ENCODED SECURITY DEVICE AND METHOD OF FABRICATION THEREOF Introduction Holographic and diffractive devices are established as useful anti counterfeit and authentication devices and established in use in a wide range of applications.

For example in security printing holographic labels or rather more elegantly hot stamping foils, stripes are applied to a range of papers as used in security documents such as passports, tax stamps and banknotes. Of course this securitization process involves both the additional cost of the diffractive element and the additional cost of the application process.

There is also a class of diffractive security devices integrated within the paper making process itself such as into the thread or window thread within a security or banknote paper where a thread carrying a holographic or diffractive image is inserted within the paper at the paper making stage.

Whilst the thread making process is good for relatively high value papers such as banknotes there is still a need for a cost effective generalised method of incorporations diffractive or holographic security devices into papers at a cost level and efficiency capable of securitising a wider ranges of more cost sensitive security applications and potentially also capable of creating new distinctive visual diffractive paper security features.

Micro dot technology has been around for some time without diffractive features as a bespoke encoded verifiable particle e.g. Data dot who produce a 1 mm diameter laser or chemically engraved plastic disc containing an individual code.

Established applications for this technology include covert making of high value goods with secure individually encoded microdots to aid for example with automobile security.

Also know is the use of encoded holographic micro dots consisting of metal platelets which have occasionally been used to apply additional security elements to articles such as consumer goods, security papers and plastic cards consisting of a small encoded micro- particle carrying a holographic image visible under a microscope and typically some sort of static code. However, such items are slow and laborious to manufacture essentially by hand in a batch process and therefore prohibitively costly in mass market applications as well as having technological disadvantages.

One of these metal holographic microdot items consists of a thin metal disc, typically nickel, produced by an electroplating growth process from a holographic master plate which has been selectively masked with photo resist and etched to for and encode the finished dots typically with a pattern visible as a shaped hole in transmission. The same effect can be similarly obtained using a masking and chemical etching process to remove material from a thin nickel shim to encode it. These techniques produce thin (c 10-25um) typically nickel holographic micro particles, typically 0.1 mm to 0.7mm size and planar containing a holographic image on one side, a matt finish on the other side as detailed in W02005078530 with an aperture carrying the encoded information picked up from the masking process during electroplating where the micro-dot material is deposited the material to form the micro-particle by a galvanic process of electroplating, the deposition being selective in the areas not covered by the mask. This process typically uses a master holographic plate, covered by a thin patterned photoresist layer defining the areas left exposed where metal is to be deposited to form the micro- particle, patterned by exposed to an encoding mask and developed away to for an encoding aperture mask over the master plate. The micro-particles are then formed on the exposed areas of the aperture by deposition on metal on the none exposed areas using a galvanic plating process where the masked master plate is used as the cathode in a electro-plating process where metal ions being dissolved from the metal anode are deposited by an electroplating process. This process can be sued to builds up the micro-dots as required which are then removed typically by scraping. A disadvantage of the process is the high rate of wastage of masters by damage in the final removal process..

The advantage of the small scale manufacturing process involved is that individual batches made off individual plates and masks can carry individual batch numbers, the disadvantage is that the dot manufacture is slow and expensive and so these micro dots tend to be used for high end individual tagging applications but have limited application in other potential areas of application such as to security documents.

An alternative manufacturing process for small scale manufacture of similar metal diffractive microdots is details in WO 2009/049562 which forms a holographic shim but electroplating which is the encoded with a resist mask to form an aperture set defining the code, in this case defining the material to be removed as opposed to the previous system where the mask defines the material to be deposited. In this alternative method the technique uses a chemical etching process to remove metal from the exposed areas of the shim using a process of etching as known the field where an acid attacks and corrodes away the exposed material areas through a patterned photo-resist selective mask to remove material from holographic shim (typically nickel) by an acid etching attack process to dissolve the metal selective to encode variable information into the microdots. This process known as etching uses acids, bases or other chemicals to dissolve away the unwanted metallic material in the shim - it is also used for example in the semi-conductor industry to form patterned metal areas by removing metal in areas left exposed by masking process. This alternative process for metal diffractive micro-particles also has a number of drawbacks such as line definition, volume of output, etc.

It is also know to produce complex holographic or diffractive security originations using electron beam lithography, high resolution optical lithography or classical holography. It is also know to reproduce such diffractive structures by thermal embossing or UV casting embossing.

Description

In one aspect of the invention there is provided a method of forming an encoded security device comprising: providing a template having a surface relief arranged to generate an optically variable image in a surface of a metallic layer formed thereover, the image being optically variable as a function of illumination angle or viewing angle; forming a layer of metallic material over the template whereby the layer has said optically variable image generated therein; forming a mask layer over the metallic material, the mask layer being arranged to expose first and second portions of the metallic layer, the first portion defining a boundary of each device, the second portion defining one or more indicia to be formed in the device; and removing the first and second portions of the metallic layer exposed by the mask layer. The one or more indicia may be indicia representing an identification code such as a batch code.

The mask layer may be a layer of patterned photoresist. - General ....

This invention refers to a new class of holographic or diffractive or interference film encoded diffractive micro-particles in this application principally metal micro-particle, whilst the case of plastic micro-particles is detailed in a co-pending application, designed as a high security covert authentication articles for application to a wide range of security items and substrates various methods.

In general these new holographic metal micro-particles are distinguished by carrying a diffractive image authenticable under microscopic assisted magnification ( e.g. x 60, x 100) carrying both defined optical diffractive effects such as images switches, movement effect and colour shifts plus even smaller microscopic features such as micro print ( few micron size text) or nano-print ( few tenths of micron text ). They are also distinguished by carrying a surface relief profile film where the

metallic reflective layer to provide reflectance to visualise the diffractive replay. The micro-particle will also incorporated encoded batch information generally added during a separate process from the holographic processes either as a surface indentation or as a a shaped aperture through the bulk of the metal forming the batch encoding. The dot can also incorporate various other functional and additional diffractive structures and layers. The advantages from these new methods and structures detailed herein include ...

In one subsidiary aspect we provide for a metal holographic microdot structure that gives holographic micro-taggant with a diffractive image viewable from both planar sides. The use of higher temperature refractory metals such as chromium, nickel etc gives increased chemical , temperature and environmental resistance by protecting surface relief and metal reflectors.

In one subsidiary aspect we detail Incorporation of one or more heat seal coating to activate and bind holographic micro-particle permanently into structure of substrate - particularly in security paper or ID card applications where the heatseal activates and seals particle into paper structure.

The potential for patterning effects during application makes room for both a covert microscopic feature combined with a bulk application to provide an unusual new visual security feature.

It is also possible using this new metal diffractive micro-dot system to integrate covert optical effects such as infra red up converters and UV features.

Advantages / applications...

The new class of holographic micro particles have several features that are novel to allow technical improvements over previous products and unit production cost improvements to enable the application of metal encoded holographic micro-taggant on a large cost effective scale to a wide range of security items.

For example the use of reel to reel processing and the application of lamination techniques and vacuum metallization in some parts of the processing and adhesion promoting coatings allows a high volume lower unit cost product to be made than using previous techniques with much better bonding to the typically paper substrate and better lifetime allowing 2 potential applications amongst others ...

One advantage of one aspect of this invention is that both sides of the dot replay an diffractive image which in one embodiment can be made identical from both directions providing a much more easily authenticated feature than previous systems.

Another advantage of this invention is that the potential use of a heat activated adhesive coated onto the dots ensure that when the paper is heated to be dried drying the paper making process the heat seal adhesive is activated and the dots bond very firmly and integrally into the paper fibre structure to give the document a long lifetime and stable printing performance.

- Features ... diffractive, interference ...

The new class of holographic micro particles have several features that are novel to allow technical improvements over previous products and unit cost reductions to enable the application of holographic micro-taggants on a large cost effective industrial scale to a wide range of security documents using methods such as spray or coating application directly into the papermaking process.

The new holographic micro particles in the reel to reel aspects of the production use typically a polymer, plastic, typically PET substrate, but other plastics or UV cured surface relief emboss structures can be used, with a holographic or diffractive image embossed into them to provide

diffractive effects and verifiable image effects ( e.g. image switch , colour shift ,etc) under microscopic examination. Advantageous materials would be for example PET film (polyethylene terphane film) direct embossed under high temperature and pressure to provide a heat stable image or more standard embossed lamination films with high temperature resistant lacquers or back coated with such as detailed below.

I Micro-optical effects using structures of a scale size of a few microns are also feasible.

Advantageous holographic microdots can contain diffractive authentication effects, static encodings and covert remotely detectable taggants within the same micro-particles to give a multiple security optical effect consisting of both diffractive and covert detectable effects. The metal surface relief microstructure on the new holographic dots provides a reflective surface to visual the diffractive images using for example aluminium or more usually durable metals if chemical resistance is required such as for example chromium, nickel or other metals to provide a greater chemical resistance.

The micro dots can also carry stationary information within the structure incorporated into the diffractive holographic layer by origination, selective metallization or selective demetallisation in patterns ( e.g. by chemical etching from / through a mask for example ) or by laser ablation depending on the application requirement. For large or intermediate run lengths the originations themselves can be encoded or the encoding date etched into each copy shim via a mask before embossing. We also envisage using alternative metals for example for different colour effects and additional chemical resistance for example chromium and copper.

In one technical spect These metal diffractive micro-dots unlike the earlier metal electroplated dots of earlier will replay a holographic / diffractive image from both viewing directions with the image from one viewing direction will be mirror reversed. - Bi-directional reading holographic micro dots and enhanced chemical and heat resistance ...

An aspect of this invention that improves over previous work is to create holographic microdots that visualise exactly the same holographic image when viewed from either planar side. This can be achieved by taking two embossed and metallised holographic laminate sheets, metallising both to form holographic images and then using a laminating adhesive to laminate both sheets together to form one sheet whose metallic layers them form the basic structure for the metal microdots. This laminated sheet would typical;ly be a release film to transfer off the thin metallised image then be mechanically or laser cut to form the new Bi-directional holographic microdots designed to visualise a right reading security image whichever planar face the dot drop onto when applied to the substrate to be secured such as a security paper or foil or article. This is an advantage over all other systems and means for example that all the metal diffractive micro-dots on a paper or article can be used for authentication as opposed to 50% if metal dost were used as previously, giving an efficiency increase of 100% over previous systems.

So these bidirectional laminated holographic micro-dots produce diffractive images when viewed from both directions and which guarantee that on every dot viewed each image is correctly orientated so is independent of which planar side is up when the dot positions itself within the paper web.

In this aspect fo the invention the laminating adhesive can preferably be chosen to be of a cross- linking chemically resistant form ( e.g. a 2 pack catalysed system) that will withstand heat attack (steam) and common aqueous based chemicals - this will protect the aluminium of the holographic film from attack and will have a melting point far above that of the holographic emboss lacquer acting as a support. This system will provide additional chemical , water and heat resistance to protect the

micro dot against the chemicals in the both the paper making process and paper wetting or chemical attack during usage to ensure a good lifetime for the micro dot and one or both of the laminates would be chosen to be releaseable films.

The use of refractory metals of high melt point ios useful to increase potential for chemical and heat resistance is also useful for micro dot applications in other more rugged environments such as car body authentication where the exposure to heat and temperatures can be far more extreme than with security papers or foils or plastic cards.

- Enhanced adhesion to substrates - Holographic plastic micro dots with heat seal coating applied ideally each side to obtain enhanced heat seal adhesion to paper - the microdots are coated with heat seal adhesive both sides to be activated during paper drying to irreversibly bond micro dots into paper fibre ...

Another particularly useful aspect of this invention which overcomes limitations of previous work is the use of a heat seal coating on one and preferably both sides of the holographic micro dot to ensure a good bond to the paper fibres as the heat-seal adhesives melts during the paper drying process and bond to the paper fibres to lock the micro taggant firmly into the body of paper after the micro dot has been sprayed or otherwise applied into the paper. This aspect applies to both single laminate dots and bi-directional readable dual laminate dots.

In this new system the holographic micro dot has on one or ideally both planar faces of the disc shaped holographic micro particle a coating of heat seal adhesive which is used to anchor the micro dot firmly and permanently into the application substrate structure, for example, during manufacture to provide a much more durable system than previously. So for example a useful thickness of adhesive is a few microns typically 3-20 urn ( or 4-20 gsm coat weight typically, optimally 7 - 10 gsm) of a heat activated adhesive chosen to be dry and stable during processing and storage but chosen to have an activation temperature a little above the steam point of 100 degrees Celsius so that at the drying temperatures employed on a paper line where steam can sometimes be superheated or the paper is taken just above the steam point to dry it so that the adhesive softens and melts to flow into the paper fibres and then hardens to bind the micro dot very firmly into the body of the paper.

Hence that the micro dot becomes integral with the application substrate anchored by the activated and set heat seal adhesive, as a bonded in part of the paper fibre structure - as opposed to a uncoated un-bonded dot simply held in between paper fibres as previously the case with metal dots. This hot melt mechanism is novel over other systems and enables the new micro dots to become essentially an integral part of the paper structure that cannot be removed without destruction of the paper itself which marks a significant advancement over previous non bonded structures.

In this new holographic metal micro dot systems the pre-forms for the metal dots and in some cases the metal diffractive dots are manufactured and coated on a reel to reel process in rolls using embossing, metallising and coating machinery. The holographic or diffractive security surface relief is embossed into a film or coated film from an embossing shim made from a master origination. This embossed surface relief is then metallised typically with aluminium or another suitable refractory metal such as copper or nickel, other alternatives are possible. To incorporate the heat seal coating the reel of holographic laminate is the passed through a coating system, typically gravure, meier bar, reverse gravure or dip coating to apply a heat-seal coating to one side of the laminate. This can optionally and advantageously be repeated to coat both sides of the holographic laminate with a heat- seal coating. The use of reel to reel processing gives the ability to up scale processes easily to meet high volume applications and to produce large volumes of diffractive security micro dots significantly more efficiently and economically than by previous techniques.

