Bleaching and dyeing; fluid treatment and chemical modification – Dye or potential dye composition – additive – treatment,... – Mixed dyes – noncomplexed
Reexamination Certificate
2000-05-25
2002-12-10
Einsmann, Margaret (Department: 1751)
Bleaching and dyeing; fluid treatment and chemical modification
Dye or potential dye composition, additive, treatment,...
Mixed dyes, noncomplexed
C008S638000, C008S639000, C008S527000, C008S919000
Reexamination Certificate
active
06491731
ABSTRACT:
The present invention relates to a novel mixture of yellow azo- and azoxystilbene dyes, a process for the preparation of concentrated storage-stable dye solutions thereof, to the dye solutions so obtained, and to the use thereof.
The self-condensation of 4-nitrotoluene-2-sulfonic acid, which leads in a simple manner to yellow azo- and azoxystilbene dyes, has long been known. Commercial preparatory methods are described for example in BIOS Report 1548. These dyes are substantive dyes which are used in particular for dyeing paper. The most important and commercially significant of them is known as C.I. Direct Yellow 11 (abbreviated as DY 11), a reddish hue yellow direct dye.
It is known that the condensation of 4-nitrotoluene-2-sulfonic acid in the presence of sodium hydroxide solution results in the formation of insufficiently water-soluble sodium salts of the azo- and azoxystilbene dyes. It is also known that numerous azo/azoxystilbene components result from said condensation reaction, having various degrees of affinity for substrates. aqueous concentrates thereof
The condensation of 4,4′-dinitro-2,2′-stilbenedisulfonic acid with caustic soda and formaldehyde, which leads in a simple manner to yellow azo- and azoxystilbene dyes, has also long been known. The dye which results, known as C.I. Direct Yellow 6 (abbreviated as DY 6), a greenish yellow dye, is also an insufficiently water-soluble sodium salt of the azo- and azoxystilbene dyes. It is known that DY 6 is composed of fewer components than DY 11. Due to the pre-formed stilbene unit, this dye has fewer structural permutations, resulting in a higher brightness and relative affinity of the dye compared to DY 11.
Concentrated aqueous solutions which are used with advantage for e.g. the dyeing of paper in the pulp cannot be prepared from these salts, as their solubility in water is only about 1 g/100 ml. There has therefore been no lack of attempts to carry out the condensation in such a manner that the dye is obtained directly in the form of a concentrated aqueous solution.
U.S. Pat. No. 3,905,949 describes a process in which a condensation is carried out using the lithium salt of 4-nitrotoluene-2-sulfonic acid as starting material in the presence of lithium hydroxide as base, affording the dye in the form of a highly concentrated and very readily water-soluble paste. The lithium salts of the azo- and azoxystilbene dyes so obtained are not only very readily water-soluble, but also have greater substantivity compared with the sodium salts. However, the lithium salts have the drawback that they do not form stable dye solutions. Instead, the concentrated solutions have a propensity during storage to gel formation, crystallization or flocculation, even in the presence of formulation auxiliaries such as urea, thus making it difficult or even impossible to use them. Furthermore, the maximum tolerance for electrolyte and non-dye solute in these formulations defines a maximum degree of optional reduction that can be tolerated, and therefore the shade of resulting dye.
The condensation of 4-nitrotoluene-2-sulfonic acid in the presence of sodium hydroxide and alkanolamines, in aqueous/alcoholic medium, is disclosed in German Offenlegungsschrift No. 31 10 261. In this process, storage-stable dye solutions are obtained due to the organic solvent. The drawback is, however, that these formulations contain a relatively high concentration of organic solvents such as glycol ethers and thus are less attractive on the basis of their VOC content.
European published patent application No. 122 224 relates to a process for the preparation of concentrated aqueous solutions of azo- and azoxystilbene dyes, which comprises carrying out the base-catalyzed condensation of 4-nitrotoluene-2-sulfonic acid in the presence of a mixture of a C
2
-C
4
monoalkanolamine and a di- or trialkanolamine, and removing the inorganic salts from the dye solution. Accordingly, in this process it is necessary to remove the inorganic salts by e.g. a membrane separation process.
