Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-02-11
2001-09-04
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06284890
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed to an aqueous process for the preparation of linear quinacridone pigments. More specifically, the present invention is directed to a process for direct synthesis of pigmentary grade quinacridones of reduced particle size which provide improved rheological properties and high transparency without requiring post-synthesis conditioning steps.
BACKGROUND OF THE INVENTION
Basic processes for forming quinacridones are well known and described, for example, in U.S. Pat. Nos. 3,157,659; 3,256,285; and 3,317,539. (See also “Quinacridones”, S. S. Labana et al.,
Chemical Review,
67, 1 through 18 (1967). U.S. Pat. No. 3,257,405 describes a method for preparing quinacridones involving the thermally induced ring closure of 2,5-dianilinoterephthalatic acid precursors or aniline-substituted derivatives thereof in the presence of polyphosphoric acid. The crude quinacridones that result from such processes must be subjected to additional finishing steps to modify the particle shape, crystal structure, and particularly the particle size, to render the quinacridones suitable for use as pigments.
Reducing the particle size of a quinacridone pigment in a coating composition, particularly a paint, leads to a more transparent (as opposed to opaque) finish. Particle size also affects the tinctorial strength and rheological properties of the pigment. Particle size can be controlled by steps taken during synthesis or by post-synthesis treatment (“conditioning”). Methods of controlling quinacridone particle size during synthesis have involved drowning of the quinacridone melt resulting from the ring closing reaction in water and/or alcohol, as described, for example, in U.S. Pat. No. 3,257,405 discussed supra. Another method for regulating quinacridone particle size, as discussed, for example, in U.S. Pat. No. 3,386,843, involves the addition of a particle size growth inhibitor which prevents the growth of crystals during isolation of the quinacridone. The addition of certain quinacridone derivatives to the ring closure step has also been reported. U.S. Pat. No. 5,368,641, for example, discloses the addition of various quinacridone derivatives as crystal growth inhibitors. (See also U.S. Pat. No. 5,457,302). U.S. Pat. No. 5,755,873 describes the introduction of a precursor of a sulfonyl-containing quinacridone additive (e.g., a sulfonyl-containing derivative of 2,5-dianilinoterephthalic acid, a sulfonyl-containing derivative of 2,5-dianilino-3,6-dioxo-1,4-cyclohexadiene-1,4-dicarboxylic acid and/or a sulfonyl-containing derivative of 2,5-dianilino-terephthalic acid) into the cyclizing step. Said precursors are described as being converted to the corresponding sulfonyl-containing quinacridone crystal growth inhibitor additive during the ring closure step.
Post-synthesis conditioning conventionally requires solvent treatment and/or ball milling of the crude quinacridone in the presence of a large amount of an inorganic salt, or premilling in a ball mill followed by homogenization with an organic paste. U.S. Pat. No. 5,084,100 describes the ball milling of a crude quinacridone in the presence of aluminum sulfate and esters of alkane dicarboxylic acid, which function as crystallizing solvents. Subsequent to ball milling, these solvents must be removed from the pigment. Another means for conditioning involves acid pasting in which the crude quinacridone is dissolved in a large quantity of concentrated sulfuric acid to form a solution, which is then drowned in water. Particle size growth inhibitors may also be introduced during conditioning. U.S. Pat. No. 4,455,173 describes the acid pasting or ball milling of a quinacridone in the presence of a 2-phthalimidomethyl quinacridone particle size growth inhibitor.
Notwithstanding the availability of the above-described methods, there has remained a need for quinacridone pigments providing improved transparency and rheological properties as well as excellent coloristic properties. Furthermore, a need remains for a process for preparing such quinacridone pigments that does not require the use of large amounts of hazardous concentrated acids, or environmentally unfriendly organic solvents.
SUMMARY OF THE INVENTION
The present invention, in brief summary, is directed to an aqueous-based process for the preparation of linear quinacridones which have a small particle size and are suitable for use as a pigment as synthesized, without requiring further conditioning steps involving the use of large excesses of concentrated acids (as in acid pasting), organic solvents treatments or premilling to further reduce particle size. Specifically, the aqueous process of the invention comprises:
(A) heating a reaction mixture containing (a) unsubstituted or substituted 2,5-diarylamino-terephthalic acid and (b) about 3 to about 10 parts by weight of polyphosphoric acid per part of component (a) to a temperature of above about 125° C. to form a melt;
(B) treating the melt resulting from (A) for about 5 to about 60 minutes with about 1 to about 30% by weight, based on the weight of component (a), of concentrated sulfuric acid, at a temperature of about 60° C. to about 150° C. to form a reaction mixture;
(C) drowning the reaction mixture of (B) in about 10 to about 30 parts by weight, based on the weight of component (a), of a liquid in which the quinacridone is substantially insoluble, at a temperature of about 30° C. to about 100° C.; and
(D) recovering the resulting quinacridone.
The process of the present invention does not rely on the introduction of a pigment additive (or a precursor thereof) into the ring closure, or cyclizing step of quinacridone formation. Instead, the melt resulting from the cyclizing step is treated with a minor amount of concentrated sulfuric acid. This treatment has been found to effectively prevent the growth of the quinacridone crystals during drowning and recovery and allows for the direct synthesis of a pigmentary grade quinacridone.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Unsubstituted and substituted derivatives of linear quinacridones of the formula:
wherein A and B each independently represent a substituent selected from H, F, Cl, C
1
-C
3
alkyl and C
1
-C
3
alkoxy are prepared via cyclization of a 2,5-diarylaminoterephthalic acid by heating a 2,5-diarylamino-terephthalic acid in the presence of a dehydrating agent, such as polyphosphoric acid. The cyclizing process results in a crude quinacridone, in the form of a melt.
Suitable 2,5-diarylaminoterephthalic acids are well known and include, for example, those derived from primary aromatic amines such as aniline (e.g., 2,-5-dianiloterephthalic acid), o-, m- and p-toluidino (e.g., 2,5-ditoluidinoterephthalic acid), and various xylidines, alpha- and beta-naphthylamine, ethyl, propyl and butyl anilines and other aromatic amines having aromatic carbon structures attached to the amine moiety; from alkoxy substituted primary aromatic amines such as o-, m- and p-anisidines; and halogen substituted primary aromatic amines such as o-, m- and p-chloroaniline, p-bromoaniline, p-iodoaniline, p-fluoroaniline, the dichloro-, dibromo-, diiodo-, and difluoro anilines and the corresponding halogen substituted derivatives of the toluidines, xylidines, naphthylamines, etc. Such 2,5-diarylaminoterephthalic acids can be used individually to form the corresponding unsubstituted or substituted quinacridone, or can be used in mixture to provide a solid solution or mixed crystal of corresponding unsubstituted and substituted quinacridone or two or more substituted quinacridones.
The dehydrating, or ring-closing agent is preferably a polyphosphoric acid thereof which provides an equivalent of at least about 105% orthophosphoric acid (H
3
PO
4
). Commercially available polyphosphoric acids suitable for use has an H
3
PO
4
equivalent of about 83% P
2
O
5
or an equivalent of about 115% H
3
PO
4
and may have a specific gravity of about 2.060 at 20° C. and contain, for example, approximately 5.7% orthophosphoric acid, 21.4% pyrophosphoric acid, 18.0% triphosphoric acid,
Ciba Specialty Chemicals Corp.
Covington Raymond
Crichton David R.
Rotman Alan L.
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