DIFFERENTIALLY VAT DYED YARNS AND METHOD OF MAKING THE SAME

Abstract

Yarns are described herein which, in some embodiments, comprise plies or single strands dyed with at least one vat dyestuff yielding a tweed or heathered appearance. In one aspect, a yarn comprises a first ply and a second ply each dyed with at least one vat dyestuff, wherein a difference in color depth (DL*) between the dyed first single strand and the dyed second single strand has an absolute value of at least 2 when the vat dyestuff is in an oxidized state. As described further herein, the first ply and the second ply are dyed in the same dyebath. In another aspect, a yarn comprises a first ply and a second ply each dyed with at least one vat dyestuff, wherein a reflectance ration between the second ply and the first ply ranges from 0.05 to 0.95.

Description

RELATED APPLICATION DATA

The present application claims priority pursuant to Article 8 of the Patent Cooperation Treaty to U.S. Provisional Patent Application Ser. No. 63/152,118 filed Feb. 22, 2021 and U.S. Provisional Patent Application Ser. No. 63/283,716 filed Nov. 29, 2021, each of which is incorporated herein by reference in its entirety.

FIELD

The present application relates to vat dyed yarns and, in particular, to vat dyed yarns comprising plies yielding a tweed or heathered appearance.

BACKGROUND

Current processes for producing colored nylon floor coverings, such as carpets, have several disadvantages. Acid dyes, for example, are commonly employed for coloration of nylon fibers used in carpet yarns due to the ease with which cationic nylon polymer accepts the dye. This ease of dyeing, however, also facilitates staining if the nylon fibers are exposed to contaminants having dye-like properties during use. Moreover, acid dyes are commonly applied to nylon fibers in batch or continuous processes. Under this approach, a risk exists of ozone fading if the material is installed in a tropical environment. Treatments have been developed to improve resistance of acid dyed nylon to ozone fading. These treatments include novolak resins, acrylic polymers, tannic acid or various combinations thereof. Such treatments, nevertheless, can alter shades of the dyed fiber and/or induce a reduction in lightfastness of the dyed fibers.

Moreover, these disadvantages further complicate producing nylon floor coverings having a tweed or heathered appearance. In many cases, acid dyed nylon plies of differing color are individually produced and subsequently twisted or entangled. Lack of tight color control in the acid dyed batches can produce color anomalies degrading the tweed or heathered effect.

SUMMARY

In view of the foregoing, yarns are described herein which comprise plies dyed with at least one vat dyestuff yielding a tweed or heathered appearance. In one aspect, a yarn comprises a first ply and a second ply each dyed with at least one vat dyestuff, wherein a denier ratio between the first ply and the second ply is greater than 1. In another aspect, a yarn comprises a first single strand and a second single strand each dyed with at least one vat dyestuff, wherein a difference in color depth (DL*) between the dyed first single strand and the dyed second single strand has an absolute value of at least 2 when the vat dyestuff is in an oxidized state. In some embodiments, an absolute value of DL* ranges from 2-50 or from 3-30. An absolute value of DL* can also range from 5-20 or 10-30, in some embodiments. As set forth herein the terminology of “first ply and second ply” can be interchangeable with “first single strand and second single strand”. As described further herein, the first ply and the second ply can be dyed in the same dyebath in a single dyeing process. In another aspect, a yarn comprises a first ply and a second ply each dyed with at least one vat dyestuff, wherein a reflectance ratio between the second ply and the first ply ranges from 0.05 to 0.95. In some embodiments, the reflectance ratio ranges from 0.4 to 0.6. The first ply and second ply of yarns described herein can be formed of any desired composition. In some embodiments, the first ply and second ply are synthetic fibers. The first ply and second ply, for example, can be formed of polyamides. Additionally, yarns described herein can be used to fabricate various textile articles including floor coverings, such as carpet.

In another aspect, a yarn comprises a first ply and a second ply each dyed with at least one vat dyestuff, wherein the first ply and second ply are formed of differing polyamides. In some embodiments, the polyamide of the first ply has lower crystallinity than the polyamide of the second ply. The first ply, for example, can be formed of nylon 6, and the second ply is formed of nylon 6,6. Moreover, the polyamide of the second ply can exhibit anionic character, in some embodiments. The polyamide of the second ply may comprise a sulfur content. The polyamide yarn can exhibit any of the denier and/or reflectance ratios described herein.

