AU752156B2 - Radioluminescent compositions - Google Patents

Description

WO 99/46340 PCT/AU99/00188 1 "RADIOLUMINESCENT

COMPOSITIONS"

This invention relates to radioluminescent compositions.

This invention has particular application to radioluminescent inks for printing, writing and drawing, and for illustrative purposes reference will be made to this application. However, it will be understood by persons skilled in the art that this invention may find use in other applications, including but not limited to radioluminescent colourants and tints for liquids and solids such as resins and plastics, fabric printing, media and the like.

Radioluminescence may be defined as a property of a compound or composition including a luminophore and a radioactive source, radioactive decay providing an energetic emission capable of excitation of the luminophore followed by decay of the exited luminophore with emission of a photon at the luminophore's characteristic visible-light wavelength.

The basic principle of radioluminescence has found application in radioluminescent paints for watch faces and the like, wherein the pigment system comprises a radioactive compound and a fluorescent pigment. Examples of such compositions include the now-banned radium/zinc sulphide instrument face compositions and their replacement, being the use of a tritiated organic binder for a zinc sulphide or other fluorescent pigment.

The usefulness of radioluminescent paints is limited by their opacity. The intensity of the luminescence is determined in the surface of the opaque paint film, emission within the film being substantially absorbed and dissipated as heat. Radioluminescent paints comprising tritiated binders tend to lose effectiveness through loss of tritium by hydrogen exchange with, for example, water vapour in the air. This is particularly so at the WO 99/46340 PCT/AU99/00188 2 important surface region of the paint film.

The radioluminescent paint compositions are by their nature unsuitable for use as a coloured ink. Firstly, the presence of solid pigments prevents their use in implements having a wick-type applicator such as a conventional fluorescent pen or other capillary applicators. Secondly, the inherent opacity of present radioluminescent paints prevent their use in applications where the colourant must allow transmission of coloured light reflected from the substrate, in the manner of a coloured ink.

Hereinafter a distinction is drawn between an ink and a paint. "Ink" is used to describe a composition of a dye and a liquid carrier wherein on application to a substrate and drying, there is left a dye residue.

"Paint" is used to describe a composition of a pigment and a binder which on application to a substrate and drying forms a protective coating.

This invention in one aspect resides broadly in a radioluminescent ink composition including a phosphor or a dye having a fluorescent moiety, a radioactive source selected to have an emission capable of exciting said fluorescent moiety or phosphor, and a liquid carrier.

The dye may comprise a soluble dye or a dispersible dye. In the case of dispersible dyes, it is preferred that these be selected from dyes forming sols or colloids in the liquid carrier such that the ink composition may be useful in capillary applicators. In any case it is preferred that the dye be a soluble dye.

The ink composition may comprise a further nonfluorescent dye or fluorescent dye not responsive to the emission of the radioactive source. Preferably, the dye is selected to be of substantially the same spectral colour as the fluorescence to allow maximum transmission.

The radioactive source may comprise a radioactive element or a compound having one or more radioactive atoms, the element or atoms being selected to have a radioactive emission capable of exciting the fluorescent WO 99/46340 PCT/AU99/00188 3 moiety to an energy level from which it may decay to emit light in the visible spectrum. The element or compound is preferably substantially non-volatile on evaporation of the carrier. The element or compound is preferably soluble in the carrier or is dispersible therein. In the case of dispersible elements or compound, it is preferred that the element or compound forms a sol or colloid in the carrier.

Alternatively, the radioactive source may comprise a substitution of an atom or atoms of the fluorescent dye with a radioactive atom thus rendering the dye autofluorescent or luminescent. The substituted atom may comprise a different element from the atom generally present at the site of substitution. The substitution may comprise a radioactive isotope of the same element at the site of substitution whereby the electronic and thus chemical and electronic-resonance nature of the dye is substantially unaltered by the substitution.

