Water-soluble stilbene dyes, their preparation and use

Details Water-soluble stilbene dyes, their preparation and use Water-soluble stilbene dyes, their preparation and use

1999-07-12

2002-10-15

Klemanski, Helene (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Marking

C534S689000

Reexamination Certificate

active

06464768

ABSTRACT:

CROSS-REFERENCES TO RELATED APPLICATIONS
The present invention is described in the German priority application No. 198 31 095.1, filed Jul. 10, 1998, which is hereby incorporated by reference as is fully disclosed herein.
BACKGROUND OF THE INVENTION
The inkjet process constitutes a contactless printing process in which droplets of the recording liquid are guided from one or more nozzles onto the substrate that is to be printed. A recording liquid consists in principle of a soluble dye which is in solution in a solvent, usually water, or in a solvent mixture. In general, the solution additionally comprises further auxiliaries, such as surface-active substances, humectants and/or preservatives, for example. In order to obtain prints of high definition and resolution, recording liquids for the inkjet printing process must meet very stringent requirements in terms, in particular, of purity, freedom from particles, storage stability, viscosity, and surface tension. These and other requirements dictate that the dyes employed to prepare the recording liquids shall contain virtually no salts or diluents and must in particular possess high solubility.
In addition, very exacting requirements are made with regard to color strength, brightness, light fastness, water fastness and rub fastness. The inkjet process and the requirements made of the dyes and recording liquids are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 5
th
Edition, Vol.A 13 (1989), 588-594.
The development of water-soluble black dyes for the inkjet printing process that have the desired combination of high color strength, high light fastness and good water fastness has hitherto proved very difficult (see for example P. Gregory, High-Technology Applications of Organic Colorants, Plenum Press, New York (1991), p. 195).
High light fastness is of great importance in particular for inkjet applications in outdoor areas and in connection with the production of inkjet prints of photographic quality.
There is therefore a need for water-soluble dyes which are superior in light fastness to the known black dyes and at the same time have the other properties required for the inkjet sector.
Black stilbene dyes have already been described in various patents. These dyes, prepared originally for the dyeing and printing of textile fibers, are in the form of, in particular, sodium salts and as a result of their preparation conventionally include considerable amounts of salts such as, for example, sodium sulfate, sodium acetate and, in particular, sodium chloride.
In addition, diluents are added to these pulverulent dyes, examples of said diluents being sodium carbonate, alkali metal phosphates, urea, and aliphatic carboxylic acids.
Solid preparations of water-soluble stilbene dyes of the formula (A)
are described, for example, in EP-A-0 057 158 and in DE-A-3 247 605.
Salt-containing dyes of this kind are unsuitable for the preparation of recording liquids for the inkjet printing process because, in particular, corrosion occurs at the nozzles, but also because of the inadequate solubility of the dyes and poor storage stability of the printing inks, which are associated with an increase in viscosity, the deposition of dye, and the blockage of the nozzles. Furthermore, disadvantages arise in respect of the surface tension, so preventing optimum ink-drop formation for use in the inkjet printing process.
Dyes of the formula (A) have been employed for the inkjet printing process in an insoluble form bound to organic or inorganic particles (EP-A-0 656 406) and for printing textile fibers, especially polyamide fibers (EP-A-0 583 133).
The inks employed in accordance with EP-A-0 583 133 for printing textile fibers contain sodium hydroxide, in order to establish an alkaline pH, and are present predominantly as sodium salts.
Because of the poor solubility of the sodium salt of the stilbene dye of the formula (A), however, this dye is not suited to the preparation of printing inks for the inkjet printing process.
The object was therefore to provide black dyes for the inkjet printing process which do not have the disadvantages of the known dyes and yet meet the abovementioned requirements on color strength, brightness, light fastness and fastness to water and rubbing.
SUMMARY OF THE INVENTION
The present invention relates to water-soluble black stilbene dye salts and to their use for preparing recording liquids for the inkjet process.
The present invention provides black stilbene dyes of the formula (1)
in which
R
1
is hydrogen, alkyl of 1 to 4 carbon atoms, or alkoxy of 1 to 4 carbon atoms;
R
2
is hydrogen, carboxyl, chloro or nitro;
R
21
is hydrogen; or R
2
and R
21
together form a benzene ring which is fused on in positions 3 and 4 of the ring A and can carry 1, 2 or 3 sulfo groups;
m is a number from 0 to 1;
n is a number from 1 to 2;
M
+
is a cation or a mixture of different cations, at least one equivalent of the cations
M
+
per mole of the dye being lithium cations and/or cations of the formula (II)
where p is a number from 1 to 30;
X is CH
2
CH
2
, CH(CH
3
)CH
2
, CH
2
CH(CH
3
) or a combination thereof and R
3
, R
4
and R
5
independently of one another are hydrogen, a group of the formula (III)
—(—X—O—)
p
H  (III)
or an aliphatic radical of 1 to 18 carbon atoms.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preference is given to dyes of the formula (I) in which M
+
is lithium cations or cations of the formulae (II) in which p is a number from 1 to 15. Particularly preferred dyes of the formula (I) comprise mixtures of lithium cations and cations of the formula (II).
Preference is also given to dyes of the formula (I) in which the definition of R
21
is hydrogen.
Preference extends to the dyes of the formula (I) in which R
1
is hydrogen, methyl, ethyl, methoxy or ethoxy.
Particularly preferred dyes are those of the formula (IB)
in which R
1
, M and m are as defined above and R
20
is hydrogen, sulfo, chloro, nitro or carboxyl.
The preparation of the stilbene dyes in the form of the sodium salts is known per se and is described, for example, in Houben-Weyl, Methoden der Organischen Chemie, Vol. X/3 (1965), pp. 339-343.
Accordingly, stilbene dyes are synthesized by alkaline condensation of 4,4′-dinitrostilbene-2,2′-disulfonic acid of the formula (IV)
with amino azo compounds in the form of their copper complexes of the formula (V)
Aternatively, formation of the copper complex can be carried out after the alkaline condensation.
Since the alkaline condensation of 4,4′-dinitrostilbene-2,2′-disulfonic acid with amino azo compounds in accordance with the methods stated is performed with sodium hydroxide, the dyes prepared in this way are in the form of sodium salts. The lithium or ammonium salts of stilbene dyes of the formula (I) according to the invention are prepared, for example, by adjusting the sodium salts of the corresponding stilbene dyes in an aqueous medium to a pH of between 0 and 3, preferably between 0 and 2, using an acid, separating off the resultant dye acids, washing them and then combining them in an aqueous medium with lithium hydroxide and/or with the lithium salt of a sufficiently weak acid and/or with an amine of the formula (VI) or with an ammonium hydroxide of the formula (VII)
R
3
R
4
N(—X—O—)
p
H  (VI)  
in which R
3
, R
4
, R
5
, X and p are as already defined above to form dye salts of the formula (I) according to the invention. Acids suitable for preparing the abovementioned dye acids are inorganic acids, such as hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid, or organic acids, such as trichloroacetic acid, methanesulfonic acid, trifluoromethanesulfonic acid or polystyrenesulfonic acid. It is also possible to use a mixture of organic or inorganic acids.
Conversion of the sodium salts of dyes of the formula (I) to the corresponding dye acids is preferably done by introducing the sodium salt into the aqueous solution of the organic and/or inorganic acid and then stirring the resultant suspe

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