CA1336779C

CA1336779C - Document

Info

Publication number: CA1336779C
Application number: CA000591661A
Authority: CA
Inventors: Gregor Antes; Christian Saxer
Original assignee: LGZ Landis and Gyr Zug AG
Current assignee: OVD Kinegram AG
Priority date: 1988-03-03
Filing date: 1989-02-21
Publication date: 1995-08-22
Anticipated expiration: 2012-08-22
Also published as: AU3084189A; JP2582847Y2; JPH026187A; JPH0966U; AU605026B2; EP0330738B1; EP0330738A1; DE3866230D1; HK24495A; US4984824A; ATE69407T1

Abstract

A document (1) is provided with a macroscopic structure (7) which is difficult to forge embossed into a substrate (3), said structure (7) being provided with an optically acting covering (4) and being protected beneath a protective cover (5). The structure (7) consists of several surface portions (8, 9, 10) which are defined by a microscopic relief structure (12, 12') and are different from each other under visual observation as a result of optical diffraction effects. Several of the surface portions (8, 9) measure less than .3 mm and can occur individually or in a row in the structure (7), whereby the distances between the surface portions (8, 9) measure less than .3 mm. The document (1) shows a pattern consisting of a mesh of dots and lines to the naked eye. An examiner viewing the document (1) through a magnifying glass will see the dots and the lines dissolve into characters, numbers and other graphic features. A device to produce a master structure for the shaping of a stamp used to emboss the document (1) is described here.

Description

~ _ 1 3 3 6 7 7 9 -~ocument The instant inventior1 rel~tes to ~ document with ~n optical-difraction safety element of the type mentioned in the introductory clause of claim l, usable a~ information on authenticity which i3 difficult to forge, especially for securities, identity papers, payment means and similar ob~ects to be protectedr and al.50 relates to a process for its m~nufacture.

It must not be poesible to duplicate documents. Modern documents ~re therefore provid~d with ~fety ~l~ments, for inst~nce auch which render information on the authenticity of the protected obJect visible even to an untrained layman through diffraction of the ~mbient light. Such 8 document and a process for its production is described in CH-PS (Swiss patent specification) 594 936.

Diffraction is obtained through embo~sed mesh effects with an optic~lly active coating which are wave-like straight-line relief structures in their simplest form. The diffruction properties of these relisf structures are determined, ~mong other factors, by the spatial frequency, i.e. the number of lines per millimeter, by the cross-section~l form of the relief structure ~nd by the differences in height within the relief structure as well as by the orientation of the relief structure on the document.

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- - ' ' ' , --1 3 3 6 7 7 9 LGZ-~6 The DE-OS (German publicly distributed printed copy of the application papers~ ~2 06 062 describes a certification device with - diffractillg structure which is composed of surface portions with varying structural parameters. Each individual surface portion is at least large enough so that light which falls on the certification device and is decomposed into its color components in a characterizing manner is recreated at a distance of 25 cm in form of a separate bundle of characterlzing colors at a solid all~le of at least 2 millir~diants, i.e.
approximately 7 minut:es of an arc. These surface portions are therefore e sy to recognize with the naked eye and stand out from adJoining surfaces through contrasting colors, or instance.

If the mesh p~r~eters ch~n~e continuously, or in small steps within the diffracting structure from surface portion to -~urface portion, color impressions moving along a predetermined path are crented on the document for the eye of the viewer when the position of the document in relation to the source of light and to the naked eye is changed. ~ocuments of this type are described in EP ~EuroEean patent) 105 Og9.

These documents can be produced economically by shsping a layer of synthetic material with an embossing stamp capable of being heated and supportirlg the negative of the safety element, said negative having been galvanically formed by a master structure.

