Leuco vat dye preparations in granule form

Details Leuco vat dye preparations in granule form Leuco vat dye preparations in granule form

1998-12-18

1999-12-28

Einsmann, Margaret

Bleaching and dyeing; fluid treatment and chemical modification

Dye or potential dye composition, additive, treatment,...

Sulfur dye or vat dye

D06P 122

Patent

active

060075872

DESCRIPTION:

BRIEF SUMMARY
Leuco vat dye preparations in granule form
The present invention relates to novel leuco vat dye preparations in granule form comprising as essential constituents a leuco vat dye, an alkali metal hydroxide and a mixture of from 10 to 100% by weight of an .alpha.-hydroxy-C.sub.1 -C.sub.4 -alkylsulfinic acid, one of its salts or derivatives and from 0 to 90% by weight of hydrosulfite as reductant.
The present invention further relates to the formation of these leuco vat. dye preparations and to their use for dyeing cellulosic textile material.
Indigoid dyes (especially indigo itself and its bromine derivatives such as Brilliant Indigo) and anthraquinonoid dyes (especially nitroviolanthrone (C.I. Vat Green 9)) are well known vat dyes, which are used for dyeing cellulosic textile material.
For dyeing the water-insoluble vat dye first has to be reduced (vatted) to convert it into the water-soluble leuco form, which has affinity for the fiber and which, after going onto the material to be dyed, is oxidized back to the water-insoluble vat dye pigment.
In existing dyeing processes, the vat dye is vatted in an alkaline medium in a vessel upstream of the dyebath by addition of inorganic reductants such as hydrosulfite (sodium dithionite) and thiourea dioxide or else organic reductants such as hydroxyacetone. Additional machine-dependent portions of reductant are consumed during dyeing, since some of the leuco dye 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 reductant also have to be added to the dyebath.
One disadvantage with the vatting of vat dye using the reductants mentioned is the high contamination of the dyehouse wastewater with sulfate (from about 3500 to 5000 mg/l, measured in the wastewater of an indigo dyehouse) in the case of hydrosulfite or with oxygen-consuming substances (COD about 8000 mg/l, measured in the wastewater of an indigo dyehouse) in the case of hydroxyacetone.
For indigo, there have also been described pulverulent solid to pasty preparations of the leuco form, which comprise polyhydroxy compounds, such as glycerol., and especially sugar derivatives, for example molasses, mixed with alkali or zinc dust as stabilizers (DE-C-200 914 or -235 047). Furthermore, GB-B-276 023 discloses the preparation of pulverulent leuco dye preparations by heating a mixture of unreduced vat dye, glycol, alkali, hydrosulfite and sodium sulfate, drying in an open vessel and subsequent grinding.
The former preparations are effective in lowering the sulfate content of the dyehouse wastewater, but they are typically difficult to meter, since even the drying preparations tend to clump, and they are very slow to dissolve in the dyebath. With the latter preparations, the sulfate level is in fact increased, since these preparations, already comprising the sulfate from the reduction of the dye in the above-described mixture, have additional sulfate added to them.
WO-A-94/23114 discloses a dyeing process wherein indigo is used in a prereduced form, as an aqueous, alkaline solution obtained from catalytic hydrogenation. This eliminates the wastewater loading with 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 leuco indigo solution used is oxidation-sensitive and has to be handled and stored in the absence of oxygen. In addition, the high water ballast of this solution is a hindrance as regards both storage and transportation.
Finally, WO-A-95/05421 describes leuco indigo preparations in granule form comprising leuco indigo and alkali metal hydroxide as essential components. These granules likewise do not always show satisfactory oxidation stability on prolonged storage in air, especially at high humidity.
Furthermore, DE-A-1 9502 968,unpublished at the priority date of the present invention, describes hydrosulfite-stabilized leuco indigo granules.
It is an object of the present invention to provide leuco vat dy

REFERENCES:
patent: 4113427 (1978-09-01), Fono et al.
patent: 5586992 (1996-12-01), Schnitzer et al.
patent: 5637116 (1997-06-01), Gaeng et al.
patent: 5888254 (1999-03-01), Gang et al.

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