- Addition of material based optical and magnetic taggants as secondary security features ....

The heat-seals or other coatings or lamination adhesive materials can carry additional optical taggants suitable for visual authentication under assisted specialist lighting such as UV sources ( e.g. red, green UV responses ) and Infra red sources ( e.g. green or red infra up converting phosphors to add secondary authentication features. Magnetically active coating can also be applied in these coatings to allow magnetic detection of the micro-particles magnetically.

- Physical sizes and shapes and forming techniques...

These can vary depending upon the application and cutting technique. A typical new metallic holographic microdot would be planar in shape i.e. wider than its thickness and a typical usual size range would fall in the range 0.1 mm ( 100 micron planar) to 0.90 mm ( 750 micron planar for a typical application. The planar thickness of there items would be between say 10um and 10Oum, typically 12-50um. For a few other application the dots can have a wider range of sizes as detailed below. The dot will be shaped - this can be an arbitrary shape but can preferentially be hexagonal, square, rectangular or circular for production convenience. This can also be customised to any graphical shape desired. The microdot would contain a microscopic diffractive image viewable under magnification for authentication with an array typically of laser verifiable optical features as known in the field and micron level features for covert authentication. For a few other applications the dots can have a wider range of sizes as detailed below.

We envisage occasional theses articles being used at other sizes .... Very small sized micro-particles down to 0.035 mm ( 35 micron discs typically 8um -40um thick ) may be used for particular applications where sizing is important with the diffractive image features scales in size to suit e.g. in fluids where it is required to pass through small apertures or to remain in suspension for example when being used in printing inks for gravure or flexographic application, or as undetectable features mixed into items.

We also envisage occasional much large micro-particles say up to 1 .5 mm in the largest planar dimension fore example when the micro particle are being patterned to give a public recognition security feature and need to be visible. For a typical security application the size can vary between 0.1 mm and 0.9 mm typically, with a centre point of utility at about 0.3-0.7 mm for most applications. The size depends essentially on how covert the application is required to be or whether a larger dot is required to make a more obviously visible and viewable public recognition feature.

It is envisaged that in the unusual case of a feature designed to be visually authenticated by the public that the dot size may go up to 1 .5 mm depending on the quality of paper adhesion required and application process and level of public recognition and viewablity as required as this would give a near visible holographic feature but manufactured during paper making.

It is envisaged that in standard applications where the diffractive feature is designed to be more covert and subtle and designed to be a diffractive feature authenticated by use of a simple optical microscope or magnifier the size is smaller - this is the more typical situation, typically around 0.25 to 0.5 mm to act as a covert holographic dot with a typical size of 0.35 -0.4 mm and a maximum size of 0.7mm.

Production methods ...

Production methods - It is envisaged that in most techniwues a portion of the dot manufacture will be produced reel to reel by reel to reel holographic embossing , metallization and coating for lamination and for heat-seal coatings. This is to improve productivity over previous methods.

The master diffractive images will be produced by holographic or diffractive origination as known in the art - e-beam lithography, optical lithography or laser interferometry. The will be recombined to master plates and copied using known techniques.

The material will be embossed reel to reels known in the art to provide volume manufacture. The material will be metallised as known in the art - usually with aluminium but possibly with other less usual metals such as chromium to impact greater chemical resistance and to provide a property for chemical removal and electrical conductivity.

This efficiently forms base reel material suitable as an import for encoded metallic diffractive microdot formation.

Encoding of the stationary batch code can be done in several possible methods depending on the batch volumes needed - for large batches within the origination , for smaller batches by etching the embossing shim with the code and then embossing ( using a resist mask and chemical etch method for example) . For very small batches the encoding can be done on sheets of finshed meatl holographic material by photo-resist masking, exposing to a film mask, developing and then chemical or galvanically removing away the non masked areas. These encoding methods for small batches are detailed elsewhere within this patent. The finished small holographic micro-particles may be formed from the reel material in a number of ways. One method for volume is to form the microdots on a reel to reel cutting process using multiple phased mechanical cutter converting reels to micro-particles to provide a variation in shapes including octagons and hexagons, rectangles and squares to cover various applications and additional methods of personalising the dots. For small batches the dot formation may be incorporated within the encoding masks and removal processes to directly form the dots - this is the most efficient way to create registered metallic diffractive dots carrying a registered aperture encoded pattern.

It is envisaged also that laser cutting ( e.g. using a carbon dioxide or Nd:Yag laser ) can be used as an alternative which could for example provide personalised shaped dots with apertures cut into them and to provide additional personalisation for small volume applications.

- Stationary encoding....

The main authenticable security in the micro dot will be the diffractive image with it typical diffractive security features of image switches, colour changes, rotation and apparent motion effects etc.

Generally for volume reel to reel manufacture the micro dots can also carry stationary information which can be incorporated in the holographic origination or for a more flexible approach etched into an individual embossing shim used for a reel to provide a smaller batch capability.

Another approach suitable for reel to reel manufacture is to use selective metallisation or demetallisation to encode further information into the dots by leaving shaped metallic coating or by use of laser ablation to remove part of the metal surface. An approach suitable for very low volumes of personalised numbers is to sheet off the reels material and then encoded for small volumes in a sheet or short elongated web from - for example by coating with a resist material, exposing to a mask, developing to remove areas of the resist where the encoding is required and then by chemically etching away the metal ( in this case a simple alkali etch

will suffice if the metallization is aluminium ). If additional heat seal coatings are required these could then be added as a bench processing procedure before cutting typically by running a short reel into a mechanical cutter to provide a set of diffractive encoded microdots. An another alterative to this is to use a laser marking machine (typically Nd:Yag) to mark the material before mechanically cutting.

- Diffractive microdot characteristics that this patent anticipates ....

- Thickness 8, 12,16, 20, 35, 40 ,50 micron and planar size typical 0.2 to 0.8 mm typically range, typical would be 15 or 35-40um thickness ( for single laminate / bi - laminate ) and 0.4 mm size hexagonal for example. Outer range 35 urn to 1000 urn ( 35 microns to 100 microns).

- Two side holographic repaly holographic metal microdot to ensure all dots replay a diffractive image the correct orientation image whatever orientation.

- If metallic pattern has been demetallised or etched then useful to use a coloured, black or tagged laminating adhesive to increase contrast on demetallised markings. - Reflective layer typically aluminium but can be more durable metals for high durability metallic metal diffractive micro-dots such as chromium, nickel copper or similar.

- Heat seal binder layer on surface of dots or a lamination layer can have taggants added to the binder coating as an optional low costs additional feature, e.g. UV fluorescence, IR up converter which are typically anti-stokes phosphors that absorb IR laser wavelength , say 980nm , and emit at visible green or red. Potentially both dot surfaces could be coated in different colour up converters to add more security effect.

- It is also possible with a bi-laminate to provide different optical effects ion each surface - so for example a holographic or diffractive image on one surface to provide say a magnified image switch and a different holographic or diffractive image ( based on a metal layer, an accurate spacer and a semi-reflector) on the other surface to provide a security feature displaying two optically variable technologies, diffractive and interference in one item or security feature for increase security against counterfeit.

Novel patterning possibilities for areas of holographic micro particles on subsrates and on foils

There are a number of potentially interesting effects that can be generated particular at the point of securitisation of a substrate by applying the dots on the substrate in distinct ways.

Generally the dots will be dry sprayed or shaken onto the substrate, for example as the paper is formed, and before or just at the start of the drying processes which can be done on hot rollers or by hot air.

The costs can also be roller coated (e.g. gravure, silk screen rotary printing / coating ) onto the surface as a flood coating in a carrier liquid or deposited locally as a localised pattern. Small micro- sots sizes of around less than 100um are advantageous for printing to ensure the particles pass onto the surface. Another alternative method to spraying in an air stream to apply the dots is to use a simpler mechanical mechanisms.

Application through say a silk screen press ( eg rotary screen) or a gravure roller can also be used with a carrier binding liquid to form an ink as printing is a useful method for localised patterning, for example.

In a typical application the dots are randomly and uniformly distributed across the substrate film (possibly from a number of spray heads) to typically act as a uniformly distributed covert feature.

However, there are application where the covert feature is desired to be generally localised , and applications hat are now where it may be an advantage to create a new subtle visual security feature out of the shaped localisation of the dot cluster in some simple graphical shape.

So there is opened up the possibility of increasing the dot density and investigating patterning of the dots to form novel unique visual optically variable security features.

So we claim a new optical security feature made of shaped areas of holographic microdot deposition, namely we claim a methods of patterning dot deposition using a method of dot spraying or similar random projection of dots towards the wet paper web, particularly allied to a masking assembly of apertures, moving apertures an shaped apertures linked in with the regular uniform movement in one direction of the paper web to provide unusual and unique graphics and effects for higher densities of dot deposition as being a novel new security feature. In particular the distance of the aperture from both the spray head and the paper controls the rate of reduction of density at the edge of the graphic which can be a sharp definition if the mask is nears the paper and can be a very blurred gradual fall off if the mask is far away. These patterning possibilities can also be further modulated by switching the dot flow on and off ( e.g. by air pressure variations in the spray nozzle or by a blocking aperture).

Another simple method to achieve this can be done entirely by spray head modulation linked into the paper web movement - foe example by modulating the air flow and this modulating both the density of dot output and spread of the stream of dots (which will be wider and higher pressure) - this can also be combined with complete cessations or a pulsing or modulation of the air pressure in a cyclic way to produce a subtle repetitive pattern effect.

This method therefore give a very flexible and simple method to combine a modulated width and density of dot spray with the linear movement of the paper web (this can be linked in via a speed sensor) to generate quite simply very characteristic graphical effects of a subtle nature consisting of random array of holographic effect dots in various indistinct and gradually changing shapes. This can created is a fairly large scale security feature consisting of a large scale pattern of dot application characterised by both a random distraction of the micro dots within it and a suitably diffuse border to make counterfeit difficult and to make the shape of the pattern very characteristic which makes it suitable for a new optical security feature.

It can be appreciated that a similar approach can be taken on applying the dots to security items such as plastic bases for ID cards and in for example PE film used for over-lamination.

This patterning effect therefore forms the basis of a possibility of using these holographic micro dots not just as an entirely covert feature but in a larger format and at greater densities using the micro dots applied in areas with a very specific and characteristic graphic effect to form a new class of optically variable security feature.

Description - novel metallic diffractive encoded micro-particles

This extensions of this invention refers to a new of holographic or diffractive or interference film or micro optic metal encoded micro-particles designed as a high security covert authentication method designed to applied to a wide range applications by various methods of application. The manufacturing technology is substantially different in comparison to other metal holographic microdot methodology giving higher volume scalability, lower production costs and greater accuracy of encoded graphics.

In general the dots are distinguished by carrying a diffractive image authenticable under microscopic assisted magnification (e.g. x60 x100) carrying both defined optical diffractive effects such as images switches, movement effect and colour shifts plus even smaller microscopic features such as micro print (few micron size text) or nano print (few tenths of micron text).

These new metal dots also contain unique or small batch encoded variable information such as text or numerals or bar codes to distinguish small individual batches. The variable identification data can be incorporated as apertures entirely through the holographic micro dot or as controlled depth indentations or a mix of both. These patterns can be made machine readable e.g. by using bar codes or more typically will be used for visual authentication under enlargement aided by a microscope.

It is also possible using this metallic diffractive micro-dot system to integrate micro-optic effects within the same micro dots and / or covert optical effects such as infra red up converters and UV features. There are several key aspects recognised in this new development on metallic diffractive micro- particle manufacture which lead improvements over previous metallic diffractive micro-particles devices and production methods to several new methods of manufacture and new metallic encoded holographic micro-particle devices ..

This patent recognises that an improvement over previous wok is to use as the basic source of the holographic or diffractive surface relief pattern an embossed plastic sheet containing an embossed surface relief made by thermal embossing or UV casting. This basic layer acts as the source of all subsequent holographic patterns in the process (In contrast to earlier systems that used thick nickel metal shims that are slow and expensive to manufacture). This plastic micro-structured surface can be made as a reel for larger volume production in reel to reel embossing or as an individual plastic sheet, say by flat bed embossing or UV casting.

A thin conductive metal layer (typically a few nanometers thick although this can vary) can be added to the surface of the plastic relief profile using again low cost high volume processes, envisaged are reel to reel vacuum metallising using say silver. An alternative process would be two component silver reduction using a silver spray process on a sheet by sheet batch process. It is then envisaged other metals could be used for this such as electroless deposition of chromium say. This is only designed as a thin conductive layer which will not form part of the final metal micro dot but will be patterned and then used to grow as a copy for the final metal micro dots.

This is then used as the source for later processes to deposit or form the diffractive micro-dots.

The thin conductor (typically silver) overlaying the plastic surface relief profile is then patterned to incorporate the individual formation for each batch - it is important to note that this conductor is not forming the final microdot but simply an accurate plating target upon which the final dot - which will consist of a much more durable metal, is formed. The patterning is done by coating the silver layer with a thin resist, exposing to a pattern mask and removing the undeveloped ressit to leave apertures and then using a chemical etchant (typically an acid attack) to leave shapes thin silver target particles in the form of the desired final dots, The unexposed photo-resist can be removed and then the target master ( in this case consisting solely of shaped encode this metal structures overlay on a surface

relief carrier to form the diffractive structure can be used as a target in a conventional electroplating process to deposits further layers of metal to form the actual microdots in a more durable metal say nickel).

It is also recognised that in some smaller volume applications it may still be more convenient to use and reuse passivated traditional metal electroplated master plates ( rather than emboss plastic master plates) and the use of this is anticipated as an alternative within the scope of the invention.

