Patent Application
20230034249
The present invention generally relates to fabric dyeing, such as fabric dyeing using indigo or sulphur dyes. In particular, a process is disclosed which provides a dyed yarn having reduced dye penetration and a white core. The process involves modification of existing sulfur dye ranges in order to more efficiently and in an environmentally improved method produce dyed yarns that may be processed into fabrics. The invention also is directed to yarns dyed on dye ranges through use of the process, and fabrics formed from the dyed yarns.
Many textiles, such as denim, consist of dyed yarns woven with other yarns that are sometimes also dyed, and other times retain their natural color. Most denim apparel consists of undyed yarns woven with dyed yarns. The current state of the art of dyeing has significant drawbacks including:
1. The application of the dye is energy, chemical and water intensive;
2. For decades, fashion trends required the removal of much of the dye fixed to the yarns, and the existing methods of dye application make this removal excessively difficult to do; and
3. The removal of the fixed dye on the yarns comes at the great expense of even more water, chemicals, and energy.
The appeal of many denim garments is the contrast between the colors on the dyed warp yarns, and the (often white) weft yarns. As stated above, for the last several decades the fashion industry has also pushed for various types of wear and abrasion in an attempt to reveal lighter shades of color, or also reveal the underlying white (or off white/natural color) of the warp yarns. These wear and abrasion techniques can be varied, such as hand sanding, which involves a laborer to actually abrade the jean with sandpaper in their hands, Dremel destruction, or laser abrasion. Laser abrasion employs the use of high-powered lasers. The controller of the laser is loaded with an abrasion or destruction file that represents a designer's target finished look and the laser then, with the emissions of light, sublimes much of the indigo or sulphur dye on the warp yarns of the woven fabric. Just as with hand sanding, the intensity of the abrasion is adjusted per the target design such that the final garment represents the intended look. This look requires the removal of some, all, or nearly all the dye, from the yarn in particular areas. With conventionally dyed yarns, the burden of fashion on the environment is exacerbated by over penetration of dye. The further the dye penetrates the surface of the yarn, more energy, more chemicals, and more water is required to remove the dye from the perimeter of the yarn as required by the original designer of the “target garment.” A target garment can be understood to mean an original garment from which subsequent garments are to be abraded and washed in a way that closely represents the original target.
Therefore, there remains needs for dye range and methods for producing adequately dark yarns which retain a larger, whiter, or lighter colored core which makes dye removal processes less water, chemical, time, and energy intensive.
In recognition of the above, the present invention provides techniques for sulphur and/or indigo ring dyeing which result in adequately dark yarns while retaining a larger, whiter, or lighter colored core which makes all dye removal processes less water, chemical, time, and energy intensive. “Adequately dark” yarns can be understood to mean yarns which are capable of being dyed to shades comparable to those dyed conventionally, while retaining a white core. There are also substantial savings of water, chemicals, and energy at the denim mill by adopting the present invention.
Referring to
The present invention provides a solution to the issue of providing adequately dark yarns while preventing excessive dye penetration of the yarns through the implementation of several embodiments. One embodiment involves the use of a barrier compound as a barrier to subsequent dye applications. A second embodiment involves performing a scouring stage without a caustic agent. A third embodiment involves bypassing conventional steps known as scouring and/or scour rising. A fourth embodiment involves the use of sodium bicarbonate or other chemicals to control the pH and alkalinity of the dye tanks. A fifth embodiment involves reducing the dye concentration and increasing the number of dye vats, when the dye is a sulphur dye. A sixth embodiment involves adding a sizing stage to the dye range.
Referring to Table 1 (dye boxes per shade), which compares a method of using fewer dye boxes according to the invention to attain an identical shade as a conventional method. The disclosed method uses fewer dye boxes to attain an identical shade, using an increased dye concentration to compensate for the lack of repeated immersion. Repeated exposure to immersion in the dye is collectively more harmful to yarn penetration (too much penetration) than the application of dye with higher concentrations and fewer boxes. Following the guidelines in Table 1 for dye shade and the corresponding number of dye boxes, it is possible to achieve darker shades with increased dye concentration and in fewer boxes, even with reduced immersion times. The disclosed method provides the same shade as conventional dyeing with a white center core.
