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The present invention relates to a process for the preparation of opaque
diketopyrrolopyrrole pigments having outstanding color strength, purity of
shade and saturation, by wet milling in an alcohol-base system.
It is known from U.S. Pat. No. 4,579,949 that a more opaque pigment form
can be obtained by heating diketopyrrolopyrrole pigments in water or an
organic solvent. Organic solvents having a boiling point above 80.degree.
C., e.g. xylenes, chlorobenzene, nitrobenzene, pyridine, cyclohexanone,
ethylene glycol monomethyl ether or dimethylformamide are preferred. In
U.S. Pat. No. 4,632,704 there is described a process for the preparation
of high yield pigments, e.g. diketopyrrolopyrrole pigments, by protolysis
of the pigment salt obtained by treating the crude pigment with a strong
base or of the pigment salt obtained in the course of the synthesis, which
process comprises treating said pigment salt, in an organic solvent, with
water such that the organic solvent is simultaneously removed during the
protolysis. The pigments so obtained have a particularly fine crystalline
form and are distinguished by excellent colour strength and transparency.
In U.S. Pat. No. 4,720,305 there is stated that by subjecting a
diketopyrrolopyrrole pigment mixture to aftertreatment in water or in an
organic solvent (preferably above 80.degree. C.) and to subsequent
communition, such as wet grinding, particularly transparent pigment forms
are obtained.
It has now been found that by wet milling certain diketopyrrolopyrrole
pigments in an alcohol-base system without heating, very surprisingly an
opaque pigment form is obtained which shows an outstanding color strength,
excellent purity of shade and unexpected high saturation.
Accordingly, the present invention relates to a process for the preparation
of opaque 1,4-diketopyrrolo-[3,4-c]pyrroles of the formula
##STR2##
wherein one of R.sub.1 and R.sub.2 is hydrogen, halogen or C.sub.1
-C.sub.4 -alkyl and the other is hydrogen, which process essentially
consists of milling the pigment in an alcohol and in the presence of a
base at a temperature below 50.degree. C., preferably between 10.degree.
and 40.degree. C.
Substituents defined as halogen may be for example fluorine, preferably
bromine and in particular chlorine.
Substituents defined as C.sub.1 -C.sub.4 -alkyl may be for example methyl,
ethyl, n-propyl, isopropyl, n-butyl, sec.-butyl or tert.-butyl.
Tert.-butyl and especially methyl are preferred.
R.sub.2 is preferably hydrogen. Most preferably both R.sub.1 and R.sub.2
are hydrogen.
A variety of alcohols are applicable to produce the opaque pigment form
including low boiling alcohols, e.g. alkanols such as methanol, ethanol,
butanol and pentanols and glycols such as ethylene glycol. The most
suitable are methanol and ethanol. Likewise, a variety of inorganic and
organic bases can be used including alkali metal hydroxides such as sodium
hydroxide, potassium hydroxide or lithium hydroxide and quaternary
ammonium hydroxides such as benzyltrimethylammonium hydroxide. Sodium and
potassium hydroxide are preferred.
The alcohol is generally present in an amount ranging from 5 to 25 times
the weight of pigment, and preferably 10 to 16 times. An appropriate
concentration range of base is 2 to 50%, based on the weight of the
pigment and preferably 20 to 40%. Inorganic bases can be added as 15 to
70%, preferably 25 to 50% aqueous solution, organic bases at 100%
concentration or at least as 50% aqueous solution. The preferred
concentration of base, however, changes with the nature of the alcohol. At
the desirable base concentration range, there is no visible formation of
the diketopyrrolopyrrole potassium, sodium or quaternary ammonium salt,
which when formed can be recognized due to its partial solubility in the
alcohol with bluish-red coloration. However, during the milling operation,
as new surfaces are generated, the mechanism of particle growth is
believed to involve formation of a very small concentration of the salt,
which is more soluble in alcohol than the diketopyrrolopyrrole itself and
thus subject to particle growth followed by alcoholysis to the pigment.
