HK1233461B - Method of forming a marking on an article, and an article having a mark thereon - Google Patents

Description

Method of forming a mark on an article and article having a mark thereon

Technical Field

The present invention relates to a method for applying a marking to an article and an article having a marking applied thereon, and in particular to a method for applying a marking to an article and an article formed of a ductile material having a marking thereon.

Background Art

The marking of items is very important for security, theft prevention and anti-counterfeiting purposes. Especially in relation to jewelry items, marking is of the utmost importance in this regard.

However, since jewelry items are generally items of ornamentation, such jewelry items should have markings that are relatively independent and do not interfere with the aesthetic qualities and properties of the jewelry item, and as such, the markings should be very small and non-obtrusive.

Typically, jewelry items are formed of metal materials such as gold, gold-based alloys, precious metals, etc., and markings for identification purposes, security purposes, and anti-theft and anti-counterfeiting purposes are applied to the metal bodies of the jewelry items.

For integrity purposes, the marking must not be easily replicable or easily removable, and must be constructed so that when such a marking is read, there is a high degree of confidence that it is indeed the original marking and therefore identifying the correct jewelry item.

While serial numbers and unique designs/logos have been used in recent years for identification purposes and applied by various means such as engraving, etching or stamping, these are often easily replicable and do not necessarily provide the level of security required.

Furthermore, the application of such markings to jewelry items can be time consuming and inconsistent, thereby reducing confidence as to whether an item bearing such a marking is indeed an original item or whether the marking is indeed original.

Summary of the Invention

Purpose of the Invention

It is an object of the present invention to provide a method of marking an article and an article having a marking applied thereto by such a method which substantially overcomes or ameliorates at least some of the disadvantages associated with the prior art.

Technical Solution

In a first aspect, the present invention provides a mold for imparting a marking to an outer surface of an article formed from a ductile material, the marking comprising an essential optical element having 2.5 dimensions (2.5D), the mold comprising:

a marking surface for imparting the marking to an outer surface of the article by localized plastic deformation of the material forming the article when the mold and the article are urged against each other, the marking surface comprising a microstructure formed by an arrangement of a plurality of micrometer-sized concave or convex entities;

The entities are arranged in a predetermined arrangement relative to one another, and the entities are arranged to have a 2.5-dimensional (2.5D) microstructure, wherein the entities are arranged in an inverse arrangement with respect to necessary optical features to be formed on a surface of the article, and the entities are arranged to provide one or more recesses extending in a direction from the marking surface into the mold;

wherein the one or more recesses are sized and shaped to impart an optical element to the article upon deformation of the ductile material when the mold is pushed against the article to conform to the surface of the multi-micron sized concave or convex entity; and

wherein the ductile material plastically deforms and is pushed into and conforms to the one or more recesses, wherein the deformation and flow of the ductile material into the recesses reduces lateral stresses imparted to the mold adjacent the recesses, and wherein the ductile material pushed into the recesses forms a portion of the material having a solid optical element having two and a half dimensions (2.5D) due to the deformation of the ductile material.

In an embodiment, wherein the entities are arranged in a periodic arrangement with a predetermined period, when the optical element is imparted to the article, upon exposure to light, light of a predetermined wavelength is reflected by the optical element such that the optical element is visible with an enhanced color effect of said wavelength.

The entities may be arranged in a predetermined geometric relationship such that the optical element imparted to the article includes the indicia therein.

In another example, the entities may be arranged in a predetermined arrangement such that light of predetermined wavelengths and angles of incidence reflects from optical elements imparted to the article in a manner that provides the projected holographic representation.The entities include entities that may be arranged randomly and irregularly distributed.

In a second aspect, the present invention provides an article formed of a ductile material, the article having indicia formed on an exterior surface of the article, the indicia including essential optical elements having 2.5 dimensions (2.5D), the indicia comprising:

A microstructure formed by an arrangement of a plurality of micrometer-sized concave or convex entities, the entities being arranged in a predetermined arrangement relative to one another, and the entities being arranged to have a 2.5-dimensional (2.5D) microstructure,

Therein, an arrangement of a plurality of micron-sized concave or convex entities provides a marking comprising an optical element.

The entities may be arranged in a predetermined arrangement in at least one direction, and the entities may be arranged in a periodic arrangement with a predetermined period, such that upon exposure of the optical element to light, light of a predetermined wavelength is reflected by the optical element such that the optical element is visible with an enhanced color effect of the wavelength.

The entities may be arranged in a predetermined geometric relationship such that the optical element article includes the indicia therein.

The entities may be arranged in a predetermined arrangement such that light of a predetermined wavelength and angle of incidence is imparted to the article in a manner that provides the projected holographic representation.

Entities can be arranged randomly and irregularly distributed.

The article is preferably formed from a metal or metal alloy, preferably gold or a gold-based metal.

Preferably, the article is an article of jewelry and the optical element preferably provides an identification mark of the article.

In a third aspect, the present invention provides a method of applying a marking to an article formed from a ductile material, the marking comprising an optical element, wherein a mould according to the first aspect is urged against an outer surface of the article such that the optical element is formed by an inversion of the arrangement of the entities of the mould.

