IMPROVEMENTS IN AND RELATING TO IMAGE ARTICLES

Field of the Invention

The present invention relates to methods of manufacturing image articles, and image articles per se.

Background to the Invention

There are many known chemical compounds which have useful security printing characteristics. For example, thermochromic agents and photochromic agents have the capability of changing colour depending on the heat or light characteristics in the region of the material. Thermochromic materials may be colourless at ambient temperatures and become coloured at lower than ambient temperatures or higher than ambient temperatures, or alternatively, may be coloured at ambient temperatures and change to colourless on raising or lowering the temperature. Photochromic agents may be coloured under ambient light, but turn colourless when exposed to ultraviolet radiation or infrared radiation; or alternatively, may be colourless under ambient lighting conditions, but turn coloured when exposed to UV or infrared radiation. These compounds are useful when manufacturing security articles such as identification cards, seals for packaging and the like.

Security articles such as identity cards and package sealing may, for example, include an image which cannot be seen under ambient conditions, comprising thermochromic or photochromic material, but when stimulated with a different wavelength of radiation, or heat or cold, is

changed to reveal a coloured image. In this way, it is possible for persons to determine whether packaging is authentic or counterfeited, and whether an identity card is a counterfeit identity card or not.

Many thermochromic and photochromic materials, phosphors and metal particles are in the form of solid particles such as powder or granules, which may be utilised per se, but due to technological restraints, have previously been applied to substrates from dispersions, whether viscous or fluid. This has restricted their use to specific printing techniques such as screen printing, lithographic printing, intaglio and the like. Many phosphors have a particle size too large for conventional types of printing. Although the use of phosphors, photochromies and thermochromics is well established, when using the above printing processes, they suffer from disadvantages such that the cost for mass producing articles using these techniques is prohibitive, and the apparatus needed to utilise these techniques effectively is too bulky and expensive for individual consumers to utilise.

Equally the wastage of ink when utilising these materials reduces the usefulness of these relatively expensive solid particles; for example, in intaglio printing up to 70% of the paste/ink can be lost due to the inefficiency of the process when utilising solid particles.

Furthermore, known methods of incorporating thermochromic and photochromic agents into image articles include the use of organic solvents and other ancillary chemicals, which raises the cost of preparing the image article considerably. It would be advantageous to be able to

apply images to substrates, containing thermochromic or photochromic materials, which can utilise water-based systems with the minimum of ancillary chemicals. It would furthermore be useful to provide methods of manufacturing image articles using thermochromic and photochromic solid particles without the need to dissolve or suspend the particles in solvents or liquid in order to apply the particles .

Many other solid particles, whether security chemicals or not, can be used to image substrates, but conventional printing techniques generally necessitate the particles to be dissolved and/or suspended in solutions and liquid. Such particles could include metal particles, activated charcoal, phosphors, mica pearlescent pigments and the like. Again, it would be advantageous to provide methods of printing image articles utilising solid particles, in which the solid particles could be printed onto a substrate directly without the use of solvents or liquid carriers. Adherence of solid particle matter to a substrate can be difficult without the use of dispersions from which to lay down the particles, and may also need adhesives present in the dispersion. Solid particles create particular problems in printing apparatus which utilise spray heads or small diameter nozzles, as they may block the nozzles and damage the apparatus.

Phosphors generally comprise inorganic particles, such as zinc sulphide activated with copper, and emit phosphorescence. They have a large particle size which is not generally useful in printing from dispersions due to the large particle size blocking print heads. If the large particles are ground to small sizes, these inorganic

phosphors generally lose their phosphorescence. The embodiments of the present invention have an object to overcome this problem.

Known printing techniques for applying solid particles to substrates generally involve blanket coating of a single tone image or raised image having a single elevation. It would be advantageous to provide image articles comprising an image formed from solid particles, which images comprise a plurality of tones, densities or elevations, for example, and which images could be applied in a simple manner using relatively inexpensive image printing equipment and materials.

It would also be useful to provide methods of manufacturing image articles, especially security prints, in which conventional ink jet technology can be utilised.

It would furthermore be advantageous to be able to print solid particles or substrates, using conventional printing technology, especially ink-jet technology, at high speeds (preferably greater than 200m/min) .

It would also be advantageous to provide methods of manufacturing image articles, especially security prints in which solid particles are used as the image, or part of the image, in which the solid particles are adhered strongly to a substrate, compared to known processes, helping to mitigate or avoid damage from abrasion and the like.

