Naphthol pigments

Description

A broad class of azoic colorants that contain a backbone of 2-hydroxy-3-naphthanilide and include many shades of red, some oranges and a green. In 1911, three German scientists at Naphtol-Chemi Offenbach coupled the acid backbone with aniline and toluidine diazonium salts. The new discovery was patented and sold as under the trade name Napthol AS. Several intense colors, reds and oranges, were produced and known as Grela Reds. They had high tinting strength and were washfast on cottons, but were laborious to make. As such, the compounds did not become popular until they were laked into pigments and used in artists paints by IG Farben. Later, a series of naphthol reds, called American Naphthol Reds, was introduced to the United States in the 1940s (Berrie and Lomax 1997). About 6% of the red colorants used in 1985 were naphthol pigments. They provide good tinting strength and good lightfastness but can bleed when exposed to organic solvents. Naphthol reds are used to color plastics, automotive finishes, architectural paints, pencils, crayon, printing inks and inexpensive artists oil paints and watercolors.

See also Beta naphthol pigment.

Synonyms and Related Terms

naphthol dye; azoic dye; Naphthol Red; Naphthol AS; napthol dye (sp); hydroxynaphthoic anilide; Naphtol Anilid Saure (Deut.); Naphtol AS (Deut.); pigment à base de naphtol (Fr.); Grela Reds

Common Naphthol Pigments

CI #	Name(s)	Color	Key Properties	Common Applications	Spectra
PR2	Naphthol Red Light	Bluish Red	Good lightfastness, poor solvent resistance	Industrial paints, printing inks
PR5	Naphthol Red	Mid-red	Good lightfastness, high color strength	Artists' paints, coatings
PR9	Naphthol Red/Scarlet	Yellowish Red	High lightfastness, good water fastness	Textiles, high-grade paints	MFA Naphthol Reds (FTIR); CHSOS (Reflectance, XRF, Raman, FTIR)
PR12	Naphthol Red	Yellowish Red	Good tinting strength, similar to Red Lake C	Printing inks, plastics, coatings
PR112	Naphthol Red Medium	Warm Red	Economical, good lightfastness, high hiding power	Watercolors, automotive, plastic	CHSOS (Reflectance, XRF, Raman, FTIR)
PR146	Carmine FBB	Bluish Red	Very high lightfastness, good heat stability	Packaging inks, high-end paints
PR170	Naphthol Red	Blue-shade Red	Versatile, high tinting strength, good lightfastness	Artists' oil/acrylic, automotive	MFA Naphthol Reds (FTIR); CHSOS (Reflectance, XRF, Raman, FTIR)
PR184	Naphthol Rubine	Bluish Red	High strength, low lightfastness	Printing inks, metal decorating
PR188	Naphthol Red	Mid/Yellowish	Excellent solvent and light stability	Automotive finishes, inks
PO5	Orthonitroaniline	Orange	Poor lightfastness and solvent bleed	Crayons, paper, inks
PO24	Naphthol Orange	Orange	Moderate lightfastness, good tinting	Inks, plastics
PG12	Naphthol Green	Green	Iron complex, good lightfastness	Industrial, artist paints	CHSOS (Reflectance, XRF, Raman, FTIR)

Physical and Chemical Properties

• Resistant to acid, alkali and soap.
• May bleed with some organic solvents
• Generally good to excellent lightfastness

Resources and Citations

• B. Berrie, S.Q. Lomax, 'Azo Pigments: Their History, Synthesis, Properties and Use in Artists' Materials', Studies in the History of Art, National Gallery of Art, Washington DC, No. 57, 1997. Comment: patented 1911
• Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993. Comment: Napthol AS = azoic coupling component
• Hoechst Celanese Corporation, Dictionary of Fiber & Textile Technology (older version called Man-made Fiber and Textile Dictionary, 1965), Hoechst Celanese Corporation, Charlotte NC, 1990
• Rosalie Rosso King, Textile Identification, Conservation, and Preservation, Noyes Publications, Park Ridge, NJ, 1985
• Fairchild's Dictionary of Textiles, Phyllis G.Tortora, Robert S. Merkel (eds.), Fairchild Publications, New York City, 7th edition, 1996
• Encyclopedia Britannica, http://www.britannica.com Comment: "Chemical Compound." (Accessed 13 May 2004). gives date of first use as 1912
• Liquitex: Naphthol Crimson