Abstract:
Dyeing a cellulosic textile substrate with reduced indigo dye in a leuco state after foaming with an inert gas to maintain the dye isolated from oxidizing substances. Following application of the foam to the substrate, it is exposed to the adjacent atmosphere, with the oxygen in the atmosphere oxidizing the reduced indigo dye to regenerate it and cause it to affix to the textile substrate. A product can be produced using the method and apparatus of the present invention that has different dye characteristics on opposite surfaces of the substrate by applying the indigo dye foam to one surface and another dye, either an indigo dye or some other dye to the opposite surface.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a method and apparatus for dyeing cellulosic textile substrates with an inert leuco state dye and a dyed product. More particularly, the present invention relates to a method and apparatus for dyeing cellulosic textile substrates with a reduced leuco state dye foamed with an inert gas and applied in the leuco foamed state to the textile substrate and oxidized thereon to affix the indigo dye to the cellulosic textile substrate. The present invention also relates to a dyed cellulosic textile product, to one surface of which is dyed by a leuco state dye and the other surface dyed by a dye having a different characteristic in shade, color or type.  
         [0002]     Dyeing cellulosic textile material, such as cotton yarn or fabric, with a leuco state dye, such as indigo dye, has a large market, particularly for cotton denim clothing items, such as blue jeans. The fastness of the indigo dye on cotton and the deep color or shade that can be obtained make indigo dyed fabric a very popular commodity. However, dyeing cellulosic textile material with indigo dye is a complicated, complex and expensive procedure, because indigo in its natural state will not affix to cellulosic fibers. To render the indigo dye capable of affixing to cellulosic fibers, it is necessary to reduce the indigo by removing oxygen as by mixing with hydro (hydrogen sulfide) or other reducing agents to render the indigo a colorless leuco state material. It then must be handled to remain in a substantially leuco state until it is applied to the cellulosic textile material. To be capable of being applied, the leuco state indigo dye must be sufficiently dilute to penetrate into the interstices of the cellulosic material. Typically, indigo dye is obtained from a supplier in a paste form that is, for example, in a 40% solution. It then must be further diluted to, for example, a 2% solution with a non-oxidizing liquid, such as hydro, to be capable of penetration into a traveling textile substrate that is immersed through a vat of the diluted indigo dye. Because of this dilution, it is necessary to pass the textile substrate through a series of sequential indigo dye vats with intermediate exposure to the atmosphere or other oxidizing agents to set the indigo applied during the preceding immersion. To obtain a desired deep color or shade, it is common to utilize a dyeing range having anywhere from four to eight, dye vats in series with arrangements of guide rolls between vats to assure proper oxidation of the indigo between vats. In addition, the dye in the vats must be continuously and rapidly recirculated in a tank or tanks into which reduced water or other similar material is added and regulated to remove oxygen taken up in the dye vats and to return any oxidized indigo dye to the reduced leuco state.  
         [0003]     A typical prior art dye vat section of a rope dyeing range is illustrated in  FIG. 1 . The section S consists of a series of eight individual dye vats, each containing a solution of indigo dye D. A rope of yarn Y is guided around a series of immersed rolls I in each bath and then guided around a series of guide rolls G above each vat V to expose the yarn Y to the atmosphere for oxidization of the indigo dye that has been picked up from the preceding vat V. The multiple applications of indigo dye through the series of vats are necessary for the dye to reach a desired shade or color depth. To maintain a level concentration of indigo dye in solution in all of the vats V, the dye solution in all of the vats V are continuously recirculated to be charged with new dye and resubjected to a reducing agent or agents to maintain the desired leuco state for application to the substrate being dyed. As a result, the indigo dyeing is expensive, complicated and inefficient.  
         [0004]     Furthermore, because both surfaces are exposed to the same dye bath when the material is immersed in the dye vats, it is practicably impossible to dye a cellulosic fabric, such as cotton denim, with an indigo dye on one surface and another dye of a different shade, color or type on the opposite surface.  
         [0005]     Another significant problem with prior art indigo dyeing ranges is that of waste water disposal. Because of the numerous vats and the amount of dye liquor that must be provided, there is a significant quantity of dye liquor that must be disposed of at the end of every dyeing operation. This creates an undesirable substantial expense and environmental problem.  
         [0006]     In contrast to the prior art, the present invention provides a method and apparatus for dyeing cellulosic material with indigo dye in a single application without requiring multiple baths and multiple oxidation sections. This greatly reduces the amount and cost of equipment, the complexity of operation and waste water disposal problems. It also allows dyeing of opposite surfaces of a fabric with dyes of different shades, colors or types.  