In a fourth aspect, the present invention provides an article having a marking comprising an optical element thereon, wherein the optical element is imparted to the article by a method according to the third aspect.

Preferably, the article is formed from a metal or metal alloy, and more preferably the article is formed from gold or a gold-based metal.The article is preferably an article of jewellery.

Preferably, the optical element imparted to the article provides an identification mark for the article.

In a fifth aspect, the present invention provides a process for forming a mold for imparting necessary optical elements to the surface of an article, the mold having a marking surface comprising a microstructure formed by a matrix (lattice) of a plurality of discrete micron-sized concave or convex entities, the entities being arranged in a predetermined arrangement relative to each other, and the entities being arranged to have a microstructure of at least 2.5 dimensions, and the entities being arranged in an inverted arrangement with respect to the necessary optical elements to be formed on the surface of the article, wherein the mold is formed by microfabrication technology, preferably including photolithography and ion beam micromachining technology.

In an embodiment, the entities may be arranged in a periodic arrangement.

The entity can be formed into a 2.5D structure.

In a sixth aspect, the present invention provides a mould when formed according to the process of the fifth aspect.

In a seventh aspect, the present invention provides a method of providing an optical element to an article, the method comprising the steps of:

(i) providing a mold according to the first aspect, and

(ii) applying molten material to the mold by a casting process.

In an eighth aspect, the present invention provides a method of providing an optical element to an article, the method comprising the steps of:

(i) providing a mold according to the first aspect, and

(ii) The article to which the optical element is to be applied is pushed against the die by a forging process.

In a ninth aspect, the present invention provides a method of providing an optical element to an article, the method comprising the steps of:

(i) providing a mold according to the first aspect, and

(ii) The article to which the optical element is to be applied is pushed against the mould by means of a stamping process.

In a tenth aspect, the present invention provides an article carrying an optical element thereon, wherein the optical element is applied to the article by a method according to any one of the seventh, eighth and ninth aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that a more accurate understanding of the invention described above may be obtained, a more particular description of the invention briefly described above will be provided by reference to specific embodiments of the invention illustrated in the accompanying drawings. The drawings presented herein may not be drawn to scale, and any reference to dimensions in the drawings or in the following description is specific to the disclosed embodiments.

FIG1 depicts a schematic diagram of the effect of a 2.5D microstructure as used in an embodiment of the present invention;

FIG2( a ) depicts a photomicrographic representation of a mold as used in an embodiment of the present invention at a magnification of 20X;

FIG2( b ) depicts a photomicrographic representation of a mold as used in the embodiment of FIG2( a ) at a magnification of 50X;

FIG2( c ) depicts a photomicrographic representation at 20X magnification of a 24K gold article having the markings from the molds of FIG2( a ) and FIG2( b ) impressed thereon;

FIG2( d ) depicts a schematic representation of a method for viewing the markings of FIG2( c );

FIG3(a) depicts a typical 2D structure for reference in relation to FIG3(b) to FIG3(f).

Figures 3(b) to 3(f) depict cross-sectional schematic representations of examples of 2.5D structures for use in molds for transferring 2.5D microstructured optical elements to articles according to the present invention;

4( a ) to 4 ( c ) depict schematic representations of a process for transferring an example of a 2.5D microstructured optical element to an article;

5( a ) to 5 ( e ) depict schematic representations of a process for producing an example of a 2.5D microstructured mold by micromachining techniques;

6( a ) and 6 ( b ) depict schematic representations of a casting process for imparting optical elements to a material using a die having a 2.5D surface microstructure;

7( a ) to 7 ( e ) depict schematic representations of a forging process for imparting 2.5D optical elements to the surface of an article;

Figures 8(a) and 8(b) depict schematic representations of a stamping process for imparting 2.5D optical elements to a surface of an article; and

FIG9( a ) shows a cross-sectional side view of a schematic representation of an article having multi-level marking according to the present invention;

Figure 9(b) shows a top view of the article of Figure 9(a); and

Figure 9(c) shows a schematic representation of the article of Figures 9(a) and 9(b) in a cross-sectional side view through line F-F of Figure 9(b).

DETAILED DESCRIPTION

Embodiments of the present invention provide for marking jewelry items with optical elements, which may utilize molds, stamps, dies, punches, etc., wherein patterns or indicia are formed for imparting a mark to an item, such as a jewelry item formed of gold, a gold-based alloy, a precious metal, etc.

In particular, embodiments of the present invention provide a mark within a ductile material from which an article is formed, such that the mark is formed on the surface of the article by providing an arrangement of microstructures in a mold for marking the article, such that the arrangement of the microstructures allows a stamping or punching process, such that a reversal of the arrangement of the microstructure arrangement is allowed.

In other embodiments, the present invention provides materials that provide optical elements to an article through a casting process or a forging process.

In the present invention, the microstructure is formed by a matrix of entities that are sized and arranged in a predetermined manner, and that may be regular or irregular, so that the marking formed on the surface of the jewelry item is an optical element.

The optical element is configured so as to generate a predetermined optical effect depending on applicable and predetermined lighting conditions.This optical effect provides an identification effect so that the jewelry item can be identified as the item it represents.

