Quinacridone mixed-crystal pigments of the gamma phase

Details Quinacridone mixed-crystal pigments of the gamma phase Quinacridone mixed-crystal pigments of the gamma phase

2000-01-12

2001-11-06

Green, Anthony (Department: 1755)

Compositions: coating or plastic

Materials or ingredients

Pigment, filler, or aggregate compositions, e.g., stone,...

C106S031770, C524S086000, C546S049000, C546S056000

Reexamination Certificate

active

06312512

ABSTRACT:

The present invention relates to novel quinacridone mixed crystal pigments and to their use as colorants for pigmenting high molecular mass organic materials.
BACKGROUND OF THE INVENTION
Quinacridones are known compounds which are used as pigments. In practice, stringent requirements are placed on their fastness and color properties. On the industrial scale they are prepared by oxidizing dihydroquinacridones in an alkaline medium in the presence of solvents and then dry- or wet-grinding the resulting coarsely crystalline crude pigments, or by ring closure of 2,5-dianilinoterephthalic acid in polyphosphoric acid or polyphosphoric ester and then phase-converting and finishing the resulting finely divided crude pigments with organic solvents.
The preparation of quinacridone mixed crystal pigments is described in the following patent documents.
U.S. Pat. No. 4,099,980 describes the preparation of quinacridone mixed crystal pigments, consisting of 85-99% unsubstituted quinacridone and 1-15% 4,11-dichloroquinacridone, which are in the &ggr; phase of the unsubstituted quinacridone.
U.S. Pat. No. 3,160,510 describes the preparation of quinacridone mixed crystal pigments by dry-milling the crude pigment mixtures with salt and then solvent-treating the isolated ground materials or by precipitating the pigment mixtures with sulfuric acid and then solvent-treating the dried finely divided crude pigments.
For unsubstituted quinacridone of the &ggr; phase, four phases are described.
The &ggr;I phase is described in U.S. Pat. No. 3,074,950 and in EP-A 0 267 877. In the X-ray spectrum, at twice the Bragg angle 2&thgr;, it shows three strong lines at 6.6°, 13.9° and 26.5°, three moderate lines at 13.2°, 13.5° and 23.8°, and four weak lines at 17.1°, 20.5°, 25.2° and 28.6°.
The &ggr;II phase is described in U.S. Pat. No. 2,844,484, in EP-A 0 267 877 and in DE-C 1 184 881. In the X-ray spectrum, at twice the Bragg angle 2&thgr;, it shows three strong lines at 6.6°, 13.9° and 26.3°, five moderate lines at 13.2°, 13.4° and 23.6°, 25.2° and 28.3° and two weak lines at 17.1° and 20.4°.
The &ggr;III phase is described In EP-A 0 530 142. In the X-ray spectrum, at twice the Bragg angle 2&thgr;, it shows four strong lines at 6.7°, 13.3°, 14.0° and 26.6°, one moderate line at 13.6°, and seven weak lines at 17.2°, 20.6°, 21.9°, 24.0°, 25.3°, 28.1° and 28.8°.
The &ggr;IV phase is described in Japanese Laid-Open Specification JP-A 53-39324. In the X-ray spectrum, at twice the Bragg angle 2&thgr;, it shows three strong lines at 6.2°, 13.6° and 26.5°, three moderate lines at 12.5°, 25.8° and 27.7°, 2&thgr; and three weak lines at 16.5°, 20.5° and 24.0°. The moderate lines at 25.8° and 27.70°2&thgr; are to be attributed to small amounts of &agr; phase.
SUMMARY OF THE INVENTION
It has been found that mixtures comprising from 82.5 to 99% unsubstituted &ggr;-phase quinacridone and from 1 to 17.5% of one or more, especially 1 or 2, substituted quinacridones will form mixed crystals, also referred to as solid solutions, under certain conditions in accordance with the invention. By mixed crystals are understood systems in which one or more components added—usually in a nonstoichiometric ratio—to a crystal phase crystallize together with the host compound in a common lattice. The X-ray diffraction diagram of a mixed crystal shows, for example, only the reflections of the (in many cases expanded) crystal lattice of the host compound or else of a similar crystal lattice or else of a markedly different crystal lattice, whereas the reflections of all the components can be detected in the X-ray diffraction diagram of a corresponding mechanical mixture.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention therefore provides mixed crystal pigments of the quinacridone series consisting of
