DE102014217099B4 - Process for the production of a security hologram with a transmission volume hologram in contact copy - Google Patents

Abstract

Method for generating a security hologram (200) with a volume transmission hologram (220), the security hologram (200) being intended for incorporation into a value or security document, comprising the steps:
providing a recording material (40),
Irradiating the recording material (40) with coherent object light (111) and reference light (121) from a first exposure side (42) of the recording material (40), the information to be stored in the volume transmission hologram (220) being transported in the object light (111), wherein a hologram master (10) is produced or provided, which contains at least one diffraction structure (20), and
the recording material (40) is brought into contact with the first exposure side (42) with a contact side (14) of the hologram master (10) and coherent incident light (100; 100') is generated and the hologram master (10) is exposed to the coherent incident light (100 ; 100') from an irradiation side (12) opposite the contact side (14) and the object light (111) is generated, which enters from the hologram master (10) and into the recording material (40) from the first exposure side (42), the at least one diffraction structure (20) in the hologram master (10) being designed in such a way that a part of the incident light (100; 100') is not diffracted and
as the reference light (121) exits the hologram master (10) and enters the recording material (40) from the first exposure side (42), so that the object light (111) and the reference light (121) interfere in the recording material (40) and expose the volume transmission hologram into the recording material (40),
the recording material (40) comprising a photosensitive layer (50), characterized in that
the hologram master (10) is prepared or produced with the at least one diffraction structure (20) in the form of a volume transmission hologram (220), which generates the generated object light (111) when irradiated with the incident light (100; 100') in such a way that the Object reconstructs a real image whose image plane deviates from the plane in which the photosensitive layer (50) of the recording material (40) is arranged, a material thickness of the recording material (40) being selected when it is provided such that there is no overmodulation in the finished volume transmission hologram (220). occurs.

Description

The invention generally relates to security holograms which are used as a security feature in value or security documents, and in particular to a method for producing such a security hologram.

It is known in the prior art to use features to protect security documents and documents of value against unauthorized manufacture, imitation, falsification or the like. Such features that make imitation, falsification, unauthorized manufacture or the like at least more difficult or impossible are referred to as security features. Documents and other objects that have such a security feature are referred to as security documents. If these also embody a value, they are also referred to as documents of value. Security documents include identity cards, passports, driver's licenses, access cards, visas, vehicle documents, driver's licenses, banknotes, credit cards, postage stamps, tokens or even anti-counterfeiting tickets or labels for identifying high-value products, to name a few examples.

Very different security features are known from the prior art. A group of security features is intended for visual inspection and verification. A subgroup of these security features use diffractive structures in order to change light incident on the security feature via diffraction and to evaluate this diffraction optically. For example, the simplest type of verification is to check whether light diffraction occurs, i.e. a diffractive structure is present. More complicated or more complex security features and their verification methods provide for a location-resolved, angle-resolved and/or wavelength-resolved detection of the light diffraction.

Holograms represent a group of diffraction structures. With these it is possible to store information in the diffraction structure. On the one hand, holograms are distinguished according to whether they reconstruct the stored information in reflection or in transmission. One speaks of a reflection hologram when the reconstructed information can be detected from the same side of the hologram from which the hologram is illuminated with suitable reconstruction light. Correspondingly, one speaks of a transmission hologram when the reconstructed information is reconstructed on the opposite side of the hologram from which the hologram is illuminated with reconstruction light. It should be noted here that transmission holograms can also be partially verified in a reflection geometry if the diffracted light is reflected on a reflecting element in addition to the diffraction.

A further distinction from holograms also takes place beyond where in a storage medium the holographic information is stored. If the holographic information is only stored in a thin layer of material or on the surface via a structuring of this surface, one speaks of a thin or surface hologram. If, on the other hand, the holographic information is stored in the volume of a material, it is referred to as a volume hologram. Volume holograms can be in the form of both transmission and reflection holograms.

From the DE 10 2008 057 784 A1 a method and a device for producing a volume transmission hologram and/or volume reflection hologram are known. The volume transmission hologram and/or volume reflection hologram are produced from a film with a carrier foil and a holographic layer, the film being guided over a drum on which it is brought into contact with the master hologram. The master hologram is moved simultaneously with the film through an exposure area in which the film and the master hologram are irradiated with a line-shaped expanded exposure laser beam to reproduce the master hologram in the holographic layer. In this case, both reflection and transmission volume holograms can be generated on a drum, for which purpose two master holograms are assigned or can be assigned to the drum and are moved synchronously with it while lying on it. The film is located radially below the first master hologram and/or radially above the second master hologram.

From the EP 0 701 183 A2 a device for copying holograms is known. The apparatus comprises a first reconstruction beam and a second reconstruction beam, the second reconstruction beam being coherent with the first. A first master hologram generates a first diffraction beam using the first reconstruction beam. A second master hologram generates a second diffraction beam using the second reconstruction beam. A holographic recording material is exposed by means of the first and second reconstruction beams and the first and second diffraction beams, a first hologram being formed by interference of the first reconst duction beam and the first diffracted beam is generated, and wherein a second hologram is generated by interference of the second reconstruction beam and the second diffracted beam.

