HK1069467B - Method for full color laser marking of id documents - Google Patents

Description

Field

The invention relates in general to an information-bearing laminar assembly suitable for use as an identification card, and more particularly, to forming information on information-bearing laminar assembly by laser engraving.

Background Identification Documents

Identification documents (hereafter "ID documents") play a critical role in today's society. One example of an ID document is an identification card ("ID card"). ID documents are used on a daily basis --to prove identity, to verify age, to access a secure area, to evidence driving privileges, to cash a check, and so on. Airplane passengers are required to show an ID document during check in, security screening, and prior to boarding their flight. In addition, because we live in an ever-evolving cashless society, ID documents are used to make payments, access an automated teller machine (ATM), debit an account, or make a payment, etc.

Many types of identification cards and documents, such as driving licenses, national or government identification cards, bank cards, credit cards, controlled access cards and smart cards, carry thereon certain items of information which relate to the identity of the bearer. Examples of such information include name, address, birth date, signature and photographic image; the cards or documents may in addition carry other variant data (i.e., data specific to a particular card or document, for example an employee number) and invariant data (i.e., data common to a large number of cards, for example the name of an employer). All of the cards described above will hereinafter be generically referred to as "ID documents".

Figs. 1 and 2 illustrate a front view and cross-sectional view (taken along the A-A line), respectively, of an exemplary prior art identification (ID) document 10. In FIG. 1, the prior art ID document 1 includes a photographic image 12, a bar code 14 (which may contain information specific to the person whose image appears in photographic image 12 and/or information that is the same from ID document to ID document), variable personal information 16, such as an address, signature, and/or birthdate, and biometric information 18 associated with the person whose image appears in photographic image 12 (e.g., a fingerprint). Although not illustrated in FIG. 1, the ID document 10 can include a magnetic stripe (which, for example, can be on the rear side (not shown) of the ID document 10), and various security features, such as a security pattern (for example, a printed pattern comprising a tightly printed pattern of finely divided printed and unprinted areas in close proximity to each other, such as a fine-line printed security pattern as is used in the printing of banknote paper, stock certificates, and the like).

Referring to FIG. 2, the ID document 10 comprises a pre-printed core 20 (also referred to as a substrate). In many applications, the core can be a light-colored, opaque material, such as, for example, white polyvinyl chloride (PVC) material that is, for example, about 0.63 mm (25 mil) thick. The core 20 is laminated with a transparent material, such as clear PVC material 22, which, by way of example, can be about 0.025-0.127 mm (1-5 mil) thick. The composite of the core 20 and clear PVC material 22 form a so-called "card blank" 25 that can be up to about 0.76mm (30 mils) thick. Information 26a-c is printed on the card blank 25 using a method such as Dye Diffusion Thermal Transfer ("D2T2") printing (described further below and also in commonly assigned United States Patent No. 6066594 ). The information 26a-c can, for example, comprise an indicium or indicia, such as the invariant or nonvarying information common to a large number of identification documents, for example the name and logo of the organization issuing the documents. The information 26a-c may be formed by any known process capable of forming the indicium on the specific core material used.

To protect the information 26a-c that is printed, an additional layer of overlaminate 24 can be coupled to the card blank 25 and printing 26a-c using, for example, 0.025mm (1 mil) of adhesive (not shown). The overlaminate 24 can be substantially transparent. Materials suitable for forming such protective layers are known to those skilled in the art of making identification documents and any of the conventional materials may be used provided they have sufficient transparency. Examples of usable materials for overlaminates include biaxially oriented polyester or other optically clear durable plastic film.

The above-described printing techniques are not the only methods for printing information on data carriers such as ID documents. Laser beams, for example can be used for marking, writing, bar coding, and engraving many different types of materials, including plastics. Lasers have been used, for example, to mark plastic materials to create indicia such as bar codes, date codes, part numbers, batch codes, and company logos. It will be appreciated that laser engraving or marking generally involves a process of inscribing or engraving a document surface with identification marks, characters, text, tactile marks -- including text, patterns, designs (such as decorative or security features), photographs, etc.

