Replicating device for copying holograms into liquid photopolymers

Abstract

The invention relates to a device for continuously replicating a hologram comprising a coating module which is designed to coat a liquid photopolymer onto a first carrier film, a lamination module which is designed to apply a second carrier film to the first carrier film coated with the photopolymer, in order to obtain a photopolymer composite including a liquid photopolymer layer between two carrier films, an exposure module, wherein the exposure module has a light source and a master element with a master hologram to be replicated, wherein the master element is axially rotatably mounted and the exposure module is designed to bring the photopolymer composite in optical contact with the master element, while the light source exposes the master hologram in order to obtain a replicated hologram in a region of the photopolymer composite, and a fixing module which is designed to cure the replicated hologram in the photopolymer composite.

Description

[0001] Replication device for copying holograms into liquid photopolymers

[0002] DESCRIPTION

[0003] The invention relates to a device for the continuous replication of a master hologram in a liquid photopolymer.

[0004] The device according to the invention comprises a coating module configured to coat a liquid photopolymer onto a first carrier film, a lamination module configured to apply a second carrier film to the first carrier film coated with the photopolymer in order to obtain a photopolymer composite comprising a liquid photopolymer layer between two carrier films, an exposure module comprising a light source and a master element, wherein the master element has a master hologram and is mounted so as to be axially rotatable. The exposure module is configured to bring the photopolymer composite into optical contact with the master element, while the light source exposes the master hologram onto a region of the photopolymer composite to obtain a replicated hologram. The device also comprises a fixing module configured to cure the replicated hologram in the photopolymer composite.

[0005] Background and state of the art

[0006] The invention relates to the field of hologram replication.

[0007] Modern micro-optical processes allow tasks such as imaging or optical monitoring to be discreetly integrated into large-format glass surfaces using holographic optical elements (HOE).

[0008] HOEs typically refer to optical components in which holographic properties are used to achieve a specific light beam path, such as transmission, reflection, diffraction, scattering, and / or deflection, etc. This allows desired optical functionalities to be implemented compactly in any substrate. The holographic properties preferably exploit the wave nature of light, particularly coherence and interference effects. Both the intensity and phase of the light are taken into account.

[0009] Such holographic elements are used in many areas, such as in transparent displays (e.g., in shop windows, refrigerated cabinets, vehicle windows), for lighting applications such as information or warning signals in glass surfaces, and light-sensitive detection systems, for example, for interior monitoring (eye tracking in vehicles or presence status tracking of people indoors). WO2020157312A1 discloses an example of a HOE that has been integrated into a vehicle window. The hologram incorporated into the window can serve as a waveguide that guides incoming light to a detector. The hologram is made from a photosensitive material, such as photosensitive glasses, dichromate gelatins, or photopolymers. These can, for example, be applied to a polycarbonate film and exposed there accordingly.The film can then be laminated to a waveguide substrate to create the waveguide and then laminated to a vehicle windshield.

[0010] WO2018054985 A1 discloses a volume hologram that is integrated into the rear light of a vehicle to give it a distinctive appearance. For this purpose, the volume hologram can be exposed into a holographic layer, for example, comprising photopolymers, and applied as a film directly to a rear light. The volume hologram can provide both a color filter function and a beam-shaping function. To achieve this, a suitable composition of light-sensitive materials can be selected. The thickness of the hologram can also be selected so that it functions as a white-light reflection hologram, with a wavelength for reconstruction being selected from a available spectrum.

[0011] WO2016202595A1 discloses a holographic element produced as an HOE layer in a spectacle lens. By integrating an HOE into the lens, relevant data can be displayed to the user or an optical functionality can be implemented. For this purpose, a liquid photopolymer is coated onto a surface of the glass substrate before it is exposed. To make a sufficient contribution to the optical function, e.g., to the prescription of the lens, a photopolymer thickness of between 50 and 100 μm is preferably used. By adding dyes to the photopolymer, the layer can also be configured to fulfill a color-filtering function. In some embodiments, the photopolymer layer is provided on a carrier film before it is applied to the lens, e.g., with a Bayfol® HX film from Covestro AG. The holographic layer is sealed by applying additional layers.This means the overall thickness of the glasses can be kept low.

