INDIGO AND RING DYEING PROCESS USING SULFUR DYE AS BARRIER, AND MATERIAL PRODUCED THEREBY

Abstract

A method of ring dyeing a yarn includes the steps of providing a cellulosic yarn chosen from the group consisting of open-end yarns and ring yarns. The yarn is immersed in only one sulfur dye box, the sulfur dye box having a sulfur concentration of 1 to 50 grams/liter. The yarn is skyed for less than 30 seconds after removal from the sulfur dye box. The yarn is rinsed in water after skying. The yarn is dyed in an indigo dye bath, with the indigo dye bath maintained at a pH of 10.8 and 12.8. The yarn is skyed after removal from the indigo dye box.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to yarn dyeing, such as yarn dyeing using indigo or sulphur dyes in general and, more particularly, to a process providing a dyed yarn having reduced dye penetration and a white core, i.e., ring dyeing effect. The invention also is directed to yarns dyed on dye ranges through use of the process, and fabrics formed from the dyed yarns. A barrier of a sulfur dye is applied initially to the periphery of the yarn to serve as a barrier minimizing dye penetration by later-applied sulfur and/or indigo dyes.

2. Description of the Related Art

Indigo and sulfur continuous yarn dyeing typically result in solid dyed (no ring dyed) or partially ring dyed yarn, particularly cellulose yarns. The parameters which control the degree of ring dyeing for indigo and sulfur continuous yarns are indigo and sulfur dye properties, immersion time, air oxidation time, pH (caustic presence in the dye bath), dyeing temperature, yarn twist, yarn tension on the continuous dyeing machine and others.

Sulfur dye, once dyed on cellulosic fiber, makes a bigger molecule due to dye and cellulose bonding. For the case of indigo dyeing over sulfur dye, the sulfur molecule covers the free sites of cellulose and provides a barrier preventing the indigo dye molecule from traveling towards the core of the yarn. To protect the core of the cellulosic yarn and create a ring of dyed fiber on the circumference of the yarn, sulfur dyeing should be in ring form. To restrict the sulfur dye to the ring form on cellulosic yarn, the dyeing recipe and process parameters of conventional practices do not achieve a satisfactory ring dye effect. For these purposes, we mean the ring dye effect as the outer periphery of the yarn being dyed with a white or near white core largely undyed. Because of the ring dye effect, laser abrading may be utilized to achieve the worn look without requiring the use of potassium permanganate and other chemicals, which are hazardous to the environment.

SUMMARY OF THE INVENTION

The present invention is directed to a method for a method for forming a sulfur dye barrier on a yarn, with the sulfur barrier minimizing dye penetration by subsequently applied sulfur and/or indigo dyes, and thereby achieving the ring dye effect.

A method of ring dyeing a yarn includes the steps of providing a cellulosic yarn chosen from the group consisting of open-end yarns and ring yarns. The yarn is immersed in only one sulfur dye box, the sulfur dye box having a sulfur concentration of 1 to 50 grams/liter. The yarn is skyed for less than 30 seconds after removal from the sulfur dye box. The yarn is rinsed in water after skying. The yarn is dyed in an indigo dye bath, with the indigo dye bath maintained at a pH of 10.8 and 12.8. The yarn is skyed after removal from the indigo dye box.

A method of ring dyeing a yarn includes the steps of providing a cellulosic yarn chosen from the group consisting of open-end yarns and ring yarns. The yarn is immersed in only one sulfur dye bath for between 6 to 14 seconds, the sulfur dye bath having a sulfur concentration of 1 to 50 grams/liter. The yarn is skyed for less than 30 seconds after removal from the sulfur dye bath. The yarn is rinsed in water after skying. Thereafter, the yarn is dyed in a dye solution for between 6 to 14 seconds, the dye solution maintained at a pH of 10.8 to 12.8. Thereafter, the yarn is skyed for 30 to 140 seconds.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated in and constitute a part of the specification. The drawings, together with the general description given above and the detailed description of the exemplary embodiments and methods given below, serve to explain the principles of the invention. The objects and advantages of the invention will become apparent from a study of the following specification when viewed in light of the accompanying drawings, in which like elements are given the same or analogous reference numerals. In these drawings:

