DYEING WARP YARNS WITH LEUCOINDIGO FOAM

Description

[0001] The present invention relates to the technical field of dyeing with indigo. Indigo has been known since ancient times to be a useful dye for dyeing textile materials. In the present age, it is used particularly for dyeing warp yarns in the manufacture of denim articles such as blue jeans for example.

[0002] Indigo is water insoluble and has no affinity for fiber and therefore must first be reduced to the water-soluble leuco form, which has moderate affinity for fiber and which, after it has gone onto the material to be dyed, is oxidized back to the indigo pigment.

[0003] Sodium dithionite is one example of a reducing agent used to reduce the indigo, but other reducing agents such as thiourea dioxide and hydroxyacetone can also be used. However, it is more advantageous to effect the reduction through catalytic hydrogenation to obtain a solution of leucoindigo, which can be metered directly into the dyebath, see EP 0 692 042 B1.

[0004] The oxidation of the leucoindigo back to indigo tends to proceed very readily, so that it is sufficient for the material to be dyed to be exposed to atmospheric oxygen after the leucoindigo has gone on. Yet the ready oxidizibility of leucoindigo has the disadvantage, on the other hand, that in many cases it is necessary to add reducing agents to the dyebath to prevent premature oxidation, and that the above-described indigo solution, obtained by catalytic hydrogenation, generally has to be transported and stored in the absence of air.

[0005] Because leucoindigo has only moderate affinity for the fiber material to be dyed, the fiber has to be dyed more than once until it has the desired depth of shade, in the form of four to eight passes through a dipbath with subsequent airing. This process is therefore relatively complex and, what is more, involves large volumes of liquor which ultimately have to be subjected to a wastewater treatment.

[0006] Another disadvantage is that the dyeing machines required are very large and have a warp yarn sheet length of 105 to 500 meters.

[0007] WO 2008/056256 A1 discloses a device and a continuous dyeing process with indigo.

[0008] Applying foamed colorant or auxiliary materials to continuous textile materials is already known and described in WO 2008/056256 A1, DE 25 23 062 and EP 0 162 018 A1 for example. The latter reference relates to a process wherein cellulosic textile material is treated with a foamed aqueous preparation comprising a reduced vat dye as colorant.

[0009] EP 1 591 578 A2 discloses a process wherein a cellulosic textile material has applied to it, on one side at least, a leucoindigo-containing foam and is subsequently exposed to an oxidizing medium, i.e., preferably air. The foam, which is produced in a foam generator, is applied to the textile material by means of nozzles. It is a particular advantage of this process that the front and back of a fabric can be dyed with different dyes or at least in different hues, providing special effects. However, dyeing warp yarns or an open sheet of warp yarn by following this process is a difficult undertaking in practice and, more particularly, does not lead to uniform dyeing of warp yarns.

[0010] It is now been found that, surprisingly, even warp yarns can be dyed very successfully by means of leucoindigo foam.

[0011] The present invention relates to a process for dyeing cellulosic warp yarns with indigo by applying a leucoindigo foam to the warp yarns and subsequently oxidizing the leucoindigo to indigo, wherein the warp yarns are led through an entry opening into a sealed foam chamber and have leucoindigo foam applied to them therein before they reemerge from the foam chamber through an exit opening, the longitudinal tension of the warp yarns being closed loop controlled such that they are in a state of free suspension within the foam chamber, wherein the warp yarn sheet is very substantially cooled down immediately before entry into the foam chamber. Cellulosic warp yarns herein are cotton warp yarns in particular, but also warp yarns composed of blends of cotton with materials such as polyester and polyamide.

[0012] The leucoindigo foam is obtainable for example by foaming an aqueous solution of leucoindigo by means of an inert gas in a commercially available foam generator. The aqueous solution of leucoindigo is obtainable by reduction of indigo with a reducing agent, in particular with sodium dithionite. However, preference is given to using a commercially available so-called indigo solution which is prepared by catalytic hydrogenation of indigo and which has an indigo concentration of 20 to 40% in particular. Indigo solution may preferably be fed directly to the foam generator from the tank container in which the indigo solution is supplied by the manufacturer. It may be the case that additional water also has to be supplied to the foam generator. This additional water is preferably first degassed and then mixed with an inert gas, preferably nitrogen.

[0013] The inert gas used is preferably nitrogen, but can also be any other inert gas. It is particularly advantageous for the foam generator to be admixed with carbon dioxide as well as the inert gas, particularly nitrogen, and thereby to lower the pH of the foam and enhance the affinity of the leucoindigo for the warp yarn. Based on the inert gas, carbon dioxide is preferably used in amounts of 5% to 80% by volume, more preferably in amounts of 20% to 50% by volume. The pH of the foam is preferably in the range from 12.6 to 10.4 and more preferably in the range from 11.6 to 11.0.

[0014] In general, foaming is effected with the assistance of a foam-former. Useful foam-formers include in particular anionic or nonionic surfactants which are known and commercially available. Suitable surfactants are discernible from EP 0 162 018 for example.

