Bleaching and dyeing; fluid treatment and chemical modification – Process of color renovating a dyed product
Reexamination Certificate
2000-02-10
2003-03-18
Einsmann, Margaret (Department: 1751)
Bleaching and dyeing; fluid treatment and chemical modification
Process of color renovating a dyed product
C008S485000, C008S504000, C008S673000, C008S680000, C008S924000, C008S929000
Reexamination Certificate
active
06533824
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to methods for spot dyeing nylon carpets and, more particularly, to methods for spot dyeing areas of such carpets that have been bleached.
2. History of the Prior Art
Until the middle of the nineteenth century, nearly all known dyes were obtained from natural sources. Although most were vegetable extracts, a few were animal products. The range of available colors was limited, as was the utility of the available dyes. If a specified natural dye did not bind to a particular material, that dye was ineffectual in changing the color of the material. The era of synthetic dyes began in 1771, when Woulfe prepared picric acid (a.k.a. trinitrophenol) by subjecting indigo to nitric acid. The resultant yellow crystalline solid proved to be a formidable explosive; when solvated, it was shown to dye silk in bright yellow hues. More than half a century passed before Laurent discovered in 1842 that phenol could be converted to picric acid. Fourteen years later, Perkin discovered mauve, a bluish purple dye obtained from aniline. Mauve, the first of the coal-tar dyes, was the first synthetic dye to be manufactured and used for practical dyeing. However, it was not until 1869, when the structure of benzene was established by Kekule, that the way was paved for the study of aromatic organic compounds, from which all synthetic dyes are synthesized. Since that time, a bewildering number of synthetic dyes have been formulated. As the twenty-first century dawns, new synthetic dyes are still being discovered with amazing regularity.
The largest group of dyes have as chromophores what are known as azo compounds—intensely colored aromatics having one or more azo linkages (—N═N—), each of which brings a pair of aromatic rings into conjugation. Each azo linkage gives an extended system of delocalized &pgr; electrons that is responsible for absorption of light in visible regions. Depending on the number of azo groups present in the molecule, they are classified as monazo, diazo, triazo, tetrakisazo and polyazo dyes. Azo dyes almost always contain one or more —SO
3
−
Na
+
groups, which not only confer water solubility on the dye, but assist in binding the dye to the surfaces of polar fibers, such as silk, wool, cofton, or nylon. Many dyes are made by coupling reactions of naphthylamines and naphthols. “H-acid” (8Amino-1-naphthol-3,6-disulfonic acid) is a particularly versatile component in dye manufacture. Not only does it contain sulfonic acid groups, but it can also couple in two different ways, depending on the pH of the medium.
Silk and wool are two naturally occurring polymers that man has used for centuries to fabricate clothing and carpets. They are both examples of a family of polymer compounds, known as proteins, in which &agr;-amino acid subunits are joined by amide linkages. Proteins are, therefore, polyamides. The search for a synthetic material with properties similar to those of silk led to the discovery of a family of synthetic polyamides called nylons. One of the most important nylons, called nylon 6,6, can be prepared from the six-carbon dicarboxylic acid, adipic acid, and the six-carbon diamine, hexamethylene-diamine. In the commercial process, these two compounds are allowed to react in equimolar proportions in order to produce a 1:1 nylon salt. Water molecules are driven off by heating the nylon salt it to a temperature of 270° C. at a pressure of 250 pounds per square inch, thereby condensing it to the polyamide. The nylon 6,6 so produced, which has a molecular weight of about 10,000 and a melting point of about 250° C., can be spun into fibers when molten. By stretching the fibers to four times their original length, the polyamide molecules orient themselves so that they are parallel to the fiber axis. Such an orientation permits hydrogen bonding between carbonyl groups and amino groups on adjacent chains. This “cold drawing” process greatly increases the strength of the fibers.
The same molecular structure that is responsible for the strength of nylon fibers also results in repeating polarized units on the surface of each fiber. It is this polarization that allows nylon fibers to be readily colored by sulfonic-acid dyes. Typically, one or more organic acid dyes are dissolved in an aqueous solution and the material to be dyed is either sprayed with or immersed in the solution. The physical characteristics of nylon fibers which permit them to be readily dyed, also make them susceptible to staining. Certain FDA-approved food colorings work equally well as nylon fiber dyes. The food colorings are likely responsible for the trashing of millions of dollars worth of nylon carpet annually, with the colors red 40 and red 3 being some of the more notorious culprits. Though it is sometimes possible to remove the food coloring, it is also possible that the carpet dye will be removed at the same time.
Another problem with the dyes used to color nylon fibers is that they are readily oxidized by chlorine bleach and certain peroxides and. Strong bases may reduce one or more of the dyes, either altering or bleaching the color. The damage to carpets caused by inadvertent spills of chlorine bleach, peroxides and strongly basic solutions may be as great as the damage caused by food colorings and other equally persistent stains.
As an alternative to replacing the entire carpet, carpet care professionals have developed certain methods for redyeing the bleached spots. The spot dying methods typically use the same types of acid dyes used by the manufacturers to impart the original color to the carpets. Typically, the conventional redyeing methods employ a color chart or color wheel, and require that a carpet matching spot dye be formulated by combining selected basic dye colors in the proper proportions. Spot dyeing kits are also available that use only the three primary dye colors: red, yellow and blue. The known kits suggest that the dyer begin with the primary color closest to the unbleached carpet color. The major problem with such redyeing methods is that accurate color matching requires a high degree of skill and compentency, as well as luck. In addition, the method suggested whereby the first primary color to be used is the one closest to the unbleached carpet color is flawed, as the suggested primary color may not have been removed by bleaching. As will be hereinafter explained, adding the suggested primary color may simply result in addition of too much of the main primary color dye and make it impossible to achieve a close match.
Although there is a great demand for competent spot dyers, the conventional spot dyeing processes have become so complex, that few individuals are sufficiently patient to learn the required skills. Twenty or more years ago, carpet colors were few and often close in color to a primary color. The then prevailing redyeing method was to use a primary color closest to the original color, and then use color theory to create a match. Though the concept is still in use today, it does not take into consideration that carpet colors are seldom close to a primary color. Additionally, many carpets are so lightly colored that the closest primary color is difficult to determine. As more shades of carpet became available, more color samples were added to spot dyeing kits. As the number of dye colors in spot dyeing kits proliferated, the kits became more expensive and more difficult to competently use. Each carpet is typically dyed with at least two, and typically, three primary dyes, each of which has its own susceptibility to a particular bleaching agent. As a general rule, when a spot on a carpet is bleached, each of the primary dyes is affected differently. For example, a particular bleach may oxidize the primary red color, but have less of an effect on the blue and yellow primary dyes. It a spot dyeing kit were to contain 60 different colors, and a bleached spot on a carpet were missing only one of three primary colors, using a formulation which matched the original color would resul
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