Note: Descriptions are shown in the official language in which they were submitted.
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Pigment preparations comprising inor8anic pigments
The invention relates to pigment preparations comprising inorganic pigments,
S especially silicon or silicon compounds, to processes for preparing them and
to their
use, especially as printing inks for ink jet printing.
Aqueous preparations of colorants, as are used, for example, for ink jet
printing,
comprise as colorants not only water-soluble dyes but also organic and
inorganic
l0 colour pigments and carbon blacks. Organic dyes, for example, when used in
ink jet
printing generally give strongly coloured prints of high brilliance, but as
compared
with colour pigments possess poorer light fastness. In comparison to inorganic
pigments, organic pigments often possess the disadvantage of inadequate light
fastness and are therefore often unsuitable for use in a variety of
applications. e.g. in
15 the exterior sector.
With other applications of liquid colorant preparations as well, improving the
light
fastness, in particular, is continually part of numerous efforts.
20 The object of the present invention is therefore to provide coloured
pigment
preparations which in particular in ink jet printing exhibit improved light
fastness in
combination with high optical density and brilliance.
Pigment preparations have now been found comprising
a) solid compounds from the group consisting of the oxides of titanium, zinc,
tin, tungsten, molybdenum, nickel, bismuth, cerium, indium, hafnium, iron
and/or silicon carbide, zinc sulphide, barium titanate, calcium titanate
and/or
silicon and/or solid silicon compounds in which silicon is present in
stoichiometric excess, having an average diameter of the primary particles of
<500 nm, preferably <150 nm, in particular <120 nm,
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b) at least one colorant other than the solid compounds specified under a),
c) optionally a dispersant and
d) optionally water.
The presence of the two components c) and d) is preferred.
Silicon and the silicon compounds of component a) have' already been disclosed
in
the as yet unpublished DE-A-19 647 294.
Elemental silicon comprises amorphous or crystalline silicon, preferably
crystalline
silicon. The size of the silicon particles is preferably between 1 nm and 120
nm, with
particular preference between 1 nm and 70 nm, with very particular preference
between 5 nm and 50 nm. These particles preferably have a size distribution
with a
half value width of 40 nm or less. Silicon particles having this mean diameter
are
preferably prepared by gas-phase reaction (CVR) in accordance with the process
described in US-A 5 472 477. Likewise possible is preparation in accordance
with
the further processes specified in DE-A 19 647 294.
The term solid compounds covers compounds which are solid at room temperature,
examples being silicides, CaSi2 and/or BaSi2. The term "compounds in which
silicon is present in stoichiometric excess" preferably covers compounds of
the
formula SixZl_X where x >0.5, preferably x >0.7 and Z = C, N, O, Ge, Ca, Ba
and Sr.
The presence of other materials shifts the energetic position of the
absorption edge
within certain limits and modifies the shape of the edge. Preferred solid
compounds
here are SixCl_x or SixGel-x~
In one preferred embodiment of the invention, the solid compounds in which
silicon
is present in stoichiometric excess have a core/shell structure. The average
diameter
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of the primary particles is preferably less than 120 nm, with particular
preference less
than 100 nm, with very particular preference less than 50 nm. These particles
preferably have a size distribution with a half value width of 40 nm or less.
The
particle preferably consists of a titanium nitride core and a silicon shell,
the volume
fraction of the silicon preferably being at least 30% per particle.
In another preferred embodiment of the invention, the silicon component a)
comprises shell particles in the form of a solid compound consisting of
silicon and
materials which are more strongly absorbing in the red spectral range
(600 nm < ~,< 700 nm) than those in the blue-green (400 nm < ~,< 550 nm)
spectral
range.
The preparation of the silicon component a) is likewise disclosed in DE-A-19
647
294 (p. 5, para. 1 of the priority text) and is subject-matter of this
specification.
In one preferred embodiment, the primary particles of the silicon component a)
are
spherical. They may also be present in the form of aggregates or agglomerates.