From the EP 0 896 260 A2 a device for producing holograms from a master hologram of a ground glass is known. A hologram master having the master hologram is brought into contact with a film. In this case, the film is arranged in front of the hologram master with the master hologram. The master hologram is a reflection hologram, so that when it shines through the film, part of the light from the hologram master, ie the master hologram, is reflectively diffracted and thus interferes with the light in the film that shines through this film. As a result, the master hologram of the hologram master is copied in contact copy. In order to individualize such a hologram, the coherent light used for illumination is passed through a modulator, which spatially modulates the coherent radiation, before it is transmitted through the film. Such modulators are also referred to as special light modulators (SLM). For example, they may be formed of liquid crystal cells as in a liquid crystal display (LCD). Holograms produced in the manner indicated are used, for example, under the Identigram brand and incorporated as security elements in passport cards and identity cards of the Federal Republic of Germany.

Although the production of such a contact-copied hologram as a security element, which contains the individualized, ie copied with different brightness levels, ground-glass screen as a hologram as a security feature, requires considerable technical effort, the associated difficulty of creating a forgery or falsification of such a security element increases with the general progress in the field of holography.

The invention is therefore based on the technical problem of creating a method for producing an improved security element, i.e. one that is more difficult to counterfeit, which can nevertheless be produced in large quantities, preferably individually, in a simple manner.

The invention is solved by a method with the features of patent claim 1. Advantageous versions result from the dependent claims.

basic idea of the invention

The invention is based on the idea of creating a volume holographic element which can be used in a security document body which has a window section in which the document body is exposed between an upper side and an underside of the document body for light of a wavelength which can be used to reconstruct the hologram. is transparent. A security element suitable for this and having a novel security feature comprises a volume transmission hologram. Such volume transmission holograms are much more difficult to produce, since no method suitable for mass production such as the contact copying method for volume reflection holograms is known from the prior art. However, in order to ensure that the recording material is completely still during exposure, even if it is only a few 10 to 100 µm thick overall, and to achieve simple and very stable generation of both the object information carrying the information of a master hologram and the reference light to produce, is provided according to the basic idea of producing and using a hologram master, which itself comprises at least one diffraction structure, which is designed as a volume transmission hologram and at which part of the incident light is diffracted in order to emerge as object light, and another part of the incident light passes the hologram master undiffracted and both the object light generated during transmission and the undiffracted light which serves as reference light are guided into a recording material which is arranged in contact with the hologram master in order to interfere there and the hologram of the to be produced n form a security element. As a result, a security hologram is thus produced which includes a volume transmission hologram and is suitable for use in a value or security document.

definitions

A security feature is any feature that prevents or makes it difficult to imitate, falsify, duplicate or similar an object.

Any physical object that has at least one security feature is referred to as a security element.

A security document is any document that has at least one security feature. A security document is always a security element as defined above. Examples of security documents are passports, identity cards, access cards, visas, driver's licenses, vehicle documents, but also entry tickets protected against forgery or product labels and seals as well as banks bills, credit cards, postage stamps, tokens, banknotes or shares, each of which has at least one security feature and which is assigned a specific value. A strict demarcation between documents of value and security documents is not necessary with regard to the invention described here. All documents of value are also regarded here as security documents.

Recording material is any material that includes a photosensitive layer into which a hologram can be exposed. A photosensitive layer provided with protective layers is also referred to as recording material.

A body or a section of a body, in particular a document body, is considered to be transparent if imaging according to geometric optics is possible through this body at at least one wavelength for which the body is to be regarded as transparent.

A security hologram is a physical entity that stores at least one hologram.

Preferred Embodiments

On the one hand, a security element is created in the form of a security hologram, which is or includes a volume transmission hologram. This is intended to create a new type of security document.

Such a new type of security document has a document body, which has an upper side and an opposite underside, with a security hologram being integrated into the document body, which comprises a diffraction structure which, when the hologram is illuminated with reconstruction light of a suitable wavelength, reconstructs information stored in the security hologram , which can be detected when viewing the upper side of the document body or when optically capturing an image from the upper side, the document body comprising at least one window section in which the document body is transparent to light of a wavelength between the upper side and the lower side, with which at least one diffraction structure of the security hologram can be reconstructed, wherein the at least one diffraction structure of the security hologram is in the window section between the top and bottom of the document body is arranged and is a transmission diffraction structure, the stored information of which can be detected when viewing the top side or capturing an optical image from the top side when illuminated with reconstruction light from the bottom side of the document body or when illuminated with reconstruction light from the top side in the form of a projection is detectable on an area behind the document body viewed from the front side of the document body. In the case of the second alternative, the projection can preferably be detected in particular through the window section.

Furthermore, a method for generating a security hologram with a volume transmission hologram is proposed, the security hologram being intended for introduction into a value or security document. Such a method comprises the steps of: providing a recording material; Irradiation of the recording material with coherent object light and reference light from a first exposure side of the recording material, the information to be stored in the volume transmission hologram being transported in the object light, it being provided that a hologram master is produced or provided which contains at least one diffraction structure and the recording material with the exposure side is brought into contact with a contact side of the hologram master and coherent incident light is generated and the hologram master is irradiated with the coherent incident light from an incident side opposite the contact side, i.e. from the side facing away from the recording material, and on one diffraction structure of the hologram master via a Diffraction of the coherent incident light, the object light is generated and occurs from the hologram master and into the recording material from the first exposure side, wherein the at least one diffraction structure is formed in the hologram master so that part of the incident light is not diffracted and exits the hologram master as the reference light and enters the recording material from the first exposure side, so that the object light and the reference light interfere in the recording material and so on Expose a volume transmission hologram into the recording material, with the hologram master being prepared or produced with the at least one diffraction structure in the form of a volume transmission hologram, which, when irradiated with the incident light, generates the generated object light in such a way that a real image is reconstructed from the object, the image plane of which is deviates from the plane in which the photosensitive layer of the recording material is arranged.