FIG. 1 illustrates various common yarn dye scenarios;

FIG. 2 illustrates schematically a dye range comprising a plurality of vats according to an exemplary embodiment of the invention;

FIG. 3 is a schematic view of a structure of a vat;

FIG. 4 is a front elevation view of a garment manufactured from yarns dyed according to the present invention;

FIG. 5 is a rear elevation view of the garment manufactured from yarns dyed according to the present invention;

FIG. 6 is Table 1 containing—Conventional Dyeing Specifications for Sulfur; and

FIG. 7 is Table 2 containing—Sulfur Barrier Dyeing Specifications according to the disclosed invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

Reference will now be made in detail to exemplary embodiments and methods of the invention as illustrated in the accompanying drawings, in which like reference characters designate like or corresponding parts throughout the drawings. It should be noted, however, that the invention in its broader aspects is not limited to the specific details, representative devices and methods, and illustrative examples shown and described in connection with the exemplary embodiments and methods.

This description of exemplary embodiment(s) is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description, relative terms such as “horizontal,” “vertical,” “up,” “down,” “upper”, “lower”, “right”, “left”, “top” and “bottom”, “front” and “rear”, “inwardly” and “outwardly” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. The term “operatively connected” is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship. The term “integral” (or “unitary”) relates to a part made as a single part, or a part made of separate components fixedly (i.e., non-moveably) connected together. The words “smaller” and “larger” refer to relative size of elements of the apparatus of the present invention and designated portions thereof. Additionally, the word “a” and “an” as used in the claims means “at least one” and the word “two” as used in the claims means “at least two”. For the purpose of clarity, some technical material that is known in the related art has not been described in detail in order to avoid unnecessarily obscuring the disclosure.

FIG. 1 depicts five common yarn dye scenarios 1.1-1.5, with the understanding that the circular shape represents a yarn, and the dark coloring represents the penetration of dye from the outside of the yarn toward the inner portions of the yarn. While we illustrate the yarn as circular, those skilled in the art understand that a yarn is not strictly circular and instead is generally circular with non-uniform diameter due to the fibers used to manufacture the yarn.

Example 1.1 is a yarn 10₁ dyed completely, or nearly completely to the core, i.e., having a complete or nearly complete dye penetration 12d, and leaving very little of an original or undyed white core 12c. The yarn 10₁ when viewed as a cross-section may appear to be solid in color, or possibly lighter in color toward the core 12c₁ but still obviously dyed through the core 12c₁.

Example 1.2 is a yarn 10₂ with significant dye penetration 12d and, to the unassisted eye, still appears quite dark. The core 12c of the yarn 10₂ may be an even lighter color, or possibly even have a few fibers within the center that appear white, but the excessive penetration creates a barrier difficult to penetrate by laser abrasion.

Example 1.3 is a yarn 10₃ with a core 12c₃ that with the unassisted eye may appear to be white, or significantly lighter shade. The dye penetration 12d is difficult to penetrate by laser abrasion alone as it extends too far inwardly from the perimeter of the yarn 10₃.

Example 1.4 is a yarn 10₄ that is dyed without consistency as measured from the perimeter of the yarn 10₄. The yarn 10₄ displays a large area of the yarn that is undyed, revealing lighter shades of dye, or even large areas of white in the yarns. These are some of the least desirable yarns, as they result in streaking and inconsistencies after weaving, with uncontrolled portions being dyed vs undyed. Similarly, laser penetration is received as randomly as the dye, leaving patches and undesirable peppering of areas that were intended to have dye removed, but many areas are impenetrable.

