What is Pigment?
A pigment is a material that changes the colour of reflected or transmitted light as the result of wavelength-selective absorption. In other words, it’s a substance that appears a certain colour because it selectively absorbs certain wavelength of light.
The primary purpose to use pigment is to provide colour to materials, whether they are textiles or paints. Some people often consider pigment and dyes to be the same but they’re quite different. The major difference between the both is in terms of their solubility. While a dye can dissolve by itself in a liquid, pigment can be dissolved in a liquid with the help of a binder. Dyes are primarily applied in the textile and paper industry, pigment are used in industries such as colouring paints, inks, cosmetics, and plastics.
Types of Pigment
Based on the method of their formulation, pigment can be categorized into two types: inorganic pigment and organic pigment.
This type of pigment occurs naturally and they’ve been used for centuries. They’re quite simple in their chemical structure. They’re named organic as they contain minerals and metals that give them their colour. Organic pigment manufacturers produce them through a simple process that’s made of washing, drying, powdering and combining into a formulation.
Compared to inorganic pigment, these usage of these pigment is less frequent and that’s why there are limited number of organic pigment suppliers. These pigment are used when the required colour strength isn’t too much.
As you can guess by its name, this type of what is pigment is exactly the opposite type of organic pigment. These pigment are also known as “synthetic pigment.” They’re formulized in labs and offer great scope of control to inorganic pigment manufacturers.Inorganic pigment are manufactured by relatively simple chemical processes such as oxidation.
Inorganic pigment suppliers supply this type of pigment mainly to paints, plastics, synthetic fibres and ink industry. In uses where bright colours are required, organic pigment are used as they bolster high colour strength. Inorganic pigment include white opaque pigment which are commonly used to lighten other colours and also to provide opacity.
Organic Pigment for Inks and CoatingsOrganic pigment are traditionally transparent. However, modern manufacturing techniques are capable of imparting properties not previously associated with the chemical type: it is now possible to produce high opacity organic pigment. Organic pigment are relatively new. Although, natural dyes have been precipitated on to inorganic bases (known as lakes) and used in artists' colors since the Middle Ages (e.g. madder lake and crimson lake), true organic pigment have only been known since the early years of the twentieth century. Metallic pigment, as implied in the name, include metal pigment such as zinc and aluminium pigment. While industrial pigment are the pigment that are widely used in the industrial applications and include organic, inorganic and the metallic pigment.
The smallest units are called primary particles. The structure and shape of these particles depends on the crystallinity of the what is pigment. During the pigment production process, primary particles generally aggregate and generate agglomerates. During the dispersion of the pigment into the polymer, high shear is generally needed to break up these agglomerates (improved tinting strength). Pigment are thus required to resist dissolving in solvents that they may contact during application, otherwise problems such as "bleeding" and migration may occur. In addition, depending on the demands of the particular application, pigment are required to be resistant to light, weathering, heat and chemicals such as acids and alkalis.
Few pigment degrade at temperatures normally associated with coatings. However, at higher temperatures, pigment become more soluble and shading can occur. Thus, for organic pigment, heat stability is closely related to solvent resistance. Pigment that prove to be satisfactory at a certain stoving temperature may be totally inadequate in an application requiring 10°C more.
Chemical stability is also likely to be critical at elevated temperatures. This is typically the case in powder coating systems. Another key area is coil coatings, as metal complex pigment may react with stabilizers at elevated temperatures, causing major shifts in shade. Modifications can also occur in the crystal structure of pigment when subjected to elevated temperatures. Pigment with a highly crystalline structure are usually more heat resistant than polymorphic pigment, where the different crystal modifications may respond differently to heat. Typically, inorganic pigment have enhanced heat stability, though an exception is yellow iron oxide, which loses water from the crystal at high temperatures. Heat stability is system dependent, and this must be reflected in any test. All tests assess color at various temperature intervals and evaluate the color difference between the sample in question and a standard that has been processed at the minimum temperature.