The primary particles of the silicon component a) may also be surrounded by an
oxide layer which prevents direct aggregation of the Si primary particles,
thereby
preventing their agglomeration. The thickness of the oxide layer is preferably
from
1 nm to 300 nm, with particular preference from 10 to 100 nm. This oxide layer
can
be effected, for example, by metering oxygen into the CVR reactor following
the
preparation of the particles. The oxide layer preferably consists of Si02.
The preparations of the invention preferably contain from 0.01 to 500, in
particular
from 0.01 to 250% by weight, in particular from 0.01 to 20% by weight of
component a), based on the colorant of component b).
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Examples of suitable colorants of component b) are organic pigments and
inorganic
pigments other than those of component a), and also carbon black or water-
soluble
and water-insoluble dyes, the term dyes also embracing optical brighteners.
S Suitable carbon blacks are, in particular, acidic to alkaline blacks from
the group of
the furnace or gas blacks, and also chemically or physically modified or
aftemeated
carbon blacks; examples of suitable inorganic pigments are zinc sulphides,
ultramarine, iron oxides, cobalt blue and also chromium oxide . pigments and
also
pigments in the form of finely particulate oxides such as silicon dioxide,
titanium
dioxide, nickel oxides, chromium antimony titanium dioxides, aluminium oxide,
and
also finely particulate metals such as copper, iron or aluminium; and examples
of
suitable organic colour pigments are those of the azo, disazo, polyazo,
anthraquinone
and thioindigo series, and also other polycyclic pigments such as, for
example, those
from the phthalocyanine, quinacridone, dioxazine, isoindolinone,
naphthalenetetra-
carboxylic acid and perylene and perylenetetracarboxylic acid series, and also
those
from the perinone, indigoid, thioindigoid and diketopyrrolopyrrole series, and
also
metal complex pigments of azo, azomethine or methine dyes, or laked dyes such
as
Ca, Mg, A1 lakes of dyes containing sulphonic acid and/or carboxylic acid
groups.
Examples of water-soluble organic dyes are acidic and basic dyes, and examples
of
water-insoluble dyes are disperse dyes or whiteners (optical brighteners).
Examples
of disperse dyes that may be mentioned are those from the azo, disazo,
anthraquinone, coumarin, isoindolenine, quinoline and methine series.
In one preferred embodiment, the preparation of the invention comprises as
colorant
oxides and/or nitrides of metals which absorb more strongly in the red
spectral range
of 600 nm < ~,< 700 nm than in the blue-green spectral range of
400 nm < ~,< 550 nm. This is particularly the case when using pigments having
an
intrinsic yellow to orange coloration. Preferred such additives are pigments
comprising titanium nitride having an average diameter of from 1 nm to 400
run,
preferably from 10 rrm to 120 nm, or its agglomerates. They can be prepared,
for
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example, in accordance with US-A S 472 477. Likewise preferred colorants are
ultramarine pigments, obtainable for example from the company Nubiola S.A.,
under
the designation Nubix~ pigments. Preference is given, furthermore, to
iron(>ZI)
hexacyanoferrate(II). Preference is also given to pigments of iridium oxide
doped
with more than 5% by weight with tin.
The particle size of the other representatives of component a) is preferably
from 1 nm
to S00 nm, with particular preference from 1 nm to 120 nm. These as well are
obtainable, inter alia, in accordance with the process described in US-A 5 472
477.
Dispersants
Dispersants are preferably regarded as being molecules having a molar mass of
from
1000 to 500,000, preferably from 1000 to 100,000 and, in particular, from 1000
to
1 S 10,000 g/mol. The dispersants can be nonionic, anionic, cationic or
amphoteric
compounds.
Examples of nonionic dispersants are the following: alkoxylates,
alkylolamides,
esters, amine oxides and alkyl polyglycosides.
Further suitable nonionic dispersants are the following: reaction products of
alkylene
oxides with alkylatable compounds, such as fatty alcohols, fatty amines, fatty
acids,
phenols, alkylphenols, arylalkylphenols, such as styrene-phenol condensates,
carbox-
amides and resin acids, for example. These dispersants are, for example,
ethylene
oxide adducts from the class of the reaction products of ethylene oxide with:
a) saturated and/or unsaturated fatty alcohols having 6 to 20 carbon atoms or
b) alkylphenols having 4 to 12 carbon atoms in the alkyl radical or
c) saturated and/or unsaturated fatty amines having 14 to 20 carbon atoms or
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d) saturated and/or unsaturated fatty acids having 14 to 20 carbon atoms or
e) hydrogenated and/or unhydrogenated resin acids.