Example 1.5 illustrates ring dyeing: a lesser degree of dye penetration forming a concentric ring 12d while leaving a central core of the yarn without dye, i.e., displaying consistency in dye penetration with a dark shade on the perimeter of the yarn 10₅ and a white or nearly white core 12c₅. This type of yarn readily receives laser energy sufficiently to avoid the need for potassium permanganate or other oxidative or reductive treatments used to remove dye during manufacturing. This type of yarn is disclosed in this invention as an improved ring dyeing effect for indigo dyeing, sulfur dyeing, or a combination thereof.

Preferably, implementation of the disclosed invention results in consistent dye penetration of about 10% to about 35% of the cross-sectional area of the yarn. Dyeing the periphery with controlled depth penetration and allowing the core to remain white is advantageous, particularly when the fabric resulting from yarn dyeing is subjected to laser abrasion, manual abrasion, and/or oxidizer treatments to remove color.

The yarn dyed according to the disclosed invention is an open-end yarn and/or a ring yarn made of cotton fibers, with the randomness of the fibers introducing some variables, which, when paired with inconsistencies in twist, etc., result in some variation in dye penetration relative to the perimeter of the yarn. The results of the disclosed invention are to minimize the variability as much as possible. The yarns of the present invention are cellulose blends, such as cotton, and modified cellulose yarns, such as Viscose, Lyocell, and their blends.

Open-end yarns are known in the art as the type of yarn that can be produced without using a spindle. The spindle is one of the core components of yarn making. Open-end yarn is produced by using a process called open end spinning. Repeatedly drawing a yarn stretched into the rotor produces open-end yarn. Open-end yarn can be produced from short fibers. Open-end yarns are different from ring yarns. Open-end yarns are limited to coarser counts. The open-end yarn is highly cost-effective since it is made by using even the shortest cotton strands. The number of twists must be greater than the ring system to assure integrity. As a result, it has a more branched or irregular structure.

Ring yarns are known in the art as produced from the long fibers of cotton. Ring yarn is divided into carded, combed, and siro spun type. The difference between open-end and ring yarns is due to the combing process. The combing process is the intensive combing process of the raw material (cotton) that feeds the machine with the help of the combs in the machine, and thus the short fibers of the cotton are separated. Depending on the cotton used and the machine settings, 5-25% fiber can be extracted from the raw material and evaluated differently. The difference of combed yarn from carded yarn is that it is produced using longer fibers obtained after the combing process. Carded and combed yarn is of higher quality than open-end yarn.

FIG. 2 depicts an exemplary embodiment of a dye range 20 for performing the method (or process) for dyeing yarn according to the disclosed invention. The dye range 20 comprises a number of stages 22₁-22₅, some of them including large boxes (vats or tanks) 24₁ and 24₃.

In view of the structural similarities of the vats 24₁ and 24₃, and in the interest of simplicity, the following discussion will sometimes use a reference numeral without a subscript to designate an entire group of substantially identical structures. For example, the reference numeral 24 will be used when generically referring to the vats 24₁ and 24₃, rather than reciting all two reference numerals.

The vats 24 are structurally substantially identical and commonly filled with liters of chemicals, water, and/or dye. The vats 24 serve different purposes, and therefore have chemicals that differ from box to box. A cross sectional view of one of the vats 24 according to the disclosed invention is illustrated in FIG. 3. The vats 24 each includes an open top container 25, a lead-in roller 28₁, a lead-out roller 28₂, a plurality of immersion guide rollers 30, and nip rollers 32. The lead-in roller 28₁ guides the yarn over an edge of the container 25 at an angle appropriate for the subsequent immersion guide rollers 30. The immersion guide rollers 30 are rollers that the yarns are threaded over or under and extend the width of the container 25. The depth of the container 25, the number of immersion guide rollers 30, the distance between the immersion guide rollers 30, the diameter of the rollers 30, and the processing speed of the dye range 20 are variables that cumulatively determine the immersion time the yarns spend in the chemistry within each box 24.

Like the lead-in roller 28₁, the lead-out roller 28₂ guides the yarn over the edge of the container 25, and sets the yarn at an approach angle towards the nip rollers 32 that follow.