In another aspect, methods of dyeing yarns are described herein. A method, in some embodiments, comprises providing a yarn comprising a first ply and a second ply, and contacting the yarn with a dyeing composition comprising at least one vat dyestuff in reduced form. Once applied to the first and second plies, the vat dyestuff is oxidized, wherein the dyed first ply exhibits a darker or deeper color than the dyed second ply. The darker or deeper color of the first ply can originate from more of the vat dyestuff being received or exhausted onto the first ply relative to the second ply. In some embodiments, a difference in color depth (DL*) between the dyed first ply or single strand and the dyed second ply or single strand has an absolute value of at least 2 when the vat dyestuff is in an oxidized state. In some embodiments, DL* ranges from 2-50 or from 3-30. Moreover, in some embodiments, a denier difference between the first ply and second ply can yield a reflectance difference, wherein the lower denier ply reflects less light leading to a lighter coloring.

These and other embodiments are further described in the detailed description which follows.

DETAILED DESCRIPTION

Embodiments described herein can be understood more readily by reference to the following detailed description, examples, and drawings. Elements, apparatus, and methods described herein, however, are not limited to the specific embodiments presented in the detailed description, examples, and drawings. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations will be readily apparent to those of skill in the art without departing from the spirit and scope of the invention.

In one aspect, a yarn comprises a first ply and a second ply each dyed with at least one vat dyestuff, wherein a denier ratio between the first ply and the second ply is greater than 1. In some embodiments, the denier ratio is greater than 1.5 or greater than 2. The denier ratio between the first ply and the second ply, for example can range from 1.2 to 10, in some embodiments. The denier ratio can be chosen according to several consideration including, but not limited to, the composition of the first and second plies, the chemical identify of the vat dyestuff, and exhaustion levels of the vat dyestuff on the first ply and the second ply. In some embodiments, the first ply has a denier of 12 or higher, and the second ply has a denier less than 12. The denier ratio or disparity between the first ply and the second ply can be employed to modulate individual reflectance values of the first and second plies. The higher denier first ply, for example, can exhibit higher reflectance while the lower denier second ply exhibits lower reflectance. This gradient in reflectance can render the second ply lighter in color to the observer, yielding the desired tweed or heathered effect.

In another aspect, a yarn comprises a first ply and a second ply each dyed with at least one vat dyestuff, wherein a reflectance ratio between the second ply and the first ply ranges from 0.05 to 0.95. In some embodiments, the reflectance ration ranges from 0.3 to 0.7 or from 0.4 to 0.6.

The first ply and second ply of yarns described herein can be formed of any desired composition. The first ply and the second ply can be formed of the same composition or differing compositions. The first ply and the second ply can comprise synthetic compositions, natural compositions, or various combinations of synthetic and natural compositions. Specific compositions of the first ply and the second ply are chosen according to the technical objectives described herein of providing a yarn with a tweed or heathered appearance. In some embodiments, for example, the first ply and second ply can be selected or chemically engineered to receive differing amounts of the vat dyestuff. The first and second plies, for example, can exhibit differing levels of crystallinity. The first ply can exhibit lower crystallinity than the second ply, thereby providing an inter-chain structure for receiving higher amounts of the vat dyestuff relative to the higher crystallinity second ply. Moreover, in some embodiments, the first ply can exhibit a chemical structure more receptive to the vat dyestuff relative to the second ply. The first ply can comprise a higher number of cationic moieties or moieties having positive dipole moments for interaction with the anionic character of the vat dyestuff relative to the second ply. Additionally, the second ply can comprise a higher number of anionic moieties or moieties having negative dipole moments for repelling or otherwise interfering with the anionic character of the vat dyestuffs during the dyeing process. Such chemical tailoring can result in more vat dyestuff being exhausted onto the first ply than the second ply, thereby yielding the desired color differential between the plies to provide a tweed or heathered appearance.

