Denim Dyeing ? Classification and Description of Denim Dyeing Process ?

Denim Dyeing :

The classical jeans were produced out of indigo-dyed Denim fabric. The special character of this fabric – only the warp thread is dyed makes it necessary to carry out dyeing in yarn form. The yarns applied for Denim were exclusively produced on ring spinning machines in former times. The development of OE yarns by applying smaller rotors with a spinning speed of up to 200 m/min has led to the application of OE rotor yarns both for warp and weft. The yarns applied for weaving must be of high quality, a high fiber for strength, regularity as well as a small part of short-stapled cotton fibres belongs to the basic features of the denim yarn. For regular jeans qualities the warp yarns are spun in a fineness of 50 to 90 tex, for the weft yarn the fineness ranges are mainly 75 to 120 tex. If Denim is made out of Tencel or Modal especially for jeans shirts the finenesses are up to 25 tex. Indigo, sulphur and indanthrene are mainly used in the dyeing process. Two methods are applicable for continuous dyeing with indanthrene dyes: rapid dyeing and vat dyeing. While processing the basic colored denim, reactive dyes are used and fixed with hot caustic soda solution. The dyeing process is mainly influenced by the dyestuff characteristics, dyeing temperature and necessary chemicals used in the process. Indigo dye is the most popular choice as it has good depth of shade and suitable rubbing and washing fastness.

When cotton yarn is dyed with indigo, it leaves a ring-dyeing effect, because of which the outer layer of warp yarn is coated with indigo, and the core of the yarn remains undyed. This gives the denim garment a unique ‘faded look’ and a rich blue shade after repeated use and wash. Originally, the warp yarns or ends were put through the dye bath side by side to form a sheet of yarn, which passed continuously through several dye baths, squeeze rollers or airing sequences. Specially two types of dyes are commonly used in factory. Vat dye and sulphur dye.

These two types of dyes use for Denim :

  1. Vat Dyes
  2. Sulphur Dyes


Denim Dyeing Process :


There are three processes in the practice for continuous denim dyeing:

1. Rope Dyeing
2. Slasher or Sheet Dyeing
3. Loop Dyeing


1. Rope Dyeing :


The indigo Rope dyeing technology for denim production is considered a superior dyeing technology, where better uniformity of dyeing is achieved than other Indigo dyeing technologies like slasher dyeing. Indigo rope dyeing was started in USA.Today rope dyeing accounts for a large percentage of warp yarn dyed for denim production. The system offers highest production, due to continuous process, as there is no stoppages for set changes. In this dyeing method, maximum continuity of shades and minimum danger of center to selvedge shade variation can be achieved. Flow diagram of rope dyeing is shown in Fig. . During dyeing process, it forms a coating in the outer layers of the cotton yarn and fiber. This produces a ring of color around the cotton yarn, with the core remains white core. This dyeing effect is known as ring dyeing.

