Process for granulating pigment compositions

A process for producing a pigment or dyestuff composition in the form of dustless readily-dispersible granules which comprises contacting, with agitation, an aqueous dispersion of a pigment, a protective colloid, an aliphatic or araliphatic amine which is liquid at temperatures below 100.degree. C., insoluble in water at pH values above 7, and soluble in water at pH values below 7, and an organic carrier, the pH value being first above 7, maintaining the temperature above the melting point of the amine compound, and reducing the pH to below 7 to render the amine compound soluble in water, and recovering the resulting granules.

The present invention relates to a process for the preparation of dustless, 
readily-dispersible pigment or dyestuff granules. 
The preparation of pigment granules by a process which comprises stirring 
together an aqueous pigment dispersion and a solution of a water-insoluble 
organic carrier in a water-immiscible organic liquid is known. However, in 
the known processes the resulting product contains some solvent, and it is 
necessary to remove the organic solvent from the product by distillation. 
We have now discovered a process in which the product is obtained directly 
in a solvent free condition. 
According to the present invention there is provided a process for 
producing a pigment or dyestuff composition in the form of dustless 
readily-dispersible granules which process comprises contacting, with 
agitation, an aqueous dispersion of a pigment, and an aliphatic or 
araliphatic amine which is liquid at temperatures below 100.degree. C., 
insoluble in water at certain pH values above 7, and soluble in water at 
pH values below 7, the pH value being first above 7, maintaining the 
temperature above the melting point of the amine compound and reducing the 
pH to below 7, to render the amine compound soluble in water and 
recovering the resulting granules. 
The aliphatic amine is preferably an aliphatic amine such as a C.sub.6 
-C.sub.12 linear, branched or substituted alkyl or cycloalkyl amine for 
example n-hexylamine, n-octylamine, di-isobutylamine, 2-ethyl hexylamine, 
cyclohexylamine or Primene 81R (a synthetic C.sub.12 branched aliphatic 
amine ex. Rohm and Haas). As araliphatic amine NN'-dimethylbenzylamine is 
mentioned. 
Usually the amount of amine used is from 0.1 to 2 parts, preferably 0.3 to 
0.6 parts by weight per part of pigment. 
The process may also be carried out in the presence of an organic carrier. 
The organic carrier may be any organic compound which is soluble in, or at 
least softened by, the amine compound, and is insoluble or can be rendered 
insoluble in water throughout the pH range used in the process. The 
carrier can be a liquid if the ratio of pigment to carrier is high, for 
example at or above 90:10; at lower proportions of pigment it is 
preferable to have a compound having a melting point above 40.degree. C. 
as carrier. 
Suitable carriers include, for example, carboxylic acid esters derived from 
alkyl, aryl, aralkyl or cycloalkyl carboxylic acid or polyacids and alkyl, 
aryl, aralkyl, or cycloalkyl mono- or polyhydroxy compounds, such as the 
fatty acid esters cetyl palmitate, glycerol tristearate, glycerol 
monostearate, glycerol tripalmitate, glycerol trioleate, ethylene glycol 
dilaurate, ethylene glycol distearate, diethylene glycol distearate or the 
benzoic acid esters, such as ethylene glycol dibenzoate, neopentyl glycol 
dibenzoate trimethylol ethane tribenzoate, trimethylol propane tribenzoate 
or the dicarboxylic acid esters, such as dibenzyl phthalate, dibutyl 
phthalate, dioctyl phthalate, dicyclohexyl phthalate, and similar esters 
of adipic, sebacic or azelaic acids; amides from the above carboxylic 
acids and ammonia, or alkyl aryl, aralkyl or cycloalkyl mono- or 
poly-amides, such as stearamide, oleamide, palmitamide, N-alkyl 
stearamides or oleamides, ethylene bis stearamide; phosphate esters such 
as triphenyl or tricresyl phosphate, resins such as hydrocarbon resins, 
xylene-formaldehyde resins, coumarone, coumarone-indene and ketone resins; 
vinyl polymers, such as polyvinyl chloride and vinyl chloride copolymers, 
acrylate and methacrylate polymers and copolymers, polyvinyl acetate and 
vinyl acetate copolymers; styrene homo and copolymers; polyolefines such 
as polyethylene, polypropylene and polyisobutylene; fatty alcohols which 
are water insoluble, such as, cetyl alcohol and stearyl alcohol; and fatty 
amines which themselves do not give water soluble salts, such as didodecyl 
amine and distearyl monomethyl amine; and fatty oxazolines; water 
insoluble carboxylic acids, for example C.sub.12 and greater fatty acids, 
such as lauric acid, stearic acid, behenic acid and the rosin derivatives, 
such as wood rosin or its hydrogenated or disproportionated versions. 