Particularly suitable ethylene oxide adducts are the alkylatable compounds
specified
under a) to e) with from 5 to 120, preferably from 5 to 60, in particular from
5 to 30,
mol of ethylene oxide.
Particular preference is given to nonionic polymeric dispersants.
Examples of dispersants regarded as polymeric are the compounds listed in the
index
"Water-Soluble Synthetic Polymers: Properties and Behavior" (Volumes I + II by
1 S Philip Molyneux, CRC Press, Florida 1983/84).
Examples of further suitable polymeric dispersants are water-soluble and water-
emulsifiable compounds, e.g. homopolymers and copolymers, graft polymers and
graft copolymers, and also random block copolymers.
Examples of particularly preferred polymeric dispersants are AB, BAB and ABC
block copolymers. In the AB or BAB block copolymers, the A segment is a hydro-
phobic homopolmyer or copolymer which ensures a connection to the pigment and
the B block is a hydrophilic homopolymer or copolymer or a salt thereof and
ensures
the dispersing of the pigment in the aqueous medium. Polymeric dispersants of
this
kind and their synthesis are known, for example, from EP-A-518 225 and EP-A-
556 649.
Further examples of suitable polymeric dispersants are polyethylene oxides,
poly-
propylene oxides, polyoxymethylenes, polytrimethylene oxides, polyvinyl methyl
ethers, polyethyleneimines, polyacrylic acids, polyarylamides, polymethacrylic
acids,
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polymethacrylamides, poly-N,N-dimethyl-acrylamides, poly-N-
isopropylacrylamides,
poly-N-acryloylglycinamides, poly-N-methacryloylglycinamides, polyvinyl
alcohols,
polyvinyl acetates, copolymers of polyvinyl alcohols and polyvinyl acetates,
poly-
vinylpyrrolidone, polyvinyloxazolidones, polyvinylmethyloxazolidones.
Also of importance are natural polymeric dispersants such as cellulose,
starch, gelatin
or derivatives thereof as polymeric dispersants. Particularly suitable
polymers are
those comprising amino acid units, e.g. polylysine, polyaspartic acid etc.
Examples of anionic dispersants are the following: alkyl sulphates, ether
sulphates,
ether carboxylates, phosphate esters, sulphosucinates, sulphosuccinate amides,
paraffinsulphonates, olefinsulphonates, sarcosinates, isothionates, taurates,
and
lignin-type compounds.
Particular preference is given to anionic polymeric dispersants.
Suitable anionic polymeric dispersants are, in particular, condensation
products of
aromatic sulphonic acids with formaldehyde, such as condensation products of
formaldehyde and alkylnaphthalenesulphonic acids or of formaldehyde,
naphthalene-
sulphonic acids and/or benzenesulphonic acids, and condensation products of
optionally substituted phenol with formaldehyde and sodium bisulphite.
Also suitable are condensation products obtainable by reacting naphthols with
alkanols, subjecting the product to addition reaction with alkylene oxide, and
converting at least some of the terminal hydroxyl groups into sulpho groups or
monoesters of malefic acid, phthalic acid or succinic acid.
Also suitable, moreover, are dispersants from the group of the sulphosuccinic
esters,
and also alkylbenzenesulphonates. Moreover, sulphated, alkoxylated fatty acid
alcohols or salts thereof. Alkoxylated fatty acid alcohols are in particular
saturated or
unsaturated C6-C2z fatty acid alcohols, especially stearyl alcohol, which have
been
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provided with from 5 to 120, preferably from 5 to 60, in particular from S to
30
ethylene oxide. Particular preference is given to stearyl alcohol alkoxylated
with from
8 to 10 ethylene oxide units. The sulphated alkoxylated fatty acid alcohols
are
preferably in salt form, especially as alkali metal or amine salts, preferably
as the
S diethylamine salt.