       SUMMARY OF THE INVENTION  
       [0007]     Briefly described, the present invention provides a method and apparatus for dyeing cellulosic textile substrate and a product dyed thereby. The method involves providing a supply of reduced dye in a leuco state, substantially isolating the leuco state dye from oxidizing substances, generating a foam of the leuco state dye and an inert gas while maintaining the dye in its leuco state, applying the foam to at least one surface of the substrate, and exposing the applied foam on the substrate to an oxidizing substance to regenerate the dye and affix it to the textile substrate.  
         [0008]     Preferably, the cellulosic textile material is cotton and may be dyed either in the form of a sheet of warp yams or in the form of a rope of yarn or in the form of a denim fabric.  
         [0009]     The dye is preferably an indigo dye used in its commercially available form as indigo paste or prereduced indigo at approximately 40% concentration.  
         [0010]     Isolating the leuco state dye from oxidizing substances can be obtained by providing a supply of the reduced dye in a closed container with an inert gas covering the top surface of the dye in the container. This inert gas is preferably nitrogen. Also, a floating cover may be applied to the dye in the container with the cover substantially covering the top surface of the dye.  
         [0011]     Preferably, the exposing of the foam to an oxidizing substance is exposing the foam to the atmosphere after it is applied to the substrate.  
         [0012]     In one form of the invention, the foam is applied to only one surface of the substrate, and another dye of the same type, or of the same form, or of a different type or form or shade or color is applied to the opposite surface so that different dye characteristics appear on the opposite sides of the substrate. The different characteristics may be differences in shade, color or type of dye.  
         [0013]     In generating the foam, a blow ratio in the range of 0.01:1 to 50:1 may be utilized, with a preferred blow ratio of approximately 3:1.  
         [0014]     The apparatus for dyeing a cellulosic textile substrate with a leuco state dye according to the present invention includes a container for containing a supply of dye in a leuco state. The container substantially isolates the dye from oxidizing substances. A foam generator generates a foam of the leuco state dye with an inert gas while maintaining the dye in the leuco state. A foam applicator applies the foam to at least one surface of the substrate with the substrate with the foam applied being free for exposure to an oxidizing substance to regenerate the dye and affix the dye to the textile substrate.  
         [0015]     Preferably, a cover is provided for floating on the dye in the supply container, with the cover covering substantially the entire surface of the dye in the container, which is preferably a closed container. A supply of inert gas is connected to the container for supplying inert gas to the container as dye is delivered from the container to the generator.  
         [0016]     In the preferred embodiment, the textile substrate is a traveling substrate and the applicator includes a nozzle extending across the traveling substrate for application of the foam to one surface of the substrate. In the preferred embodiment, the applicator includes a distribution chamber that uniformly distributes foam across the extent of the nozzle and onto the substrate.  
         [0017]     If desired, another foam applicator may be provided for applying foam to the opposite surface of the substrate.  
         [0018]     Preferably, the apparatus is open exteriorly of the applicator for exposure of the foam applied to the substrate to the atmosphere for oxidation of the dye, thereby affixing the dye to the substrate.  
         [0019]     In the preferred embodiment, the dye is an indigo dye in leuco state and the cellulosic textile product is a cotton denim fabric with a first indigo dye on one surface of the fabric and a different second dye on the opposite surface. The two dyes may have different characteristics, such as differences in shade, color or type, and they both may be regenerated indigo dyes or may be of different dye types.  
         [0020]     Also, in the preferred embodiment the apparatus is purged of any oxygen before providing the leuco state dye by purging the apparatus with a fluid that does not contain oxygen, such as an inert gas or reduced water. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a schematic illustration of a prior art indigo dyeing section of a rope dyeing range;  
         [0022]      FIG. 2  is a schematic illustration of an apparatus for dyeing according to the preferred embodiment of the method and apparatus of the present invention, producing the dyed product of the present invention;  
         [0023]      FIG. 3  is a vertical sectional view of a supply tank containing dye in leuco state in the apparatus of  FIG. 1 ; and  
         [0024]      FIG. 4  is an alternate form of an indigo supply container for use with the apparatus of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]     The apparatus  10  of the preferred embodiment of the present invention is illustrated in  FIGS. 2, 3  and  4 . Referring first to  FIG. 2 , the apparatus includes a supply container or feed tank  12  containing a supply of indigo dye  14  in a reduced leuco state. Conveniently, this indigo dye  14  can be used in the form received from a supplier, which typically may be a paste of 40% concentration. However, it is to be understood that various concentrations may be used as desired for particular dyeing application. For example, water can be added to reduce the concentration to any other suitable amount, such as 20%. Also, conventional pigments, penetrants and foaming agents can be added to vary the shade or color and to facilitate application. In a typical example, the pigment and penetrant additives may reduce the indigo dye concentration to, for example, 32%.  
