EP3245562A1

EP3245562A1 - Method and master for producing a volume hologram

Info

Publication number: EP3245562A1
Application number: EP16700341.7A
Authority: EP
Inventors: Andreas Schilling; Wayne Robert Tompkin; Norbert Lutz; Achim Hansen
Original assignee: OVD Kinegram AG; Leonhard Kurz Stiftung and Co KG
Current assignee: OVD Kinegram AG; Leonhard Kurz Stiftung and Co KG
Priority date: 2015-01-14
Filing date: 2016-01-11
Publication date: 2017-11-22
Also published as: US10642221B2; DE102015100513A1; CN107111275A; WO2016113226A1; US20180004156A1; CN107111275B

Abstract

The invention relates to a method for producing a volume hologram having at least one 1st area in a 1st colour and at least one 2nd area in a 2nd colour, having the steps of: a) providing a volume hologram layer comprising a photopolymer; b) arranging a master with a surface structure on the volume hologram layer; c) exposing the master to coherent light, wherein light that strikes at least one 1st subarea of the surface of the master is diffracted or reflected in the direction of the at least one 1st area of the volume hologram layer and light that strikes at least one 2nd subarea of the surface of the master is diffracted or reflected in the direction of the at least one 2nd area of the volume hologram, and wherein the light diffracted or reflected by the 1st and 2nd subareas differs in at least one optical property.

Description

Method and master for producing a volume hologram

The invention relates to a method and a master for producing a volume hologram, a security element with such

Volume hologram, as well as a security document with such a security element. Holograms are used as security elements to protect

Security documents, such as banknotes, passports, security cards or the like, used to achieve a high security against counterfeiting. Surface relief holograms are frequently used for mass products, which, on the one hand, do not produce an optimal image impression and, on the other hand, can be copied by molding the surface relief. Volume holograms, also known as white light holograms or

Reflection holograms are called, usually with the help of one

produced on the light diffraction at the so-called Bragg levels of a transparent layer, whereby the transparent layer has local refractive index differences and produce a brilliant, but monochromatic image impression. They can not be copied by molding a surface relief.

If volume holograms are to be produced with several areas of different colors, it is generally necessary to use several masters for the illumination of the volume hologram with light of different wavelengths. When replacing the master it necessarily comes to

Positioning inaccuracies that reduce the quality of the volume hologram.

It is therefore an object of the present invention to provide a method and a master for producing improved volume holograms. It is a further object of the invention to provide a security element with an improved volume hologram, as well as a security document with such a security element

To provide volume hologram.

This object is achieved with the subject matter of claims 1, 30, 36 and 39. Such a method of producing a volume hologram having at least a first area in a first color and at least a second area in a second color comprises the steps of: a) providing a volume holographic layer of a photopolymer; b) arranging a master with a surface structure on the

Volume hologram layer; c) exposing the master by means of coherent light, wherein light incident on at least a first subregion of the surface of the master, in the direction of the at least one first region of the

Diffracting or reflecting the volume hologram layer and diffracting or reflecting light incident on at least a second portion of the surface of the master toward the at least one second portion of the volume hologram, and wherein the light diffracted or reflected by the first and second portions is at least one optical property is different.

The invention further relates to a master for use with such a method, comprising a surface structure having a first and a second portion, which differ in their optical properties

differ.

By the method described, a security element with a volume hologram layer can be obtained, in which a volume hologram is formed with at least two areas each having a different color. A security element can be understood, for example, as a transfer film, a laminating film or a security thread for a document, a banknote or the like. Using such a security element may include

Security document to be created, which in particular as

Identification document, passport document, visa document, credit card, banknote, security or the like is formed. The security element may in particular be displayed in a window of the security document, i. in a transparent area, in particular an opening in the

Security document arranged.

With such a method, it is thus possible to multicolored

To generate volume holograms using a single master, but the exposure must be made not mated to the master. The differently colored areas are nevertheless always in the perfect register, ie in the desired fixed positional relationship, arranged relative to one another and in perfect register with the diffractive motif-forming structures of the master. In contrast to using multiple masters for successive exposure steps, no additional measures need to be taken to correct the register-containing, i. To ensure accurate positioning of the respective color areas. The method is therefore both particularly simple and particularly reliable. It also allows very high resolutions of differently colored areas, especially in the micrometer range.

As exact fit or accurate register, the relative positionally accurate position of two elements or areas is understood to each other. The positionally accurate positioning can in particular by means of optically detectable registration marks or Register marks take place. These registration marks or register marks can either represent special separate elements or areas or even be part of the elements or areas to be positioned. An area can be connected or consist of spatially separated sub-areas.