Further examples of anionic polymeric dispersants are the salts of polyacrylic
acids,
polyethylenesulphonic acids, polystyrenesulphonic acid, polymethacrylic acids
and
polyphosphoric acids.
Additional examples of anionic polymeric dispersants are copolymers of acrylic
monomers, which are indicated by way of example in the following table by a
combination of the following monomers, which are synthesized to random,
alternating or graft copolymers:
acrylamide, acrylic acid;
acrylamide, acrylonitrile;
acrylic acid, N-acryloylglycinamide;
acrylic acid, ethyl acrylate;
acrylic acid, methyl acrylate;
acrylic acid, methylenebutyrolactam;
N-acryloylglycinamide, N-isopropylacrylamide;
methacrylamide, methacrylic acid;
methacrylic acid, benzyl methacrylate;
methacrylic acid, diphenylmethyl methacrylate;
methacrylic acid, methyl methacrylate;
methacrylic acid, styrene.
Further anionic polymeric dispersants are styrene-malefic anhydride
copolymers,
copolymers thereof with the abovementioned acrylic monomers, and also
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polyurethane-based polymers, e.g. those based on star-branched oligourethanes
as per
EP-A 331 066 or EP-A 400 410.
Also suitable are graft polymers and graft copolymers where nonionic and/or
anionic
vinyl monomers have been grafted onto a polymeric base. Synthetic or natural
protective colloids can be used as the polymeric base.
Also particularly suitable are ligninsulphonates, e.g. those obtained by the
sulphite or
kraft process. They are preferably products which in part are hydrolysed,
oxidized,
propoxylated, sulphonated, sulphomethylated or disulphonated and fractionated
by
known processes, for example in accordance with the molecular weight or in
accordance with the degree of sulphonation. Mixtures of sulphite and kraft
ligninsulphonates are also highly effective. Particularly suitable
ligninsulphonates are
those having an average molecular weight of more than 1000 to 100,000, an
active
ligninsulphonate content of at least 80% and, preferably, a low polyvalent
cation
content. The degree of sulphonation can vary within wide limits.
Examples of cationic dispersants are as follows: quaternary alkylammonium
compounds and imidazoles.
Particular preference is given to cationic polymeric dispersants.
Examples of cationic polymeric dispersants are the salts of
polyethyleneimines,
polyvinylamines, poly(2-vinylpyridines), poly(4-vinylpyridines), poly(diallyl-
dimethylammonium) chloride, poly(4-vinylbenzyltrimethylammonium) salts and
poly(2-vinylpiperidine).
Examples of amphoteric dispersants are the following compounds: betaines,
glycinates, propionates and imidazoiines.
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Anionic and cationic polymers are summarized as polyelectrolytes and are fully
or
partly dissociable in an aqueous and/or organic phase.
The dispersant used is used preferably in an amount of from 0.1 to 200% by
weight,
in particular from 0.5 to 100% by weight, based on components a) and
optionally b).
If water-insoluble dyes or pigments or carbon black are used as colorants,
then the
amount of dispersant used is based preferably on the sum of components a) and
b).
In addition to the dispersant used, the pigment preparations of the invention
may also
comprise further cationic, anionic, amphoteric and/or nonionic and/or surface-
active
compounds, examples being those listed in the index "Surfactants Europa, A.
Directory of surface Active Agents available in Europe" (Edited by Gordon L.
Hollis,
Royal Socity of Chemistry, Cambridge (1995).
Where the dispersant used contains ionic groups, these auxiliaries should
preferably
be nonionic or of the same ionicity.
Especially the pigment preparations which are used as printing inks for ink
jet
printing preferably contain as further component e) an organic solvent.
