DESC:FIELD
The present disclosure relates to a process for continuous dyeing of cellulosic fiber yarns.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
Regenerated cellulose fiber: Regenerated cellulose fiber is a class of materials manufactured by the conversion of natural cellulose to a soluble cellulosic derivative and subsequent regeneration to a fiber form.
Rope Dyeing: Rope dyeing of yarns includes bundling the yarns into a rope, which is then quickly dipped into dyeing baths. Typically, in the rope dyeing method, warping and dyeing are done in the form of rope and sizing is done separately. In rope dyeing method, the steps of dyeing, washing and drying are carried out in a series. The rope dyeing is a faster process as well as ensures even dyeing through out the production cycle.
Slasher Dyeing: Slasher dyeing deploys a sheet of yarns, which is arranged directly onto a warp beam. In the Slasher dyeing, dye is applied in a series of multiple dip and oxidation process followed by washing and sizing on the same machine in the form of a yarns sheet (warp).
VAT Dye: Vat dyes are a class of dyes that are classified because of the method by which they are applied. Vat dyeing is a process that refers to dyeing that takes place in a bucket or vat and characteristically requires a reducing agent as well as alkali, to solubilize them.
Leuco form of a dye: A leuco form of a dye is an intermediate transient soluble form of insoluble dyes, obtained by application of reducing agents. For examples, in case of Vat dyes, the change of insoluble keto-group to soluble enol-group creates the leuco form. This is a reversible process.
Dwell time: The term “dwell time” referred to as a period of time wherein a substrate is subjected to a specific condition such as immersion into a liquor bath or passing through a drying oven.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Dyeing of cellulose fibers by using vat dyes such as indigo or sulfur dyes is well known in the textile industry. In order to dye a cellulosic material with indigo or sulfur dyes, which are insoluble in water, it is necessary to reduce the dye into a water-soluble leuco form prior to dyeing of the fibers. After the treatment of the fibers with the leuco form, the leuco form on the surface of the fibers is oxidized back into a dye form. Regenared cellulose fiber yarns can also be dyed using indigo and sulphur dyes.
However, due to the low absorption of the indigo or sulfur dyes by the regenerated cellulosic fibers, dyeing process of the fiber with indigo or sulfur dyes requires plurality of dyeing iterations with an intermittent oxidation between each dyeing step. Most of the conventional process of dyeing the cellulosic material by using indigo or sulfur dyes involve five to eight steps, with or without combination of vat or pigment dyes. Overall, dyeing the cellulosic material with indigo or sulfur dyes is a problematic at higher scales due to the requirement of dye liquors of large volume, and a low amount of the dye is transferred on the material in each step of short dipping step as well as squeezing and oxidizing steps.
Typically, indigo or sulphur dyeing (with or without combination of vat or pigment) of cellulosic or regenerated cellulosic fiber or blends thereof is performed at a pH in the range of 12.5 to 13.5. Due to the use of highly alkaline conditions, a significant loss of the yarn strength (around 30-40% against the original yarn strength) of regenerated cellulosic fiber is observed. The reduced fiber yarn strength makes it challenging to handle the yarns during multiple dyeing iterations even at a normal dyeing machine speed of 15-40 meter/min. Hence, for industrial application, the commercial use of indigo or sulfur dyes has been restricted essentially to cotton fibers.
Another problem in the conventional methods of dyeing the regenerated cellulosic fibers by using indigo or sulfur dyes, is the uneven / inadequate coloration of indigo or sulfur colours on the fibers.
There is, therefore, felt a need for a process for dyeing of regenerated cellulosic fibre yarns that mitigates the drawbacks of conventional methods.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Another object of the present disclosure is to provide a process for continuous dyeing of cellulosic fiber yarns.
