Vat acid dyeing of textile fibers

Details Vat acid dyeing of textile fibers Vat acid dyeing of textile fibers

2002-08-20

2004-08-24

Einsmann, Margaret (Department: 1751)

Bleaching and dyeing; fluid treatment and chemical modification

Organic additive for dye composition, dye composition...

Sulfur-containing

C008S592000, C008S594000, C008S650000, C008S653000, C008S922000, C008S924000, C008S925000, C008S926000, C008S529000

Reexamination Certificate

active

06780205

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a method of dyeing textile fibers using a vat acid dyeing method and, more particularly, to a vat acid dyeing method which utilizes additional reducing agent(s) to dye a variety of fibers to obtain deep shades and excellent washfastness.
DESCRIPTION OF BACKGROUND ART
Vat alkaline dyeing processes for use with textile fibers are known; see, for example, British Patent 534,085, International Patent Application WO96/04420, and U.S. Pat. No. 3,353,900. A vat neutral dyeing process has been disclosed for use with polypropylene fibers, American Dyestuff Reporter, March 1997, pp. 15-18, 66.
Vat acid dyeing processes have been disclosed in British Patents 709,150 (in which, however, the reduced dye is reoxidized before the dyeing step), 712,418 and 1,383,451, U.S. Pat. Nos. 2,627,449 and 3,527,556, Applications of Leuco Vat Acid Dispersion on Polyester (S. N. Chevli, Master's Thesis, University of Leeds, UK, 1997), and American Dyestuff Reporter, Sep. 17, 1951, pp. 585-596.
The use of sulfinic acid reducing agents in alkaline vat dyeing has been disclosed in U.S. Pat. No. 6,007,587 and British Patent 1,430,179 and, in post-dyeing reduction clearing, in International Patent Application WO98/03725. The use of sodium formaldehyde sulfoxylate with vat dyes in printing and its instability in dilute acids have been disclosed in The Merck Index, Eighth Edition, Merck & Co., Inc., 1968, p. 959 and in Rongolit® C trade literature from BASF (TI/T 5952e, February 1997).
However, none of these processes provides adequate depth of shade, washfastness, or stain-resistance, and an improved dyeing method is still needed.
SUMMARY OF THE INVENTION
The process of the present invention for dyeing a fiber comprising a synthetic polymer selected from segmented polyurethanes, segmented polyurethaneureas, segmented polyetheresters, polyesters, polyamides, and poly(meta-phenylene isophthalamide), comprises the steps of:
(a) preparing a vat acid dye by:
(i) reducing a vat dye with a first reducing agent in water in presence of a surfactant at an alkaline pH; and
(ii) lowering the pH by the addition of a carboxylic acid;
(b) forming a dyebath by combining:
(i) said vat acid dye;
(ii) an aqueous solution of a carboxylic acid having a pH of about 5.2-6.5; and
(iii) a second reducing agent in an amount sufficient to maintain said dye in a reduced state, wherein said second reducing agent comprises at least about 20 mole %, based on the total of said second reducing agent, of a compound selected from the group consisting of &agr;-hydroxyalkyl-sulfinic acids having 1-6 carbon atoms, water soluble salts thereof, 1,2,4-trithiolane and mixtures thereof;
(c) contacting said fiber with said dyebath and heating to at least about 95° C. for a time sufficient to dye the fiber; and
(d) oxidizing the dye in the fiber.
Also provided is a solid mixture comprising at least one vat acid dye, at least one carboxylic acid having 12-22 carbon atoms, at least one reducing agent selected from the group consisting of sodium dithionite, &agr;-hydroxyalkylsulfinic acids having 1-6 carbon atoms, water-soluble salts of such acids, sodium dithionite, 1,2,4-trithiolane, and mixtures thereof, and at least one surfactant.
DETAILED DESCRIPTION OF THE INVENTION
It has now been unexpectedly found that deeply dyed textile fibers can be obtained by a vat acid dyeing process in which the pH is in a particular range during dyeing, additional selected reducing agent is added during the dyeing step, and the dyeing takes place at or above a specified minimum temperature. These dyed fibers have excellent washfastness and a low propensity to stain other fibers.