Suitable organic solvents (e) are: aliphatic C1-C4-alcohols, such as methanol,
ethanol, isopropanol, n-propanol, n-butanol, isobutanol or tert-butanol, 1,5-
pentadiol,
aliphatic ketones, such as acetone, methyl ethyl ketone, methyl isobutyl
ketone or
diacetone alcohol, polyols, such as ethylene glycol, propylene glycol,
butylene glycol,
diethylene glycol, triethylene glycol, trimethylolpropane, polyethylene glycol
having
an average molar weight of from 100 to 4000, preferably from 400 to 1500 g/mol
or
glycerol, monohydroxy ethers, preferably monohydroxyalkyl ethers, with
particular
preference mono-C1-C4-alkyl glycol ethers such as ethylene glycol monoalkyl,
monomethyl, diethylene glycol monomethyl ether or diethylene glycol monoethyl
ether, diethylene glycol monobutyl ether, dipropylene glycol monoethyl ether,
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thiodiglycol, triethylene glycol monomethyl ether or monoethyl ether, and also
2-
pyrrolidone, N-methyl-2-pyrrolidone, N-ethylpyrrolidone, N-vinyl-pyrrolidone,
1,3-
dimethyl-imidazolidone, dimethylacetamide and dimethylformamide.
S Also suitable are mixtures of the abovementioned solvents.
The amount of organic solvent is preferably from 0 to 40, in particular from 2
to 20%
by weight, based on the pigment preparations.
Preferably, the amount of water and organic solvent is from 20 to 99% by
weight,
preferably from 30 to 97% by weight, based on the pigment preparations.
The pigment preparations may further comprise agents for adjusting the
viscosity of
the ink, such as, for example, polyvinyl alcohol, polyvinylpyrrolidone,
methylcellulose and other agents known to the person skilled in the art,
provided that
they do not adversely affect the stability of the printing ink, the printing
behaviour
and the drying behaviour on paper.
As a further addition, compounds from the group of the terpenes, terpenoids,
fatty
acids and fatty acid esters are to be mentioned. Preferred compounds that may
be
mentioned include:
ocimene, myrcene, geraniol, nerol, linalool, citronellol, geranial,
citronellal, neral,
limonene, menthol, for example (-)-menthol, menthol or bicyclic monoterpenes,
saturated and unsaturated fatty acids having 6 to 22 carbon atoms, such as for
example stearic acid, oleic acid, linoleic acid and linolenic acid or mixtures
thereof.
In principle the pigment preparations may include further additives such as
preservatives (biocides), further wetting agents or surfactants, spacers,
flatting agents,
stabilizers, further W absorbers, plasticizers, lubricants and optionally pH
regulators.
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Examples of suitable biocides are isothiazolones and benzisothiazolones.
Suitable spacers or flatting agents have average particle diameters in
particular in the
S range from 0.2 pm to 30 p.m and are described, for example, in DE 3 331 542.
The
spacers are preferably water-insoluble and resistant to the solvent additions
used in
the inks. Examples of suitable spacers or flatting agents are polymethyl
methacrylate,
polystyrene, styrene-divinylbenzene copolymer, crosslinked polymethyl
methacrylate, and crosslinked or non-crosslinked polyvinyltoluene.
Suitable stabilizers are o-, m- and p-dihydroxybenzenes, hydroxychromans,
5-hydroxycumarans, spirochromans, spiroindanes, p-alkoxyphenols, sterically
hindered phenols, gallic acid derivatives, methylenedioxybenzenes,
aminophenols,
aminoanilines, sterically hindered amines, derivatives having esterified or
etherified
phenolic hydroxyl groups, and derivatives having acylated or alkylated
aromatic
amino groups, metal complexes.
Particularly suitable stabilizers are sterically hindered amines, preferably
compounds
based on 2,2,6,6-tetraalkylpiperidine, with particular preference compounds
based on
2,2,6,6-tetraalkylpiperidine which contain at least one covalently bonded
2,2,6,6-
tetraalkylpiperidine fragment.
In many cases, the use of certain combinations of colour image stabilizers has
proven
to be particularly effective.
Suitable UV absorbers are described, for example, in DE 195 03 885.
Plasticizers and lubricants used are, for example, core-shell latices having a
soft core
and a hard shell, latices which consist of a soft core and a shell of
crosslinked
gelatine, and those with soft intermediate layers.
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Examples of pH regulators are NaOH, ammonia or aminomethylpropanol, N,N-
dimethylaminoethanol.
Examples of preservatives are methyl- and chloromethylisothiazolin-3-one, benz-
isothiazolin-3-one or mixtures thereof.