In this case, it is preferable for the light diffracted or reflected by the first and second subregions to differ by at least 10%, preferably by at least 50%, in intensity for a given diffraction order and / or polarization and / or reflection direction and / or wavelength.

In this way, it is possible to generate the areas of the volume hologram even with a full-area exposure of the master, i. it is not necessary to separately illuminate the first and second sub-areas of the master to create the differently colored areas. This facilitates the exact control of the exposure process and in particular so allows the aforementioned high resolutions. In a preferred embodiment, a master with different depth binary grids is used.

Binary grids are grids with a substantially rectangular grid profile. So elevations and valleys alternate with essentially vertical flanks. Deep binary grids can be designed so that they act like a mirror for a first wavelength, so strong in the zeroth

For a second wavelength, however, they have a weak zeroth order and rather bend it strongly in the first order. This This is achieved by not using the two binary grids with one

But with a phase depth of π / 2 + η ^* 2π, where n is a small integer representing the overphasing factor

described in Handbook of Laser Technology and Applications: Volume III: Applications by Colin E. Webt, Julian D, C. Jones, Institute of Physics

Publishing Ltd., p. 2639) the desired effect is achieved and the

desired wavelength-specific portions of the master can be generated particularly easily.

For this purpose, it is particularly advantageous if a master is used which has a binary grating with different structure depth in the first and second region. For a given wavelength and grating period, the intensity of the beams diffracted in the zero and first order, respectively, is determined essentially by the texture depth, so that in this way the desired wavelength selectivity can be realized particularly easily. The optimum structure depth depends on the refractive index of the covering photopolymer.

It is particularly expedient in this case if a master is used which in the first subregion has a structure depth of 350 nm to 510 nm, preferably 400 nm to 460 nm, and in the second subregion a structure depth of 450 nm to 630 nm, preferably 510 nm to 570 nm having. The exact values here depend on the refractive index of the covering photopolymer and the exposure wavelengths. The refractive index was assumed to be n = 1, 51 in the present case. For the illumination wavelengths was 640 nm (red) and 532 nm (green). For other pairs of wavelengths correspondingly different structure depths apply.

In the first subregion, such a master has a strong zero order and a weak first order for red light and in the second subrange a strong zero order and a weak first order for green light. In this way, so visually appealing two-tone, red-green

Volume holograms are generated. Accordingly, it is possible to produce differently colored volume holograms with differently configured masters. In particular, e.g. the following

Interesting color combinations: red-turquoise, red-blue, orange-turquoise, orange-blue, yellow-turquoise, yellow-blue. The texture depth for the two binary lattices of a particular color combination is obtained by applying the above-described "overphasing" and determining the "overphasing" factor "n" such that for a first wavelength the one binary lattice acts like a mirror, that is strong in For a second wavelength, however, it has a weak zero order and rather diffracts strongly into the first order, for which calculations are usually carried out by means of exact electromagnetic diffraction theory.

Furthermore, it is advantageous if a master is used which has a grating period of 500 nm to 10,000 nm, preferably from 1000 nm to 3000 nm. Alternatively, it is also possible to use a master who has a

multi-stage, in particular four-stage grid has. Like a binary grid, such a grid has substantially vertical flanks, but does not consist of a regular sequence of equally deep valleys and the same high elevations, but rather from a repetitive sequence of several stages with increasing or decreasing structural depth. Such, also known as phase gratings structures have a particularly high

Wavelength sensitivity and can be used in particular to produce more than two colors in the volume hologram. In the

Use of three primary colors, e.g. RGB (Red Green Blue) and a corresponding color grid thus the generation of true color holograms with high register accuracy is possible. It is advantageous if a master is used whose structure depth differs between adjacent stages by from 80 nm to 600 nm, preferably from 120 nm to 400 nm.

It is also possible to use a master with a blazed grating. In contrast to the binary grids already described, blaze grids have a sawtooth-shaped cross-sectional profile. Depending on

Incident angle during exposure also changes the diffraction angle of the diffracted light and thus also the Bragg plane distance in the exposed volume hologram. In this way can also multicolored

Holograms are generated using a single master.

It is useful if a master is used, in which the

Blazegitter in the first and in the second portion is disposed on relatively inclined planes, wherein preferably the absolute

Inclination angle of the arranged in the first and second part Blazegitter against the plane spanned by the Volumenhologrammschicht plane

is different. In such a master, the angle of incidence of the light used for the exposure is relative to the surface normal of the master kept constant, nevertheless different angles of incidence relative to the blaze grids arranged there result for the partial regions, so that different diffraction angles and thus different colors in the regions result for the light diffracted in the direction of the regions of the volume hologram. This allows a particularly simple exposure.

It is advantageous if the planes are inclined by 5 ° to 90 °, preferably from 20 ° to 60 ° to each other. It is also possible to use a master having a Fabry-Perot layer system. Such a layer system can also for

Realization of a wavelength-selective master can be used.

