Hypercolor was a line of clothing, mainly T-shirts and shorts, that changed color with heat.[1]
They were manufactured by Generra Sportswear Company of Seattle and marketed in the United States as Generra Hypercolor or Generra Hypergrafix and outside the US as Global Hypercolor. They contained a thermochromic (temperature sensitive) pigment made by Matsui Shikiso Chemical of Japan, that changed between two colors – one when cold, one when warm. The shirts were produced with several color change choices beginning in 1991.[2][3] The effect could easily be permanently damaged, particularly when the clothing was washed in hotter than recommended water, ironed, bleached or tumble-dried.[2]
Generra Sportswear Co. had originally been founded as a men's sportswear distributor and importer in Seattle in 1980. The company was sold to Texas-based Farah Manufacturing Co. in 1984 and bought back by its founders in 1989. In 1986, the company added childrenswear and womenswear items to their portfolio. They struggled to meet the overwhelming [[demand for Hypercolor products.[4] Between February and May 1991 they sold $50 million in Hypercolor garments.[5] Generra went bankrupt due to mismanagement and fading demand in 1992.[6] The Hypercolor business for the U.S. market was sold to Seattle T-Shirt Company in 1993; Generra kept the rights for the international market.[7][8] The company emerged from bankruptcy in 1995 as a licensing business.[9][10] The Generra name was acquired by Public Clothing Co. of New York in 2002.[11] Today, Generra Co. is a contemporary women's and men's apparel brand headquartered in New York City.[12][13][14][15]
In the early 2000s, the technique was revived by a number of apparel brands.[16][17][2]
Substances that can change color due to a change in temperature are called thermochromes. There are two types of thermochromes: liquid crystals (used in mood rings) and leuco dyes (used in Hypercolor T-shirts).
The color change of Hypercolor shirts is based on combination of two colors: the color of the dyed fabric, which remained constant, and the color of the thermochromic dye. The dye is enclosed in microcapsules, tiny (few micrometers in diameter) drops of liquid sealed in a transparent shell, bound to the fibers of the fabric.
When it is cold the mixture in the capsule is solid and the carbon molecules in the leuco dye are attached to each other in a ring shape. When the capsule experiences a rise in temperature the molecules change shape, just like liquid crystals. They break open the carbon ring. This change means that the dyes absorb and release light differently, and the color seen is different.
The liquid is a leuco form of a dye (in this case crystal violet lactone), a weak acid (benzotriazole), and a quaternary ammonium salt of a fatty acid (myristylammonium oleate) dissolved in a solvent (1-dodecanol). At low temperatures, the weak acid forms a colored complex with the leuco dye, interrupting the lactone ring. At high temperatures, above 24-27 °C, the solvent melts and the salt dissociates, reversibly reacts with the weak acid and increases the pH. The pH change leads to closing of the lactone ring of the dye, which then regains its colorless (leuco) form.
Therefore, at the low temperature the color of the shirt is the combination of the color of the microcapsules with the color of the dyed fabric, while at higher temperatures the capsules become colorless and the color of the fabric prevails.