Furthermore, according to the invention, the material thickness of the recording material is chosen so that in the finished volume transmission holo gram no overmodulation occurs. In simplified terms, this can be imagined in such a way that the material thickness of the photosensitive layer must be designed in such a way that the light generated via the diffraction is not itself diffracted at diffraction structures located deeper in the volume. If such an effect occurs, a corresponding hologram is referred to as overmodulated.

The advantage of this method is that a large number of volume transmission holograms can be produced in a simple manner and the geometric lighting conditions, which also influence a later reconstruction of the security hologram produced, are precisely maintained, since both the object light and the reference light are generated directly in the at least one diffraction structure of the hologram master from the coherent incident light used for exposure.

A corresponding device for producing such a security hologram with a volume transmission hologram, the security hologram being intended for introduction into a valuable or security document, comprises: a transport device for a recording material; a light source for generating coherent incident light; an optics unit for guiding the coherent incident light, so that at least one section of the recording material is illuminated with coherent object light and reference light from a first exposure side of the recording material, the information to be stored in the volume transmission hologram being transported in the object light, it being provided that with the transport device a hologram master is coupled, wherein the hologram master contains at least one diffraction structure, and the control device is designed to cause the transport device to bring the at least one section of the recording material with the first exposure side into contact with a contact side of the hologram master and the light source and/or the Optical unit to control that the coherent incident light is generated and the hologram master with the coherent incident light from a contact side opposite the incident side, ie from the of the the side facing away from the recording material, while at least one section of the recording material is in contact with the hologram master, and the object light is generated at the at least one diffraction structure of the hologram master via diffraction of the coherent incident light and out of the hologram master and into the recording material from the first exposure side, wherein the at least one diffraction structure in the hologram master is formed in such a way that part of the incident light is not diffracted and enters the recording material from the hologram master as the reference light and from the first exposure side, so that the object light and the reference light in the interfere with at least one section of the recording material and expose the volume transmission hologram of the security hologram into the recording material, the hologram master being the at least one diffraction structure a volume transmission onshologram which, when irradiated with the incident light, generates the generated object light in such a way that a real image is reconstructed from the object, the image plane of which deviates from the plane in which a photosensitive layer of the recording material is arranged... This device has the same advantage as the method, namely in particular that a very simple and robust production of a large number of security holograms is made possible.

In order to have several identical hologram masters available and/or to be able to easily replace them with a similar hologram master as soon as this is worn out or damaged during production, a copied master hologram referred to as an H2 hologram is preferably used as the hologram master. In other embodiments, the at least one diffractive structure is an H3 hologram or even higher "generation number".

A material which comprises at least one photosensitive layer is used as the recording material. Since photosensitive layers are usually also sensitive to the environment, ie moisture, gaseous substances present in the atmosphere and the like, a recording material is preferably produced or provided from a photosensitive layer and at least one protective layer, preferably two protective layers, so that the photosensitive Layer and the at least one protective layer are in contact and the at least one protective layer covers the entire surface of the photosensitive layer and protects it. As a rule, the photosensitive layer is covered over an area on each side by a protective layer. The protective layers are preferably produced from a transparent material which allows light to pass through almost unhindered at the wavelength with which the volume transmission hologram of the security hologram to be produced is produced. The recording material is preferably provided as a film, ie as a laminate of a photosensitive layer enclosed on both sides by a protective film. When the recording material is brought into contact with the hologram master, an indirect mechanical contact between the photosensitive layer, i.e. the actual material in which the hologram is exposed and in which it is stored, and the hologram master. In the case of the hologram master, too, the actual diffractive structure, for example a master hologram stored in a film, can be covered by a protective film.

Although the diffractive structure of the master hologram and the photosensitive layer of the recording material are not directly brought into direct mechanical contact, there is indirect mechanical contact via the protective layers and foils arranged in between. However, a significant advantage of the copying method is not based on the fact that the photosensitive layer and the diffraction structure are in close proximity to one another, but rather on the fact that mechanical movement of the photosensitive layer relative to the diffractive layer to be copied is prevented. This is achieved in the same way via the indirect contact, via the protective layers and protective films. Bringing the recording material into contact thus means that a direct or indirect mechanical coupling is established between the photosensitive layer and the diffraction structure in the hologram master during the production of the security hologram.

In one embodiment according to the invention, the hologram master is produced or provided with the at least one diffraction structure in the form of a volume transmission hologram which, when irradiated with the incident light, generates the generated object light in such a way that a real image is reconstructed from the object, the image plane of which deviates from the plane, in which the photosensitive layer of the recording material is arranged. Depending on the position of the image plane of the volume transmission hologram of the hologram master, a hologram is copied into the recording material, which during reconstruction floats in front of the physical plane in which the hologram is stored or behind the plane in which the hologram is physically stored. In another embodiment, it is possible for the image plane to coincide with the photosensitive layer so that the hologram appears to be formed in the plane in which it is also physically stored.

