On the other hand, inorganic pigments like: Metal oxides and sulphides, carbon black, etc. get more easily dispersed in the resin. Amongst the inorganic pigments titanium dioxide is the most widely used pigment in the plastics industry.

Pigments are used in the coloration of paints, printing inks, ceramics and plastics. They can be used on a much wider variety of substances than dyes because they are not reliant on water solubility for their application. A pigment is a finely divided solid which is essentially insoluble in its application medium. In most cases the pigment is added to a liquid medium e.g. wet paint or a molten thermoplastic. The medium is then allowed to solidify by solvent evaporation or cooling and so the pigment molecules become fixed mechanically in the solid state.

The chromophores used in pigments are usually the same as those used in dyes but the pigments are large molecules and do not have solubilising groups. They contain groups that form intermolecular bonds that help to reduce solubilities. The larger the molecule, the more opaque the pigment.

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Special effects are used in addition to or in combination with pigments to impart a unique look to fabrics. Some of the special effects examined in this bulletin include resist, discharge, and burnout techniques. Alternative pigment types such as thermotropic, phototropic, puff, and plastisol technologies will also be described.

A textile pigment print system includes the following parameters:

• Pigment: A pigment colorant is a colored organic substance that is not readily soluble in most common solvents and imparts coloration to textile substrates only when incorporated with an adequate binder system.

• Binder: A pigment binder is the latex polymer resin that forms a three-dimensional film on the surface of the fiber. This film contains the dispersion of textile pigment and will act to adhere the pigment to the surface of the substrate. The permanence of this film is dependent on the polymer type and the application conditions. Binder chemistry, performance, and application is covered in Technical Bulletin ISP 1008.

• Thickener: The pigment system is composed of the textile pigment dispersed in the polymerizable resin binder, which is further mixed into a synthetic thickener system, comprised of a long chain acrylic acid. The thickener enables the pigmented print paste to stay in place once it is deposited onto the fabric prior to drying. This system is applied to the textile substrate by the following means: rotary screen printing, flatbed screen printing, engraved roller printing, coating, padding, spraying, or immersion.

Coloured pigments (as well as titanium dioxide) can be fixed onto the fibre surface though they are not bound to the fibre substance either by covalent bonds or by any other bonds normally presents between dyes and fibre substance like ionic bond, hydrogen bond, Vander waals forces etc. This is achieved in pigment printing by using suitable binders, which form transparent, soft, pliable films, which trap the pigment particles between the film and the fabric surface and react with the fibre surface.

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