In another embodiment The thin conductor (typically silver) overlaying the plastic surface relief profile is used a electro-plating target to form a fully continuous diffractive shim directly in a durable metal of a typical thickness 2 to 10 urn (widest range 1 to 30 micron. This shim consisting typically of a plastic carrier layer as a surface relief former and a thicker durable metal layer (e.g. nickel, chromium) can the be patterned to create using a 'reverse galvanic process of patterning' as detailed below,

In another embodiment the use of reel to reel vacuum metallization processes (e.g. traditional resistance boat metallising and sputter coating or electron beam source metallising to provide some examples ) to deposit immediately in one process all of high temperature metals ( e.g. nickel, chromium etc) directly the plastic embossed surface relief former to relatively thick layer coating ( say 3 to 5 urn typically but not restrictively) which can then be acted upon directly to be encoded to form the holographic micro-particles so eliminating one production step.

A important feature of this new work is to recognise that a process of 'reversed galvanics' or 'reverse electroplating' offers a new and effective way to selectively encode and form holographic micro- particles. In traditional electroplating metal is deposited on the metal plating target when a metal plate is used as the cathode in an electro-plating process where metal ions are being dissolved from the metal reservoir anode are deposited by an electroplating process on the cathode to build up metal here.

In this new none traditional 'reverse electroplating' method of encoding we are disclosing here the anode and cathode connections on the electroplating bath are reversed in polarity such that the target holographic plate now becomes the sacrificial anode of the system from which metal ions are removed and the normal plating anode becomes the cathode to which metal is deposited. So in this 'reverse electroplating' process metal is now removed form the target holographic plate which is being used as the anode and is deposited at the cathode. It is important to realise this is not a conventional chemical etching methods but a controlled electrochemical galvanic method of metal removal. This process can be usefully be used for encoding the metal diffractive microdots by electrochemical metal removal in the following way ...

- A holographic / diffractive metal shim is formed in the desired metal - typically a high temperature resistant metal such as nickel, chromium or the like. Less resistant metals such as copper and aluminium may also be used. This can be formed as a traditionally copy of a holographic master plate as known in the art or in the various ways we detail above. One method is to use an plastic embossed former coated with a thin conductive layer as a traditional electroplating system target where nickel or the like is deposited on the electroplating target to form the thickness of metal required for the finished micro-dot - typically 3 to 15 microns. This enables to enable high volume manufacture and allow the master forming plates to be discarded at the end of the process whilst at the same time acting as carriers of the encoded shaped microdot through the process before final removal. An alternative method of making the nickel or high temperature diffractive shim material this process is direct vacuum metallising using a suitable source for high temperature metals to deposit a thick layer of nickel , copper or the like directly on the embossed plastic former. - The diffractive shim is encoded using a photo-resist mask to hold the encoding data as follows ... the shim is coated with a thin layer of photo-resist material (e.g. by spin or roller coating to lamination to a resist film) which if necessary is then baked as required. An encoding film-work mask is

produced carrying the shape of the holographic microdots and the individual aperture encodings to be formed. The encoded mask is contact copied to the resist layer on the shim by exposure to UV or similar light (depending on the resist) and the exposed / unexposed material ( depending on whether positive or negative photo-resist used developed away. This leave a holographic metal shim coated with a thin photo-resist layer with open apertures revealing the underlying metal defining the coding and the edges of the micro-particles i,e. defining the areas of metal to be removed.

-To form the encoded holographic micro-particles the new process of 'reversed αalvanics' or 'reverse electroplating' is used.

The holographic shim with the encoding mask on it is placed in an electroplating tank but with the anode and cathode connections reverse so that in this case the masked holographic shim becomes the sacrificial anode from which metal material is removed and deposited at the cathode when a current is passed through the electroplating apparatus. In this new none traditional 'reverse electroplating' method of encoding we are disclosing here the anode and cathode connections on the electroplating bath are reversed in polarity such that the target holographic plate now becomes the sacrificial anode of the system from which metal ions are removed and the normal plating anode becomes the cathode to which metal is deposited. So in this 'reverse electroplating' process metal is now removed form the target holographic plate electrolytically which is being used as the anode and is deposited at the cathode in the electrochemical galvanic process.

The metal removal only happens on the anode side where the metal is exposed by the apertures in the resist mask and so the encoded pattern in the resist mask is transferred to areas of metal removal from the holographic shim. This then transfers by metal removal the cutting out of the shape of the individual microdots and also the aperture batch encoding as either indentations ( partial cut through) or full cut through for full apertures. It is important to realise this is neither a conventional chemical etching method which uses a simple acid attack to remove metal a but a controlled electrochemical galvanic method of metal removal by reversing the traditional electroplating process to remove metal.

After the reverse electroplating the finished dots can easily be removed from the underlying plastic holographic shim by plating or dissolution using solvents. It can be advantageous to form the underlying plastic holographic shim layer as a holographic transfer film (e.g. by using an embossed holographic stamping foil as a holographic shim base) which would simply allow release of the finished holographic micro-particles from the base film leaving a thin small layer of foil base attached to be removed with a solvent wash if needed.

This process provides a high number aperture fidelity and high accuracy on encoding graphics by removing material from the flat side of the shim so that the highest definition on the aperture appears from the front of the shim ( the holographic side). The process also is self stopping to allow for accurate and high fidelity shapes as the process automatically self stops when a full and complete individual dot shape and aperture has been 'reverse electrolytically' or 'reverse electroplated' removed as the formation of a full micro-dot automatically break the electrically conductivity to quench the process when the metal depth had been etched away, whilst any mis-shapen microdot ( for example with a defect in the outer shape) would keep having material removed and would thus be automatically removed. .

This stop point can also be adjusted with small artwork changes to the outer shape of the microdot. This is a very useful property which means that it is automatic and simple to ensure a good quality of material removal and good quality of aperture definition as the process stopping point is automatically set by the self limiting nature of the process. In the case of plastic holographic master sheets where the aluminium or nickel ( or fore example) some other high temperature metal) has been applied using vacuum metallization then the

holographic micro-dots will present a holographic replay from both planar side, although one image will be mirror reversed. Previously systems only present a one sided viewable diffractive image.

- Method of production 1 - formation of precision individual encoded masters and precise copying

The new class of holographic micro particles have several features that are novel to allow technical improvements over previous products and unit cost reductions to enable the range of holographic micro-taggants on a larger cost effective industrial scale to a wide range of security applications.

The method of production envisaged is as follows...

The basic source of the holographic or diffractive surface relief pattern is an embossed plastic sheet containing an embossed surface relief made by thermal embossing or UV casting. This basic layer acts as the source of all subsequent holographic patterns in the process (In contrast to earlier systems that used thick nickel metal shims that are slow and expensive to manufacture). This plastic micro-structured surface can be made as a reel for larger volume production in reel to reel embossing or as an individual plastic sheet, say by flat bed embossing or UV casting.

A thin conductive metal layer (typically a few nanometers thick although this can vary) is added to the surface of the plastic relief profile using again low cost high volume processes, envisaged are reel to reel vacuum metallising using say silver. An alternative process would be 2 component silver reduction using a silver spray process. It is then envisaged other metals could be used for this. This is only designed as a thin conductive layer which will not form part of the final metal micro dot but will be patterned and then used to grow as a copy for the final metal micro dots.

The thin conductor overlaying the plastic surface relief profile is then patterned to incorporate the individual formation for each batch - it is important to note that this conductor is not forming the final microdot but simply an accurate plating target upon which the final dot - which will consist of a much more durable metal, is formed.

The patterning can be performed as follows... Coat the surface of the conductor with a thin layer of photoresist by spinning, dipping, roll or Meier bar coating as known in the art and thermally cure this layer if needed. A thin resist layer can also be laminated onto the plastic holographic master as known in the field. A typical and preferred layer thickness would be 2 to 7 microns to maintain graphic resolution accuracy.

Light expose (typically UV) the photoresist through a high resolution film work containing the graphic for the shapes and individual data for the microdots. Then remove unexposed resist with developer leaving a selective patterning over the plastic holographic surface and the thin metallic conductor.

Chemically etch (or similar) or remove the silver or thin conductor in the areas of the holographic plastic layer not covered by photoresist. An alternative method that can be used would be to run a "reverse plating process" wherein the silver or other thin conductor is removed by the plating process by reversing the polarity of the plating bath so that material is removed from the plating target by a reversed galvanic process. As the silver (or other) conductor is a very thin layer then a very high resolution thin metal conductive pattern in the shape of the desired holographic microdots and with

the desired encoding will be left on the holographic surface together with the masking photoresist material.

Remove the residual mask material by flood exposing the remaining photoresist mask with (generally) UV light and then removing this with resist developer. At the end of this stage we have a plastic holographic surface relief pattern forming the profile of the diffractive structure with a detailed pattern carrying the exact information and pattern of the microdots to be made incorporated into a thin patterned conductive layer (usually silver) with no other masking material present. This plastic master is then key to growing galvanically or by chemical processes exact metal replicas of the microdots patterns in the desired durable metal. It is important to note that etching or reversing plating away the thin silver conductor allows for a very accurate definition of microdot structure to be obtained which is also easy to check optically by microscope during the various development stages to get the artwork exactly correct. It is also very important that each microdot shape within the thin conductor layer retains a small conductor line to the greater conductive areas to allow conductive continuity for later replication by plating. The final stage is to grow the hard high temperature microdots galvanically effectively using any high temperature metal that can be electroplated using the shaped plated silver conductive areas as plating targets for growth. The types of high temperature metals envisaged are nickel, nickel alloys with harder material such as chromium, chromium itself and stainless steel. These materials would be chosen to have much higher resistance to temperature or chemical attack than the original materials to allow usage of the security microdots in more aggressive environments such as those requiring the particles to remain authenticable after fire. The plastic holographic plate would impart the desired holographic surface relief to the structure whilst the conductive patterned layer, containing the shape of the individual microdots and their individual coding will be retained within the patterned shape of the conductor layers which will be faithfully copied within the plating process as the nickel or other metal is galvanically or deposited onto this. It is envisaged that the hard metal layer will be grown to a thickness of preferably between 5 and 15 micron (outer limits 3 to 25 microns).

The final stage is removal of the formed high temperature and chemical resistant microdots from the plastic forming target. These would very typically be of nickel metal. A convenient way to do this is to use a solvent to dissolve the plastic former leaving the free microdots. The microdots can also be scraped off the target mechanically as they are not bound or encased in any other layers. The plastic master target being easy to make in reasonably high volume can be sacrificed at the end of the process with little cost if needed. The vestiges of the very thin silver layer may be removed with, for example, a dilute acid wash (e.g. nitric acid) which will attack and remove the silver far more quickly than the underlying nickel.

- Method of production 2 nickel shim production then masking and "reverse electroplating" to remove exposed non exposed non masked material to encode shim

An alternative production route 2 also has novel features based on reverse electro-plating to remove material as follows...

The method of production is envisaged as follows...

The basic source of the holographic or diffractive surface relief pattern is an embossed plastic sheet containing an embossed surface relief made by thermal embossing or UV casting. This basic plastic layer acts as the source of all subsequent holographic patterns in the process (in contrast to earlier systems that used thick nickel metal shims that are slow and expensive to manufacture). This plastic

micro-structured surface can be made as a reel for larger volume production in reel to reel embossing or as an individual plastic sheet, say by flat bed embossing or UV casting. Note that this technique will equally work with a conventional thick nickel master but the plastic master offers considerable advantages in terms of cost and efficiency. A thin conductive metal layer (typically a few nanometres thick although this can vary) is added to the surface of the plastic surface relief profile using again low cost high volume processes, envisaged are reel to reel vacuum metalizing using say silver. An alternative process would be 2 component silver reduction using a silver spray process. It is envisaged other metals could be used for this. This is only designed as a thin conductive layer which will not form part of the final metal micro dot but will be pattered and then used to grow as a copy the final metal microdots.

The thin conductor is used as a target in a galvanic platic process to deposit a layer of (typically) nickel on this silver material overlaying the plastic surface relief profile or form a holographic shim as known in the art (e.g. Saxby Practical Holography). The metal used may be one of a range of high temperature metals that can be electro-plated (e.g. chromium, stainless steel) to impart physical, temperature and chemical resistance to the final product. This forms a typically nickel shim as known in the art.

The key stage then is then in the next stages to incorporate the individual information for each batch within this nickel shim. In this case we rely on a process of reverse plating using a reverse galvanic process to remove material from the holographic shim where it is exposed in the plating solution and the electrodes (anode, cathode) are reversed.

The patterning to incorporate the individual data can be performed as follows...

Coat the surface of the shim (ideally the reverse surface but not necessarily) with a thin layer of photoresist by spinning, dipping, roll or Meier bar coating as known in the art and thermally cure this layer if needed. A thin resist layer can also be laminated onto the nickel as known in the field. A typical and preferred layer thickness would be 2 to 7 microns to maintain graphic resolution accuracy.

Light expose (typically UV) the photoresist through a high resolution film work containing the graphic for the shaper and individual data for the microdots. Then remove unexposed resist which in this case will define exposed areas around the microdots and where material needs to be removed for encoding using resist developer leaving a selective patterning over the plastic holographic surface and the nickel shim.

The masked shim is replaced in a plating bath (still attached to the original master or not - if not the reverse side will need protecting from the plating solution). The plating process is now reversed ("reversed plating") so that instead of depositing nickel on the exposed areas of the shim the plating bath removes nickel material galvanically to selectively remove material from the exposed areas of the nickel shim to form the individual information on the microdots and the microdot shapes as required. Chemically etch (or similar) or remove the silver or thin conductor in the areas of the holographic plastic layer not covered by photoresist.

The residual mask material can then be removed by flood exposing the remaining photoresist mask with (generally) UV light and then removing this with resist developer. The final stage is removal of the formed high temperature and chemical resistant microdots from the plastic forming target. These would very typically be of nickel metal. A convenient way to do this is to use a solvent to dissolve the plastic former leaving the free microdots. The microdots can also be scraped off the target mechanically as they are not bond or encased in any other layers. The plastic master target being easy to make in reasonably high volume can be sacrificed at the end of the process with little cost if needed. The vestiges of the very thin silver layer may be removed with for

example, a dilute acid wash (e.g. nitric acid) which will attack and remove the silver far more quickly than the underlying nickel.

