Лако-красочные материалы — производство

Since 1950, particular efforts have been made to develop new azo pigments that combine excellent overspray fastness and bleed resistance with high fastness to light as well as weathering. As a result of this work, two different concepts found by Ciba and Hoechst, respectively, proved to be very successful:

1. Enlarging the pigment molecule, as done with disazo con­densation pigments by Ciba [2].

2. Introduction of substituents which lower the solubility of the pigment molecule, as first introduced by Hoechst [3].

Taking advantage of the second principle, it was found that carbonamide moieties in the pigment molecules reduce their solubility. Pursuing this path, pigments were developed that contain five — or six-membered heterocyclic carbonamides such as tetrahydroquinazoline-2,4-dione, tetrahydroquinoxalinone-dione, or benz — imidazolone. In contrast to an open carbonamide group, the cyclic moieties improved the fastness to light considerably. Among the various ring structures considered, benzimidazolone based colorants have been the most successful.

Regarding pigment shades, the development of benzimidazolone pigments occurred during two eras: the mid 1960s to the early 1970s, with occasional intro­duction of new products in subsequent years. During this first period, mainly red pigments appeared on the market. In 1960, Hoechst applied for patent protection for water-insoluble mono azo benzimidazolone dyestuffs [3a]. The pigments had been synthesized by diazotization of aminobenzoic acid amides and subsequent coupling of the resulting diazonium compounds with 2-hydroxy-3-naphthoic acid de­rivatives of 5-aminobenzimidazolone. Later, the use of alkoxy-substituted aminoben-

zoic acid amides as diazo components provided bluish red pigments [4]. Among the diazo components claimed in other disclosures were amino benzene sulfonic acids [5], simple anilines such as nitro — or chloroanilines [3a] and ester functionalized aromatic amines [6].

The second period in benzimidazolone development focused on the application of acetoacetylamino benzimidazolone derivatives as coupling components, resulting in the formation of yellow or orange pigments. The first yellow benzimidazolone pig­ment on the European market was PV Fast Yellow H2G. This pigment was obtained by coupling diazotized 5-aminoisophthalic acid dimethyl ester with acetoacetylated 5-aminobenzimidazolone [7]. The marriage of the two concepts described above has been accomplished with PV Fast Yellow HG (P. Y. 180), introduced several years ago. P. Y. 180 represents a benzimidazolone disazo pigment. Cromophtal™ Orange GP (P. O. 64) is a reddish orange pigment synthesized from 6-methyl-5-aminobenzimid — azolone as diazonium salt and barbituric acid as coupler. However, P. O. 64 is the only benzimidazolone pigment of commercial relevance that is not based on couplers 1 or 2.

After the discovery of the benzimidazolone pigments, Hoechst was the only manu­facturer in the 1960s and 1970s. Today, however, there are numerous manufac­turers of such pigments, including Clariant, Ciba Specialty Chemicals, and Dai — nippon Ink & Chemicals (see Section 10.6, Pigment Manufacturers, Economics), providing a wide range of benzimidazolone pigment types for printing inks, paints and plastics. Originally applied in azo pigments, the benzimidazolone con­cept has been extended to create improved heterocyclic pigments, such as Pig­ment Yellow 192 (Sandofil™ Yellow S-RL, CAS-No. 56279-27-7) and, very recently, Hostaperm™ Blue R5R (Clariant), the first commercial example of a property — enhanced triphendioxazine comprising this structural feature. (For further informa­tion, see Chapter 20.) Recent research by Clariant led to the expansion of the benz­imidazolone ring system by one carbonyl group. This effort yielded new yellow qui — noxalinedione-based azo pigments with outstanding properties, for example Hosta­perm™ Yellow H5G (P. Y. 213) [8].

Hostaperm™ Yellow H5G (P. Y.213)

10.3