[0012] As the examples demonstrate, HOEs can be used for a wide variety of applications due to their space-saving design and diverse functionalities. Therefore, there is a need for series-ready hologram replication processes that can preferably be integrated into a wide variety of components, particularly glass surfaces. However, the manufactured holographic elements must exhibit different properties depending on the application, such as light sensitivity, layer thicknesses, or material compositions. With reference to the above examples, it may be necessary, for example, for different properties of the holographic elements to be used between spectacle lenses of different colors or strengths, or between taillights of different brands or models.There is therefore a need for efficient series production of holographic elements with different properties - preferably without the need to use several different devices to produce the holograms or to adapt them extensively.

[0013] The production of holographic optical elements as inserts typically requires the use of a carrier substrate and a light-sensitive layer. The traditionally used light-sensitive layer is a dichroic gelatin. A preferred alternative is the use of photopolymers, which are usually available in dried film composites in specific sizes, thicknesses, and compositions optimized for different purposes, e.g., for exposure to light of a specific wavelength.

[0014] EP3065002B1 discloses a method for producing holographic security elements. Each holographic security element is built up step by step, providing a carrier film with a replication layer. The replication layer has a relief structure produced by embossing. A photopolymer in liquid form is applied to the replication layer to fill the valleys of the relief structure. A doctor blade is used to partially remove the photopolymer from areas of the relief structure, so that the photopolymer layer can have a varying thickness. The layer buildup is then passed over the outer surface of a cylindrical master element so that the liquid photopolymer layer comes into contact with the outer surface. In some embodiments, the outer surface has a further relief structure, which is transferred to the liquid photopolymer layer by printing.At the same time, the master element is exposed to inscribe a volume hologram in the liquid photopolymer layer. The deformability of the photopolymer serves to produce a security element that features both a relief structure and a volume hologram. After the photopolymer layer is cured in an exposure station, an adhesive film is applied to its surface.

[0015] DE102006016139 A1 discloses another method for the mass production of holographic security elements. Here, too, the holographic security elements are built up step by step and comprise a liquid photopolymer layer. This layer is brought into contact with a relief structure of a master element to emboss the relief structure into the security element. Simultaneously, a master hologram is replicated into the liquid photopolymer layer by exposure. The provision of liquid photopolymer layers during contact with a master element is motivated in EP3065002B1 and DE102006016139 A1 by the desired transfer of a relief structure.

[0016] However, the exposed photopolymer layer also comes with disadvantages. Firstly, the processes exhibit increased sensitivity to mechanical influences. Secondly, the type and properties of the photopolymer used are limited, as the viscosity or consistency of the liquid photopolymer may need to be adjusted to achieve a stable layer thickness, a stable relief structure, and / or low adhesion to the master element. Furthermore, thorough cleaning or the use of repellent coatings on the master element is necessary to prevent the buildup of photopolymer residues.

[0017] WO2019 / 215272A1 discloses another process for the mass production of holographic security elements. A light-sensitive film is used as the starting material for the production of the holographic elements. This film is preferably in the form of a composite of two plastic films, between which a dried, heat-stable photopolymer is sandwiched. The photopolymer is then exposed using a conventional process. Particularly in cases where no embossing process is to be performed, this starting material for the exposure of volume holograms is mechanically more robust than the deformable alternatives using liquid photopolymers that contact the master elements, and it avoids photopolymer residues.

[0018] Holographic films comprising a film substrate and a light-sensitive photopolymer layer are commercially available, for example, from Covestro Deutschland AG under the Bayfol® product line. W02018 / 206503A1 discloses, by way of example, a manufacturing process for providing a film-bound photopolymer film for exposure with a hologram. The light-sensitive film contains a layer structure comprising a curable protective layer C, a dried photopolymer layer B, and a carrier layer A. This is intended to produce durable photopolymer films in which the holograms can also be easily replicated.