         [0026]     To maintain the dye in its leuco state in the feed tank  12 , a floating cover  16  is positioned on top of the dye  14  in the feed tank  12 . The cover  16  has a flat base  18  extending over substantially the entire surface of the dye  14 , leaving only sufficient clearance at the edges for the cover to be able to move freely in response to the change in the level of the dye in the tank. To guide the movement of the cover and provide a seal of the dye from air or inert gas in the tank above the level of the dye, the cover  16  is formed with a peripheral, upstanding flange  20 . The clearance between the peripheral flange  20  and the wall of the feed tank  12  is only of an extent sufficient to permit free movement of the cover within the container. For example, a gap  22  of no more than 1/16 th  inch can be employed. Some small amount of dye will flow into the gap  22 , and the top surface of that dye may be exposed to air in the tank, which will oxidize the exposed dye, creating indigo particles, which themselves contribute to forming a seal in the gap  22 , thereby facilitating the isolation of the dye in its leuco state from the air above the cover  16 .  
         [0027]     The feed tank  12  may be open to the atmosphere above the supply of dye  14 , but preferably, as illustrated in  FIG. 3 , the feed tank  12  is covered by a top plate  26  and an inert gas, such as nitrogen, is fed through the top plate  26  from an upstanding inlet pipe  24 .  
         [0028]     If desired, a soft resilient seal of any conventional material can be provided around the peripheral flange  20  to further maintain isolation of the reduced indigo dye from exposure to any air or other oxygen that may be in the feed tank  12  above the floating cover  16 . The floating cover  16  may not be necessary, if the feed tank  12  and its top plate  26  provide a sufficient seal so that air cannot leak into the feed tank  12  above the level of the dye in the tank and contaminate the nitrogen or inert gas sufficiently to result in undesirable oxidation of the dye.  
         [0029]     A purge pipe  30  is mounted on the top plate  26  and opens into the interior of the feed tank  12  with a flap valve or other conventional valve preventing reverse flow of atmosphere through the purge pipe  30  into the interior of the feed tank  12 . When inert gas is fed through the inlet pipe  24 , the purge pipe  30  allows escape of air or other gases as they are being replaced by the nitrogen. The purge pipe  30  also allows escape of nitrogen so as to maintain a desired pressure of nitrogen in the feed tank  12 . The purge pipe  30  further serves to allow initial purging of the feed tank  12  prior to initial loading of dye into the feed tank. This purging is accomplished by nitrogen or other inert gas being introduced into the bottom of the feed tank  12  through a purge feed line  32  controlled by a valve  34 .  
         [0030]     While nitrogen is used as the preferred inert purging material, other inert fluids, such as reduced water, which is water containing hydro (sodium hydro-sulfide), may be used. With the entire apparatus filled with fluid, there will not be any air in the apparatus to oxygenize the leuco dye.  
         [0031]     Feed of the dye liquor supply  14  into the feed tank  12  is through an inlet pipe  28  near the bottom of the feed tank  12  and is controlled in a conventional manner with sensors (not shown) that sense the level of the dye liquor  14  in the feed tank  12  to control feed of the dye liquor through the inlet pipe  28  to maintain the level of the dye liquor  14  in the feed tank  12  between set limits.  
         [0032]     The reduced indigo dye  14  in its leuco state is conveyed through a conduit  36  at the bottom of the feed tank  12  through a conventional strainer/filter mechanism  38  to a foam generator  40 . This foam generator  40  is a conventional foam generator of the type commonly used to generate dye carrying foam for application to traveling textile substrates, such as yarns and fabric. It differs in use from a conventional foam generator in that instead of the gas for foaming being air, it is nitrogen or some other inert gas that, by its nature, will maintain the isolation of the reduced indigo dye from oxidation. The nitrogen is supplied through a nitrogen supply line  42 . The foam generated in the foam generator  40  is conducted through a foam feed line  44  to the inlet  48  of an applicator  50 . The applicator  50  may be of any conventional type suitable for a desired application. In the preferred embodiment, the applicator is the type disclosed in Zeiffer U.S. Pat. No. 4,655,056, issued Apr. 7, 1987. It includes a parabolically shaped distribution chamber  52  with the inlet  48  located in the center of the base chord and a parabolically shaped divider panel  54  mounted in the distribution chamber  52  at a spacing therewithin so that the foam entering the inlet  48  flares upwardly and outwardly to the edge of the panel  40  and then over the edge of the panel and vertically downward to a nozzle  56  at the base of the distribution chamber  52 . In this manner, the distance of travel of the foam to the nozzle is of the same length along the nozzle  56  and the foam will be in the same condition for disposition on a traveling substrate uniformly across the width of the nozzle  56 . The substrate  58  is a cellulosic material, such as cotton or rayon. In one embodiment, the substrate  58  is a sheet of warp cotton yarns intended for weaving denim blue jean fabric. The substrate  58  travels beneath the nozzle  56 , which extends transversely across the traveling substrate for application of foam  60  thereto. If desired, more than one nozzle may be utilized and other forms of nozzles and applicators can be used.  