Thus, the present invention provides the use of an optical element for marking jewelry or decorative items formed from gold or a gold-based material for:

- assess the authenticity of jewelry items or decorative items,

- identification of jewelry items or decorative items,

- certify the origin of jewellery or decorative items,

- secure identification of jewelry items or decorative items, and

- Protection of jewelry items or decorative items against counterfeiting and theft.

The use of the present invention for forming optical elements on the surface of jewelry items or decorative items formed from ductile materials provides advantages over existing marking techniques used to mark such items.

In particular, the present invention provides for marking ductile materials with optical elements having a 2.5-dimensional (2.5D) microstructure and a process for making a mold having such a microstructure.

2.5-dimensional (2.5D) arrangement of the present invention

As provided by the present invention, markings formed by micro-entities on an article from a mould or stamp are provided by a stamping process.The material from which the article is formed is a ductile material, such as a metal alloy, for example gold or a gold alloy.

The mould or die is formed with a marking surface by localised plastic deformation of the material from which the article is formed, the marking surface having a surface area for imparting a marking to an outer surface of the article.

The marking surface comprises a microstructure formed by a matrix of a plurality of discrete micron-sized concave or convex microentities.

The entities are arranged in a predetermined arrangement relative to each other, and the micro-entities are arranged to have a 2.5-dimensional (2.5D) microstructure, and the entities are arranged in an inverted arrangement with respect to necessary optical elements to be formed on the surface of the article.

Within the predetermined arrangement of the micro-entities of the mould, recesses or rebates, which may also be considered as concave portions, are provided which are defined by the adjacent material forming the mould or stamp.

The recess or notch extends into the mold or stamp in a direction opposite to that against which the mold or stamp is urged when applying the marking to the ductile material so that the ductile material flows into the recess or notch when the mold or stamp is urged against the ductile material to form the marking.

The recess or notch does not have any laterally extending "undercuts" so that material pushed into the recess or notch and formed into a shape defined by the geometry of the recess or notch is not damaged when the mould or stamp is subsequently removed from the marked article.

Thus, the mark formed in the ductile material is a 2.5D microstructure and the ductile material pushed into the recess or notch forms part of the mark consisting essentially of a 2.5D arrangement of microentities, which can be considered to be the inverse of the arrangement of microentities of the mold or stamp.

In the prior art, stamping dies used to mark ductile materials such as gold have very low lifespans, typically having a useful life of less than 100 cycles. Such dies degrade or crack due to stresses in the die from the stamping process, which can lead to inconsistent markings and the cost of replacing the die, potential complications in forming the die exactly the same, delays in production, and increased uncertainty about the originality when, for example, a marked item is evaluated using a marked master copy.

As will be understood by those skilled in the art, when fine details are required for the formation of complex geometries, the portion of the mold that imparts the pattern to the micro-entities is exposed to high loads due to the loads required to plastically deform ductile materials such as gold or gold-based materials. Consequently, localized stresses applied to the micro-entities of the mold can lead to failure of the mold.

In particular, at a portion of the mold that is smaller than other portions of the mold, excessive stress applied to such small portion can lead to failure of the mold.

Thus, by providing stress relief features to markings as provided by the present invention, the inventors are able to provide a mold for repeatedly imparting markings comprising optical elements to the surface of an article formed of a material such as gold or a gold-based material, which mold:

(i) provide a 2.5D marker including optical elements suitable for security purposes, and the advantages associated therewith as discussed further below, and

(ii) providing a mould which is capable of withstanding localised stresses during marking of the article, and the advantages associated therewith as discussed further below.

By including recesses or notches in the mould or impression according to the present invention, the inventors have been able to eliminate the disadvantages and drawbacks of the prior art by providing recesses or notches which allow the material to flow in the necessary direction in a controlled manner, which eliminates stresses during the impression process and reduces the stresses applied to the mould transversely to the direction of movement when the mould and article are pushed towards each other.

Furthermore, as will be described further below, a marker or micro-entity having a 2.5D structure also provides an enhanced optical effect of the marker, which can be used in the identification process.

Furthermore, the present invention allows for more complex markings to be applied to articles, providing enhanced anti-counterfeiting properties.

Thus, the present invention provides advantages over the prior art from both a manufacturing and end product perspective.

The invention is particularly useful for marking gold or gold-based articles, such as jewellery or decorative items, whereby consistency of marking and difficulty of imitation are important, as well as being small enough to be concealed and not detract from the overall optical properties of the article.

The 2.5D arrangement can be used according to the present invention for irregular or regular arrangements of micro-entities. Thus, the present invention includes the following two embodiments of optical elements as given ductile materials by means of a 2.5D mold:

(i) a holographic effect , in which embodiment a predetermined arrangement of micro-entities is formed in a mold such that when the arrangement is imparted to an article and illuminated with a light source of a predetermined wavelength, light is reflected from the article such that a holographic effect is projected onto an adjacent viewing panel,

(ii) periodic or quasi-periodic arrangements , whereby optical elements can be applied to the surface of an article having a periodic arrangement extending in at least one direction. Such elements can be viewed with and without the aid of a microscope under white light or under specific predetermined lighting conditions as discussed below, and

(iii) Non-periodic arrangements , whereby optical elements can be applied to the surface of an article having a non-periodic arrangement and such elements can be viewed with or without the aid of a microscope and using specific lighting conditions.