In order to individualize the security hologram produced, one embodiment provides that the incident light is spatially modulated in terms of its intensity, so that different areas of the hologram master are illuminated with different intensities of the incident light. Information is then stored in this intensity pattern, for example a facial image or else alphanumeric characters. Both a black-and-white-type coding and a grayscale-type coding are possible, with black-and-white-type coding producing a diffraction efficiency between two values, for example 0 and 80%, and with a grayscale-type expression different diffraction efficiencies between 0 and 90% or between 10% and 90%, to name just a few examples, can be trained.

It is particularly advantageous for such an individualization if a hologram of a scatterer, in particular a diffusing screen or a ground-glass screen, is stored in the hologram master, i.e. in the diffraction structure of the hologram master, which converts an incident light beam of directed light into an expanded light beam in which the light propagates in different directions of a solid angle range around a particular direction. In one embodiment, the at least one diffraction structure of the hologram master comprises a transmission volume hologram of a ground glass screen, which converts light that is incident in a directed manner into diffusely scattering light. In particular, embodiments are preferred in which the light is scattered around a preferred direction. For example, directed light that falls on the master at a first angle relative to a surface normal of an impingement surface of a planar master designed with plane-parallel surfaces is diffracted in such a way that it exits diffusely scattered about a preferred direction, with a second angle of the preferred direction relative to a surface normal of the outlet side is measured. The first and the second angle are preferably different in terms of absolute value. Vertically incident light is diffusely scattered, for example, about a preferred direction which is inclined by 45° with respect to the surface normal. The light is diffusely scattered in a lobe around the preferred direction.

In such an embodiment, the information stored in the master hologram is homogeneous over the surface, so that a variation in the diffraction efficiency caused by modulation of the light intensity during copying in the copy produced is not superimposed by the information stored in the master hologram and intensity fluctuations caused thereby.

In other embodiments, a volume transmission hologram of a three-dimensional object is stored in the master hologram. The volume transmission hologram thus stores at least part of the spatial structure of the three-dimensional object. Also a such a hologram master can be copied individually.

In one embodiment, the recording medium is provided with protective layer or layers transparent to the wavelength or wavelengths of the object light and the reference light.

In addition, the hologram master is produced or provided in such a way that the at least one diffraction structure produces the object light and the reference light with an intensity ratio such that a predefined contrast is formed in the volume transmission hologram. Theoretically, an intensity ratio of 1:1 would be optimal to expose a very high-contrast volume transmission hologram. In practice, however, an intensity distribution is selected in which the reference light component is greater than the object light intensity component. Preferred intensity ratios of object light intensity to reference light intensity are between 1:1 and 1:10.

A security hologram that is particularly difficult to imitate is obtained if a hologram master is used which is additionally manufactured or provided with at least one further diffraction structure which, with a corresponding exposure through the contact side of the hologram master, reconstructs a reflection hologram, and the incident light is guided via an optical unit which comprises at least one beam splitter and optical light-guiding elements or lowering elements, so that part of the incident light is guided by the optics unit onto the exposure side of the hologram master in order to expose the volume transmission hologram into the recording material, and also part of the incident light through the recording material onto the contact side of the hologram master is guided in order to expose the reflection hologram of the further diffraction structure in the recording material. A security hologram produced in this way can reconstruct both a reflection hologram when viewed from an upper side and the corresponding volume transmission hologram when illuminated through the underside.

In a particularly preferred embodiment, both the volume transmission hologram and the volume reflection hologram are exposed at the same time. In this case, different areas of the recording material are preferably exposed at the same time.

Areas in the hologram master which store the volume reflection hologram are preferably offset laterally with respect to those areas in which the volume transmission hologram is stored. As a result, when copying, areas of the reflection volume hologram stored therein are different from the areas in which the volume transmission hologram is stored, even in the security hologram that is produced. This makes it possible to achieve a maximum possible diffraction efficiency for the respective hologram types both in the volume reflection hologram and in the volume transmission hologram.

If the areas that store the volume transmission hologram and those areas that store the volume reflection hologram are laterally nested, but not overlapping, and the physical dimensions of the individual areas are chosen to be small, a viewer of both the reflection volume hologram and the volume transmission hologram will experience Reconstruction nevertheless full-surface information representations with a suitable choice of the information stored in the respective hologram types. If both volume types in the hologram master embody, for example, ground glass screens, a suitable nesting, for example a strip-shaped alternating nesting, of the areas that form the volume transmission hologram and the areas that form the reflection volume hologram in the hologram master results in a similar strip-like pattern in the security hologram that is produced Nesting of the areas. In the reconstruction of the areas that store a volume reflection hologram, however, a uniform surface of a ground glass screen results overall. The same applies to the reconstruction of the volume transmission hologram. The prerequisite is, of course, that the area sizes, for example the strip widths, are so small that the human observer does not resolve the strips separately when capturing the reconstructed hologram.

The hologram master is preferably formed with the plurality of diffraction structures by these being introduced into different photosensitive layers, in particular being exposed, and then being arranged one above the other. In particular, if the areas of the photosensitive layer in which the volume transmission hologram to be copied and the reflection hologram to be copied are arranged do not overlap and are also spatially separated from one another in such a way that the areas that reproduce common information are coherent and not nested with one area of the other Are formed hologram type, so there are only minor relative positioning difficulties.

• 1 eine schematische Darstellung eines holografischen Aufzeichnungsmaterials und eines Hologrammmasters zur Erläuterung der Herstellung eines Sicherheitshologramms;
• 2 eine schematische Darstellung einer Vorrichtung zum Herstellen eines Sicherheitshologramms;
• 3 eine weitere schematische Darstellung zur Erläuterung der Herstellung eines Sicherheitshologramms und
• 4 eine schematische Darstellung eines Sicherheitsdokuments mit einem Sicherheitshologramm.