[0019] Since the production of light-sensitive films is usually carried out separately from exposure and fixation, these film composites must first be mass-produced with the desired properties. Adapting the properties of the film composite containing the photopolymer is disadvantageous. Instead, a new light-sensitive film must be developed for each change in layer thickness, carrier substrate, or photopolymer sensitivity. This is particularly disadvantageous for pre-production and small-batch holograms, for example, if special adaptations to the film-bound photopolymer are necessary for special holographic systems, and the additional development effort required burdens the overall costs.

[0020] Furthermore, the use of conventional hologram exposure methods results in a slow replication process that is sensitive to mechanical and positioning errors.

[0021] EP0896260A2 discloses an example of a method and device for copying holograms. For this purpose, a master hologram in the form of a ground glass screen is arranged parallel to a light-sensitive film. Depending on the type of hologram, a laser is positioned to scan the master hologram line by line. During this process, it is important that the position of the film remains stable relative to the master hologram. The holograms are exposed one after the other, with interruption times slowing down the process. Similar to WO2019 / 215272A1, EP0896260A2 also uses a prefabricated light-sensitive film as the starting material. The properties of the film cannot be subsequently adjusted for process-related reasons; instead, they would have to be developed and manufactured separately with modified properties. Economical production of pre-production or small series is either impossible or difficult.

[0022] As an alternative to prefabricated light-sensitive films, some prior art proposals have proposed applying the liquid photopolymer directly to the product into which an HOE is to be integrated. The method according to DE102019130022A1 for integrating a hologram into a composite lens with a curved geometry, as well as the above-mentioned method for producing eyeglasses from WO2016202595A1, are examples of such an in situ coating.

[0023] However, the proposed method is complex and inefficient, as the coating cannot be carried out continuously. The process is further slowed by the fact that each substrate must be cleaned and activated by plasma pretreatment before coating. Furthermore, this method makes it difficult to precisely adjust the desired thickness of the photopolymer layer.

[0024] There is therefore a need for a faster and higher-quality device for the serial replication of holograms, which can then be easily integrated into various components depending on the application and in which adjustments to set the desired properties of the replicated holograms are possible with little time and cost. Object of the invention

[0025] The object of the invention is to provide a device for the continuous replication of holograms without the disadvantages of the prior art. In particular, it was an object of the invention to provide a device that can replicate holograms with high precision and speed, while simultaneously being characterized by a high degree of flexibility for adjusting the desired properties of the replicated holograms.

[0026] Summary of the invention

[0027] The object is achieved by the features of the independent claim. Advantageous embodiments of the invention are described in the dependent claims.

[0028] The invention relates to a device for the continuous replication of a hologram comprising a. a coating module which is configured to coat a liquid photopolymer onto a first carrier film, b. a lamination module which is configured to apply a second carrier film to the first carrier film coated with the photopolymer in order to obtain a photopolymer composite comprising a liquid photopolymer layer between two carrier films, c. an exposure module, wherein the exposure module has a light source and a master element comprising a master hologram to be replicated, wherein the master element is mounted so as to be axially rotatable and the exposure module is configured to bring the photopolymer composite into optical contact with the master element, while the light source exposes the master hologram to an area of ​​the photopolymer composite in order to obtain a replicated hologram, and d.a fixation module which is designed to cure the replicated hologram in the photopolymer composite.

[0029] By providing a replication device with the aforementioned modules, the liquid photopolymers themselves can advantageously be used directly as starting material for replication. Preferably, the photopolymers can also be mixed in situ, and the finished mixture can be delivered to the coating module (also referred to synonymously as the "application module" within the meaning of the invention). Alternatively, the coating module is supplied with a finished, light-tight liquid photopolymer mixture. The liquid photopolymers can thus be changed between successive series or provided with different additives. Thus, a wide range of liquid photopolymers can be used in the same device and adapted with regard to the desired properties of the resulting polymer composite.Instead, the state of the art has been to carry out replication in already finished polymer composites whose properties cannot be easily changed.