Such systems comprise a partially reflective, in particular semitransparent, layer and a reflective, in particular opaque layer, between which a particularly transparent spacer layer is arranged. A part of the incident light is reflected at the partially reflective layer, another part penetrates it and is reflected at the reflective layer. The

Wavelength selectivity results from the interference of the two resulting emergent partial beams and can be adjusted by the layer thickness of the spacer layer.

The layer thickness of the spacer layer is typically between 100 nm and 500 nm, but also layer thicknesses down to 50 nm or up to several micrometers are conceivable.

In this case, it is expedient for a plane distance of the Fabry-Perot layer system to differ from 10 nm to 200 nm, preferably from 20 nm to 100 nm, between the first and the second partial region. Under the Plane spacing is the layer thickness described above

Spacer layer to understand.

In a further preferred embodiment, a master is used in which in the first and / or second subarea a polarizing

Surface structure is provided. This allows selective exposure of the subregions. If, for example, a polarizing surface structure is provided in the first subregion and the master is irradiated with light whose plane of polarization is perpendicular to the plane of polarization of this structure, the first subregion is selectively excluded from the exposure. Subsequently, it is possible, for example, to expose light of a different wavelength, which is parallel to the polarizing one

Surface structure is polarized, so that now the first portion is selectively exposed. Under polarization can be understood here both linear and circular polarization.

It is particularly expedient if a master is used in which the polarization direction of the polarizing surface structure differs between the first and the second partial region.

For this purpose, it is possible, for example, to use a master which in each case has a zero-order diffraction structure with a grating period smaller than the wavelength of the light used for the exposure of the master in the first and second subregions, the diffraction structures being the one

Influence the polarization of the incident light differently. As a result, both partial areas can be selectively exposed in the manner described. It is particularly advantageous if the polarization planes are perpendicular to each other in the first and second sub-areas. It is also expedient if the exposure takes place in at least two successive exposure steps.

As a result, the different optical properties of the two subregions of the master can be utilized to produce the differently colored regions of the volume hologram. A repositioning of the master is not necessary, so that a very good register accuracy can be achieved.

It is advantageous if the exposure steps are carried out at different wavelength and / or different exposure angle and / or different polarization direction of the incident light.

The selected optical properties of the light used for the exposure depend on the optical properties of the subregions of the master, as already explained above.

It is useful if one of the exposure steps at a

Wavelength of 600 nm to 660 nm, preferably from 620 nm to 640 nm and another of the exposure steps at a wavelength of 500 nm to 560 nm, preferably from 520 nm to 550 nm is performed. As a result, red-green holograms can be generated. This is particularly advantageous when using a master with a binary or phase grating. at Using other wavelengths for the exposure, other colors can be generated. For example, exposure to lasers in the range of 560 nm to 590 nm can produce yellow or orange holograms, and exposure to lasers in the range of 400 nm to 480 nm can produce blue holograms.

Furthermore, it is expedient if the polarization planes of the light used for two of the exposure steps differ by 90 °. The different polarization directions can be combined with different wavelengths to achieve the desired color effect.

It is also advantageous if at least one of the exposure steps is performed over the entire surface. As a result, solid color surfaces can be generated in the hologram.

However, it may also be advantageous to perform at least one of the exposure steps in a grid. This is particularly useful when small, i. high-resolution, the raster-forming color areas are to be combined to produce a mixed color impression. Also, to create a lightly colored background for a motif, a screening may be appropriate.

It is advantageous if the grid is a dot or line grid. In this context, dot screens should generally be understood to mean pitches that are made up of distinct, small elements. These may be circular but may take on other structures such as stars, squares, alphanumeric characters, and the like. In this case, the grid preferably has a screen ruling from 30 μm to 500 μm, particularly preferably from 50 μm to 300 μm. It is furthermore expedient for a plurality of exposure steps to be carried out in which exposure is made in each case to offset dot patterns. In this case, for example, the rotation of the grid can be changed to each other. Likewise, it may be useful to use a point or line grid in a first exposure step and to expose the entire surface in a second step.

In particular, it is advantageous to use the individual exposure steps at different wavelengths, in particular at the primary colors, e.g. RGB (Red Green Blue). This way can be rasterized

Real color holograms are generated.

Preferably, the exposure is carried out with a light intensity of 2 mJ / cm ² to 200 mJ / cm ^2, preferably from 5 mJ / cm ² to 50 mJ / cm ²

It is also advantageous if the first and / or second area a

Design element, in particular a symbol, logo, image, in particular a portrait or an alphanumeric character, training.