a) from 82.5 to 99% by weight, preferably from 85 to 95% by weight, in particular from 87 to 93% by weight, of unsubstituted &ggr;-phase quinacridone of the formula (I)
in which R
1
and R
2
are hydrogen atoms and
b) from 1 to 17.5% by weight, preferably from 5 to 15% by weight, in particular from 7 to 13 % by weight, of one or more 2,9- and/or 3,10-substituted quinacridones of the formula (I) in which the substituents R
1
and R
2
are identical or different and are chlorine, bromine or fluorine atoms or C
1
-C
4
-alkyl, C
1
-C
4
-alkoxy or carboxamido groups which can be substituted by C
1
-C
6
-alkyl groups, and R
1
can additionally be a hydrogen atom.
Preferred mixed crystal pigments are those which comprise one or two substituted quinacridones (b) of the formula (I) in which R
1
is hydrogen, chloro, methyl, methoxy or carboxamido, and R
2
is chloro, methyl, methoxy or carboxamido.
The color properties of the mixed crystal pigments of the invention differ considerably from those of the corresponding mechanical mixtures of the individual components. In particular, they possess deeper hues and have high color strengths. The process can also be used to obtain highly transparent pigments which are therefore particularly suitable for the production of metallic paints. The fastness properties are excellent.
The present invention also provides a process for preparing the above described mixed crystal pigments, which comprises cyclizing the 2,5-dianilinoterephthalic acid of the formula (Ia)
on which the compound a) is based and the substituted terephthalic acid(s) of the formula (Ib)
on which the compound b) is based in a ratio of from 82.5:17.5 to 99:1, preferably from 85:15 to 95:5, in particular from 87:13 to 93:7, in the presence of polyphosphoric acid, a polyphosphoric ester, preferably polyphosphoric methyl ester, or a mixture thereof, hydrolyzing the ring closure mixture which is present after cyclization, at a temperature of at least 110° C., by metering into an amount of at least 70% strength by weight, preferably from 75 to 98% strength by weight, in particular from 80 to 90% strength by weight, aqueous orthophosphoric acid which is such that at the end of the metered addition the concentration of aqueous orthophosphoric acid in the hydrolyzed mixture is at least 85% by weight, and then isolating the mixed crystal pigment, directly or following a fine division step and/or a finish treatment.
As the ring closure agent use is generally made of from 2.5 to 10 times, preferably from 3 to 5 times, the amount by weight of polyphosphoric acid or polyphosphoric ester, based on the dianilinoterephthalic acids. The P
2
O
5
content of the polyphosphoric acid or ester is judiciously between 80 and 87% by weight, preferably between 83 and 85% by weight, corresponding to a phosphoric acid equivalent of from 110 to 120%. Larger amounts of ring closure agent can be used but are generally unnecessary. The ring closure temperature is judiciously from 80 to 200° C., preferably from 120 to 140° C. The time taken to complete cyclization is in general from 0.5 to 24 hours, but usually only 1 to 2 hours.
The ring closure mixture which is present after the cyclization is hydrolyzed at a temperature of at least 110° C., preferably at from 120 to 180° C., in particular from 130 to 160° C. In this case the ring closure mixture, under pressure if desired, is metered into the orthoohosphoric acid, it being possible to use a continuous or batchwise procedure. It is advantageous to operate continuously in a static or mechanical mixer. Based on the polyphosphoric acid, it is judicious to use from 0.8 to 10 times the amount of orthophosphoric acid. In principle it is also possible to use a less than 70% strength by weight orthophosphoric acid. However, since the final concentration of the orthophosphoric acid at the end of the hydrolysis must not be below 85% by weight, in order to obtain the desired &ggr; phase, in this case the amount by volume of orthophosphoric acid to be used would be so small that the hydrolysis mixture would be of a consistency that was no longer stirtable. Preferably, the concentration of orthophosphoric acid in the hydrolysis mixture at the end of the hydrolysis is from 87 to 98% by weight, in particular from 88 to 95% by weight.

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