The nip rollers 32 are pairs or sets of rollers that apply pressure between themselves and to the yarn passing therebetween. In the case of dye range 20, the nip rollers 32 squeeze the yarns and pull the yarns through the dye range 20. Each time the yarns are immersed in a container 25 of a vat 24, the yarns are, without exception, subsequently passed to nip rollers 32. Squeezing the yarn between two rollers 32 removes much of the liquid and chemistry on the yarn, and returns that liquid and chemistry back to the vat 24 from which the yarn just emerged. The pressure between the top and bottom nip rollers 32 is adjusted predominantly through air pressure applied to cylinders that press the top nip roller 32 down onto the bottom nip roller 32, although sometimes additional weights are added to the top roller. The squeezing pressure of the nip rollers 32 can be in the range of 40 to 95 PSI and the preferred range is 60 to 85 PSI.

Each vat 24 may include a heating element 34 within the container 25. Heating elements 34 each include a series of pipes that are immersed in the chemistry or water within the container 25. The pipes are filled with steam when the range operator determines it wishes to heat a vat 24, thereby steam heating the vat. In order best utilize the steam of heating elements 34, the wash boxes are used with direct steam heating and the dye boxes are used with indirect steam heating. This is because when steam is used for heating, it condenses in the vat 24 when used as direct heating. In the case of a dye box, the condensate steam may reduce the dye concentration, so heating is done indirectly (with a closed circuit coil). The size or proportions of the containers 25 are a variable, with many different configurations throughout the world. Likewise, the size, placement, and number of the rollers before and within the immersion stage and after are a variable, with many different configurations throughout the world.

Conventional dyeing methods use high concentration of caustic as a pretreatment, and include sulfur dyeing with one or more dye boxes 24, longer immersion times, higher skying tines, and use of wetting agents in the sulfur dye chemistry. Table 1 shows that even after the usage of caustic for pretreatment there is no ring dye effect achieved with conventional methods. The disclosed invention produces good ring dyeing by reducing the immersion time of the yarn in the dye vat, reducing the skying time for sulfur-dyed yarn, and utilizing full skying time for indigo dye.

The method for dyeing the yarn according to the present invention comprises a series of stages.

First, in sulfur dyeing stage 22₁, best shown in FIG. 2, the ring yarn without caustic pretreatment or like chemical is immersed into and passed through a single (i.e., only one) sulfur dye vat 24₁ containing sulfur dye. The sulfur in the sulfur dye vat 24₁ is maintained at a pH between 10.0 and 13.7, and the immersion time is between 6 to 14 seconds. When the sulfur dye is used in bottoming, the concentration of the sulfur dye in the sulfur dye vat 24₁ is in the range of 1 to 50 grams/liter, considering 100% strength of dyes. This is the case when no pre-treatment of the cellulosic yarn is done, as noted above, and the yarn directly goes to the sulfur dye vat 24₁ in the dry state. The temperature of the sulfur dye in the sulfur dye vat is in the range of 50 to 100° C., preferably between 65° C. and 85° C. The sulfur dye can be applied in the millivolt (MV) range of −480 to −750 MV. The preferred MV range is −580 to −700 mv. Based on the shade required, the concentration of the sulfur dye required may increase and thus the MV increases. The darker the shade, the higher the concentration of sulfur and thus the higher the MV. Reducing chemicals may be used to keep MV in the preferred range, and excess usage is avoided to avoid slow oxidation of dye. Reducing chemicals, such as glucose, sodium sulfide, sodium hydrosulfide, and polysulfide in the sulfur dye can be measured by testing the MV of the dye solution. The sulfur dye in the sulfur dye vat 24₁ is maintained at a temperature in the range of 50 to 100° C., preferably 65° C. to 85° C.

