Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
1998-02-10
2001-04-03
Stockton, Laura L. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C568S312000
Reexamination Certificate
active
06211383
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a family of colorants and colorant modifiers. The colorant modifiers, according to the present invention, are capable of stabilizing a color to ordinary light and/or rendering the colorant mutable when exposed to specific wavelengths of electromagnetic radiation.
BACKGROUND OF THE INVENTION
A major problem with colorants is that they tend to fade when exposed to sunlight or artificial light. It is believed that most of the fading of colorants when exposed to light is due to photodegradation mechanisms. These degradation mechanisms include oxidation or reduction of the colorants depending upon the environmental conditions in which the colorant is placed. Fading of a colorant also depends upon the substrate upon which they reside.
Product analysis of stable photoproducts and intermediates has revealed several important modes of photodecomposition. These include electron ejection from the colorant, reaction with ground-state or excited singlet state oxygen, cleavage of the central carbon-phenyl ring bonds to form amino substituted benzophenones, such as triphenylmethane dyes, reduction to form the colorless leuco dyes and electron or hydrogen atom abstraction to form radical intermediates.
Various factors such as temperature, humidity, gaseous reactants, including O
2
, O
3
, SO
2
, and NO
2
, and water soluble, nonvolatile photodegradation products have been shown to influence fading of colorants. The factors that effect colorant fading appear to exhibit a certain amount of interdependence. It is due to this complex behavior that observations for the fading of a particular colorant on a particular substrate cannot be applied to colorants and substrates in general.
Under conditions of constant temperature it has been observed that an increase in the relative humidity of the atmosphere increases the fading of a colorant for a variety of colorant-substrate systems (e.g., McLaren, K.,
J. Soc. Dyers Colour,
1956, 72, 527). For example, as the relative humidity of the atmosphere increases, a fiber may swell because the moisture content of the fiber increases. This aids diffusion of gaseous reactants through the substrate structure.
The ability of a light source to cause photochemical change in a colorant is also dependent upon the spectral distribution of the light source, in particular the proportion of radiation of wavelengths most effective in causing a change in the colorant and the quantum yield of colorant degradation as a function of wavelength. On the basis of photochemical principles, it would be expected that light of higher energy (short wavelengths) would be more effective at causing fading than light of lower energy (long wavelengths). Studies have revealed that this is not always the case. Over 100 colorants of different classes were studied and found that generally the most unstable were faded more efficiently by visible light while those of higher lightfastness were degraded mainly by ultraviolet light (McLaren, K.,
J. Soc. Dyers Colour,
1956, 72, 86).
The influence of a substrate on colorant stability can be extremely important. Colorant fading may be retarded or promoted by some chemical group within the substrate. Such a group can be a ground-state species or an excited-state species. The porosity of the substrate is also an important factor in colorant stability. A high porosity can promote fading of a colorant by facilitating penetration of moisture and gaseous reactants into the substrate. A substrate may also act as a protective agent by screening the colorant from light of wavelengths capable of causing degradation.
The purity of the substrate is also an important consideration whenever the photochemistry of dyed technical polymers is considered. For example, technical-grade cotton, viscose rayon, polyethylene, polypropylene, and polyisoprene are known to contain carbonyl group impurities. These impurities absorb light of wavelengths greater than 300 nm, which are present in sunlight, and so, excitation of these impurities may lead to reactive species capable of causing colorant fading (van Beek, H.C.A.,
Col. Res. Appl.,
1983, 8(3), 176).
Therefore, there exists a great need for methods and compositions which are capable of stabilizing a wide variety of colorants from the effects of both sunlight and artificial light.
There is also a need for colorants that can be mutated, preferably from a colored to a colorless form, when exposed to a specific predetermined wavelength of electromagnetic radiation. For certain uses, the ideal colorant would be one that is stable in ordinary light and can be mutated to a colorless form when exposed to a specific predetermined wavelength of electromagnetic radiation.
SUMMARY OF THE INVENTION
The present invention addresses the needs described above by providing compositions and methods for stabilizing colorants against radiation including radiation in the visible wavelength range. In addition, the present invention provides certain embodiments in which the light-stable colorant system is mutable by exposure to certain narrow bandwidths of radiation. In certain embodiments, the colorant system is stable in ordinary visible light and is mutable when exposed to a specific wavelength of electromagnetic radiation.
In one embodiment, the present invention provides a composition comprising a colorant which, in the presence of a radiation transorber, is mutable when exposed to a specific wavelength of radiation, while at the same time, provides light stability to the colorant when the composition is exposed to sunlight or artificial light. The radiation transorber may be any material which is adapted to absorb radiation and interact with the colorant to effect the mutation of the colorant. Generally, the radiation transorber contains a photoreactor and a wavelength-specific sensitizer. The wavelength-specific sensitizer generally absorbs radiation having a specific wavelength, and therefore a specific amount of energy, and transfers the energy to the photoreactor. It is desirable that the mutation of the colorant be irreversible.
The present invention also relates to colorant compositions having improved stability, wherein the colorant is associated with a modified photoreactor. It has been determined that conventional photoreactors, which normally contain a carbonyl group with a functional group on the carbon alpha to the carbonyl group, acquire the ability to stabilize colorants when the functional group on the alpha carbon is removed via dehydration.
Accordingly, the present invention also includes a novel method of dehydrating photoreactors that have a hydroxyl group in the alpha position to a carbonyl group. This reaction is necessary to impart the colorant stabilizing capability to the photoreactor. The novel method of dehydrating photoreactors that have a hydroxyl group in the alpha position to a carbonyl group can be used with a wide variety of photoreactors to provide the colorant stabilizing capability to the photoreactor. The resulting modified photoreactor can optionally be linked to wavelength-selective sensitizer to impart the capability of decolorizing a colorant when exposed to a predetermined narrow wavelength of electromagnetic radiation. Accordingly, the present invention provides a photoreactor capable of stabilizing a colorant that it is admixed with.
In certain embodiments of the present invention, the mixture of colorant and radiation transorber is mutable upon exposure to radiation. In this embodiment, the photoreactor may or may not be modified as described above to impart stability when admixed to a colorant. In one embodiment, an ultraviolet radiation transorber is adapted to absorb ultraviolet radiation and interact with the colorant to effect the irreversible mutation of the colorant. It is desirable that the ultraviolet radiation transorber absorb ultraviolet radiation at a wavelength of from about 4 to about 300 nanometers. It is even more desirable that the ultraviolet radiation transorber absorb ultraviolet radiation at a wavelength of 100 to 300 na
MacDonald John Gavin
Nohr Ronald Sinclair
Kilpatrick & Stockton LLP
Kimberly--Clark Worldwide, Inc.
Stockton Laura L.
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