The embodiments of the invention may be applied individually or any combinations thereof to existing dye range to reduce and optimize dye penetration in order to form dyed yarns resembling yarn 1.5 shown in
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 and wherein:
An example of the workflow on a dye range 100 is shown in
The dye range 100 first scours the yarns 106 to wash them of impurities, such as oils and waxes, in scour vats (tanks or boxes) 102a. The scouring process (scouring stage) prepares the yarns 106 for dyeing. After scouring, the yarns 106 are washed, typically in a vat filled with water that is flowing with fresh water causing contaminated water to overflow to a drain, in a scour rinse vat 102d to remove chemicals used in the scour vat 102a from the yarns 106 (scour rinsing stage). The yarns 106 are then dyed in a plurality of dye vats 102b (dyeing stage). After each dye vat 102b, the yarns 106 are exposed to air by passing through a plurality of regular rollers 104b above the dye vats 102b to allow the dye to oxidize (oxidation stage). After dyeing, the yarns 106 are passed through rinse vats 102c to remove excess dyes on the yarns 106 (dye rinse stage). Once rinsed, the yarns 106 are dried, e.g., such as by using drying cans 108.
The dye range 100 begins with the scouring process. The scouring process traditionally involves one or more scour tanks (vats or boxes) 102a within which yarns 106 are passed over and under a series of rollers 104a, 104b. The scour vats 102a are filled with water and chemicals, such as caustic soda, chelate agents, and wetting agents, such as Primasol™ from Archroma, for example; and composed of a series of regular rollers 104b that cause the yarns 106 to be immersed in the chemicals as the yarns 106 move through the range 100.
After having passed through the scour vat(s) 102a, the yarns 106 are then rinsed in water. We refer to this step as the scour rinsing stage, which occurs in one or more scour rinse vats 102d. The scour rinse is desirable and removes the caustic and contaminants before the yarns 106 are passed through the dye vats 102b containing dye chemistries.
Dye vats 102b are large tanks containing a dye solution (or dye chemistry), within which the yarns 106 pass over a series of rollers 104. The size of the dye vats 102b is typically over 250 gallons each, with some as large as 700 gallons. The yarn path over or under regular rollers 104b in dye vat 102b typically immerses the yarns 106 in the dye chemistry.
After each dye vat 102b, the yarns 106 are processed through a nip roller 104a and then enter a dye oxidation stage. It is during the dye oxidation stage that the yarns 106 are exposed to air through a series of regular rollers 104b. Sulfur and indigo dyes are not water-soluble. During the immersion stage, the dyes are reduced to a soluble state through the removal of oxygen. Once the yarns 106 exit the dye vats 102b and begin the exposure to oxygen, the dye returns to an insoluble state, effectively bonding the dye to the yarns 106.
After the last dye cycle of dye immersion and oxidation (with the nip rollers 104a in between), the yarns 106 proceed to a dye rinse stage, which typically occurs in one or more dye rinse vats 102c. This dye rinse stage rinses the yarns 106 of excess dye and removes dye that has not fasted to the yarns 106 during the oxidation phase. The number of dye rinse vats 102c at a given mill on a given range 100 may vary between one to three.
The present invention involves modifying conventional dye ranges and processes to produce a yarn with an adequately dark dyed periphery, while its core remains white, preferably whiter or lighter than compared to conventionally dyed yarns. The disclosed technology also provides significant savings in chemicals, water, and energy compared to conventional sulfur dyeing processes.
A first embodiment of the invention involves applying a barrier to the yarns 106 before exposing the yarns 106 to a dye which gives the yarns 106 their final color. The barrier preferably has a larger particle size than the dye. For example, sulphur dyes, compared to indigo dyes, have a larger mean particle size. Without being bound to any particular theory, the larger particles of the barrier particles are believed to act, based on experimental results described in the next paragraph for sulphur bottom dyeing, as a physical impedance to the penetration of the dye, while the barrier particles adhere to the outer surface of the yarns 106. The concept being that a chemical application to the yarns 106 of the barrier, such as a sulphur dye, at least partially, inhibits the penetration of the dye, such as indigo or additional subsequent sulphur dye application, into the core of the yarns 106.