[0030] The ability of the device according to the invention to replicate holograms in still-liquid photopolymers instead opens up significantly greater process flexibility. With the help of the device according to the invention, process parameters such as the layer thickness of the photopolymer composite, its light sensitivity, or the properties of the carrier films can be easily adapted to the respective desired applications. The ability to quickly change these properties without providing prefabricated light-sensitive films makes the production of small-batch holograms economical.

[0031] For this purpose, a device advantageously comprises a coating module for applying a liquid photopolymer to a first carrier film, a lamination module for applying a second carrier film, an exposure module for inscribing the hologram into the liquid photopolymer, and a fixing module for curing. In particular, various compositions of liquid photopolymers designed for the desired exposure conditions can advantageously be supplied to the device. Likewise, the desired layer thickness of the photopolymer composite can be specified using the coating module. The subsequent processes, such as exposure or curing of the photopolymer, can be adapted using the corresponding downstream modules in the device.

[0032] The provision of a device that continuously replicates holograms in a roll-to-roll process also enables high process speeds while simultaneously reducing the risk of errors. An operator does not need to intervene during a series. Adjustments preferably only need to be made between series. This is particularly advantageous compared to the known state of the art, in which a master hologram over a liquid photopolymer layer is positioned and adjusted not only between series but also between individual replications.

[0033] By providing a lamination module in the device, the film thicknesses and carrier film properties can be easily adjusted between series. The liquid photopolymer can be sealed by lamination between two films to ensure high durability and prevent contamination. The lamination also protects the liquid photopolymer from unwanted deformation due to shear forces. This reduces the susceptibility to errors during hologram production. The device is particularly characterized by an exposure module with an axially rotatably mounted master element, so that the photopolymer composite is brought into optical contact with the master element, while the light source exposes the master hologram onto an area of ​​the photopolymer composite to create a replicated hologram."Bringing into contact" in this sense refers to optical contact, although additional mechanical contact may also be preferred. The axially rotatably mounted master element allows, in particular, continuous integration of the exposure process into a roll-to-roll process. Process interruptions, as in conventional processes using ground glass plates as master holograms, are avoided.

[0034] By providing a rotatable master element, the master hologram or multiple master holograms can be repeatedly exposed at a speed that is also easily and extremely precisely synchronized with the process flow of a photopolymer composite. The exposure process can be carried out quickly and continuously using the axially rotatable master element, without pausing between individual replication steps. Adjusting the position of a light-sensitive object to the master hologram can also be made easier. The increased exposure speed also reduces interference from extraneous light, thus leading to a more precise replication process.

[0035] Equipping the device with a fixing module further improves the precision of the replication process. Since liquid photopolymers are sensitive to mechanical disturbances, the provision of the fixing module in the same device allows for a particularly rapid and trouble-free transfer of the exposed liquid photopolymer from the master hologram to the fixing agent, thus avoiding possible mechanical or electromagnetic distortions.

[0036] Due to the speed and precision of the device, a drying station between the coating and the exposure modules is not required. This allows for even more cost-effective production of small batches.

[0037] For the purposes of the invention, a "module" preferably refers to a workstation in a continuous manufacturing process, which is preferably equipped with the necessary technical means to carry out the process step. Different modules can be separated from each other by a housing or a partition wall, but this is not required.