It is therefore an aim of preferred embodiments of the present invention to overcome or mitigate at least one

problem in the prior art, whether expressly disclosed herein or not

Summary of the Invention

According to the present invention in a first aspect there is provided a method of manufacturing an image article comprising the steps of:

(a) providing a substrate;

(b) coating an organic acid or salt of an organic acid on at least a portion of the substrate; the organic acid or salt of an organic acid being wetted with an aqueous medium, and (c) applying solid particles to at least a portion of the wetted organic acid or salt of an organic acid, to form an image.

Preferably different areas of the coating of the organic acid or salt of an organic acid are differentially wetted with an aqueous medium. Thus, when differentially wetted, the coating of organic acid or salt of an organic acid effects differential adhesive strength across different regions of the organic acid or salt of an organic acid, and therefore may selectively adhere varying concentrations of solid particles on different regions of the substrate.

The organic acid or salt of an organic acid may be differentially wetted by applying different amounts of aqueous medium containing the organic acid or salt of an organic acid to different areas of the coating of organic acid or salt of an organic acid. Alternatively or

additionally, the organic acid or salt of an organic acid may be differentially wetted by coating the organic acid or salt of an organic acid on the substrate at different concentrations in an aqueous medium over different areas of the substrate. Alternatively or additionally, the organic acid or salt of an organic acid may be coated onto the substrate, dried, then differentially wetted by applying different amounts of aqueous medium to different areas of the coating of organic acid or salt of an organic acid.

Thus the present invention provides a method of printing an image using a "tacky" organic acid or salt of an organic acid to adhere solid particles to a substrate. The organic acid or salt of an organic acid, when wetted, becomes "tacky", or adhesive, and due to its water-soluble nature, can be laid down on the substrate by many conventional printing techniques.

Suitably, the substrate is a sheet material, which may be planar or otherwise. The substrate may comprise any suitable material, such as paper, card, wood, glass, metal

(including alloy) , ceramic, stone, mineral, including mineral-based paper, plastics, hair and keratinous substances, composite, polymeric, or textile material, for example. Suitable textile material includes leather, cotton, synthetic textiles such as polyester, nylon or rayon, linen, flax, hemp, jute and silk.

Preferred substrates are sheets of card, paper, plastics, textile materials or metal.

Suitable plastics materials as substrates include polyurethanes, polyesters, poly vinyl chlorides, polyamides, and mixtures and co-polymers thereof.

Many organic acids and salts of organic acids are cheap and abundant, and do not interfere with the chemical mechanisms of many of the target solid particles useful in the invention, such as thermochromic and photochromic materials. Many organic acids and salts of organic acids are highly soluble in water, and therefore their use is relatively environmentally friendly. Aqueous solutions of organic acids and salts of organic acids may be conveniently ink jet printed, without damaging or clogging ink jet print heads.

The organic acid preferably comprises one or more carboxylic acid groups and the salt of an organic acid may comprise one or more carboxylate groups.

Suitably the organic acid or salt of an organic acid comprises no more than 30 carbon atoms, and more preferably comprises a linear or branched C ₁ -C ₃₀ alkyl group, still more preferably a linear or branched C ₁ -C2 ₀ alkyl group, and most preferably a linear or branched Ci- C12 alkyl group.

Preferred organic acids include citric acid, malic acid, maleic acid, formic acid, succinic acid, malonic acid, salicylic acid, propionic acid, acetic acid, bitanetetracarboxylic acid, bitanetricarboxylic acid and any hydroxyl acid, or any mixtures thereof.

Preferred salts include alkali metal, alkaline metal and ammonium salts of any of the above mentioned organic acids, more preferably sodium, potassium, calcium, magnesium or ammonium salts .

There may be a single organic acid or salt of an organic acid, or a plurality of organic acids, salts of organic acids or a mixture of both one or more organic acids and one or more salts of organic acids.

The or each organic acid and/or salt of an organic acid may be coated on the substrate in an aqueous solution and, the solvent may be partially removed from the coating to effect wetting of the organic acid or salt of an organic acid, and thus the adhesive properties of areas of the coating to solid particles. The strength of the adhesive properties of the wetted organic acid or salt of an organic acid is proportional to the amount of water present. Suitably the organic acid or salt of an organic acid is present in the aqueous solution before coating the substrate in an amount of at least 5% w/v of the total weight of the aqueous solution, more preferably at least 10% w/v, still more preferably at least 15% w/v and most preferably at least 20% w/v, and especially at least 30% w/v.