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-The manner of producing this master structure is known from EP 169 326. A layer of synthetic material is elastically shaped in a small, circular zone by a matrix which supports a predetermined relief structure.
The surface facing the matrix is heated locally by means of a light bundle until the synthetic material is softened in a surface area limited by the light bundle and the relief structure is transferred to the surface.
A master structure produced in this manner can consist of a great number of surface portions which vary from their adjoining surfaces through their diffraction properties. Forgery is made much more difficult by the great number of surface portions diffracting in different ways.
The object of the instant invention is to create a document of the type mentioned initially, as well as a device for its production, with a structure which can be copied or forged only at great expense, which has lines and surface portions visible without any device through visual observation and with addi-tional graphic features that cannot be seen without a device.
A construction in accordance with the present invention comprises a document with an embossed macroscopic structure of large surface and acting through optical diffraction which is composed of numerous surface portions with predetermined relief structures with spatial frequencies of over 10 lines/mm, acting through optical diffraction, whereby the relief structure of each surface portion is different from those of the directly adjoining surface portions, characterized in that at least one group of the surface portions has a m~x;mllm dimension of less than .3 mm.
A process in accordance with the present invention comprises the production of a master struc-ture which serves to reproduce embossing stamps by galvanic means for the embossing of documents and which is produced on a support which is transparent to electromagnetic radiation in a thermoplastic cover layer absorbing an electromagnetic radiation, whereby the cover layer is shaped elastically by means of an unheated matrix having a predetermined microstructure which is applied with pressure and whereby the cover layer is softened up locally and briefly by the radia-tion which is focused through a surface and through the support on said cover layer so that local plastic deformation occurs and so that the micro-structure acting through optical diffraction is transferred as a permanent copy on the cover layer, characterized in that the surface of the matrix which is provided with the microstructure is pressed uniformly on the entire cover layer, in that the back of the matrix is borne upon by through a flexible intermediary layer by a pressure-producing means, in that essentially the entire surface of the cover layer is shaped elastically and in that the matrix is rotated around its axis, is laterally shifted or is replaced by a matrix with a different microstructure only after completion of the transfer of a predetermined number of surface portions.

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Embodiments of the invention are explained below through the drawing in which Fig. 1 is ~ schematic repre~entation of a docum-nt appll-d to an ob~ect to be protected, Fi~. 2 shows examples of surface portion~ of a diffr-cting structure, Flg. 3 ahow~ ~ vi8u~1 im~ge appear~nce of the document, Fig. 4 shows an enl~rged detail of a surface portion of Fig. 2 and Fig. 5 shows a dsvice for the production of a m~ster structure for these documents.

A document 1 is shown in Fig. 1, whereby part of document 1 is cut off for the sake of greater clarity. Surface 2 therefore shows document 1 in cross-section. The document 1 consists of substrate 3 with an optically active coating 4 and a transparent protective layer 5.

The optically active coating 4 i8 typically a thin metal or dielectric layer with a thickness in the order of 100 nm, but the :. , -, . ..
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-1 336779 L~2-~

optical effect can also be produced by a difference between the refractive index o the protective layer 5 and of the substrate 3 ~lone.

Substrate 3 can for example be a pl~stic 11m to ~e paAted on an obJect 6 to be protected. If the obJect 6 to be protected is a piece of paper, a film or a fabric, substrate 3 can also take the form of a plastic layer applied directly on this background by a printing method. If the ob~ect ~ to be protected is it~elf made of a ~-ynthetic materi~1, it c~n be used directly ~s su~strate 3, i.e. the document 1 ~nd the obJect 6 to be protected constitute an inseparable unit. Document 1 is difficult to forge or to copy and ~erves as a proof of authenticity for identity documents, payment means, securities~ documents, etc.

For example, a macrosco~ic ~tructure 7 acting through opticul diffraction is embo~sed by me~ns of a he~ted stamp before or after application of the optically effective coating 4 in the substrate 3. The wave length of the light used for the viewing of the diffraction effect and the selection of the materials for the substrate 3, for the optically acting coating ~ and for the protective layer 5 determine whether the structure 7 acting throuyh optic~l diffrnction is A phase or an amplitude mesh or whether structure 7 must be viewed in transmission or in .. .. . .
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1 336779 L~Z-46 reflection. A combination of both types of mesh and~or of both manners of VieWill9 iS also possible.