One way to laser mark thermoplastic materials involves irradiating a material, such as a thermoplastic, with a laser beam at a given radiation. The area irradiated by the laser absorbs the laser energy and produces heat which causes a visible discoloration in the thermoplastic. The visible discoloration serves as a "mark" or indicator; it will be appreciated that laser beams can be controlled to form patterns of "marks" that can form images, lines, numbers, letters, patterns, and the like. Depending on the type of laser and the type of material used, various types of marks (e.g., dark marks on light backgrounds, light marks on dark backgrounds, colored marks) can be produced. Some types of thermoplastics, such as polyvinylchloride (PVC), acrylonitrile butadiene styrene (ABS), and polyethylene terephthalate (PET), are capable of absorbing laser energy in their native states. Some materials which are transparent to laser energy in their native state, such as polyethylene, may require the addition of one or more additives to be responsive to laser energy.

For additional background, various laser marking and/or engraving techniques are disclosed, e.g., in U.S. Patent Nos. 6,022,905 , 5,298,922 , 5,294,774 , 5,215,864 and 4,732,410 . In addition, U.S. Patent Nos. 4816372 , 4894110 , 5005872 , 5977514 , and 6179338 describe various implementations for using a laser to print information.

US4529992 discloses a multi-colour record material comprising respective layers for each colour, each layer comprising colour-forming material, colour developer, and an infrared absorbing material which absorbs infrared radiation of a specific wavelength. The respective regions of the layers are activated to produce colour as desired by laser beams of the respective infrared wavelength.

EP0279104 discloses a multi-colour record material including a layer of microcapsules each containing a leuco dye and including a wavelength specific infrared absorber, the layer being superimposed upon a developer layer on a substrate. Respective colours are produced by laser beams of the wavelength corresponding to the absorption peaks of the respective infrared absorbers.

EP0734870 discloses a recording material similar to that of EP0279104 but in which the microcapsules are embedded in a matrix layer incorporating the developer material.

EP0739748 discloses a recording medium comprising an infrared dye in combination with a leuco dye, the medium again being activated by laser.

US5409797 discloses a recording medium in which a layer of microcapsules containing a first colouring component is supported on a heat-sensitive layer comprising a second colouring component and an infrared absorbing dye.

EP0637514 discloses a laser marking system in which a recording medium comprises a colour former, a colour developer and an infrared absorbing material formed as a layer on a substrate, the material being marked by directing laser light onto the layer.

Summary

Using laser beams to write or engrave information to ID cards presents a number of advantages over conventional printing. For example, the foaming of the thermoplastic that can occur with some types of laser engraving can be adapted to provide an indicium having a tactile feel, which is a useful authenticator of a data carrier that also can be very difficult to counterfeit or alter. In addition, laser engraving generally does not require the use of ink, which can reduce the cost of consumables used to manufacture an ID card. Laser engraving can also be more durable than ink printing, and more resistant to abrasion (which can be particularly useful if a counterfeiter attempts to "rub off an indicium on an ID card). The resolution and print quality of laser engraving often can be higher than that of conventional ink-based printing. Laser engraving also can be a more environmentally friendly manufacturing process than printing with ink, especially because solvents and other chemicals often used with ink generally are not used with laser engraving.

The present invention provides improved methods for laser engraving identification documents. An identification document can be produced to allow a full color image to be formed on (or within) an identification document by laser addressing the document with multiple lasers (e.g., three near infrared lasers).

The present invention provides a method of producing an identification document as set out in claim 1.

The foregoing and other features and advantages of the present invention will be even more readily apparent from the following Detailed Description, which proceeds with reference to the accompanying drawings.

Brief Description of the Drawings

The advantages, features, and aspects of embodiments of the invention will be more fully understood in conjunction with the following detailed description and accompanying drawings, wherein:

• FIG. 1 is an illustrative example of a prior art identification document;
• FIG. 2 is an illustrative cross section of the prior art identification document of FIG. 1, taken along the A-A line;
• FIG. 3 is an illustrative flow chart of a method for full color laser engraving, in accordance with one embodiment of the invention;
• FIG. 4 is a cross sectional view of an imaging layer manufactured, in accordance with one embodiment of the invention; and
• FIG. 5 is a cross sectional view, after laser engraving, of an ID card manufactured using the imaging layer of FIG. 4. and the method of FIG. 3

The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In addition, in the figures, like numbers refer to like elements.

