What is Rope Dyeing?
Rope dyeing technique dates from 1915, when the first rope dyeing machine appeared. This dyeing is considered a superior dyeing technology where the dyeing uniformity achieved is better than other indigo dyeing technologies like slasher dyeing or sheet dyeing. However, rope dyeing is also a more difficult dyeing technology. One needs to master its nitty-gritties to get the best out of the system.

Rope dyeing is the oldest way to dye warp yarns (ropes) and does not have any risk concerning “side to side” problem. Moreover, dyestuff absorption is almost the same since that all the ropes have the same tension during the process.

Believed to be the best possible indigo dyeing method for yarn, the threads of denim yarn are initially twisted into a rope, then undergo a repetitive sequence of dipping and oxidization. The more frequent the dipping and oxidizing, the stronger the indigo shade.

Rope dyeing consists of twisting the yarns into a rope that is then quickly dipped into indigo baths. It is considered the best method for dyeing denim, as the short dyeing time does not allow the indigo to fully penetrate the fibers, thus creating ring-dyed yarn that fades better and faster than fully dyed yarn.

Dyeing of fabric in rope form is in practice from the oldest days of hand dyeing of fabrics. As the speed of dyeing and handling more fabric at a time was demanded, machines such as winch and jet dyeing were developed. Dyeing in rope form can be done for woven fabrics as well as knitted fabrics. For delicate and light fabrics, ropes dyeing is preferred.

Rope Dyeing Range:
In this type of denim range, warp threads are extended along the range in the form of a rope. Yarn groups are composed of 300 or 400 ends forming ropes or cables. The total width of rope ranges is taken up by a number of ropes ranging between 12 and 48, depending on the width of the machine. The total number of ends, depending on the number of ropes, can range between 3,600 and 19,200. A dye box in the denim warp rope dye range is shown in Figure 1.

Flow Chart of Rope Dyeing

Ball warping

↓

Rope dyeing

↓

Re-beaming

↓

Sizing

↓

Weaving

↓

Finishing

The passage of yarn in rope dyeing is as follows:

Pre-scouring

↓

Hot wash

↓

Cold wash

↓

Dye baths

↓

Hot wash

↓

Cold wash

↓

Application of softener

Rope Dyeing Process:
The yarn coming out from the ring frames is wound into cheeses or cones and then placed on the ball warper on which 350–400 warp threads are bound on the ball warper machine to very thick cables of 10,000–15,000 m in length (sometimes the length of cables may exceed 25,000 m). Generally 12–36 cables are first fed into one or more scouring baths containing wetting agents, detergents and sodium hydroxide. The scouring baths are used to remove naturally occurring impurities found in cotton fibers such as dirt, minerals, ash, pectin and naturally occurring waxes. It is very important to remove these substances in order to achieve uniform wetting and uniform dyeing. Then, the cables are fed into one or more water rinsing baths.

After that, the cables are dipped into a bath of leuco indigo with an immersion time of 12–20 s, and then are squeezed to give 70%–80% wet pick-up after each dip, followed by exposure to air for oxidation, multiple times. The oxidation time takes at least 80 s. Generally, four to eight dyeing vats are used for dipping. This results in the fine layer of indigo on the surface of yarn. The cables of yarn are washed in various water baths to eliminate the non-fixed dye. Next they pass through a softener box, which assists in obtaining a better opening of the cables in the long chain beamer. Finally, they are dried on Teflon covered cylinders and coiled into large cans.

In rope dyeing, ball warps are continuously fed into the rope or chain-dyeing range for application of the indigo dyeing. Typically, 12–36 individual ropes of yarn are fed side-by-side simultaneously into the range. The ropes are kept separate from each other throughout the various parts of the dye range.

Why Softener is Used in Rope Dyeing?
The rope is going to be opened at long chain beamer. If the softener is not used, opening will be hampered. It is generally 1.2% of the weight of the yarn. It is a cationic softener. It is always having pH in the range of 4–55. Softening is done at room temperature. If high temperature is used, there is always some chance of tendering of yarn.

Machinery of Rope Dyeing:
In the market, six companies generally produce the indigo rope ranges for the production of denim fabrics. These companies are Morrison Textile Machinery (USA), Master S.r.l. (Italy), Karl Mayer Textilmaschinenfabrik GmbH (Germany), Looptex Company (Italy), Komatsubara Iron Works Ltd. (Japan) and Smartec Machinery & Engineering Inc. (China).

Advantages and Disadvantages of Rope Dyeing:

Advantages are:

1. Better squeezing takes place, resulting uniform and better oxidation, because it is squeezing in rope form
2. Better color fastness
3. No stripe effect
4. Less side–centre–side variation

A disadvantage is:

1. The process sequence is high, leading to more space and a higher worker requirement

Advantages of Rope Dyeing against Slasher Dyeing:

1. Large quantities can be dyed continuously.
2. In this dyeing technique, ropes are dipped into the dye pads with identical tension and angle; therefore, there is not any risk of “side to side” problem.
3. Dyeing machine does not have to stop while feeding new dyeing parties which means energy saving.
4. Yarn wastage is not that much.

References:

1. Textile Dyeing By Dr. N. N. Mahapatra

2. Denim: Manufacture, Finishing and Applications Edited by Roshan Paul

3. Sustainability in Denim Edited by Subramanian Senthilkannan Muthu

4. Textile Handbook By The Hong Kong Cotton Spinners Association
5. Handbook of Value Addition Processes for Fabrics By B. Purushothama
6. Textile Chemistry By Thomas Bechtold and Tung Pham
7. Textile Dyes By Dr. N. N. Mahapatra

You may also like:

1. Slasher / Sheet Dyeing Process with Advantages and Disadvantages
2. Denim Dyeing Process with Indigo Dyes
3. Different Types of Dyeing Methods
4. Process Flow Chart of Yarn Dyeing | Methods of Yarn Dyeing

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.

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