- Method of production 3 - direct vacuum deposition of nickel or refectory metal in reel to reel process then subsequent masking and chemical etching or metal removal by "reverse electroplating" to remove exposed non masked material to encode nickel

An alternative production route 3 also has novel features based on reverse electro-plating to remove material as follows... The method of production envisaged is for a high volume capability as follows...

The basic source of the holographic or diffractive surface relief pattern is an embossed plastic sheet containing an embossed surface relief made by thermal embossing or UV casting. This basic plastic layer acts as the source of all subsequent holographic patterns in the process (in contrast to earlier systems that used thick nickel metal shims that are slow and expensive to manufacture). This plastic micro-structured surface can be made as a reel for larger volume production in reel to reel embossing or as an individual plastic sheet, say flat bed embossing or UV casting.

A conductive metal layer of a high temperature resistant metal suitable for the final application is vacuum deposited onto the embossed reel by a process of vacuum metallisation.

High temperature resistance metals are usually hard to evaporate in conventional resistance boat metallisers so in this case is it envisaged that the layer of heat resistant layer is relatively thin. In this case a further heat resistant lacquer would be coated upon the layer of nickel (or copper etc) to provide subsequent support and carry the embossed metal profile. In this case the embossed film moulding form could be suitably be of a release film type such as a stamping foil to allow easy transfer off the heat resistant layers. In other embodiments the web may be multiple metallised several times to provide a thick enough nickel (or other heat resistant metal) coating to be self supporting. In this case any microdot formed would be bi directional reading which would be a very useful property.

A more efficient way of depositing high temperature resistant materials is using sputter vacuum metallisation and it can be envisaged that multiple passes and or multiple spluttering heads would be enough to deposit a self supporting layer. In all cases these reel fed high temperature micro dots will have holographic information visible from both directions.

Once the high temperature metal has been deposited by vacuum deposition is can be individually encoded into dots in one of the various methods as detailed above.

The key stage then is then in the next stages to incorporate the individual information for each batch within this nickel or other high temperature resistant metal (e.g. copper, titanium etc) vacuum coated layer. In this case we rely on a process of reverse plating using a reverse galvanic process to remove material from the holographic nickel where it is exposed in the plating solution and the electrodes (anode, cathode) are reversed

The patterning to incorporate the individual data can be performed as follows... Coat the surface of the shim (ideally the reverse surface but not necessarily) with a thin layer of photo-resist by spinning , dipping, roll or Meier bar coating as known in the art and thermally cure this

layer if needed. A thin resist layer can also be laminated onto the nickel as known in the field. A typical and preferred layer thickness would be 2 to 7 microns to maintain graphic resolution accuracy.

Light expose (typically UV) the photo-resist through a high resolution film work containing the graphic for the shapes and individual data for the microdots. Then remove the unexposed resist which in this case will define exposed areas around the microdots and where material needs to be removed for encoding using resist developer leaving a selective patterning over the plastic holographic surface and the nickel shim.

The masked shim is replaced in a plating bath (still attached to the original master or not is the reverse side will need protecting from the plating solution). The plating process is now reversed ("reversed plating") so that instead of depositing nickel on the exposed areas of the shim the plating bath removes nickel material galvanically to selectively remove material from the exposed areas of the nickel shim to form the individual information on the microdots and the microdot shapes as required. Chemically etch (or similar) or remove the silver or thin conductor in the areas of the holographic plastic layer not covered by photo-resist. Please note that step 4 can equally be obtained by using a conventional chemical etching solution in this case onto the vacuum deposited high temperature resistant metal.

The residual mask material can then be removed by flood exposing the remaining photo-resist mask with (generally) UV light and then removing this with resist developer.

The final stage is removal of the formed high temperature and chemical resistant microdots from the plastic forming target or carrier reel section. A convenient way to do this is to use a solvent to dissolve the plastic former leaving the free microdots. The microdots can also be scraped off the target mechanically as they are not bound or encased in any other layers. The plastic master target being easy to make in reasonably high volume can be sacrificed at the end of the process with little cost if needed. In the case when the vacuum deposited nickel or other high temperature metal required a further support this would be added a high temperature lacquer coating in a reel to reel coating process prior to removal of the original carrier layer (possibly a release film or hot foil assembly). This high temperature lacquer bonded to the nickel layer would then form the carrier reel for the chemical etching or galvanic etching of the nickel. The dots could be separated into individuals by choice of an solvent based type etchant or final process that attacked the high temperature lacquer where not protected by the nickel layers to separate the dots - this may be particularly appropriate with the use of a two pack cross linking lacquer where some time is taken or an additional heating stage is required to form the final cross linked structure. Alternatively the material could simply be etched with individual batch numbers and then generically cut using mechanical cutting means. These vacuum deposited nickel layers will usefully give microdots with bidirectional reading diffractive images where a right reading and mirror reversed holographic images is visible from both sides of the microdot - all plating processes only provide a single sided reading dot. This is an advantage over all other metallic based systems and means for example that all the dots on a paper or article can be used for authentication as opposed to 50% previously giving an efficiency increase of 100% over previous metal systems.

- Addition of material based optical taggants as secondary security features...

The other coatings or lamination materials can carry additional optical taggants suitable for visual authentication under assisted specialist lighting such as UV sources (e.g. red, green UV responses)

and infra red sources (e.g. green or red infra) up converting phosphors to add secondary authentication features.

- Physical sizes and shapes...

These can vary depending upon the application and customer choice and can vary between 0.035mm ( 35 micron) and 1 .0 mm ( 1000 micorn) in size and many various shapes. Samml dosts may no necessarily carry an aperture encoding.

It is envisaged that in standard applications where the diffractive feature is designed to be more covert and subtle and designed to be a diffractive feature authenticated by use of a simple optical microscope or magnifier the size is smaller - this is the more typical situation, typically around 0.1 to 0.6 mm to act as a covert holographic dot with a typical size of 0.35 - 0.4 mm and a maximum size of 1 .0 mm.

- Stationary encoding... The main authenticable security in the micro dot will be the diffractive image with it typical diffractive security features of image switches, colour changes, rotation and apparent motion effects etc.

An approach suitable for very low volumes of personalised numbers is to sheet off the reels material and then encoded for small volumes in a sheet or short elongated web from - for example by coating with a resist material, exposing to a mask, developing to remove areas of the resist where the encoding is required and then by chemical etching away the metal for example (in this case a simple alkali etch will suffice if the metallization is aluminium).

If additional heat seal coatings are required these could then be added as a bench processing procedure before cutting typically by running a short reel into a mechanical cutter to provide a set of diffractive encoded microdots. An another alternative to this is to use a laser marking machine ( typically Nd:Yag ) to mark the material before mechanically cutting.

- Size of the micro dots for magnifier verification and to be kept at a covert level, typically small particles such as 0.35mm as a covert magnifier verifiable feature. Smallest in the would be c 0.05mm, largest say 1 .00mm

It is also possible to replace the holographic diffractive structures of scale size 1 urn with micro optical structures of scale size 10+ micron which rely on classical optics for image switches on rotation etc. This term should be viewed interchangeably with the term holographic or diffractive in the above description.

It is also envisaged that these metallic diffractive metal micro particle security device items can be used for article security mark for value items ( e.g. motor vehicles, copper cables ) which will containing diffractive metal micro particle security device according to any of the above examples. The metal diffractive have an advantage in this respect as the use of high temperature resistance metals such as copper and chromium can imparts fire resistance to the micro-particles enable authentication after fire.

Security Articles and further embodiments...

We reveal herein new devices and methods of manufacture as follows.

1. A security device consisting of a planer metal holographic encoded holographic platelet characterised in that the micro particle contains a holographic or diffractive image visible under magnification to an observer for verification of authenticity further characterised in that the micro dot holographic platelet contains an authenticable individual batch code where the micro particle consists of a high temperature resistant metal made by some or all of the processes of ...

Method of production 1 -formation of precision individual encoded masters and precise copying

The basic source of the holographic or diffractive surface relief pattern is an embossed plastic sheet containing an embossed surface relief made by thermal embossing or UV casting. This basic plastic layer acts as the source of all subsequent holographic pattern in the process (in contrast to earlier systems that used thick nickel metal shims that are slow and expensive to manufacture). This plastic micro - structured surface can be made as a reel for larger volume production in reel to reel embossing or as an individual plastic sheet, say by flat bed embossing or UV casting.

A thin conductive metal layer (typically a few nanometres thick although this can vary) is added to the surface of the plastic surface relief profile using again low cost high volume processes, envisaged are reel to reel vacuum metalizing using say silver. An alternative process would be 2 component silver reduction using a silver spray process. It is envisaged other metals could be used for this. This is only designed as a thin conductive layer which will not form part of the final metal micro dot but will be patterned and then used to grow as a copy the final metal microdots. The thin conductor overlaying the plastic surface relief profile is then patterned to incorporate the individual information for each batch - it is important to note that this conductor is not forming the final microdot but simply an accurate plating target upon which the final micro dot which will consist of a much more durable metal, is formed.

The patterning can be performed as follows...

Coat the surface of the conductor with a thin layer of photoresist by spinning, dipping roll or Meier bar coating as known in the art and thermally cure this layer if needed. A thin resist layer can also be laminated onto the plastic holographic master as known in the field. A typical and preferred layer thickness would be 2 to 7 microns to maintain graphic resolution accuracy. Light expose (typically UV) the photoresist through a high resolution film work containing the graphic for the shapes and individual data for the microdots. Then remove unexposed resist with developer leaving a selective patterning over the plastic holographic surface and the thin metallic conductor.

Chemically etch (or similar) or remove the silver or thin conductor in the areas of the holographic plastic layer not covered by photoresist. An alternative method that can be used would be to run a "reverse plating process" wherein the silver or other thin conductor is removed by plating process by reversing the polarity of the plating bath so that material is removed from the plating target by a reversed galvanic process. As the silver (or other) conductor is a very thin layer then a very high resolution thin metal conductive pattern in the shape of the desired holographic microdots and with the desired encoding will be left on the holographic surface together with the masking photoresist material.

Remove the residual mask material by flood exposing the remaining photoresist mask with (generally) UV light and then removing this with resist developer.

At the end of this stage we have a plastic holographic surface relief pattern forming the profile of the diffractive structure with a detailed pattern carrying the exact information and pattern of the microdots

to be made incorporated into a thin patterned conductive layer (usually silver) with no other masking material present. This plastic master is then key to growing galvanically or by chemical processes exact metal replicas of the microdots patterns in the desired durable metal. It is important to note that etching or reverse plating away the thin silver conductor allows for a very accurate definition of microdot structure to be obtained which is also easy to check optically by microscope during the various development stages to get the artwork exactly correct. It is also very important that each microdot shape within the conductor layer retains a small connector line to the greater conductive areas to allow conductive continuity for later replication by plating.

The final stage is to grow the hard high temperature microdots galvanically effectively using any high temperature metal that can be electroplated using the shaped silver conductive areas as plating targets for growth. The types of high temperature metals envisaged are nickel, nickel alloys with harder material such as chromium, chromium itself and stainless steel. These materials would be chosen to have a much higher resistance to temperature or chemical attack than the original materials to allow usage of the security microdots in more aggressive environments such as those requiring the particles to remain authenticable after fire. The plastic holographic plate would impart the desired holographic surface relief to the structure relief to the structure whilst the conductive patterned silver layer, containing the shape of the individual microdots and their individual microdots and their individual coding will be retained within the patterned shape of the conductor layers which will be faithfully copied within the plating process as the nickel or other metal galvanically or deposited onto this. It is envisaged that the hard metal layer will be grown to a thickness of preferably between 5 and 15 micron (outer limits 3 to 25 micron).

The final stage is removal of the formed high temperature and chemical resistant microdots from the plastic forming target. These would very typically be of nickel metal. A convenient way to do this is to use a solvent to dissolve the plastic former leaving the free microdots. The microdots can be scraped off the target mechanically as they are not bound or encased in any other layers. The plastic master target being easy to make in reasonably high volume can sacrificed at the end of the process with little cost if needed. The vestiges of the very thin silver layer may be removed with, for example, a dilute acid wash (e.g. nitric acid) which will attack and remove the silver far more quickly than the underlying nickel. 2. A security device consisting of a planer metal holographic platelet characterised in that the micro particle contains a holographic or diffractive image visible under magnification to an observer for verification of authenticity further characterised in that the micro dot holographic platelet contains an authenticable individual batch code where the micro particle consists of a high temperature resistant metal made by some or all of the processes of ...

Method of production 2 - nickel shim production then masking and "reverse electroplating" to remove exposed non masked material to encode shim

An alternative production route 2 also has novel features based on reverse electro-plating to remove material as follows... The method of production envisaged is as follows...

The basic source of the holographic or diffractive surface relief pattern can be an embossed plastic sheet containing an embossed surface relief made by the thermal embossing or UV casting. This can also be a traditional metal holographic master plate. This basic layer acts as the source of all subsequent holographic pattern in the process (in contrast to earlier systems that used thick nickel metal shims that are slow and expensive to manufacture). The plastic micro-structured surface can be made as a reel for larger column production in reel to reel embossing or as an individual plastic sheet,

say by flat bed embossing or UV casting. Note that this technique will equally work with a conventional thick nickel master as an alternative but the plastic master offers considerable advantages in terms of cost and efficiency.

A thin conductive metal layer (typically a few nanometres thick although this can vary) is added to surface of the plastic relief profile using again low cost high volume processes, envisaged are reel to reel vacuum metalizing using say silver. An alternative process would be 2 component silver reduction using say a silver spray process. It is envisaged other metals could be used for this. This is only designed as a thin conductive layer which will not form part of the final metal microdot but will be patterned and then used to grow as a copy the final metal microdots. The thin conductor is the used as a target in a galvanic plating process to deposit a layer of (typically) nickel on this silver material overlaying the plastic surface relief profile to form a holographic shim as known in the art (e.g. Saxby practical holography). The metal used may be one of a range of electroplateable high temperature metals (e.g. chromium stainless steel) to impart physical, temperature and chemical resistance to the final product. This forms a typically nickel shim as known in the art. At this point the metal shim having been grown may be peeled away from the plastic former or metal plate former carrying the original microstructure.