Detailed Description of the Invention Terminology

In the foregoing discussion, the use of the word "ID document" is broadly defined and intended to include all types of ID documents, including (but not limited to), documents, magnetic disks, credit cards, bank cards, phone cards, stored value cards, prepaid cards, smart cards (e.g., cards that include one more semiconductor chips, such as memory devices, microprocessors, and microcontrollers), contact cards, contactless cards, proximity cards (e.g., radio frequency (RFID) cards), passports, driver's licenses, network access cards, employee badges, debit cards, security cards, visas, immigration documentation, national ID cards, citizenship cards, social security cards, security badges, certificates, identification cards or documents, voter registration and/or identification cards, police ID cards, border crossing cards, security clearance badges and cards, legal instruments, gun permits, badges, gift certificates or cards, membership cards or badges, and tags. Also, the terms "document," "card," "badge" and "documentation" are used interchangeably throughout this patent application.). In at least some aspects of the invention, ID document can include any item of value (e.g., currency, bank notes, and checks) where authenticity of the item is important and/or where counterfeiting or fraud is an issue.

In addition, in the foregoing discussion, "identification" at least refers to the use of an ID document to provide identification and/or authentication of a user and/or the ID document itself. For example, in a conventional driver's license, one or more portrait images on the card are intended to show a likeness of the authorized holder of the card. For purposes of identification, at least one portrait on the card preferably shows an "identification quality" likeness of the holder such that someone viewing the card can determine with reasonable confidence whether the holder of the card actually is the person whose image is on the card. "Identification quality" images, in at least one embodiment of the invention, include covert images that, when viewed using the proper facilitator (e.g., an appropriate light source), provide a discernable image that is usable for identification or authentication purposes.

There are a number of reasons why an image or information on an ID document might not qualify as an "identification quality" image. Images that are not "identification quality" may be too faint, blurry, coarse, small, etc., to be able to be discernable enough to serve an identification purpose. An image that might not be sufficient as an "identification quality" image, at least in some environments, could, for example, be an image that consists of a mere silhouette of a person, or an outline that does not reveal what might be considered essential identification essential (e.g. hair or eye color) of an individual.

Of course, it is appreciated that certain images may be considered to be "identification quality" if the images are machine readable or recognizable, even if such images do not appear to be "identification quality" to a human eye, whether or not the human eye is assisted by a particular piece of equipment, such as a special light source. For example, in at least one embodiment of the invention, an image or data on an ID document can be considered to be "identification quality" if it has embedded in it machine-readable information (such as digital watermarks) that also facilitate identification and/or authentication.

Further, in at least some embodiments, "identification" and "authentication" are intended to include (in addition to the conventional meanings of these words), functions such as recognition, information, decoration, and any other purpose for which an indicia can be placed upon an article in the article's raw, partially prepared, or final state. Also, instead of ID documents, the inventive techniques can be employed with product tags, product packaging, business cards, bags, charts, maps, labels, etc., etc., particularly those items including marking of an laminate or over-laminate structure. The term ID document thus is broadly defined herein to include these tags, labels, packaging, cards, etc.

"Personalization", "Personalized data" and "variable" data are used interchangeably herein, and refer at least to data, images, and information that are "personal to" or "specific to" a specific cardholder or group of cardholders. Personalized data can include data that is unique to a specific cardholder (such as biometric information, image information, serial numbers, Social Security Numbers, privileges a cardholder may have, etc.), but is not limited to unique data. Personalized data can include some data, such as birthdate, height, weight, eye color, address, etc., that are personal to a specific cardholder but not necessarily unique to that cardholder (for example, other cardholders might share the same personal data, such as birthdate). In at least some embodiments of the invention, personal/variable data can include some fixed data, as well. For example, in at least some embodiments, personalized data refers to any data that is not pre-printed onto an ID document in advance, so such personalized data can include both data that is cardholder-specific and data that is common to many cardholders. Variable data can, for example, be printed on an information-bearing layer of the ID card using thermal printing ribbons and thermal printheads.