This dynamic particle ripening system eventually permits particle growth
to the desirable equilibrium size.
The apparatus used for the grinding can be any device for subjecting the
pigment and carrier to mechanical forces in a liquid medium. Apparatus of
this type is known in a relatively large number of embodiments. They are
based, for example, on the principle of a large velocity gradient produced
in a liquid medium or on a sudden change of direction, or, in particular,
on the impacting action or mutual friction of particles of the grinding
medium, such as metal, glass or ceramic spheres, plastic granules or
grains of sand, which are set in motion by the rotation of the vessel or
by vibrators or stirrer-like devices, for example in glass or ceramic bead
mills.
The milling operation proceeds by methods known in the art, generally by
charging the crude diketopyrrolopyrrole, alcohol and base to an
appropriate mill, introducing the milling elements, milling the system at
a temperature below 50.degree. C., preferably between 10.degree. and
40.degree. C. and isolating the resulting diketopyrrolopyrrole pigment.
The milling is preferably conducted in a ball mill using sand, glass or
ceramic grinding beads of 0.8 to 2.5 mm size. The most preferred grinding
beads are made from crystalline zirconia phase and amorphous silica phase
by fusion of the oxides (product of Quartz Products Corporation).
If desired, various dispersants, extenders or particle growth inhibitors
can be introduced by the alcohol/base milling operation, provided the
additives are not subject to inactivation by the basic medium. Simple
addition of anionic, cationic, or nonionic surfactants to the liquid
milling operation, assuming the materials are not water soluble, will
cause them to come out in a uniform manner on the surface of the pigment
and consequently alter the pigment behavior. Additionally, introduction of
as little as 3-6%, by weight, based on weight of pigment of a dispersant
(e.g. DISPERBYK.RTM. 160, BYK Chemie) after milling produces a product
which by drawdown in lithographic varnish shows somewhat increased gloss
relative to a product prepared without the dispersant.
The pigment can be isolated directly from the milled slurry after grinding
media separation by filtration and washing the presscake with alcohol or
also by separating the pigment slurry from the milling media by means of
alcohol and/or water dilution and milling media washing with either
solvent, followed by alcohol distillation from the mixed alcohol-water
slurry. The alcohol can thus be recovered, and pigment isolated from a
nonflammable slurry by filtration. After isolation, the pigment is washed
with water until free of base.
It can also be advantageous to add specific amounts of texture improving
agents preferably to the isolated pigment after milling. Suitable texture
improving agents are, in particular, fatty acids of not less than 18
carbon atoms, for example stearic or behenic acid or the amides or metal
salts thereof, preferably magnesium salts, as well as plasticizers, waxes,
resin acids such as abietic acid, colophonium soap, alkyl phenols or
aliphatic alcohols such as stearyl alcohol or vicinal diols such as
dodecane-1,2-diol, and also modified colophonium/maleate resins or fumaric
acid/colophonium resins. The texture improving agents are preferably added
in amounts of 0.1 to 30% by weight, most preferably of 2 to 15% by weight,
based on the final product. A peculiar property of the pigments obtained
by the process of the present invention is their high crystallinity.
Pigmented systems which contain the pigment obtained by the process of the
present invention as a component of mixtures of substances, possibly in
addition to other components, include: pastes, flush pastes, preparations,
printing colors, distempers, binder colors or lacquers and varnishes of
all kinds, such as physically and oxidatively drying lacquers and
varnishes, acid, amino and peroxide curing varnishes or polyurethane
varnishes. The pigment may also be present in synthetic, semisynthetic or
natural macromolecular substances, such as thermoplastic resins, e.g.,
polyvinyl chloride, polystyrene, polyethylene, polyesters, phenoplastis,
aninoplasts and rubber. The pigment may also be present in admixture with
natural, regenerated or synthetic fibers, such as glass, silicate,
asbestos, wood cellulose, acetylcellulose, polyacrylonitrile, polyester,
polyurethane and polyvinyl chloride fibers or mixtures of the same, and
also in powders, for example organic or inorganic pigments. With the
pigment obtained by the process of the invention there are obtained
prints, paint and varnish coatings, coverings, shaped articles, such as
sheets, threads, plates, blocks, granulates and rods with a brilliant red
color of excellent durability.
