A series of organic color pigments used in printing inks. Alkali Blues"] and Reflex Blues ('CI Pigment Blue 56 No. 42800', CI Pigment Blue 18 No. 42770, and CI Pigment Blue 61 No. 42765:1') are the strongest blue pigments available. They comprise a wide range of shades of blue (from reddish to greenish), and possess varying degrees of lightfastness and chemical resistance. PB 56 has the greatest color strength and the most alkali resistance, while PB 18 and 61 have poor alkali resistance. These blues have poor lightfastness, moderate resistance to heat, and good resistance to acids. New formulations of these types of blues have found particular use in flexographic inks; as flushed colors they are also used in lithographic and gravure inks. Alkali Blues are most commonly added to black pigments to reduce their brownish tone and, interestingly, are primarily responsible for the "blackness" of some black pigments. (See Organic Color Pigments.)
|