The inventors, while practicing their trials regarding indigo dyeing trials, had encountered sulphur bottom requirements from different mills. Sulphur bottom dyeing is a dyeing technique which involves first applying a base layer of sulphur dye, so that the subsequent applications of indigo are applied to a yarn that has a base color of gray, resulting in a darker shade of blue and grey indigo cast preferred by designers than could otherwise be possible, with all conditions of the indigo dyeing. Conventional sulphur bottom dyeing, however, did not result in the desired white core. In order to achieve the desired effect, the temperatures, concentrations of dye, and immersion times of the sulphur bottom application were all reduced in an attempt to preserve the white core associated with indigo dyeing according to the disclosed invention. The details of the reductions are described below.
The use of the present invention for indigo dyeing of yarns vastly improves the core retention compared to the conventional indigo dyeing. What surprised the inventors was that the trials that involved the modified sulphur bottom concentrations, immersion times, and temperatures accentuated white core retention. For some time, sulphur dyes were used in sulphur bottom applications to achieve very dark greys and blacks in the yarn shade prior to subsequent dye applications and, as described above, to darken blue colors using sulphur bottom or sulphur top applications. A sulphur bottom involves sulphur application before dye. Sulphur top is when the application of indigo precedes the application of sulphur dye, emphasizing the gray color over blue, rather than a blue color over gray. A yarn indigo dyed using the present invention (barrier application before indigo or sulphur dyeing) appreciably inhibits the penetration of indigo or sulphur dye, resulting in improved post-production laser and wash efficiency, which improves both attainable shades as well as cost and resource savings.
When the target shade (intended shade) does not call for the darkening effect created by sulphur dye, alternatives are utilized. One such alternative is to use complimentary colors. When dyeing yarns an indigo blue color, the base sulphur application can be blue as well. Blue sulphur dye was originally created and marketed as a less expensive, more ecofriendly alternative to indigo. This is because the indigo plants necessary for creating indigo dye are a lower yield crop with a relatively high-water consumption requirement. The application of sulphur dyes is unique to the application of indigo dyes. The sulphur compounds do not tend to bond well with the yarns unless the dye is first heated, typically in a range of 85°-90° C. Due to this heating requirement associated with sulphur dyes, the yarns tend to expand, opening up the structure of the yarn, allowing the dye to further penetrate toward the core. This increased penetration made the later removal of the dye in laser and washing processes lengthier, less effective, and more costly. This approach of applying blue sulphur was difficult to market, as the industry recognized the difficulties and increased expenses. When conventional sulphur dyed yarns are later treated with hand sanding, laser treatment, and both physically and chemically abrasive wash cycles, the result also appears much flatter, resulting in a less visual dynamic with fewer colors and fewer interruptions of color when compared to an indigo garment finished or treated similarly after dyeing/weaving. This is, at least in part, attributable to the increased fastness and excessive penetration of the sulphur dyes, when applied conventionally.
The inventive method of applying sulphur dyes as a barrier, rather than as a purposeful dye application, involves using lower temperatures, lower pH, and/or reduced immersion times with minimum to no air oxidation time, which results in lessened dye penetration, but results in a perimeter of a yarn with large sulphur molecules which appear to act as barrier to subsequent applications of dye. As stated previously, conventional sulphur dye applications are applied in vats operating with temperatures of 85-95° C. Pursuant to the invention, sulphur barrier applications are applied in dye vats 102b, with a preferred temperature range of 50° C.-80° C. Conventional pH ranges of sulphur dye tanks 102b are largely determined by shade, because of the high concentrations of caustic used to reduce and stabilize sulphur dyes. Pre-reduced sulphur dyes are inbuilt with a high amount of caustic and reducing agent to keep them in stable condition. The application of chemistries discussed throughout this application is often referred to as a percentage add-on. The weight of a yarn is known, and is considered the average weight of a set measure of yarn (10 meters, 12 yards, etc.) such that a particular diameter yarn has an accepted weight throughout the industry. When a mill intends to add dye, sizing, or other such chemicals, or even humidity retained from the range or absorbed from the air, it is known as a percentage add on or % add-on. This is the weight of the yarn, plus a variable percentage of a chemistry. When shades result in normal 10% or greater add on weight, the pH of the dye chemistry is typically increased above 12.5, which, for the purposes of a barrier application, is an excessively alkaline condition. Worse, conventionally the dye tanks have excess additional caustic added as well, as much as 150 g/L that increases the already high alkalinity. With the disclosed method, the additional caustic added to the dye stuffs for a barrier application is in a preferred range of 1.0-8.0 grams per liter of 100% caustic flake. In some cases, no additional caustic is added to the already pre-reduced sulphur dye stuffs commercially available. This is particularly true with lower twist yarns (3.8 to 4.5 twist multiple (tm)). Specifications for sulphur dye tanks with a preferred pH range of 11.6-12.5 achieve best results. However, positive results are still be attainable outside of this range, but these results would be increasingly diminished as the pH values were to rise above 12.5.