Denim Dyeing : The classical jeans were produced out of indigo-dyed Denim fabric. The special character of this fabric – only the warp thread is dyed makes it necessary to carry out dyeing in yarn form. The yarns applied for Denim were exclusively produced on ring spinning machines in former times. The development of OE yarns by applying smaller rotors with a spinning speed of up to 200 m/min has led to the application of OE rotor yarns both for warp and weft. The yarns applied for weaving must be of high quality, a high fiber for strength, regularity as well as a small part of short-stapled cotton fibres belongs to the basic features of the denim yarn. For regular jeans qualities the warp yarns are spun in a fineness of 50 to 90 tex, for the weft yarn the fineness ranges are mainly 75 to 120 tex. If Denim is made out of Tencel or Modal especially for jeans shirts the finenesses are up to 25 tex. Indigo, sulphur and indanthrene are mainly used in the dyeing process. Two methods are applicable for continuous dyeing with indanthrene dyes: rapid dyeing and vat dyeing. While processing the basic colored denim, reactive dyes are used and fixed with hot caustic soda solution. The dyeing process is mainly influenced by the dyestuff characteristics, dyeing temperature and necessary chemicals used in the process. Indigo dye is the most popular choice as it has good depth of shade and suitable rubbing and washing fastness. When cotton yarn is dyed with indigo, it leaves a ring-dyeing effect, because of which the outer layer of warp yarn is coated with indigo, and the core of the yarn remains undyed. This gives the denim garment a unique ‘faded look’ and a rich blue shade after repeated use and wash. Originally, the warp yarns or ends were put through the dye bath side by side to form a sheet of yarn, which passed continuously through several dye baths, squeeze rollers or airing sequences. Specially two types of dyes are commonly used in factory. Vat dye and sulphur dye. These two types of dyes use for Denim : Vat Dyes Sulphur Dyes Denim Dyeing Process : There are three processes in the practice for continuous denim dyeing: 1. Rope Dyeing 2. Slasher or Sheet Dyeing 3. Loop Dyeing Rope Dyeing : The indigo Rope dyeing technology for denim production is considered a superior dyeing technology, where better uniformity of dyeing is achieved than other Indigo dyeing technologies like slasher dyeing. Indigo rope dyeing was started in USA.Today rope dyeing accounts for a large percentage of warp yarn dyed for denim production. The system offers highest production, due to continuous process, as there is no stoppages for set changes. In this dyeing method, maximum continuity of shades and minimum danger of center to selvedge shade variation can be achieved. Flow diagram of rope dyeing is shown in Fig. . During dyeing process, it forms a coating in the outer layers of the cotton yarn and fiber. This produces a ring of color around the cotton yarn, with the core remains white core. This dyeing effect is known as ring dyeing. Slasher Dyeing : In continuous slasher/sheet dyeing and sizing machine, direct warping beams are used, instead of ball warping logs in case of Indigo rope dyeing system. The Slasher Dyeing machine is capable of handling Ne count form 9/s to 30/s (OE and Slub both). Typical schematic sheet dyeing range is shown in Figure. At the back end of the slasher/sheet dyeing range, the direct warping beams are creeled. The yarns sheet from each beam is pulled over and combined with the yarns from the other beams so that multiple sheets of yarns can be made. When dyeing according to the sheet dyeing method, instead of cables the warp threads are fed to the machine parallel next to each other. These are much smaller compared to the rope dyeing machines. Another advantage is that the cables don’t need to be open after dyeing. Moreover, each yarn wets much faster and in this way reduces the dipping and wetting times during dyeing. All in all, each thread has a larger surface compared to a dyeing cable and this requires somewhat more hydrosulphite to prevent a premature oxidation of the indigo. Loop Dyeing : In the loop dyeing process, the yarn is dyed in a single bath instead of several. The desired depth of color is attained by passing the yarn through the vat several times. Subsequently, as a part of the same process, the yarn is sized. The advantages and disadvantages of loop dyeing are the same as with sheet dyeing.
Figure : Rope Denim Dyeing Process

2. Slasher Dyeing :


In continuous slasher/sheet dyeing and sizing machine, direct warping beams are used, instead of ball warping logs in case of Indigo rope dyeing system. The Slasher Dyeing machine is capable of handling Ne count form 9/s to 30/s (OE and Slub both). Typical schematic sheet dyeing range is shown in Figure. At the back end of the slasher/sheet dyeing range, the direct warping beams are creeled. The yarns sheet from each beam is pulled over and combined with the yarns from the other beams so that multiple sheets of yarns can be made. When dyeing according to the sheet dyeing method, instead of cables the warp threads are fed to the machine parallel next to each other. These are much smaller compared to the rope dyeing machines. Another advantage is that the cables don’t need to be open after dyeing.
Moreover, each yarn wets much faster and in this way reduces the dipping and wetting times during dyeing. All in all, each thread has a larger surface compared to a dyeing cable and this requires somewhat more hydrosulphite to prevent a premature oxidation of the indigo.