[0038] A "lamination" or "lamination" within the meaning of the invention is preferably a material-to-material, thermal joining process without auxiliary materials such as adhesives. Within the meaning of the invention, this is also referred to as "lamination," while the lamination module is also referred to as a "laminating module." The lamination module preferably comprises at least one laminating roller or laminating roller heated to 5–300°C, preferably 15–200°C, or even 20–100°C. At these preferred temperatures, particularly effective lamination or laminating can be carried out, with the liquid photopolymer also being able to cool quickly before exposure. The lamination is preferably designed to create a permanent bond between the first and second carrier films, preferably by partial melting along one or both uncoated edges of the carrier films.The liquid photopolymer is then preferably sealed between the carrier films.

[0039] It is particularly preferred that the liquid photopolymer be cooled to a temperature below 40°C prior to exposure to ensure optimal replication quality of the master hologram in the liquid photopolymer. Exposure of liquid photopolymers at lower temperatures promotes the inscription of diffraction patterns, which remain stable in the material.

[0040] A "composite" within the meaning of the invention is preferably a multilayer material consisting of two or more different components with different physical properties that are bonded together at an interface. Preferably, the bond between the individual components is such that it cannot be separated by even a slight force and is therefore considered permanent.

[0041] In the context of the invention, "exposure" is preferably understood to mean the targeted directing of electromagnetic radiation onto a correspondingly sensitive surface, preferably to form a hologram. Various methods for exposing a hologram are known, including transmissive or reflective techniques for producing volume holograms. Examples of these will be explained in more detail later in this text.

[0042] For the purposes of the invention, a "light source" (or "radiation source") is preferably a device for emitting electromagnetic radiation, which in particular serves for exposure. The emitted electromagnetic radiation can comprise visible light and / or radiation with wavelengths outside the visible range of the electromagnetic spectrum. Preferably, the light source emits a coherent light beam.

[0043] A “master element” is preferably a three-dimensional unit comprising a master hologram in a shape which ensures that a movement of the master element directly leads to a corresponding movement of the master hologram. If the “master element” is referred to as “axially rotatable”, this preferably means that the master element is mounted so as to be rotatable along an axis in the exposure module. An axially rotatable mounting therefore characterizes a mounting which enables rotation of the master element about its axis. The axis is preferably located in the center of a cross-section of the master element so that rotation of the master element can take place in a space-saving manner. The master element is preferably prismatic, i.e. it has a constant cross-section of any shape, e.g. square, polygonal, elliptical or circular.The ends of the master element, which have the shape of the cross-section, can be referred to as the "base surface." The elongated surface of the master element, which lies between the two ends, can be referred to as the "lateral surface."

[0044] A "master hologram" within the meaning of the invention is preferably a holographic-optical element comprising at least one hologram to be replicated. The master hologram is designed for an optical function (e.g., diffraction, reflection, transmission, and / or refraction) for one or more wavelengths. For this purpose, for example, several holograms, each diffracting light of one wavelength, and / or multiplex holograms diffracting light of multiple wavelengths, can be arranged as hologram stacks. The master hologram can, for example, be a diffractive optical element (DOE). Diffractive optical elements (DOEs) utilize a surface relief profile with a microstructure for their optical function. Alternatively, the microstructure can also be present in the volume of the element in the form of a local difference in the refractive index.The light transmitted through a DOE can be converted into almost any desired distribution through diffraction and subsequent propagation. This could be an image, a logo, text, a refraction pattern, or similar.

[0045] The process for producing the master hologram may preferably be referred to as "hologram origination" or "hologram mastering." The master hologram can be created using an analog or digital process. In an exemplary analog process, a first coherent beam, the object beam, is reflected from an object and onto a recording material, which is simultaneously exposed to a second coherent beam, the reference beam. The object beam and the reference beam interfere, creating an interference pattern on the recording material. This interference pattern, or fringe pattern, is recorded by light-sensitive material, which, after processing, takes the form of a surface relief pattern on a surface of the material or of spatially varying refractive indices just a few micrometers below the surface.To view an image of the original object, the master hologram can be illuminated with light diffracted by the recorded surface relief pattern or refractive index pattern. This diffracted beam contains the image of the original object. The master hologram can then be used as a new object when creating further copies with the same image. The master hologram can preferably be computer-generated. The microscopic gratings that create the diffraction effects can be produced, for example, by laser interference lithography. In this technique, two or more coherent light beams are configured to interfere at the surface of a recording material. The positions of the light beams relative to the recording material can be controlled by a computer. Depending on the strength of the laser, the recording material can be made of almost any material.Other techniques such as electron beam lithography can also be used to digitally create the master hologram. The master hologram can preferably comprise glass, silicon, quartz, UV varnish, a photopolymer composite, and / or a metal such as nickel.