As the yarns proceed across the dye range, they are exposed to various chemicals within various vats, or boxes. The time spent within a given chemistry is known as the immersion time. One embodiment of the invention is the reduction in immersion times. The amount of time a yarn spends within any particular box is a result of the length of the yarn immersed in the box, and the processing speed of the range or the rate of travel the yarns are processed from the beginning of the range to the end. The most common immersion times for most conventional dye and rinse boxes 102b, 102c at the most common range speeds is from 14-25 seconds per box. Dye ranges with smaller boxes typically have slower processing speeds, whereas dye ranges with larger dye boxes typically have faster processing speeds, resulting in immersion times that typically fall within the stated range. The preferred barrier, dye, and rinse immersion times for practicing the present invention are approximately half of this time, 7 to 12.5 seconds. Operating with slightly longer or shorter immersion times may also produce results that would be positive in comparison with the conventional practices but, as with the pH variations disclosed previously, with increased deviation comes decreased benefit of the invention. Without exception, each dye range encountered by the inventors or their representatives throughout the world has been threaded in a manner that is described herein as conventional. This is to be understood to mean, the yarns are threaded in such a way that utilizes all of the rollers 104a, 104b the manufacturers installed in the equipment, typically resulting in the longest time the yarns could spend in any one stage (longest immersion), and/or all stages across the dye range 100. An example drawing of a box or vat threaded in a conventional way is provided in
Dye ranges are driven by many electric motors that pull the yarns through the various stages of the dye range. The normal operating speed of the dye range is typically within 85-90% of its maximum speed. One of the limitations in this speed is the drying capacity on the dye range. When a range is designed, the range of operating speeds are calculated. Both the respective range speed as well as the drying capacities are designed as a result. Considerations in designing the drying capacity are to be sufficient for the highest motor speed (or range speed), with the largest yarns, with the highest water retention expected on the range (typically 5-7%). Simply increasing the speed would overwhelm this designed limitation of drying capacity, resulting in excessively wet yarns which quickly degrade. When the inventors were looking for a method to significantly reduce the time the yarns 106 spent during the various chemical and water immersion stages, making the dye range operate twice as fast was not an option, so innovation was required. The novel solution was a rethreading or changing the path the yarns take through the dye range. Rethreading the dye range can be understood to mean that the yarns are removed wholly or partially from the dye range, and the path the yarns take over, under, or bypassing rollers is changed accordingly. Examples of such a rethreading are shown in
The application of sulphur dyes to act as an impedance (or barrier) of further dye penetration is an embodiment of this invention. As the application of sulphur dye barrier does not change based on the chromophore (color) bound to the sulphur compound, the color or lack of color of the sulphur chemistry does not impact the novelty of this inventive method. The introduction of sulphur dye as a barrier should change the shade, but the sulphur dye creates such a fine layer that it negligibly contributes to changing the shade. The application of subsequent sulphur dyes is an embodiment of this invention. This involves the application of a sulphur dye or sulphur compound as a barrier prior to subsequent applications of sulphur dyes. The first sulphur dye works as a barrier to the second sulphur dye application. This is because the first layer is applied with a very short immersion time (7 to 12.5 seconds) and not allowed more time in air oxidation (as air oxidation is slow and allows more dye to penetrate). It is washed with minimum air oxidation threading. The fresh water used for washing oxidizes the sulfur dye on the outer surface. The oxidized dye layer works as barrier for the second dye which is in reduced form. The oxidized dye does not convert in reduced form immediately, hence blocking the second dye being applied at later stage.