The above three embodiments of the use of the 2.5D mold according to the present invention are discussed in detail below, as well as the advantages as provided by the 2.5D mold of the present invention.

General Background Description of Some Embodiments of the Invention

By way of background and with reference to FIG. 1 , there is shown a schematic diagram of the manner and function of implementing a 2.5D microstructure as used in accordance with some embodiments of the present invention when imparting a pattern or marking to an article 100 .

When a plane wave of wavelength λ is incident normally (which in this example is normal to the regular periodic arrangement with the grating), each 2.5D microstructure acts as a quasi-point source from which the reflected light propagates in all directions.

After light interacts with the grating, the diffracted light is composed of the sum of the interfering wave components emanating from each slit in the grating. Due to the phase changes at different points caused by the path length difference of each slot in the grating, the light intensity increases or decreases from each other to generate peaks and troughs.

When the path difference between the light from adjacent slits is equal to half a wavelength, λ/2, the waves will cancel each other to produce a point of minimum intensity. Similarly, when the path difference is λ or an integer multiple of λ, the phases will add together and a maximum will be produced.

For a given angle of incidence α, a maximum occurs when a relationship known as the ideal grating equation mλ = d(sinα±sinβ) is satisfied, where m is the diffraction order and d is the grating period.

As shown in FIG. 1 , when incident light includes two monochromatic beams having wavelengths λ1 and λ2 , thereby schematically representing a 2.5D microstructure, the resulting diffraction angles β1 and β2 are different and wavelength-dependent dispersion of light occurs.

The efficiency of the grating is related to the period d, widths w1, w2, and heights h1, h2. By changing these parameters, the grating efficiency can be adjusted.

The mold formed according to the present invention has a microstructure that can be formed by a matrix comprising a plurality of micro-sized entities, which can be protrusions, recesses, or a combination thereof. The micro-entities can be arranged in a regular or irregular arrangement to form optical elements used in the embodiments described above.

Examples of holographic optical elements - irregular arrangement

Referring to Figures 2(a) through 2(d), the present invention can use molds that form 2.5D microstructures to impart optical elements to articles, such as jewelry articles formed from gold or gold-based materials. The optical elements can reflect light, making visible a holographic image that can serve as an anti-counterfeiting mark. In other embodiments, depending on the holographic requirements, 2D structures or portions thereof can be used. However, the incorporation of the 2.5D aspects of the present invention, as discussed in further detail below, provides advantages for using such molds. Such 2.5D features incorporated into the mold provide stress relief and flow of the ductile material forming the article during the stamping or marking process.

By suitable MEMS fabrication techniques, patterns can be formed in a hard material such as nickel or a nickel alloy as mold 201, as shown at 20X magnification in FIG. 2(a) and at 50X magnification in FIG. 2(b).

When forming the mold 201, in order to obtain a clear and non-distorted projected holographic image of the mark as discussed below, the pixel size utilized in forming the mold 201 should be as small as possible, and sizes less than 1 micron are preferred. In addition to pixel size, a larger pixel density is preferred.

When designing the layout of pixels representing micro-entities formed in the mold 201 , a holographic pattern is generated through complex optical theory calculations.

As will be mentioned in Figures 2(a) and 2(b), there are only a number of points with an irregular distribution that form a fingerprint-like pattern. This pattern is very difficult to replicate, which leads to the increased security aspect of the present invention. The pixel distribution as utilized in this example will be observed to be completely and completely random.

To mark an article, as shown in Figure 2(c), a mold 201 including the patterns of Figures 2(a) and 2(b) is pushed against the outer surface of an article 202 formed of a suitable ductile material such as gold, a gold-based alloy, a precious metal, etc., and the material is cold worked so as to provide an inverted representation of the pattern of the mold in the article 202.

In other embodiments, other methods of applying a pattern to article 201 may be implemented as discussed below without departing from the invention and may also be applied to the present embodiment.

After a short pressing duration, the mold 201 and the pressed article separate, and features of the pattern are transferred from the mold 201 to the pressed article 202, as shown in Figure 2(c).

The marking can be applied by an automatic press, such as a pneumatic or hydraulic press. Alternatively, a manual press, such as a pneumatic or hydraulic press, can be utilized. In this manual process, the duration for marking the material is only a few seconds or so.

As will be mentioned, the pattern on the article 202 of Figure 2(c) appears random and non-uniform without any optically distinguishable pattern or features, and the indicia itself is not geometrically represented on the article.

As schematically shown in FIG. 2( d ), to view the holographic image, a light source 220 is directed toward a pattern 210 on the article 200 , and the light is reflected toward a viewing panel 230 , on which a predefined pattern 240 can be viewed.

Referring to the pattern as imparted to the article as shown in FIG2( c ), the pattern is designed so that a holographic image can be projected, whereby both the necessary wavelength and angle of incidence for viewing the marking are determined during the design process of the pattern, and for this example, 532 nm green light is used with a 10 degree angle of incidence in order to project the holographic image.

