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Patent No. 6470891 Photochromatic tattoo (Carroll, Oct 29, 2002)
Abstract
A tattoo that is invisible to the naked eye until the tattoo is exposed to ultraviolet radiation, whereupon the tattoo becomes visible to the naked eye, and which reverts to invisible upon removal from exposure to ultraviolet radiation. The tattoo is formed by embedding in the skin a mixture including a non-pigmented carrier and one or more photochromic compounds that undergo a photochemical transformation from colorless to colored upon exposure to ultraviolet radiation, and which revert to colorless upon removal from exposure to ultraviolet radiation.
Notes:
SUMMARY
OF THE INVENTION
The invention provides a tattoo that is permanent or semi-permanent, does not
wash off or bleed on clothes, and remains invisible until the wearer desires
it to be seen.
More particularly, the invention comprises a photochromatic tattoo in which
photochromic compounds normally invisible to the naked eye, but which become
visible upon exposure to sunlight or other sources of ultraviolet radiation
(UV), are embedded in the skin to create a tattoo. The photochromic compounds
are mixed in a non-pigmented or clear carrier that is substituted for the normal
pigmented ink or dye that is used to apply a tattoo. The tattoo thus remains
invisible to the naked eye until it is exposed to UV.
Examples of suitable photochromic compounds are described in U.S. Pat. Nos.
5,581,090 and 5,730,961, the disclosures of which are incorporated in full herein
by reference. As noted in the '090 and '961 patents, photochromic substances
are known in the art for their utilization in optics as storage media or as
a means to detect UV, such as, e.g., the photochromic ultraviolet detector disclosed
in the '090 patent. Among the large family of photochromic compounds are the
spiropyrans and spiroxazines groups of molecules. These molecules are known
for their property of changing from clear to a variety of colors and shades.
Normally appearing as colorless, these spiro-compounds undergo a photochemical
transformation to intensely colored form when exposed to UV. The '961 patent,
in particular, discloses a material which remains clear until exposed to UV
and which then exhibits color and thus becomes visible. The active chemical
disclosed in the '961 patent is identified as a photochromic substance such
as spiropyrans or spiroxazines molecules. However, this patent relates to a
nail polish applied to the surface of the nails of a wearer, and does not relate
to a tattoo applied transdermally to the skin of the wearer.
A carrier for the photochromic compounds could comprise an invisible skin-marking
ink such as that made by Sirchie Finger Print Laboratories of Youngsville, N.C.,
under the name "Invisible Skin Marking Ink #743", and described more fully in
U.S. Pat. No. 5,878,155. However, other suitable commercially available, transparent,
non-toxic carriers could be used to embed the photochromic compounds in the
skin.
U.S. Pat. No. 5,166,345 describes a photochromic compound which exhibits high
color density, is stable against heat and solvent, and which has a great repeating
durability in coloring-decoloring cycles. For improved performance, the photochromic
compound used to produce a tattoo in accordance with the present invention can
be formulated using the teachings of this patent, the disclosure of which is
incorporated in full herein, whereby the stability, durability and color intensity,
for example, of the compound are optimized.
Further, the composition used to make the photochromatic tattoo of the invention
may be formulated so that it is operative only for a predetermined period of
time, e.g., days, weeks or months, etc., after which the photochromic composition
is no longer effective to produce a visible tattoo when exposed to UV. Alternatively,
or in addition, the composition may be formulated so that once exposed to UV,
the tattoo will remain visible only for a predetermined period of time, e.g.,
minutes, hours or days, etc.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The tattoo of the present invention is invisible to the naked eye until the
tattoo is exposed to sunlight or other source of ultraviolet radiation, at which
time the tattoo undergoes a photochemical change from clear or colorless to
intensely colored, thereby producing a visible tattoo. Upon removal from exposure
to UV, the tattoo again becomes invisible. By appropriate formulation, the tattoo
can be made to return to clear and therefore become invisible almost immediately,
or following a predetermined desired period of time.
To produce the tattoo of the invention, a photochromic compound is mixed with
a suitable carrier, such as the ink disclosed in U.S. Pat. No. 5,878,155, for
example, and embedded in the skin by utilizing conventional tattooing methods.
The photochromic compound is preferably selected from the spiropyrans and spiroxazine
groups of the photochromic family of compounds, such as those disclosed in U.S.
Pat. 5,581,090, for example. The spiropyrans and spiroxazine compounds normally
appear as colorless but undergo photochemical transformation and exhibit intense
colors when exposed to UV radiation.
The spiropyrans or spiroxazine compounds may be added to the carrier in a proportion
of about 0.1 to about 1.0 percent by weight. Higher concentrations yield more
intense colors. Different color hues are obtained by mixing two or more spiropyrans
or spiroxazine compounds in the carrier, as necessary or desired.
During application of the tattoo, it is necessary to expose the area being tattooed
to UV radiation so that the design is visible to the tattooist. Upon exposure
to UV radiation from a lamp or sunlight, for example, the tattoo becomes fully
visible after only about five (5) seconds.
A commercially available stabilizer may be added to the composition to reduce
oxidation processes and thereby extend the useful life of the photochromic compound.
Commercially available stabilizers suitable for their performance under sunlight
are Tinuvin 765 and Tinuvin 144 Hindred Amine Light Stabilizers, available from
the Additive Division of Ciba Geigy.
The stabilizers may be added in a proportion of from about 2.5% up to about
3.0% by weight.
The photochromatic tattoo of the invention can be applied using conventional
tattooing methods and equipment, and when visible appears as a conventional
tattoo. It can have the permanence, individuality, artistry and intricate detail
of a conventional tattoo, but remains invisible until exposed to UV radiation.
Thus, the person wearing the tattoo can dress in formal clothing or swim wear,
etc., without displaying the tattoo, and when desired can activate the tattoo
for display simply by exposing it to UV radiation. If desired, the tattoo can
even be made to remain invisible when the person wearing the tattoo is exposed
to sunlight or other source of UV radiation by covering the tattoo with an appropriate
sun (UV) block.
While particular embodiments of the
invention have been illustrated and described in detail herein, it should be
understood that various changes and modifications may be made to the invention
without departing from the spirit and intent of the invention as defined by
the scope of the appended claims.