Bleed resistance, pigment

Llthol Reds. Lithol Red or Pigment Red 49 1/7103-38-4] is one of the most important of the precipitated salt pigments. They comprise a family of sodium (PR 49), barium (PR 49 1), calcium (PR 49 2), and strontium (PR 49 3) salts of dia2oti2ed Tobias acid or 2-naphthylamine-l-sulfonic acid coupled with 2-naphthol. The most popular are the barium and calcium salts, the former being yellower in shade. These reds are used where brightness, bleed resistance, and low cost ate of primary importance. They are neither resistant to heat nor chemicals, and are used primarily in printing inks and some inexpensive air-dried industrial paints where good durabiUty is not requited. 

The pigments are used primarily in plastics, including polypropylene fibers, because of very good bleed resistance, heat stabiUty, and lightfastness. The reds also find use in printing inks, primarily for high quaUty products. 

A third form of cadmium pigments includes the mercury cadmiums. Mercuric sulfide (HgS) forms soHd solutions up to about 20 mol % with the oranges, reds, and maroons. The heat stabiUty is improved up to 370°C, and the costs are somewhat lower than the CP grades. The mercury cadmiums are slightly more reactive, but have excellent bleed resistance. 

Table 4 Relation between the heat stability of azo pigments in an alkyd-melamine resin baked system, their fastness to overpainting in this paint system, and their bleed resistance in plasticized PVC.

P.Y.183 is bleed resistant in plasticized PVC, where its poor tinctorial strength is of some disadvantage. 1/3 SD samples (5% TiOz) require 1.64% pigment. Such systems provide a lightfastness which is equal to step 6 on the Blue Scale 1/3 SD transparent colorations correspond to step 6-7 on the Blue Scale. 

The pigment also lends itself to application in elastomers, such as natural rubber blends. It is migration fast enough to satisfy most specifications. P.R.53 1 is also completely bleed resistant in natural rubber, although some color is transferred into the wet cotton cloth liner, the wrapper (Sec. 1.8.3.6). P.R.53 1 is lightfast enough for most applications. Products containing P.R.53 1 are not always entirely fast to hot water or alcohol. 

P.R.239 is a comparatively recent product. It enjoys limited regional impact and is used very little in Europe. Its exact chemical constitution remains to be published. P.R.239 affords dull, bluish shades of red. Its main application media are plastics. The pigment is bleed resistant in plasticized PVC. Its shade in this medium equals that of P.R.247, a member of the same class of pigments, which, however, has the advantage of providing a much cleaner shade. Incorporated in HDPE, P.R.239 is of average tinctorial strength and is heat stable up to 270°C. 

Benzimidazolone pigments, especially those covering the red range of the spectrum, were originally developed and used mostly for plastics. None of them were found to adversely affect the physical characteristics of their host medium. Benzimidazolone pigments do not bloom in plasticized PVC and other polymers. They are usually bleed resistant under typical application conditions. 

P.R.248 exhibits excellent bleed resistance in plasticized PVC. Transparent specimens equal step 8 on the Blue Scale for lightfastness, while 1/3 SD samples match step 7. The pigment does not perform as well in terms of weatherfastness, for instance in PVC plastisols for coil coating. P.R.248 was also recommended for use in elastomers, polyurethane, and unsaturated polyester. 

Significant pigment attributes are tinctorial strength, durability (photochemical stability), biding power, transparency, and heat and solvent resistance. Other properties include brightness (saturation), gloss, rheology, crystal stability, bleed resistance, flocculation resistance, and other properties associated... 

The most important advance in pigment technology after World War I was the discovery of the relatively complex structure but easily synthesized copper phthalocvanines, which were characterized by excellent brightness, strength, bleed resistance, and lightfastness. See also Phthalocyaninc Compounds. 

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