The foregoing technical principles are illustrated by forming the first ply and the second ply of differing polyamides. The first ply, for example, can be nylon 6, and the second ply is nylon 6,6. The nylon 6 exhibits lower crystallinity relative the nylon 6,6. The lower crystallinity can provide a more open structure for receiving greater amounts of the vat dyestuff. Additionally, the nylon 6 may include greater number of cationic amine groups for interaction with the vat dyestuff. In contrast, the nylon 6,6 fiber can comprise a sulfur content for generating anionic moieties or functionalities for repelling or otherwise interfering with anionic character of the vat dyestuff in the dyeing process. In some embodiments, the nylon 6,6 can comprise a sulfur content of at least 2,000 ppm. The nylon 6,6, for example can have a sulfur content of 2,000 to 3,300 ppm.

Yarns having construction and properties described herein can be used to provide a variety of textile products. In some embodiments, the yarns are employed in floor coverings, such as carpets. The yarns, for example, can be tufted and coated to produce a finished tweed or heathered carpet. Alternatively, the yarn comprising the first ply and the second ply can be tufted into a greige carpet construction, and subsequently dyed in batch mode or continuous mode using a vat dyeing system. The vat dyes greige is subsequently coated to provide a finished tweed or heathered carpet.

In addition to exhibiting the color differentiation between the first and second plies described herein, the dyed yarns can also display enhanced lightfastness, wet fastness, color fastness to ozone and/or resistance to household bleach. Dyed yarn, for example, can be resistant to undiluted household bleach or diluted bleach of 0.3% sodium hypochlorite solution. In some embodiments, the nylon fibers dyed with one or more vat dyestuffs can meet one or more criteria set forth in Table I.

TABLE I
Properties of Dyed Nylon Fibers
		Grayscale
Property	Test	(GS) Rating
Lightfastness	AATCC Test Method 16, Option	3-5
Color Fastness to Ozone	AATCC 129	4-5
Wet Fastness	Transfer to undyed control	4-5
Household Bleach	Application of household	4-5
Resistance	bleach (24 hrs)

Any vat dyestuff not inconsistent with the objectives of the present invention can be applied to nylon fibers having construction and/or properties described. Suitable vat dyestuffs can contain two or more ketone groups separated by a system of conjugated bonds. In some embodiments, vat dyestuffs include indigo and derivatives thereof. Vat dyestuffs may also include various derivatives of anthroquinones. Table II provides a non-limiting list of vat dyes for use with nylon fibers according to some embodiments described herein.

TABLE II
Vat Dyestuffs for Nylon Fiber Dyeing
Vat Yellow 33
Vat Green 13
Vat Brown 1
Vat Brown 3
Vat Brown 57
Vat Blue 6
Vat Black 22
Vat Black 25
Vat Black 27
Vat Yellow 4
Vat Green 1

In another aspect, methods of dyeing yarns are described herein. A method, in some embodiments, comprises providing a yarn comprising a first ply and a second ply, and contacting the yarn with a dyeing composition comprising at least one vat dyestuff in reduced form. Once applied to the first and second plies, the vat dyestuff is oxidized, wherein the dyed first ply exhibits a darker or deeper color than the dyed second ply. The darker or deeper color of the first ply can originate from more of the vat dyestuff being received or exhausted onto the first ply relative to the second ply, as described herein. Moreover, in some embodiments, a denier difference between the first ply and second ply can yield a reflectance difference, wherein the lower denier ply reflects less light leading to a lighter coloring. Notably, the first ply and the second ply are combined to form the yarn prior to dyeing in the same or common vat dyebath. Therefore, the differential color effects between the dyed first ply and second ply are achieved in a single dyebath or single vat dyeing process. The ability to achieve the differential color effects in a single or common process realizes process efficiencies over individual dyeing of the first ply and second ply followed by combining the individually dyed plies into the yarn construction.

The dyeing composition can include one or more vat dyestuffs in any amount not inconsistent with the objectives of the present invention. In some embodiments, vat dyestuff is present in the dyeing composition at an add-on level of at least 0.1% on weight fiber. Vat dyestuff can also be present in the dyeing composition at add-on levels according to Table III.

