Colorant stabilizers

Details Colorant stabilizers Colorant stabilizers

1999-04-06

2001-01-02

Klemanski, Helene (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Marking

C106S031780

Utility Patent

active

06168654

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a family of colorant stabilizers. The colorant stabilizers, according to the present invention, are capable of stabilizing a colorant when it is exposed to electromagnetic radiation. The colorant stabilizers enable the production of an ink set wherein each ink of the ink set, regardless of color, possesses substantially similar light fastness properties.
BACKGROUND OF THE INVENTION
A major problem with colorants is that they tend to fade when exposed to electromagnetic radiation such as sunlight or artificial light and the like. 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 need for methods and compositions which are capable of stabilizing a wide variety of colorants from the effects of both sunlight and artificial light.
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.
The present invention also relates to colorant compositions having improved stability, wherein the colorant is associated with a colorant stabilizer. In one embodiment, the colorant stabilizer comprises one or more porphines that have an extremely short triplet state lifetime. (See e.g., Kub{acute over (a)}t, et al., Photophysical properties of metal complexes of meso-tetrakis (4-sulphonatophenyl) porphyrin,
J. Photochem. and Photbio. A: Chemistry
96 (1996), pgs 93-97 which is incorporated herein by reference). Particularly suitable porphines include, but are not limited to, porphines having the following structure:
wherein R is any proton-donating moiety and M is iron, cobalt or copper. Desirably, R is SO
3
H,
COOH, or R
1
COOH wherein R
1
is an alkyl group of from 1 to 6 carbons.
Examples of such porphines are Cu-meso-tetra-(4-sulfanatophenyl)-porphine (designated CuTPPS4) and Cu-meso-tetra-(N-methyl-4-pyridyl)-porphine, having the following structures:
The copper ion can also be substituted with an iron or cobalt ion. Other metal ions can be substituted in the porphine molecule as long as the molecule has a relatively short-lived triplet state.
In a further embodiment of the present invention, the colorant stabilizer comprises at least one porphine in combination with at least one metal or metal salt. Unexpectedly, it has been discovered that the incorporation of a relatively small concentration of metal or metal salt into a porphine-containing composition results in superior colorant stability. Preferred metals or metal salts include, but are not limited to, lanthanides and lanthanide salts. Lanthanide elements include scandium, yttium, lanthanum, cerium praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.
In order to improve the solubility of the metal or metal salt in solution, metal solubility-enhancing agents may be added. Particularly useful metal solubility-enhancing agents include, but are not limited to, chelating agents. Optionally, a surfactant can be added to the metal/porphine composition to increase the interaction of the metal or metal salt and the porphine. In addition to surfactants, other additives such as TINUVIN® compounds (Ciba-Geigy Corporation) may be incorporated into the colorant composition.
The substrates to which the colorant stabilizers are applied include, but are not limited to, paper, wood, a wood product or composite, woven fabric, nonwoven fabric, textile, plastic, glass, metal, or any other substrate that would benefit from having a stabilized colorant thereon.
In another embodiment, a colorant stabilizer is present in a polymer coating of a heat transfer product, such as is used for transferring graphic images onto clothing.
Accordingly, each of the embodiments of the present invention provide stabilizing molecules that, when one or more of the stabilizing molecules are associated with a colorant, stabilizes the colorant. Therefore, the stabilizing molecules can be used as an additive to any colorant composition. For example, as certain of the stabilizing molecules are poorly soluble in water, they can be directly added to solvent or oil based (not water based) colorant compositions. Additionally, the stabilizing molecules can be added to other colorant compositions that contain additives enabling the solubilizatio

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