The key novel stage then is then in the next stages to incorporate the individual information for each batch within this nickel shim. In this case we rely on a process of reverse plating using a reverse galvanic process to remove material from the holographic shim where it is exposed in the plating solution and the electrodes (anode, cathode, are reversed).

The patterning to incorporate the individual data can be performed as follows...

Coat the surface of the shim (ideally the reverse surface but not necessarily) with a thin layer of photoresist by spinning, dipping, roll or Meier bar coating as known in the art and thermally cure this layer of needed. A thin resist layer can also be laminated onto the nickel as known in the field. A typical and preferred layer thickness would be 2 to 7 microns to maintain graphic resolution accuracy.

Light expose (typically UV) the photoresist through a high resolution film work containing the graphic for the shapes and individual data for the microdots. Then remove unexposed resist which in this case will define exposed areas around the microdots and where material needs to be removed for encoding using resist developer leaving a selective patterning over the plastic holographic surface and the nickel shim.

The masked shim is replaced in a plating bath (this can still be attached to the original maser or not - if not the reverse side will need protecting from the plating solution). The plaiting process is now reversed ("reversed plating") so that instead of depositing nickel on the exposed areas of the shim the plating bath removes nickel material galvanicallv to selectively remove material from the exposed areas of the nickel shim to form the individual information on the microdots and the microdot shapes as required for encoding. The residual mask material can then be removed by flood exposing the remaining photoresist mask with (generally) UV light and then removing this with resist developer.

One alternative final stage is removal of the formed high temperature and chemical resistant microdots from the plastic forming target. These would very typically be of nickel metal. A convenient way to do this is to use a solvent to dissolve the plastic former leaving the free microdots. If the masking and etching has been done directly on a metal shim without a plastic former then the micro- particles will be liberated as soon as the mask is dissolved away. The microdots can also be scraped off the target mechanically as they are not bound or encased in any other layers. The plastic master target being easy to make in reasonably high volume can be sacrificed at the end of the process with little cost if needed. The vestiges of the very thin silver layer may be removed with, for example, a

dilute acid wash (e.g. nitric acid) which will attack and remove the silver far more quickly than the underlying nickel.

3. A security device consisting of a planer metal holographic encoded holographic platelet characterised in that the micro particle contains a holographic or diffractive image visible under magnification to an observer for verification of authenticity further characterised in that the micro dot holographic platelet contains an authenticable individual batch code where the micro particle consists of a high temperature resistant metal made by some or all of the processes of...

- Method of production 3 - direct vacuum deposition of nickel or refractory metal in reel to reel process then subsequent masking and chemical etching or metal removal by "reverse electroplating" to remove exposed non masked material to encode nickel

An alternative production route 3 also has novel features based on reverse electro-plating to remove material as follows...

The method of production envisaged is for a high volume capability as follows...

The basic source of the holographic or diffractive surface relief pattern is an embossed plastic sheet containing an embossed surface relief made by thermal embossing or UV casting. This basic plastic layer acts as the source of all subsequent holographic patterns in the process (in contrast to earlier systems that used thick nickel metal shims are slow and expensive to manufacture). This plastic micro - structured surface can be made as a reel for larger volume production in reel to reel embossing or as individual plastic sheet, say by flat bed embossing or UV casting.

A conductive metal layer of a high temperature resistant metal suitable for the final application is vacuum deposited onto the embossed reel by a process of vacuum metallisation.

High temperature resistance metals are usually hard to evaporate in conventional resistance boat metallisers so in this case it is envisaged that the layer of heat resistant layer is relatively thin. In this it is envisaged that the layer of heat resistant layer is relatively thin. In this case a further heat resistant lacquer would be coated upon the layer of nickel (or copper etc) to provide subsequent support and carry the embossed metal profile, in this case the embossed film moulding form would suitably be of a release film type such as a stamping foil to allow easy transfer off of the heat resistant layers.

In other embodiments the web may be multiple metallised several times to provide a thick enough nickel (or other heat resistant metal) coating to be self supporting. In this case any microdot formed would be bidirectional reading which would be a very useful property.

A more efficient way of depositing high temperature resistant materials is using sputter vacuum metallisation and it can be envisaged that multiple passes and or multiple sputtering heads would be enough to deposit a self supporting layer. In all cases these reel fed high temperature micro dots will have holographic information visible from both directions.

Once the high temperature metal has been deposited by vacuum deposition it can be individually encoded into dots in one of the various methods as detailed above. The key stage then is then in the next stages to incorporate the individual information for each batch within this nickel or other high temperature resistant metal (e.g. copper titanium etc) vacuum coated layer. In this case we rely on a process of 'reverse electro-plating' using a reverse galvanic process to

remove material from the holographic nickel where it is exposed in the plating solution and the electrodes (anode, cathode are reversed).

The patterning to incorporate the individual data can be performed as follows... Coat the surface of the shim (ideally the reverse surface but not necessarily) with a thin layer of photo-resist by spinning, dipping, roll or Meier bar coating as known in the art and thermally cure this layer if needed. A thin resist layer can also be laminated onto the nickel as known in the field. A typical and preferred layer thickness would be 2 to 7 microns to maintain graphic resolution accuracy.

Light expose (typically UV) the photo-resist through a high resolution film work containing the graphic for the shapes and individual data for the microdots. Then remove unexposed resist which in this case will define exposed areas around the microdots and where material needs to be removed for encoding using resist developer leaving a selective patterning over the plastic holographic surface and the nickel shim.

Step of encoding ... The masked shim is replaced in a plating bath (still attached to the original master or not - if not the reverse side will need protecting from the plating solution). The plating process is now reversed ("reversed plating") so that instead of depositing nickel on exposed areas of the shim the plating bath removes nickel material galvanically to selectively remove material from the exposed areas of the nickel shim to form the individual information on the microdots and the microdot shapes as required. Chemically etch (or similar) or remove the silver or thin conductor in the areas of the holographic plastic layer not covered by photo-resist.

Please note that step of encoding can equally be obtained by using a conventional chemical etching solution in this case onto the vacuum deposited high temperature resistant metal.

The residual mask material can then be removed by flood exposing the remaining photo-resist mask with (generally) UV light and then removing this with resist developer.

The final stage is removal of the formed high temperature and chemical resistant microdots from the plastic forming target or carrier reel section. A convenient way to do this is to use a solvent to dissolve the plastic former leaving the free microdots. The microdots can also be scraped off the target mechanically as they are not bound or encased in any other layers. The plastic master target being easy to make in a reasonably high volume can be sacrificed at the end of the process with little cost if needed.

In the case where the vacuum deposited nickel or other high temperature metal required a further support this would be added a high temperature lacquer coating in a reel to reel coating process prior to removal of the original carrier layer (possibly a release film or hot foil assembly). This high temperature lacquer bonded to the nickel layer would then form there carrier reel for the chemical etching or galvanic etching of the nickel. The dots could be separated into individuals by choice of an solvent based type etchant or final process that attacked the high temperature lacquer where not protected by the nickel layers to separate the dots - this may be particularly appropriate with the use of a two pack cross linking lacquer where time is taken or an additional heating stage is required to form the final cross linked structure. Alternatively the material could simply be etched with individual batch numbers and then generically mechanically cut using mechanical cutting means.

These vacuum deposited nickel layers will usefully give microdots with bidirectional reading images where a right reading and mirror reversed holographic images is visible from both sides of the microdot - all plating processes only provide a single sided reading dot. This is an advantage over all

other metallic based systems and means for example that all the dots on a paper or article can be used for authentication as opposed to 50% previously giving an efficiency increase of 100% over previous metal systems.

4. A method of manufacturing a security device consisting of a planer holographic encoded holographic platelet characterised in that the micro particle contains a holographic or diffractive image visible under magnification to an observer for verification of authenticity further characterised in that microdot holographic platelet contains an authenticable individual batch code where the micro particle consists of a high temperature resistant metal made by some or all of the processes of...

Method of production 1 -formation of precision individual encoded masters and precise copying.

The basic source of the holographic or diffractive surface relief pattern is an embossed plastic sheet containing an embossed surface relief made by thermal embossing or UV casting. This basic plastic layer acts as the source of all subsequent holographic patterns in the process (in contrast to earlier systems that used thick nickel metal shims that are slow and expensive to manufacture). This plastic micro-structured surface can be made as a reel for larger volume production in reel to reel embossing or as an individual plastic sheet, say by flat bed embossing or UV casting.

A thin conductive metal layer (typically a few nanometres thick although this can vary) is added to the surface of the plastic surface relief profile using again low cost high volume processes, envisaged are reel to reel vacuum metalizing using say silver. An alternative process would be 2 component silver reduction using say a silver spray process. It is envisaged other metals could be used to this. This is only designed as a thin conductive layer which will not form part of the final metal microdot but will be patterned and then used to grow as a copy the final metal microdots.

The thin conductor overlaying the plastic surface relief profile is then patterned to incorporate the individual information for each batch- it is important to note that this conductor is not forming the final microdot but simply an accurate plating target upon which the final microdot which will consist of a much more durable metal, is formed.

The patterning can be performed as follows... Coat the surface of the conductor with a thin layer of photoresist by spinning, dipping roll or Meier bar coating as known in the art and thermally cure this layer if needed. A thin resist layer can also be laminated onto the plastic holographic master as known in the field. A typical and preferred layer thickness would be 2 to 7 microns to maintain graphic resolution accuracy.

Light expose (typically UV) the photoresist through a high resolution film work containing the graphic for the shapes and individual data for the microdots. Then remove unexposed resist with developer leaving a selective patterning over the plastic holographic surface and the thin metallic conductor.

Chemically etch (or similar) or remove the silver or thin conductor in the areas of the holographic plastic layer not covered by photoresist. An alternative method that can be used would be to run a "reversed plating process" wherein the silver or other thin conductor is removed by the plating process by reversing the polarity of the plating bath so that material is removed from the plating target by a reversed galvanic process. As the silver (or other) conductor is a very thin layer then a very high resolution thin metal conductive pattern in the shape of the desired encoding will be left on the holographic surface together with the masking photoresist material.

Remove the residual mask material by flood exposing the remaining photoresist mask with (generally) UV light and then removing this with resist developer.

At the end of this stage we have a plastic holographic surface relief pattern forming the profile of the diffractive structure with a detailed pattern carrying the exact information and pattern of the microdots to be made incorporated into a thin patterned conductive layer (usually silver) with no other masking material present. This plastic master is then key to growing galvanically or by other chemical processes exact metal replicas of the microdots patterns in the desired durable metal. It is important to note that etching or reverse plating away the thin silver conductor allows for a very accurate definition of microdot structure to be obtained which is also easy to check optically by microscope during the various development stages to get the artwork exactly correct. It is also very important that each microdot shape within the thin conductor layer retains a small connector line to the greater conductive areas to allow conductive continuity for later replication by plating.

The final stage is to grow the hard temperature microdots galvanically effectively using any high temperature metal that can be electroplated using the shaped patterned silver conductive areas as plating targets for growth. The types of high temperature metals envisaged are nickel, nickel alloys with harder material such as chromium, chromium itself and stainless steel. These materials would be chosen to have a much higher resistance to temperature or chemical attack than the original materials to allow usage of the security microdots in more aggressive environments such as those requiring the particles to remain authenticable after fire. The plastic holographic plate would impart the desired holographic surface relief to the structure whilst the conductive patterned silver layer, containing the shape of the individual microdots and their individual coding will be retained within the patterned shape of the conductor layers which will be faithfully copied within the patterned shape of the conductor layers which will be faithfully copied within the plating process as the nickel or other metal is galvanically or deposited onto this. It is envisaged that the hard metal layer will be grown to a thickness of preferably between 5 and 15 micron (outer limits 3 to 50 micron).

The final stage is removal of the formed high temperature and chemical resistant microdots from the plastic forming target. These would very typically be of nickel metal a convenient way to do this is to use a solvent to dissolve the plastic former leaving the free microdots. The microdots can also be scraped off the target mechanically as they are not bound or encased in any other layers. The plastic master target being easy to make in reasonably high volume can be sacrificed at the end of the process with little cost if needed. The vestiges of the very thin silver layer may be removed with, for example, a dilute acid wash (e.g. nitric acid) which will attack and remove the silver far more quickly than the underlying nickel.

5. A method of manufacturing a security device consisting of a planer metal holographic encoded holographic platelet characterised in that the micro particle contains a holographic or diffractive image visible under magnification to an observer for verification of authenticity further characterised in that the microdot holographic platelet contains an authenticable individual batch code where the micro particle consists of a high temperature resistant metal made by some or all of the processes of....

Method of production 2 -nickel shim production then masking and "reverse electroplating" to remove exposed non masked material to encode shim

An alternative production route 2 also has novel features based on reverse electro-plating to remove material as follows...

The method of production envisaged is as follows.... The basic source of the holographic or diffractive surface relief pattern is an embossed plastic sheet containing an embossed surface relief made by thermal embossing or UV casting. This basic plastic

layer acts as the source of all subsequent holographic pattern in the process (in contrast to earlier systems that used thick nickel shims that are slow and expensive to manufacture). This plastic micro- structured surface can be made as a reel for larger volume production in reel to reel embossing or as an individual plastic sheet, say by flat bed embossing or UV casting. Note that this technique will equally work with a conventional thick nickel holographic master shim containing he master surface relief to be copied but the plastic master offers considerable advantages in terms of cost and efficiency.

A thin conductive metal layer (typically a few nanometres thick although this can vary) is added to the surface of the plastic surface relief profile using again low cost high volume processes, envisaged are reel to reel vacuum metalizing using say silver. An alternative process would be 2 component silver reduction using a silver spray process. It is envisaged other metals could be used for this. This is only designed as a thin conductive layer which will not form part of the final metal microdot but will be patterned and then used to grow as a copy for the final metal microdots.