Ring yarn, when treated directly with sulfur dye as mentioned above without caustic pretreatment, creates a sulfur barrier that allows less dye penetration compared to open-end yarn. Both yarn compactness and natural impurities of fats and waxes of cellulose reduce dye penetration. Sulfur dye application according to the disclosed invention further restricts the dye to a ring form, on an outer circumference of the cellulosic yarn, and the ring dyeing further restricts indigo dye penetration when applied in sulfur dye vat 24₁ with restricted immersion time. Ring yarn, when dyed with the sulfur barrier according to the invention, achieves the ring dye effect, leaving a clean white core inside the yarn that can be treated with laser and/or hand sanding. The use of potassium permanganate to create the worn look is not necessary and can be eliminated. The sulfur dye concentration in the sulfur dye vat 24₁ for bottoming prior to the indigo dye application is from 1 gram/liter to 50 gram/liter.

After the step of sulfur dyeing the yarn, the yarn moves to a sulfur skying stage 22₂ for skying the ring yarn in the air (i.e., air oxidation using oxygen of air), for less than 30 seconds, preferably 1 to 18 seconds. As the skying time increases from 1 second to 30 seconds the dye penetration increases. The preferred range of exposing the dyed yarn to air is between 1 to 18 seconds. Based on the availability of the machine, the minimum yarn passage is utilized by bypassing the skying zone.

Next, in sulfur rinsing stage 22₃, best shown in FIG. 2, the ring yarn is rinsed in at least one sulfur rinse vat 24₃ filled with non-contaminated natural or fresh water, preferably at room temperature to remove residual sulfur. According to the disclosed invention, the sulfur rinse vat 24₃ follows immediately after the sulfur dye vat 24₁ and the sulfur skying stage 22₂. The dye range 20 may include as few as one sulfur rinse vat 24₃ or as many as 5 or more sulfur rinse vats 24₃ (i.e., one or more sulfur rinse boxes 24₃). The sulfur rinse box(es) 24₃ removes the chemistry on the yarn from the preceding step. The sulfur rinsing stage 22₃ immediately follows the sulfur skying stage 22₂ and reduces or eliminates the sulfur dye solution and contaminants absorbed by the yarns during the sulfur dyeing stage 22₁ before the next stage of yarn treatment. The removal of excess sulfur by a water wash can be tested by checking the pH and controlling it up to about pH 11.4. The preferred pH in the sulfur rinse vats 24₃ is 10.5 to 11. After the sulfur barrier application, the yarn is rinsed and then indigo dye is applied. The pH of the indigo is 11.4 to 11.6, so the sulfur rinse vats 24₃ pH should not be above 11.4.

Fresh water is continuously supplied to the sulfur rinse vat 24₃ immediately after the sulfur dye box 24₁. The fresh water provides fresh oxygen to oxidize the reduced sulfur dye. The oxidized dye is insoluble and does not react with cellulose by chemical bonds. The lower temperature of the water in sulfur rinse vats 24₃ limits dye travel toward the core of the yarn. Dye travel rate increases as temperature increases. The yarn coming from sulfur dye vat 24₁ is at an elevated temperature, and thus the sulfur dye tends to travel towards the core of the yarn. The immediate exposure of dyed yarns with fresh incoming water gives a thermal shock to the dyed yarn, and the temperature of the dyed yarn immediately reaches room temperature. At room temperature, the rate of travel for the dye molecule is minimized and the ring dye effect is preserved.

The water in the sulfur rinse vat 24₃ should be replenished continuously, so oxygen is available to oxidize the sulfur dye. The rate of water supply can be optimized in the range of 1 to 4 liter/kg of yarn, and it can be optimized by testing the pH of the water in the sulfur rinse vat 24₃ and controlling the pH under 11.4. The sulfur rinse vat 24₃ is preferably equipped with squeezing rollers 32, best shown in FIG. 3, that are arranged to remove unreacted sulfur dye from the yarn.