These acids may also be added to the pigment as their alkali metal or 
ammonium salt dissolved in water: in this case the process is preferably 
carried out in the presence of water soluble inorganic salts, e.g. sodium 
chloride or calcium chloride. 
These acids are applied as their soluble salts and may also be combined 
with the non-water soluble carriers, especially the sorbitan esters; such 
combinations give granules which are extremely useful for pigmentation of 
PVC. 
The weight ratio of pigment or dyestuff to carrier may be up to 33.3:66.7, 
preferably from 95:5 to 50:50, more preferably from 90:10 to 60:40. 
When the process is carried out in the presence of an organic carrier, the 
amount of amine compound used is that which will form a solution of or at 
least soften the carrier. When using high ratios of pigment to carrier or 
when using a carrier which is poorly soluble in the amine compound, higher 
proportions of the amine compound may be needed to form satisfactory 
granules. 
The pigments and dyestuffs that can be used are those which are water 
insoluble and stable in the pH range required for granule formation and 
isolation. Suitable pigments are azo, azomethine, anthraquinone, 
phthalocyanine, nitro, perinone, perylene, dioxazine, thioindigo, 
isoindolinone, quinacridone, quinophthalones azo or azomethine metal salts 
or complexes; mixtures of pigments may also be used. Water insoluble 
dyestuffs are those such as the solvent soluble azo and phthalocyanine 
dyes. These dyes can also be used as mixtures and in admixture with the 
pigment. 
The organic carrier may be added with the amine compound, either dissolved 
or dispersed in the amine or both may be added prior to any heating or at 
any point during the heating cycle. The carrier may also be added in the 
form of an aqueous dispersion, for example, an aqueous dispersion of a 
polymer or resin such as polyvinyl chloride, vinyl chloride copolymer or 
low molecular weight (oxidised) polyethylene. 
As well as using pure pigments or dyestuffs, ready-for-use pigment 
preparations may be used, i.e. preparations which contain, in addition to 
the pigment, for example 5 to 90 percent, preferably from 10 to 40 percent 
by weight of a carrier. 
Preferably a protective colloid is added to the mixture to assist in the 
formation of granules and the production of granules of a more uniform 
size distribution. When used it is preferably mixed with an aqueous 
pigment slurry or an aqueous dispersion of the amine compound before the 
pigment and amine compound are brought together. Suitable protective 
colloids include cellulose derivatives such as hydroxy ethyl cellulose, 
hydroxy propyl cellulose, polyvinyl alcohol, polyethylene oxide, 
polypropylene oxide, copolymers of ethylene oxide and propylene oxide, 
adducts of ethylene oxide or propylene oxide, polyvinyl pyrrolidone and 
its copolymers or mixtures of these compounds. The preferred compounds are 
those of the hydroxy ethyl cellulose type as exemplified by the Natrosol 
range of the Hercules Powder Company. The amount of protective colloid may 
be up to 15 percent, but is preferably less than 5 percent by weight of 
the pigment. 
The process may be carried out at a selected temperature, at which the 
carrier is at least softened, but preferably dissolved in the amine 
derivative at the temperature used. 
The mixture is originally formulated at or adjusted to a pH of at least 
that at which the amine compound is insoluble in water. The mixture is 
stirred at least until the pigment has migrated from the aqueous phase to 
the organic phase. Sufficient stirring is used to keep the droplets (or 
granules) in suspension. The size of granule is controlled to some extent 
by the speed of stirring. Increased stirring or turbulence gives a 
reduction in granule size. High turbulence and therefore small granules 
can be obtained by use of the modified mixed/emulsifier. The granules may 
be from 0.1 to 5 mm in diameter, but preferably from 0.5 to 2 mm in 
diameter. 
The time of the process can be varied depending on the pigment used and the 
desired properties of the product. For example some pigments, particularly 
azo pigments, are susceptible to crystal growth when maintained in contact 
with the aniline compound, the amount of growth being dependent on the 
time of contact and the temperature. Increased crystal size gives a 
pigment having higher opacity. Therefore, in these cases and if a product 
with good opacity and improved rheology in the application system is 
required, the time of contact of the pigment with the amine compound can 
be increased. If, on the other hand, a pigment of this type is used but a 
product having good transparency is required, the process time can be 
shortened to that which is sufficient for the pigment to migrate into the 
organic phase. In these cases the addition of a carrier assists robust 
granule formation, thereby further shortening the process time. Selection 
of amine can also affect the opacity/transparency: aliphatic amines have 
less crystallising effect than aromatic amines and thus produce more 
transparent compositions. 
With those pigments which show little or no tendency to crystal growth in 
the process, there is no benefit from increased time of contact of the 
pigment with the amine compound beyond that required to form granules. 