It should be noted that other wavelengths and angles of incidence may still be used to view images from the markings on the article, however the difference will be the sharpness of the projected pattern size.

In a mold used to form such markings, the micro-entities may have a height of 3 microns or less, which can be used to form a pattern suitable for projecting a holographic image.

Both wavelength and angle of incidence affect diffraction efficiency and thus pattern quality. Wavelength also affects the size of the projected pattern. Projection of the pattern does not require particularly specialized equipment and can utilize a coherent light source such as from a laser pointer.

The secret or unique identification mark applied to the article is unique and has a very high degree of difficulty for a third party to reproduce, as it requires a complex theoretical design incorporated into the pattern formed in the mold that is then imparted to the gold article. As such, this technique provides excellent anti-counterfeiting protection.

Regular arrangement of micro-entities - periodic or quasi-periodic

According to the present invention, a 2.5D mold can be formed with a regular arrangement of micro-entities in a periodic or quasi-periodic arrangement, for example, by a die-stamping process, in the inverse of the structure to be imparted to an article formed of a ductile material, such as gold or a gold-based material. Alternatively, as discussed below, the arrangement can be imparted to the article by a forging or casting process.

When arranged in a regular arrangement and a geometric shape is imparted to the article (such as a periodic or quasi-periodic arrangement), the diffracted light has an interference effect so that the marked part of the article has an enhanced color effect, which can be illuminated by a white light source or a light source of a predetermined wavelength.

In such embodiments, the mold comprises micro-entities arranged to form optical elements that may be configured in a predetermined arrangement and may also be formed so as to define a predetermined pattern, such as indicia, when imparted to an article.

This can provide unique and difficult to replicate lighting effects, which can also be combined with markings or pattern effects.

According to an embodiment of the present invention, the optical element is applied to an article formed of a ductile material such as gold or a gold-based material, for example, by a cold die-stamping process, whereby the optical element is imparted by a mold having the optical element inverted therein.

In an example of a regular arrangement, the mold includes a periodic grating arrangement formed by microstructures, whereby the entities are arranged in a predetermined spatial arrangement so that when the mark is imparted to a ductile material such as gold, the inverse of the grating effect is imparted to the surface of an article formed from gold, etc., thereby applying an optical element thereto.

Periodic microstructures can change the properties of a surface, and in this application this can be achieved using diffraction gratings.

Due to the wavelength-dependent reflection, diffraction gratings can be utilized in order to display colored patterns and can thus be used to improve the appearance of an article, or to provide optically recognizable effects, as described with reference to FIG. 1 .

Furthermore, the diffraction grating can comprise different patterns which can function as anti-counterfeiting or identification markings, for example by markings. Thus, in addition to the entities arranged in a periodic arrangement, the matrix can also be arranged in a pattern so that markings are imparted to the gold object.

The implementation of periodic microstructures on objects, such as jewelry items, can be achieved in a mass-producible and cost-effective manner.

In such an arrangement, the period of the microstructures may be around 10 microns and their depth down to below 1 micron in order to provide applicable light effects according to the present invention.

The layout of this example includes the following:

(i) Optical viewing - In a first arrangement, the entity is arranged so that a grating effect is provided by the optical element which allows the optical element as a marking on the article to be distinguished by the naked eye under visible light (e.g. under daylight or fluorescent conditions, as well as such white light conditions).

In this arrangement, the indicia can be visually identified for authentication purposes and specialized equipment is not necessary or required for viewing the indicia.

In such an arrangement, a color effect may be imparted to the article, which optionally in combination with a specific marking, provides a unique identification mark for a gold or gold-based article of jewelry or ornamentation.

(ii) Other viewing means . In other arrangements, the optical element may include a specific pattern, such as a marking that is only observable under a certain range of wavelengths of light, and only in this case is this hidden marking visible.

In such an arrangement, special devices or equipment are necessary and require means for identification and their authentication.

This arrangement can be used to provide a unique identification mark for a gold or gold-based item of jewellery or ornamentation and provides increased security and difficulty in copying and counterfeiting.

As will be appreciated by those skilled in the art, the present invention may be used to provide metal jewelry items, particularly gold jewelry items, with intricate patterns that reduce the ability of unscrupulous persons to easily replicate such patterns.

In this embodiment, the microstructure forming the optical element imparted to a jewelry item or ornament formed of a gold material is 2.5-dimensional (2.5D) and provides the optical element to the item as a marker for purposes including those described above.

Examples of periodic 2.5D arrangements of molds of the present invention

As shown in FIG. 3( a ), a typical 2D structure 300 a including a protruding structure 311 a is depicted, which is used for reference in connection with FIG. 3( b ) to FIG. 3( f ), wherein a 2.5D structure for a mold for transferring optical elements to a deformable material is depicted and described in FIG. 3 ( b ) to FIG. 3 ( f ).