The mixtures of substances which contain as active coloring ingredient the
opaque red pigment obtained by the instant wet milling process, may be of
solid, elastic, pasty, viscous, mobile or thixotropic consistency. They
may be obtained by conventional methods. Aqueous pastes may be obtained
for example by stirring the pigment into water, possibly with the addition
of a wetting or dispersing agent or by stirring or kneading the pigment
into a dispersing agent in the presence of water and possibly of organic
solvents or oils. These pastes may for example be used for the production
of flush pastes, printing colors, distempers, plastic dispersions and
spinning solutions. The pigment may also be introduced by stirring,
rolling, kneading or grinding into water, organic solvents, non-drying
oils, drying oils, lacquers, varnishes, plastics or rubber. Finally, it is
also possible to work up the pigment by dry mixing with organic or
inorganic masses, granulates, fibrous materials, powders and other
pigments, to form mixtures of substances.
In addition to its excellent hiding power, outstanding color strength and
purity of shade with very high saturation, the pigments obtained by the
process of the invention also show good allround fastness properties, such
as fastness to light and weathering, overspraying, migration and heat as
well as excellent rheological properties.
The pigments obtained by the instant wet milling process are preferably
suitable for coloring aqueous and/or solvent-containing varnishes,
especially automotive varnishes.
The following examples further illustrate the embodiments of this invention
.
EXAMPLE 1
In a 500 ml wide-necked glass flask with screw cap, 14 g of crude
3,6-diphenyl-1,4-diketopyrrolo-[3,4-c pyrrole, 15 g of 30% aqueous sodium
hydroxide solution and 180 ml of methanol together with 350 ml of ceramic
beads having a diameter of 1.6 to 2.5 mm and consisting on average of
about 69% of ZrO.sub.2 and 31% of SiO.sub.2 are rotated for 48 hours at
20.degree.-25.degree. C. on a roller gear table such that the centrifugal
forces are greater than the gravitational forces, so that the beads remain
on the wall of the flask during rotation (corresponding to a speed of
65-100 rpm).
The ceramic beads are thereafter separated, the pigment suspension is
filtered, and the filter cake is washed with methanol until free from
alkali, dried at 80.degree. C. in a vacuum drier and pulverized to give
13.6 g of red pigment. When incorporated in plastics and varnishes, this
pigment gives opaque red colorations of high purity and saturation as well
as of excellent fastness to light, head and weathering.
EXAMPLE 2
The procedure of Example 1 is repeated, except that the flask is shaken on
a Turbula laboratory shaker supplied by the firm of Willy A. Bachofen,
Basle (CH). A pigment having comparably good properties is obtained.
EXAMPLE 3
The procedure of Example 2 is repeated, except that 350 ml of glass beads
having an average diameter of 1 mm are used instead of ceramic beads. A
pigment having comparably good properties if obtained.
EXAMPLE 4
The procedure of Example 1 is repeated using crude
3,6-bis(4-chlorophenyl)-1,4-diketopyrrolo-[3,4-c]pyrrole instead of
3,6-diphenyl-1,4-diketopyrrolo-[3,4-c]pyrrole, affording a pigment that
gives bluish-red opaque colorations of excellent color strength and
purity.
EXAMPLE 5
The procedure of Example 4 is repeated using
3,6-bis(4-bromophenyl)-1,4-diketopyrrolo-[3,4-c]pyrrole instead of
3,6-bis(4-chlorophenyl)-1,4-diketopyrrolo-[3,4-c]pyrrole and 10 g instead
of 15 g aqueous sodium hydroxide solution. When incorporated in plastics
and varnishes, the resultant pigment gives bluish-red colorations of
excellent color strength and purity.