As used herein, the term "fixed data" refers at least to data which is identical for each ID card. Fixed data can, for example, be preprinted on an overlay patch, a laminate or an information-bearing layer of the ID card. Fixed data can also be printed on each individual ID card during the process of printing and optionally laminating the ID card. The term "variable data" refers generally to data which differs for each ID card and is associated with personal information, an image of the ID card holder or a unique reference number for security purposes assigned by the issuing agency.

As used herein, an "information-bearing layer" refers at least to the parts of an ID document where pictures, images, text, bar codes, fixed and/or variable data are printed. The information-bearing layer can include a separate receiver layer adapted to accept inks, dyes, pigments and resins from thermal print ribbons. The information-bearing layer can itself be the receiver layer. Depending on the particular design of the ID document, the information bearing layer can be the substrate or core layer, but also can be a laminate applied thereto, or to another laminate layer on the card. There can be different information bearing layers in an ID document for pre-printing and for personalization.

"Laminate" and "overlaminate" include (but are not limited to) film and sheet products. Laminates usable with at least some embodiments of the invention include those which contain substantially transparent polymers and/or substantially transparent adhesives, or which have substantially transparent polymers and/or substantially transparent adhesives as a part of their structure, e.g., as an extruded feature. Examples of potentially usable laminates include at least polyester, polycarbonate, polystyrene, cellulose ester, polyolefin, polysulfone, and polyamide. Laminates can be made using either an amorphous or biaxially oriented polymer as well. The laminate can comprise a plurality of separate laminate layers, for example a boundary layer and/or a film layer. Other possibly usable laminates include security laminates, such as a transparent laminate material with proprietary security technology features and processes, which protects documents of value from counterfeiting, data alteration, photo substitution, duplication (including color photocopying), and simulation by use of materials and technologies that are commonly available. Laminates also can include thermosetting materials, such as epoxy. Laminates can include synthetic resin-impregnated or coated base materials composed of successive layers of material, bonded together via heat, pressure, and/or adhesive.

The material(s) from which a laminate is made may be transparent, but need not be. The degree of transparency of the laminate can, for example, be dictated by the information contained within the identification document, the particular colors and/or security features used, etc. The thickness of the laminate layers is not critical, although in some embodiments it may be preferred that the thickness of a laminate layer be about 0.025 - 0.51 mm (1-20 mils). Lamination of any laminate layer(s) to any other layer of material (e.g., a core layer) can be accomplished using any conventional lamination process, and such processes are well known to those skilled in the production of articles such as identification documents. Of course, the types and structures of the laminates described herein are provided only by way of example, those skilled in the art will appreciated that many different types of laminates are usable in accordance with the invention. Various lamination processes are disclosed in assignee's U.S. Patent Nos. 5,783,024 , 6,007,660 , 6066594 , and 6,159,327 . Other lamination processes are disclosed, e.g., in U.S. patent Nos. 6,283,188 and 6,003,581 .

For purposes of illustration, the following description will proceed with reference to ID document structures (such as TESLIN-core, multi-layered ID documents) and fused polycarbonate structures. It should be appreciated, however, that the present invention is not so limited. Indeed, as those skilled in the art will appreciate, the inventive techniques can be applied to many other structures formed in many different ways to provide information full color laser engraved information thereon. Generally, the invention has applicability for virtually any product which is to be printed and especially those products which are to be laser engraved or marked and/or which need to be uniquely identified and/or protected against fraud and/or tampering. For example, at least some embodiments of the invention are usable to form non visible indicia on articles formed from paper, wood, cardboard, paperboard, glass, metal, plastic, fabric, ceramic, rubber, along with many man-made materials, such as microporous materials, single phase materials, two phase materials, coated paper, synthetic paper (e.g., TYVEC, manufactured by Dupont Corp of Wilmington, Delaware), foamed polypropylene film (including calcium carbonate foamed polypropylene film), plastic, polyolefin, polyester, polyethylenetelphthalate (PET), PET-G, PET-F, and polyvinyl chloride (PVC), and combinations thereof.

