Pigmentation Industry

The principal uses for 2-naphthalenol are in the dyes and pigments industries, eg, as a coupling component for azo dyes, and to make important intermediates, such as 3-hydroxy-2-naphthalenecarboxyhc acid (BON) (28) and its anilide (naphthol AS), 2-naphtholsulfonic acids, aminonaphtholsulfonic acids, and l-nitroso-2-naphthol/77/-5 /-5(/ (29). 

The two most important pieces of chemical control legislation enacted affecting the dye and pigment industries are the United States Toxic Substance Control Act (TSCA) and EEC s Classification, Packaging, and Labeling of Dangerous Substances and its amendments. Table 2 is a comparison of TSCA and the 6th Amendment of the EEC classifications. 

Water is used in the chrome pigment industry mainly to cool most of the equipment such as heat exchangers, generate steam in the boilers, make slurry of raw materials, scrub the reactor vent... 

Some other types of treatment processes can be employed in the chrome pigment industry in order to achieve safer industrial practices in terms of pollution. Processes such as ion exchange, biological oxidation, and use of glass for filtration before settling have potential application in this industry. 

Within the pigments industry itself, there has been a growing realisation that the physical state of pigments is of the greatest importance to pigment users. Most suppliers now offer several products based on the same chemical structure and the physical form in which it is supplied is chosen to suit the intended application. Thus, the 1997 edition of Pigments and... 

Para red (2.11), which has already been mentioned, was the earliest pigment of this type. Toluidine red (Cl Pigment Red 3) was first made in 1905. To make it, the amine m-nitro-p-toluidine (called MNPT in the pigments industry) is diazotised and coupled to 2-naphthol, the same coupling component that was used to make Para red. 

The pigment industry today provides the user with a wide variety of pigment preparations to suit all purposes. In these pigment preparations, the pigment is in an already dispersed form. Purchasing a pigment in such a form considerably facilitates its application. Details regarding the composition, synthesis, and application of such preparations are described under the respective applications (Sec. 1.8.1, 1.8.2,1.8.3). 

The following list includes starting materials which have found their way to large-scale production and application in the azo pigment industry. 

The dominant role of the batch operation over the continuous process throughout the pigment industry is somewhat in contrast to the patent literature, which includes numerous proposals for complete azo pigment manufacture by the continuous process as well as descriptions of the partial steps, such as the diazotization or the coupling reaction. 

The pigment industry produces primarily the more transparent diarylide yellow pigment types. This has its advantages, particularly in the field of printing inks, since yellow is printed as the last color in three or four color printing (Sec. 1.8.1.1). Highly transparent varieties are almost exclusively resinated and are often easy to disperse. 

Only very few (3-naphthol pigments continue to play an important role in today s pigment industry. The list of important products includes Toluidine Red (P.R.3) and Dinitroaniline Orange (P.O.5). Other compounds, such as P.R.6, Parachlor Red, which is the positional isomer of P.R.4 P.O.2, Orthonitroaniline Orange, which is the positional isomer of the para toner P.R.l are only of regional importance. Table 16 lists the commercially available (3-naphthol pigments. The Colour Index numbers are listed along with the common names, since older products are frequently referred to by these names. 

In the past it used to be quite common for customers of the pigment industry, especially for printing ink manufacturers throughout western Europe, to be supplied with the sodium salts of the sulfonated (3-naphthol compounds. Pigment formation, e.g., precipitation was then typically carried out by the printing ink manufacturer. 

As with p-naphthol pigment lakes, there is only a limited number of BONA pigment lakes that are marketed in large volume. Two of these pigments, however, maintain an important position within the pigments industry. Table 20 lists the currently available BONA pigment lakes. 

P.Y.151 maintains an important position throughout the pigment industry. Its main area of application is in the paint industry, which uses P.Y.151 particularly... 

Some 20 years later, W.S. Struve (1955) at Du Pont was the first to recognize the impact of linear quinacridone on the pigment industry. In due course, the first industrially useful synthetic pathway was found. Three commercial types of unsubstituted quinacridone consisting of two crystal modifications were introduced in 1958 [3]. From then on, quinacridone pigments have been one of the most recent classes of pigments to experience rapid development, especially throughout the USA and Western Europe. 

Several synthetic pathways for the commercial manufacture of quinacridone pigments have been published. In this context, only those routes are mentioned which were developed for industrial scale production. There are four options, the first two of which are preferred by the pigment industry. It is surprising to note that these are the methods which involve total synthesis of the central aromatic ring. On the other hand, routes which start from ready-made aromatic systems and thus might be expected to he more important actually enjoy only limited recognition. 

Dichloroisoviolanthrone was supplied by the pigment industry in the form of a pigment preparation, which was a specialty product for use in spin dyed viscose fibers. This pigment preparation has only recently been withdrawn from the market. The shade of P.V.31 is a reddish violet, which is distinctly redder than that of the known... 

At present, dioxazines no longer enjoy commercial significance as dyes. The pigments industry shows little interest in substituted derivatives of the described parent structure other than this violet pigment. 

Those pigments of the dioxazine series which are of importance to the pigment industry provide a clean violet (considerably bluish red) shade. They demonstrate excellent lightfastness and weatherfastness, even in light shades. There is a certain disadvantage to the fact that these pigments, and especially the most important one, tend to bleed if incorporated in plastics. 

This book is intended for all those who are interested in organic pigments, especially chemists, engineers, application technicians, colorists, and laboratory assistants throughout the pigments industry and in universities and technical colleges. We have specifically avoided an in-depth discussion of the underlying scientific and theoretical framework, but there are references to the pertinent literature. 

For the dyestuff and pigment industry, a better knowledge of dediazoniation under such conditions would be useful because we estimate the loss in yields of industrially produced azo compounds due to competitive (unwanted) dediazoniations to be at least 10% of the production. These 10% are mainly diazo tars which have been investigated systematically in only three papers since the 1950s124. 

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