Phthalocyanine pigment

Since phthalocyanine pigments are produced using the metal copper, copper phthalocyanines have, at least temporarily, become PBTs. The voluntary waste minimization PBT notice included copper as one of the metals declared to be PBTs. As a result, copper phthalocyanine pigments became PBTs. 

Two processes have been used for making copper phthalocyanine, but neither yields a form suitable for immediate use as a pigment since the physical form and size distribution of the resulting particles are far from the optimum. The product is generally referred to as crude blue and requires purification and a sometimes complex series of finishing processes before it is in a form ready for use as a pigment. 

The reactants are phthalic anhydride, urea and copper(n) chloride, which are heated in a high-boiling aromatic solvent such as 1,2,4-trichlorobenzene, nitrobenzene or m-dinitrobenzene in the presence of a catalyst, usually ammonium molybdate. The solvent also acts as a heat-transfer medium. On heating to 120 °C an exothermic reaction begins and this temperature is maintained for about an hour. The temperature is then raised to 160-180 °C and kept constant for 6-12 hours. During this time ammonia and carbon dioxide are evolved, together with some solvent the reaction is complete when ammonia evolution ceases. The remaining solvent is then removed by either steam or vacuum distillation. The yield is 90-95%. For many years the solvent process was in almost exclusive use. 

Another approach is to use high-boiling aliphatic solvents with minimal aromatic content boiling points are in the range 150-250 °C. Much higher ratios of solvent to reactants are needed than when aromatic solvents are used, owing to the high viscosity of the system. 

Yet another method of avoiding PCB formation in the solvent process is to dispense with the need for urea as a reactant by using the more expensive phthalonitrile instead of phthalic anhydride. 

Conversion of crude blue into copper phthalocyanine blue pigments 

Depending on type of substitution and crystal form, different quinacridone pigments with orange, maroon, scarlet, magenta and violet colors are available on the market. Some examples are Pigment Red 122, 192, 202, 207 and 209. 

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It has a limited use in the preparation of the phthalocyanine pigments into which it is readily converted on heating with metallic salts. 

Photochromic Organic Dyes. Intensive investigations into this category of substances have led to numerous patent appHcations. Copper—phthalocyanine pigments, organic dyes based on cyanine (Ricoh, Pioneer), naphthochinone (Nippon Denki), and ben2othiopyrane (Sony) (123) have been described. They did not lead, however, to any commercial use. Surveys on the possibiUties of optical data storage with photochromic dyes can be found (124,125). 

The second process to finish phthalocyanine, which is more important for P-copper phthalocyanine, involves grinding the dry or aqueous form in a ball mill or a kneader (64). Agents such as sodium chloride, which have to be removed by boiling with water after the grinding, are used. Solvents like aromatic hydrocarbons, xylene, nitrobenzene or chlorobenzene, alcohols, ketones, or esters can be used (1). In the absence of a solvent, the cmde P-phthalocyanine is converted to the a-form (57,65) and has to be treated with a solvent to regain the P-modification. The aggregate stmcture also has an impact on the dispersion behavior of a- and P-copper phthalocyanine pigments (66). 

Phthalocyanine pigments account for approximately 23% of the total worldwide organic pigment consumption of 225,000 tons. Approximately 20,000 t are used in printing inks, 10,000 t in paints, 9,000 t in plastics, 3,000 t in textiles, 7,000 t in dyes, and 2,000 t in specialty uses. Table 1 shows the worldwide distribution of cmde phthalocyanine capacity. The production history of phthalocyanine in the United States from 1980 to 1990 is given in Table 2 (161). The 1990 prices of phthalocyanine blue and green pigments were ca 11—22/kg and 21—27/kg, respectively. 

At present, synthetic routes to more than 40 metal complexes other than the copper complex are known. Apart from a cobalt phthalocyanine pigment (P.B.75) which was introduced to the market just recently, none of the resulting products, however, has stimulated commercial interest as a pigment. Nickel complexes, however, are found in reactive dyes, while cobalt complexes of this basic structure are employed as developing dyes. 

Heading the list of suitable organic starting materials [8] for phthalocyanine pigments are phthalic anhydride and phthalonitrile. 

Knowledge of the most important types of copper phthalocyanine pigments is useful for the understanding of the processes concepts underlying pigment manufacture. Heading the list are the a- and [i-modil i cations of unsubstituted Copper Phthalocyanine Blue (Sec. 3.1.2.3). The a-modification exhibits an unstabilized and a stabilized form as to change of crystal modification. 

Polyhalogenated green copper phthalocyanine pigments are not polymorphous and thus exempt from change of modification. 

Copper phthalocyanine pigments also demonstrate good overall stability to organic solvents. A number of solvents, however, especially aromatics, may cause a change of modification in unstable types or overcrystallization in stable varieties. This phenomenon is largely due to the tendency of the stable phase to nucleate. The particle size of the resulting cystals decreases as the number of nuclei rises. (3-Copper Phthalocyanine Blue is the thermodynamically stable modification. 

Phthalocyanine pigments, which show high tinctorial strength, provide an excellent ratio of strength versus price. The strongest member is a-Copper Phthalocyanine Blue, while yellowish Copper Phthalocyanine Green is the weakest representative. 

The a- and (i-types of Copper Phthalocyanine Blue reign supreme among commercially available phthalocyanine pigments. There is also an increasing amount of interest in the phase-stabilized form of the a-crystal modification. Both modifications are also supplied as flocculation resistant types. 

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