With reference to Figures 3(b) to 3(f), examples of schematic representations of 2.5D microstructures of a mold for transferring optical elements to an article according to embodiments of the present invention are depicted. Such a mold includes such microstructures to provide recessed portions or microstructures according to the present invention, which allow for flow of a deformable material therein. The use of such a mold of Figures 3(b) to 3(f) in providing optical elements as indicia is further discussed below with reference to Figures 4(a) to 4(c).

As shown in FIG. 3( b ), a concave microstructure 312 is provided on top of a convex structure 311 b of a microstructure 300 b .

In the example of FIG. 3( c ), a concave structure 314 is provided at the bottom of the convex structure 311 c of the microstructure 300 c .

An example of FIG. 3( d ) is provided, which has a concave structure 315 at the bottom of a convex structure 311 d of a microstructure 300 d .

An example of FIG. 3( e ) is provided, which is provided with a concave structure 316 at the bottom of a protruding structure 311 e of a microstructure 300 e , and with a protruding structure 317 at the top of the protruding structure 311 e of the microstructure 300 e .

Referring to the example of FIG. 3( f ), concave structures are provided at the bottom 318 and top 319 of the convex structure 311 f of the microstructure 300 f .

Within the present invention, the concave structures 312, 314, 315, 316, 318, and 319 are provided according to the present invention. When a mold embodying such concave microstructures is utilized in forming an optical element in a deformable material, the present invention provides a relief structure, whereby the optical element can be a mark, pattern, or indicia according to the present invention. The manner in which such concave microstructures can be manipulated is further discussed below.

4(a) to 4(c), a process according to the present invention is depicted for forming a 2.5D microstructure in a ductile material 421. In this example, the 2.5D microstructure of FIG3(e) is used for illustrative purposes.

As shown in FIG4(b), during the molding process, the material is pressed and squeezed to conform to the protruding structures 411 and the concave structures 415 of the mold 400, wherein the ductile material 421 is pushed into the concave structures 415. The mold 400 can be considered similar to the example of the mold shown and described with reference to FIG3(d).

After removing the mold, on the surface, the material of the article forms small protrusions 422 corresponding to the concave structures 415 on the major protrusions 423 as shown in Figure 4(c), and the 2.5D pattern is then transferred from the mold 400 to the molded article.

As will be seen, ductile material 421 is urged into concave structure 415 where it is urged to flow and extend in a direction towards mold 400 as shown by protrusion 422 .

By providing this feature according to the present invention, ductile material 421 is allowed to flow in a vertical direction toward mold 400, so that ductile material 421 does not flow in a horizontal direction transverse to the direction in which mold 400 moves relative to ductile material 421, which can lead to damage to mold 400, which in turn leads to mold degradation and reduces dimensional accuracy and the reproduction of markings, patterns, or indicia, which reduces the consistency and necessity of mold replacement. As mentioned below, prior art molds have a low life cycle, typically less than 100 uses due to degradation and failure.

In addition to other advantages as set forth and discussed below, providing such a relief feature as provided by the present invention also has the effect of placing less stress on the mold 400 during the process of imparting markings, patterns, or indicia to an article formed from the ductile material 421, which has the technical effect of increasing the life of the mold and enhancing the repeatability of the markings, patterns, or indicia applied to the article. Other technical advantages of a 2.5D mold that provides such a feature that allows the ductile material 421 to flow in a vertical direction, as provided by a mold according to the present invention, are discussed further below.

2.5D mold and mark, pattern or mark of the present invention

This advantage can be applied to regular 2.5D microstructure molds as shown in Figures 3(a) to 3(f) and Figures 4(a) to 4(c), as well as irregular 2.5D microstructures such as those used in embodiments of holographic representation applications as described with reference to Figures 2(a) to 2(d), and other irregular 2.5D microstructures.

According to the present invention, the topography of the microstructure arrangement does not necessarily need to be defined by only vertical and horizontal surfaces, but may include curved or contoured surfaces. However, in order to provide features that allow the ductile material to flow in a direction away from the surface of the article formed from the ductile material or having a layer of ductile material, it is necessary that the concave structures do not have "undercuts" so that the mold can be easily removed from the ductile material after the mark, pattern or indicia is formed in the ductile material.

As will be appreciated, while the examples above present molds depicting sharp corners and only completely horizontal and vertical surfaces, there may be a small amount of curvature at the intersection of the horizontal and vertical surfaces. Furthermore, the surfaces do not necessarily need to be precisely horizontal and vertical, and as long as a 2.5D microstructure is provided that provides the necessary functional properties (including any necessary optical properties) for a mark, pattern or marking applied to an article, and a relief structure that allows vertical flow of ductile material, a mold for providing a mark, pattern or marking, a mark, pattern or marking applied to an article, and an article supporting such a mark, pattern or marking are provided. Furthermore, the microstructure may be multi-layered and not necessarily have parallel depth or protrusion properties. Thus, any combination of microstructures including concave relief portions is considered to fall within the scope of the present invention.

Example of manufacturing the mold of the present invention

There are several ways in which a mold according to the present invention can be made, and examples of these are provided.

5( a ) to 5 ( e ), a process for forming a 2.5D mold 500 for disposing optical elements in a ductile material according to the present invention by microfabrication techniques is depicted.

