Chelating agents for improved color fidelity

Details Chelating agents for improved color fidelity Chelating agents for improved color fidelity

1997-06-26

2001-10-02

Diamond, Alan (Department: 1751)

Bleaching and dyeing; fluid treatment and chemical modification

Cleaning or laundering

C252S008910, C510S521000, C510S522000, C510S531000, C510S533000, C510S320000, C510S321000, C510S322000, C510S327000, C510S328000, C510S329000, C510S330000

Reexamination Certificate

active

06296670

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to processes for maintaining or restoring the colors or whiteness of fabrics during a rinsing operation.
BACKGROUND OF THE INVENTION
A wide variety of ingredients have been suggested for use in laundering operations to enhance the appearance of fabrics. Detergents, of course, provide a basic cleaning function. Rinse-added fabric softeners provide both softening and anti-static benefits to fabrics. More recently, cellulase enzymes have been employed to improve the appearance of colored cotton garments.
Formulators of fabric cleaning products have clearly recognized the need to improve the color fidelity of dyed fabrics. As noted above, the use of cellulase is one modern method for achieving this desirable result. Other formulators have approached this challenge from the standpoint of more effective cleaning. For example, various bleaches are advertised as being able to maintain color brightness. Another means for addressing the problem of color fidelity employs dye transfer inhibiting agents in the laundering liquor. This approach is based on the discovery that vagrant dyes present in the laundering liquor can undesirably redeposit onto fabrics, thereby gradually changing, and generally darkening, colors and whites. While the use of cellulases, dye transfer inhibiting agents and bleaches can meet certain consumer needs for maintaining color fidelity, there is a continuing search for improvements in this area.
The present invention addresses the problem of color fidelity in laundered fabrics from an entirely different aspect. It has now been determined that metal cations, especially transition metals, and most particularly copper and nickel ions, present in aqueous rinse baths can undesirably interact with fabric dyes and change their perceived hue. This also often translates into a darkening of the dye material, which tends to cause the colored fabrics to appear drab. Interactions of metal ions with residual soils may also tend to clear a drab appearance. While many conventional washing compositions contain metal ion sequestrants which may minimize this problem during the actual washing operation, it has heretofore been overlooked that the freshly laundered fabrics are subsequently subjected to aqueous rinse baths which do not contain such sequestrants. It has now been discovered that metal ions present in the rinse can also undesirably interact with dyed fabrics, resulting in a loss of color fidelity and brightness.
While not intending to be limited by theory, it may be speculated that functional substituent groups present in complex dye molecules bind with metal ions, thereby causing a change in color which is generally perceived as drabness and an overall appearance of fabric aging. This has now been found to occur with common ortho-hydroxy diazo dyes and with certain direct dyes. A similar undesirable interaction may also occur between metal cations and the “optical brighteners” which are commonly used to enhance the perception of whiteness and brightness of white fabrics, thereby resulting in reduced fluorescence of the fabrics. Whatever the reason for the drabness and change in appearance, it has now been discovered that such problems associated with loss of color fidelity can be overcome by the fabric treatment process herein which is conducted in the rinse bath.
By the practice of the present invention, dyed or white fabrics are rinsed in an aqueous rinse bath which contains a metal ion chelating agent. The chelating agent is present in an amount sufficient to scavenge metal ions, especially copper and nickel, thereby preventing undesirable metal interactions with dyes or optical brighteners. Moreover, the invention also can be used to remove metal ions which have already combined with dye or optical brightener molecules on fabrics in the laundering process, thereby providing a restorative benefit to colors which have become drab due to metal ion interactions, especially due to interactions with copper cations and nickel cations, but also manganese cations, iron cations, and transition metal cations, among others. These and other objects are secured by the present invention, as will be seen from the following disclosure.
BACKGROUND ART
The use of various chelators and polycarboxy ingredients for several disclosed purposes in laundry rinse additives or other products appears in: U.S. Pat. No. 3,756,950; U.S. Pat. No. 3,904,359; U.S. Pat. No. 3,954,630; DE 3,312,328; EP 165,138 (85:12:18); EP 168,889 (86:01:22); EP 271,004 (88:06:15); EP 534,009 (93:03:31; WO 9,306,294); CA 913,309 (00:01:00 priority 68:08:01 68CA-026,440); and JP HEI4 [1992] 275,956. See also Method AATCC-161-1992 “Chelating Agents: Disperse Dye Shade Change Caused by Metals; Control of”. The preferred EDDS chelator used herein is described in U.S. Pat. No. 4,704,233.
SUMMARY OF THE INVENTION
The present invention encompasses a method for improving the color of dyed fabrics, or the whiteness of white fabrics, said fabrics having been laundered in the conventional manner in water which contains copper ions, nickel ions, or both, comprising rinsing said fabrics in water which contains chelating agents for copper and/or nickel cations.
In a convenient and preferred mode, the method herein involves a fabric washing/rinsing operation, comprising the steps of:
(a) washing fabrics with a laundry detergent composition; and
(b) following said washing, rinsing said fabrics in water comprising at least about 2 ppm, preferably at least about 5 ppm, of a chelating agent or mixture of chelating agents for copper, nickel and mixtures thereof.
The method herein can be conducted under varying conditions, depending on such factors as the amount of copper and nickel metal ions present in the rinse water supply, the degree of prior dye or optical brightener interaction with metal ions, and the like. In a preferred mode, the dyed fabrics are immersed in the chelator-containing rinse water for a period of at least about 1 minute. The method can be conducted at a temperature in the range from about 5° C. to the boil.
In addition to the chelator, the method disclosed herein may be conducted in rinse water which additionally contains a member selected from the group consisting of fabric softeners, cellulase enzymes, chlorine scavengers, dye transfer inhibiting agent and mixtures thereof, thereby providing additional or improved fabric care and color care benefits. Preferred dye transfer inhibiting agents for such use include members selected from the group consisting of “PVP”, “PVPVI” and “PVNO”, as described hereinafter. Preferred chlorine scavengers for such use include members selected from the group consisting of ammonium chloride and monoethanolamine. Preferred fabric softeners for such use include any of the known cationic softeners, especially those disclosed hereinafter. Preferred cellulase enzymes for such use include cellulases derived from fungi. A highly preferred cellulase is CAREZYME from NOVO.
The invention herein also encompasses compositions comprising the chelating agents and other ingredients noted above, and disclosed in more detail hereinafter.
All percentages, ratios and proportions herein are by weight, unless otherwise specified. All documents cited are, in relevant part, incorporated herein by reference.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is employed to provide improved color fidelity to fabrics. By “improved color fidelity” or “improving the color” of the fabrics herein is meant not only the maintenance or restoration of the true colors and gradations of colors imparted by colored dyes, but also whiteness. As noted hereinabove, the hues of various colored dyes can be undesirably modified by metal cations, especially copper and nickel. Likewise, the optical brighteners commonly used to enhance the perception of whiteness and brightness in white fabrics can also be undesirably modified by exposure to metal cations, thereby causing white fabrics to have less apparent fluorescence, and to appear drab.
The improvement in

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