Still another object of the present disclosure is to provide a process for continuous dyeing of cellulosic fiber yarns which provides dyed yarns having similar single yarn strength as compared to the yarns that are not dyed.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY
The present disclosure provides a process for continuous dyeing of cellulosic fiber yarns. The process comprises the following steps:
a) the yarns are pre-wetted at a first predetermined temperature for a first predetermined dwell time in a pre-wetting bath (1) comprising a pre-heated slurry to obtain pre-wetted yarns;
b) a first dye bath (3a) containing a first dye and at least one first additive maintained at a first predetermined pH is provided and connected to an electrolyser source; and a second dye bath (3b) containing a second dye and at least one second additive maintained at a second predetermined pH is provided and connected to an electrolyser source;
c) the pre-wetted yarns are passed through said first dye bath and the first dye is simultaneously reduced at a first predetermined potential for a second predetermined dwell time to obtain yarns treated with reduced first dye;
d) the reduced first dye is partially oxidized by exposing the yarns treated with reduced first dye, to air for a first predetermined time period to obtain partially treated yarns;
e) the partially treated yarns are passed through the second dye bath and the second dye is simultaneously reduced at a second predetermined potential for a third predetermined dwell time to obtain yarns treated with reduced second dye;
f) the second reduced dye is oxidized by exposing said yarns treated with reduced second dye, to air for a second predetermined time period to obtain dye treated yarns;
g) the dye treated yarns are washed in a washing bath (4) containing at least one fluid medium at a temperature in the range of 25 to 45 °C for a dwell time in the range of 20 to 30 seconds to obtain washed yarns;
h) washed yarns are finished in a finishing bath (5) containing at least one finishing agent for a dwell time in the range of 20 to 30 seconds to obtain finished yarns; and
i) drying said finished yarns in a drying unit (6) at a temperature in the range of 110 °C to 150 °C to obtain dyed yarns.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The process of the present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates a schematic representation of the process of the present disclosure.
List of Reference Numerals
PRE-WETTING BATH 1
NIP ROLLERS 2a- 2e
DYEING BOXES 3a-3b
WASHING BATH 4
FINISHING/ SOFTENING BATH 5
DRYING UNIT 6

DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, known processes or well-known apparatus or structures, and well known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure are not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
The conventional methods for dyeing yarns made of regenerated cellulosic fibers with Indigo or sulfur are associated with various disadvantages such as large number of the process steps, reduction in strength and higher elongation of dyed yarns.
To overcome the drawbacks of the conventional methods, the present disclosure provides a process for dyeing yarns made of regenerated cellulosic fiber and blends thereof with Indigo and sulfur dyes.
The process comprises the following steps:
The present disclosure provides a process for a continuous dyeing of cellulosic fiber yarns. The process is described in detail as follows:
In step a), the yarns are pre-wetted at a first predetermined temperature for a first predetermined dwell time in a pre-wetting bath (1) comprising a pre-heated slurry to obtain pre-wetted yarns.
In accordance with the embodiments of the present disclosure, the yarns are regenerated cellulose fiber yarns.
Typically, the cellulosic fiber yarns of the present disclosure is regenerated using Viscose method.
In accordance with the embodiments of the present disclosure, the yarns are in the form selected from a rope and a warp sheet and the dyeing is carried out by a method selected from a rope dyeing and a slasher dyeing. In an exemplary embodiment, the yarns are in the form of the rope and the dyeing is carried out by using the rope dyeing. In another exemplary embodiment, the yarns are in the form of the warp sheet and the dyeing in carried out by using the slasher dyeing.
In accordance with the embodiments of the present disclosure, the slurry contains a dispersing agent selected from anionic acrylic co-polymers (DEKOL SN), anionic aromatic sulphonic acid condensation product (SETAMOL WS), in an amount in the range of 0.05 to 0.2 wt.% with respect to the total weight of the slurry. In an exemplary embodiment, the dispersing agent is anionic acrylic co-polymers (DEKOL SN) and the amount is 0.1 wt.% with respect to the total weight of the slurry.
