Bleaching and dyeing; fluid treatment and chemical modification – Bleaching – Chemical
Patent
1997-01-16
1998-01-06
Diamond, Alan
Bleaching and dyeing; fluid treatment and chemical modification
Bleaching
Chemical
510309, 510318, 510247, 510253, 252180, 252181, D06L 302
Patent
active
057049475
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/EP95/01646 filed Apr. 29, 1995.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the use of water-soluble, phosphorus-free polymers containing sulfonate and/or carboxylate groups and polyhydroxymono- or dicarboxylates for preventing the deposition of magnesium and calcium silicate in the bleaching of textiles with peroxides.
To make a natural yellow fiber, for example cotton, white, a pretreatment has to be carried out. One of the process steps is bleaching of the colored impurities ("yellow components"), normally by chemical oxidation.
In practice, hydrogen peroxide (H.sub.2 O.sub.2) is used for chemical oxidation. Its relatively low potential enables it to be universally used in hot and cold processes in long-term and shock treatments without any significant problems in regard to machine corrosion and process safety. The critical agent in the "bleaching reaction" is the perhydroxyanion HOO.sup.- which is formed in known manner by self-dissociation of the H.sub.2 O.sub.2 under alkaline conditions.
An unwanted competitive process is the self-decomposition of the H.sub.2 O.sub.2 into radicals which attack not only the yellow components, but also the fibers and thus damage them.
The decomposition of H.sub.2 O.sub.2 into radicals is catalyzed, for example, by the heavy metals always present in practice. These catalysts are very effectively inactivated by colloidal magnesium silicate which is formed by the addition of magnesium salts and soluble silicate (for example waterglass) to the bleach liquor. A disadvantage of stabilizing H.sub.2 O.sub.2 by inorganic additives lies in the formation of poorly soluble alkaline earth metal silicates from the soluble silicate and the calcium/magnesium hardness emanating from the fibers (for example cotton).
The alkaline earth metal silicates accumulate as a deposit on machine parts and as an incrustation on the fibers. Complexing additives are used for colloidally stabilizing these alkaline earth metal silicates in the liquor ("threshold effect"). However, these additives have to be effective in less than stoichiometric quantities because otherwise the unwanted complexing dissolution and hence deactivation of the colloidal magnesium silicate will occur.
In addition to water, therefore, typical bleach liquors also contain hydrogen peroxide, alkali metal hydroxide, a water-soluble magnesium salt, a water-soluble alkali metal salt of a silicate, surfactants and a deposition inhibitor.
2. Discussion of Related Art
According to the prior art, the combination of alkali metal silicate with phosphonates or phosphonate combinations as deposition inhibitor results in the effective stabilization of peroxide in the bleach liquor and, at the same time, prevents deposits of alkaline earth metal silicate from forming on the hard surfaces of the machine parts.
EP-A-0 112 801 describes a combination of a magnesium complex of oligomeric phosphonic acid esters with an organic polyhydroxy compound, more particularly hydroxycarboxylic acids, as a stabilizer for hydrogen peroxide in bleach liquors. However, scaling on the bleaching apparatus and incrustations on the treated fibers can only be obtained by completely eliminating the silicates.
EP-A-0 210 952 describes the use of mixtures of a phosphorus-containing compound with a polyhydroxy compound, more particularly polyhydroxycarboxylic acids, for suppressing the decomposition of the per component in bleach liquors. Scaling on the bleaching apparatus and incrustations on the treated fibers can be avoided in this way despite the high percentage silicate content.
In "Textilpraxis international", 1991, pages 1343 et seq., U. Denter and E. Schollmeyer describe the influence of combinations of waterglass and polyhydroxycarboxylic acids on the stabilization of hydrogen peroxide in bleach liquors.
GB-A-2,192,202 describes a process for stabilizing bleaching solutions containing alkaline peroxide for textiles and paper pulps using poly-.alpha.-hydroxyacrylic acid salts.
DE-A-3 204 834
REFERENCES:
patent: 4515597 (1985-05-01), Guth et al.
patent: 4711725 (1987-12-01), Amick et al.
patent: 4725281 (1988-02-01), Stehlin et al.
Textilpraxis International (1991) p. 1343 et seq. (Month Unknown).
Baehr, deceased Bernd-Dieter
Baehr, executrix Sylvia
Kaiser Heribert
Kurzendoerfer Claus-Peter
Nitsch Christian
Diamond Alan
Grandmaison Real J.
Jaeschke Wayne C.
Szoke Ernest G.
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