Bleeding dyes from cleaned items are observed almost daily in drycleaning plants. According to IFI’s Garment Analysis statistics, solvent-soluble dyes and pigments lead the category of manufacturer responsibility for garment damage.
Yet, dyes which remain in solvent are the drycleaner’s problem. According to the IFI Garment Analysis statistics, 11 percent of the drycleaner responsibility category was caused by redeposition of dyes and soils in solvent.
Therefore, the importance of solvent color in drycleaning systems cannot be overemphasized. The cleaner must deal with discolored solvent promptly, otherwise the dissolved dye will redeposit on items in the load and discolor light colored items. The cleaner is responsible for a dye transfer that results from discolored solvent.
Testing for Fugitive Dyes
It is the manufacturer’s responsibility to use dyes that are resistant to water or drycleaning solvents. However, in practice this is not always done. In many instances, the dye bleeding items, or “bleeders,” can be easily identified in the plant.
To test an article for colorfastness, an unexposed area of the item should be lightly rubbed with a white paper towel, a blotter, or fabric wet with solvent.
Fugitive dyes are most common on velvets and corduroys, especially blues, reds, and blacks. In some cases, immersion of just one item in drycleaning solvent causes extensive dye bleeding, which in turn can discolor the entire drycleaning bath.
Function of Activated Carbon
Distillation is the most effective method of removing all impurities, including dyes, from solvent. However, distillation is not always the most economical way to remove small amounts of dyes from solvent. It is the activated carbon’s job to take care of the free dye and restore the solvent color to an acceptable condition.
In the past, when cleaners were using mostly powder filtration (i.e., rigid screen or tube, or flex tube), removal of dyes from the solvent was a relatively easy task. All the operator had to do was add additional powdered activated carbon into a filter system. Powdered carbon removes dyes much faster, and subsequently expires its efficiency faster than granulated carbon. Besides, the powdered carbon together with the filter powder was discarded every day, so the next cleaning day started with fresh powder and carbon.
On the other hand, granulated carbon used in cartridges acts slower than powdered carbon in dye removal. This slow action is intentional. Unlike powdered carbon, the granulated carbon in the cartridges should be effective for about 800 to 1,000 pounds of clothes cleaned under normal cleaning conditions. However, in cases of severe dye contamination in the solvent, this slow action becomes a drawback. Even with fresh carbon core cartridges, the time during which the solvent passes through the cartridges is usually too short to effectively remove dyes from solvent.
Controlling Color With Cartridges
According to IFI’s Equipment and Plant Operation Survey from March 1989, 86 percent of respondents use cartridge filtration.
Currently, granulated activated carbon is used in three types of cartridges. The most common type is a carbon-core cartridge. It usually contains about two pounds of granulated carbon for solvent color control. The second, an adsorptive type of cartridge, contains a mixture of granulated carbon in addition to granulated activated clay to control nonvolatile residue. However, the main function of both types of cartridges is to filter soil particles from the solvent. The third type, the all-carbon cartridge, serves the sole purpose of dye removal from the solvent.
Usually, the carbon-core part of the cartridge exhausts its power to remove dyes before the filter paper in the cartridge reaches its soil removal capacity. Because of this, it is recommended that drycleaning plants use all-carbon cartridges to increase the usefulness of carbon-core cartridges.
The all-carbon cartridges can be used in two ways: One is to use all-carbon cartridges in combination with the carbon-core cartridges in the same filter housing. The second option is to use one filter housing only for all-carbon cartridges. In smaller capacity drycleaning machines where, for example, only four carbon-core cartridges are used in two filter housings, the installation of an additional filter housing for all-carbon cartridges is a good idea.
The advantage of a separate filter housing for use of all-carbon cartridges is evident from two practical points. First, in cases where the all-carbon cartridges are exhausted, only these cartridges have to be replaced; providing that the carboncore cartridges are still performing their filtration duty well. Second, the separate housing for the all-carbon cartridges allows the operator to use the all-carbon action when needed. All the operator has to do is to shut off the carbon-core cartridge housings (when the machine is not in regular wash cycle) and open the valve into the all-carbon housing to allow the solvent to pass through the all-carbon cartridges as long as needed. Ideally, the solvent should pass through the all-carbon cartridges at a lower flow rate than normally used for the regular wash cycle. This will prolong the residence of the dye contaminated solvent in the all-carbon cartridge housing, thus increasing the color removal efficiency.
An Alternative Method
There is another option for drycleaning suspected bleeders. The alternative is to save all those deeply colored garments for the last load of the day. Use a pre-wash (batch) operation with the addition of two or three ounces of existing detergent per 10 pounds cleaned. Simply fill the loaded wheel with distilled solvent, add detergent, and continue the batch operation for three to five minutes without engaging the filters. Then pump and extract the solvent into the still. If you continue to clean this load in the regular wash cycle (engaging filter cartridges), the load in some instances will still bleed, although not as much as during the pre-wash cycle. If this happens after the last wash cycle, continue the solvent circulation Solvent color is relatively easy to control with proper filtration and the recommended distillation rate of solvent. However, a tiny amount of dye can cause a severe discoloration of solvent, which in turn causes loss of whiteness, yellowing, or graying on items cleaned in the load. Activated carbon is the through your cartridges or through the all-carbon cartridges. In this manner, the decolorized solvent should be ready for cleaning the next day.
Using Carbon in Disc Filtration
Lately, the use of disc filtration is on the rise. Both the powder and powderless filtrations are designed to perform one basic duty: the separation of solid impurities from the solvent. The quality of the solvent is maintained by distillation. However, some manufacturers provide a separate filter housing for the all-carbon cartridge(s). Therefore, if the discoloration of the solvent occurs due to dye bleeding, solvent is passed through the all-carbon cartridge, bypassing the washer. This eliminates a more costly distillation.
Checking the Color of Solvent
It is a good idea to visually check the solvent color before and after the circulation of the solvent through the cartridges for the decolorization treatment. You need two clean glass jars. Take the initial solvent sample from the button trap, or the sampling valve (if available), and save it for the comparison purposes. Then, after 30 to 40 minutes of carbon treatment, take another solvent sample and compare the appearance and color against the initial sample. Remember, the correct color of solvent should be the color of a light straw. Do not rely on the solvent sight glass to make color comparison judgements.
Conclusion
Solvent color is relatively easy to control with proper filtration and the recommended distillation rate of solvent. However, a tiny amount of dye can cause a severe discoloration of solvent, which in turn causes loss of whiteness, yellowing, or graying on items cleaned in the load. Activated carbon is the most effective medium for removing this extremely small amount of dye. If the carbon treatment is ineffective for dye removal, it is because the discoloration is caused by a pigment, which is hard to remove by carbon, or the granulated carbon dye removal efficiency is exhausted to the point that it cannot perform an adequate job.
This article is from DLI’s TOI 647 – Dye Bleeders and Solvent Maintenance.