A method of preparing dyes of low electrolyte content is disclosed in U.S. Pat. No. 4,560,745, wherein the dye is initially converted into a lipophilic amine salt in the absence of a co-solvent, in order to separate it from the salt-containing synthesis solution. The diethanolammonium salt of the dye is subsequently prepared by addition of diethanolamine and the lipophilic amine is recovered. When this process is applied to azo- and azoxystilbene dyes, it has the disadvantage that no good separation of the liquid phases is obtained with higher carbon lipophilic amines, and low carbon (≦C
12
) lipophilic amines are subject to impractical degree of loss in the aqueous waste stream along with the electrolyte. These factors contribute to less attractive economic and environmental performance than is desirable.
It is an object of the present invention to provide a process which can be easily carried out by which azo- and azoxystilbene dyes are obtained from 4,4′-dinitro-2,2′-stilbenedisulfonic acid which have the shade characteristics of C.I. Direct Yellow 11, but which perform with superior levels of cellulosic affinity, lighffastness and fastness to acid and alkali. It is a further object of the present invention to provide concentrated aqueous solutions of said dyes which are storage-stable and substantially free from organic solvents and inorganic salts and are obtainable at strengths much higher than obtainable by other DY 11 processes.
It has now been found that a mixture of yellow azo- and azoxystilbene dyes having the shade of a C.I. Direct Yellow 11 dye is obtainable by self-condensing 4,4′-dinitro-2,2′-stilbenedisulfonic acid in the presence of an alkali metal hydroxide and with an excess of formaldehyde beyond that needed for the conversion of 4,4′dinitro-2,2′-stilbenedisulfonic acid to Direct Yellow 6, to obtain a dye in the form of an alkali metal salt, preferably as the sodium salt. It has also been found that such dyes may be obtained in the form of concentrated aqueous solutions by conversion of this dye, in the form of an alkali metal salt, in a two-phase system consisting of a water-insoluble low molecular weight ketone and water, into a readily water-soluble alkanolammonium salt by double cation exchange via a lipophilic ammonium salt.
C.I. Direct Yellow 6 dye is obtained by self-condensing 4,4′-dinitro-2,2′-stilbenedisulfonic acid in the presence of an alkali metal hydroxide and with 2.0-2.5 moles of formaldehyde per mole of 4,4′-dinitro-2,2′-stilbene-disulfonic acid. It has been found that the greenish yellow hue this dye can be shifted toward the red by employing an excess of formaldehyde. Advantageously a 55-80% molar excess of formaldehyde, i.e. about 3.5-4.1 moles per mole of 4,4′-dinitro-2,2′-stilbene-disulfonic acid is employed. A 70-80% excess of formaldehyde, i.e. about 3.9-4.0 moles per mole of 4,4′-dinitro-2,2′-stilbene-disulfonic acid is preferably employed. Most preferably about a 75% molar excess of formaldehyde, i.e. 3.95 moles per mole of 4,4′-dinitro-2,2′-stilbene-disulfonic acid is employed.
Accordingly, one aspect of the invention relates to a process for the preparation of a concentrated storage-stable aqueous solution of a reddish-hued mixture of yellow azo- and azoxystilbene dyes which comprises self-condensation of 4,4′-dinitro-2,2′-stilbenedisulfonic acid in the presence of an alkali metal hydroxide and 3.5 to 4.1 moles, preferably 3.9-4.0 moles, per mole of 4,4′-dinitro-2,2′-stilbene-disulfonic acid of formaldehyde, and then converting the sparingly soluble alkali metal salt of the dye into a water-soluble alkanol-ammonium salt by a double cation exchange via a lipophilic ammonium salt, in which process the double ion exchange is carried out in a two-phase system of a water-insoluble low molecular weight ketone and water and using, for the first ion exchange a trialkylamine having a total of 12 to 40 carbon atoms and, for the s
Ciba Specialty Chemicals Corporation
Einsmann Margaret
Mansfield Kevin T.
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