TECHNOLOGY

Solvent dyeing shows promising economics Dow and Allied dye textiles from chlorinated solvents and undermine traditional aqueous methods

From the resplendent dyed silks of ancient times to the psychedelically colored polyesters of modern living, the dyeing of textiles has developed upon one fundamental premise: that water, once the only available solvent, is technically and economically the best of all possible solvents. But now Dow Chemical, a leading producer of chlorinated solvents, and Allied Chem­ical, a leading maker of dyes, are fast proving out the technology of solvent dyeing—a technology that marks the beginning of a new era in the chem­istry and operations of dyeing textiles.

Thus, the fundamental premise that water affords the most economical dyeing no longer appears to be valid.

Last week, Dow shipped a pilot processing line for evaluating solvent dyeing to the research laboratories at Allied's dye plant in Buffalo, N.Y. Dow engineers designed the line from their experience with the nine com­mercial chlorinated solvent systems which the company has been leasing since 1966 for finishing fabrics with fluorochemical stain repellents, such as 3M's Scotchgard and Du Pont's Zepel, and wool stabilization resins, such as Du Pont's Zeset. In these systems, the chlorinated solvent is usu­ally 1,1,1,-trichloroethane although tri-chloroethylene and perchloroethylene can be used.

Allied chemists are now beginning to evaluate the continuous solvent dyeing of nylon, polyester, and acrylic carpets with the pilot equipment that is designed to process carpet construc­tions up to 6 inches wide. Allied's Dr. Charles E. McGinn, director of re­search, dyes, comments: "Solvent dyeing carpets is the first logical ap­plication inasmuch as the economic advantages appear obvious. Right now, we're anxious to work out these operating economics. I think we can handle all the technical problems."

Dow's George P. Souther, project manager, textile solvent systems, says: "We're already beginning to design a commercial solvent dyeing system for 15-foot, 9-inch-width carpets. From the interest we've found on a recent trip to nearly all the carpet mills, we want to move fast."

Dow and Allied are developing the new technology at a time when the carpet mills are just beginning to think

about converting from batch (Beck) dyeing to continuous (Kuster) dyeing and are, therefore, receptive to the new technology of solvent dyeing. Last year, U.S. carpet face fiber pro­duction totaled 704 million pounds (85% of which was synthetic fibers) or 448 million square yards of finished carpet that sold wholesale at $1.6 bil­lion. Nearly all this production was batch dyed except for small amounts of carpet made with precolored yarns and the first production runs of carpet from two new Kuster dyeing lines.

Dow's Lewis W. Stump, marketing manager, textile solvent systems, ex­pects the company to start leasing the first commercial solvent dyeing sys­tems for carpets early next year. The textile mill's total monthly charges, including equipment, solvent, and ser­vices, will be about 5 cents a pound of dyed carpet, depending on quan­tity runs, he says.

Mr. Stump estimates that the dyer's overall solvent dyeing costs will be measurably lower than his current costs for all three synthetic fibers. To­day's batch dyeing costs, evaluated at 1 to 2% dye add-on and at 1.5 pounds of face fiber per square yard of carpet, are about 15 cents a pound for nylon and 25 cents a pound for polyester. Acrylics are difficult to dye in aqueous dyebaths and are generally pig­mented during fiber extrusion. Chlo­rinated solvent dyeing, however, may well permit continuous piece dyeing of acrylic carpets.

Mr. Stump lists further process advantages of solvent dyeing over Beck and Kuster dyeing:

• Dyeing contact times: solvent, 30 to 45 seconds for nylon, polyester, and acrylic; Beck, 3 to 5 hours for nylon and polyester; Kuster, 8 to 15 minutes for nylon.

• Dyeing rates: solvent, 10 yards per minute; Beck, equivalent of half a yard per minute; Kuster, 10 yards per minute.

• Drying costs: vaporizing sol­vents such as 1,1,1-trichloroethane re­quire one tenth the energy and cost of evaporating water from Beck- and Kuster-dyed carpets.

• Floor space (linear): solvent, 15 feet; Beck, 15 feet (one solvent dye­ing line is equivalent in output to 14 Becks); Kuster, 300 feet.

• Pollution factors: Solvents are recovered in a closed cycle with un­used dye, lint, and other contaminants collected as solids; the dye-depleted Beck and Kuster solutions must be dis­carded as liquid waste.

At Allied, meanwhile, the research plan is to formulate a dyebath pack­age containing the dyes and whatever related textile chemicals such as car­riers and surfactants might be needed for a solvent dyeing system, Dr. Mc­Ginn says. Such a package would then be sold as a ready-to-use system to the textile dyeing houses.

Dr. McGinn explains that the re­search work involves modifying exist­ing dyes rather than synthesizing en­tirely new colorant molecules. The modifications typically mean convert­ing an organic dye molecule from, say, its sodium salt form which is wa­ter soluble to some fatty form which is solvent soluble. So far, Dr. McGinn adds, the research group has devel­oped a number of disperse, basic, and acid dye modifications. It is planning to round out a library of eight or nine colors—which it hopes to have avail­able at the end of this year—for each of the three synthetic fibers.

In other applications, the solvent dyeing of textile fabrics will probably develop very slowly for two reasons: First, the permanent press resins and soil release agents which textile mills prefer to apply along with the dye from one dyebath have been devel­oped as water-based systems and do not lend themselves to solvent appli­cation. Second, there are stricter specifications for color, wash, and per­spiration fastness for dyed apparel than for dyed carpets.

Comments about solvent dyeing from other leading dye manufacturers: A spokesman for the dyes and chemi­cals division of Du Pont says that the company is doing no development work in solvent dyeing.

Geigy's John Komninos, manager of chemical development, says, "There's a real void of scientific data about solvent dyeing—most dyestuflFs have been empirically found."

Badische Anilin-& Soda-Fabrik's Dr. Erwin F. Hahn, technical director, colors, planning department, says: "I'm interested in solvent dyeing. It seems to show good economics."

46 C&EN APRM- 7, 1969