EXAMPLE 6
The procedure of Example 4 is repeated using 7.0 g of 50% aqueous potassium
hydroxide instead of 15 g of 30% aqueous sodium hydroxide solution. A red
pigment having comparably good properties is obtained.
EXAMPLE 7
In a 100 ml wide-necked glass flask with screw cap, 2.5 g of crude
3,6-bis(4-methylphenyl)-1,4-diketopyrrolo-[3,4-c]pyrrole, 2.5 g of 30%
aqueous sodium hydroxide and 37 ml of methanol together with 68 ml of
ceramic beads having a diameter of 1.6 to 2.5 mm and consisting on average
of about 69% of ZrO.sub.2 and 31% of SiO.sub.2 are rotated for 60 hours at
20.degree.-25.degree. C. on a roller gear table such that the centrifugal
forces are greater than the gravitational forces, so that the beads remain
on the wall of the flask during rotation (corresponding to a speed of
70-105 rpm).
The ceramic beads are thereafter separated, the pigment suspension is
filtered, and the filter cake is washed with methanol until free from
alkali, dried in a vacuum drier at 80.degree. C. and pulverized to give
2.4 g of a red pigment. When incorporated in plastics and varnishes, this
pigment gives scarlet opaque colorations of excellent hiding power, purity
and saturation, as well as of excellent fastness to light, heat and
weathering.
EXAMPLE 8
The procedure of Example 1 is repeated using non-aqueous ethanol instead of
methanol, to give a red pigment having comparably good properties.
EXAMPLE 9
A 2.85 liter mill is charged with 2500 g of ceramic beads ranging in size
from 1.6 to 2.5 mm and consisting on average of about 69% ZrO.sub.2 and
31% SiO.sub.2, 50 g of crude 3,6-diphenyl-1,4-diketopyrrolo[3,4-c]pyrrole,
1000 ml methanol and 75 g 44% aqueous potassium hydroxide. The mill is
rotated for 72 hours at a temperature of 20.degree.-27.degree. C. and
65-70 rpm, which is about 70% of critical speed. The mill is discharged
onto a screen which retains the ceramic beads. The beads are washed with
800 ml of methanol, essentially all pigment being collected as a slurry.
The slurry is transferred to a four-neck flask equipped with a stirrer,
thermometer and condenser. Steam is passed through the slurry and methanol
together with some water is distilled off. The temperature slowly rises to
93.degree. C. as the methanol is distilled off and is maintained for 10
minutes whereupon the distillation is discontinued. The product is
isolated by filtration from the hot slurry and the pigment washed free of
base with warm water. After drying at 80.degree. C., 48.2 g of pigment are
obtained, which, on incorporation into plastics and varnishes, gives
opaque red colorations with outstanding color strength, purity of shade
and saturation as well as excellent fastness properties.
EXAMPLE 10
A mixture of
130 g of steatite balls (diameter=8 mm)
47.5 g of a thermosetting acrylic resin varnish consisting of
41.3 g of VIACRYL.RTM. VC 373 acrylic resin, 60% (ex VIANOVA Kunstharz AG),
16.3 g of MAPRENAL.RTM. TTX melamine resin, 55%, (ex HOECHST AG),
32.8 g of xylene,
4.6 g of ethyl glycol acetate,
2.0 g of butyl acetate, and
1.0 g of silicone oil A.RTM., 1% in xylene (ex Bayer), and
2.5 g of the 1,4-diketopyrrolo-[3,4-c]-pyrrole pigment obtained in Example
1
is dispersed in a 200 ml glass bottle with twist-off stopper for 72 hours
on a roller gear bed. The steatite balls are removed and then
8.0 g of the dispersed masstone mixture,
0.6 g of ALCOA.RTM. aluminum paste (60-65% aluminum content, ex Aluminium
Corp. of America),
1.0 g of methyl ethyl ketone and
18.4 g of the above thermosetting acrylic varnish
are thoroughly mixed and the mixture is sprayed onto aluminium sheets and
subsequently baked for 30 minutes at130.degree. C., to give very strong
opaque red metal effect finishes of excellent fastness properties.