Structure ~ h~s ~ gre~t number of aurface portlon~ 8, ~, 10, wlth microscopic relief structures 12. An border 11 separates each surface portion 8, 9, 10 from the others, whereby the border 11 is only a means of describing the form-4 of the individual surface portions 8, 9, lO and to render them visible in the drawing. In re~lity, each of the surf~ce portions ~, g, 1~ is defined by the type and by the orientation of the relief structure 12. When the document 1 is viewed, the qurface portions 8, 9, 10 diferentiate themselves from each other through the shapes of their borders 11 and through their diffr~ction effects which are determined by the selection of p~rameters and by the orientation of the embossed relief atructure 12.

As an example, the relief structures 1~ can have cross-sectional configur~tions of known periodic functions with the spatial frequencies of o~er 10 lines per millimeter which are effective for the diffraction of visible light. Limits which are imposed by production imperatives restrict the pr~ctical, usable r~nge to approximately 2,500 lines per millimeter. But cross-sectional configurations with aperiodic functions containin~ loc~l spatial frequencies within that range, such as for example matte structures, Call however also be used. The difference in hei~ht of this relief structure 12 lies typically between 50 nm and 10,000 nm.

In an embodiment of document 1 according to Fig. 2, the surface portions 8 and 9 are ~urrounded by a surface portion 10 of structure 7. The surface portion 8 for example, i5 different from the ad30illing ~urface portions 9 only through their respective forms as delined by the border 11, while the surface portion 10 st3nds out from the two immediately adJoininy surface portions 8 and 9 through a relief structure 12' with different diffraction effects. Ths surf~ce p~rtion ~ or 9 could for inctance represent ~ number or some other fe~ture which is different from surface portion 10 because of the intensity and the color of the surface portion 10 when the document 1 is viewed.

A normally ~ighted human eye recognizes the ~eatures of surface portions 8 and ~ without ths use of any device, on condition that they appear under a viewing angle of somewhat over 1 minute of an arc. At the normal viewing distance to the eye of approximately 25 cm, the naked, normally sighted human eye therefore sees without difficulty if the details which define surfaces are at distances of over ;1 mm from each other. The dimensions of the surf~ce portions 8 and ~ themselves must thersfors be measursd in , . .
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1 336779 LGZ-4~

multiples of .1 Jnm So that their forms, representing a character for example, may be distinguiched.

If the largest dimen~lon of ~ aurface portion 8, g measures .3 mm or less, the naked human eye aees it at the normal viewing distance, dependin~ upon the degree of contrast, only s a ~hapeless point 13 <Fig. 3) on the document 1.

In Fig. 2, several surface portions 8, 9 are aligned in a row to a maximum height h, whereby the distance between the surface portions is less than .3 mm ~nd therefore less, at normal viewing distance, than the distance that would be necessary at the minimum viewing angle. To the naked eye, they form a line lg with a width b that is equal to the height h on the document 1.
If width b is le.~s th~n .3 mm, line 1~ is provided with an unobtrusive, formless border.

The surface portions ~, 9 can be 50 sm~11 th~t their surf~ces defined by border 11 can form a character, a number or some other graphically formed feature, for example, while the largest dimension in form of width b or height h does not exceed approximately .~ mm. Therefore the surface portions 8, 9, if they ~re ~een ~t .~ re perceived ~e dots 13 (Fi~. 3~ or lines 14.

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-1 336779 L~2-~6 With these dots 13 and these lines 14 as the mesh elements, it is posaible to con~titute macroecopic patterns 15 on the document 1 which are easily recognized by the n~ked eye, with no limits set to the designs of these patterns 15.

The naked eye distinguishes pattern 15 ~gain~t the ~ckground of the diffraction effects of structure 7 produced in the other surface portions 1~ only in ~ play of colors and luminosity dependent upon t~ iewing and illumination conditions ~nd determined by the diffraction on the relief structures 12, 12'.

For example, on document 1, in a model designed for a bank note, a national emblem is contained in every dot 13 and texts are contained in e~ery line 1~, whereby the latter give ~n indic~tion of the issuer or of tl,e face value. These additional data cun only be recognized when the diffracting structure 7 is viewed through a simple magnifying glass. With this device, an examiner c~n reco~niz~ _h~r~ct~rs, numbers or other fe~tures that ~re hidden in the dots 13 or in the lines 1~ and which thus give an assurance of the authenticity of the document 1.