Preferably the solvent is partially removed in varying amounts from different areas of the coating to effect differential wetting of different areas of the coating and thus effect different adhesive strength to solid particles across different areas of the coating.

Alternatively or additionally different concentrations of organic acid or salt of an organic acid in an aqueous media may be coated on different areas of the substrate and the solvent partially evaporated, or differentially partially evaporated to effect a coating having regions of differential adhesive strength.

Alternatively or additionally, differential wetting of the organic acid or salt of an organic acid may be effected by varying the amount of aqueous solution or ink containing the organic acid or salt of an organic acid, coated on the substrate.

The aqueous solution may contain further ingredients, including humectants, lubricants, preservatives, dyes, pigments, surfactants, emulsifiers and the like, for example. Suitable preservatives include the Cibafast range of sulphonated benzotriazines, supplied by Ciba, UK.

The aqueous solution may contain one or more co-solvents, for example, alcohols such as methanol, ethanol, N- methylmorpholine-N-oxide, and alkylene glycols such as propylene glycol and ethylene glycol, and the like.

Dyes, pigments or other colouring agents may be added to the aqueous medium.

The inclusion of dyes and pigments in the aqueous solution containing the organic acid or salt of an organic acid capable of adhering solid particles, allows for secondary images to be formed by coating the substrate with the aqueous solution. The solid particles subsequently applied to the organic acid or salt of an organic acid may

for example be thermochromic or photochromic powders which are coloured or colourless at ambient conditions but turn colourless from coloured, or coloured from colourless, upon exposure to a suitable stimulus. If these particles are coated onto a substrate previously coated with a coating comprising the organic acid or salt of an organic acid and one or more dyes or pigment, then upon exposure to the stimulus, in the case of thermochromic or photochromic powders which are coloured at ambient conditions, the thermochromic or photochromic powders will turn colourless, revealing a coloured image formed by the pigment or dye in the undercoating. Likewise for thermochromic and photochromic powders that are colourless at ambient conditions, they will turn coloured, and obscure the coloured dye or pigment, or form a different colour due to blending of the colours of the dye/pigment and the photochromic/thermochromic powder. In this way, the aqueous solution containing a dye or pigment may be considered an ink.

In other embodiments a substrate may be coated with the organic acid or salt of an organic acid when wetted with an aqueous medium, and subsequently image-wise coated with water and dye or pigment, to wet the organic acid or salt of an organic acid and image-wise apply a colour to the substrate. The coloured substrate may then be image-wise coated with solid particles such as thermochromic powder or photochromic powder.

Suitably the aqueous solution comprising the organic acid or salt of an organic acid is printed onto the substrate. Suitable printing methods include ink jet printing, roller

printing, lithographic, or gravure printing and the like, but especially preferred is ink jet printing.

Ink jet printing is a preferred method of coating the aqueous solution or ink comprising the organic acid or salt of an organic acid. Ink jet printing is a very flexible form of printing, utilising relatively inexpensive equipment. Ink jet printers are commonly used in domestic environments as well as industrial environments. The use of ink jet printing allows for accurate image-wise printing of the aqueous solution or ink onto the substrate, in any desired image pattern. Ink jet printing also allows blanket printing of the entire substrate if desired. The use of organic acids or salts of organic acids as agents capable of adhering solid particles when wetted with an aqueous medium, enables aqueous solutions to be prepared, which do not clog up or damage ink jet printing heads, and are able to be dispersed as a very fine spray or mist. Organic acids and salts thereof do not suffer the same problems on polymers or more bulky chemicals in handling and efficient application by ink-jet printing, and do not require airing or other processing after coating onto the substrate.

When the aqueous solution or ink containing the organic acid or salt of an organic acid is arranged to be ink-jet printed, preferably the solution or ink comprises an electrolyte to provide conductance to allow for ink-drop deflection in an electrical field, particularly for continuous ink-jet printing, in high-speed ink-jet printers .

The organic acid or salt of an organic acid is preferably co-coated with a humectant, such as a polyalkylene glycol, ^• ethylene glycol or the like, for example. Humectants are particularly useful for ink jet printing to prevent ink jet printing heads from drying out during application of the compositions.