In accordance with the embodiments of the present disclosure, the slurry contains a deaerating agent selected from anionic phosphoric acid ester (PRIMASOL NF) and non-ionic phosphoric acid ester in an amount in the range of 0.05 to 0.2 wt.% with respect to the total weight of the slurry. In an exemplary embodiment, the deaerating agent is anionic phosphoric acid ester (PRIMASOL NF) and the amount is 0.1 wt.% with respect to the total weight of the slurry.
In accordance with the embodiments of the present disclosure, the slurry is pre-heated to a temperature in the range of 30 to 40 oC, the first predetermined temperature is in the range of 25 to 35 oC and the first predetermined dwell time is in the range of 20 to 30 seconds. In an exemplary embodiment, the slurry is pre-heated to 35 oC, the first predetermined temperature is 30 oC and the first predetermined dwell time is 25 seconds.
In step b), a first dye bath containing a first dye and at least one first additive maintained at a first predetermined pH and connected to an electrolyser source is provided. Further, a second dye bath (3b) containing a second dye and at least one second additive maintained at a second predetermined pH and connected to an electrolyser source is provided.
In accordance with the embodiments of the present disclosure, the first dye and the second dye is selected from Indigo and sulphur dyes. In an exemplary embodiment, the dye is Indigo dye.
In accordance with the embodiments of the present disclosure, the concentration of the first dye in the first dye bath is in the range of 1 to 5 wt.% of the total weight of the first dye bath and the concentration of the second dye in the second dye bath is in the range of 1 to 5 wt.% of the total weight of the second dye bath. In an exemplary embodiment, the first dye is Indigo dye and the concentration of the first dye in the first dye bath is 2.5 wt.% of the total weight of the first dye bath and, the second dye is Indigo dye and the concentration of the second dye in the second dye bath is 2.5 wt.% of the total weight of the second dye bath.
In accordance with the embodiments of the present disclosure, the first additive and the second additive is selected from a reducing agent, a crosslinking polymer and a combination thereof.
In accordance with the embodiments of the present disclosure, the reducing agent is sodium hydrosulfite and a concentration of sodium hydrosulfite is in the range of 0.05 to 0.2 wt.% with respect to the total weight of the respective dye bath. In an exemplary embodiment, the concentration is 0.15 wt.% with respect to the total weight of the respective dye bath.
In accordance with the embodiments of the present disclosure, the crosslinking polymer is polyacrylic copolymer (SULFAID DESIGN EFFECT S311) and a concentration of the crosslinking polymer is 1 to 10 wt.% of the total weight of the respective dye bath. In an exemplary embodiment, 2.5 wt.% of the total weight of the respective dye bath.

In conventional Indigo dyeing process, the pH of the dye bath is highly alkaline (around 14), which is detrimental to the cellulosic yarns which are stable only up to 10.5 to 11. The cross linking co-polymer added in the first and the second dye bath prevents the damage to the cellulosic yarns in highly alkaline and highly reducing environment by reducing the pH of the dye bath to suitable pH condition. This is because the crosslinking polymer solution itself has a pH of 2-3. Further, the polyacrylic polymer forms an acrylate film on the yarns which is resistance to highly reducing conditions (upto -900 mV).

Conventionally, for dyeing cellulosic fiber yarns using Indigo dye, the redox potential of around -760 to -860 millivolt (mV) is used. At this redox potential, the cellulosic yarns become very weak due to the formation of hydro cellulose and leading to yarn strength loss of around 20-30% when compared to the original yarns. This results in the high breakages of the yarns and the yarns handling becomes very difficult. In the process of present application, the cross-linking copolymer protects the cellulosic yarns which is subjected to high alkaline and high reducing/oxidizing potential without affecting the yield of the Indigo dyeing process.