However, it can also be provided that the one area provides information and the other area forms the environment or the background from which the information stands out. The information may be For example, to act a logo that appears bright against a dark background in one viewing position and dark in the other viewing position against a light background. It can therefore be provided that when tilting or moving the volume hologram a change from a positive representation to a negative representation occurs and vice versa. Further, the regions may be formed such that one region forms the edge of the other region. For example, one area may render the border of an alphanumeric character and the other area the alphanumeric character itself.

In order to obtain a long-term stable hologram, the volume hologram layer, which is formed in particular of UV-curing polymers, is further fixed by curing, in particular by means of UV radiation, after exposure.

The volume hologram may be combined with other security features in a security element and / or on a security document. In particular, adjacent to and / or overlapping with the volume hologram, diffractive and / or refractive effects may still be present

Surface relief structures arranged with an optical effect enhancing reflection layer, e.g. of vapor-deposited or printed semitransparent or opaque metal and / or of transparent HRI (High Refractive Index) layers, e.g. from metal oxides or

Nanoparticles such as e.g. consist of a mixture of poly (dibutyl titanate) polymer and poly (styrene-allyl alcohol) copolymer or zinc sulfide and

Titanium dioxide. In this case, it is preferable that the HRI layer has a refractive index of more than 1.8, more preferably more than 2.0. Likewise, it is possible to adjacent and / or overlapping to the

Volume hologram applied by known printing methods

To arrange security prints, for example, one or more guilloches of very fine, especially multi-colored lines.

By such combinations, the respective different ones

Security features relative to each other have a very high register accuracy, the optical effect, but also the security against forgery of such a security element or security document can be further increased. In particular, the combined security features can form a common overall motif, with different ones in each case

Motiv elements are formed from different security features.

Preferably, a master used for the method described comprises a metallic base body, in particular of nickel.

The invention will now be explained in more detail with reference to exemplary embodiments. Show it

Fig. 1 is a schematic representation of an embodiment of a multi-colored volume hologram;

Fig. 2 is a schematic representation of an alternative

Embodiment of a multi-colored volume hologram;

Fig. 3 is a schematic sectional view through a

Embodiment of a master for producing a multi-colored volume hologram;

Fig. 4 is a schematic representation of the diffraction of light one

first wavelength on the master of Fig. 3; Fig. 5 is a schematic representation of the diffraction of light of a second wavelength at the master of Fig. 3;

6 is a graphic representation of the dependence of

Diffraction intensity of red light on a binary grating with a grating period of 2 μιτι of the structure depth of the grating;

7 is a graphic representation of the dependence of

Diffraction intensity of green light on a binary grating with a grating period of 2 μιτι of the structure depth of the grating;

8 is a graphical representation of the dependence of

Diffraction intensity of red light on a binary grid with a

Grating period of 3 μιτι of the structure depth of the grid;

9 is a graphical representation of the dependence of

Diffraction intensity of green light on a binary grating with a grating period of 3 μιτι of the structure depth of the grating; Fig. 10 is a schematic sectional view through a

Embodiment of a master with a step grid for producing a multi-colored volume hologram;

Fig. 1 1 is a schematic sectional view through a

Embodiment of a master with a Blazegitter for producing a multi-colored volume hologram in a

Exposure angle of 15 °;

Fig. 12 is a schematic sectional view through a

Embodiment of a master with a Blazegitter for producing a multi-colored volume hologram at an exposure angle of 0 °; Fig. 13 is a schematic sectional view through a

Embodiment of a master with a Blazegitter for producing a multi-colored volume hologram at an exposure angle of 30 °; 14 is a graphic representation of the dependence between

Angle of incidence and resulting wavelength for a blazed grating;

Fig. 15 is a schematic sectional view through a

Embodiment of a master with a Blazegitter for producing a multi-colored volume hologram with mutually inclined lattice planes;

Fig. 16 is a schematic plan view of an embodiment of a

Masters with a blaze grating for producing a multi-color volume hologram with mutually inclined lattice planes, as well as the resulting hologram; 17 is a schematic sectional view through the master of FIG.

16;

Fig. 18 is a schematic plan view of an embodiment of a

Masters with a polarizing filter for producing a multicolor volume hologram; 19 a schematic representation of a raster mask for exposure of a volume hologram;

Fig. 20A-E A schematic representation of the manufacturing steps for a screened volume hologram;

Fig. 21 A schematic illustration of the exposure of a

Volume hologram; 22 shows a schematic illustration of the exposure of a volume hologram by means of a master with a sealing-wax layer;

Fig. 23 A schematic illustration of the exposure of a

Volume hologram by means of a master with a sealant layer einbnenden the surface structures;

Fig. 24 A schematic illustration of the exposure of a

Volume hologram by means of a volume hologram master;

Fig. 25 is a schematic illustration of the halftoned exposure of a volume hologram by means of a master and a raster mask;

Fig. 26 is a schematic illustration of the halftoned exposure of a volume hologram by means of a master and periodic modulation of an exposure laser;

In Figures 1 and 2 are two embodiments of

Volume holograms 1 shown, each having areas 1 1 with red color and areas 12 with green color. In the embodiment according to FIG. 1, the regions 1 1, 12 form a graphic motif in the form of flowers, in FIG. 2 a lettering

In general, the areas 1 1, 12 can form graphic motifs in the form of a symbol, a logo, an image or an alphanumeric character.