The organic acid or salt of an organic acid may be applied to substantially the entire surface of the substrate or may be image-wise applied to a surface of the substrate. In particular the organic acid or salt of an organic acid may be image-wise applied to a surface of the substrate such that the dimensions of the coating of the organic acid or salt of an organic acid on the substrate correspond to the dimensions and position where it is desired to apply solid particles. Thus, the image-wise application of the organic acid or salt of an organic acid corresponds to the subsequent image-wise application of solid particles.

In preferred embodiments the organic acid or salt of an organic acid is applied to the substrate in solution, then the solvent or solvents substantially removed, and subsequently wetted with an aqueous medium, whether image- wise or over the entire coating of organic acid or salt of an organic acid.

If the substrate is entirely coated with the organic acid or salt of an organic acid then dried, the dried coating may be image-wise wetted with an aqueous medium, to create adhesive image areas capable of adhering solid particles. In this way step (b) may comprise coating the organic acid- or salt of an organic acid in solution, drying the

coating, and subsequently wetting at least a portion of the dried coating of the organic acid or salt of an organic acid. Suitably the dried organic acid or salt of an organic acid is image-wise differentially wetted by the aqueous medium such that different areas of the coating have different adhesive strength to solid particles.

Preferably the solid particles comprise a solid powder or granules, preferably dry particles. The size of the solid particles will depend on the nature of the solid and its intended use. If the particle size is relatively large, image-wise adhesion of the solid particles to the wetted organic acid or salt of an organic acid may affect embossing of the substrate, creating raised image areas, useful for example, as Braille text.

The solid particles preferably comprise any one or more agents selected from pigments (including pearlescent pigments), thermochromic materials, phosphors, photochromic materials, glass, polymeric beads and particles, activated charcoal or carbon, solid pigment toners (used in laser toner printing) , metals (including alloys) or any mixture thereof. Each of the above solids is particularly useful in creating articles which change in optical characteristics upon application of a suitable stimulus, whether chemical or physical (such as light, heat, radiation, pressure, movement, etc) .

Particularly preferred solid particles are thermochromic materials, photochromic materials, phosphors and magnetic metals. Particularly preferred methods utilise a thermochromic, photochromic or magnetic material in step

(C) .

It has been found that the adhesive property of wetted organic acids and salts thereof ensures efficient binding of thermochromic and photochromic materials to the substrate without detracting from their ability to change colour upon exposure to a suitable stimulant.

The solid particles may be applied to the substrate by any suitable method.

The substrate containing a coating of wetted organic acid or salt of an organic acid may be immersed in the solid particles, such that the solid particles adhere only to the wetted organic acid or salt of an organic acid. Excess particles may be removed by agitating the substrate after removal from the particles, such as shaking, tapping and the like, or by effecting airflow across the surface of the substrate comprising the organic acid or salt of an organic acid and particles.

Alternatively the whole area of the substrate coated with wetted organic acid or salt of an organic acid may be contacted with solid particles, such as by sprinkling, spreading or blowing solid particles onto the surface of the substrate coated with the organic acid or salt of an organic acid.

In some embodiments the solid particles may be printed onto the substrate, including by charged deposition (as in laser-toner printing) . Printing of the solid particles allows image-wise application of the particles to all or a portion of the wetted organic acid or salt of an organic acid. For example if an entire surface of the substrate

has been coated with wetted organic acid or salt of an organic acid then the solid particles may be image-wise applied, leaving areas of wetted organic acid or salt of an organic acid to which no particles are adherent. The non-adhered regions of the organic acid or salt of an organic acid may then be contacted with different solid particles dried to remove their adhesive properties, or removed or masked by any suitable method, such as washing or ablation.

Preferably the solid particles are image-wise applied to the organic acid or salt of an organic acid.

There may be a step after step (c) of drying the image article. Drying may be effected by allowing any solvents and/or atmospheric water present to evaporate under ambient conditions, or by heating the image article to facilitate accelerated evaporation, for example.

Step (c) may comprise applying a plurality of different types of solid particles to the wetted organic acid or salt of an organic acid. The different types of solid particles may be mixed together and applied in a single step. Alternatively or additionally the different types of particles may be applied separately and may be image- wise applied on different areas of wetted organic acid or salt of an organic acid to produce different image patterns .

The method may comprise repeating steps (b) and (c) . For example, after wetted organic acid or salt of an organic acid has been image-wise coated onto the substrate and a first type of solid particle adhered to the wetted agent,

a second coating of wetted organic acid or salt of an organic acid may be applied to at least a portion of the substrate, in the same or different image pattern to the first coating, and a second type of solid particle adhered to the second image coating of wetted organic acid or salt of an organic acid. In this way steps (b) and (c) may be repeated as many times as desired to build up an image on the substrate comprising a plurality of different solid particles .