[0046] In the context of the present invention, the term "liquid" or a liquid photopolymer is preferably defined as a substance that continuously deforms when subjected to a shear stress of any magnitude (p. 13, Munson et al., Fundamentals of Fluid Mechanics, Wiley: 2010). A liquid can also preferably be characterized by its viscosity and distinguished from other semi-solids.

[0047] The dynamic viscosity of the liquid photopolymer used as raw material at 300 K is preferably between 0.2 mPas (millipascal second) and 200 Pas (Pascal second), more preferably between 1 and 10,000 mPas. The dynamic viscosity of the liquid photopolymer at the time of exposure is preferably between 0.2 mPas and 200 Pas. It may be preferable to pre-crosslink the liquid photopolymer after application to the carrier film and before exposure, converting it into a viscoelastic state.

[0048] The viscoelastic state of the liquid photopolymer can be characterized by its complex viscosity. The real part q' of the complex viscosity correlates with the viscous properties or the liquid behavior (and the so-called loss modulus G"), while the imaginary part q" correlates with the elastic properties or the solid content (and the storage modulus G'). In preferred embodiments, the material properties of the liquid photopolymer during exposure are such that the ratio between a storage component (solid behavior) or the storage modulus G' and a loss component (liquid behavior) or the loss modulus G" is at least 1:10. The higher the storage component in the ratio, the more favorable the effect on the exposure capability of the replication process.In preferred embodiments, the ratio of storage modulus G' to loss modulus G" can be at least 1:5, at least 1:2, 1:1, 2:1, 5:1 or more. Preferably, the ratio between the storage modulus G' and the loss modulus G" is at most 10:1. Within these parameter limits, particularly good results can be achieved with regard to the stability of the photopolymer during exposure and the quality of the replicated holograms. The ratio can be adjusted by adapting the composition of the photopolymer, e.g. by adding thixotropic agents, pre-crosslinking the photopolymer or evaporating solvents after applying the liquid photopolymer to a first carrier film and before covering the liquid photopolymer with a second carrier film and laminating them. The viscoelastic properties of the liquid photopolymers can also be optimized by cooling the liquid photopolymer before or during exposure.

[0049] "Fixation" preferably refers to a process step for curing a liquid material, in particular a liquid photopolymer, wherein electromagnetic and / or thermal energy is preferably applied to the material. The energy can preferably be applied uniformly to a surface of the sensitive material to ensure simultaneous curing. Preferably, all layers of the photopolymer composite, in particular including the photopolymer layer, are solidified at this stage.

[0050] The general functioning of some components of the device according to the invention will now be explained in more detail in sequential order before going into specific details of the preferred embodiments.

[0051] Due to the device's high processing speed, liquid photopolymers with a short storage life of just a few days, hours, or minutes can be used. Due to their light sensitivity, these liquid photopolymers should preferably be handled with extreme care. The coating module is therefore preferably optically isolated from ambient light.