TABLE III
Amount of Dyestuff(s) on weight fiber (owf)
≥0.25
≥0.5
≥1
0.1-1
0.25-1

The dyeing composition including one or more vat dyestuffs can be prepared according to several techniques. In some embodiments, an aqueous dispersion of one or more vat dyestuffs is initially provided. Purified water free or substantially free of hardening species such as calcium and magnesium can be used as the dispersion continuous phase. Alternatively, one or more water softening agents can be added to the dispersion to sequester hardening species. Such purified or treated water is generally referred to as soft water herein. Vat dyestuff(s) are added to the continuous aqueous phase in amounts consistent with the add-on levels provided in Table III. The continuous aqueous phase may be heated to a temperature of 30-35° C. and mixing may be employed to assist in dispersion of the vat dyestuff(s).

A reducing system is prepared for combination with the aqueous dispersion of the vat dyestuff(s). In some embodiments, a reducing system comprises one or more chemical species for reducing the vat dyestuff(s), thereby placing the dyestuff(s) in the water soluble form. Reduction of the vat dyestuff(s) may convert the dyestuff(s) to leuco form, in some embodiments. Any suitable reductant species not inconsistent with the objectives of the present invention can be employed. Sodium dithionite and/or sodium hydrosulfite, for example, can be a reductant for one or more vat dyestuffs. In some embodiments, ferrous sulfate can be used in conjunction with sodium dithionite for dyestuff reduction. The reducing agent can be added to soft water to provide the reducing system. In some embodiments, the water is heated to a temperature of 30-35° C., and the one or more reductants are added with mixing or other mechanical agitation. Amounts of reducing agent added to the soft water can be sufficient to reduce all or substantially all of the vat dyestuffs employed in the dyeing process. Once dispersion and wetting of the reducing system has been achieved, it can be added to the exhaust dyeing equipment containing the dispersed form of the vat dyes and an initial water charge. In some embodiments, a reducing system is not necessary as the vat dyestuffs are provided in reduced form from the manufacturer. For example, a solution of reduced vat dyestuff can be commercially available and used in accordance with methods described herein.

One or more alkaline species for adjusting the pH of the dyeing composition is dispersed in soft water. Caustic soda (NaOH) or aqua ammonia, for example, can be employed as an alkaline pH adjusting agent. Other pH adjusting agents are well-known in the art and may also be used. Once produced, the pH adjusting composition is added to the exhaust dye equipment. In a further step of the dyeing composition, dispersing agent(s) and/or leveling agent(s) are added. Polyvinylpyrrolidone, for example, can serve as a dispersing agent for the vat dyestuffs as well as a providing some retarding and leveling action. Moreover, if carrier is found to be useful for a given formulation, benzyl alcohol can be used. Additionally, many options exist for dispersing agents, leveling agents, carriers and/or swelling agents that may be useful for nylon fiber dyeing compositions. Table IV provides amounts of reducing and pH adjustment agents for dyeing compositions having various dyestuff concentrations (owf) for application by exhaust dyeing systems.

TABLE IV
Reducing and pH Adjustment Agents
	Dyestuff Concentration	Sodium Dithionite	Caustic Soda 50%
	(owf)	(g/L)	(g/L)
	0.1%	2-3	2.5-3.5
	0.11-1.0%	2-3	4-5
	>1.0%	3-4	5-7

Table V provides amounts of reducing and pH adjustment agents for dyeing compositions having various dyestuff concentrations (owf) for application by a continuous dyeing system at 450% wet pick up.

TABLE V
Reducing and pH Adjustment Agents
	Dyestuff Concentration	Sodium Dithionite	Caustic Soda 50%
	(owf)	(g/L)	(g/L)
	0.1%	4-5	9-10
	0.11-1.0%	5-7	14-16
	>1.0%	6-8	17-20

Table VI provides amounts of reducing and pH adjustment agents for dyeing compositions having various dyestuff concentrations (owf) for application by continuous space dyeing at 100% wet pick up.