The thin conductor is used as a target in a galvanic plating process to deposit a layer of (typically)nickel on this silver material overlaying the plastic surface relief profile to form a holographic shim as known in the art (e.g. Saxby Practical Holography). The metal used may be one of a range of electroplateable high temperature metals (e.g. chromium, stainless steel) to impart physical, temperature and chemical resistance to the final product. This forms a typically nickel shim as known in the art. The key stage then is then in the next stages to incorporate the individual information for each batch within this nickel shim. In this case we rely on a process of reverse plating using a reverse galvanic process to remove material from the holographic shim where it is exposed in the plating solution and electrodes (anode, cathode are reversed).

The patterning to incorporate the individual data can be performed as follows...

Coat the surface of the shim (ideally the reverse surface but not necessarily) with a thin layer of photoresist by spinning, dipping, roll or Meier bar coating as known in the art and thermally cure this layer if needed. A thin resist layer can also be laminated onto the nickel as known in the field. A typical and preferred layer thickness would be 2 to 7 microns to maintain graphic resolution accuracy. Light expose (typically UV) the photoresist through a high resolution film work containing the graphic for the shapes and individual data for the microdots. Then remove unexposed resist which in this case will define exposed areas around the microdots and where material needs to be removed for encoding using resist developer leaving a selective patterning over the plastic holographic surface and the nickel shim. The masked shim is replaced in a plating bath (still attached to the original master or not - if the reverse side will need protecting from the plating solution). The plating process is now reversed ("reversed plating") so that instead of depositing nickel on the exposed areas of the shim the plating bath removes nickel material galvanically to selectively remove material from the exposed areas of the nickel shim to form the individual information on the microdots and the microdot shapes as required. Chemically etch (or similar) or remove the silver of thin conductor in the areas of the holographic plastic layer not covered by photoresist.

The residual mask material can then be removed by flood exposing the remaining photoresist mask with (generally) UV light and then removing this with resist developer.

The final stage is removal of the formed high temperature and chemical resistant microdots from the forming target. These would very typically be of nickel metal. A convenient way to do this is to use a

solvent to dissolve the plastic former leaving the free microdots. The microdots can also be scraped off the target mechanically as they are not bound or encased in any other layers. The plastic master target being easy to make in reasonably high volume can be sacrificed at the end of the process with little cost if needed. The vestiges of the very thin silver layer may be removed with, for example, a dilute acid wash (e.g. nitric acid) which will attack and remove the silver far more quickly than the underlying nickel.

6. A method of manufacturing a security device consisting of a metal or partially metal planer holographic encoded holographic platelet characterised in that the micro particle contains a holographic or diffractive image visible under magnification to an observer for verification of authenticity further characterised in that the microdot holographic platelet contains an authenticable individual batch code where the micro particle consists of a high temperature resistant metal made by some or all of the processes of...

Method of production 3 - direct vacuum deposition of nickel or refractory metal in reel to reel process then subsequent masking and chemical etching or metal removal by "reverse electroplating" to remove exposed non masked material to encode nickel

An alternative production route 3 also has novel features based on reverse electro-plating to remove material as follows....

The method of production envisaged is for a high volume capability as follows.... The basic source of the holographic or diffractive relief pattern is an embossed plastic sheet containing an embossed surface relief made by thermal embossing or UV casting. This basic plastic layer acts as the source of all subsequent holographic patterns in the process (in contrast to earlier systems that used thick nickel shims that are slow and expensive to manufacture). This plastic micro- structured surface can be made as a reel for larger volume production in reel to reel embossing or as an individual plastic sheet, say by flat bed embossing or UV casting.

A conductive metal layer of a high temperature resistant metal suitable for the final application is vacuum deposited onto the embossed reel by a process of vacuum metallisation.

High temperature resistance metals are usually hard to evaporate in conventional resistance boat metallisers so in this case it is envisaged that the layer of the heat resistant layer is relatively thin. In this case a further heat resistant lacquer would be coated upon the layer of nickel (or copper etc) to provide subsequent support and carry the embossed metal profile, in this case the embossed film moulding form would suitably be of a release film type the embossed film moulding form would suitably be of a release slim type such as a stamping foil to allow easy transfer off of the heat resistant layers. In other embodiments the web may be multiple metallised several times to provide a thick enough nickel (or other heat resistant metal) coating to be self supporting. In this case any microdot formed would be bi directional reading which would be a very useful property.

A more efficient way of depositing high temperature resistant materials is using sputter vacuum metallisation and it can be envisaged that multiple passes and or multiple sputtering heads would not be enough to deposit a self supporting layer. In all cases these reel fed formed high temperature metal microdots will have holographic information visible from both directions.

Once the high temperature metal has been deposited by vacuum deposition it can be individually encoded into dots in one of the various methods as detailed above.

The key stage then is then in the next stages to incorporate the individual information for each batch within this nickel or other high temperature metal (e.g. copper, titanium etc) vacuum coated layer. In this case we rely on a process of reverse plating using a reverse galvanic process to remove material from the holographic nickel where it is exposed in the plating solution and the electrodes (anode, cathode are reversed)

The patterning to incorporate the individual data can be performed as follows...

Coat the surface of the shim (ideally the reverse surface but not necessarily) with a thin layer of photo-resist by spinning, dipping roll or Meier bar coating as known in the art and thermally cure this layer if needed. A thin resist layer can also be laminated onto the nickel as known in the field. A typical and preferred layer thickness would be 2 to 7 microns to maintain graphic resolution accuracy.

Light expose (typically UV) the photoresist through a high resolution film work containing the graphic for the shapes and individual data for the microdots. Then remove unexposed resist which in this case will define exposed areas around the microdots and where material needs to be removed for encoding using resist developer leaving a selective patterning over the plastic holographic surface and the nickel shim.

Step of encoding... The masked shim is replaced in a plating bath (still attached to the original master or not - if not the reverse side will need protecting from the plating solution). The plating process is now reversed ("reversed plating") so that instead of depositing nickel on the exposed areas of the shim the plating bath removes nickel material galvanically to selectively remove material from the exposed areas of the nickel shim to form the individual information on the microdots and the microdot shapes as required. Chemically etch (or similar) or remove the silver or thin conductor in the areas of the holographic plastic layer not covered by photoresist.

Please note that the encoding step can equally be obtained by using a conventional chemical etching solution in this case onto the vacuum deposited high temperature resistant metal. The residual mask material can then be removed by chemical development and removal of all the remaining resist mask or alternatively by flood exposing the remaining photoresist mask with (generally) UV light and then removing this with resist developer.

The final stage is removal of the formed high temperature and chemical resistant microdots from the plastic forming target or carrier reel section. A convenient way to do this is to use a solvent to dissolve the plastic former leaving the free microdots. The microdots can also be scraped off the target mechanically as they are not bound or encased in any other layers. The plastic master target being easy to make in reasonably high volume can be sacrificed at the end of the process with little cost if needed.

In the case where the vacuum deposited nickel or other high temperature metal required a further support this would be added a high temperature lacquer coating in a reel to reel coating process prior to removal of there original carrier layer (possible a release film or hot foil assembly). This high temperature lacquer bonded to the nickel layer would then form the carrier reel for the chemical etching or galvanic etching of the nickel. The dots could be separated into individuals by choice of an solvent based type etchant or final process that attacked the high temperature lacquer where not protected by the nickel layers to separate the dots - this may be particularly appropriate with the use for a two pack cross linking lacquer where some time is taken or additional heating stage is required to form the final cross linked structure. Alternatively the material could simply be etched with individual batch numbers and then generically mechanically cut using mechanical cutting means.

These vacuum deposited nickel layers will usefully give microdots with bidirectional reading images where a right reading and mirror reversed holographic images is visible from both sides of the microdot - all plating processes only provide a single sided reading dot. This is an advantage over all

other metallic based systems and means for example that all dots on a paper or article can be used for authentication as opposed to 50% previously giving an efficiency increase of 100% over previous metal systems.

Examples...

In one example of usage of this patent a typical product description and construction would be...

The holographic metal micro particles are designed as a high security covert authentication method to enable the application of individually batch encoded holographic micro-taggants on a large cost effective industrial scale to a wide range of security products. The diffractive security image on the foil is of the highest possible security standard containing optically variable features such as rotation, apparent motions, image switches and depth effects. These effects are manufactured by highly sophisticated custom origination equipment base on sophisticated interferometric optical lithography and the quality and scope of these effects are not accessible with simpler types of optical imaging such as holography. These origination techniques also include covert techniques including a sophisticated range of micro, nano and machine verifiable features. This provides public recognition security and anti-counterfeit security. The images are designed to be viewed under microscope illumination where the range of image features can be authenticated.

The dot consists of a typically 8-20 micron thickness micro disc and can be made to various sizes and shapes typically a 350um hexagon or rectangles or squares in a size range 150-1000 micron diameter.

Further Examples ...

Further examples of this invention are ... 1 . A diffractive metal micro particle security device consisting of a small planar encoded holographic micro-particle platelet where the micro particle contains a optically variable image generating structure providing defined optical variable effects such as colour changes, images switches and apparent motion effects visible under magnification under illumination for verification of authenticity, and characterised that the platelet is substantially composed of metal materials. 2. A security device as in example 1 wherein the optically variable image is a diffractive or holographic image wherein the optically variable image generating structure is a metal diffractive surface relief structure.

3. A diffractive metal micro particle security device as in examples 1 and 2 further containing a batch code within the platelet for batch tracking formed as an aperture within the planar micro-particle. 4. A diffractive metal micro particle security device as in any of the above examples characterised that the micro-particle is made by a forming process of reverse electroplating wherein a reverse galvanic processs has been used to electro-galvanically remove material from a metal holographic layer to form the dot shapes.

5. A diffractive metal micro particle security device as in examples 4 characterised that the micro- particle is made and also encoded by a process of reverse electroplating wherein a reverse galvanic process has been used to electro-galvanically remove material from a metal holographic layer to form

both the dot shapes and the encoded batch code as apertures or indents the metal holographic shim.

6. A diffractive metal micro particle security device as in example 5 characterised that the micro- particle is made by a process of reverse electroplating wherein a reverse galvanic process has been used to remove material from a metal holographic layer to form the dot shapes and the encoded batch code wherein the process involved using a photo- resist mask to define the areas of metal for removal by the reverse galvanic process to form the aperture encoding and wherein the masked metal holographic shim has been used as an anode in an electroplating arrangement to remove metal in the areas exposed by the batch encoding and micro-dot forming mask. 7. A diffractive metal micro particle security device as in any of examples 1 through 6 characterised that the diffractive micro-particle intermediate shim is made by using an intermediate plastic embossed surface relief forming element as a source of the diffractive surface relief profile.

8. A diffractive metal micro particle security device as in example 7 further characterised that intermediate plastic embossed surface relief has been formed in a reel to reel process. 9. A diffractive metal micro particle security device as in any of the preceeding claims consisting of a planar substantially metallic holographic micro particle characterised such that the authenticable diffractive or holographic image remains visible from both sides of observation of the micro particle and remains visible from both sides of observation of the platelet for ease of authentication.

10. A diffractive metal micro particle security device as in any of the preceeding claims characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed in all or part using vacuum metallization process.

1 1 . A diffractive metal micro particle security device as in example 10 characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed in entirety using a vacuum metallization process using a high temperature resistant metal such as copper, nickel, chromium.

12. A diffractive metal micro particle security device as in example 9 and 10 characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed in entirety using a vacuum metallization process using a high temperature resistant metal such as copper, nickel, chromium and subsequently encoded by masking and encoding a resist mask and selectively chemical etching away the batch code and dot shape through the encoded mask using a dilute acids or similar.

13. A diffractive metal micro particle security device as in claims 10 and 12 characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed by both vacuum metallisation initailly of a conductive metal, such as silver or aluminium, followed by a galvanic plating deposition process to deposit additional high temperature resistant metal such as copper, nickel, chromium.

14. A diffractive metal micro particle security device as in examples 10 and 12 and 13 characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed by both vacuum metallisation initially of a conductive metal, such as silver or aluminium, followed by a a masking and encoding process to form a resist mask, followed by a reverse electroplating process or chemical etching process to remove exposed areas of the first vacuum deposited metal , followed by removal of the photoresist to form a micro-particle encoded master plate , followed by a galvanic plating deposition process to deposit additional high temperature resistant metal such as copper, nickel, chromium to form immediately upon the shaped and encoded master plates the final micro- dots, followed by removal of the micro-dots from the master plate.

15 . A d if tractive metal micro particle security device as in examples 10 and 12 and 13 and 14 characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed by both initially an electroless deposition of a conductive metal, such as silver spray reduction, of a conductive metal followed by a galvanic plating deposition process to deposit additional high temperature resistant metal such as copper, nickel, chromium.

16. A diffractive metal micro particle security device as in examples 10 and 12 and 13 and 14, 15 and

16 characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed by both initially an electroless deposition of a conductive metal, such as silver spray reduction, of a conductive metal followed by , followed by a a masking and encoding process to form a resist mask, followed by a reverse electroplating process or chemical etching process to remove exposed areas of trhe first vacuum deposited metal , followed by removal of the photoresist to form a micro-particle encoded master plate , followed by a galvanic plating deposition process to deposit additional high temperature resistant metal such as copper, nickel, chromium to form immediately upon the shaped and encoded master plates the final micro-dots, followed by removal of the micro-dots from the master plate.

17. 1 . A diffractive metal micro particle security device as in any of the preceeding claims wherein the planar dimesions are within the range 35 micron to 1000 micron and the thickness is 60% or less of the planar largest dimension.

18. A diffractive metal micro particle security device as in any of the above examples further characterised in that the micro particle is coated on one or both faces with a heat sealable adhesive designed to improve the adhesion of the micro dot into paper when applied to substartes and heated.

19 A diffractive metal micro particle security device as in any of the above examples further incorporating an optical taggant visible under infra red or ultra violet light .

20. A diffractive metal micro particle security device as in any of the above example further incorporating an magnetic taggant detectable with magnetic detectors.