Forming full color laser engraved images

In one embodiment, the invention provides a method for forming a full color laser engraved image on an ID card. As described below, a special image capable layer is prepared that is addressable by one or more near infrared (NIR) lasers. Each type of particle contained within the image capable layer is associated with a particular color (e.g., cyan, magenta, or yellow) and is responsive (i.e., can selectively absorb) a particular wavelength of laser energy to form a laser engraved pixel in that respective color. In one embodiment, the particles are selected such that the wavelengths that they respond to do not overlap significantly. By providing discrete physical particles and preventing a given particle from responding to more than one laser wavelength, it can be possible to minimize so-called "cross talk" between the cyan, magenta, and yellow centers and minimize contamination and/or chemical mixing of image formers. This helps to ensure image accuracy and quality.

FIG. 3 is an illustrative flow chart of a method for color laser engraving (including full color laser engraving), in accordance with one embodiment of the invention. First select a leuco dye and IR dye pair (step 100). Our preferred embodiment employs three leuco dyes representing cyan (C), yellow (Y) and magenta (M) colors, and three infrared (IR) absorbing dyes, one for each leuco dye. In one embodiment, we use leuco dyes that have been shown to produce photographic quality images at high resolution (e.g., > 500 dpi). The leuco dyes change to a specific color (e.g., Y, M, or C) when activated with appropriate laser energy. Of course, those skilled in the art will appreciate that other types of dyes can be used in alternate embodiments as well.

In at least one embodiment, selection of the leuco dye and/or the IR dye is accomplished so that the leuco dye and IR absorbing dye have indexes of refraction that are a substantial match to the carrier material in which the particles are to be disposed, so that the image capable layer formed as described below will be substantially transparent.

In at least one embodiment, the infrared dyes (IR) are selected so that they are transparent in the visible region (or spectrum) and absorb at selected maxima in the near IR spectrum. For example, in one advantageous embodiment, the infrared dyes absorb at maxima of 810 nanometers (nm), 850 nm, and 890 nm. These maxima are chosen such that each IR dye can be addressed with an appropriate near infrared (NIR) laser without activating the other two IR dyes, but to an extent capable of activating the leuco dyes.

The reaction to the colored state is a unimolecular rearrangement that is driven by heat. It is, therefore, not generally necessary to consider viscosity of the reaction medium in designing the imaging system. Preferably, it should be ensured that enough of the IR dye is in proximity to the leuco dyes so that excitation of the IR dye(s) provides enough localized temperature gradients to produce the unimolecular transformation of the color dye to the colored state.

Referring again to FIG. 3, for each pair of leuco dye and IR dye selected in step 100, a brittle, grindable compound, such as a matrix, is created (step 105). In one embodiment, this is accomplished by constructing an acrylate matrix for each leuco dye and IR dye pair. We cast each acrylate matrix (through methods well known to those skilled in the art) onto a so-called "release" web at a fixed thickness (e.g., about 10-20 micrometres). The acrylate matrix is then fully cured (e.g., through an appropriate curing method for the matrix, such as ultraviolet (W) based curing), to create the brittle grindable matrix. In one embodiment, the acrylate monomers, initiators, etc. are chosen to yield a brittle matrix and a very high cure rate (e.g., substantially 100% cured).

Each fully cured acrylate/leuco dye/IR dye matrix is then removed from the reusable "release" carrier and ground (step 110) to a desired particle size. In one embodiment, the desired average particle size is roughly 10 micrometres thick (about 10-20 micrometres square --max). The grinding can occur in many different ways, as will be appreciated by those skilled in the art. In one embodiment, we use cryogenics to grind the fully cured acrylate/leuco dye/IR dye matrix. The resultant particles can have any shape, although the grinding tends to produce irregularly shaped particles. In this fashion, we prepare three separate acrylate matrices each with its own leuco dye/IR dye pair.