TABLE VI
Reducing and pH Adjustment Agents
	Dyestuff Concentration	Sodium Dithionite	Caustic Soda 50%
	(owf)	(g/L)	(g/L)
	0.1%	18-22	28-32
	0.11-1.0%	23-27	33-37
	>1.0%	28-32	38-42

Additionally, Table VII provides various liquor ratios (LR) for exhaust dyeing, continuous dyeing and continuous space dyeing processes according to some embodiments.

TABLE VII
Liquor Ratios
Dyeing Process   Liquor Ratio
Exhaust          25:1
Continuous       4.5:1
Continuous Space 1:1

With reference to application by exhaust dyeing equipment, initial mixing and wetting out of the nylon fiber, yarn or greige by the dyeing composition can be allowed to occur over a time period of at least 15 minutes at a temperature of 30-35° C. A temperature ramp is subsequently administered. In some embodiments, temperature is ramped at 1.5° C./min to an 80° C. hold for 45 minutes. Once the dyeing cycle is complete, the bath can be overflowed for initial cooling followed by draining off the spent dyebath from the exhaust dyeing apparatus. A rinse bath of ambient water is then provided, and the dyed nylon fibers are circulated through the bath for a minimum of 15 minutes to remove any unfixed material from the fiber surfaces. Depending on dyeing composition, it may be helpful to add an organic acid component, such as acetic acid, to assist in unfixed material removal and to lower pH of the nylon fibers. In some embodiments, 30-80 percent dyestuff exhaustion is achieved.

After rinsing, the dyed nylon fibers are removed from the exhaust dyeing apparatus and extracted to mechanically remove as much water as possible, without fiber damage. The extracted fibers are then subjected to air drying. Air drying can occur at ambient temperature or elevated temperatures. In some embodiments, for example, air drying occurs at temperatures of 200-300° F., such as 240-260° F. Drying is continued until a moisture content of 5% or less is achieved. The drying process also serves as an oxidation step for the vat dyestuffs on the nylon fibers. This drying and oxidation fixes the vat dyestuffs on the nylon fibers, greatly improving their fastness properties listed in Table I herein. Dyestuff oxidation and fixing during the heating process fundamentally differs from prior processes where one or more oxidizing agents are employed for vat dyestuff oxidation. For example, prior processes can use peroxide and/or other oxidants for dyestuff oxidation. The present method surprisingly oxidizes and fixes the vat dyestuffs in the absence of such oxidizing species, thereby simplifying the dyeing process.

For continuous dyeing processes, the main difference with exhaustion processes is the separation of the vat dyestuff dispersion from the reducing system until just prior to application of the dyeing composition to the nylon fibers. For example, a bath containing the pre-dispersed vat dyestuff(s) can be held in Tank A while Tank B contains the reducing system, pH adjustment agent(s) and other auxiliary materials such as wetting agents, leveling agents, carriers and the like. The contents of Tanks A and B are metered and mixed together in appropriate ratio to provide the dyeing composition. The dyeing composition is then applied to the nylon yam or carpet greige being processed continuously through either a space dye line (in the case of yam) or a continuous broad loom dye range (in the case of nylon carpet greige). After the two baths are combined and applied, the fiber can be exposed to heat to promote exhaustion of the vat dyestuff(s) on the fibers. Generally, saturated steam can be used as the heat source. After the heating cycle, the dyed fibers can be rinsed, extracted and dried as described above. The drying process oxidizes the vat dyestuff(s).

In some embodiments, a pretreatment process is applied to one or more of the plied, including the cationic ply and/or the anionic ply. The pretreatment process can be incorporated into example methods to increase the hydrophobic character of the cationic poly and/or the anionic ply. For instance, the pretreatment can include contacting a ply with a wax (e.g., in the form of a wax emulsion) to produce a wax-finished ply.

Certain embodiments of the disclosure can include a yarn made from at least two plies (e.g., a first ply and a second ply), where one of the at least two plies is a wax-finished ply. In these embodiments, the yarn can have a construction defining the spatial relationship between the wax-finished ply and one or more other plies of the at least two plies, along the length of the yarn. As an example for illustration, one type of construction can include a “barberpole” construction, where the wax-finished ply and one of the other plies are twisted or otherwise wrapped around each other to create a diagonal stripping effect. With such a striping effect, a point moving from one position on the yarn to a second position along the length of the yarn would cross from the wax-finished ply to the other ply wrapped around it and then cross the wax-finished ply again repeating the pattern.

