How is fabric colored

Dye solution is forced alternately from the outside of the packages inward and from the inside out under pressure. Computers are used increasingly in dyeing processes to formulate and match colors with greater speed and accuracy.

Printing colored designs on cotton cloth is similar to printing on paper. Long runs of the same fabric design are produced on a roller print machine operating at speeds between 50 to yards a minute.

As many as of 10 different colors can be printed in one continuous operation. A typical printing machine has a large padded drum or cylinder, which is surrounded by a series of copper rollers, each with its own dye trough and doctor blade that scrapes away excess dye. The number of rollers varies according to the fabric design, since each color in the design is etched on a separate roller.

As the cloth moves between the rotating drum and rollers under great pressure, it picks up color from the engraved area of each roller in sequence. The printed cloth is dried immediately and conveyed to an oven that sets the dye. Automatic screen-printing is another principal method for imparting colored designs to cotton fabrics. Although slower than roller printing, it has the advantage of producing much larger and more intricate designs, elaborate shadings and various handcrafted effects.

In flat bed screen-printing, the fabric design is reproduced on fine mesh screens, one for each color. On each screen, the areas in the design that are not to be penetrated by the dye are covered with lacquer or some other dye-resistant coating.

Once the dyeing process reaches equilibrium, a portion of the dye remains in the dye bath and becomes part of the dye process wastewater. The exhaustion ratio depends on the quality of the dye and the characteristics of the fiber. Leveling agent: Used in disperse dyeing to regulate or slow the uptake of dye onto synthetic fibers to ensure that the color level is uniform.

Leveling agents are often nonionic surfactants that increase the solubility of the dye and slow adsorption. Mordant: Also called a dye fixative, a substance used to chemically bond a dye to natural fibers to ensure fastness. Mordant chemicals include alum, caustic soda, and metal salts.

The mordant forms a coordination complex with the dye, increasing its molecular weight and making it insoluble. Pigment: Insoluble materials, usually in powder form, that add color to inks, paints, plastics, cosmetics, and foods. When used on textiles, they require binders or other additives to attach to the fibers. Pigments can be derived from minerals but can also be made synthetically. Because they are not soluble in water, they can last longer than dyes.

To reduce this burden, Huntsman has developed a line of dyes for cotton called Avitera that bonds to the fiber more readily.

According to the company, the colors require one-quarter to one-third less water and one-third less energy. Thanks to these extra reactive groups, the dye step lasts about four hours, compared with seven hours for conventional dyes.

Still, it takes a lot of legwork to sell customers on a new suite of dyes. Different regions and countries have different cost structures, he says. Another way to improve the bond between dyes and cotton fibers is a process called cationization. In North Carolina, textile industry veteran Tony Leonard is taking that approach.

Leonard is the inventor and technical director behind ColorZen, a start-up that has developed a cotton pretreatment step. ColorZen treats raw cotton fiber right from the field after the seeds are removed.

After treatment, cotton is spun into yarn at customer facilities. It also cuts out almost half the dye compared with processes that call for salts in the dye bath. The company has a partnership with the manufacturing technology firm Jabil to help it scale up its plant in Mebane, N. It is also in a program run by the apparel start-up incubator Fashion for Good.

Hohenstein developed Oeko-Tex, a series of standards and tools for certifying nontoxic textiles. The first version of the standard was called Oeko-Tex for the number of chemicals it tracked. Oeko-Tex certification is now up to more than chemicals.

Synthetic indigo, used to make blue jeans blue, is an example of a dye that can release unreacted chemicals downstream of manufacturing. Indigo is unlike most dyes in that in its unreduced form it is not soluble. So companies like Archroma upgrade it into easier-to-use, prereduced solutions that are more water soluble. The company became concerned after seeing published reports that about metric tons of aniline per year escapes the dyeing process from 70, metric tons of indigo.

Archroma developed a technology for prereducing indigo to prevent aniline from carrying through as a contaminant. Finished textiles colored with the dye contain a nondetectable amount of aniline, whereas competitor dyes can contain up to 2, ppm of the chemical, according to Archroma. Carnahan acknowledges differing views about how big a problem aniline is in the textile industry.

It has a better reputation than the category 1 carcinogenic amines that cleave off of azo dyes and were an early target for elimination by clothing brands. Of course, in the beginning, indigo came from a plant, not a factory. The very first pair of modern-style blue jeans, made by Levi Strauss, debuted in That was about 25 years before chemists developed the synthetic route to indigo dye—with its unappetizing starting materials of aniline, formaldehyde, and hydrogen cyanide.

The ambition at Stony Creek Colors is to return to those early days. Founder Sarah Bellos says a complete life-cycle review of the production and use of synthetic indigo provides plenty of reasons to look again at indigo from plants. Dyeing : Warm temperature, long process time, requires addition of large amounts of salt and alkali fixatives. Washing : Long, energy- and water-intensive process using multiple baths, with at least one at boiling temperature.

Washing : Shorter process requiring less energy, water, and chemicals than cotton. Uses alkali and chemical reducing agent. Washing : Similar to cotton but shorter process, possibly due to less unfixed dye to be removed. Stony Creek is developing varieties of leguminous indigo plants that can provide a high-yield, high-profit crop for Tennessee farmers looking for an alternative to tobacco.

The company is selling all the dye it can make; its goal is to expand U. That could displace 2. Dye houses can reduce natural indigo in bacterial fermentation vats or use more common reducing systems, she adds. Other start-ups have also turned to biology—in particular, engineered microbes—to reduce the use of chemicals in textile dyes. All that is required to scale up are fermentation tanks and sugar.

The idea for Colorifix came out of a biological sensor program in Nepal and Bangladesh. David Nugent and colleagues were in the region to test drinking water wells for arsenic. They asked local village governments what other substances in their water concerned them.

The team was already using color made by microorganisms to act as a sensor for water contaminants. Soon, Nugent says, it became clear the researchers could engineer them to produce natural colors, including anthocyanins and carotenoids. Not all the colors that engineered microbes can make meet textile industry requirements for lightfastness and temperature stability.

But microbes that produce stable colors can be adopted by dye houses with very little change to their normal processes. First the microbes go into a solution like a regular dye and get embedded in the textile fiber.

Then they are given nutrients that cause them to grow. Nugent says the process works like a very efficient reactive dye that requires only a single finish wash. Colorifix is setting up pilot operations in Italy and France; partner dye houses first have to get a certification to work with genetically modified microbes.

Pili got its start as a biology outreach program. Stock Dyed - This stage of dyeing takes place at the fiber stage fiber spun together creates yarn.

Fiber is compressed in a large tank like a washing machine and dyed. Once it is dyed, the fiber can be mixed called blending with other colors to create a yarn that has multiple colors in it. Yarn Dyed - In this process, white yarn is wound onto a spool, and then dyed in a chamber. This process offers uniformity of color across the yarn.

The multiple colors of yarn can then be woven to create multi-colored patterns.