But it can also be provided that the one area 1 1, 12 a

Provides information and the other area 12, 1 1 forms the environment from which the information stands out. The information may be For example, to act a logo that appears bright against a dark background in one viewing position and dark in the other viewing position against a light background. It can therefore be provided that when tilting or moving the volume hologram a change from a positive representation to a negative representation occurs and vice versa. Further, the areas 1 1, 12 may be formed so that the one area 1 1, 12 forms the edge of the other area 12, 1 1. For example, one area may render the border of an alphanumeric character and the other area the alphanumeric character itself.

To produce such a volume hologram is a

Volume hologram layer of a photopolymer exposed by irradiation of a master 2 with coherent light. The photopolymer is preferably a photopolymer in which the desired

Refractive index changes can be triggered by exposure or irradiation. For example, the photopolymer is the

Photopolymer Omni DX 706 from DuPont. Other examples are silver halide emulsions, liquid photopolymer or dichromated gelatin, with a layer thickness of 3 μιτι to 100 μιτι.

During the exposure of the master 2, light incident on at least a first subregion 21 of the surface of the master 2 is diffracted or reflected in the direction of the at least one first region 1 1 of the volume hologram layer and light which is incident on at least a second subregion 22 of the surface of the master Masters 2, diffracted or reflected in the direction of at least a second portion 12 of the volume hologram. In this case, the light diffracted or reflected by the first and second partial regions differs in at least one optical property. This is illustrated in detail in FIG. 21. The volume hologram 1 is brought into direct contact with the master 2 during the exposure, so that an incident laser beam 4 is diffracted by the master 2 into a photopolymer layer 18 of the volume hologram 1 and can interfere there with the incident beam. Adjoining the photopolymer layer 18 is another layer structure 5, which here comprises a lacquer layer 51 and a carrier foil 52. With such a method, it is thus possible to multicolored

Volume holograms 1 using a single master 2 to produce. The differently colored areas 1 1, 12 are therefore always in the perfect register, ie in the desired fixed positional relationship, arranged to each other.

In this case, it is preferable for the light diffracted or reflected by the first partial region 21 and the second partial region 22 to be present for a given time

Diffraction order and / or polarization and / or reflection direction and / or wavelength by at least 10%, preferably by 50% in intensity

different.

The master 2 preferably comprises a metallic base body, in particular of nickel, on the surface of which the surface structures are formed.

The surface structures of the master 2 can also be sealed with a thin and transparent sealing layer 27 (see FIG. 22).

Alternatively, the sealing layer 27 may also be thicker and the structures completely cover or level (see Fig. 23). Furthermore, master 2 can be used, which instead of a surface relief

Volume hologram 28 have (see Fig. 24). This volume hologram master 2 may also optionally be provided with a sealing layer 27. It is also conceivable, the master of a combination of a

Form surface structure and a volume hologram, wherein the surface structure and the volume hologram can be arranged adjacent to each other and / or overlapping each other. A first example of the surface structure of a master 2 is shown in FIG. It is a binary grid.

For a second wavelength, however, they have a weak zeroth order and rather bend it strongly in the first order. Thus, the desired wavelength-specific subregions 21, 22 of the master 2 can be generated particularly easily. This is illustrated in FIGS. 4 and 5.

In the first subregion, such a master has a strong zero order and weak first order for red light and in the second subrange a strong zero order and weak first order for green light. In this way, visually appealing two-color, red-green volume holograms can be generated.] Accordingly, it is possible to produce differently colored volume holograms with differently configured masters. In particular, for example, are the following

The essential structural parameter for this wavelength specificity is the structure depth of the binary grid. As can be seen in FIG. 3, the surface structure of the master 2 in the subregions 21 and 22 differs only by the texture depth.