We then blend the three matrices (step 115) to obtain a mix that is added to a carrier to form an image capable layer (120) - that is, a layer that is capable of having an image formed (i.e., laser marked or laser engraved) thereon by the application of appropriate laser energy. In one embodiment, the mix is cast into a thickness of roughly 0.025 - 0.127 mm (1 - 5 mils). This thickness of mix can result in an image capable layer that is capable of generating a full color image, with appropriate color balance, when laser energy is applied (step 125).

FIG. 4 is a cross sectional view of an imaging layer 200 manufactured, in accordance with one embodiment of the invention. The imaging layer includes a plurality of particles 202, 204, 206, each particle comprising a pair, respectively, of yellow, cyan, and magenta with an appropriate leuco dye. Note that although FIG. 4 illustrates all of the particles 202, 204, 206 as having substantially uniform size, that is provided merely for illustration and is not required for the invention. In fact, in many embodiments of the invention, the particle size will be random. In addition, FIG. 4 illustrates each particle as having equal, symmetrical portions of leuco dye (shown as "L") and colored IR dye (shown, e.g., as "Y", "M", and "C"), but these are provided entirely for the purpose of illustration, and are not intended to show literally what the particles look like.

As those skilled in the art will appreciate, the image capable layer 200 can be formed as a laminate, a coating, or an adhesive

In FIG. 4, first, second, and third lasers 208, 210, 212 each transmit energy at a different wavelength, and only one type of particle 202, 204, 206 will be responsive to a given laser 208, 210, 212. For example, the yellow particle 202 could be responsive only to the first (850nm) laser 208.

The lasers 208, 210, 212 can be operated in many ways. In a preferred embodiment, each laser is operated sequentially. However, in at least one embodiment, two or more lasers operate at the same time. Furthermore, although FIG. 4 shows that the lasers 208, 210, 212 are disposed along side each other to direct laser energy in separate location, the lasers can, in fact be co-located and/or can direct their energy to the same spot, without affecting the quality or appearance of the full color laser engraving as described here.

Referring again to FIG. 3, in one embodiment, this mix is provided in a carrier where the index of refraction approaches (or equals) that of each of the acrylate matrices. Generally, any polymer having an index of refraction that matches that of the resultant particles and that can hold the particles in suspension is usable as a carrier.

The image capable layer (step 125) has a preset distribution (because of the mixing and blending of steps 100-120) CYM particles (all preferably transparent) each capable of absorbing specific NIR radiation to achieve the necessary color formation. We also have separation of the CYM imaging centers in that they are each encased in a highly cross-linked acrylate matrix within another "carrier" resin system. Thus, "cross talk" between the CYM centers is minimized, as is contamination and/or chemical mixing of image formers.

FIG. 5 is a cross sectional view, after laser engraving, of an ID card manufactured using the imaging layer of FIG. 4 and the method of FIG. 3. In FIG. 5, the image capable layer 200 of FIG. 4 is coupled to the core layer 50 of an ID card 10. Full color information 54h-k is shown as being engraved into the image capable layer 200. A layer of overlaminate 58 is applied over the image capable layer 200. In at least one embodiment, the overlaminate 48 is transparent to laser radiation and can be applied prior to the laser engraving of the image capable layer 200. In one embodiment, the overlaminate 58 absorbs laser radiation and so is coupled to the image capable layer 200 after the laser engraving occurs.

In one embodiment, the "carrier resin" system can be solvent cast (e.g., no dissolution of the acrylate matrices), UV - 100% solids, or extrudable resin systems. All three can be used to incorporate the imaging layer into a document structure.

Concluding Remarks

Having described and illustrated the principles of the technology with reference to specific implementations, it will be recognized that the technology can be implemented in many other, different, forms.

Although certain words, languages, phrases, terminology, and product brands have been used herein to describe the various features of the embodiments of the invention, their use is not intended as limiting. Use of a given word, phrase, language, terminology, or product brand is intended to include all grammatical, literal, scientific, technical, and functional equivalents. The terminology used herein is for the purpose of description and not limitation.