Comparably good finishes are obtained by using a pigment of any one of
Examples 2 to 9 instead of the pigment of Example 1.
EXAMPLE 11
A mixture of 130 g of steatite balls having a diameter of 8 mm, 47.5 g of
an alkyd/melamine stoving varnish consisting of 60 g of alkyd resin
(Beckosol.RTM. 27-320, Reichhold Chemie AG), 60% in xylene, 36 g of
melamin resin (Super-Beckamin.RTM. 13-501, Reichhold Chemie AG), 50% in a
2:1 mixture of xylene/butanol, 2 g of xylene and 2 g of ethylene glycol
monomethyl ether, and 2.5 g of the diketopyrrolopyrrole pigment obtained
in Example 1 are dispersed in a 200 ml glass flask with twist-off cap for
120 hours on a roller gear bed. After separating the steatite balls, the
dispersed full shade mixture is sprayed onto aluminum sheets and
subsequently stoved for 30 minutes at 130.degree. C. to give very strong
opaque red finishes with a very high saturation and excellent fastness
properties.
EXAMPLE 12
A mixture of 1.0 g of the pigment obtained in Example 4, 1.0 g of an
antioxidant (.RTM.IRGANOX 1010, ex Ciba-Geigy AG) and 1000 g of high
density polyethylene granules (.RTM.Vestolen A 60-16, ex Chem. Werke Huls)
is stirred for 15 minutes in a glass flask on a roller gear table. The
mixture is then extruded in two passes in a single screw extruder. The
granulate so obtained is moulded to plates at 220.degree. C. in an
injection moulding machine (Allround Aarburg 200) and then posttreated for
5 minutes at 180.degree. C. The mouldings are coloured in strong red
shades of excellent fastness properties.
EXAMPLE 13
0.6 g of each one of the pigments obtained in the Examples 1 to 9 are mixed
each with 67 g of polyvinyl chloride, 33 g of dioctyl phthalate, 2 g of
dibutyltin laurate and 2 g of titanium dioxide and each mixture is
processed to a thin sheet on a two roll mill for 15 minutes at 160.degree.
C. The PVC sheets so obtained are colored in a very strong opaque red
shade which is fast to migration and light.
EXAMPLE 14
1000 g of polypropylene granules (.RTM.DAPLEN PT-55, ex Chemie Linz) and 20
g of a 50% pigment preparation consisting of 10 g of the pigment obtained
in Example 4 and 10 g of magnesium behenate are thoroughly mixed in a
mixing drum. The granules so obtained are melt spun at
260.degree.-285.degree. C. to red filaments of good lightfastness and
textile fibre properties.
EXAMPLE 15
8 g of the pigment obtained in Example 4 are thoroughly dispersed in a
DISPERMAT.RTM. disperser (ex Hediger, Basserdorf) with 1 mm glass beads in
a solution consisting of 21.5 g of cellulose acetobutyrate (25% in butyl
acetate), 1 g of zirconium octoate 6 (NUODEX.RTM.), 12 g of an aromatic
solvent (SOLVESSO.RTM. 150, ex ESSO), 17.5 g of butyl acetate and 13 g of
xylene.
After removal of the glass beads, the to dispersion is mixed with 24 g of
polyester resin (DYNAPOL.RTM. H 700, 60%, ex DYAMIT NOBEL) and 3 g of
melamine resin (MAPRENAL.RTM. MF 650, 55%, ex HOECHST AG). The pigment
varnish so obtained is sprayed onto aluminum sheets and then baked at
130.degree. C., to give strong opaque red finishes of excellent gloss.
EXAMPLE 16
The procedure of Example 15 is repeated, except that 0.48 g of a dispersant
(DISPERBYK.RTM. 160, BYK Chemie) is used in addition to 8 g of the
pigment. Red colorations having even better rheological properties and
excellent gloss are obtained.
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