The exact dependence of the diffraction intensity on the structure depth is illustrated in FIGS. 6 to 9 for different exposure wavelengths and angle of incidence. It can be clearly seen that, for example, at an angle of incidence of 0 ° and a grating period of 2 μιτι a high diffraction efficiency for red light at 640 nm at a structure depth of 440 nm in the zeroth order and at a structure depth of 540 nm in the first Order is achieved (Fig. 6). On the other hand, upon irradiation with green light of 532 nm, high efficiency is achieved in the zero order at a pattern depth of 550 nm and in the first order at a pattern depth of 470 nm (Figure 7). For a given structure depth, such binary gratings therefore have a high wavelength selectivity. This also applies to grids with a period of 3 μηη (Figures 8 and 9). The combination of binary gratings with partial regions 21, 22 of different structural depth shown in FIG. 3 is thus very well suited to the desired differently colored regions 1 1, 12 of the

Volume hologram to produce.

In addition to the described binary gratings, multistage gratings can also be used, as shown in FIG. Instead of alternating valleys and peaks, these have in profile a repetitive sequence of steps with increasing or decreasing structural depth.

Such structures, also known as phase gratings, have a particularly high wavelength sensitivity and, in particular, can be used to produce more than two colors in the volume hologram. When using three primary colors, e.g. RGB (Red Green Blue), the generation of true color holograms with high register accuracy is thus possible.

It is advantageous if a master is used whose structure depth differs between adjacent stages by from 80 nm to 600 nm, preferably from 120 nm to 400 nm.

It is also possible to use a master with a blazed grating. This is illustrated in FIGS. 11 to 13.

In contrast to the binary grids already described, blaze grids have a sawtooth-shaped cross-sectional profile. Depending on

Incident angle during exposure also changes the diffraction angle of the diffracted light and thus the Bragg plane distance in the exposed Volumenhologrannnn. In this way can also multicolored

Holograms are generated using a single master.

As shown in Fig. 1 1, when exposed to a green laser with a wavelength of 532 nm and an angle of incidence of 15 ° to

Area normal of an exemplary Blaze grating a green area in the resulting volume hologram. At an angle of incidence of 0 °, a blue-green area is obtained under otherwise identical conditions (FIG. 12), and at a beam angle of 30 ° a yellow-green area is obtained (FIG. 13).

Overall, for a given exposure wavelength and blazed grating, there is a linear relationship between angle of incidence and the resulting color of the exposed volume hologram, as illustrated in FIG.

The desired effect can be generated by varying the angle of incidence during the exposure. However, this makes a relatively expensive

Control of the exposure laser necessary because of the angle of incidence in

Dependence on the position of the laser beam on the master must be changed. The achievable resolution would also be limited by the comparatively large dimensions of the respective local irradiation surface of the exposing laser beam.

Therefore, it is expedient if a master 2 is used, in which the blazed grating is arranged in several subregions 21, 22, 23 on planes 24, 25, 26 which are inclined relative to one another. An exemplary embodiment of such a master 2 is shown schematically in FIGS. 15 and 17. If, in such a master 2, the angle of incidence of the light used for the exposure is kept constant relative to the surface normal of the master 2, different incidence angles nevertheless result for the subregions 21, 22, 23 relative to the blaze gratings arranged there, so that the corresponding blaze gratings are used Areas 1 1, 12, 13 of

Volume hologram diffracted light give different diffraction angles and thus different colors in the areas. This allows a particularly simple exposure. Instead of blaze grids, other diffractive structures, such as linear or crossed sine, linear or crossed binary grids,

Fresnel lens-like structures or structures combined with isotropic or anisotropic matte structures may be used. In particular, linear sine grid structures with a structure depth which is a maximum

Diffraction efficiency results in a higher than the first diffraction order, can be used here with advantage.

It is advantageous if the planes are inclined by 5 ° to 90 °, preferably from 20 ° to 60 ° to each other.

The partial regions 21, 22, 23 can also be arranged in complex patterns in order to realize any graphic designs. A schematic plan view of such a master 2 and the resulting volume hologram 1 is shown in FIG. 16.

Another alternative embodiment for a master 2 is shown in FIG. The wavelength selectivity of the subregions 21, 22 is realized here by respective polarizing structures. If, for example, a polarizing structure is provided in the first subregion and the master 2 is irradiated with light whose plane of polarization is perpendicular to the polarization plane of this polarizing structure, the first subregion is selectively excluded from the exposure. Subsequently, it is possible, for example, to expose light of a different wavelength, which is polarized parallel to the plane of polarization of the polarizing structure, so that now the first subregion is selectively exposed. By contrast, the plane of polarization of the polarizing structure in the second partial region is preferably arranged perpendicular to that of the polarizing structure in the first partial region. In the first exposure, therefore, the second portion is selectively exposed and excluded from the exposure during the second exposure.