The invention is explained in more detail below with reference to a drawing. Here show:

• 1 a schematic representation of a holographic recording material and a hologram master to explain the production of a security hologram;
• 2 a schematic representation of a device for producing a security hologram;
• 3 a further schematic representation to explain the production of a security hologram and
• 4 a schematic representation of a security document with a security hologram.

In 1 a hologram master 10 and a recording material 40 arranged in contact thereon are shown schematically. The hologram master 10 has an underside 11 which is also referred to as the irradiation side 12 . A top 13 forms a contact side 14. The hologram master 10 is in contact with the recording material 40 with this. This means that the underside 41 of the recording material is mechanically in contact with the hologram master 10 or the contact side 14 of the hologram master 10 . The hologram master 10 includes a diffraction structure 20 which is indicated by broken vertical lines 22 .

If the hologram master 10 is illuminated from the irradiation side 12 with coherent irradiation light 100, preferably laser light, this is partially diffracted at the diffraction structure 20. The diffracted light 110 carries information that is stored in the diffraction structure 20 of the hologram master 10 . The diffracted light 110 thus represents object light 111 for forming a transmission hologram 210. The light 120 passing through the hologram master without diffracting represents reference light 121 for producing the transmission hologram 210. Both the object light 111 and the reference light 121 emerge from the first exposure side 42, ie the underside 41, into the recording material 40. The recording medium 40 includes a photosensitive layer 50 in which interference caused by the interference of the object light 111 and the reference light 121 is recorded as a transmission hologram 210 . The holographic information thus stored in the recording material 40 is similar to the information stored in the diffraction structure 20 in the hologram master 10 . During the execution of the exposure, the hologram master 10 and the recording material 40 are at rest relative to each other. After the exposure has been carried out, the recording material 40 is moved relative to the hologram master and a further transmission hologram is produced in the recording material, which is preferably in the form of roll material. Since the interference information is stored in the volume of the recording material 40, the transmission hologram 210 is referred to as a so-called volume transmission hologram 220. A security hologram 200 is thus created in the recording material 40, which can then be integrated into a security document. The volume transmission hologram 220 is used there as a security feature.

In the example shown, the hologram master 10 is exposed to the irradiation side 12 with irradiation light 100 in such a way that it strikes the hologram master 10 perpendicularly. In the illustrated embodiment, the object light 111 is diffracted at an angle of 45°. The reference light 121 passing through without diffraction thus strikes the first exposure side 42 of the recording material 40 perpendicularly, while the object light enters at an angle of 45°. These angles can be freely selected within wide limits. These are specified when the hologram master is manufactured.

The hologram master usually includes a so-called H2 hologram. An H2 hologram is a hologram that is created from a first hologram, an H1 hologram, in a copying process. The H1 hologram is produced as a volume transmission hologram, for example of a scatterer, in particular a ground glass screen. The fully developed first volume transmission hologram H1 is then irradiated with coherent reconstruction light, so that a real image of the object stored in the volume transmission hologram is generated. For example, the recording material for the copied H2 hologram is arranged in the image plane of the real image and an interference of the reconstructed real image and the reference light is generated with reference light. It is also possible and preferred to arrange the recording material for the copied H2 hologram in a plane that deviates from the image plane. Hereby it is achieved that the copied object appears to float in front of the plane of the hologram or appears to float behind the plane of the hologram when viewing the later reconstruction of the H2 hologram. The direction of incidence for the incident light relative to the hologram master and the direction of diffraction of the object light 111 are defined via the selection of the original exposure direction of the H1 hologram or of the H2 hologram.

It is thus clear to the person skilled in the art that angles deviating from the angles shown here can be selected. For manufacturing reasons, vertical irradiation of the incident light is preferred. Deviating from this, however, the incident light can also be made at an angle to a surface normal of the incident side of the hologram master and then, for example, the object light can be deflected in such a way that it exits perpendicularly from the contact side of the hologram master. However, embodiments are also possible in which the incident light is incident at a first angle to a surface normal of the irradiation side and the object light exits at a second angle to a surface normal of the contact side of the hologram master, with the first angle and the second angle being zero as well are different from each other.

In order to increase protection against forgery of the security hologram, in some embodiments it is provided that a volume reflection hologram is also exposed in the security hologram in addition to a volume transmission hologram.

In 2 a schematic representation of a hologram master 10 and a recording material 40 is shown in order to schematically represent a production of such a security hologram 200 . The dimensions shown, both of the holographic recording material 40 and of the hologram master 10, do not correspond to the real situation, as in the other figures, but are chosen only to illustrate the invention. The same technical features are provided with the same reference symbols in all figures.

In this embodiment, the hologram master 10 has a carrier 15 which is formed from a transparent solid body, for example quartz or quartz glass. This carrier 15 is preferably clear and completely transparent for the wavelength of the light with which the security hologram 200 is to be exposed. A master volume transmission hologram 16 and a master volume reflection hologram 17 offset laterally are arranged on the carrier 15 . The master volume transmission hologram 16 and the master volume reflection hologram 17 can be stored in separate holographic storage materials, e.g. B. photopolymer layers, which are arranged next to each other. The master volume transmission hologram 16 and the master volume reflection hologram 17 can also be formed together in a holographic storage material. It is also possible for the master volume transmission hologram and the master volume reflection hologram to be stored interleaved, for example in alternating strips, in the hologram storage material. In this case, the alternating strips are preferably chosen so narrow that when the volume transmission hologram or the volume reflection hologram is reconstructed, a two-dimensionally closed image is reconstructed and a human observer cannot resolve the individual strips at a typical viewing distance of a security element of around 30 cm to 60 cm and perceives a closed, two-dimensional image. This applies in particular when a scatterer, for example a diffusing screen or a matte sheath, is stored as information in the master volume transmission hologram and/or the master volume reflection hologram.