For characters, numbers or features whose greatest dimension is less than .3 mm, stroke width s (Fig. 4) of less than 60 um in width sre required so that they may be properly formed. The surface portions 8, 9 are composed of circular surface elements .. .... .: ~

16 with a diameter s, equal to the finest ~troke width a'.
Greater stroke width s' muy be composed of the surface element 16 used for the finest stroke widths and overlapping each other, auch aa for ex~mple in the letter "i" in Fig. ~.

An identical orientation ~nd identic~l parameters of the relief atructure 12 in all ~urface portions 8, 9 which are different from the relief structure 12' of the surface portion 10 promotes e~e of recognition ~dv~nt~geously. The ex~miner ~rmed with a magnifying gl~ss recognizes such surf~ce portions 8, 9 of same color and same luminosity which stand out in color and luminosity from the surrounding surface portion 10.

A group of characters (Fig. 2) can be repeated -~everal times on one line 12. ~or example, group m4y spell out a sentence, whereby the aurface portiona 8, 9 diatinguiah themaelves for each word of the sentence through a different relief structure 12, so thot each word appears in a different color and with a different luminosity.

To mass-produce such documents 1 efficiently ~Fig. 1) the preferred embossing processes are those in which a heated emboaGing matrix plastically shapes the ~urface of substrate 3.

,. ' .. ,t~ ! . , ';, , ' ~ ' ', ;,, 1 3 3 6 7 7 9 LGZ-~6 To produce the embossing matrix, a master structure is advanta-geously made on a support 17 by means of a device shown in Fig. 5 and a negative i8 then taken galvanically from this master -~tructure to be then used as the embossing matrix. The device transfers one surface element 16 ~Fig. 4) after the other from an m~trix 18 which cannot be heated to a th~rmoplustic cover layer 19 of the support 17.

The device can consist for example of a r~diation source 20 emitting electromagnetic radiation 21, of a modulator 22 for the intenaity of the radiation 21, of a focusing means 23, of a ray deflection device 2~, of a rigid, flat surface 25 for the support 17 of the thermoplastic cover layer 19 and of a means 26 to press the matrix 1~ ag~inst the cover layer lg which is enclosed between itself and the support 17.

It is also possible to use the surface 25 directly as the support 17 of the cover layer 19, in order to avoid reflection losses on their common interface 27. The surface 25 must be easy to replace in that case.

The matrix 18 may be designed so as to be rigid or flexible and is provided with a microstructure 28 with ~n are~ of ~ few square centimeters in the surfa~e facing the cover layer 1g. In order to compensate for unevenness in the cover layer 19s and to ~, ., ~, - . -achieve uniform distribution of pressure of the cover layer 19, a 1exible mstrix 18 m~de of ~ thin metal film ia prefersbly u~ed.
A pre~sure-producing m~n~ 26 bears upon the b~ck of the mstrix 18 through ~ flexible intermediary layer 29.

The me~ns 26 pre~es the unheated m~trix 18 with its surfsc~
oupporting th~ microstructure 28 ~gainst the thermopl~stic cover lsyer 19 in ~uch manner that the microstructure 28 shapes the cover lsyer 19 elastically over the entire contsct surface.

The electrom~gnetic radi~tion 21 penetr~tes through the tr~napsrent surface 25 and through the tranapsrent support 17.
The focusing means 23 concentrates the electromagnetic radi~tion 21 into 8 foc~l point in the pl~ne of the thermoplsstic cover layer 19. The illumin~ted ~pot can b~ ~hifted in the plsne of cover layer 19 by me~ns of the ray deflection device.

Appropri~te means such ~s colorsntc or csrbon bl~ck abfiorb in the cover layer 19 the radiation 21 controlled in their intensity by mean~ of the modul~tor 22 and he~t the thermopl stic cover layer 19 locally at the illuminated spot. The cover layer 19 aoftenc within surfsce element 16 (Fig. 4), whereby the hest deflection effected by the support 17 (Fig. 5) and the matrix 18, the r~diation energy ~nd the duration of the action of the r~diation 21 determine the diameter g (Fig. 4) of the surface element 16.

