Crystal growth inhibitor

A crystal growth inhibitor for azo pigments is disclosed. The crystal growth inhibitor comprises: (1) one or more sulfonated or carboxylated amines, and (2) one or more coupling components selected from the group consisting of acetoacetanilides, naphthanilides, pyrazalones and benzamidazoles; the coupling component being bonded to the sulfonated or carboxylated amines. The crystal growth inhibitor can be produced separately and added to the coupling component prior to the coupling reaction, or it can be formed in situ with the pigment. Preferably, an improved pigment according to the invention includes 2% to 5% by weight of the crystal growth inhibitor. Monoazo pigments including the crystal growth inhibitor have been shown to have greatly improved gloss, transparency and tinctorial strength.

FIELD OF THE INVENTION 
The invention relates to a crystal growth inhibitor for azo pigments, and 
azo pigment compositions that include the crystal growth inhibitor. Azo 
pigments including the crystal growth inhibitor have improved gloss, 
transparency, and tinting strength in various application media, including 
oleo resinous, aqueous and non-aqueous (such as hydrocarbon solvents). 
BACKGROUND OF THE INVENTION 
Pigments are discrete colored particles which, when dispersed in the 
applicable media, impart color to it. The physical properties of pigments 
such as the particle size, size distribution, and the crystal structure 
are some of the parameters that determine the effectiveness and 
suitability of a particular pigment for a particular application, such as 
use in an aqueous media, non-aqueous media, or with plastics. 
Azo pigments represent an important class of coloring agents used primarily 
in the manufacture of water-based inks, solvent-based inks, plastics, 
water-based paints and solvent-based paints. Some commonly utilized azo 
pigments are diarylide pigments including Pigment Yellow 12, Pigment 
Yellow 13, Pigment Yellow 14, Pigment Yellow 17 and Pigment Yellow 83. 
Other examples are disazo pyrazolone pigments, including Pigment Orange 
13, Pigment Orange 34, Pigment Red 37, Pigment Red 38, Pigment Red 41 and 
Pigment Red 42. 
Azo pigments are synthesized from various primary aromatic amines by a 
pigment synthesis process well known in the art, which includes the steps 
of diazotization and coupling. The diazotization preferably involves 
treating a primary aromatic amine with nitrous acid and the resulting 
compound is called diazonium salt. This diazonium salt is reacted with a 
coupling component to form the azo pigment in a reaction called a coupling 
reaction. Examples of coupling components are phenols, naphthols, and 
compounds that contain an enolyable methylene group, such as 
acetoacetanilides or pyrazalones. 
Azo pigments, however, have deficiencies in certain applications and, in 
general, can be improved upon. For instance, in the graphic art industry, 
more specifically in multicolor printing, pigments of high color strength 
(i.e., high tinctorial strength) pure shade, good light fastness, and good 
flow properties (flow properties are also referred to as rheology) are 
needed. Moreover, especially in the case of yellow pigments, the ink 
industry has been able to obtain superior qualities in yellow pigments 
through the use of diarylide yellow pigments. Diarylide yellow pigments 
are undesirable, however, because of health hazards associated with 
dichlorobenzidine, which is used to manufacture the pigment and which is a 
carcinogen suspect. Therefore, monoazo pigments are used to avoid the 
health hazards associated with diarylide pigments despite the fact that 
monoazo dye properties are generally inferior. 
One way to improve the properties of pigments is to alter their crystalline 
structure. It is generally understood by those skilled in the art that 
pigment particles aggregate or crystallize after the pigment is formed in 
a pigment synthesis process. It is also known that when a pigment is 
dispersed in the applicable media in which it is used, to some extent, the 
physical act of dispersion breaks apart these crystals or particle 
aggregations (hereinafter referred to simply as "crystals"). If allowed 
to, however, the pigment will separate from the media and recrystalize 
into large, aggregate particles. Pigment properties are improved if 
crystal growth can be inhibited, either prior to the initial formation of 
the crystals during pigment synthesis, or prior to recrystallization in an 
applicable media, because smaller crystals impart better pigment 
properties than larger crystals. 