21 . A holographic micro particle security device as in any of the above examples of a planar disc shaped character such that the largest dimension is in the range 35 micron to I OOOmcron and such that the thickness remains always less than 60% of the planar dimension.

22. A holographic micro particle security device as in any of the above examples wherein the batch encoding has been created by incorporation by etching into the embossing shim prior to film embossing.

23 An article containing a holographic micro particle security device as described in any of the above claims.

24. A security article as in example 19 to wherein the heat sealable adhesive is chosen to activate at the drying temperature of the paper making process - typically + 100 deg Celsius - and then to be thereafter substantially water insoluble.

25. A security device containing multiple holographic micro particle security devices where the area of application of the micro dots is formed into simple shapes using a higher density of application to forma new public recognition optical security feature made of shaped areas of holographic microdot deposition,

26. A public recognition security article containing multiple holographic micro particle security devices as in any of the above examples or any of the above claims made methods of patterning dot deposition using a method of dot spraying or similar random projection of dots towards the substrate web, particularly allied to a masking assembly of apertures, moving apertures an shaped apertures

linked in with the regular uniform movement in one direction of the paper web to provide unusual and unique graphics and effects for higher densities of dot deposition as being a novel new security feature,

27. A new public recognition security article as in the above examples using a method to combine a modulated width and density of application of multiple holographic micro particle security devices application with the linear movement of the paper web to generate graphical effects of a subtle nature consisting of random array of holographic effect dots in various indistinct and gradually changing shapes.

28. A security article as in any of the above examples made by applying the holographic micro particle security device to security items including as plastic bases and laminates for ID cards and passport data pages.

29. A security article as in any of the above examples made by applying the holographic micro particle security device to security items including as plastic bases and laminates for ID cards and passport data pages. 30. A security article as in example 29 incorporating diffractive metal micro particle security devices characterised that the diffractive metal micro particle security devices have been left joined with small sections together to form a mesh structure for incorporation into card laminate bodies more easily.

31 . A security article as in example 29 and 30 incorporating diffractive metal micro particle security devices characterised that the diffractive metal micro particle security devices have been left joined with small sections together to form a mesh structure for incorporation into card laminate bodies more easily characterised that the micro-particle mesh is made by a process of reverse electroplating wherein a reverse galvanic process has been used to remove material from a metal holographic layer to form the dot shapes and the encoded batch code wherein the process involved using a photoresist mask to define the areas of metal for removal by the reverse galvanic process to form the aperture encoding and wherein the masked metal holographic shim has been used as an anode in an electroplating arrangement to remove metal in the areas exposed by the batch encoding and microdot forming mask.

32. A joined array of diffractive metal micro particle security devices according to any of the above claims further characterised that the diffractive metal micro particle security devices have been left joined with small sections together to form a mesh structure for incorporation into card laminate bodies more easily characterised that the micro-particle mesh is made by a process of reverse electroplating wherein a reverse galvanic process has been used to remove material from a metal holographic layer to form the dot shapes and the encoded batch code wherein the process involved using a photo- resist mask to define the areas of metal for removal by the reverse galvanic process to form the aperture encoding and wherein the masked metal holographic shim has been used as an anode in an electroplating arrangement to remove metal in the areas exposed by the batch encoding and micro-dot forming mask.

30. A security article as in any of the above examples can be taken on applying the dots to hot stamping foils and then subsequently transferring the hot stamping foil and the attached micro dots in a hot stamping process as known in the art to create further security items such as security paper with post applied dots during final personalisation plastic bases for ID cards and in for example PE film used for over-lamination rather than security paper.

31 . A manufacturing method for a diffractive metal micro particle security device as in any of the above examples characterised that the micro-particle is made by a process of reverse electroplating wherein a reverse galvanic process has been used to remove material from a metal holographic layer to form at least the dot shapes wherein the process involved using a photo- resist mask to define the

areas of metal for removal by the reverse galvanic process to form the shape encoding and wherein the masked metal holographic shim has been used as an anode in an electroplating arrangement to remove metal in the areas exposed by the micro-dot forming mask.

32 A manufacturing method for a diffractive metal micro particle security device as in any of the above examples characterised that the micro-particle is made by a process of reverse electroplating wherein a reverse galvanic process has been used to remove material from a metal holographic layer to form the dot shapes and the encoded batch code wherein the process involved using a photoresist mask to define the areas of metal for removal by the reverse galvanic process to form the aperture encoding and wherein the masked metal holographic shim has been used as an anode in an electroplating arrangement to remove metal in the areas exposed by the batch encoding and microdot forming mask.

33 A manufacturing method for a diffractive metal micro particle security device as in any of examples the above characterised that the diffractive micro-particle intermediate shim is made by using an intermediate plastic embossed surface relief forming element as a source of the diffractive surface relief profile.

34 A manufacturing method for a diffractive metal micro particle security device as in any of the preceeding examples characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed in all or part using vacuum metallization process.

35. A manufacturing method for a diffractive metal micro particle security device as in any of the above examples characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed in entirety using a vacuum metallization process using a high temperature resistant metal such as copper, nickel, chromium.

36. A manufacturing method for a diffractive metal micro particle security device as in any of the above examples characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed in entirety using a vacuum metallization process using a high temperature resistant metal such as copper, nickel, chromium and subsequently encoded by masking and encoding a resist mask and selectively chemical etching away the batch code and dot shape through the encoded mask using a dilute acids or similar.

37. A manufacturing method for a diffractive metal micro particle security device as in any of the above examples characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed by both vacuum metallisation initially of a conductive metal, such as silver or aluminium, followed by a galvanic plating deposition process to deposit additional high temperature resistant metal such as copper, nickel, chromium.

39. An article security mark containing diffractive metal micro particle security device according to any of the above examples.

Figures ...

This invention is now explained further with a set of Figures as follows ...

Figure 1 : Figures 1 A, 1 B, 1 C shows a metal micro particle security device according to this invention (1 ) with a difrecative or holographic image (2) and a batch encoding formed as an aperture (3).

Figure 1 A - shows a shows a metal micro particle security device according to this invention (1 ) with a diffractive or holographic image (2) and an batch encoding formed as an aperture (3).

Figure 1 B shows a cross section of a first article of a metal micro particle security device (1 ) made by an electroplating process where one side of the planar metal micro particle security device carries a holographic image and a diffractive surface relief (4) and its diffractive image replay (9) for an observer under illumination - whereas the opposite side due to the electroplating process used in manufacture carries a plain ( matt) face( 5).

Figure 1 C shows a cross section of a first article of a metal micro particle security device (8) made by an vacuum deposition process where both sides of the planar metal micro particle security device carries a holographic image and a diffractive surface relief (6 and 7) and its diffractive image replay (9 and also (10) for an observer under illumination - where the opposite side image is diffractive and has an accurate surface relief due to the vacuum deposition process used due to the electroplating process used in manufacture and replays a mirror image diffractive image (10) compared to the right reading image replay side (9).

Figure 2 : Figure 2A shows a cross section of a embossed plastic former as used in the manufacture of metal micro particle security devices according to this patent. The former(21 ,22) is made by reel to reel embossing (21 ,22) and then optionally is metallised (24) to provide either a thin silver conductor suitable for later plating or optionally a much thicker finished metallic layer directly suitable for subsequent encoding.

Figure 2B The plastic former consists of a plastic base 23, typically PET, coated PET or a release film such as a stamping foil release structure, a surface relief diffractive pattern imparted by heat and pressure or UV casting , and vacuum deposited metallic layer (24). These surface relief forms can be used for later plating processes and encoding processes and avoid the need for plating manufacture of numerous master plates, though this remains possible for small volumes.

Figure 3 shows a process diagram for forming a metal micro particle security device (8) made by means of this invention.

Figure 3A - plastic former carrying surface relief (31 ) and thin conductive silver or other vacuum metallised layer (32) before electroplating process (39).

Figure 3B - After electroplating process (39) nickel or other refractory metal thick layer (33) 5-10 micron thick is formed to act as body of micro-particle.

Figure 3C - After resist encoding ( 310) leaving islands of resist protecting areas of nickel ( 33) not to be removed in reverse electro-plating (35) ... nickel shim coated with resist , exposed to film work (contact copy) with encoded data and exposed resist ( or vice versa) developed away to leave islands of resist (35) forming the encoded data areas and dot shapes to be transferred to the final metal diffractive micro-particle security device.

Figure 3D - After reverse electroplating (31 1 ) to remove exposed areas of resist by reverse galvanic process or reverse electroplating process - nickel shim placed as anode in the electrolytic cell to remove material from the exposed nickel areas when a current is passed (36). This process self quenches when the etching processes to the plastic and electrical conductivity is lost at this point (removal down to 31 ) leaving islands of resist protecting areas of nickel ( 33) not removed in reverse the electro-plating (35) to form the independent diffractive encoded micro-particles ... the encoded data areas and dot shapes have been transferred to the final metal diffractive micro-particle security device.

Figure 3D - After metal diffractive micro-particle removal (312) from substrate (31 ) Leaves diffractive metal microdots carrying shapes and aperture batch encoding transferred from resist masking structures where the encoded data areas and dot shapes have been transferred to the separated (38) final metal diffractive micro-particle security devices (33,34,35 and 38).

Figure 4 shows a process diagram for forming a metal micro particle security device (8) made by means of this invention from a plastic reel former (41 ) vacuum deposited with a relatively thick layer of refractory metal (42) e.g. nickel, copper, possibly aluminium if less environmental resistance needed which avoids the need for any additional plating stage as this will directly form the body of the diffractive metal micro-particle.

Figure 4A - plastic former carrying surface relief (41 ) and other vacuum metallised layer (42) also carrying a copy of this surface relief sufficiently thick to use directly as body of micro-particle..

Figure 3B - Move directly to masking process, as vacuum deposited )nickel or other refractory metal thick layer (42) will act as body of micro-particle. Figure 4B - After resist encoding ( 410) leaving islands of resist (45) protecting areas of nickel ( 42) not to be removed in reverse electro-plating (45) ... nickel shim coated with resist , exposed to film work (contact copy) with encoded data and exposed resist ( or vice versa) developed away to leave islands of resist (45) forming the encoded data areas and dot shapes to be transferred to the final metal diffractive micro-particle security device.

NOTE that both sides of nickel show a diffractive replay as optical microstructure reproduces both sides of nickel as it is a vacuum deposited layer.

Figure 4C - After reverse electroplating (41 1 ) to remove exposed areas of resist by reverse galvanic process or reverse electroplating process - nickel shim placed as anode in the electrolytic cell to remove material from the exposed nickel areas when a current is passed (46). This process self quenches when the etching processes to the plastic and electrical conductivity is lost at this point (removal down to 41 ) leaving islands of resist protecting areas of nickel ( 45) not removed in reverse the electro-plating (45) to form the independent diffractive encoded micro-particles ... the encoded data areas and dot shapes have been transferred to the final metal diffractive micro-particle security device.

Figure 4D - After metal diffractive micro-particle removal (412) from substrate (41 ) Leaves diffractive metal microdots carrying shapes and aperture batch encoding transferred from resist masking structures where the encoded data areas and dot shapes have been transferred to the separated (48) final metal diffractive micro-particle security devices (42,45 and 48).

NOTE that both sides of nickel show a diffractive replay as optical microstructure reproduces both sides of nickel as it is a vacuum deposited layer. (49, 50) so one side of micro-particle replays diffractive image and second side replays mirror image of first diffractive image. (49,50)

So Figure 4 shows that in a vacuum deposition process where both sides of the planar metal micro particle security device carries a holographic image and a diffractive surface relief and its diffractive image replay for an observer under illumination - where the opposite side image is diffractive and has an accurate surface relief due to the vacuum deposition process used due to the electroplating process used in manufacture and replays a mirror image diffractive image (49) compared to the right reading image replay side (50).

Figure 5 shows the principle of selective metal removal and encoding that is used herein using a process of 'reverse electro-plating' or 'reversed galavanics' which removes metal from nickel shim

under the application of plating current (59) in an electroplating bath ( 53) when the shim to be encoded by metal removal ( 51 1 1) is placed in the batch as the sacrificial anode position (58).

Figure 5A shows conventional electroplating (54) , a plating bath containing electrolyte solution (53) has an anode (55) of sacrificial metal and a cathode (56) where the metal is deposited on the substrate to be coated (52) which conventionally (54) under the application of voltage and current (59)causes a current to flow and metal ions to be deposited at the cathode so building up shim material as known in the art. Metal material is lost by anode (55) , generally a large amount of nickel stock and is deposited at cathode(56) as a coating on the substarte to be coated (52) .

Figure 5B shows the principle of selective metal removal and encoding that is used herein using a process of 'reverse electro-plating' or 'reversed αalvanics' (510) which removes metal from nickel shim (51 ) placed AT THE SACRIFICIAL ANODE POSITION ( 58) under the application of plating current (59) in an electroplating bath ( 53) when the shim to be encoded by metal removal ( 51 1 ) is placed in the batch as the sacrificial anode position (58). To encode a masked substrate (51 10 the substrate is selectively masked with photoresist and then the unmasked material is removed by this reverse electroplating process which provides a precisely quench removal of material down to the point of finished dots where the continuity of conductivity becomes lost. This is an advantage over other methods to provide an accurate and self modulating end point, the encoding process is described in Figures 3 and 4.

Embodiments of the invention may be understood with reference to the following numbered paragraphs:

1 . A diffractive metal micro particle security device consisting of a small planar encoded holographic micro-particle platelet where the micro particle contains a optically variable image generating structure providing defined optical variable effects such as colour changes, images switches and apparent motion effects visible under magnification under illumination for verification of authenticity, and characterised that the platelet is substantially composed of metal materials.

2. A security device as in paragraph 1 wherein the optically variable image is a diffractive or holographic image wherein the optically variable image generating structure is a metal diffractive surface relief structure.

3. A diffractive metal micro particle security device as in paragraphs 1 and 2 further containing a batch code within the platelet for batch tracking formed as an aperture within the planar micro-particle.