5(b), a photoresist 520 is coated on the surface of the material forming the mold 500. The mold 500 is preferably formed of a hard material such as nickel or a nickel alloy.

In FIG. 5( c ), the photoresist 520 undergoes an exposure process through a conventional photomask or through direct writing techniques (including laser, electron beam, etc.).

After the exposure process of FIG. 5( c ), as depicted in FIG. 5( d ), the surface of the mold 500 is etched to a necessary depth.

After the etching process of Figure 5(d), as depicted in Figure 5(e), the photoresist 520 is then removed via, for example, ion beam technology, and small features including both protruding and recessed structures can be generated in the surface of the mold 500, where the mold is formed similarly to the mold depicted in Figure 3(b).

6( a ) and 6( b ), as described with reference to FIG. 5( a ) to FIG. 5( d ) and in accordance with the present invention, a casting process may be used in conjunction with mold 600 to form optical features in a material using a mold having a surface periodic or non-periodic 2.5D microstructure.

Molten material 610 is injected into the mold body 615, and the 2.5D structures on the surface of the mold 600 are filled with the molten material 610. This molten material 610 can be any material that can be suitable for applying optical elements to an article.

To ensure the flow of molten material 610, a mold 600 similar in geometry to that of FIG3(b) may be heated to a sufficiently high temperature. After cooling and solidifying the molten material 610, the 2.5D structure is transferred from the mold 600 to a cast object 630 as shown in FIG6(b).

7( a ) to 7 ( e ), by depicting a die formed by the die 700 and having a surface periodic 2.5D microstructure, optical elements are applied to materials 720 a , 720 b , 720 c through a forging process using the die 700 as described with reference to FIG. 5 ( a ) to FIG. 5 ( e ).

Sufficiently ductile material 720a, 720b, 720c is placed on the die and then pressed. This configuration can be open forging in FIG7(a), closed forging in FIG7(b), or flash forging in FIG7(c). Due to the pressure, the material on the surface will deform to conform to the die surface as shown in FIG7(d), thereby transferring the 2.5D structure to the forged object as shown in FIG7(e).

8(a) and 8(b), a stamping process is depicted using a stamp having a surface periodic 2.5D microstructure. The stamp is a stamp of the mold described with reference to FIG5(a) to FIG5(d).

As shown in Figure 8(a), a stamp 800 having a surface 820 covered with 2.5D microstructures is pressed onto an article 820 to which an optical element is to be applied.

7( a) to 7( e), the material 820 is pressed and deformed into a shape conforming to the surface of the stamp 800. In this way, the 2.5D microstructure 820 is transferred to the stamped article 820 as shown in FIG8( b).

In additional or alternative embodiments, the mold may be formed by laser direct writing techniques or by photoresist/LIGA techniques without departing from the scope of the present invention.

Although the above examples refer to periodic 2.5D structures, according to the present invention, non-periodic 2.5D structures can be imparted to articles in a similar manner.

9a, 9b and 9c, a schematic representation of a multilayer structure is formed in an article having multiple layers 900. As apparent, the micro-solid structure is an irregular, non-periodic arrangement whereby the article is marked with a mold having the inverse shape of the outline shown.

According to the present invention, such a mold includes recesses or notches that allow protrusions 902 and 904 to be formed as micro-entities without imparting excessive transverse stresses on the mold.

As will be understood by those skilled in the art, complex 2.5D patterns such as those used in holographic applications can be provided. Although the calculation of the topography and geometry of such a mold is complex, the appropriate necessary molds can be provided for reflection of light 906 in such applications.

2.5D mold advantages

The use of a 2.5D mold for forming indicia according to the present invention provides several advantages over the prior art, including:

(i) The 2.5D structure provides a "relief" feature in the mold, and so when used in a die or forging process, ductile material can flow into the relief space. This causes less stress to be imparted to the mold and thereby increases fatigue life cycle.

For anti-counterfeiting purposes, an identification mark such as that provided by the present invention must be difficult to replicate and must be consistent. Thus, by providing a high life cycle mold, as opposed to prior art impression molds that typically fail in less than 100 uses, the need to replace such molds is eliminated, thereby providing consistent marking for many items, thereby enhancing security by having a consistent mark of origin for the items.

Furthermore, such molds are relatively expensive to produce, and high life cycle molds provide additional cost benefits.

(ii) Moulds as provided by the present invention can be highly complex and difficult to replicate due to such complex geometric complexity and the 2.5D features used, and thus, high life cycle complex moulds offer increased benefits from a security and anti-counterfeiting perspective.

(iii) The 2.5D mould according to the present invention provides less damage to the article to be marked, with reduced local stress in the article, and the relief structure provides ease of stress reduction during cold working processes such as stamping.

As a result, the marking applied to the article is more consistent, which increases the ease with which the marking (and hence the article to which the marking is applied) can be originally identified and assessed.

(iv) Since reduced stress is induced in both the mould and the article during formation of the mark, this provides ease of removal of the mould which causes local damage and distortion of the mark, which also increases the ease of original identification and assessment of the mark (and therefore the article to which it is applied).