One example of a specific pigment problem due to large crystal size is 
disclosed in U.S. Pat. No. 4,474,609. There, the inventors explain that 
certain azo pigments show a certain solubility in some organic solvents or 
solvent-containing binding agents, which can adversely affect their 
applicability. For example, when certain pigments are dispersed in varnish 
binding agents the tinctorial strength increases at first as the 
dispersing period increases, but eventually levels off. Also, the 
tinctorial strength decreases upon storing ready-made varnish (i.e., which 
already includes the pigment dispersed in a media), and tinctorial 
strength tends to decrease more rapidly at higher temperatures because the 
pigment particles crystallize to form a large aggregate. The loss in 
tinctorial strength is in most cases accompanied by a decreasing 
transparency, and frequently also by an alteration of the shade. 
The factor responsible for these undesirable processes in the preparation 
and storage of those varnishes is believed to be the recrystallization of 
the dispersed pigment particles in the solvents present. Owing to known 
physical laws, the small crystal particles having a high surface energy 
are dissolved, whereas the larger particles already present continue to 
grow, their ultimate size depending upon the solubility conditions. The 
resulting large crystal size leads to a loss in tinctorial strength and a 
reduced transparency. 
U.S. Pat. No. 4,474,609 also discloses a recrystallization-resistant 
monoazo pigment of alleged high tinctorial strength. Col 2, 11. 5-8. The 
monoazo pigment mixtures are obtained by coupling diazotized amines of the 
benzedine series onto acetoacetic acid arylamides. Col. 2, 11. 9-11. A 
percentage of the diazo and/or coupling component contains acid groups, 
preferably sulfo and/or carboxy groups. Col. 2, 11. 14-16. Subsequently, 
the reactive acid groups of the product obtained by the coupling are 
reacted with cation-active quaternary compounds, especially quaternary 
ammonium or phosphonium compounds. Col. 2, 11. 16-18. 
The present invention differs from the prior art in that the crystal growth 
inhibitor has a molecular structure of such geometry, with a polar group 
so situated, that it efficiently inhibits the growth of large pigment 
crystals (i.e., large aggregates of pigment particles). More specifically, 
the present invention discloses crystal growth inhibitors having a 
molecular structure similar to that of the azo pigments with which they 
are used, and containing at least one acid functional group (preferably 
sulfonic or carboxylic). The crystal growth inhibitors can be made in situ 
during synthesis of an azo pigment or added during synthesis of the 
pigment, preferably prior to the inception of pigment crystals. 
The crystal growth inhibitor of the present invention does not utilize 
quaternary compounds, is a monoazo compound and covers a wide field of 
application, i.e., it can be used with all types of azo pigments and is 
not limited to diarylide yellow, arylamide yellow, .beta.-naphthol red or 
arylamide red. It results in significant improvements, such as superior 
gloss, tinctorial strength and transparency in products such as 
water-based inks, solvent flexo inks, solvent gravure inks and 
oleoresenous inks. 
SUMMARY OF THE INVENTION 
Disclosed herein is a crystal growth inhibitor for use with azo pigments. 
Generally, the crystal growth inhibitor comprises two constituents: (1) a 
diazotisable aromatic amine including one or more acid groups and with or 
without functional groups, which is preferably one or more sulfonated 
and/or carboxylated amines, and (2) one or more coupling components bonded 
to the amines. If a sulfonated amine is used, it is preferably selected 
from one or more of the following: (1) aniline 3-sulfonic acid and its 
isomeric compounds containing other groups; (2) aniline 4-sulfonic acid 
and isomeric compounds containing other groups; and/or (3) aniline 
2-sulfonic acid containing other groups. If a carboxylated amine is used, 
it is preferably selected from one or more of the following: (1) 2-amino 
benzoic acid and its isomeric compounds containing other groups; (2) 
3-amino benzoic acid and its isomeric compounds containing other groups; 
and/or (3) 4-amino benzoic acid and its derivatives containing halogen, 
nitro, methoxy, ethoxy, or other functional groups. Any one, or any 
combination of, the above sulfonated or carboxylated amines may be used. 
