurring. However, they two can sometimes be interoperable, e.g., some of the anthraquinone dyes can be used as both dyes and pigments; sometimes pigments and dyes can be converted to each other; for example, we can convert the dye to insoluble lake to be used as a pigment . Pigment is a kind of indispensable raw material in the painting industry. In addition, it is also widely used in the printing industry, rubber industry, plastics industry, chemical industry, paper industry, ceramic industry, glass industry, ceramic industry, printing and dyeing industry, building materials industry, inks, paints, color lead (wax) pen, makeup pigment and so on. It can endow the products with decorative property, opacity, durability or special function. With advances in technology, various kinds of high performance pigments will be further developed.

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