How to Prevent Spotting When Using Disperse Dyes
Dye spots when using Disperse Dyes have been a common issue in most exhaust dyeing operations on polyester and polyester blend fabrics. There is no one cause to this issue. Listed below are the major causes of these dye spots. The cause of spots may one or more items listed:
- Residual oil remaining in the fabric
- Compatibility of the chemicals used in dyeing process
- Disperse dyes used
- Compatibility of dyes with the chemicals
- Defoamer
These all have equal importance and need for evaluation when resolving issues.
How to Prevent Spotting
Residual Oils Remaining in Fabric:
Please refer to the FSW, LLC website: www.fsw.cc and the detailed Blog from Angelo Ardino, Senior Technical Manager FSW, LLC: Preparing Polyester Fabrics: Saving Time Down the Line
Compatibility of the Chemicals Used in the Dyeing Process:
This is often overlooked and with the increasing number of chemicals being used, especially wicking agents, reduction blockers, dispersants, levelers, etc., compatibility is a concern. Depending on the products used, you must develop a procedure to make certain there are no stability issues. This may require pre-diluting certain chemicals, and making the product in separate tanks before adding to machine.
In some instances, certain chemicals are not compatible no matter the procedure. When this occurs, alternates must be evaluated and used.
Disperse Dyes Used:
The number of Disperse Dye manufacturers has increased significantly, especially for commodity dyes. If the dye has poor solubility, the chance for dye spots increases significantly. The supplier should be requested to supply Certificate of Analysis on all products/lots which include filter test results. This should include filter time and residue—especially spots on the filter paper. And you should attach a photo of the filter paper.
Even when a Disperse Dye has a good filter tests results, spotting can still occur with certain dyes.
With these dyes, we recommend the addition of:
1-2 G/L SORA SPERSE T-N LIQUID
0.5 G/L SORA LEV HTD
These should be added to the make-up tank prior to the dyes and mixed for 15- 20 minutes after dyes are added.
However, there are certain dyes, depending on the manufacturer and dye molecule, where the dispersion may not withstand the sheer force of jets and package machines. In this case, alternative dyes must be used.
Compatibility of Dyes with the Chemicals:
In many instances, this is the most difficult to determine. There are Disperse Dyes where the dispersion is affected by the chemicals with the shearing force experienced during the dyeing process. Large molecule dyes, such as phthalocyanine turquoises, are an example. This requires extensive lab evaluation.
Defoamer:
For years, this was considered—right or wrong—to be the major cause of spotting. Especially with the early silicone defoamers.
The amount of defoamer used has been significantly reduced with the introduction of low-foaming chemistry and multifunction products such as:
SORA SCOUR LF-MD
SORA SPERSE T-N LIQUID
SORA PLUS LDE
SORA LEV HTD
Products must be checked for compatibility with all other chemicals. When used, the defoamer must be pre-diluted before adding to the chemical tank.
This is only a guideline. Please contact FSW, LLC for assistance by clicking the picture below.
About the Author: Ed Tessener