As used herein, “spandex” means a manufactured fiber in which the fiber-forming substance is a long chain synthetic polymer comprised of at least 85% by weight of a segmented polyurethane; fibers similarly comprising a segmented polyurethaneurea (a sub-class of segmented polyurethanes) are also within the definition of spandex. By “segmented” is meant a polymer which has a plurality of segments of two classes. Each segment of the first class is the residue remaining after removal of the terminal hydrogen atoms from a polymeric glycol. The glycols typically have a melting point below 50° C. and a number-average molecular weight above 600. Each segment of the second class contains at least one repeating unit of a fiber-forming polymer, typically having a melting point above 200° C. “Vat dye” means a colored aromatic compound containing two or more carbonyl groups conjugated with each other through double bonds. Vat dyes are generally used by reducing and dissolving them with a reducing agent in the presence of strong base, contacting the fibers to be dyed with the reduced dye, and then oxidizing the dye to its colored form in the fiber. Vat dyes are to be distinguished from “solubilized vat dyes” in that the latter are sulfuric acid esters of corresponding reduced vat dyes and have different chemical characteristics. “Vat acid dyeing process” means a process in which, after reduction and dissolution of the dye, the dye solution is made acidic before contact is made with the fiber. “Blends” of fibers means fibers which have been mingled with each other, for example by covering one fiber with another, by mechanically- or jet-mingling them, or by simultaneously knitting or weaving the fibers into a fabric.
The sodium salt of hydroxymethylsulfinic acid, generally available as the monosodium salt dihydrate, HOCH
2
SO
2
Na.2H
2
O, is also known as sodium formaldehyde sulfoxylate and hydroxymethanesulfinic acid (sodium salt); sodium dithionite is also known as sodium hydrosulfite.
In the process of the invention, a vat acid dye is formed by reducing a vat dye with a first reducing agent in water at an alkaline pH and lowering the pH of the resulting solution with a carboxylic acid, preferably to about pH 5.2-6.5 (more preferably to about 5.5-6.0), to form the vat acid dye in leuco form. The first reducing agent can be selected from sodium dithionite, 1,2,4-trithiolane, &agr;-hydroxyalkylsulfinic acids, water-soluble salts thereof, and mixtures thereof. The weight ratio of reducing agent to vat dye is preferably at least 2 to 1, more preferably at least 3 to 1, to fully convert the vat dye to its leuco form. A surfactant is added before lowering the pH of the solution of reduced alkaline vat dye. Anionic surfactants are preferred for improved stability against settling of the vat acid dye from the water. For greater storage stability, additional reducing agent can be added to the solution of vat acid dye, for example about 15 wt % based on total solution.
Examples of dyes that can be used in the method of the invention include Colour Index (C.I.) Vat Blue 1(indigo), C.I. Vat Violet 1 (indanthrene brilliant violet), C.I. Vat Green 1 (indanthrene brilliant green), C.I. Vat Orange 15 (duranthrene orange), C.I. Vat Red 41 (thioindigo), C.I. Vat Red 13 (indanthrene red), and mixtures thereof, but any vat dye or vat dye mixture that is stable to the conditions of the dyeing process and can subsequently be oxidized to its corresponding pigment form can be used. For instance, a deep black color can be obtained on polyester bicomponent fibers (for example, comprising poly(ethylene terephthalate) and poly(trimethylene terephthalate)) using a mixture of 3 wt % Vat Blue 1, 6 wt % Vat Blue 18 and 1.5 wt % Vat Orange 15. Dyes having one or two carbonyl groups (for example dibenzanthrones) were observed to give deeper shades than those having nitrogen-containing rings, and the former are preferred. Further, the fiber(s) to be dyed can affect the selection of the dye. For example, C.I. Vat Red 13 was observed to give deeper shades on polyamides, polyurethanes, and cotton than on polyester.
The vat acid dye and a second reducing agent which contains at least about 20 mole % (based on total second reducing agent) of a compound selected from the group consisting of 1,2,4-trithiolane, &agr;-hydroxyalkylsulfinic acids having 1-6 carbon atoms, water-soluble salts of such acid

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