The coupling component may be one, or any combination of (1) an 
acetoacetanilide, (2) a naphthanilide, (3) a pyralzalone, or (4) a 
benzamidazalone. 
The exact mechanism of how the crystal growth inhibitors disclosed herein 
improve pigment properties is not completely understood, and the invention 
is by no means limited to the mechanism by which it works. As previously 
discussed, however, it is known in the art that pigment particles 
aggregate together (or crystallize), and that relatively small crystals 
have superior properties than larger pigment crystals. By utilizing the 
crystal growth inhibitor of the present invention, the resulting pigment 
is believed to contain only sub-micron size crystals, which results in 
improved tictorial strength, gloss and transparency. 
The crystal inhibitors of the invention may be formed separately and added 
to the synthesizing azo pigment (preferably prior to crystal formation), 
or are prepared in situ during the synthesis of the pigment, so that they 
are present prior to crystal formation. 
DETAILED DESCRIPTION OF THE INVENTION 
The crystal growth inhibitor disclosed herein can be used with monoazo and 
disazo pigments, the molecular structures and the process for making azo 
pigments being known to those skilled in the art. Pigments of this type 
are described, for instance, in W. Herbst, K. Hunger, Industrielle 
Organsche Pigmente, VCH-Verlag (1987), P. F. Gordon, P. Gregory, Organic 
Chemistry In Color (Springer-Verlog 1983); H. Zollinger, Color Chemistry 
(VCH Verlegseselschaft MBH 1987); P. Gregory, High-Technology Applications 
of Organic Colorants Plenum Press 1991); and J. Griffiths, Colour and 
Constitution of Organic Molecules (Academic Press 1976), the disclosures 
of which are incorporated herein by reference. 
The crystal growth inhibitor of the present invention has two components. 
The first is a diazotisable aromatic amine with or without functional 
groups and including one or more acid groups. The second is called a 
coupling component. 
More specifically, the diazotisable aromatic amine including an acid group 
is preferably one or more sulfonated and/or carboxylated amines, or 
similar compounds, which may have one or more functional groups such as 
halogen, methyl, ethyl, methoxy, ethoxy, carbomethyl, carbamido, 
carbanilido, nitro and others. These are reacted with one or more of the 
compounds called coupling components, which include acetoacetanilides and 
their derivatives, naphthanilides and their derivatives, pyrazalones and 
their derivatives, and benzamidazolones and their derivatives, to form a 
crystal growth inhibitor according to the invention. 
Some sulfonated amines that may be used to practice the invention are: (1) 
aniline 4-sulfonic acid, which may include one or more groups such as 
halogen methyl, ethyl, methoxy, ethoxy, carbomethyl, carbamido, 
carbanilido and nitro; (2) aniline-2-sulfonic acid which may include one 
or more groups such as halogen methyl, ethyl, methoxy, ethoxy, 
carbomethyl, carbamido, carbanilido and nitro; (3) aniline-3 sulfonic acid 
which may include one or more groups such as halogen methyl, ethyl, 
methoxy, ethoxy, carbomethyl, carbamido, carbanilido and nitro. Some 
carboxylated amines that may be used to practice the invention are: (1) 
2-amino benzoic acid which may include one or more groups such as halogen, 
methyl, ethyl, methoxy, ethoxy, carbomethyl, carbamido, carboanilide and 
nitro; (2) 3-amino benzoic acid which may include one or more groups such 
as halogen methyl, ethyl, methoxy, ethoxy, carbomethyl, carbamido, 
carbanilido and nitro; and (3) 4-amino benzoic acid which may include one 
or more groups such as halogen methyl, ethyl, methoxy, ethoxy, 
carbomethyl, carbamido, carbanilido and nitro. 
