Bleaching and dyeing; fluid treatment and chemical modification – Organic additive for dye composition – dye composition... – Carboxylic acid or salt thereof
Reexamination Certificate
2002-10-15
2004-11-09
Einsmann, Margaret (Department: 1751)
Bleaching and dyeing; fluid treatment and chemical modification
Organic additive for dye composition, dye composition...
Carboxylic acid or salt thereof
C008S602000, C008S611000, C008S594000, C008S604000, C008S623000, C008S650000, C008S652000, C008S653000, C008S918000
Reexamination Certificate
active
06814763
ABSTRACT:
The present invention relates to mediator systems obtainable by mixing one or more salts of a metal capable of forming a plurality of valence states with at least one amino-containing complexing agent (K1) and at least one hydroxyl-containing but amino-devoid complexing agent (K2) in an alkaline aqueous medium, wherefor the complexing agents may be present as salts and the molar ratio of K1 to metal ion is from 0.1:1 to 10:1 and the molar ratio of K2 to metal ion is from 0.1:1 to 5:1.
The invention also provides a process for reducing dyes, a process for dyeing cellulosic textile material using these mediator systems and the cellulosic textile materials dyed by this process.
Vat dyes and sulfur dyes are important classes of textile dyes.
Vat dyes are of major significance for dyeing cellulose fibers on account of the high fastnesses of the dyeings in particular. To use these dyes, the insoluble oxidized dye has to be converted into its alkali-soluble leuco form by a reducing step. This reduced form has high affinity for cellulose fiber, goes onto the fiber and once on the fiber is converted back into its insoluble form by an oxidizing step.
The class of sulfur dyes is particularly important for the production of inexpensive dyeings having average fastness requirements. The use of sulfur dyes likewise involves the need to carry out a reducing step and an oxidizing step in order that the dye may be fixed on the material.
The literature describes a wide range of reducing agents for use on an industrial scale, eg. sodium dithionite, organic sulfinic acids, organic hydroxy compounds such as glucose or hydroxyacetone. In some countries sulfur dyes are still being reduced using sulfides and polysulfides.
A feature common to these reducing agents is the absence of a suitable way for regenerating their reducing effect, so that these chemicals are discharged after use into the wastewater together with the dyebath. As well as the costs for fresh chemicals to be used, this also creates the additional expense of having to treat the wastewaters produced.
Further important disadvantages of these reducing agents are the very limited means to influence their reducing effect or their redox potential under application conditions in the dyebath and the absence of simple control technology for regulating the dyebath potential.
A further group of reducing agents was discovered in the class of iron(II) complexes. Iron(II) complexes are known with triethanolamine (WO-A-90/15182, WO-A-94/23114), with bicine (N,N-bis(2-hydroxyethyl)glycine) (WO-A-95/07374), with triisopropanolamine (WO-A-96/32445) and also with aliphatic hydroxy compounds which may contain a plurality of hydroxyl groups and may additionally be functionalized with aldehyde, keto or carboxyl groups, such as di- and polyalcohols, di- and polyhydroxyaldehydes, di- and polyhydroxyketones, di- and polysaccharides, di- and polyhydroxymono- and -dicarboxylic acids and also hydroxytricarboxylic acids, preference being given to sugar-based compounds, especially the acids and salts thereof, eg. gluconic and heptagluconic acid, and citric acid (DE-A-42 06 929, DE-A-43 20 866, DE-A-43 20 867, prior German patent application DE-A-199 19 746, unpublished at the priority date of the present application, and also WO-A-92/09740).
These iron(II) complexes have a reducing effect which is sufficient for dyeing reduction and which is described by the (negative) redox potential which is measurable in alkaline solution at a certain molar ratio of iron(II):iron(III). Numerous of these iron(II) complexes, eg. the complexes with triethanolamine, bicine, gluconic acid and heptagluconic acid, also have the advantage of being electrochemically regenerable and hence of usefulness as mediators in an electrochemical reduction of dyes and also in electrochemical dyeing processes.