In the illustrated embodiment 2 the recording material 40 consists on the one hand of a photosensitive layer 50 and two protective layers 60, 70, which adjoin the lower side 51 and the upper side 53 of the photosensitive layer and cover these in each case and protect them against environmental influences. The protective layers 60, 70 are transparent at least for the wavelengths used to expose the hologram or holograms. A bottom 61 of the protective layer 60 forms the bottom 41 of the recording material 40. The top 63 of the protective layer 60 is in contact with the bottom 51 of the color-sensitive layer 50. FIG. The top 53 of the photosensitive layer 50 is in turn in contact with the bottom 71 of the protective layer 70 . The upper side 73 of the protective layer 70 forms the upper side 43 of the recording material 40.

The volume transmission hologram 220 is exposed into the photosensitive layer 50 or the recording material 40 in a manner analogous to that described above in connection with FIG 1 already explained. Irradiation of incident light 100 takes place via an incident side 12 of the hologram master 10 and thus from below through the hologram master 10 into the recording material 40. A copy of the master volume reflection hologram 17, on the other hand, occurs when incident light 100' is irradiated through the recording material 40 and from the contact side 14 into the hologram master 10. There, the incident light 100' is reflectively diffracted at a further diffraction structure 30 of the master volume reflection hologram 17. The reflectively diffracted light 130 interferes with the incident light 100' in the recording material 40. The further diffraction structure 30 of the master volume reflection hologram 17 is indicated by horizontal broken lines 32. The exposure of the volume transmission hologram 220 and the Volu The production time, ie the exposure time for the production of the entire security hologram 200, can be reduced as a result. Alternatively, it is possible to carry out the volume reflection hologram 230 before or also after the exposure of the volume transmission hologram 220 . In particular, if the two types of hologram are formed in a spatially nested manner in the recording material, such a temporally separate production can be advantageous in order to avoid undesirable side effects.

As an alternative to the variant, which is 2 is shown, the method, which is shown schematically in 1 is shown can be expanded to the effect that the further diffraction structure is formed with the master volume reflection hologram in a further hologram master, which is arranged opposite the hologram master adjacent to the recording material. In such an embodiment, the recording material is arranged in a quasi-sandwich fashion between the hologram masters, both of which are brought into contact with the recording material on opposite sides thereof. In such an embodiment, exposure of the volume reflection hologram with incident light from the same side as exposure of the volume transmission hologram is possible. The hologram master of the volume transmission hologram preferably has no diffraction structures in those areas in which the further hologram master has diffraction structures of the volume reflection hologram and vice versa. As a result, a maximum desired diffraction efficiency can be achieved for both types of hologram.

In this alternative embodiment, one of the hologram masters can be provided as a film similar to the recording material. Reliable contact without gas pockets between the hologram master and the recording material can be ensured via a pressure roller, which simultaneously rolls over the hologram master provided as a film and the recording material on the other master provided as a solid body.

Other embodiments use two hologram masters, both of which are in the form of film and are guided between two rollers. It is also possible to use two hologram masters designed as solid bodies, one hologram master preferably being placed first with an edge when it is placed on the recording material, which is arranged between the two hologram masters, and then placed on the recording material with a rotary movement around the edge will. This also makes it possible to avoid gas inclusions.

A thickness of the recording material is chosen in such a way that no overmodulation takes place in the recording material. The diffraction structure of the volume transmission hologram is preferably formed in such a way that an intensity of the object light 111 is lower than an intensity of the reference light 121 . Intensity ratios between 1:1 to 1:3 or 1:10 between object light intensity and reference light intensity are preferred.

In 3 a device 300 for producing a security hologram 200 is shown schematically. The hologram master 10 resembles, for example, a hologram master as shown in 2 is shown. The hologram master 10 is arranged in a recording device 360 which has a recess or a window 370 in order to enable exposure and transmission of the hologram master 10 with the at least one diffraction structure 20 .

The recording material 40 is provided on a roll 310 as a photosensitive film 50 provided with protective layers 60, 70 and guided over the hologram master 10 step by step. The exposed recording material is rolled up on a further roll 320 after exposure. In order to achieve good contact between the recording material 40 and the hologram master 10, after the recording material 40 has been transported by a length which corresponds to at least a length 330 of the volume transmission hologram 16 stored in the hologram master, it can be pressed against the hologram master 10 via a pressure roller 340. This is, for example, initially returned in the opposite direction to the transport direction during the transport of the recording material 40 and then rolled over the recording material 40 embodied as a film and the hologram master 10 in the transport direction in order to press the holographic recording material 40 against the hologram master 10 . The two rollers 310, 320 and the pressure roller 340, together with a drive unit for the rollers (not shown), form a transport device 350.