The technology disclosed herein can be used in combination with other technologies. Examples include the technology detailed in the following applications: 09/747,735 (filed 12/22/00 ), 09/969,200 (filed 10/2/01). Also, instead of ID documents, the inventive techniques can be employed with product tags, product packaging, business cards, bags, charts, maps, labels, etc., etc., particularly those items including engraving of an over-laminate structure. The term ID document is broadly defined herein to include these tags, labels, packaging, cards, etc. In addition, while some of the examples above are disclosed with specific core components, it is noted that-laminates can be sensitized for use with other core components.

Claims (12)

1. A method of producing an identification document comprising the steps of:

   selecting at least a first leuco dye for a first color and at least a first infrared absorbing dye selected so that the infrared-absorbing dye is transparent in the visible region and absorbs infrared radiation at respective maxima in the near infrared spectrum so that the infrared dye can be addressed with an appropriate infrared laser wavelength,

   pairing the leuco dye with the infrared-absorbing dye,

   providing the leuco dye and infrared-absorbing dye in an image-capable layer on a core layer, and

   forming an image in the image-capable layer by means of applying infrared laser light at the appropriate wavelength, characterised by the steps of:

   for the leuco dye/infrared-absorbing dye pair, creating, with the dye pair, a first brittle grindable matrix material, and grinding the material to provide a quantity of particles, mixing together the particles from the first brittle material in a carrier, forming from the resulting mixture an image-capable layer upon a core layer and subsequently forming a laser-engraved image in the image-capable layer by means of applying infrared laser light at the appropriate wavelength;

   characterised in that the leuco dye undergoes a unimolecular rearrangement driven by heat generated from absorption of infrared radiation by the infrared-absorbing dye.
2. A method according to Claim 1, characterised in that the matrix material is an acrylate matrix material.
3. A method according to Claim 1 or Claim 2, characterised in that any of the leuco dyes has an index of refraction that substantially matches an index of refraction of the carrier.
4. A method according to claim 3, wherein the image-capable layer is substantially transparent.
5. A method according to any preceding Claim, characterised in that the leuco dye/infrared-absorbing dye pair is substantially transparent until the pair is irradiated with a sufficient quantity of infrared radiation at a predetermined infrared wavelength.
6. A method according to any of the above Claims, characterised in that the carrier holds the particles in suspension and has an index of refraction that substantially matches that of the particles.
7. A method according to any of the above Claims, characterised in that the image-capable layer is formed of at least one of a laminate, a coating, and an adhesive.
8. A method according to any of the above Claims, characterised in that the infrared radiation comprises wavelength of at least one of: about 810 nm, about 850 nm, and about 890 nm for cyan, yellow and magenta leuco dyes, respectively.
9. A method according to Claim 8, characterised in that each infrared dye can be addressed with an appropriate infrared radiation without activating any other dyes.
10. A method according to Claim 8 or claim 9, characterised in that infrared radiation of two or more wavelengths is applied to the image-capable layer at the same time.
11. A method according to any of Claims 8 to 10, characterised in that the respective wavelengths of the infrared radiation are applied in at least one of: separate locations, co-locations and the same spot of the image-capable layer.
12. A method according to any of the above Claims, characterised by further comprising:

    selecting at least a second leuco dye for a second color and a second infrared absorbing dye selected so that the second infrared-absorbing dye is transparent in the visible region and absorbs infrared radiation at respective maxima in the near infrared spectrum so that the second infrared dye can be addressed with a second appropriate infrared laser wavelength without activating the first infrared dye,

    pairing the second leuco dye with the second infrared-absorbing dye;

    providing the second leuco dye and infrared-absorbing dye in an image-capable layer on a core layer, and

    forming an image in the image-capable layer by means of applying infrared laser light at the second wavelength, characterized by the steps of:

    for the second leuco dye/infrared-absorbing dye pair, creating with the dye pair a second grindable matrix material, and grinding the second material to provide a quantity of particles, mixing together the particles from the first brittle material and the second brittle material in a carrier, forming from the resulting mixture an image-capable layer upon a core layer and subsequently forming a laser-engraved image in the image-capable layer by means of laser light of the respective infrared wavelengths,

    characterised in that the first and second leuco dye undergoes a unimolecular rearrangement driven by heat generated from absorption of infrared radiation by the first and second infrared-absorbing dye, respectively.