This method involves the application of a sulphur barrier, as described above, with reduced immersion, temperatures, and pH values which result in large particle accumulation on the perimeter of the yarn which later inhibits the penetration of the subsequent or following application(s) of sulphur dye. In this scenario, the barrier application is meant to alter the color of the yarn minimally or unrecognizably, and the more prominent dye is applied afterward, with the penetration of the second dye application reduced as a result of the former. Examples and embodiments of this invention should be understood to mean that in the case of a target shade being black, the yarns could experience a sulphur barrier application, colored or colorless, before a desired shade of sulphur black dye, or any alternative sulphur color, is applied. In the case of a target blue, the yarns are first dyed with a colored or colorless sulphur barrier before subsequent exposure to indigo dye. This application of a barrier of a sulphur compound or other chemical compound (as disclosed below) may be applied in the conventional scour box 102a, or sulphur bottom dye applications, or a traditional dye box 102b. Importantly, however, concentration, temperature, pH, and immersion times are changed from conventional dyeing methods as herein disclosed.
The barrier application, using of a sulphur dye, a sulphur compound, or other chemical compound (e.g., caustic soda), being applied before subsequent applications of the dye may be practiced with several different methods. One such method is the application of the barrier layer using a sulphur dye, sulphur compound, or other chemical compound in the box typically associated with the scour stage (scour box 102a). This stage is typically associated with scouring and is oftentimes also used for sulphur bottom applications as well. These applications may be for sulphur bottom indigo top, or simply an application of sulphur dye where the shade requires more than one dye vat of sulphur. Practicing the disclosed method of dyeing may use this stage for the barrier application of the pre-reduced sulphur dye, sulphur compounds, or other chemical compounds to act as a barrier, as described above. The application of a light, colorless, or nearly colorless sulphur dye is preferred for yarn colorations that are intended to be lighter colors, such as a shade of blue associated with a light add-on of 2-4%. Typically the application of sulphur dye stuffs as a barrier requires a reduced concentration, as detailed above. This is necessary so as to be certain that the barrier application does not substantially alter the desired color or shade of the subsequent dyes. Alternatively, using the application of sulphur compounds as a barrier to subsequent applications of sulphur dye, allows the concentrations and visual impact of the sulphur compounds in this sulphur barrier/scour stage to be increased slightly. In a conventional range, the sulphur dye concentrations may be from 10 g/l to 50 g/L, with a dye vat temperature of 85° C.-95° C. Implementing the method of dyeing according to the invention allows a reduced immersion time in the dye vat to the preferred immersion range of 7-12.5 seconds, with diminishing benefits with increased deviation from this range. The purpose and intent of the chemistry in dye reduction is to alter a naturally water insoluble dye to a soluble state, depriving the dye of oxygen. After the application of dye, this process is reversed. Conventionally, the dye stuffs are returned to the insoluble state after the dye has intermixed with the yarns by exposure to air and the oxygen in the air. This is often referred to as “sky-time” as the yarns are typically spooled through a series of rollers high above the dye vats such that the yarns undergo 30-140 seconds of sky time. Practicing the disclosed method, the yarns 106 being dyed are followed by a water oxidation stage with minimal to no air oxidation between the dyeing and the water oxidation stage. This is true for both the application of barrier, as well as the subsequent applications of sulphur dyes. Indigo dyes, however, still undergo the conventional sky time.
Other chemicals not typically associated with dyeing may be used as a barrier to dye penetration. Chemistries that may be used to act as a barrier as described may be dimethylol dihydroxyethyleneurea (DMDHEU). DMDHEU is typically associated with wrinkle resistance of garments. It is believed that DMDHEU forms an essentially permanent bond to the yarns and, when applied thoroughly to the core, dramatically reduces the core penetration of dye. Application of DMDHEU preferably occurs during the spinning of the yarn. High density polyethylene (HDPE) may be similarly applied and act similarly as a physical barrier to dye penetration. The application of these alternatives to sulphur compounds can occur in the same scouring tank as described above.