Some coupling compounds that may be used to practice the invention are: (1) 
acetoacetanilides, including (a) acetoacetanilide; (b) 
acetoacet-o-anisidide; (c) acetoacet-p-anisidide; (d) 
acetoacet-o-toluidide, and (e) acetoacet-2,5-dimetheoxy-4-choloranilide; 
(2) naphthanilides, including: (a) naphthol AS, naphthol AS-D, naphthol 
AS-BS, naphthol AS-OL, naphthol AS-KB, naphthol AS-LC, naphthol AS-CA, 
naphthol AS-PH and others known in the industry; (3) pyrazalones, 
including: (a) 3-methyl 1-phenyl pyralzalone; and (b) pyralzalone 
compounds, including those containing halogen, nitro, methyl, methoxy, or 
other groups in the benzene ring; and (4) benzamidazalones such as 
3-hydroxyl-n-(2-oxo-5-benzimidazoline)-2-naphthamide. 
The formulas of the aforementioned naphthanilides are known to those 
skilled in the art and are as follows: 
##STR1## 
If X=Y=Z=S=H (or hydrogen), the compound is naphthol AS. If X=CH.sub.3, 
Y=H, Z=H and S=H, the compound is naphthol AS-D. 
If X=H, Y=NO.sub.2, Z=1 and S=H, the compound is naphthol AS-BS. 
If X=OCH.sub.3, Y=H, Z=H and S=H, the compound is naphthol AS-OL. 
If X=CH.sub.3, Y=H, Z=H and S=Cl (or chlorine), the compound is naphthol 
AS-KB. 
If X=OCH.sub.3, Y=H, Z=Cl and S=OCH.sub.3, the compound is naphthol AS-LC. 
If X=OCH.sub.3, Y=H, Z=H and S=Cl, the compound is naphthol AS-CA. 
If X=OC.sub.2 H.sub.5, Y=H, Z=H and S=H, the compound is naphthol AS-PH. 
Further, one, or combination of, any of the above coupling components can 
be added to any one, or combination of, the above amines to form a crystal 
growth inhibitor according to the invention. The crystal growth inhibitor 
may be included in an azo pigment according to the invention from 0.1% to 
25% by weight, but the preferred range is 2-5% by weight. 
A major application of pigments made according to the invention is in the 
manufacture of printing inks. As explained below, printing inks including 
the improved pigments of the invention have much improved gloss, 
transparency and tinctorial strengths. The improved pigments of the 
present invention may also be used in paints and plastics. With regards to 
ink, paint and plastic, their respective formulations are disclosed in: R. 
H. Leach, editor, The Printing Ink Manual, Fourth Edition, Van Nostrand 
Reinhold (International) Co. Ltd., London (1988), particularly pages 
282-591; with regard to paints: C. H. Hare, Protective Coatings, 
Technology Publishing Co., Pittsburgh (1994), particularly pages 63-288; 
and with regard to plastics: T. G. Webber, Coloring of Plastics, John 
Wiley & Sons, New York (1979), particularly pages 79-204. The foregoing 
references are hereby incorporated by reference herein for their teachings 
of ink, paint and plastic compositions, formulations and vehicles in which 
the compositions of this invention may be used. 
The crystal growth inhibitor can be made in situ. Or it can be made 
separately and added during synthesis of the azo pigment either at the 
start of the pigment synthesis process, but preferably prior to 
crystallization of the pigment. All the constituents listed below are 
expressed by parts by weight.

The following examples illustrate the composition of the present invention 
and its methods of preparation. Unless otherwise indicated in the 
following examples or elsewhere in the specification or claims, all parts 
and percentages are by weight, temperatures are in degrees centigrade and 
pressures are at or near atmospheric. 