The device 300 also includes a light source 400, which is embodied as a laser, for example. The laser generates the incident light 100. This is widened into a light stripe 520 in a first lens unit 510 in the illustrated embodiment. This widening, which is perpendicular to the drawing, is over a section tion level takes place, spatially indicated. A part 106 of the light stripe 520 is guided as incident light 100′ through an upper side 43 of the recording material 40 into the hologram master 10 and is diffractedly reflected there at the further diffraction structure 30, so that reflected light 130 is produced. Interference of the incident light 100' and the reflective diffracted light 130 results in interference in the recording material, which copies the volume reflection hologram 230 in the recording material 40 and exposes it. Another portion 105 of the incident light 100 embodied as a strip is guided past the recording material 40 via deflection units 540 and from below through the hologram master 10 into the recording material 40 . Here, diffraction takes place at one diffraction structure 20, which is the master volume transmission hologram 14, so that diffracted object light 111 is produced and the rest of the undiffracted light 120 forms the reference light 121 in order to expose the volume transmission hologram 220 in the recording material 40. In order to indicate the widening in the plane perpendicular to the plane of the drawing, two schematic excerpts are again inserted.

In a development of the device, a local light modulator 550, English spatial light modulator—SLM, can be arranged in the beam path, which is formed, for example, as a liquid crystal structure in cooperation with a polarization filter 560. The spatial light modulator has individual, individually controllable pixels which, in conjunction with a polarization filter 560, can modulate a light intensity between 0% and 100%. The light intensity can thus be modulated differently along the light stripe direction 521 along the light stripe 520 . In this way, information that is encoded in the corresponding light intensities can be stored in the volume reflection hologram 230 as well as in the volume transmission hologram 220 . Such an embodiment is particularly suitable for a master volume reflection hologram 17 and for a master transmission hologram 16, each of which contains a scatterer, for example a ground glass screen, stored as object information. When reconstructing the respective volume holograms, this results in almost homogeneous images of the screens, which are modulated with regard to their brightness. There can be a light-dark modulation in the sense of a black-and-white modulation or also a gray scale modulation, depending on how the light modulation is coordinated with regard to the intensity ratios during exposure.

The components used for guiding and, if necessary, modulating the incident light 100, 100' form a so-called optical unit 500.

The manufacturing process is controlled via a control device 600, for example a computer or the like, which controls the transport device 350 and the optics unit 500 and/or the light source 400.

In 4 a security document 1000 is shown schematically. This is made from a plurality of substrate layers 1100, in particular from plastic layers, which are connected to one another in a lamination process. The security hologram 200 is applied between these layers 1100 or on these layers. For this purpose, for example, adhesion promoters or adhesives can be used, in particular hot melt adhesives or UV-activatable adhesives. Security document 1000 is preferably configured such that it is transparent in volume, at least in region 1200 in which volume transmission hologram portion 221 of security hologram 200 is configured, i.e. light can pass through at least every wavelength from an upper side 1003 to an underside 1001, which is the reconstruction of the volume transmission hologram 220 is necessary. The passage of light is possible in such a way that imaging according to geometrical optics with this wavelength through the document body 1005 is possible. In the area 1300 of the volume reflection hologram 230, the document body does not have to be completely transparent. Rather, it is sufficient if the document body 1005 is transparent between the security hologram 200 and the top 1001 of the document body 1005 .

There are different ways of verifying the security hologram in the security document. When reconstruction light 1400 is irradiated via the underside 1001 of the security document 1000, the viewer 2000 can perceive a virtual image of the volume transmission hologram 220 from the top 1003, which corresponds to the original object, optionally modulated with the information that is impressed on the spatial light modulator. In the illustrated exposure geometry, the light is irradiated according to FIG 2 perpendicularly through the underside 1001. It is also possible to project a real image on a screen above the security document.

In order to reconstruct the reflection hologram, it is sufficient to radiate light 1500, for example perpendicularly, via the upper side 1003 and to view the document at a 45° angle in order to verify a reconstruction of the volume reflection hologram 230.

Overall, diverse possibilities are opened up for producing differently designed security holograms with the method described, which lead to different effects in the verification.

In one embodiment, the security document has a transparent layer 1110 between the underside 1001 of the document body 1005 and the security hologram 200, which has a color-filtering effect in such a way that it selects the wavelength or the wavelength range from white light in which the light for a Reconstruction of the volume transmission hologram 220 is located. This creates the possibility of reconstructing the volume transmission hologram 220 with a white light source and obtaining an image with sharp contours. Without color filtering, the volume hologram is reconstructed with white light illumination for the different light colors in slightly different directions, so that images of the information stored in the hologram that are offset and superimposed in different colors are created.

In addition to forming the volume transmission hologram as an image of a ground glass screen, a barcode can be imaged onto the hologram film through a lens so that a focal plane lies in the recording material and a Fourier hologram is thus generated as a volume transmission hologram. In addition, many other variants are possible. For example, three-dimensional objects can also be stored in the volume transmission hologram.

Other embodiments provide that multiple volume reflection holograms or volume transmission holograms in the hologram master are superimposed or interleaved laterally to each other, which diffract the light of different wavelengths, for example the colors red, green and blue, so that a full-color image is stored holographically by the superimposition or suitable interleaving or can be reconstructed.