In accordance with the embodiments of the present disclosure, the first additive is a combination of sodium hydrosulfite in an 0.05 to 0.2 wt.% with respect to the total weight of the first dye bath and polyacrylic copolymer (SULFAID DESIGN EFFECT S311) in an amount 1 to 5 wt.% of the total weight of the first dye bath. In an exemplary embodiment, the first additive is a combination of sodium hydrosulfite in an amount 0.15 wt.% with respect to the total weight of the first dye bath and polyacrylic copolymer (SULFAID DESIGN EFFECT S311) in an amount 2.5 wt.% with respect to the total weight of the first dye bath.
In accordance with the embodiments of the present disclosure, the second additive is a combination of sodium hydrosulfite in an 0.05 to 0.2 wt.% with respect to the total weight of the second dye bath and polyacrylic copolymer (SULFAID DESIGN EFFECT S311) in an amount 1 to 5 wt.% of the total weight of the second dye bath. In an exemplary embodiment, the second additive is a combination of sodium hydrosulfite in an amount 0.15 wt.% with respect to the total weight of the second dye bath and polyacrylic copolymer (SULFAID DESIGN EFFECT S311) in an amount 2.5 wt.% with respect to the total weight of the second dye bath.
In accordance with the embodiments of the present disclosure, the first predetermined pH and the second predetermined pH is in the range of 11 to 11.5 and the first predetermined pH and the second predetermined pH is maintained by using a mild alkali selected from sodium carbonate and sodium bicarbonate. In an exemplary embodiment, the first predetermined pH and the second predetermined pH is 11 and the first predetermined pH and the second predetermined pH 11 is maintained by using sodium carbonate.
Typically, the conventional process of dyeing is carried out at around pH of 12.5-13.5. At such high alkaline conditions, the cellulosic fiber becomes weak leading to higher yarn strength loss of around 30-40%. In such condition, it is very difficult to dye the cellulosic yarns using indigo dye even at normal dyeing machine speed of 25 meter/min. In the process of the present disclosure, the pH of the first and second dye bath is optimized to 11 – 11.5 without affecting the yield of the indigo dyeing process. Further, due to the pH optimization of the first and second dye bath, the single yarn strength of the cellulosic fiber is preserved.

In step c), the pre-wetted yarns are passed through the first dye bath and the first dye is simultaneously reduced at a first predetermined potential for a second predetermined dwell time to obtain yarns treated with reduced first dye.
In accordance with the embodiments of the present disclosure, the second predetermined dwell time period is in the range of 20 to 30 seconds, the first predetermined potential is in the range of -760 to -860 mV. In an exemplary embodiment, the first predetermined time period is 50 seconds, the predetermined potential is -780 mV.
In step d), the reduced first dye is partially oxidized by exposing the yarns treated with reduced first dye, to air for a first predetermined time period to obtain partially treated yarns.
In accordance with the embodiments of the present disclosure, the first predetermined time period is in the range of 40 seconds to 80 seconds. In an exemplary embodiment, the first predetermined time period is 60 seconds.
In step e), the partially treated yarns are passed through the second dye bath and the second dye is simultaneously reduced at a second predetermined potential for a third predetermined dwell time to obtain yarns treated with reduced second dye.
In accordance with the embodiments of the present disclosure, the third predetermined dwell time is in the range of 20 to 30 seconds, and the second predetermined potential is in the range of -760 to -860 mV. In an exemplary embodiment, the third predetermined dwell time is 25 seconds, and the second predetermined potential is -780 mV.
In accordance with the embodiments of the present disclosure, a speed of the dyeing is in the range of 15 to 40 m/min. In an exemplary embodiment, the speed is 25 m/min.