In the case of substitution of an atom of the dyestuff to provide the radioactive source, it is preferred that the site of substitution be selected to be relatively stable against atomic exchange and rearrangement which may result in loss of radioactive source. Accordingly, it is preferred that the substitution be in respect of a covalently bonded atom that is not dissociable in the carrier or by water, and is not likely to undergo reaction, exchange or rearrangement in the environment of the ink in use.

In the case of organic dyes, the substitution may advantageously comprise tritiation at one or more stable hydrogen sites.

The radioactive source is preferably selected to be resistant to absorption through the skin or epithelia.

For example, certain triatiated cellulose derivatives may be selected for resistance to absorption.

The carrier may take any suitable form for ink carriers having regard to the physical and chemical characteristics of the dye and radioactive source. In WO 99/46340 PCT/AU99/00188 4 general the carrier will not comprise the radioactive source since by definition at least a major proportion of the carrier is lost by evaporation.

The ink may include opaque masking agents such as Titanium Dioxide or Carbon Black, for example.

The invention will be further described with reference to the following examples.

EXAMPLE 1 Suitably prepared crystalline ZnS phosphor suspended in a glycerine/water mixture with the addition of deltatritiated sodium n-butanoate to a specific activity of Ci/mL. Delta-carbon substituted n-butanoate places the T atom(s) as far as possible from the carboxyl group in all arrangements of a sigma-bonded chain. Alkalinity is provided by the sodium butanoate.

EXAMPLE 2 An ethanol/glycerine mixture containing deltacarbon-tritiated sodium n-butanoate to a specific activity of ~1-5 Ci/mL and fluorescein to form an ink composition.

EXAMPLE 3 The composition of Example 2 was mixed with methyl green dye for a daylight-visible ink. The addition of dye allows the writing to be seen in ambient light.

EXAMPLE 4 The composition of Example 3 has added thereto Titanium dioxide as an opacifying or masking agent, rendering the ink white in daylight.

EXAMPLE WO 99/46340 PCT/AU99/00188 To the ink of Example 5 was added a methyl green dye.

EXAMPLE 6 An ethanol/glycerine mixture was mixed to a specific activity of ~1-5 Ci/mL with fluorescein tritiated by replacing several hydrogens on the benzoic acid side-ring to form an ink composition.

EXAMPLE 7 Suitably prepared crystalline ZnS phosphor suspended in a glycerine/water mixture as per Example 1 was mixed with a carbon-5 tritiated ~10-ring-chain cellulose hydrolysate to a specific activity of ~1-5 Ci/mL.

EXAMPLE 8 An ethanol/glycerine mixture was mixed with a tritiated ~10-ring-chain cellulose hydrolysate to a specific activity of "1-5 Ci/mL and fluorescein to form an ink composition.

It will, of course, be realised that the above has been given by way of illustrative example(s) of the invention. Any variations, modifications, or omissions, as would be apparent to persons skilled in the art, are deemed to fall within the broad scope of this invention.

Claims (5)

1. A radioluminescent ink composition which is visible to the naked eye during conditions of low ambient light, the composition including a 3 dye having a fluorescent moiety, a radioactive source selected to have an emission capable of exciting said fluorescent moiety, and a liquid carrier.

2. A radioluminescent ink composition according to claim 1, wherein io said dye is selected from a soluble dye and a dye forming a sol or colloid with said carrier.

3. A radioluminescent ink according to claim 2, wherein said radioactive source is selected from a radioactive compound and a radioactive atomic substitution of said dye.

4. A radioluminescent ink according to claim 3, wherein said radioactive atomic substitution comprises a radioactive isotope of the same element at the site of substitution.

5. A radioluminescent ink according to claim 4, wherein said dye is an organic dye, and wherein the substitution comprises tritiation at one or more stable hydrogen sites thereof. 2- A radioluminescent ink according to any one of claims 1 to 5, which includes a masking or opacifying agent.