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1 336779 LGZ-4~
The local pressure of the matrix 18 (Fig. 5) is sufficient to plaAtic~lly sh~pe the hot cover layer 19 locally. Controlled by ~uch devices as the r~y deflection device 22 for example, the illuminated spot in the cover l~yer 19 wander~ on, or the radiation 21 is switched off by the modulator 22. As soon ~s the radiation 21 no longer act- upon the surface element 16 (Fig. 4) the surface cover 19 (Fig. 5) solidifies once more and now has a permanent reproduction of the microstructure 2~ at that location.

A l~ser is used to advantage as the sourc~ of radiation 20. To reproduce the microstructure 28, the radiation 21 can be focused in the entire plane of the cover layer 19 precisely so that the illuminated spot warms the cover layer 19 in the surface element 16 ~Fig. 4), the diameter s of which me~asures less than 60 um.

By using the described device it i5 possible to produce stroke widths s' of less than 60 um, since no laterAl mechanical forces which could shift matrix 18 in an uncontrollable manner during reproduction of the microstructure 28 and would therefore set 8 lower limit of radiation 21 ~Fig. 5) in spite of good focu~ing, act upon the matrix 1~ ~Fig. 5). Strolce widths s' ~Fig. 4) of less than 60 um are necessary to produce characters, numbers and other graphically designed features if the naked human eye should no longer be able to recognize them. The speed of writing is .. . .

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`~ 1 336779 determined by the capacity of radiation 21 (Fig. 5) at the focal point.

In ~ irst tep the device places a group of surface portlon- 8, 9, 10 ~Fi~. 2~ of structure 7 successively into the master structure, all h~ving the identical orientation and identical parametera for the relief structure 12, 12'.

In a second embodiment of the device, ~ pin diaphragm (not shown here) in the modulator 22 is optically reproduced by means of the focu~ing means 23 on the cover layer 19 and heats said cover l~yer 19 in ~ diaphr~gm image for the reproduction of microstructure 28. This dev$ce also produces surface elements 16 (Fig. ~) with ~ di~meter s and stroke widths s' of over 60 um and accelerates the production of the master structure.

In a third embodiment of the device the group of all surface portions 8, 9, 10 of structure 7 with an identical orientation and identical parameters for the relief atructure 12, 12' are pl~ced simult~neously into the master structure. Inste~d of the pin diaphragm, a diaphragm with cut out shapes of this group are used and are optic~lly reproduced for that purpose by means of the focusing me~ns ~3 ~Fig. 5) on the cover l~yer 19, whereby a prefer~bly impulse-like radiation he~ts up the cover layer 19 in all illuminated locations of the diaphragm image at the same time '''.'. ' ~'' "'" ,'' ' . ' . . :, :' ' , . _ I ' . ' . . ' ~ ' , . . , ' _- 1 336779 LGZ-~6 so that copies of the microstructure 28 remaining there are r~produced in the ma~ter ~tructure.

The diaphragms can be replaced in the modulator 22 and are mounted rotatably in order to achieve maximum flexibility of the devlce.

The matrix 18 is then lifted off from the cover l~yer 1g, is rotated around an axis 30 which is perpendicular to the plane of m~trix 18, i5 shifted laterally or i~ replaced by a matrix 18 with ~ different microstructure 28.

In the following steps additional groups of surface portions 8, 9, 10 ~Fig 4) are transferred by means of one of the above-de~cribed method, whereby surface elements 1~ of the cover layer 19 (Fig. 5) can again be shaped. This process of form reproduction is repe~ted until ~ll surf~ce portions 8, g, 10 ~Fig. 1) of structure 7 have been produced.

In a fourth embodiment of the device a controllable drive, instead of the ray deflection device 2~ <Fig. 5) produces ~

relative mechanical movement between Q source of radiation 31 con~isting of components 20; 22 and 23 ~nd an ~ggregate ~2 consisting of components 17; 18; 1g; 25; 26 and 29, whereby the ',,~ " ' : . ' ' ' .' . ' ' ~, . ' ' ' , ' ,.-' . .

illuminated location, i.e. the focal point or the diaphragm image is shifted in the plane o the cover layer 1~.