EXAMPLE 1 
Preparation of Azo Pigment 
(a) 16.8 parts of m-nitro o-anisidine (MNOA) are dissolved in 250 parts of 
water containing 32.5 g 28% hydrochloric acid. The solution is cooled to 0 
degrees C. with ice. While stirring, 7.0 gm sodium nitrite as 10% solution 
in water is added. Stirring at 0 degrees C. is continued until the 
diazotisation is complete. The excess nitrous acid is neutralized with 
sulfamic acid. 
(b) To 600 cc water containing 10.0 parts of caustic soda, 21.3 parts 
acetoacet-o-anisidide (AAOA) is added while stirring. When the solution is 
complete, 14 parts glacial acetic acid is added to reprecipitate AAOA. 
(c) Solution (a) is added to solution (b) over a 60-70 minute period with 
adequate stirring. At the end, there is preferably no reaction for diazo. 
The slurry is heated to boil and boiled for one hour. Then it is filtered 
and washed, preferably until no soluble salts are detected. This is dried 
with a yield of approximately 37.0 parts. 
EXAMPLE 2 
Preparation of Crystal Growth Inhibitor in Situ 
Example 1 is repeated except 2.5% of MNOA is replaced by o-nitro-aniline 
4-sulfonic acid in step (a). This procedure makes approximately 2.5% by 
weight of crystal growth inhibitor and 97.5% by weight of pigment in situ. 
EXAMPLE 3 
Separate Preparation of Crystal Growth Inhibitor 
In a separate vessel, 0.6 parts of o-nitro-aniline 4-sulfonic acid is 
diazotised in the regular way and reacted (or coupled) with 0.53 grams of 
acetoacet-o-anisidide. These reactions are known by those skilled in the 
art. The resulting dye is added to step (b) in example 1 and the coupling 
reaction of step (c) is completed. 
Comparison 
The pigments prepared in Examples 1, 2 and 3 were each evaluated in the 
following water vehicle: 
Preparation of the Water Vehicle 
In a vessel, prepare: 
Joncryl 61 (from S. C. Johnson)=227.0 parts 
Colloid 999=17.0 parts 
Diethylene Glycol=83.0 parts 
Water=1373.0 parts 
The above is mixed thoroughly. Afterwards, the pigments of Examples 1, 2 
and 3 above were prepared for testing in the manner described below: 
Preparation of the Inks From the Pigments of Example 1, 2 and 3 
In an 8 oz. jar, prepare: 
Pigment=15.0 grams 
Water Vehicle=85.0 grams 
Glass Beads=200 grams 
These are mixed for 90 minutes on a Red Devil Shaker. 
Results 
Drawdowns of the above inks were made on Lenta form 3NT-3 using #5 Meyer 
Rod in accordance with the test method known by those in the art. The 
results are shown in the following chart: 
______________________________________ 
Ink Made From The 
Pigment of Example: 
Transparency 
Gloss Tinctorial Strength 
______________________________________ 
1 -- -- 100% 
2 +4 +4 110% 
3 +5 +5 115% 
______________________________________ 
Where 1 is equal; 2 is slightly; 3 is moderately; 4 is very good; and 5 is 
excellent; these values being understood by those skilled in the art. As 
can be seen, using the standard azo pigment of Example 1 as a basis, 
printing inks made with azo pigments including the crystal growth 
inhibitor of the present invention (i.e., Examples 2 and 3) have much 
improved transparency, gloss and tinctorial strength as compared to the 
same pigment without the crystal growth inhibitor (i.e., Example 1). 
Having now described a preferred embodiment of the invention, deviations 
and modifications that do not depart from the spirit of the invention will 
occur to others. Thus, the invention is not limited to the foregoing 
description but is instead set forth in the following claims and legal 
equivalents thereof.