The preferred number of sulfur rinse vats 24₃ is a minimum one and a maximum 5 vats. The combination of restricted dye immersion time for the cellulosic yarn, restricted dyed yarn exposure time to air, and immediate water wash to oxidize the dye on cellulosic yarn and remove the unreacted dye helps maintain the sulfur dye in ring form on the outer circumference of the yarn. These techniques of sulfur dye application can be used for all types of fashion requirements of denim dyeing, including sulfur dye bottoming and indigo dye topping on the same yarn.

If the yarn is to have an indigo dye applied, then indigo dyeing stage 22₄ is best shown in FIG. 2. In indigo dyeing stage 22₄ the sulfur-dyed ring yarn is immersed into and passed through one or more indigo dye vats 24₄ containing indigo dye located immediately downstream of the sulfur rinse vats 24₃. The indigo in the indigo dye vat 24₄ is maintained at a pH between 10.8 and 12.8, preferably 11.4 to 11.6, and the immersion time in indigo dye vats 24₄ is between 6 to 14 seconds, preferably 7 to 11 seconds. The higher the immersion time, the higher is the dye penetration. Hence the immersion time in indigo dye vat 24₄ is restricted to optimized limits as shown above where a perfect ring dyeing is achieved with uniformity.

The indigo shade can be dyed in range of 0.5% to 7% as per the fashion requirement as an individual indigo shade or with sulfur dye combination of bottoming or topping or bottoming and topping both.

The MV of indigo dye vats is in the range of −680 to −780, and the preferred range is −715 to −725. In the case of indigo the redox potential is measured for the presence of free sodium dithionite (Sodium hydrosulfite, sometimes known as “Free Hydro”. The Free Hydro is the availability of excess sodium hydrosulfite in the indigo solution which keeps the indigo dye in fully reduced form. If the ‘Free Hydro’ reading falls below 0 gram/liter, then the amount of sodium hydrosulfite in the indigo solution is less than the amount required to keep indigo in reduced form. The higher the amount of ‘Free Hdro’, the reading represents excess hydrosulfite. The higher the presence of Free Hydro in the indigo solution, the slower the air oxidation of indigo when the yarn is skyed after leaving the indigo vat (after squeezing in nip rolls) and the dye penetration increases. So, to restrict the indigo dye penetration and to keep the indigo dye in a stable form in the dyeing vats, the amount of ‘Free Hydro’ is optimized and maintained in the range of 0.05 to 0.4 gram/liter, and the preferred range is 0.05 to 0.25 gram/liter.

The indigo shade can be dyed in a range of 0.5% to 7% as per the fashion requirement as an individual indigo shade or with sulfur dye combination of bottoming or topping or bottoming and topping. The sulfur shade can be applied in the range of 0.1% to 35% considering 100% strength of sulfur dye for topping after application of sulfur as a barrier in the range of 1 to 50 grams/liter.

The indigo dye vats 24₄ are large tanks containing a dye solution, such as sulfur black, sulfur brown, or indigo, within which the yarns 10 pass over a series of rollers 30. Various shades of sulfur may be used, such as olive, grey, brown, blue, red, yellow, etc.

The size of the indigo dye vats 24₄ is typically over 250 gallons each, with some as large as 700 gallons. The yarn path over or under rollers in the indigo dye vats 24₄ immerses the yarns 10 into the indigo dye solution. Good ring dyeing effect is achieved because the previously applied sulfur dye about the circumference of the yarn acts as a barrier to resist penetration of the core by the indigo dye.

Immersion of the yarn in the indigo dye vats is restricted, much as immersion is restricted for sulfur application, unlike sulfur, the indigo-dyed yarns are given maximum skying time to allow air oxidation of the dye. The skying time ranges from 30 to 140 seconds after each immersion in indigo. The preferred range of air oxidation is 45 to 120 seconds. The longer the skying time, the better is the oxidation.

After the step of indigo dyeing the yarn, the yarn moves to an indigo skying stage 22₅ for skying the dyed yarn for 30 to 140 seconds. As noted above, the air skying oxidizes the indigo dye.