As a further particular embodiment of the invention, there are the pigment
prepara-
tions of the invention comprising in addition to components a) and b) and
optionally
c) and d), in addition, sterically hindered amines, preferably those based on
2,2,6,6-
tetraalkylpiperidine, with particular preference compounds based on 2,2,6,6-
tetra-
alkylpiperidine which contain at least one covalently bonded 2,2,6,6-tetra-
alkylpiperidine fragment.
The pigment preparations of the invention contain preferably:
from 0.01 to 500% by weight, preferably from 0.01 to 250% by weight, in
particular
from 0.01 to 20% by weight of component a), based on the colorant of component
b)
from 1 to 99.95% by weight, preferably from 1 to 65% by weight of a colorant
of
component b), based on the preparation,
from 0.1 to 200% by weight, in particular from 0.5 to 100% by weight of a
dispersant
of component c), based on the component a) optionally based on the sum of
components a) and b), and
from 0 to 98% by weight, in particular from 0.2 to 98% by weight, with
particular
preference from 10 to 98% by weight, with very particular preference from 30
to 98%
by weight of water, based on the pigment preparation.
The invention further relates to a process for preparing the pigment
preparations as
printing inks for ink-jet printing, which is characterized in that a pigment
of
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component a) and the colorant b), especially if it is an organic or inorganic
pigment,
or is a water-insoluble dye or whitener, is homogenized with at least part of
the
dispersant c) and optionally further additives and this homogenized mixture is
optionally subjected to wet comminution.
In accordance with the invention, preparing the pigment preparations includes
optionally a surface modification of pigments of comp. a) in water and/or
polar
organic solvent, in order to convert the "crude pigments" obtained from the
pigment
production into the desired state of fine division and in order to
deagglomerate and/or
deaggregate them. Processes for this purpose are described, for example, in EP-
0 650 945 A2.
A further possibility for deagglomerating pigments of comp. a) is to pretreat
the
pigment powders by means of dilute ammonia solution.
In accordance with the invention, pigment preparations comprising comp. a) and
also
pigment preparations comprising pigments or water-insoluble colorants of comp.
b)
alone can be prepared separately first of all and subsequently can be mixed to
give
the pigment preparation of the invention.
In the case of the use of water-insoluble colorants of component b), the
pigment of
component a), optionally after surface modification, optionally together with
the
colorants of component b) in powder form or in the form of the water-moist
presscakes, together with at least some of the dispersant and water,
preferably
deionized water, is generally beaten (i.e. introduced and homogenized) to a
homogenous milled suspension by means, for example, of a stirring vat,
dissolves
and similar equipment, optionally after a precomminution stage.
The milled suspension may further contain fractions of low-boiling solvents
(boiling
point < 150°C) which may be carned off by evaporation in the course of
the
subsequent fine grinding. However, it may also include fractions of higher-
boiling
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solvents or further additives, as are described above, e.g. grinding aids,
defoamers or
wetting agents.
The wet comminution of comp. a) or of comp. b), or a) + b) together, embraces
both
the precomminution and the fine grinding. In this case, the pigment
concentration of
the suspension is preferably above the desired concentration of the finished
pigment
preparation or printing ink. The desired final pigment concentration is
preferably
established following wet comminution. Following precomminution, grinding
takes
place to the desired state of particle fine division. Suitable milling
equipment for this
grinding stage comprises, for example, kneading apparatus, roll mills,
kneading
screws, ball mills, rotor-stator mills, dissolvers, corundum disc mills,
vibratory mills
and especially high-speed, continuously or discontinuously charged stirred
ball mills
containing grinding media having a diameter of from 0.1 to 5 mm. The grinding
media can be of glass, ceramic or metals, e.g. steel. The grinding temperature
is
preferably within a range from 0 to 250°C, but generally lies at room
temperature, in
particular below the cloud point of the dispersant of component c) that is
used and of
the optionally used surface-active agent.