[0015] Foaming can further be effected in the presence of further auxiliaries. Wetting agents capable of enhancing the penetration of the leucoindigo into the warp yarn can be added for example. Such wetting agents are commercially available, and mixtures of mono- and diesters of phosphoric acid with, for example, 2-ethylhexanol are particularly useful.

[0016] Wetting agents are preferably used in amounts of 1% to 20%, more preferably 2% to 8%, based on the mixture to be foamed.

[0017] Foaming can further be effected in the presence of auxiliaries which bring about a fastness improvement and also of auxiliaries which minimize yellowing of the indigo-dyed textile material under the influence of harmful gases such as ozone or nitrogen oxides. Such auxiliaries are available.

[0018] Useful fastness-improving auxiliaries include for example reactive resins capable of crosslinking on the surface of the textile material. The use of epichlorohydrin-modified polyamides or polyamidoamines will be found particularly advantageous here.

[0019] Useful yellowness inhibitors include for example condensation products of fatty acids with hydroxyalkylamines. Preferred reaction components here include for example stearic acid, tallow fatty acid and oleic acid and also di- and triethanolamine and also N-(aminoethyl)ethanolamine. It is additionally advantageous when the nitrogen in the reaction product is additionally quaternized in a second reaction step. Quaternizing agents used include, for example, dimethyl sulfate or methyl p-toluenesulfonate. In addition, polymers having long-chain hydrocarbyl chains and forming barrier layers also find use as yellowness inhibitors. These include, for example, polyethylenes and also polymers having pendant hydrocarbyl chains, examples being polyacrylates and polyurethanes. The hydrocarbyl chain should preferably have a length of more than 12 carbon atoms in order that an effective barrier layer can be formed.

[0020] The auxiliaries mentioned are preferably used in amounts of 1% to 15% and more preferably 2% to 8%, based on the mixture to be foamed.

[0021] Foam generators are known and can operate statically or preferably dynamically. They are described in DE 25 23 062 and US 4,118,526 for example and are commercially available.

[0022] It is preferable to maintain the foam at a constant temperature, in which case temperatures of 15 to 70°C particularly of 25 to 40°C are particularly preferred. It is particularly helpful for this purpose to equip the foam generator with a double-walled housing through which a heat transfer medium circulates to maintain the desired temperature.

[0023] The leucoindigo foam is applied to the warp yarns in the foam chamber. To this end, the foam chamber is equipped with or connected to at least one suitable leucoindigo foam applicator device which is supplied from the foam generator. The applicator device used can be any device which presses or sucks the foam uniformly onto the warp yarns. Such applicator devices are known and described in DE 2523062 for example.

[0024] Preferred applicator devices are those which include a parabolic distribution chamber, as described for example in US 4,655,056 and EP 1 065 308 A2. It is preferable, in the process of the present invention, for a plurality of applicator devices, in particular 2 to 5, to each be disposed transversely to the warp yarn sheet at short distances apart, so that the foam chamber is supplied with foam uniformly over the entire width of the warp yarn sheet. It is advantageous in this connection for all applicator devices to be supplied from one foam generator.

[0025] The foam chamber is ideally small in dimensions and encloses the warp yarn sheet as closely as possible. The entry and exit openings for the warp yarn sheet are advantageously slot shaped such that the warp yarn sheet can pass through without touching at the top or bottom.

[0026] To prevent ingress of atmospheric oxygen into the foam chamber, it is preferable for gas locks to be disposed upstream of the entry opening and downstream of the exit opening.

[0027] In the process of the present invention, the warp yarn sheet is very substantially cooled down immediately before entry into the foam chamber. More particularly, the warp yarn sheet is cooled down to temperatures of 25 to -10°C, more preferably 15 to -5°C.

[0028] Cooling can be effected by following any known cooling process, but preference is given to using contact cooling which operates via cooling cylinders. It is particularly preferable to cool through brief direct contact of the warp yarn sheet with a liquid coolant, for example liquid ammonia or, in particular, liquid nitrogen.

[0029] It is particularly preferable to keep the temperature difference between the leucoindigo foam and the warp yam sheet constant via closed loop control of the foam and warp yarn sheet temperatures. Temperature differences of 10 to 70°C, in particular of 15 to 40°C, are preferred.

[0030] In a further preferred embodiment of the process of the present invention, the warp yarn sheet is subjected to a pretreatment before dyeing. In this pretreatment, auxiliaries and/or colorants can be applied to the warp yarn sheet. Auxiliaries are for example the commercially available wetting agents described above and also the fastness improvers also described above.

[0031] Colorants are for example customary sulfur, vat, reactive and direct dyes. The pretreatment typically is followed by a drying step which in turn is followed by the dyeing step.

[0032] The process of the present invention provides in particular an acceptable depth of shade on a single pass of the warp yarn sheet through the foam chamber. As a result, appreciably smaller volumes of wastewater are generated, so that appreciable economic advantages are achieved.

[0033] It will be appreciated that it is nonetheless possible to pass the warp yarn sheet through the foam chamber as often as desired.