In repeated steps (b) , the subsequent coating of wetted organic acid or salt of an organic acid may be image-wise applied over areas of the substrate previously coated with wetted organic acid or salt of an organic acid, not previously coated, or mixtures thereof.

After each repetition of step (c) , there may be a further step of drying the coated substrate. Thus, the substrate coated with wetted organic acid or salt of an organic acid to which solid particles are adhered may be dried before the next step (b) is repeated.

Step (c) may comprise contacting a plurality of different solid particle types on a plurality of different regions of the wetted organic acid or salt of an organic acid.

Once all of the desired solid particles are adhered to the substrate, preferably the coated substrate is dried to remove substantially all remaining solvent.

There may be a step after step (c) , and preferably after drying, of fixing the image produced on the image article.

Fixing may be achieved by any suitable method, and may comprise fixing with a chemical agent, and/or fixing by physical means.

If the substrate also comprises chemical groups that are capable of taking part in a cross-linking process, then the organic acid or salt of an organic acid may also bind the substrate surface, giving enhanced durability to subsequent washing and attrition. Examples of substrates having suitable groups include paper and card bearing hydroxyl groups, capable of being cross-linked by agents such as DMDHEU (dimethylol-4, 5-dihydroxyethyleneuren) .

Alternatively or additionally the image may be fixed by coating the image article with a suitable cover layer. The cover layer may comprise a layer of lacquer, paint or varnish, for example.

Alternatively or additionally the image may be fixed by laminating or affixing a cover sheet to the image article, over the image .

According to a second aspect of the present invention there is provided an image article comprising a substrate on which at least a portion is coated with a organic acid or salt of an organic acid and an image comprising solid particles coated on at least a portion of the organic acid or salt of an organic acid.

Preferably the organic acid or salt of an organic acid is differentially wetted to effect differential solid particle adhesive properties on different regions of the coating.

The substrate, organic acid or salt of an organic acid and solid particles are preferably as described hereinabove for the first aspect of the invention.

The image article may comprise, for example, a printing form, an electronic part or a mask to a printing form or electronic part.

Suitable printing forms include printing plates, printing cylinders, identity cards, artworks, security articles, packaging, textiles such as clothing and the like.

The electronic part is preferably a printed circuit board.

According to a third aspect of the invention there is provided an image article produced by the method of the first aspect of the invention.

According to a fourth aspect of the present invention there is provided a printing apparatus comprising an ink- jet printer through which a substrate is arranged to pass, and a means to apply solid particles to the substrate downstream of the ink-jet printer.

The means to apply solid particles may comprise a receptacle in which the particles are located and into which or through which the substrate is arranged to pass. Alternatively, the means to apply solid particles may comprise means to spray or blow solid particles onto the substrate, downstream of the ink-jet printer. In other embodiments the means to apply solid particles may comprise a laser-toner apparatus.

The various aspects of the invention will now be described, by way of example only, in the following examples :

EXAMPLES

Example 1

Card and paper substrates were ink-jet printed with a ^λ tack' generating ink on an Apollo P-1200 ink-jet printer to yield a printed image template which demonstrated differential ^λ tack' properties; the ink being formulated in accordance with the following recipe:

400 gdrrf ³ citric acid (Aldrich, UK) 5 gdπf ³ Polypropylene glycol 425 0.5 gdπf ³ Cibafast W (Ciba) pH 3.8

De-ionised water to 1 litre

The ^λ tack' image template was covered with a commercially available black 25 ⁰ C thermochromic powder (supplied by B+H The Colour Change Company, UK) and any non-adhered particles removed by gently tapping the card. The printed image heated at 100 ⁰ C for 5 minutes to dry the substrate and the thermochromic powder further fixed to the substrate by spraying the image with a commercially available clear acrylic lacquer spray (supplied by RS Components, UK) . The resulting print achieved exhibited a black and white photographic quality image, which when heated above 25°C became colourless; the black and white image returning when the print was cooled to room temperature .

Example 2

The process described in Example 1 was repeated, but in this case the black and white photographic image was fixed to the substrate by laminating it between two clear plastic sheets. A black and white photographic quality image was again achieved, which when heated above 25 ⁰ C became colourless; the black and white image returning when the print was cooled to room temperature.