[0052] The viscosity of the liquid photopolymers is preferably adjusted by mixing and / or heating before they are fed to the coating module. Preferably, the light sensitivity, color sensitivity, and refractive index jump of the liquid photopolymer are also adjusted before it is fed to the coating module. The coating module preferably allows for the adjustment of the thickness of an applied liquid photopolymer layer. This can be done in various ways, e.g., by adjusting the flow rate from a slot die or by adjusting the distance between adjacent rollers. The coating module can be designed differently depending on the rheological properties and the desired thickness of the liquid photopolymer layer, as explained in more detail later.Preferably, the device comprises multiple coating mechanisms arranged one behind the other so that only the respective coating type is applied for the series. This has the advantage of allowing a much wider range of possible photopolymer layer thicknesses, which can be adjusted between series. The carrier film to which the liquid photopolymer is applied is preferably optically transparent, particularly for applications in transparent displays. Preferably, a polycarbonate material is used, although a variety of other materials can also be used, as disclosed in detail herein. Preferably, at least one of the first and second carrier films is crystal-clear, transparent, and largely uncolored.

[0053] The device according to the invention also comprises a lamination module, which can also be synonymously referred to as a "laminating module," and which is configured to apply a second carrier film to the first carrier film coated with the photopolymer in order to obtain a photopolymer composite comprising a liquid photopolymer layer between two carrier films. The composition of the photopolymer is preferably configured such that it does not cure during a lamination process. The first and second carrier films are preferably designed as a (randomly long) web, so that the lamination module is configured to produce a (randomly long) composite web comprising a liquid photopolymer layer.

[0054] The device according to the invention further comprises an exposure module, wherein the exposure module has a light source and a master element comprising a master hologram to be replicated, wherein the master element is mounted so as to be axially rotatable and the exposure module is configured to bring the photopolymer composite into optical contact with the master element, while the light source exposes the master hologram to a region of the photopolymer composite to obtain a replicated hologram.

[0055] An "optical contact" should preferably allow a light beam to pass between the photopolymer layer and the master hologram without experiencing significant interference or absorption. Direct, material-to-material contact between the photopolymer composite and the master element is possible, but not necessary. Instead, an intermediate layer can be provided between the master element and the photopolymer composite, which is preferably transparent to the light from the light source of the exposure module, for example, in the form of a transparent film.

[0056] The exposure to replicate the master hologram in the exposure module can be performed using various techniques. Hologram replication processes can be divided into relief holograms and volume holograms.

[0057] Relief holograms are formed by physical contact between a deformable sensitive layer and a master hologram, so that the diffraction pattern of the master hologram is imprinted into the sensitive layer. A volume hologram is preferably written into a sensitive layer by the interference of two light beams (a so-called reference beam and an object beam). Preferably, a volume hologram is written into the liquid photopolymer layer. This can preferably be done using a transmission or reflection technique. The interference of object and reference beams within the hologram volume preferably creates a sequence of Bragg planes. A volume hologram therefore preferably has a non-negligible extension in the propagation direction of the light beams, whereby the Bragg condition applies to reconstruction on a volume hologram.For this reason, volume holograms exhibit wavelength and / or angle selectivity. The ability of volume holograms to store multiple images simultaneously enables, among other things, the production of colored holograms. Light sources that emit the three primary colors blue, green, and red can be used to record the holograms. The three beams of light preferably expose the photopolymer layer simultaneously at the same angles. After exposure, three holograms are stored simultaneously in the volume hologram. To reproduce the color hologram, it can be exploited that each partial hologram can be reconstructed using only the color with which it was recorded. Thus, the three reconstructed color separations superimpose themselves to form a colored, true-to-original image, provided the color components are correctly weighted.

[0058] In a reflection hologram, an incident direction of the reference beam (preferably an incident light beam from the light source) and the object (in this case, the master hologram) can be arranged on opposite sides of the liquid photopolymer layer. A reference beam penetrates the liquid photopolymer, which in this case is preferably enclosed between two light-transmitting carrier films, and is then reflected by the master hologram back into the liquid photopolymer layer. The master hologram can preferably be applied to a surface of the master element that is preferably not completely transparent, but at least partially reflective. A transparent master element is also applicable.