A colorless or near colorless sulphur compound application, or other colorless or nearly colorless chemical compound being used as a barrier compound is an embodiment of this invention. A colorless or nearly colorless sulphur compound can be understood to mean a chemical compound that applies no significant or perceivable color change to the natural cotton, or a color change that is disproportionately faint when compared to conventional sulphur dyes. Preferably, such colorless sulphur compounds is similar to a sulphur dye, but without a chromophore. For example, a sulphur dye can be visibly apparent with dye box conditions being conventional with temperatures of 85-90° C., a pH around 12 to 13.5 and mV range of −500 to −680 and a concentration of dye being in a range of 20 g/L. A colorless or nearly colorless sulphur compound may be applied at a similar concentration range with similar dyeing conditions with an impact on color unobservable or deemed insignificant, while still applying the barrier properties of the larger sulphur compound typically associated with sulphur dyes. Truly colorless sulphur compounds can be applied at significantly higher concentrations, for example 200-350 grams/L, exaggerating the effect of the large molecule blocking subsequent dye applications. Dyeing applications of this nature with a colorless or nearly colorless sulphur compound is an embodiment of this invention and allows core penetrations of the colorless sulphur compound to further limit the first dye migration toward the inner core portion of the yarn.
The inventors have discovered, via trial results, that even nearly imperceptible applications of sulphur barrier (up to 5 grams/liter dye concentration in the vat) inhibit the progression of subsequent indigo dye, or even subsequent sulphur dyes, from penetrating further into the yarn core. The efficacy of sulphur dye as a barrier application is heavily influenced by temperature. Higher temperatures increase the amount of dye added to the yarn, by increasing the affinity of sulphur dye to the cellulose fibers, as well as the opening or expansion of the surface of the yarn, resulting in an increased surface area for the sulphur and other dye compounds to fix to the yarn. This higher temperature (80° C. or higher) opens the yarn, which increases the penetration of the dye towards the core of the yarn. The pH also impacts the application of sulphur dye. The higher the pH, the increased amount of dye added [Applied?] to the yarn. In dyeing applications, caustic is typically the chemical associated with increased pH levels. The caustic is associated with continued mercerization or causticization effect of cellulosic yarns, even during dyeing. Concentration of dye particles in a dye vat also contributes to the amount of dye added to the yarns. Immersion time and oxidation time also play important roles in potential core penetration.
A light or low concentration application of sulphur as a barrier involves using minimal values for some or all of these variables and represent embodiments and methods to achieve light sulphur applications. For example:
1. If while using a particular brand from a supplier of sulphur dyes the preferred operating temperature is 80-90° C., then the very light application may occur with a dye box maintained at approximately 50-80° C. or less, such as room temperature.
2. If using a concentration of 50-125 grams/L of a sulphur dye in a dye bath would typically produce a medium shade of gray, then a light application of sulphur may use a concentration of 0.5-5.0 grams/L in sulphur bottoming and indigo top combination. For sulphur bottom and sulphur top, the bottom concentration of sulphur may be 6 to 50 g/l.
3. If at a given concentration of sulphur dye at a particular temperature results in a medium shade of gray and the dye bath has a pH of 12.5, then the addition of sodium bicarbonate until the pH of the dye vat 102b is significantly reduced (11.0-12.5) relative to the pH commonly associated with target shade is one way to reduce the alkalinity of the dye stuffs (collective chemistries) and consequently reduce the impact the dye stuffs have on the yarn, but still applies sufficient sulphur dye to the yarns to inhibit subsequent applications of dye.
Each of the dozens of manufacturers of sulphur dye employ the use of complex chemistries with varying concentrations of chemicals within. The amount of dye required to attain the same shade will vary per the manufacturer and model within manufacturers, as will the pH and mV values which correspond to these respective dyes.
The inventors have identified, as a first technique, the use of sulphur dyes, sulphur compounds, or other compounds as a barrier to the further penetration of subsequent dyes.
A second embodiment of the present invention involves the elimination of scouring agents (caustic) from the scour box 102a (no barrier application). Conventionally scoured yarns are treated with both wetting agents and caustic. The purpose of the scouring is to break down the dirt, oils and waxes within the yarn, and the wetting agent (a surfactant) is used to reduce the surface tension of the chemistries within the box. The wetting agents help to lessen the hydrophobic properties of the yarns. Wetting agents act as a surfactant, increasing the permeation of dyes and other chemistries through the yarn. An example of a wetting agent may be, but is not limited to, Primasol from Archroma. When used with caustic, the two chemicals work in unison to further cleanse the yarns. When used alone, the wetting agent simply makes the surface of the yarn less hydrophobic which increases the consistency of the dye penetration in the perimeter of yarn that absorbs dye, resulting in a more even coloring. The absence of wetting agents before or during the dyeing stages often results in streaks of dyed, lightly dyed, and undyed portions of the yarn, which are undesirable. Scouring boxes encountered throughout the world by the inventors have, without exception, contained both caustic and wetting agents together. One embodiment is the elimination of the scouring caustic chemistry. This technique, with the yarn exposure to a wetting agent concentration range of 0.5 g/L to 4.5 g/L based on strength of wetting agent commercially available in the market, aids in creating uniformly dyed yarns without excess dye penetration. Thus, in the second embodiment, the caustic is removed from the scouring box 102a but not the wetting agent.