When the exposures are at different wavelengths, a multicolor volume hologram can also be generated using a single master. In all the embodiments described above, the exposure can take place over the entire surface. However, it has been shown that especially good

Results can be obtained by a raster exposure. This is exemplified in Fig. 25. For this purpose, a raster mask 3 is arranged between the exposing laser beam and the master 2. If multiple exposures are performed, a halftone exposure can also be combined with a full-area exposure. Instead of a mask, it is also possible to use a screened exposure in which a scanning and possibly focused first laser beam is intensity-modulated (see FIG. 26). The laser beam is preferably switched on and off (by internal or external modulation). Alternatively, the laser beam can be expanded and a so-called spatial light modulator can be used, which modulates the intensity distribution. If multiple exposures are performed, the halftoned exposure can also be combined with a full-area exposure. This is particularly useful when small, ie high-resolution, the grid forming color areas are to be combined to one

To produce mixed color impression. Also, to create a lightly colored background for a subject rastering, especially for generating a halftone of the background color may be appropriate.

Examples of raster masks 3 designed as a dot or line raster are shown in FIG.

In this context, dot screens should generally be understood to mean pitches that are made up of distinct, small elements. These may be circular but may take on other structures such as stars, squares, alphanumeric characters, and the like.

Preferably, the grid has a grid width of 50 μιτι to 300 μιτι on.

In Fig. 20, the production of a multi-color screened volume hologram is shown in detail. For this purpose, the master shown in FIG. 20A is first provided, whose partial regions 21, 22 form a logo here. For the Subsections 21, 22 of the master can all the surface structures described above to produce the desired

Wavelength selectivity can be applied. For the first exposure, the screen mask 3 shown in FIG. 20B with non-transparent regions 31 and transparent regions 32 is arranged in the beam path so that it overlaps the master 2 as shown in FIG. 20C. The exposure then takes place with red light, which is diffracted by the first portion 21 and the second portion 22 weak.

This gives the intermediate product shown in FIG. 20D. In the first region 1 1 of the volume hologram into which the red light has been diffracted by the first subregion 21 of the master 2, a pattern of intensely red pixels 14 is formed, while in the second region 12 only a weak exposure occurs and thus only weakly red pixels 15 are formed.

Then the raster mask is removed and a further exposure to green light is performed. This is done over the entire surface. The green light is now strongly diffracted by the second subregion 22 of the master, so that intensively green pixels 16 now form in the previously unexposed parts of the second region 12 of the volume hologram 1, as shown in FIG. 20E, while in the first region 1 1 only weakly green pixels 17 are formed. By controlling the ratio of the light intensities of the first and second exposure, the color impression can be easily varied.

Overall, this results in the volume hologram 1 shown in FIG. 20F with a red logo on a green background with a red border. The Screen ruling of the mask used is preferably below the resolution of the human eye, so that there is a continuous color impression.

- Reference list

1 volume holograms

1 1 area

12 area

13 area

14 pixels

15 pixels

16 pixels

17 pixels

18 volume hologram layer

2 masters

21 subarea

22 subarea

23 subarea

24 level

25 level

26 level

27 lacquer layer

3 grid mask

31 area

32 area

4 laser beam

5 layer structure

51 paint layer

52 carrier layer

Claims

claims

A method of producing a volume hologram having at least a first region in a first color and at least a second region in a second color, comprising the steps of:

a) providing a volume hologram layer of a

Photopolymer;

b) arranging a master having a surface structure on the volume hologram layer;

c) exposing the master by means of coherent light, wherein light incident on at least a first portion of the surface of the master is diffracted or reflected toward the at least one first portion of the volume hologram layer and light incident on at least a second portion of the surface of the master is incident, diffracted or reflected in the direction of the at least one second region of the volume hologram, and wherein the differs from the first and second sub-range diffracted or reflected light in at least one optical property.

2. The method according to claim 1,

characterized,

in that the light diffracted or reflected by the first and second subregions differs in intensity for a predetermined diffraction order and / or polarization and / or reflection direction and / or wavelength by at least 10%, preferably by at least 50%.

3. The method according to claim 1 or 2,

characterized,

that a master is used with a binary grid.

4. The method according to claim 3,

characterized,

that a master is used, which has a binary grid with different texture depth in the first and second subarea.

5. The method according to claim 4,

characterized,

that a master is used, which in the first subsection a

Structure depth of 350 nm to 510 nm, preferably from 400 nm to 460 nm, and in the second subregion has a pattern depth of 450 nm to 630 nm, preferably from 510 nm to 570 nm. Method according to claim 4 or 5,

characterized,

that a master is used which has a grating period of 500 to 10,000 nm, preferably from 1000 nm to 3000 nm.

Method according to claim 1 or 2,

characterized,

that a master is used, which has a multi-level, in particular four-level grid.

Method according to claim 7,

characterized,

a master is used whose structure depth differs between adjacent stages by from 80 nm to 600 nm, preferably from 120 nm to 400 nm.

Method according to claim 3,

characterized,

that a master is used with a Blaze grating.