         [0033]     As the substrate  58  with the foam  60  deposited thereon travels away from the applicator  50 , the foam is exposed to the atmosphere and is free for oxidation of the reduced indigo dye as the foam degenerates on and in the traveling substrate  58 . As the indigo dye is oxidized, it regenerates and affixes to the substrate  58 .  
         [0034]     In operation, the apparatus is readied for application of the indigo dye by first purging the feed tank  12  by introducing nitrogen into the feed tank  12  through the nitrogen inlet pipe  24 . Reduced dye in a leuco state is then fed into the feed tank  12  through the dye supply inlet pipe  28  until a desired level of dye is in the feed tank  12 . The operation is then begun by feeding the dye from the supply  12  to the foam generator  40 . The operation of the foam generator is adjusted to generate foam at a blow ratio suitable for the particular application. This blow ratio may be in the range of 0:01 to 50:1. In a typical operation, the blow ratio may be approximately 3:1.  
         [0035]     The foam  60  is then fed from the foam generator  40  to the applicator  50  and is maintained in its reduced leuco state isolated from any oxidizing substance, such as air. With the foam so isolated, it passes through the applicator  50  and is deposited on the traveling sheet of warp yarns  58  and is then free for contact by the atmosphere, the oxygen in which oxidizes the originally reduced indigo dye  14  as the foam dissipates on the substrate, with the result that the indigo dye affixes itself in and to the yarn  58 . The oxidation can be facilitated by applying an oxidizing gas in addition to the atmosphere as the substrate leaves the applicator  50 .  
         [0036]     Foaming agents of any desired known type can be introduced in the foam generator to facilitate foaming and pigments, reactives, sulfurs and penetrants may be added to the dye before or while the dye  14  is in the feed tank  12 .  
         [0037]     It can be advantageous for the dye to be applied once to obtain a desired color or shade, contrary to the multiple immersions required to build a shade with conventional indigo dyeing apparatus.  
         [0038]     One of the advantages of the apparatus of the present invention that may be taken advantage of is dyeing different surfaces of a traveling substrate with dyes of different shade, color or type. For example, the apparatus  10  illustrated in  FIG. 2  can be used to apply a second foam to the surface of the substrate opposite that to which the foam is applied by the apparatus described heretofore. In this case, the foam applied by the first, second or both applicators may be controlled so that the dye carried in the foam from one or both of the applicators would not penetrate fully through the fabric on to the opposite surface.  
         [0039]     The second applicator  50 ′ and the components that feed foam to it are identical to those described above, which are indicated with the same reference numerals with a prime symbol. This apparatus  10 ′ includes a feed tank  12 ′ containing a supply of reduced indigo dye in leuco state, which may be a different shade, color or type than that applied by the first applicator  50 ′. This second apparatus  10 ′ also includes a foam generator  40 ′ to which a supply line  42 ′ supplies nitrogen, and from which the foam  60 ′ is supplied to the applicator  50 ′ that applies the foam  60 ′ to the traveling substrate  58 ′.  
         [0040]     If desired, a dye other than indigo can be applied to the second surface of the substrate by the second apparatus  10 ′, which dye may be a reduced dye using the apparatus as described or it can be any other conventional dye that is foamed in any other conventional manner and applied to the surface of the substrate. Also, some other second apparatus may be used to apply foamed or non-foamed dye.  
         [0041]      FIG. 4  illustrates an alternative to the feed tank  12  illustrated in  FIGS. 2 and 3 . In this alternative, instead of a feed tank, a replaceable container  62  of the type received from a supplier containing reduced indigo dye in a leuco state is attached directly to the feed line  36  to the foam generator  40 . This container  62  is closed and has an inlet tube  64  through which the supplier filled the container  62  and which is maintained closed during operation. A vent tube  66  opens into the container  62  for venting of the interior of the container when the reduced indigo dye is introduced. When the container  62  is emptied during operation, another container  62  will be substituted and the operation continued.  
         [0042]     After a dyeing operation has been concluded, the remaining indigo dye is drained from the apparatus and the components are flushed to remove any remaining dye, particularly any indigo dye that has been oxidized and regenerated into insoluble particles. Preferably, the flushing is accomplished using reduced water, which, when coming in contact with regenerated indigo dye particles, will cause reduction of the particles into clear soluble material that can be easily drained from the system with the reduced water. Reduced water can also be used during operation by being added to the feed tank  12  to counteract any tendency of the indigo dye to oxidize.  
         [0043]     In view of the aforesaid written description of the present invention, it will be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications, and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to preferred embodiments, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended nor is to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.