Aspects of barber pole constructions can include a regular or irregular striping effect. In a regular stripping effect, the positions of the wax-finished ply and the other ply wrapped around it are regularly spaced so that along a length of the yarn, the position of the wax-finished ply repeats at least every 2 mm (e.g., between 0.2 cm and 2 cm, between 0.5 cm and 1.5 cm, between 0.5 and 1 cm, or between 0.6 and 0.8 cm). This effect can be adjusted in several manners. For instance, the thickness of the wax-finished ply and/or the other ply wrapped around it may be adjusted. Alternatively or additionally, the number and/or density of twists in the yarn may be adjusted. For constructions having an irregular stripping effect, the position of the wax-finished ply is not regularly spaced and so does not have a specific repeating value.

More particularly, some constructions can be produced by arranging the first ply and the second ply to produce the construction. Aspects of arranging the first ply and the second ply can include introducing twists into the yarn at a density of 1 twists per inch to 10 twists per inch, such as 2 to 8, 1 to 5, or 8 to 10 twists per inch. In these constructions, the twists can be regularly spaced to produce a regular stripping effect or irregularly spaced to produce an irregular striping effect. In certain constructions the density of twists may vary along the length of the yarn or may be constant.

Embodiments of the disclosure can also include methods for producing a dyed yarn. Example methods for producing a dyed yarn can include obtaining a first ply and a second ply, optionally, applying a pretreatment process to at least one of the first ply, the second ply, or both arranging the first ply and the second ply to form a yarn having a construction, for example, a barberpole construction, exposing the yarn to a dyebath including at least one vat dyestuff in reduced form (i.e. reduced vat dyestuff), and oxidizing the vat dyestuff applied to the yarn.

Some advantages of preparing dyed yarns according to methods of the present disclosure can include improved color differentiation between the first ply and the second play. For instance, it has been discovered that pretreatment of the ply or plies prior to dyeing the yarn can produce a greater difference in color values between the first play and the second ply in comparison to untreated ply or plies. Additionally, properties such as ionic character (e.g., anionic or cationic) can impact dyestuff uptake. Further, these differences in dye uptake can be realized in a more economic manner by exposing the yarn including the plies to the dyebath together, rather than separately dying each of the plies. Thus yarns in accordance with the present disclosure may demonstrate improve color values for providing a heathered or tweed appearance, while also presenting economic advantages in manufacturing.

In some example embodiments, various fiber properties can be achieved through differentiation between a first ply and a second ply, for example to achieve a barberpole and/or heathered effect with a vat dyestuff application. In some instances, a first ply or filament can be darker after dyeing and a second ply or filament can be lighter after dyeing. Differences between the plies after dyeing can enable the tuning of various properties of a fiber. In some embodiments, total ply denier can be varied where a first ply has a total denier greater than a second ply, and a second ply has a total ply less than the first ply. In some embodiments, denier per filament can be varied where a first ply has a high denier per filament relative to a second ply (i.e. fewer filaments of larger cross section) and the second ply has a lower denier per filament relative to the first ply (i.e. higher number of total filaments of smaller cross section). In some embodiments, luster level (e.g. TiO₂ content) can be varied where a first ply has a higher luster value relative to a second ply (i.e. lower TiO₂ content) and the second ply has a lower luster value relative to the first ply (i.e. higher TiO₂ content). In some embodiments, filament cross section (e.g. modification ratio) can be varied where a first ply has a higher modification ratio (MR) cross section relative to a second ply (i.e. more angular cross section), and the second ply has a lower MR cross section relative to the first ply (i.e. more rounded cross section). In some embodiments, a nylon chemical property can be varied where a first ply is cationic or highly cationic and/or having a high amine group content (e.g. relative to a second ply), and a second ply is anionic or highly anionic, having a high sulfur content (e.g. relative to the first ply). In some embodiments, nylon physical characteristics can be varied where a first ply has a low crystallinity (e.g. nylon 6 type) and a second ply has a higher crystallinity (e.g. nylon 6.6 type). In some embodiments, extrusion finish properties can be varied where a first ply has a high wetting speed finish (i.e. to promote high dyestuff exhaustion) and a second ply has a low wetting speed finish or a repellant finish, for example a wax finish (e.g. to promote low dyestuff exhaustion).

