T. Kaneko Product Information Team Manager Senka Corporation

Stopgap measures for dealing with major cases of faulty dyeing one by one as they occur will not eliminate the fundamental reasons behind faulty dyeing. It is important that these reasons be carefully studied and eliminated.

In dyeing plants in South America, for example, uneven dyeing cannot be eliminated effectively regardless of the quantity of leveling agents used. This is due to problems with the water quality. Similar problems can also be found in China where major problems related to uneven dyeing repeatedly occur in dyeing plants using jet dyeing machines. Use of the chelating agent Multifine 25, however, will eliminate rope marks and major cases of uneven dyeing. While poor water quality can also lead to clogging of dyestuff in cheese and muff dyeing, it is important to note that not all problems can simply be attributed to the water.

While its chemical formula is H₂O, water often contains various impurities. Thus as a first step towards level dyeing, the water quality must be carefully examined. If any problems are found, a chelating agent can be used in order to alter the basic dyeing conditions. In the case of jet dyeing, the following 7 points should be checked before commencement of operations.

1. Preventing major problems related to uneven dyeing and rope marks: The reason for these problems is not limited to poor water quality. They can also be the result of poor operational conditions of the jet dyeing machine or winch. Furthermore, failure to check the levelness of the dyestuff can lead to uneven dyeing and rope marks. Problems can also be caused by errors in the use of leveling agents, in the dyeing temperature program or in the setting of the liquor ratio.

   Illustrative examples of measures for the prevention of problems in jet and winch dyeing are introduced below.

2. Prevention of rope marks: In the case of polyester, examination of the preset conditions of the substrate before dyeing will ensure no problems occur, but rope marks will occur if this examination is omitted. Poor conditions during relax scouring can result in rope marks, as can unskilled use of a jet dyeing machine, such as errors in setting the fabric speed, or unsuitable settings for the speed of the reel moving the fabric, the rate of flow in the dyeing tank or the length of fabric for one circulation. Mistakes in the method of cooling the dyeing solution after the conclusion of dyeing can also lead to rope marks.

3. Prevention of friction marks: Measures for the prevention of friction marks are the same as those for item (2) above.

4. Prevention of floating: Uneven dyeing can occur in jet and winch dyeing due to the fabric floating out of the dye solution on foam. This can be avoided by treating the fabric in hot water with a suitable auxiliary before dyeing. This ensures that the substrate is completely wet and thus sinks into the dyebath. However, it is necessary to ensure a balance between the circulation speed of the cloth in the dyeing machine and the total length of the substrate.

5. Prevention of minor cases of uneven dyeing: Minor cases of uneven dyeing can occur when a disperse dyestuff with poor covering properties is used. When the use of a disperse dyestuff with poor covering properties cannot be avoided, an auxiliary for raising the level of covering should be used.

6. Prevention of topping: This can be prevented by thorough reduction clearing. The most suitable reduction clearing agent varies according to the fiber or blend being treated. Prevention of staining is important in the case of polyester/polyurethane blends and for this UNIONAL SN can be used as an anti-staining agent. In removing stains from blends of polyester and other fibers, the soaping agent Senkanol ES-1 can be effective.

7. Maintaining the level of colorfastness: Dyestuffs resistant to post-processing should be used to prevent any reduction in the level of colorfastness. Alternatively, the use of a post-processing agent can be considered. This will prevent any reduction in the level of colorfastness of the dyed fabric.

Choosing auxiliaries

The basic measures for dealing with faulty dyeing have been outlined above.

Trying to improve the properties of migration or dispersing without a solid grasp of these basics will prove a fruitless endeavor. Selection of auxiliary agents for improving the migration and dispersing properties can only be reached after systematic implementation of the measures outlined in the above seven items.

For example, in order to improve the migration and dispersing properties in the dyeing of polyester when using a disperse dyestuff with poor dispersing properties as opposed to a common, frequently used one, a leveling agent to improve the migration properties should be used. However, a leveling agent which produces good results in dyeing plant A will not necessarily produce good results in dyeing plant B. This is because the levelness of the dyeing at the plants is decided by the disperse dyestuffs used. Since in some cases better dyeing results may be obtained through the use of a leveling agent with good dispersing ability rather than one with good migration, leveling agents should not all be considered as having the same properties.

Using the analogy of human ailments, let's say A has a liver complaint while B is in the early stages of tuberculosis. Medicine taken by A for treating his liver will not be effective in the treatment of B's tuberculosis. Similarly, in choosing a leveling agent, one cannot simply follow another factory's lead.