These iron complexes nonetheless have specific weaknesses. For instance, cathodic reduction is possible at high cathodic current density as a diffusion-controlled electrode reaction using triethanolamine or bicine as complexing agent, but the corresponding iron complexes are not sufficiently stable in the more weakly alkaline region at pH ≦11.5, which greatly limits the usefulness of these complexes as electrochemically regenerable reducing agents in indigo dyebaths for denim manufacture. True, iron complexes with gluconate or heptagluconate are very stable in a pH range of 10-12, but the cathodic current densities obtainable with these complexes leave something to be desired, so that correspondingly larger electrolytic cells have to be used and/or the concentration of iron complex has to be increased, which is disadvantageous for the user with regard to energy requirements, chemical consumption, costs and wastewater loading.
From textil praxis international, 47, pages 44-49 (1992) and Journal of the Society of Dyers and Colourists, 113, pages 135-144 (1997) it is also known to use mixtures of these iron complexes as reducing agents. For instance, the first paper mentioned describes a mixture of iron(II) sulfate, triethanolamine and citric acid in a molar ratio of 1:12.4:0.02 as a reducing agent for the analytical determination of indigo. The latter paper proposes using a mixture of iron(III) sulfate, triethanolamine and sodium gluconate in a molar ratio of 1 (based on iron):6.3:0.04 as a mediator for the electrochemical dyeing with indigo.
But these mixtures too are observed to have the disadvantages associated with the individual complexes, especially the lack of stability at lower pH.
It is an object of the present invention to remedy the disadvantages mentioned and to make it possible to reduce dyes in an advantageous, economical manner.
We have found that this object is achieved by the mediator systems defined at the beginning.
The invention also provides a process for electrochemical reduction of dyes in an alkaline aqueous medium and also a process for dyeing cellulosic textile material with vat dyes or sulfur dyes by electrochemical dye reduction in the presence of metal complexes as mediators, which each comprise using the mediator systems defined at the beginning.
The invention lastly provides cellulosic textile materials which have been dyed by this process.
An essential feature of the mediator systems according to the invention is a combination of the metal ion with the complexing agents K1 and K2 in a molar ratio K1 to metal ion of from 0.1:1 to 10:1, preferably from 0.5:1 to 6:1, and a molar ratio of K2 to metal ion of from 0.1:1 to 5:1, preferably from 0.5:1 to 3:1.
The mediator systems according to the invention are obtainable by mixing the individual components, which may be used in the form of their water-soluble salts, in an alkaline aqueous medium. The metal ion becomes complexed in the process, the prevailing pH, which is generally about 10-14, determining that the particular most favored complex is formed preferentially.
The metal ion M1 can be used not only in low-valent form but also in higher-valent form. For example, in the case of the particularly preferred metal iron, not only iron (II) salts may be used but also iron(III) salts, which are initially readily reduced to iron(II) electrochemically.
Useful amino-containing complexing agents K1 for the invention include in particular aliphatic amines that have at least two coordination-capable groups containing at least one hydroxyl group and that are soluble in water or aqueous organic media or miscible with water or aqueous organic media.
The complexing agents K1 can additionally contain carboxyl groups. Examples of preferred complexing agents K1 are alcoholamines, especially mono-, di- and trialcohol- (especially -alkanol)amines, such as triethanolamine and triisopropanolamine, and also mono-, di- and polyhydroxyaminocarboxylic acids such as N,N-bis(2-hydroxyethyl)glycine. Particularly preferred complexing agents K1 are triisopropanolamine and especially triethanolamine.
It will be appreciated that it is possible to use mixtures of complexing agents K1.
Useful hydroxyl-containing amino-devoid complexing agents K2
Bechtold Thomas
Grund Norbert
Hiebsch Wolfgang
Mohr Stefan
Schrott Wolfgang
Connolly Bove & Lodge & Hutz LLP
DyStar Textilfarben GmbH & Co. Deutschland KG
Einsmann Margaret
LandOfFree
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