Only a few of the expensive matrixe~ 18 are sufficient with this device to produce an unlimited number of different m~ster structures.

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Claims

1. Document with an embossed macroscopic structure (7) of large surface and acting through optical diffraction which is composed of numerous surface portions (8, 9, 10) with predetermined relief structures (12, 12') with spacial frequencies of over 10 lines/mm, acting through optical diffraction, whereby the relief structure (12, 12') of each surface portion (8, 9, 10) is different from those of the directly adjoining surface portions (8, 9, 10), characterized in that at least one group (8, 9) of the surface portions (8, 9, 10) has a maximum dimension of less than .3 mm.

2. Document as in claim 1, characterized in that the surface portions (8, 9) the largest dimension of which measures less than .3 mm have the shape of a geometric figure, of a character, a number or a shape of that type.

3. Document as in claim 2, characterized in that it shows a straight or curved line (14) that is at least visually visible when viewed with the naked human eye and which is composed of those surface portions (8, 9) the largest dimension of which measures less than .3 mm, and in that these surface portions (8, 9) are aligned in a row, whereby the distance between them is less than .3 mm.

4. Document as in claim 3, characterized in that lines (14) and/or dots (13) visible to the naked human eye form a predetermined pattern (15).

5. Document as in claim 1, 2, 3 or 4, characterized in that an optically acting structure (7) is embossed in an adhesive film which is applied to an object (6) to be protected.

6. Document as in one of the claims 1, 2, 3 or 4, characterized in that the optically acting structure (7) is embossed into a layer which is applied by a printing method.

7. Process for the production of a master structure which serves to reproduce embossing stamps by galvanic means for the embossing of documents according to one of the claims 1 to 6 and which is produced on a support (17) which is transparent to electromagnetic radiation (21) in a thermoplastic cover layer (19) absorbing an electromagnetic radiation (21), whereby the cover layer (19) is shaped elastically by means of an unheated matrix (18) having a predetermined microstructure (28) which is applied with pressure and whereby the cover layer (19) is softened up locally and briefly by the radiation (21) which is focused through a surface (25) and through the support (17) on said cover layer (19) so that local plastic deformation occurs and so that the microstructure (28) acting through optical diffraction is transferred as a permanent copy on the cover layer (19), characterized in that the surface of the matrix (19) which is provided with the microstructure (28) is pressed uniformly on the entire cover layer (19), in that the back of the matrix (18) is borne upon by through a flexible intermediary layer (29) by a pressure-producing means (26), in that essentially the entire surface of the cover layer (19) is shaped elastically and in that the matrix is rotated around its axis (30), is laterally shifted or is replaced by a matrix (14) with a different microstructure (28) only after completion of the transfer of a predetermined number of surface portions (8, 9, 10).

8. Process as in claim 7, characterized in that a diaphragm located in the modulator (22) is reproduced on the cover layer (19) by means of the radiation (21) and the focusing means (23), causing the cover layer (19) to be heated at an illuminated location of the diaphragm image.

9. Process as in claim 7, characterized in that the radiation (21) is reproduced on the cover layer (19) by means of a focusing means (23) in a focal point, causing said cover layer (19) to be heated at the illuminated location.

10. Process as in one of the claims 8 or 9, characterized in that the illuminated location is shifted within the plane of the cover layer (19) by means of a ray deflection device (24) and in that the microstructure (28) is transferred successively in surface elements (16) to predetermined locations on the cover layer (19).

11. Process as in one of the claims 8 or 9, characterized in that a relative movement between an irradiation source (31) and an aggregate (32) is produced by means of a controlled drive, in that the illuminated location in the plane of the cover layer (19) is shifted and in that the microstructure (28) is successively transferred in surface elements (16) to predetermined locations on the cover layer (19).

12. Process as in claim 7, 8 or 9, characterized in that the radiation (21) is absorbed simultaneously into the cover layer (19) in a predetermined number of surface portions (8, 9, 10) and in that the same microstructure (28) is simultaneously transferred in surface portions (8, 9, 10) to predetermined locations on the cover layer (19).