In a likewise preferred procedure, grinding can take place in part or in whole
in a
high-pressure homogenizer or in a so-called jet disperser (known from DE-A
19 536 845), by means of which the amount of grinding media detritus in the
suspension, and/or the release of soluble substances from the grinding media
(i.e.
ions from glass media), can be reduced to a minimum or avoided completely.
In a dilution step, the resulting pigment preparation is mixed in a manner
known per
se into water, optionally with the remaining amounts of dispersant and
optionally
further additives, and homogenized, and is adjusted to the desired final
pigment
concentration or colour strength of the preparation or printing ink. In this
case, it is
optionally possible to add a further part of the dispersant in order, for
example, to
prevent reagglomeration of fine pigment particles in the dilution.
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Of particular advantage is a process for preparing the pigment preparations in
which
in the grinding step for preparing the pigment concentrate sufficient
dispersant is
made available for stabilization. Subsequently thereto or after dilution with
water,
excess surface-active agents and/or dispersant that is present in solution and
is not
S adsorbed on the pigment is preferably removed and, subsequently, the desired
pigment preparation is standardized by adding the remaining fractions of the
pigment
preparation.
A method of removing dispersant present in solution is, for example, the
centrifugation of the suspension and subsequent decantation of the
supernatant.
Membrane filtration or microfiltration techniques are also suitable.
Furthermore, it is possible to add other additives, such as, for example,
polyurethane
polymers or acrylic polymers in order, optionally, to improve further the
water
1 S fastness. These polymers may be either water-soluble or else water-
emulsifiable in
nature, or may be soluble in one of the components present in b).
In a preferred procedure, the pigment preparations are mixed and homogenized
using
a jet disperser or high-pressure homogenizer in order to suppress the
formation of
foam and to prevent possible reagglomeration.
The standardization of the desired pigment preparations is accompanied by
standardization to the desired viscosity, colour strength, hue, density and
surface
tension of the ink.
Before the use of the pigment preparations as printing inks, the inks are
optionally
fine-filtered by means, for example, of 0.5 to S pm membrane filters or glass
filters.
In general, the physical ink properties are standardized to use in
conventional ink jet
printers, the surface tension being preferably between 20 and 70 mN/m and the
viscosity being preferably less than 20 mPa s, in particular from 0.5 to 10
mPa s.
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The printing inks of the invention and the printing inks used in accordance
with the
invention, when used as printing ink in ink jet printing, give prints having
excellent
light fastness and high optical density, and further possess the following
advantages:
outstanding dispersion stability and storage stability within a wide
temperature range,
no blockage in the printing head (known as cogation or clogging), high water
fastness
and migration fastness of the prints on various substrates, e.g. on mechanical
paper,
medium-grade paper, sized and coated paper, polymeric films, transparencies
for
overhead projection, no bleeding in mufti-colour printing, even when used
together
with dye inks or other pigmented inks.
The pigment preparations described above are used preferably as printing inks
for
ink-j et printing.
Ink jet printing is known per se and generally takes place such that the
printing ink is
filled into an acceptor vessel of an ink jet printing head and is sprayed in
small
droplets onto the substrate. The ejection of the ink in droplet form takes
place
preferably by way of a piezoelectric crystal, a heated cannula (bubble jet or
thenmo-
jet process) or by mechanical pressure increase, where pressure is exerted on
the ink
system and drops of ink are ejected accordingly. The droplets are fired from
one or
more small nozzles in a targeted manner onto the substrate such as, for
example,
paper, wood, textiles, plastic or metal. Under electronic control, the
individual
droplets are collated on the substrate to form textual symbols or graphic
patterns.
Also possible is a process in which, by means of electrostatic deflection,
very small
volumes in the form of drops are brought onto a substrate from one jet of ink.
The invention further relates to the use of the pigment preparations as
printing inks
for ink jet printing and for pigmenting and colouring natural or synthetic
materials,
especially plastics, leather and paper in the mass and on the surface.
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In particular, the pigment preparations are also suitable for preparing
automotive
paints, emulsion paints, dispersion coating materials, printing inks, water-
dilutable
coating systems, aqueous flexographic and gravure inks, wallpaper colours,
aqueous
wood preservative systems and woodstains, renders, and for pigmenting coloured
pencil leads, fibre-tip pens, ink jet inks, Indian inks, pastes for ballpoint
pens, chalks,
laundry detergents and cleaning products, shoe polishes, non-woven webs, paper
stock colourings, coloured paper coating slips, cardboard packaging printing
inks,
colouring of latex products, abrasives, spin dyeings and films.
