Colored pigments, preparation

Madder lake n. Lightfast, non-bleeding, red-colored pigment prepared from the coloring matter of madder root. 

The colorant is prepared by leaching the annatto seeds with an extractant prepared from one or more approved, food-grade materials taken from a hst that includes various solvents, edible vegetable oils and fats, and alkaline aqueous and alcohoHc solutions (46,47). Depending on the use intended, the alkaline extracts are often treated with food-grade acids to precipitate the annatto pigments, which ia turn may or may not be further purified by recrystallization from an approved solvent. Annatto extract is one of the oldest known dyes, used siace antiquity for the coloring of food, textiles, and cosmetics. It has been used ia the United States and Europe for over 100 years as a color additive for butter and cheese (48—50). 

As already mentioned, certain azo colorants have low aqueous solubility but not sufficiently low for them to be usable as pigments. These azo colorants are prepared from amines and coupling components containing hydroxyl or carboxyl groups in their sodium salt form as a result of alkaline coupling conditions. 

In pigment preparations the pigment is present in dispersed form which, with appropriate choice of carrier material, enables the plastic to be colored uniformly, homogeneously and reproducibly under normal processing conditions. 

There are a number of mixing and processing techniques which have been used successfully to color granulated or powdered polyolefin with pigments or pigment preparations. Powders, for instance, are processed primarily with high-speed mixers, while granulated types respond better to slower mixers. 

Azomethine metal complex pigments replace the metal with tin stabilizers, resulting in a change in shade. In the case of manganese-laked pigments trouble can also be expected in the presence of epoxy compounds. Pigment preparations based on epoxidized soya bean oil are normally used instead of diisodecyl phthalate pastes in the automotive sector e.g. for coloring PVC roofs etc. 

Pigment preparations are frequently used in the PVC cable industry for coloration. The pigment content is often selected in such a way that one part by weight of the preparation is used to color 100 parts by weight of the polymer compound. The shades and color codes for cables and insulated lines are specified in standards in various European countries [35],... 

Pigment preparations are also marketed for coloring thermoplastic PUR. Their carrier materials range from vinyl chloride or vinyl acetate copolymers, such as are used for PVC, through low-molecular polyethylene to PUR itself. 

Rubber compounds are colored with powder pigments and increasingly with granulated pigment preparations, known in the rubber industry too as master-batches. 

Due to the disadvantage of comparatively poor migration resistance, P.R.5 is not used in plasticized PVC, but it can be applied in rigid PVC. Its lightfastness is excellent in this medium, transparent and opaque colorations (up to 0.01% pigment + 0.5% TiOz) equal step 7 and, respectively, step 6-7 on the Blue Scale. Dispersed pigment preparations are available for the mass coloration of viscose films as well as for spin dyeing of viscose rayon and viscose cellulose. 

P.R.164 was also found in cast resin composed of methacrylate and unsaturated polyester. The pigment does not affect the hardening process of such media, which may be carried out, for instance, by using peroxides. An important field of application was in the coloration of various polyurethanes, for which the pigment was also sold in the form of a pigment preparation. 

P.R.176 provides very lightfast polyacrylonitrile spin dyeing products. The samples equal step 6-7 on the Blue Scale. Dry and wet crocking may affect the objects to a certain extent. P.R.176 is also used in polypropylene spin dyeing, especially for coarse textiles, such as carpet fibers, split fibers, filaments, bristles, or tape, but also for finer denier yams. A special pigment preparation for this purpose is commercially available. 1/3 SD samples tolerate exposure to up to 300°C for one minute or up to 290°C for 5 minutes. In terms of lightfastness, 0.1% colorations equal step 5-6 on the Blue Scale, while 2% samples match step 7. 

High transparency makes P.Y.24 a valuable pigment for metallic finishes. It is used in relatively light shades, typically at a ratio of one part of color pigment to three parts of aluminum pigment. Thus prepared systems demonstrate excellent weatherfastness. Flavanthrone Yellow, like P.Y.108, tends to seed (Sec. 3.7.3.1). The pigment is heat stable up to 200°C and thus satisfies all possible heat stability requirements in this area. Flavanthrone Yellow is used in various industrial paints, especially in automobile O.E.M. finishes and in automotive refinishes. 

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