A third embodiment of the present invention involves the elimination of a scouring (or prewetting) stage, and the subsequent scour rinse entirely. It is customary for a denim mill to operate a scour vat 102a for all yarns 106. A scour vat 102a may also be referred to as a prewet vat. The purpose of the scouring stage is to clean the yarn, the amount dependent on the amount of caustic and the efficacy of the rinse, as well as to introduce wetting agents to the yarn. This preparation is considered necessary by the current state of the art as it is thought as the only solution for consistent dyeing across the length of the dyed yarns. Elimination of the scour stage may be done through the rethreading of the yarns, such that the yarns are not immersed in any chemistry of the scour rinse, or simply through a minimal immersion in water as a respective dye range may dictate due to the setup of the rollers from the beginning of the dye range and the path to the dye tanks. This embodiment relies on the caustic within the dye tanks to clean only an outside portion of the yarn during the dyeing stage. The addition of a low concentration of wetting agent of 0.25 to 3.0 g/L to the dye vats 102b aids in the uniformity of dyeing relative to the perimeter shape of the yarn. One embodiment is the complete bypassing of this scouring and scour rinsing stage, and instead relying on an alkaline condition within dye vats 102b with the addition of the low dose (up to 1 g/L) of a wetting agent in the dye bath. The use of the wetting agent is preferred in order to have uniformity of the dye penetration of the yarns, but may be eliminated as well. Another embodiment is the complete bypassing of the scouring stage but not the scour rinsing stage. In this case, the yarns are processed through a scour rinsing vat 102d filled with water, so that they are wet before being introduced into the dye tanks 102b. The purpose of this introduction to water is to eliminate the increased uptake of chemistry that yarns experience when dry yarns are immersed. This designation is referred to as wet to wet, vs dry to wet immersion.
A fourth embodiment involves the use of sodium bicarbonate, or acidic chemistries to the dye vats 102b, to reduce alkalinity indicated by high pH levels (ph>12.7) often associated with higher concentrations of sulphur dye usage. As previously disclosed, pre-reduced sulphur dyes contain caustic and other reducing chemistries, which result in an elevated pH. When increased concentrations of pre-reduced dye are required, the pH necessarily increases because of the accompanying caustic. Reducing the pH and alkalinity of the dye stuffs reduces the affinity the dye has on the yarn, lessening the dye penetration toward the center of the yarn. Preferably, 5 g/L to 20 g/L of sodium bicarbonate is added to the dye vats 102b.
Both indigo dyes and sulphur dyes are distributed as either powder or pre-reduced liquid. The chemistry associated with the reduction (turning the dye from an insoluble state to a soluble state) of sulphur involves high concentrations of caustic as a solubilizing agent and reducing chemicals for reduction of the dye. This dye chemistry is then added to a dye vat 102b with water. The reducing chemistry reduces the amount of oxygen within the dye vat 102b. The darker the desired shade, the more dye and dye chemistry that is added to the dye vat 102b (increasing the concentration of the dye and dye chemistry in the dye vat 102b). The amount of dye used for each dyeing application is dependent on the target shade which is determined by the customer or the mill. As this dye is mixed or premixed with caustic and other chemicals, adding more dye necessarily results in adding substantially more caustic, as well as the other chemicals used in dye reduction. The amount of dye added will vary based on the desired shade, and the volume of the dye box (dilution). Conventional dyeing with sulphur dyes with darker shades, the mills simply dye with these elevated pH levels of 12.5 or higher.