Conventional process for dyeing the cellulosic fiber yarns using Indigo dye requires up to at least 8 dyeing iteration for adequate color absorption and even coloration. Each dyeing iteration consists of about 25 second dwell time of yarn in each dye bath with intermediate drying of about 60 seconds. In the present disclosure, similar color absorption and even coloration is achieved using only two dye baths/iteration and remaining 4-6 dye baths are eliminated leading to making the overall dyeing process economical. Essentially, in the process of the present disclosure, the dwell time of the cellulosic yarns in the highly alkaline conditions in the dye baths is decreased by 75% with an increased intermediate drying. Surprisingly, there is no effect on the yield of Indio dyeing process and also does not have any impact on the physical properties of dyed yarns or warp sheet.

In step f), the second reduced dye is oxidized by exposing the yarns treated with reduced second dye,to air for a second predetermined time period to obtain dye treated yarns.

In accordance with the embodiments of the present disclosure, the second predetermined time period is in the range of 140 seconds to 220 seconds. In an exemplary embodiment, the second predetermined time period is 150 seconds.

In step g), the dye treated yarns are washed in a washing bath containing at least one fluid medium at a temperature in the range of 25 to 45 °C for a dwell time in the range of 20 to 30 seconds to obtain washed yarns. In an exemplary embodiment, the temperature is 35°C and the dwell time is 25 seconds.
In accordance with the embodiments of the present disclosure, the fluid medium is at least one selected from acetic acid and hydrogen peroxide. In an exemplary embodiment, the fluid medium is a mixture of acetic acid and hydrogen peroxide in a volume ratio of 1:1.
In step h), the washed yarns are finished in a finishing bath containig at least one finishing agent for a dwell time in the range of 20 to 30 seconds to obtain finished yarns. In an exemplary embodiment the dwell time is 25 seconds.
In accordance with the embodiments of the present disclosure, the finishing agent is selected from a polyacrylic copolymer binder (SULFAID DESIGN EFFECT S311) and a silicone oil or combination of both. In an exemplary embodiment, the finishing agent is a combination of polyacrylic copolymer binder (SULFAID DESIGN EFFECT S311) and a silicone oil.
In step i), the finished yarns are dried in a drying unit at a temperature in the range of 110 to 150 °C to obtain dried dyed yarns. In an exemplary embodiment, the temperature is 150 °C.
In accordance with the embodiment of the present disclosure, the dried dyed yarns are characterized by having a) reduction in single yarn strength up to 5%; and b) elongation of up to 10%. In an exemplary embodiment, the reduction is single yarn strength is 3% and elongation is 10%.
In the conventional processes for dyeing the yarns made of regenerated cellulosic fibers, the single yarn strength of the dyed yarns is reduced by approximately 30 to 40%. Moreover, the loss on elongation in the dyed yarn is more than 10%.
The process of the present disclosure is capable of providing the dyed yarns from 100% regenerated cellulose yarns. Drop in single yarn strength is reduced to less than 5 % and elongation is restricted to a maximum of 10% from its original values. The dyed cellulosic yarns produced as a result of the process of the present disclosure meets the standard of denim industries in terms of the yarn breakerage. The breakages of the cellulose fiber yarn at the dyeing stage of the process of the present disclosure is about 1-2 and 2-3 per million meter at long chain beamer which is the requirement for the denim industries.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be tested to scale up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
EXPERIMENTAL DETAILS
Experiment 1: Process of dyeing a rope prepared by using a regenerated cellulosic yarns with an uptake of 3% indigo dye in accordance with the present disclosure:
The dry rope prepared by using the regenerated cellulosic yarns was pre-wetted in a pre-wetted bath having a slurry at 35 oC comprising a DEKOL SN (Acrylic copolymer) as a dispersing agent in an amount of 0.1 wt% with respect to the total weight of the slurry and PRIMASOL NF (salt of anionic phosphoric acid ester) as a de-aerating agent in an amount 0.1 wt% of the total weight of the slurry at 35oC for a dwell time of 25 seconds to obtain a pre-wetted rope. Dyeing of the pre-wetted rope was carried out by using two dye baths provided with electrolyser source (separately to each dye bath) for applying redox potential. Firstly, the pre-wetted rope was passed through a first dye bath having a dyeing solution containing indigo dye liquor in an amount of 2.5 wt% with respect to the total weight of the first dyebath, sodium hydrosulfite in an amount of 0.15 wt% with respect to the total weight of the first dyebath and polyacrylic copolymer (SULFAID DESIGN EFFECT S311) in an amount 2.5 wt% with respect to the total weight of the first dyebath for a dwell time of 25 seconds. During the dwell time of the pre-wetted rope in the first dye bath, reduction potential of -780 mV was applied to reduce indigo dye molecules in the first dye bath to obtain a rope treated with a reduced first dye. pH of the first dye bath was maintained at 11 to 11.5 by using sodium carbonate. The rope treated with a reduced first dye was allowed to travel through air for 60 seconds for oxiding the dye molecules present on the surface of the rope to obtain a partially treated rope.The partially treated rope was passed through a second dye bath having the same dye solution (same as the solution in the first dye bath) for dwell time of 25 seconds. During the dwell time of the partially treated rope in the second dye bath, reduction potential of -780mV was applied to reduce the dye molecules in the second dye bath to obtain a rope treated with a reduced second dye. The rope treated with a reduced second dye was allowed to travel through air for 150 seconds for oxidizing the dye molecules present on the surface of the reduced second dye treated rope to obtain dye treated rope. The dye treated rope was passed through a washing bath containing a mixture acetic acid and hydrogen peroxide at 35 °C for a dwell time of 25 seconds to obtain a washed rope. The washed rope was passed to a finishing bath containing silicone oil and polyacrylic polymer as a finishing agent for a dwell time of 25 seconds to obtain a finished rope. The finished rope was dried at 150° °C to obtain a dyed rope. The speed of the dyeing process was maintained at 25 m/min.The amount of the dye deposited on the rope by using the process of experiment 1 is 3.0 wt.% with respect to the total weight of the rope.
The color shade of the dyed cellulosic yarns using the process of the present disclosure can be changed by changing the concentration of the dye in the dye baths.

Experiment 2: Process of dyeing a warp sheet prepared by using a regenerated cellulosic yarns with indigo dye in accordance with the present disclosure:
The experiment 2 was carried out in a manner similar to experiment 1, except the warp sheet prepared by using the regenerated cellulosic yarns was used.
Comparative experiment: Dyeing of cellulosic yarns by using the conventional method.
The cellulosic yarns were pre-wetted in bath comprising caustic soda in an amount.15 wt% with respect to the total weight of the respective prewet bath, SETAMOL WS (Acrylic copolymer) as wetting agent in an amount 2.5 wt% on weight of respective pre-wet bath, Hyperwet WT as a deaerating agent in an amount 2.5 wt% with respect to the total weight of respective pre-wet bath) at 90 oC. The step of prewetting was performed twice with a dwell time of 25 seconds each. The yarns were then washed with water in a first wash bath at 90 oC for a dwell time of 25 seconds followed by washing with water in a second wash bath at 40 oC for a dwell time of 25 seconds to obtain washed yarns. The washed yarns were dyed (by using nipping and dipping) in 8 stages using 8 different dye baths comprising Indigo dye, sodium hydrosulfide, caustic soda. The dye bath were provided with electrolyser. During dyeing of the yarns, the dye molecules in the dye bath were simultaneously reduced using the electrolyser by using the reduction potential of -780 mV. A dwell time in each dye bath was 25 second and the dyed yarn was exposed to air for 60 seconds to carry out aerial oxidation. pH of dyeing bath was maintained at 12.5-13.5. The dyed yarns were then washed in 4 washing stages using 4 different washing baths at following conditions to obtain washed yarns:
First and second wash bath – temperature - 80 oC, dwell time of 25 seconds;
Third wash bath comprising acetic acid- temperature - 40 oC, dwell time of 25 seconds;
Fourth wash bath (silicone oil (RUCOFIN KMN 400) as a finishing agent) - temperature - 40 oC, dwell time of 25 seconds.