Denim Dyeing : The classical jeans were produced out of indigo-dyed Denim fabric. The special character of this fabric – only the warp thread is dyed makes it necessary to carry out dyeing in yarn form. The yarns applied for Denim were exclusively produced on ring spinning machines in former times. The development of OE yarns by applying smaller rotors with a spinning speed of up to 200 m/min has led to the application of OE rotor yarns both for warp and weft. The yarns applied for weaving must be of high quality, a high fiber for strength, regularity as well as a small part of short-stapled cotton fibres belongs to the basic features of the denim yarn. For regular jeans qualities the warp yarns are spun in a fineness of 50 to 90 tex, for the weft yarn the fineness ranges are mainly 75 to 120 tex. If Denim is made out of Tencel or Modal especially for jeans shirts the finenesses are up to 25 tex. Indigo, sulphur and indanthrene are mainly used in the dyeing process. Two methods are applicable for continuous dyeing with indanthrene dyes: rapid dyeing and vat dyeing. While processing the basic colored denim, reactive dyes are used and fixed with hot caustic soda solution. The dyeing process is mainly influenced by the dyestuff characteristics, dyeing temperature and necessary chemicals used in the process. Indigo dye is the most popular choice as it has good depth of shade and suitable rubbing and washing fastness. When cotton yarn is dyed with indigo, it leaves a ring-dyeing effect, because of which the outer layer of warp yarn is coated with indigo, and the core of the yarn remains undyed. This gives the denim garment a unique ‘faded look’ and a rich blue shade after repeated use and wash. Originally, the warp yarns or ends were put through the dye bath side by side to form a sheet of yarn, which passed continuously through several dye baths, squeeze rollers or airing sequences. Specially two types of dyes are commonly used in factory. Vat dye and sulphur dye. These two types of dyes use for Denim : Vat Dyes Sulphur Dyes Denim Dyeing Process : There are three processes in the practice for continuous denim dyeing: 1. Rope Dyeing 2. Slasher or Sheet Dyeing 3. Loop Dyeing Rope Dyeing : The indigo Rope dyeing technology for denim production is considered a superior dyeing technology, where better uniformity of dyeing is achieved than other Indigo dyeing technologies like slasher dyeing. Indigo rope dyeing was started in USA.Today rope dyeing accounts for a large percentage of warp yarn dyed for denim production. The system offers highest production, due to continuous process, as there is no stoppages for set changes. In this dyeing method, maximum continuity of shades and minimum danger of center to selvedge shade variation can be achieved. Flow diagram of rope dyeing is shown in Fig. . During dyeing process, it forms a coating in the outer layers of the cotton yarn and fiber. This produces a ring of color around the cotton yarn, with the core remains white core. This dyeing effect is known as ring dyeing. Slasher Dyeing : In continuous slasher/sheet dyeing and sizing machine, direct warping beams are used, instead of ball warping logs in case of Indigo rope dyeing system. The Slasher Dyeing machine is capable of handling Ne count form 9/s to 30/s (OE and Slub both). Typical schematic sheet dyeing range is shown in Figure. At the back end of the slasher/sheet dyeing range, the direct warping beams are creeled. The yarns sheet from each beam is pulled over and combined with the yarns from the other beams so that multiple sheets of yarns can be made. When dyeing according to the sheet dyeing method, instead of cables the warp threads are fed to the machine parallel next to each other. These are much smaller compared to the rope dyeing machines. Another advantage is that the cables don’t need to be open after dyeing. Moreover, each yarn wets much faster and in this way reduces the dipping and wetting times during dyeing. All in all, each thread has a larger surface compared to a dyeing cable and this requires somewhat more hydrosulphite to prevent a premature oxidation of the indigo. Loop Dyeing : In the loop dyeing process, the yarn is dyed in a single bath instead of several. The desired depth of color is attained by passing the yarn through the vat several times. Subsequently, as a part of the same process, the yarn is sized. The advantages and disadvantages of loop dyeing are the same as with sheet dyeing.Figure : Slasher/Sheet Denim Dyeing Process

3. Loop Dyeing :


In the loop dyeing process, the yarn is dyed in a single bath instead of several. The desired depth of color is attained by passing the yarn through the vat several times. Subsequently, as a part of the same process, the yarn is sized. The advantages and disadvantages of loop dyeing are the same as with sheet dyeing.