The inventive approach limits the penetrative action of the dye that is caused by the elevated alkalinity the caustic imparts on the yarns. The sodium bicarbonate (or other acid) is introduced specifically to better reduce the pH of the sulphur dye tanks 102b to a pH range of 12.3-13. Sodium bicarbonate is a basic salt with a pH that is higher than neutral but lower than that of the caustic. Adding the sodium bicarbonate to a tank with caustic results in the creation of carbonic acid, a weak acid that reduces alkalinity, sodium carbonate, a very weak base, and water, essentially reducing the caustic left in the tank and lowering the pH. This approach, when practiced as described, yields a sufficiently reduced dye, without the excess aggressive alkalinity acting on the yarns. The inventors found sodium bicarbonate as a preferred chemical to control (lower) pH and alkalinity, however, other chemicals may be used. The concept is to control the pH and alkalinity to a pH range of 12.3-13, preferably 12.5-13, to prevent further dye penetration while still retaining optimal dye solubility.
A fifth embodiment involves an increase in the number of sulphur dye boxes 102b when the dye (not just the barrier) is a sulphur dye. One obstacle in obtaining a dark shade with sulphur black applications is the conventional method of doing so. With conventional indigo dye applications, it is customary to use as many as a dozen dye vats 102b for dye applications but, without exception, the inventors have yet to see any example of sulphur dye application that involved more than two sulphur dye tanks. To achieve darker shades with sulphur dye, the conventional practice is simply to increase the concentrations of the sulphur dye in one or both boxes. As disclosed elsewhere in this application, one significant hurdle when dyeing with sulphur is the high amount of caustic and other reducing chemistries necessary for dye reduction as well as the increase in alkalinity associated with increased dye concentrations. This conventional technique can result in sulphur dye tanks with concentrations as high as 250 g/L of sulphur dye, and the accompanying reducing agents. One inventive technique to resolve the issues that arise from these higher concentrations is to dye with sulphur using an increased number of dye tanks 102b and a lower concentration of dye (and as a result, lower accompanying reducing agents) in each respective dye tanks 102b to better control dye penetration with reduced alkalinity. For example, a fabric with a target color may require 12% shade or add-on of dye. Conventional techniques may call for dye concentrations in two different dye boxes to be high, 250 g/L, for example, in order to achieve that shade. Practicing the invention of sulphur dying, three or more sulphur dye vats 102b with a lower concentration, for example 150 g/L or less, are used. This concept is novel in comparison to the methods in the industry regarding sulphur dyes, and particularly so when also employing the other embodiments of this invention.
A sixth embodiment of the present invention involves % add on of sizing and specificity in the type of sizing. Sizing is a chemistry that is applied after completion of the dyeing process and results in strengthening of the yarns, which is may be necessary to withstand the forces the yarns experience in weaving. The application of sizing is done through immersion, not dissimilar to the immersion of the yarns in dye. Sizing is also applied in a vat process which may or may not be located on the dye range. Sizing is understood to mean the application of starches or engineered chemicals to yarns which act as a lubricant and improve strength in the weaving stage. Starches may be potato starch, corn starch, rice starch, tapioca starch, etc. Engineered chemicals, such as carboxy methyl cellulose (CMC) or polyvinyl alcohol (PVA), are often used with, or in replacement of natural starches for the same purpose. PVA is an attractive alternative to many mills, as the cost compared to natural starches is often lower. The starches are necessary for the yarns to withstand the weaving process, but the starches also require removal before the final garment can be finished and worn by a consumer. PVA is inefficiently removed with high water temperature (>85° C.) or through chemical processes, such as the one described in the Shell Oil patent U.S. Pat. No. 3,682,583. The issue with PVA sizing, as well as the excessive application of natural starches, is that when energies, which are applied to the garment to selectively remove the dye, are absorbed and wasted by the sizing applications. Because the radiation is absorbed by the sizing, additional energy must be used to remove the dye. The use of PVA or excessive natural starches results in garment staining and dull finishes from laser application, for example. The inventive parameters call for the application of natural sizing with potato, rice, corn, or tapioca in the lowest percent add-on that results in an acceptable proficiency in weaving, typically between 5% and 12%, based on yarn size.
Although certain presently preferred embodiments of the invention have been specifically described herein, it will be apparent to those skilled in the art to which the invention pertains that variations and modifications of the various embodiments shown and described herein may be made without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention be limited only to the extent required by the appended claims and the applicable rules of law.
This application is related to and claims the priority of U.S. Provisional Patent Application No. 63/224,244, filed Jul. 21, 2021, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63224244 | Jul 2021 | US |