The washed yarns were dried at 150 oC. Through-out the process, the speed of the machine was 25 m/min.

The dyed materials as obtained in experiments 1, 2 and the comparative experiment were characterized by using the test methods summarized below in the table:
Table 1: Characterization methods for testing the physical properties
Test Parameters Test methods
Yarn Strength ISO:2062:2009
Yarn CSP ISO 1671:1977
Yarn Elongation ISO:2062:2009
Yarn Hairiness ISO 16549:2004 €
Table 2: Comparison of the physical properties of the yarns before and after dyeing by the process of the present disclosure
Particulars Before dyeing with Indigo After Indigo Dyeing Remarks
Single yarn Strength (RKm) in cN/Tex 17.19 16.64 Around 3 % single yarn Tensile strength drop
Yarn CSP
(Count Strength product) 2657 2524 Around 5 % drop
Elongation (%) 13.43 12.2 Around 10 % elongation drop
Hairiness
(In VSF, Modal, Excel, it is absolute Value) 6.62 6.82 Around 3 % increase in hairiness
From table 2, it is observed that the process for dyeing the cellulose fiber yarns of the present disclosure is capable of reducing the drop in single yarn strength to below 5% and the drop in elongation of the dyed fiber can be restricted to 10%.
Table 3: Comparison of change in physical properties of the yarns before and after dyeing by the process of the present disclosure and by using the conventional process
Conventional process Process of the present disclosure
Drop in Single yarn Strength (RKm) in cN/Tex before and after dyeing 20 to 30% 3%
Drop in Elongation (%) 15-20% 9.8%
From table 3, it is observed that the process of dyeing cellulose fibers of the present disclosure is capable of reducing the drop in a single yarn strength to below 5%, however after dyeing the yarns using the conventional process, the single yarn strength dropped by 20 to 30%.
The technical advancement due to the process of the present disclosure is:
• the process of the present disclosure provides the dyed yarns with less than 10% reduction in yarn strength and with less than 10% elongation drop;
• dyed yarns have breakages during the entire dyeing process of around 4 per million meter;
• the process is adoptable to existing technology without change of machines;
• the process uses low amounts of chemicals, dye boxes, and water;
• producing lesser effluent, thereby providing an environment friendly process; and
• the process reduces repeated unit/dyeing operations; thereby providing an economical process.
TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for a continuous dyeing of cellulosic fiber yarns, which:
• economical and reduces the number of dyeing iterations;
• provides the dyed yarns with less than 5% reduction in yarn strength and with less than 10% elongation.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:WE CLAIM:
1) A process for continuous dyeing of cellulosic fiber yarns, said process comprising the following steps:
a) pre-wetting said yarns at a first predetermined temperature for a first predetermined dwell time in a pre-wetting bath (1) comprising a pre-heated slurry to obtain pre-wetted yarns;
b) providing a first dye bath (3a) containing a first dye and at least one first additive maintained at a first predetermined pH and connected to an electrolyser source; and providing a second dye bath (3b) containing a second dye and at least one second additive maintained at a second predetermined pH and connected to an electrolyser source;
c) passing said pre-wetted yarns through said first dye bath and simultaneously reducing said first dye at a first predetermined potential for a second predetermined dwell time to obtain yarns treated with reduced first dye;
d) partially oxidizing said reduced first dye by exposing said yarns treated with reduced first dye, to air for a first predetermined time period to obtain partially treated yarns;
e) passing said partially treated yarns through said second dye bath and simultaneously reducing said second dye at a second predetermined potential for a third predetermined dwell time to obtain yarns treated with reduced second dye;
f) oxidizing said second reduced dye by exposing said yarns treated with reduced second dye to air for a second predetermined time period to obtain dye treated yarns;
g) washing said dye treated yarns in a washing bath (4) containing at least one fluid medium at a temperature in the range of 25 to 45 °C for a dwell time in the range of 20 to 30 seconds to obtain washed yarns;
h) finishing said washed yarns in a finishing bath (5) containing at least one finishing agent for a dwell time in the range of 20 to 30 seconds to obtain finished yarns; and
i) drying said finished yarns in a drying unit (6) at a temperature in the range of 110 °C to 150 °C to obtain dyed yarns.