Method according to claim 9,

characterized,

in that a master is used in which the blazed grating is arranged in the first and in the second partial region on planes inclined relative to one another, wherein the absolute angle of inclination of the blaze grids arranged in the first and second partial regions is preferably different from the plane spanned by the volume hologram layer.

1 1. Method according to claim 10,

characterized,

that the planes are inclined by 5 ° to 90 °, preferably from 20 ° to 60 ° to each other.

12. The method according to claim 1 or 2,

characterized,

that a master is used which has a Fabry-Perot layer system.

13. The method according to claim 12,

characterized,

in that a plane spacing of the Fabry-Perot layer system differs between 10 nm and 200 nm, preferably between 20 nm and 100 nm, between the first and the second partial region.

14. The method according to any one of the preceding claims,

characterized,

a master is used in which a polarizing structure is provided in the first and / or second subarea.

Method according to claim 14,

characterized,

a master is used in which the polarization direction of the polarizing structure differs between the first and the second partial area. Method according to one of claims 13 to 15,

characterized,

a master is used which in each of the first and second subregions has a zeroth-order diffraction structure with a grating period smaller than the wavelength of the light used for the exposure of the master, or a blaze grating with a polarizing superstructure, the respective diffraction structures being the Influence the polarization of the incident light differently.

Method according to one of the preceding claims,

characterized,

the exposure takes place in at least two successive exposure steps.

Method according to claim 17,

characterized,

that the exposure steps at different wavelength and / or different exposure angle and / or different

Polarization direction of the incident light can be performed.

Method according to claim 17 or 18,

characterized,

that one of the exposure steps at a wavelength of 600 nm to 660 nm, preferably from 620 nm to 640 nm, and another of the

Exposure steps at a wavelength of 500 nm to 560 nm, preferably from 520 nm to 550 nm is performed.

20. The method according to any one of claims 17 to 19,

characterized,

the polarization planes of the light used for two of the exposure steps differ by 45 ° to 135 °, preferably by 90 °.

21. The method according to any one of claims 17 to 20,

characterized,

that at least one of the exposure steps is performed over the entire area over the two partial areas.

22. The method according to any one of claims 17 to 21,

characterized,

that at least one of the exposure steps is performed in a grid.

23. The method according to claim 22,

characterized,

that the grid is a dot or line grid. 24. The method according to claim 22 or 23,

characterized,

that the grid has a grid width of 50 μιτι to 300 μιτι.

25. The method according to any one of claims 22 to 24,

characterized,

in that a plurality of exposure steps are carried out, in which exposure is made in each case in offset bit screens.

26. Method according to one of the preceding claims, characterized in that

the exposure takes place with a light intensity of 2 mJ / cm ² to 200 MJ / cm ² , preferably 5 MJ / cm ² to 50 MJ / cm ² .

27. Method according to one of the preceding claims,

characterized,

the light intensity is periodically modulated during the exposure to produce a raster.

28. Method according to one of the preceding claims,

characterized,

that the first and / or second area is a design element,

in particular a symbol, logo, image, alphanumeric characters, trains.

29. The method according to any one of the preceding claims,

characterized,

that after exposure the volume hologram layer through

Curing is fixed.

30. A master for use with a method according to any one of claims 1 to 29, comprising a surface structure having a first and a second portion, which differ in their optical properties.

31. Master according to claim 30,

characterized, in that diffracted or reflected light differs from the partial regions for a given diffraction order and / or polarization and / or reflection direction and / or wavelength by at least 10%, preferably by at least 50%, in intensity.

Master according to claim 30 or 31,

characterized,

that the surface structure is a binary grid, a multi-level

Phase grating, a blazed grating, a Fabry-Perot layer system, a polarizing filter layer or combinations thereof.

Master according to one of claims 30 to 32,

characterized,

the master comprises a metallic base body, in particular nickel.

Master according to one of claims 30 to 33,

characterized,

in that the master comprises at least one further surface structure arranged adjacent or overlapping to the surface structure.

Master according to one of claims 30 to 34,

characterized,

that the master comprises a lacquer layer which the

Surface structure covered.

36. Security feature with a volume hologram layer, in which a volume hologram is formed with at least two regions of different color, obtainable by a method according to one of claims 1 to 29.

37. The security element according to claim 36,

characterized,

in that the volume hologram layer is formed from a photopolymer, in particular from Omni DX 796 (DuPont), silver halide emulsions or dichromated gelatin.

38. The security element according to claim 36 or 37,

characterized,

the volume hologram layer has a layer thickness of 3 μm to 100 m.

39. Security document with a security element according to one of claims 36 to 38. 40. Security document according to claim 39,

characterized,

the security document is in the form of an identity document, passport document, visa document, credit card, banknote, security or the like.