Example 3

The process described in Example 1 was repeated, but in this case the black 25 ⁰ C thermochromic powder was replaced with a cyan 15 ⁰ C thermochromic powder (B+H The Colour Change Company) to yield a colourless print at room temperature. On cooling below 15 ⁰ C, a blue and white photographic quality image was achieved, which again became colourless on heating to room temperature.

Example 4

The process described in Example 1 was repeated, but in this case the ^tack' generating ink contained 400 gdrrf ³ ammonium citrate (supplied by Aldrich Ltd, UK) in place of the citric acid. A black and white photographic quality image was again achieved, which when heated above 25 ⁰ C became colourless; the black and white image returning when the print was cooled to room temperature.

Example 5 The process described in Example 1 was repeated, but in this case the ^λ tack' generating inks also contained water soluble textile dyes (30 gdnf ³ ) ; the dyes used being Sumifix Supra Turquoise Blue BGF, Sumifix Supra Brilliant

Yellow 3GF and Sumifix Supra Brilliant Red 3BF (supplied by Sumitomo Chemical, Japan) . Thus, a multi-coloured ^x tack' image was printed by replacing the cyan, magenta and yellow inks present in a tri-colour ink-jet cartridge with the above inks. On application of the 25°C black thermochromic powder to the multi-coloured ^λ tack' template, a black and white photographic quality image was again achieved. On heating the black and white image above 25 ⁰ C, the multi-coloured image once more became visible; the black and white image returning when the print was cooled to room temperature.

Example 6

The process described in Example 5 was repeated, but in this case the black 25°C thermochromic powder was replaced with a cyan 15 ⁰ C thermochromic powder (supplied by B+H The

Colour Change Company, UK) . In this case, a multi-coloured image was achieved, which on cooling below 15 ⁰ C gave rise to a blue photographic quality image; the multi-coloured image returning once more as the print was heated to room temperature.

Example 7

The process described in Example 1 was repeated, but in this case the thermochromic powder was replaced with a photochromic powder. The photochromic powder was prepared by dissolving a commercially available photochromic dye, such as Reversacol Flame Orange (supplied by James Robinsons Ltd, UK) , in a clear polyurethane varnish and allowing the varnish to cure. The cured varnish was ground to a fine powder and then applied to the ^λ tack' image template. A colourless photographic quality print was achieved, which on exposing to ultra-violet light became

orange; the image eventually becoming colourless once more in the absence of ultra-violet light.

Example 8 The process described in Example 1 was repeated, but in this case the black thermochromic powder was replaced with a red pigment powder, HD Pigment Red 112 (supplied by Holliday Dispersions, UK) to yield a red photographic quality print.

Example 9

The process described in Example 1 was repeated, but in this case the black thermochromic powder was replaced with a commercial black toner powder to yield a black photographic quality print.

Example 10

The process described in Example 1 was repeated, but in this case the black thermochromic powder was replaced with carbon powder to yield a black photographic quality print.

Example 11

A ^λ tack' template was produced on card using the process described in Example 1, but in this case the printed template was coated with a scented activated carbon powder prepared as follows. The scented carbon powder was prepared by stirring activated carbon powder (Aldrich, UK) in an alcoholic solution of cologne (supplied by Boudicca, UK) . The powder was collected by filtration, dried at room temperature and finally applied to the *tack' template to yield a photographic quality print which emitted a scented fragrance.

Example 12

The process described in Example 1 was repeated, but in this case the black thermochromic powder was replaced with glass powder. A photographic quality image was produced, which exhibited unusual optical effects dependent on viewing conditions .

Example 13

A coloured ^' 'tack' template was printed on card in accordance with the procedure described in Example 1, but in this case the black thermochromic powder was replaced with glass powder to yield a photographic quality image, which exhibited unusual optical effects dependent on viewing conditions.

Example 14

The process described in Example 1 was repeated, but in this case the black thermochromic powder was replaced with copper powder to produce a metallic photographic quality print.

Example 15

The process described in Example 1 was repeated, but in this case the black thermochromic powder was replaced with tin powder to produce a metallic photographic quality print.

Example 16

The process described in Example 1 was repeated, but in this case the black thermochromic powder was replaced with iron powder to produce a metallic photographic quality print. The iron print achieved could be readily verified by its attraction to a strong magnet.

Example 17

The process described in Example 1 was used to produce a printed circuit, but in this case the black thermochromic powder was replaced with silver powder. The silver coated printed circuit formed was shown to be conductive along its length using a conductivity meter.