It will be understood by those skilled in the art that only exemplary embodiments are described and that the features described in the individual embodiments can be combined and used to implement the invention.

reference list

10

hologram master

11

bottom

12

irradiation side

13

top

14

contact page

15

carrier

16

Master volume transmission hologram

17

Master volume reflection hologram

20

diffraction structure

22

vertical openwork stripes

30

further diffraction structure

32

horizontal broken lines

40

recording material

41

bottom

42

first exposure side

43

top

50

photosensitive layer

51

bottom

53

top

60

protective layer

61

bottom

63

top

70

another layer of protection

71

bottom

73

top

100, 100'

single beam light

105

Part of the light (single beam light 100')

106

Part of the light (single beam light 100)

110

diffracted light

111

object light

120

undiffracted light

121

reference light

130

reflective diffracted light

200

security hologram

210

transmission hologram

220

volume transmission hologram

221

volume transmission hologram fraction

230

volume reflection hologram

300

Device for producing a security hologram

310

role

320

another role

330

Length of the volume transmission hologram

340

pinch roller

350

transport device

360

recording device

370

window (or recess)

400

light source

500

optical unit

510

lens unit

520

streaks of light

521

light stripe direction

540

deflection units

550

local light modulator

560

polarizing filter

1000

security document

1001

bottom

1003

top

1005

document body

1100

substrate layers

1200

area (transparent window)

1300

Area

1400

Reconstruction light (volume transmission hologram)

1500

Reconstruction Light (Volume Reflection Hologram)

2000

viewer

Claims (9)

Method for producing a security hologram (200) with a volume transmission hologram (220), the security hologram (200) being intended for incorporation into a value or security document, comprising the steps: providing a recording material (40), irradiating the recording material (40) with coherent object light (111) and reference light (121) from a first exposure side (42) of the recording material (40), with the information to be stored in the volume transmission hologram (220) being transported in the object light (111), with a hologram master (10) is manufactured or provided, which contains at least one diffraction structure (20), and the recording material (40) is brought into contact with the first exposure side (42) with a contact side (14) of the hologram master (10) and coherent incident light (100; 100' ) is generated and the hologram master (10) with the coherent incident light (100; 100 ') from one of the Ko tact side (14) opposite irradiation side (12) and at the at least one diffraction structure (20) of the hologram master (10) via diffraction of the coherent irradiation light (100; 100') the object light (111) is generated, which emerges from the hologram master (10) and enters the recording material (40) from the first exposure side (42), the at least one diffraction structure (20) in the hologram master (10) being so is formed such that part of the incident light (100; 100') is not diffracted and exits the hologram master (10) as the reference light (121) and enters the recording material (40) from the first exposure side (42), so that the Object light (111) and the reference light (121) interfere in the recording material (40) and expose the volume transmission hologram in the recording material (40), the recording material (40) comprising a photosensitive layer (50), characterized in that the hologram master (10 ) is prepared or produced with the at least one diffraction structure (20) in the form of a volume transmission hologram (220) which, when irradiated with the incident light (100; 100' ) the generated object light (111) is generated in such a way that a real image is reconstructed from the object, the image plane of which deviates from the plane in which the photosensitive layer (50) of the recording material (40) is arranged, with a material thickness of the recording material (40 ) is selected when it is provided in such a way that no overmodulation occurs in the finished volume transmission hologram (220). procedure after claim 1 , characterized in that the recording material (40) is produced from the photosensitive layer (50) and at least one protective layer (60; 70) or is provided with the photosensitive layer (50) and at least one protective layer (60; 70), so that the photosensitive layer (50) and at least one protective layer (60; 70) are in surface contact and the at least one protective layer (60; 70) covers and protects the photosensitive layer (50) over its entire surface. Method according to one of the preceding claims, characterized in that the Incident light (100; 100') is spatially modulated in terms of its intensity, so that different areas of the hologram master (10) are illuminated with different intensities of the incident light (100; 100'). Method according to one of the preceding claims, characterized in that the recording material (40) is provided with a protective layer (60; 70) transparent for the wavelength or for the wavelengths of the object light (111) and the reference light (121). Method according to one of the preceding claims, characterized in that the hologram master (10) is produced or provided in such a way that the at least one diffraction structure (20) produces the object light (111) and the reference light (121) with an intensity ratio such that the predetermined contrast is formed in the volume transmission hologram (220). Method according to one of the preceding claims, characterized in that . that the at least one diffraction structure (20) is a volume transmission hologram of a scatterer or a diffusing screen, which converts an incident light beam with directed light into an expanded light beam, in which the light propagates in different directions of a solid angle range around a specific direction. Procedure according to one of Claims 1 until 5 , characterized in that the at least one diffraction structure (20) is a volume transmission hologram of a three-dimensional object whose spatial structure is at least partially stored in the volume transmission hologram. Method according to one of the preceding claims, characterized in that the hologram master (10) is additionally produced or provided with at least one further diffraction structure (30) which, with a corresponding exposure through the contact side (14) of the hologram master (10), reconstructs a volume reflection hologram, and the incident light (100; 100') is guided via an optics unit (500), comprising light-guiding elements, so that a part (105) of the incident light (100) is projected from the optics unit (500) onto the exposure side (42) of the hologram master (10) is guided in order to expose the volume transmission hologram (220) into the recording material (40) and a part (106) of the incident light (100') is guided through the recording material (40) onto the contact side (14) of the hologram master (10), to expose the volume reflection hologram of the further diffraction structure (30) in the recording material (40). Method according to one of the preceding claims, characterized in that the incident light (100; 100') is spatially modulated with regard to its intensity, the intensity being fixed individually between a minimum value and a maximum value.

Images