Also, wetting chemicals or surface active agents are eliminated from the indigo dye solution. Wetting agents facilitate the dye penetration, and result in diffused dyeing. This is opposite to the ring dye effect being sought according to the present invention. So, in the present invention, the wetting agents are eliminated.

Following the indigo skying stage 22₅, the yarn moves to drying stage 22₆. Yarn drying in the drying stage 22₆ is accomplished by drying cans 38. The goal in drying the yarns is to match the moisture in the yarns with the humidity in the ambient air.

Sulfur barrier dyeing specifications according to conventional and the disclosed invention are shown in Tables 1 and 2.

Table 1, FIG. 6, contains data for conventional sulfur dyeing specifications, including specifying the pretreatment that was used. Examination of garments manufactured from yarns sulfur dyed by these specifications established that the ring dye effect was not achieved. Instead, the sulfur penetrated the yarn so that the core also was dyed. Such a yarn is difficult to laser abrade, typically requiring treatment by potassium permanganate. In Table 1, columns B to E are parameters common to conventional practices and disclosed invention. Columns H to N contain parameters for the pretreatment tank and rinsing after pretreatment. Columns O to V show data for the indigo vats. Column Q shows conventional indigo dyeing with immersion time longer than disclosed invention. Column V shows wetting agent in indigo.

Table 2, FIG. 7, contains data on sulfur barrier dyeing in accord with the disclosed invention. Included is the shade or dye type applied over the sulfur, the type of yarn, and its twist. The yarns in Table 2 had indigo applied over the sulfur barrier. Examination of the yarns of Table 2 established that the ring dye effect had been achieved. Column H shows pretreatment with sulfur dyes as a barrier for indigo dye. Columns H to O show parameters for sulfur pretreatment and rinsing after pretreatment. Column L shows temperature. Column M shows immersion time in in the sulfur bath and Column N shows skying time. Columns P to W show indigo dye parameters. Column R shows indigo immersion time, and Column W shows elimination of wetting agent.

FIG. 4 is an image of a garment manufactured from fabric produced according to the invention and without the use of potassium permanganate spray. The legs of FIG. 4 clearly have excellent detail, even though potassium permanganate treatment was not used.

FIG. 4 is an image of a garment with the legs made with fabric from yarns dyed according to the present invention. The garment of FIG. 4 was treated with a laser for the wearing effect. This garment was then washed with commercial washes. Conventional industry practice involves the application of potassium permanganate (PP) spray at the intermediate stage. The PP spray was not applied on the lasered area. The present invention shows a bright white wearing effect in the right leg of FIG. 4 due to the white core of the yarn. The garment of FIG. 4 shows how the present invention provides a fabric achieving the desired commercial look, conventional fabrics show the need for potassium permanganate spray to break down the dye on the lasered area, resulting in a non-bright effect.

FIG. 5 is an image of a garment produced from a fabric formed from yarns sulfur-barrier dyed according to the invention and thereafter laser abraded without use of potassium permanganate.

The sulfur dye molecule on the yarn in ring form works as a second barrier to minimize dye penetration. The combination treatment sequence for the dual barrier concept includes caustic pretreatment followed by washing to remove excess caustic. The yarn is then treated with sulfur dyes with restricted immersion time and minimized air oxidation time to achieve ring dyeing. Thereafter quick rinsing of the yarn in water is used to oxidize the sulfur dyes and remove unreacted dyes from the yarn. After rinsing, the yarn is dyed with indigo dyes utilizing restricted immersion time and full air oxidation, frequently with with multiple dye immersions based on the shade requirement of the yarn.

The foregoing description of the exemplary embodiments of the present invention has been presented for the purpose of illustration in accordance with the provisions of the Patent Statutes. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments disclosed hereinabove were chosen in order to best illustrate the principles of the present invention and its practical application to thereby enable those of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated, as long as the principles described herein are followed. Thus, changes can be made in the above-described invention without departing from the intent and scope thereof. It is also intended that the scope of the present invention be defined by the claims appended thereto.