Various embodiments of the invention have been described in fulfillment of the various objectives of the invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention.

EXAMPLES

The examples herein provide aspects of embodiments of the present disclosure. These examples are not meant to limit embodiments solely to such examples, but rather to illustrate some possible implementations.

Table 1 was developed by, first, producing 11 different twisted, heatset yarn packages, using dyeable commercial yarns for carpet use. Self-plied yarn packages were produced from each yarn type, using 5.25 twist per inch settings, and Superba heat setting.

The 1200 Ascend yarn, 2200 parts sulfur, was used to create a series of dyed yarn skeins, using a range of strengths, from 0% (no dyestuff present) to 1.5% owf dyestuff, in increments of 0.25% owf dyestuff. This information was used to create a relationship between L* value (depth of color) and the % owf of the dyestuff, for estimating how much dyestuff was present on the dyed yarn combinations produced for this study.

The dyestuff used was color index Vat Black 27, sold by Dystar as Indanthrene Olive R Liquid. An Ahiba lab dyeing apparatus was used and a Gretag Macbeth Color-eye 7000A was used for color measurements to determine the tristimulus values of the cut end of the dyed skeins. The L* information was used to determine DL* (delta L*) differences between the two yarns dyed competitively in each test case, as well as to determine an estimate of the amount of Vat Black 27 present on each yarn skein.

TABLE 1
Example attributes of dyed yarn skeins.
		Nylon	Total						OL R
	Vendor	Type	Denier	Info	DPF	Comments	L*	% OL R	% of Tot	DL*
1a	Ascend	6.6	1200	2200 pts S	7	semi dull	54.65	0.502	42.91	−4.54
2	Invista	6.6	1425		12	semi dull	50.11	0.6678	57.09
1b	Ascend	6.6	1200	2200 pts S	7	semi dull	56.68	0.436	30.03	−13.6
3	Ascend	6.6	1700	KET	26	semi dull	43.1	1.016	69.97
1c	Ascend	6.6	1200	2200 pts S	7	semi dull	48.79	0.737	50.46	0.3
4	Ascend	6.6	1352	3300 pts S	21	semi dull	49.09	0.7237	49.54
1d	Ascend	6.6	1200	2200 pts S	7	semi dull	58.53	0.3831	29.91	−12.9
5	Ascend	6.6	1360	NET	20	semi dull	45.67	0.8977	70.09
1e	Ascend	6.6	1200	2200 pts S	7	semi dull	53.14	0.553	44.63	−3.39
6	Ascend	6.6	1352	2200 pts S	21	semi dull	49.75	0.686	55.37
1f	Ascend	6.6	1200	2200 pts S	7	semi dull	53.31	0.5449	19.22	−22.6
7	Invista	6.6	1245		19	bright	30.67	2.29	80.78
1g	Ascend	6.6	1200	2200 pts S	7	semi dull	54.66	0.498	22.17	−20.4
8	Ascend	6.6	1320	KET	20	semi dull	34.25	1.748	77.83
1h	Ascend	6.6	1200	2200 pts S	7	semi dull	62.12	0.2922	29.07	−12.9
9	Ascend	6.6	1285	NET	10	semi dull	49.18	0.7128	70.93
1i	Ascend	6.6	1200	2200 pts S	7	semi dull	58.77	0.382	16.67	−25.9
10	Aquafil	6	1395		19	semi dull	32.88	1.91	83.33
1j	Ascend	6.6	1200	2200 pts S	7	semi dull	56.24	0.445	28.15	−15.2
11	Ascend	6.6	1200	CET	7	bright	41.08	1.136	71.85

Table 2 displays dying properties for two twisted yarn packages. In one of the packages, a wax pretreatment (NF818 5%) applied prior to dying. The resulting dyed yarn has a larger DL* value compared to the yarn without pretreatment.