4. A diffractive metal micro particle security device as in any of the above paragraphs characterised that the micro-particle is made by a forming process of reverse electroplating wherein a reverse galvanic process has been used to electro-galvanically remove material from a metal holographic layer to form the dot shapes. 5. A diffractive metal micro particle security device as in paragraph 4 characterised that the micro- particle is made and also encoded by a process of reverse electroplating wherein a reverse galvanic process has been used to electro-galvanically remove material from a metal holographic layer to form both the dot shapes and the encoded batch code as apertures or indents the metal holographic shim. 6. A diffractive metal micro particle security device as in paragraphs 4 and 5 characterised that the micro-particle is made by a process of reverse electroplating wherein a reverse galvanic process has been used to remove material from a metal holographic layer to form the dot shapes and the encoded batch code wherein the process involved using a photo- resist mask to define the areas of metal for removal by the reverse galvanic process to form the aperture encoding and wherein the masked metal holographic shim has been used as an anode in an electroplating arrangement to remove metal in the areas exposed by the batch encoding and micro-dot forming mask.

7. A diffractive metal micro particle security device as in any of paragraphs 1 through 6 characterised that the diffractive micro-particle intermediate shim is made by using an intermediate plastic embossed surface relief forming element as a source of the diffractive surface relief profile.

8. A diffractive metal micro particle security device as in paragraph 7 further characterised that intermediate plastic embossed surface relief has been formed in a reel to reel process.

9. A diffractive metal micro particle security device as in any of the preceeding paragraphs consisting of a planar substantially metallic holographic micro particle characterised such that the authenticable diffractive or holographic image remains visible from both sides of observation of the micro particle and remains visible from both sides of observation of the platelet for ease of authentication. 10. A diffractive metal micro particle security device as in any of the preceeding paragraphs characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed in all or part using vacuum metallization process.

1 1 . A diffractive metal micro particle security device as in paragraph 10 characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed in entirety using a vacuum metallization process using a high temperature resistant metal such as copper, nickel, chromium.

12. A diffractive metal micro particle security device as in paragraph 9 and 10 characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed in entirety using a vacuum metallization process using a high temperature resistant metal such as copper, nickel, chromium and subsequently encoded by masking and encoding a resist mask and selectively chemical etching away the batch code and dot shape through the encoded mask using a dilute acids or similar.

13. A diffractive metal micro particle security device as in paragraphs 10 and 12 characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed by both vacuum metallisation initailly of a conductive metal, such as silver or aluminium, followed by a galvanic plating deposition process to deposit additional high temperature resistant metal such as copper, nickel, chromium.

14. A diffractive metal micro particle security device as in paragraphs 10 and 12 and 13 characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed by both vacuum metallisation initially of a conductive metal, such as silver or aluminium, followed by a a masking and encoding process to form a resist mask, followed by a reverse electroplating process or chemical etching process to remove exposed areas of the first vacuum deposited metal , followed by removal of the photoresist to form a micro-particle encoded master plate , followed by a galvanic plating deposition process to deposit additional high temperature resistant metal such as copper, nickel, chromium to form immediately upon the shaped and encoded master plates the final microdots, followed by removal of the micro-dots from the master plate.

15 . A diffractive metal micro particle security device as in paragraphs 10 and 12 and 13 and 14 characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed by both initially an electroless deposition of a conductive metal, such as silver spray reduction, of a conductive metal followed by a galvanic plating deposition process to deposit additional high temperature resistant metal such as copper, nickel, chromium.

16. A diffractive metal micro particle security device as in paragraphs 10 and 12 and 13 and 14, 15 and 16 characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed by both initially an electroless deposition of a conductive metal, such as silver spray reduction, of a conductive metal followed by , followed by a a masking and encoding process to form a resist mask, followed by a reverse electroplating process or chemical etching

process to remove exposed areas of trhe first vacuum deposited metal , followed by removal of the photoresist to form a micro-particle encoded master plate , followed by a galvanic plating deposition process to deposit additional high temperature resistant metal such as copper, nickel, chromium to form immediately upon the shaped and encoded master plates the final micro-dots, followed by removal of the micro-dots from the master plate.

17. 1 . A diffractive metal micro particle security device as in any of the preceeding paragraphs wherein the planar dimesions are within the range 35 micron to 1000 micron and the thickness is 60% or less of the planar largest dimension.

18. A diffractive metal micro particle security device as in any of the above paragraphs further characterised in that the micro particle is coated on one or both faces with a heat sealable adhesive designed to improve the adhesion of the micro dot into paper when applied to substartes and heated.

19 A diffractive metal micro particle security device as in any of the above paragraphs further incorporating an optical taggant visible under infra red or ultra violet light .

20. A diffractive metal micro particle security device as in any of the above paragraphs further incorporating an magnetic taggant detectable with magnetic detectors.

21 . A holographic micro particle security device as in any of the above paragraphs of a planar disc shaped character such that the largest dimension is in the range 35 micron to I OOOmcron and such that the thickness remains always less than 60% of the planar dimension.

22. A holographic micro particle security device as in any of the above paragraphs wherein the batch encoding has been created by incorporation by etching into the embossing shim prior to film embossing.

23 An article containing a holographic micro particle security device as described in any of the above paragraphs.

24. A security article as in paragraph 19 to wherein the heat sealable adhesive is chosen to activate at the drying temperature of the paper making process - typically + 100 deg Celsius - and then to be thereafter substantially water insoluble.

25. A security device containing multiple holographic micro particle security devices where the area of application of the micro dots is formed into simple shapes using a higher density of application to forma new public recognition optical security feature made of shaped areas of holographic microdot deposition,

26. A public recognition security article containing multiple holographic micro particle security devices as in any of the above paragraphs or any of the above paragraphs made methods of patterning dot deposition using a method of dot spraying or similar random projection of dots towards the substrate web, particularly allied to a masking assembly of apertures, moving apertures an shaped apertures linked in with the regular uniform movement in one direction of the paper web to provide unusual and unique graphics and effects for higher densities of dot deposition as being a novel new security feature,

27. A new public recognition security article as in the above paragraphs using a method to combine a modulated width and density of application of multiple holographic micro particle security devices application with the linear movement of the paper web to generate graphical effects of a subtle nature consisting of random array of holographic effect dots in various indistinct and gradually changing shapes.

28. A security article as in any of the above paragraphs made by applying the holographic micro particle security device to security items including as plastic bases and laminates for ID cards and passport data pages.

29. A security article as in any of the above paragraphs made by applying the holographic micro particle security device to security items including as plastic bases and laminates for ID cards and passport data pages.

30. A security article as in paragraph 29 incorporating diffractive metal micro particle security devices characterised that the diffractive metal micro particle security devices have been left joined with small sections together to form a mesh structure for incorporation into card laminate bodies more easily. 31 . A security article as in paragraph 29 and 30 incorporating diffractive metal micro particle security devices characterised that the diffractive metal micro particle security devices have been left joined with small sections together to form a mesh structure for incorporation into card laminate bodies more easily characterised that the micro-particle mesh is made by a process of reverse electroplating wherein a reverse galvanic process has been used to remove material from a metal holographic layer to form the dot shapes and the encoded batch code wherein the process involved using a photoresist mask to define the areas of metal for removal by the reverse galvanic process to form the aperture encoding and wherein the masked metal holographic shim has been used as an anode in an electroplating arrangement to remove metal in the areas exposed by the batch encoding and microdot forming mask. 32. A joined array of diffractive metal micro particle security devices characterised that the diffractive metal micro particle security devices have been left joined with small sections together to form a mesh structure for incorporation into card laminate bodies more easily characterised that the micro-particle mesh is made by a process of reverse electroplating wherein a reverse galvanic process has been used to remove material from a metal holographic layer to form the dot shapes and the encoded batch code wherein the process involved using a photo- resist mask to define the areas of metal for removal by the reverse galvanic process to form the aperture encoding and wherein the masked metal holographic shim has been used as an anode in an electroplating arrangement to remove metal in the areas exposed by the batch encoding and micro-dot forming mask.

30. A security article as in any of the above paragraphs can be taken on applying the dots to hot stamping foils and then subsequently transferring the hot stamping foil and the attached micro dots in a hot stamping process as known in the art to create further security items such as security paper with post applied dots during final personalisation plastic bases for ID cards and in for example PE film used for over-lamination rather than security paper.

31 . A manufacturing method for a diffractive metal micro particle security device as in any of the above paragraphs characterised that the micro-particle is made by a process of reverse electroplating wherein a reverse galvanic process has been used to remove material from a metal holographic layer to form at least the dot shapes wherein the process involved using a photo- resist mask to define the areas of metal for removal by the reverse galvanic process to form the shape encoding and wherein the masked metal holographic shim has been used as an anode in an electroplating arrangement to remove metal in the areas exposed by the micro-dot forming mask.

32 A manufacturing method for a diffractive metal micro particle security device as in any of the above paragraphs characterised that the micro-particle is made by a process of reverse electroplating wherein a reverse galvanic process has been used to remove material from a metal holographic layer to form the dot shapes and the encoded batch code wherein the process involved using a photo- resist mask to define the areas of metal for removal by the reverse galvanic process to form the aperture encoding and wherein the masked metal holographic shim has been used as an anode in an

electroplating arrangement to remove metal in the areas exposed by the batch encoding and microdot forming mask.

33 A manufacturing method for a diffractive metal micro particle security device as in any of paragraphs the above characterised that the diffractive micro-particle intermediate shim is made by using an intermediate plastic embossed surface relief forming element as a source of the diffractive surface relief profile.

34 A manufacturing method for a diffractive metal micro particle security device as in any of the preceding paragraphs characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed in all or part using vacuum metallization process. 35. A manufacturing method for a diffractive metal micro particle security device as in any of the above paragraphs characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed in entirety using a vacuum metallization process using a high temperature resistant metal such as copper, nickel, chromium.

36. A manufacturing method for a diffractive metal micro particle security device as in any of the above paragraphs characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed in entirety using a vacuum metallization process using a high temperature resistant metal such as copper, nickel, chromium and subsequently encoded by masking and encoding a resist mask and selectively chemical etching away the batch code and dot shape through the encoded mask using a dilute acids or similar. 37. A manufacturing method for a diffractive metal micro particle security device as in any of the above paragraphs characterised that the diffractive micro-particle intermediate diffractive surface relief shim of metal has been formed by both vacuum metallisation initially of a conductive metal, such as silver or aluminium, followed by a galvanic plating deposition process to deposit additional high temperature resistant metal such as copper, nickel, chromium. 39. A valuable article security mark containing diffractive metal micro particle security device according to any of the above paragraphs.

It is to be understood that herein by the term polymer and plastic we mean a naturally occurring or synthetic compound of high molecular weight consisting of a very large number of repeated links of simple molecules or monomers. The plastics we refer to are a subset of polymers and are synthetic man made polymers usually supplied as films or coatings - typically we anticipate structure based on polyethylene terphane film (PET) optionally with an embossable coating and an additional reflector layer coated on the emboss surface relief. Numerous other polymers are possible in this application such as cellulous acetates, polypropylene, and ultra violet light cross linked polymers that can be coated on a surface relief as a liquid and then cross linked with UV light to form the polymer coating on the film which conforms to the surface relief profile.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. Embodiments of the invention provide a new security device consisting of a planer metal holographic encoded holographic platelet characterised in that the micro particle contains a holographic or diffractive image visible under magnification to an observer for verification of authenticity further characterised in that the micro dot holographic platelet contains an authenticable individual batch code where the micro particle consists of a high temperature resistant metal made by some or all of the processes defined herein.

This is a new class of holographic or diffractive or micro-optic metal encoded micro-particle designed as a high security covert authentication method designed to be applied in a wide range of applications. The manufacturing technology is different in comparison to other metal holographic microdot methodology giving higher volume scalability, lower production costs and greater accuracy of encoded graphics.

In general dots are distinguished by carrying a diffractive image authenticable under microscopic assisted magnification ( e.g. x 60, x 100 ) carrying both defined optical diffractive effects such as image switches, movement effects and colour shifts plus even smaller microscopic features. These new metal dots also contain unique or small batch encoded variable information such as text or numerals or bar codes to distinguish small individual batches. The variable identification can be incorporated as apertures entirely through the holographic microdot as per previous work or as controlled depth indentations or a mix of both.

The methods envisaged are as follows ....

The source of the diffractive relief pattern is an embossed plastic sheet containing an embossed surface relief made by thermal embossing or UV casting. The plastic micro- structured surface can be made as a reel for larger volume production in reel to reel embossing.

A thin conductive metal layer is added to the surface of the plastic surface relief profile using again low cost high volume processes, envisaged as reel to reel metallising. This will be patterned and then used to grow as a copy the final metal microdots, The thin conductor overlaying the plastic surface is then patterned to incorporate the individual information for each batch. The patterning can be performed with a thin layer of photoresist coated as is known in the art and thermally cured if needed. Light exposure (typically UV) of the photo resist through a high resolution film work mask containing the graphics for the shapes and individual data for the microdots. Then remove unexposed resist with developer leaving a selected patterning over the plastic holographic surface and the thin metallic conductor. Remove the residual mask material by flood exposing the remaining resist mask with (generally) UV light and then removing this with resist developer. T he precursors to final encoding process is to form galvanically sheets using a high temperature metal that can be electroplated using the shaped silver conductive areas as plating targets for growth or other encoding methods.

The encoding is done via a number of methods including a novel 'reverse electro-plating process' as detailed herein. The types of high temperature metals envisaged are nickel, nickel alloys with harder metals such as chromium. The plastic holographic plate would impart the desired holographic surface relief to the structure whilst the conductive patterned layers, containing the shape of the individual microdots and their individual coding will be retained within the patterned shape of the conductive layers which will be copied.

It is envisaged that the hard metal layer will be grown to a thickness of preferably between 5 and 15 microns (outer limits 3 to 25 microns). An alternative production route can use also novel features based on vacuum metallization and subsequent patterned removal.