Claims

1. A method of ring dyeing a yarn, comprising the steps of: providing a cellulosic yarn chosen from the group consisting of open-end yarns and ring yarns;immersing the yarn in only one sulfur dye box, the sulfur dye box having a sulfur concentration of 1 to 50 grams/liter;skying the yarn for less than 30 seconds after removal from the sulfur dye box;rinsing the yarn water after skying;dyeing the yarn in an indigo dye bath, the indigo dye bath maintained at a pH between 10.8 and 12.8; andskying the yarn after removal from the indigo dye box.

2. The method as defined in claim 1, including maintaining the sulfur dye bath at a temperature of 50 to 100° C.

3. The method as defined in claim 2, including maintaining the sulfur dye bath at a temperature of 65 to 85° C.

4. The method as defined in claim 1, including the step of providing a continuous water flow at room temperature for rinsing the yarn.

5. The method as defined in claim 1, including the step of skying the yarn after removal from the sulfur dye bath for less than 18 seconds.

6. The method as defined in claim 1, including the step of maintaining the indigo dye bath at a pH between 11.4 to 11.6.

7. The method as defined in claim 1, including the step of maintaining the indigo dye bath at −680 to −780 MV.

8. The method as defined in claim 7, including the step of maintaining the indigo dye bath at −715 to −725 MV.

9. The method as defined in claim 1, including the step of skying the yarn for 45 to 120 seconds after removal from the indigo dye bath.

10. The method as defined in claim 1, including the step of maintaining the sulfur dye at a pH of 10.0 and 13.7.

11. The method as defined in claim 1, including the step of maintaining the pH in the sulfur rinse bath under 11.4.

12. The method as defined claim 1, including the step of immersing the yarn in the sulfur dye bath for 6 to 14 seconds.

13. The method as defined in claim 1, including the step of skying the yarn for between 30 to 140 seconds after removal from the indigo dye bath.

14. A method of ring dyeing a yarn, comprising the steps of: providing a cellulosic yarn chosen from the group consisting of open-end yarns and ring yarns;immersing the yarn in only one sulfur dye bath for between 6 to 14 seconds, the sulfur dye bath having a sulfur concentration of 1 to 50 grams/liter;skying the yarn for less than 30 seconds after removal from the sulfur dye bath;rinsing the yarn in water after skying;thereafter dyeing the yarn in an indigo dye solution for between 6 to 14 seconds, the dye solution maintained at a pH of 10.8 to 12.8; andthereafter skying the yarn for 30 to 140 seconds.

15. The method as defined in claim 14, wherein the dye solution is one of indigo, sulfur black, and shades of sulfur.

16. The method as defined in claim 14, including the step of maintaining the sulfur dye at a temperature of 50 to 100° C.

17. The method as defined in claim 14, including the step of skying the yarn after removal from the sulfur dye bath for less than 18 seconds.

18. The method as defined in claim 14, including the step of rinsing the yarn with continuous water flow at room temperature.

19. The method as defined in claim 14, wherein skying the yarn lasts for between 45 to 120 seconds after removal from the indigo dye bath.

20. The method as defined in claim 14, including the step of maintaining the sulfur dye at a pH of 10.0 to 13.7.

21. A method of dyeing yarn, comprising the steps of: Providing a cellulosic yarn;Immersing the yarn in a caustic solution;Rinsing the yarn in water to remove excess caustic;Immersing the yarn is sulfur dyes for a limited immersion time;Skying the yarn after dyeing for a limited time to minimize air oxidation of the dye;Rinsing the yarn in water to oxidize the sulfur dyes and remove unreacted dyes from the yarn;Immersing the yarn in indigo for a limited immersion time; andSkying the yarn for a period sufficient to oxidize the indigo dye.

22. The method of claim 14, including the step of applying the sulfur dye with a MV between −680 and −800.

23. The method of claim 22, including the step of maintaining the MV between −715 and −725 MV.

24. A garment manufactured from a fabric having yarns dyed as defined in claim 1.