2) The process as claimed in claim 1, wherein the cellulosic fiber yarns are regenerated cellulose fiber yarns.
3) The process as claimed in claim 1, wherein said yarns are in the form selected from a rope and a warp sheet; and wherein the dyeing is carried out by a method selected from a rope dyeing and a slasher dyeing.
4) The process as claimed in claim 1, wherein said first dye and said second dye is selected from Indigo dye and sulphur dye.
5) The process as claimed in claim 1, wherein said slurry comprises at least one dispersing agent selected from anionic acrylic copolymer and anionic aromatic sulphonic acid condensation product in an amount in the range of 0.05 wt.% to 0.2 wt.% of the total weight of said slurry, and at least one deaerating agent selected from a salt of anionic phosphoric acid ester and a salt of non-ionic phosphoric acid ester in an amount in the range of 0.05 wt.% to 0.2 wt.%, of total weight of said slurry.
6) The process as claimed in claim 1, wherein the slurry is pre-heated to a temperature in the range of 30 to 40 oC , the first predetermined temperature is in the range of 25 to 35 oC and the first predetermined dwell time is in the range of 20 to 30 seconds.
7) The process as claimed in claim 1, wherein said first additive and said second additive is selected from a reducing agent, a crosslinking polymer and a combination thereof.
8) The process as claimed in claim 7, wherein the reducing agent is sodium hydrosulfite, and wherein the crosslinking polymer is polyacrylic copolymer.
9) The process as claimed in claim 8, wherein said first additive and said second addtive is a combination of sodium hydrosulfite and polyacrylic copolymer, and wherein the sodium hydrosulfite is in an amount in the range of 0.05 to 0.2 wt.% with respect to the total weight of said first dye bath; and polyacrylic copolymer is in an amount in the range of 1 to 5 wt.% with respect to the total weight of said first dye bath.
10) The process as claimed in claim 1, wherein said first predetermined pH and said second predetermined pH is in the range of 11 to 11.5 and said first predetermined pH and said second predetermined pH is maintained by using a mild alkali selected from sodium carbonate and sodium bicarbonate.
11) The process as claimed in claim 1, wherein said first predetermined dwell time and said second predetermined dwell time is in the range of 20 to 30 seconds, said first predetermined potential and said second predetermined potential is in the range of -760 to -860 mV, and the first predetermined time period is in the range of 50 to 90 seconds.
12) The process as claimed in claim 1, wherein the third predetermined dwell time is in the range of 20 to 30 seconds and the second predetermined time period is in the range of 140 to 220 seconds.
13) The process as claimed in claim 1, wherein a concentration of said first dye in said first dye bath is in the range of 1 to 5 wt.% with respect to the total weight of the first dye bath and a concentration of said second dye in said second dye bath is in the range of 1 to 5 wt.% with respect to the total weight of the second dye bath.
14) The process as claimed in claim 1, wherein a speed of the dyeing is in the range of 15 to 40 m/min.
15) The process as claimed in claim 1, wherein said fluid medium is a mixture of acetic acid and hydrogen peroxide.
16) The process as claimed in claim 1, wherein said finishing agent is selected from a polyacrylic binder and a silicone oil.
17) The process as claimed in claim 1, wherein said dyed yarns are characterized by having:
a) reduction in single yarn strength up to 5%; and
b) drop in elongation of up to 10%
when compared to the yarns before the pre-wetting.