(v) Due to the reduced stress of the 2.5D mold, a mold of smaller size than that of the prior art can be provided, which provides the advantages that (a) more complex security marks can be formed on the article and (b) the increased difficulty of positioning hidden security marks can be obtained due to the reduced physical size.

Furthermore, when using 2.5D stencils in holographic applications as described above, increased clarity of the projected image can be produced, which increases the ease of original identification and assessment of the marking (and hence the item to which the marking is applied).

The new technology described above provides a mold for providing a security mark for metal articles, in particular gold or gold-based or other suitable precious metals forming articles (such as jewelry articles). The mark can be of very high precision and great complexity and is difficult to replicate.

The present invention provides an optical element for marking jewelry or decorative items formed of gold or a gold-based material for:

- assess the authenticity of jewelry items or decorative items,

- identification of jewelry items or decorative items,

- certify the origin of a jewellery item or decorative item,

- secure identification of jewelry items or decorative items, and

- Anti-counterfeiting and anti-theft protection of jewelry items or decorative items.

Claims (19)

1. A mold for affixing a mark to the outer surface of an article formed of a ductile material, the mark comprising necessary optical elements having 2.5-dimensional (2.5D), the mold comprising: A marking surface for imparting a mark to the outer surface of the article by means of localized plastic deformation of the ductile material forming the article when the mold and the article are pushed against each other, the marking surface comprising a microstructure formed by an arrangement of a plurality of micron-sized recessed or protruding entities; The entities are arranged in a predetermined arrangement related to each other, and the entities are arranged to have a 2.5-dimensional (2.5D) microstructure, wherein the entities are arranged in an inverted arrangement with respect to the necessary optical elements to be formed on the surface of the article, and the entities are arranged to provide one or more recesses extending in a direction from the marking surface to the mold. Wherein, the one or more recesses are sized and shaped such that: when the mold pushes against the article, the necessary optical elements are imparted to the article by the deformation of the ductile material, thereby conforming to the surface of the plurality of micron-sized recessed or protruding entities; The recess does not have any laterally extending undercut, ensuring that the ductile material pushed into the recess and forming a shape defined by the geometry of the recess is not damaged when the mold is removed from the article after the mark is formed; and Wherein, when the ductile material is plastically deformed and pushed into one or more recesses and coincides with the recesses, the recesses serve as stress relief features, wherein the deformation and flow of the ductile material into the recesses reduces the lateral stress imposed on the mold adjacent to the recesses, and the ductile material pushed into the recesses forms part of the ductile material due to the deformation of the ductile material imparting the necessary optical elements having 2.5 dimensions (2.5D). 2. The mold according to claim 1, wherein the entities are arranged periodically in at least one direction. 3. The mold according to claim 2, wherein the entities are arranged periodically at a predetermined period, such that when the necessary optical elements are applied to the article, light of a predetermined wavelength is reflected by the necessary optical elements when light is exposed to the necessary optical elements, making the necessary optical elements visible, thereby having an enhanced color effect of the wavelength. 4. The mold according to claim 3, wherein the entities are arranged in a predetermined geometric relationship such that the necessary optical elements of the article are included therein as markings. 5. The mold according to claim 1, wherein the entity is arranged in a predetermined arrangement such that light of a predetermined wavelength and incident angle is reflected from the necessary optical elements of the article in a manner that provides a holographic representation of the projection. 6. The mold according to claim 5, wherein the entity comprises entities arranged in a random and irregular distribution. 7. A method of applying a mark to an article formed of a ductile material, the mark including necessary optical elements, wherein a mold according to any one of claims 1 to 6 is pressed against the outer surface of the article such that the mark including the necessary optical elements is formed by an inversion of the arrangement of the physical form of the mold. 8. An article having a mark, the mark comprising necessary optical elements thereon, wherein the necessary optical elements are imparted to the article by the method according to claim 7. 9. The article of claim 8, wherein the article is formed of metal or metal alloy. 10. The article according to claim 8 or 9, wherein the article is formed of gold or a gold-based metal. 11. The article according to claim 8, wherein the article is a jewelry article. 12. The article of claim 8, wherein the necessary optical element provides an identification mark for the article. 13. A method for forming a mold according to any one of claims 1 to 6, the mold being used to impart necessary optical elements to the surface of an article, wherein the mold is formed by microfabrication technology. 14. The method of claim 13, wherein the microfabrication process includes photolithography and ion beam processes. 15. A mold formed by the method according to claim 13 or 14. 16. A method for providing necessary optical elements to an article, the method comprising the steps of: (i) providing a mold according to any one of claims 1 to 6, and (ii) Applying molten material to the mold through a casting process. 17. A method for providing necessary optical elements to an article, the method comprising the steps of: (i) providing a mold according to any one of claims 1 to 6, and (ii) The article to which the necessary optical elements are to be applied is pushed against the mold by a forging process. 18. A method for providing necessary optical elements to an article, the method comprising the steps of: (i) providing a mold according to any one of claims 1 to 6, and (ii) The article to which the necessary optical elements are to be applied is pushed against the mold through the molding process. 19. An article having necessary optical elements thereon, wherein the necessary optical elements are applied to the article by means of the method according to any one of claims 16 to 18.