TABLE 2
Comparison of dying properties between wax pretreated yarn and control
Vendor	Type	Denier	Info	DPF	L*	% OL R	% of Tot	DL*
Ascend	6.6	1200	2200 S	7	48.32	0.7508	44.39189	4.39
Aquafil 5 min	6	1395	control	19	44.16	0.9405	55.60811
Ascend	6.6	1200	2200 S	7	48.88	0.7122	38.82257	6.06
Aquafil 5 min	6	1395	NF818 5%	19	40.67	1.1223	61.17743

Claims

1. A yarn comprising:

a first single strand and a second single strand each dyed with at least one vat dyestuff, wherein a difference in color depth (DL*) between the dyed first single strand and the dyed second single strand has an absolute value of at least 2 when the vat dyestuff is in an oxidized state.

2. The yarn of claim 1, wherein the first single strand and the second single strand are dyed with the same vat dyestuff.

3. The yarn of claim 1, wherein the first single strand and second single strand are formed of polyamides.

4. The yarn of claim 3, wherein the polyamides of the first single strand and the second single strand are different.

5. The yarn of claim 4, wherein the polyamide of the first single strand has lower crystallinity than the polyamide of the second single strand.

6. The yarn of claim 4, wherein the first single strand is formed of nylon 6, and the second single strand is formed of nylon 6,6.

7. The yarn of claim 4, wherein the polyamide of the first single strand has a differing number of amine end groups relative to the polyamide of the second single strand.

8. The yarn of claim 1, wherein the first single strand and the second single strand have differing sulfur contents.

9. The yarn of claim 1, wherein the first single strand and the second single strand exhibit a difference in wetting speed of the vat dyestuff.

10. The yarn of claim 9, wherein the first single strand or the second single strand includes a wax finish.

11. The yarn of claim 1, wherein the first single strand and the second single strand have differing TiO2 contents.

12. A textile composition comprising the yarn of claim 1.

13. The textile composition of claim 12, wherein the textile composition is a floor covering.

14. The textile composition of claim 13, wherein the floor covering is carpet.

15. A method of dyeing a yarn comprising:

providing a yarn comprising a first single strand and a second single strand;

contacting the yarn with a dyeing composition comprising at least one vat dyestuff in reduced form; and

oxidizing the vat dyestuff applied to the yarn, wherein the dyed first strand exhibits a darker color than the dyed second strand.

16. The method of claim 15, wherein a difference in color depth (DL*) between the dyed first single strand and the dyed second single strand has an absolute value of at least 2 when the vat dyestuff is in the oxidized state.

17. The method of claim 15, wherein the first single strand and the second single strand are dyed with the same vat dyestuff.

18. The method of claim 15, wherein the first single strand and second single strand are formed of polyamides.

19. The method of claim 18, wherein the polyamides of the first single strand and the second single strand are different.

20. The method of claim 19, wherein the polyamide of the first single strand has lower crystallinity than the polyamide of the second single strand.

21. The method of claim 19, wherein the first single strand is formed of nylon 6, and the second single strand is formed of nylon 6,6.

22. The method of claim 19, wherein the polyamide of the first single strand has a differing number of amine end groups relative to the polyamide of the second single strand.

23. The method of claim 15, wherein the first single strand and the second single strand have differing sulfur contents.

24. The method of claim 15, wherein the first single strand and the second single strand exhibit a difference in wetting speed of the vat dyestuff.

25. The method of claim 24, wherein the first single strand or the second single strand includes a wax finish.

26. The method of claim 15, wherein the first single strand and the second single strand have differing TiO2 contents.

27. A yarn comprising:

a first ply and a second ply each dyed with at least one vat dyestuff, wherein at least one of the first ply and the second ply is wax-finished

28. The yarn of claim 27, wherein the first ply and the second ply are twisted around one another to produce a barberpole construction.

29. The yarn of claim 27, wherein the first ply and the second ply are dyed with the same vat dyestuff.