Claims

1. A process for dyeing cellulosic warp yarns with indigo by applying a leucoindigo foam to the warp yarns and subsequently oxidizing the leucoindigo to indigo, wherein the warp yarns are led through an entry opening into a sealed foam chamber and have leucoindigo foam applied to them therein before they reemerge from the foam chamber through an exit opening, the longitudinal tension of the warp yarns being closed loop controlled such that they are in a state of free suspension within the foam chamber, wherein the warp yarn sheet is very substantially cooled down immediately before entry into the foam chamber.

2. The process as claimed in claim 1 wherein the foam chamber is equipped with or connected to at least one suitable leucoindigo foam applicator device which is supplied from the foam generator.

3. The process as claimed in claim 1 and/or 2 wherein the foam chamber is equipped with or connected to a plurality of applicator devices, in particular 2 to 5, which are each disposed transversely to the warp yarn sheet at short distances apart.

4. The process as claimed in claim 3 wherein the foam chamber is equipped with or connected to 2 to 5 applicator devices.

5. The process as claimed in one or more of claims 1 to 4 wherein gas locks are disposed upstream of the entry opening and downstream of the exit opening of the foam chamber.

6. The process as claimed in claim 1 wherein the warp yarn sheet is cooled down to temperatures of 25 to -10°C immediately before entry into the foam chamber.

Ansprüche

1. Verfahren zum Färben von zellulosischen Kettfäden mit Indigo durch Auftragen eines Leukoindigoschaums auf die Kettfäden und folgendem Oxidieren des Leukoindigos zu Indigo, wobei die Kettfäden durch eine Eingangsöffnung in eine versiegelte Schaumkammer geleitet werden, worin Leukoindigoschaum darauf aufgebracht wird, bevor sie aus der Schaumkammer durch eine Ausgangsöffnung austreten, wobei der Längszug der Kettfäden geregelt wird, sodass diese innerhalb der Schaumkammer in einem Zustand freier Suspension befinden, wobei die Kettfadenschar unmittelbar vor dem Eingang in die Schaumkammer sehr substantiell abgekühlt wird.

2. Verfahren nach Anspruch 1, wobei die Schaumkammer ausgestattet oder verbunden ist mit mindestens einer geeigneten Aufbringvorrichtung des Leukoindigoschaums, die von dem Schaumgenerator versorgt wird.

3. Verfahren nach einem der Ansprüche 1 und/oder 2, wobei die Schaumkammer ausgestattet oder verbunden ist mit mehreren Aufbringvorrichtungen, insbesondere mit 2 bis 5, die jeweils quer zu der Kettfadenschar in kurzen Abständen voneinander angeordnet sind.

4. Verfahren nach Anspruch 3, wobei die Schaumkammer ausgestattet oder verbunden ist mit 2 bis 5 Aufbringvorrichtungen.

5. Verfahren nach einem der vorherigen Ansprüche 1 bis 4, wobei Gasschleusen stromaufwärts der Eingangsöffnung und stromabwärts der Ausgangsöffnung der Schaumkammer angeordnet sind.

6. Verfahren nach Anspruch 1, wobei die Kettfadenschar unmittelbar vor dem Eingang in die Schaumkammer auf eine Temperatur von 25 bis -10 °C abgekühlt wird.

Revendications

1. Procédé de teinture de fils de chaîne cellulosiques avec de l'indigo consistant à appliquer une mousse de leuco-indigo sur les fils de chaîne et ensuite à oxyder le leuco-indigo en indigo, dans lequel les fils de chaîne sont conduits, à travers une ouverture d'entrée, dans une enceinte de mousse hermétiquement fermée et s'y voient appliquer une mousse de leuco-indigo avant de ré-émerger de l'enceinte de mousse à travers une ouverture de sortie, la tension longitudinale des fils de chaîne étant contrôlée en boucle fermée de sorte qu'elles soient dans un état de suspension libre à l'intérieur de l'enceinte de mousse, dans lequel la feuille de fils de chaîne est très sensiblement refroidie juste avant de pénétrer dans l'enceinte de mousse.

2. Procédé selon la revendication 1 dans lequel l'enceinte de mousse est équipée de, ou reliée à, au moins un dispositif applicateur de mousse de leuco-indigo convenable qui est fourni par le générateur de mousse.

3. Procédé selon la revendication 1 et/ou 2 dans lequel l'enceinte de mousse est équipée de, ou reliée à, une pluralité de dispositifs applicateurs, en particulier 2 à 5, qui sont chacun placés en position transversale par rapport à la feuille de fils de chaîne et à faible distance les uns des autres.

4. Procédé selon la revendication 3 dans lequel l'enceinte de mousse est équipée de, ou reliée à, 2 à 5 dispositifs applicateurs.

5. Procédé selon l'une quelconque des revendications 1 à 4 dans lequel des bouchons de gaz sont placés en amont de l'ouverture d'entrée et en aval de l'ouverture de sortie de l'enceinte de mousse.

6. Procédé selon la revendication 1 dans lequel la feuille de fils de chaîne est refroidie à des températures de 25 à -10°C juste avant de pénétrer dans l'enceinte de mousse.