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
2004-09-14
Einsmann, Margaret (Department: 1751)
Bleaching and dyeing; fluid treatment and chemical modification
Organic additive for dye composition, dye composition...
Carboxylic acid or salt thereof
C008S611000, C008S618000, C008S650000, C008S652000, C008S653000, C008S918000
Reexamination Certificate
active
06790241
ABSTRACT:
The present invention relates to mediator systems obtainable by mixing a salt of an electrochemically active complexing metal (M1) capable of forming a plurality of valence states with a hydroxyl-containing complexing agent, which may likewise be present as salt, and with a salt of an electrochemically inactive complexing metal (M2) in an alkaline aqueous medium, wherefor the molar ratio of metal ion M2 to metal ion M1 is from 0.8:1 to 2:1.
The invention also provides a process for reducing dyes, a process for dyeing cellulosic textile material using these mediator systems and cellulosic textile materials dyed by these processes.
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, 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-A42 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 invention, and also WO-A-92/09740).
These iron(II) complexes have a reducing effect which is sufficient for dye 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.
It is further known to use mixtures of these iron complexes as reducing agents. For instance, textil praxis international, 47, pages 44-49 (1992) and Journal of the Society of Dyers and Colourists, 113, pages 135-144 (1997) describe mixtures of iron salts, triethanolamine and respectively citric acid or gluconic acid. The latter paper also utilizes as mediators mixtures of iron salts, calcium salts and gluconic acid and/or heptagluconic acid where the molar ratio of calcium to iron is in the range from 0.5 to 0.75.
However, the known mediator systems have certain weaknesses. True, the iron complexes based on triethanolamine or bicine have a sufficiently negative redox potential for dye reduction, but they are not sufficiently stable in the more weakly alkaline region at pH≦11.5, which greatly limits their electrochemical regenerability in indigo dyebaths for denim manufacture. True, the mediator systems based on gluconate or heptagluconate have very good complex stability in the pH range of 10-12, but the known systems have to have a relatively large fraction of iron(II) complex to achieve a redox potential of ≦−700 mV (Ag/AgCl, 3 M KCl reference electrode), as is required, for example, to maintain the requisite bath stability for dyeing with indigo. But the large fraction of iron(II) complex required is disadvantageous especialy with regard to dyeing with indigo in denim manufacture, since the textile material is here dyed layer by layer by repeated immersion in the dyebath and subsequent air oxidation of the dye, so that the mediator in the dyebath is completely oxidized with every air passage and first has to be reduced again for the next dyeing cycle, and this entails high electricity consumption, which in turn requires high mediator concentrations or correspondingly large electrolytic cells by way of compensation.
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. More particularly, stable mediator systems having a powerful reducing action shall be provided.
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 electrochemically active metal ion M1 with an electrochemically inactive, but likewise complexation-capable metal ion M2 and with a hydroxyl-containing but amino-devoid complexing agent in a molar ratio of metal ion M1 to metal ion M2 of from 0.8:1 to 2:1, preferably from 0.9:1 to 1.1:1, particularly preferably about 1:1.
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, which generally has a pH of about 10-14. In the course of the mixing, the metal ions M1 and M2 are at least partially complexed, preferably forming an approximately equimolar complex.
The amount of complexing agent is not critical and has only minor importance given a predetermined ratio of reduced to oxidized form of the metal ion M1. The minimum amount of complexing agent normally used will be the amount theoretically required for completely complexing M1, ie. at least 0.5 mol, preferably 1 mol per mole of M1. In principle there is no upper limit to this molar ratio, but cost reasons will generally rule out the use of an amount of more than 5 mol, especially 3 mol, in particular 1.5 mol, of complexing agent per mole of M1.
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 hydroxyl-containing complexing agents
Bechtold Thomas
Burtscher Eduard
Grund Norbert
Maier Peter
Schnitzer Georg
Connolly Bove & Lodge & Hutz LLP
DyStar Textilfarben GmbH & Co. Deutschland KG
Einsmann Margaret
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