Leucoindigo preparatations in granule form

Details Leucoindigo preparatations in granule form Leucoindigo preparatations in granule form

1996-02-12

1997-06-10

Einsmann, Margaret

Bleaching and dyeing; fluid treatment and chemical modification

Dry dye composition other than mere mixture of two or more...

Dye in specified form other than mere powder

8653, 8618, 8651, 8918, D06P 122, D06P 520

Patent

active

056371160

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to novel leucoindigo preparations in granule form consisting essentially of leucoindigo and alkali metal hydroxide.
The invention further relates to the production of these leucoindigo preparations and to their use for dyeing cellulose-containing textile material.
Indigo is a well known vat dye which is used for dyeing cellulose-containing textile material, especially cotton warp yarns for blue denim articles.
For dyeing, the water-insoluble indigo first has to be converted by reduction (vatting) into the water-soluble leuco form which, after absorption by the material to be dyed, is then oxidized back to the pigment.
In the customary dyeing processes, indigo is vatted in an alkaline medium in a vessel upstream of the dyebath by addition of inorganic reducing agents such as sodium dithionite and thiourea dioxide or else organic reducing agents such as hydroxyacetone. Additional machine-dependent portions of reducing agent are consumed during dyeing, since some of the leucoindigo is oxidized by air contact in the air passages and at the dyebath surface and has to be revatted, which is why small amounts of reducing agent are also added to the dyebath.
One disadvantage with the vatting of indigo using the reducing agents mentioned is the high load on the dyehouse waste water due to sulfate (from about 3,500 to 5,000 mg/l, measured in the waste water from an indigo dyehouse) in the case of sodium dithionite or due oxygen-consuming substances (COD about 8,000 mg/l, measured in the waste water from an indigo dyehouse) in the case of hydroxyacetone. Additionally the reduction, for example with sodium dithionite, requires the addition of a large amount of alkali.
It is also known to have pulverulent solid to pasty preparations of leucoindigo containing as stabilizers polyhydroxy compounds, such as glycerol and especially compounds derived from sugars, eg. molasses, mixed with alkali or zinc dust (DE 200 914 or 235 047). If these preparations are used for dyeing, it is true that the sulfate content of the dyehouse waste water can be effectively lowered, but the result is a high load on the waste water due to dissolved organic hydroxy compounds, measured as TOC (total organic carbon), COD (chemical oxygen demand) or BOD (biological oxygen demand); for example, a 60% by weight leucoindigo preparation containing 25% by weight of molasses produces a COD of about 8,000 mg/l.
FR-A-360 447 also discloses a process for the production of solid indigo white preparations in which neutral solutions of the alkali metal salts of leucoindigo are evaporated to dryness in very thin layers. However, the products obtained in this way do not have granule form and are stabilized by mixing with unslaked lime.
Finally, the earlier German Patent Application P 43 10 122.4 describes a dyeing process wherein indigo is used in pre-reduced form, in the form of the aqueous, alkaline solution obtained in catalytic hydrogenation. This eliminates the waste water load due to organic substances, while the sulfate level is reduced to the amount of hydrosulfite required for the air contact during the dyeing process. However, it is disadvantageous that the leucoindigo solution used is oxidation-sensitive and has to be handled under strict exclusion of oxygen.
It is an object of the present invention to provide a leucoindigo preparation which does not have the disadvantages mentioned and is advantageous for dyeing.
We have found that this object is achieved by leucoindigo preparations in granule form consisting essentially of leucoindigo and alkali metal hydroxide.
We have also found a process for preparing these leucoindigo preparations, comprising the step of concentrating an aqueous alkaline solution of leucoindigo to dryness under conditions of thorough mixing and oxygen exclusion.
Finally, the invention provides for the use of the leucoindigo preparations for dyeing cellulose-containing textile material.
The leucoindigo preparations of the invention contain the essential constituents leucoindigo and alkali metal hydrox

REFERENCES:
patent: 833654 (1906-10-01), Wimmer
patent: 2088213 (1937-07-01), Perkins
patent: 5053078 (1991-10-01), Koike et al.

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