Denim Dyeing : The classical jeans were produced out of indigo-dyed Denim fabric. The special character of this fabric – only the warp thread is dyed makes it necessary to carry out dyeing in yarn form. The yarns applied for Denim were exclusively produced on ring spinning machines in former times. The development of OE yarns by applying smaller rotors with a spinning speed of up to 200 m/min has led to the application of OE rotor yarns both for warp and weft. The yarns applied for weaving must be of high quality, a high fiber for strength, regularity as well as a small part of short-stapled cotton fibres belongs to the basic features of the denim yarn. For regular jeans qualities the warp yarns are spun in a fineness of 50 to 90 tex, for the weft yarn the fineness ranges are mainly 75 to 120 tex. If Denim is made out of Tencel or Modal especially for jeans shirts the finenesses are up to 25 tex. Indigo, sulphur and indanthrene are mainly used in the dyeing process. Two methods are applicable for continuous dyeing with indanthrene dyes: rapid dyeing and vat dyeing. While processing the basic colored denim, reactive dyes are used and fixed with hot caustic soda solution. The dyeing process is mainly influenced by the dyestuff characteristics, dyeing temperature and necessary chemicals used in the process. Indigo dye is the most popular choice as it has good depth of shade and suitable rubbing and washing fastness. When cotton yarn is dyed with indigo, it leaves a ring-dyeing effect, because of which the outer layer of warp yarn is coated with indigo, and the core of the yarn remains undyed. This gives the denim garment a unique ‘faded look’ and a rich blue shade after repeated use and wash. Originally, the warp yarns or ends were put through the dye bath side by side to form a sheet of yarn, which passed continuously through several dye baths, squeeze rollers or airing sequences. Specially two types of dyes are commonly used in factory. Vat dye and sulphur dye. These two types of dyes use for Denim : Vat Dyes Sulphur Dyes Denim Dyeing Process : There are three processes in the practice for continuous denim dyeing: 1. Rope Dyeing 2. Slasher or Sheet Dyeing 3. Loop Dyeing Rope Dyeing : The indigo Rope dyeing technology for denim production is considered a superior dyeing technology, where better uniformity of dyeing is achieved than other Indigo dyeing technologies like slasher dyeing. Indigo rope dyeing was started in USA.Today rope dyeing accounts for a large percentage of warp yarn dyed for denim production. The system offers highest production, due to continuous process, as there is no stoppages for set changes. In this dyeing method, maximum continuity of shades and minimum danger of center to selvedge shade variation can be achieved. Flow diagram of rope dyeing is shown in Fig. . During dyeing process, it forms a coating in the outer layers of the cotton yarn and fiber. This produces a ring of color around the cotton yarn, with the core remains white core. This dyeing effect is known as ring dyeing. Slasher Dyeing : In continuous slasher/sheet dyeing and sizing machine, direct warping beams are used, instead of ball warping logs in case of Indigo rope dyeing system. The Slasher Dyeing machine is capable of handling Ne count form 9/s to 30/s (OE and Slub both). Typical schematic sheet dyeing range is shown in Figure. At the back end of the slasher/sheet dyeing range, the direct warping beams are creeled. The yarns sheet from each beam is pulled over and combined with the yarns from the other beams so that multiple sheets of yarns can be made. When dyeing according to the sheet dyeing method, instead of cables the warp threads are fed to the machine parallel next to each other. These are much smaller compared to the rope dyeing machines. Another advantage is that the cables don’t need to be open after dyeing. Moreover, each yarn wets much faster and in this way reduces the dipping and wetting times during dyeing. All in all, each thread has a larger surface compared to a dyeing cable and this requires somewhat more hydrosulphite to prevent a premature oxidation of the indigo. Loop Dyeing : In the loop dyeing process, the yarn is dyed in a single bath instead of several. The desired depth of color is attained by passing the yarn through the vat several times. Subsequently, as a part of the same process, the yarn is sized. The advantages and disadvantages of loop dyeing are the same as with sheet dyeing.
Figure : Loop Denim Dyeing Process


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