With particular preference, the pigment preparations are used as printing inks
for ink-
jet printing.
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Examples
Preparation and use of zinc oxide as light stabilizer in ink jet inks
S Example 1
A stock solution (A) (stock ink) of a magenta dye, in the form of the sodium
salt, of
the formula
-
having an E1/1 value of 12 was prepared by homogenous mixing of
22.8 g of an aqueous, salt-free solution of the abovementioned magenta dye
having an E111 value of 53, (pure dye content about 10.4% by weight)
6.2 g of 1,5-pentadiol
6.2 g of 2-pyrrolidone and
64.8 g of water.
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(EI/I value: Extinction value of the longest-wavelength band in the light
spectrum,
obtained by measuring a 1 % strength solution of the dye in a
measuring cell with a path length of 1 cm.
Also prepared was a solvent mixture (B) consisting of
8.0 of 1,5-pentanediol
g
8.0 of 2-pyrrolidone
g
84.0 of water.
g
Subsequently,
S g of the stock solution (A)
4.4 g of the solvent mixture (B) and
I 5 0.6 g of an aqueous zinc oxide dispersion consisting of
30% by weight of zinc oxide having a primary particle
diameter of 10 - 30 nm measured by means of transmission
electron microscopy (TEM) or an agglomerate particle size
determined, from which the following mass distribution
resulted by means of measurement with an ultracentrifuge.
50% by mass of the particles smaller than 43 nm (dsp of
43 nm)
90% by mass of the particles smaller than 65 nm (d5p of
65 nm)
10% by mass of the particles smaller than 25 nm (dso of
25 nm)
less than 2% by weight of polyacrylic acid and residual water
were homogeneously mixed to form a printing ink, and
printing was carried out using a thermal ink jet printer of the
type HP Deskjet S00 C (from Hewlett Packard) by filling the
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ink thus prepared into the black cartridge type HP S 1626 A as a
replacement for the ink originally present.
The ink of the invention was printable flawlessly and possesses
very good storage stability.
S
Full-area prints were produced on standard paper (Agfa 701,
Agfa-Gevaert) and on special ink jet paper (HOMO-
GENTISATE PHYTYLTRANSFERASE Premium, Hewlett-
Packard) and the prints were subsequently exposed with xenon
light whose intensity was 750 W/mZ for 12 hours, UV light
below a wavelength of 290 pm being excluded by means of a
filter. The light fastness was evaluated on the basis of the
residual colour difference DE* and of the hue angle difference
Hab* in accordance with the Cielab system in comparison
against the respective unexposed print.
The results are set out in Table 1.
The lower the value of the residual colour difference, the better
the light fastness.
Example 2
As described in Example 1, a printing ink was prepared, consisting of
5 g of the stock solution (A),
2.5 g of the solvent mixture (B) and
2.5 g of the same zinc oxide dispersion as in Example 1, and was printed and
tested
as in Example 1.
Comparative example
As described in Example 1, a printing ink was prepared, consisting of
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g of the stock solution (A) and
S g of the solvent mixture (B)
without the addition of a light stabilizer and was printed and tested as in
S Example 1.
Table 1
Cielab after
coord. 12 h
of exposure
unexposed versus
print unexposed
print
Printing ink Paper C* h* DE* H ab*
according to
Example 1 AGFA 701 60.16 348.38 26.11 0.70
Example 2 AGFA 701 59.37 353.48 12.60 - 0.32
Comparative exampleAGFA 701 62.92 349.94 35.42 2.50
Example 1 HP Premium69.17 346.35 36.89 - 0.01
Example 2 HP Premium64.87 355.41 8.24 - 1.73
Comparative exampleHP Premium69.52 349.30 59.13 3.25
It was found that the dye inks prepared and printed in accordance with Example
1
and 2 exhibit a markedly improved light fastness.