Granule formation in such instances is substantially assisted by the use 
of a carrier. In these cases granule formation is further assisted by the 
use of inorganic salts dissolved in the water during the contacting 
process. Especially typical of such pigments are those which have been 
treated with a crystallising solvent during a previous process stage, e.g. 
halogenated copper phthalocyanine (green). 
The pH of the mixture is then reduced to below that at which the amine 
compound becomes completely soluble in water. This is usually below 7, 
preferably below 5, by the addition of an acid which will form a 
water-soluble salt with the amine compound. The preferred acids are 
hydrochloric acid and acetic acid. This causes the amine compound to 
dissolve in the water as a salt, leaving the organic carrier if used, and 
pigment granules in suspension. If necessary, e.g. to promote solution, or 
if desired for handling or product performance, the temperature of the 
mixture may be increased or decreased. The granules are then recovered by 
sieving, washing and drying. Any granules that are too small to be 
recovered in this way may be filtered off and re-used in a subsequent 
batch. 
To recover the solvent, the pH of the filtrate is raised, usually to a pH 
above 7, e.g. 10, whereupon the solvent becomes insoluble, separates from 
the water and can be recovered for subsequent use by decantation for 
example. The aniline derivative may be further purified, if necessary, by 
steam distillation. 
It is also possible to combine the granulation process of the present 
invention with a pigment solvent treatment process, to improve those 
pigment properties known to be improved by a solvent treatment. The 
solvent treatment can be carried out before or during the granulation 
step. For example, a phthalocyanine in a highly aggregated state of an 
.alpha./.beta. crystal form mixture, as produced by dry grinding may be 
de-aggregated and converted substantially to the .beta.-form using the 
amine compound as the solvent in a solvent treatment process. 
The granules, especially those of &lt;1 millimeter diameter can be improved in 
free flowing nature initially and during storage by the addition of a 
small percentage for instance up to 2% by weight, of a finely divided 
inorganic or modified inorganic material conventionally used for imparting 
such properties, such as a finely divided silica or silicate; such 
materials may conveniently be added to the granules by simple mixing. 
Especially advantageous materials of this type are the finely divided 
silicas with surface modifications by organic groups such as the Aerosil R 
972 ex. Degussa. 
The products of the invention may be used for the pigmentation of any 
system, such as surface coating media, e.g. paint and ink, or plastics. 
The carrier used will normally be selected so as to be compatible with the 
system to be pigmented. The product, when incorporated into the system, 
releases the pigment from the granule to colour the material.

The invention is illustrated by the following Examples, wherein parts are 
parts by weight. 
EXAMPLES 1-8 
20 Parts of a pigment present in an aqueous slurry formed by conventional 
azo coupling techniques and 0.2 parts hydroxyethyl cellulose (Natrosol 
250HR) were heated at pH8 to 85.degree. C. A solution of 5 parts of an 
organic carrier in 15 parts of the appropriate amine was added and the 
mixture stirred for 1 hour at 85.degree. C. The pH was then adjusted to 
.about.1 and the granules recovered by filtration, washing and drying. All 
products could be dispersed into lithographic varnish. The following Table 
gives pigment carrier and amine used. 
__________________________________________________________________________ 
EXAMPLE 
PIGMENT CARRIER AMINE 
__________________________________________________________________________ 
1 C1 Pigment Yellow 13 
Hardened castor oil 
NN'-dimethylbenzylamine 
2 C1 Pigment Yellow 13 
Hardened castor oil 
Di-isobutylamine 
3 C1 Pigment Yellow 13 
Hardened castor oil 
n-octylamine* 
4 C1 Pigment Yellow 13 
Hardened castor oil 
Primene 81R 
5 C1 Pigment Yellow 13 
Hardened castor oil 
2-ethyl hexylamine 
6 C1 Pigment Yellow 13 
Dicyclohexyl 
2-ethyl hexylamine 
phthalate 
7 C1 Pigment Yellow 14 
Hercures A80 
2-ethyl hexylamine 
8 C1 Pigment Yellow 12 
Dicyclohexyl 
2-ethyl hexylamine 
phthalate 
__________________________________________________________________________ 
*C.sub.12 branched primary amine ex Rohm and Haas. 
EXAMPLE 9 
20 Parts of CI Pigment Yellow 13 as an aqueous slurry as prepared according 
to Example 9, 0.2 parts hydroxyethyl cellulose (Natrosol 250HR) and 5 
parts dicyclohexylphthalate were heated at pH8 from 15.degree. C. to 
85.degree. C. and 15 parts of 2 ethyl hexylamine was then added. The 
mixture was maintained at 85.degree. C. for 1 hour, then adjusted to pH1.5 
with 10N hydrochloric acid and the granules covered by filtration, washing 
and drying at 55.degree. C. The product could be dispersed into a 
lithographic varnish.