[0059] The light source for a reflection hologram can be arranged such that the reference beam is incident on the liquid photopolymer layer in a desired direction, preferably in a direction that is desired for later reconstruction. In a preferred embodiment, the light source is oriented with respect to the master element such that the photopolymer composite is located between the light source and the master element. The light source can, for example, be aligned below the master element such that the reference beam is incident upwards in a predetermined direction onto its lateral surface. The reference beam is preferably at least partially reflected by the master element in the form of an object beam back into the photopolymer composite. The reference beam and the object beam thus enter the photopolymer composite from opposite sides and interfere in its photopolymer layer to replicate the hologram.

[0060] In a transmission hologram, the liquid photopolymer layer is preferably arranged such that it can be illuminated by a reference beam and an object beam from the same side. The light source is preferably oriented with respect to the master element such that a light beam first passes through the master element and the master hologram before reaching the photopolymer composite. This arrangement is exemplary, although other arrangements are also conceivable. The light can preferably be arranged such that it passes through a preferably transparent master element from a side of the lateral surface opposite the photopolymer composite. The incident light beam is preferably refracted by the master element such that a reference beam and an object beam are created, the object beam preferably corresponding to the portion of the light that is diffracted by the master hologram.The object beam preferentially interferes with the undiffracted reference beam in the liquid photopolymer layer to replicate the hologram.

[0061] In a further embodiment of the invention, the exposure module can be configured for replication of the master hologram by an edgelit (edge-illuminated hologram). For this purpose, the master element is preferably provided as a light guide, and the light source is preferably configured to direct light onto a base surface of the master element. As with other arrangements for transmission holography, the light is preferably split by the master element into a reference beam, which penetrates the master hologram without diffraction, and an object beam, which is diffracted by the master hologram. The light beam within the master element preferably propagates by reflections, preferably total internal reflections. Light losses in the regions of the lateral surface that are not in optical contact with the photopolymer composite are preferably reduced to a minimum.The majority of the light can preferably exit the master element at a point through a master hologram arranged on the lateral surface in order to replicate the hologram into the photopolymer layer.

[0062] By aligning the light source onto a base surface, the device can be arranged in a particularly space-saving manner with maximum usable space around the lateral surface. This space can be used to accommodate the master hologram, additional optical layers, and greater contact between the master element and the photopolymer composite. By aligning the light onto a flat surface of the master element, the device can also be made less sensitive to minor changes in laser alignment, e.g., due to vibrations. In a preferred embodiment, a coherent light beam is emitted from the light source. Coherence preferably refers to the property of optical waves according to which there is a fixed phase relationship between two wave trains. As a result of the fixed phase relationship between the two wave trains, spatially stable interference patterns can arise.With regard to coherence, a distinction can be made between temporal and spatial coherence. Spatial coherence preferably represents a measure of a fixed phase relationship between wave trains perpendicular to the propagation and is present, for example, for parallel light beams. Temporal coherence preferably represents a fixed phase relationship between wave trains along the propagation direction and is present in particular for narrowband, preferably monochromatic light beams.

[0063] The coherence length preferably refers to the maximum path length or travel time difference between two light beams from a starting point, so that a (spatially and temporally) stable interference pattern is still created when they superpose. The coherence time preferably refers to the time it takes for the light to travel a coherence length.

[0064] In preferred embodiments, the light source is a laser. Particularly preferably, it is a narrowband, preferably monochromatic laser with a preferred wavelength in the visible range (preferably 400 nm to 780 nm). Lasers preferably refer to light sources that emit laser radiation. Non-exhaustive examples include solid-state lasers, preferably semiconductor lasers or laser diodes, gas lasers, or dye lasers.

[0065] Other light sources, preferably coherent light sources, can also be used. Narrowband light sources, preferably monochromatic light sources, such as light-emitting diodes (LEDs), optionally in combination with monochromators, are preferred.

[0066] For the creation of relief holograms, the coherence of the light beams is of lesser importance. However, for the replication of volume holograms, in particular, it is preferable that the light beams used for replication be sufficiently coherent.

[0067] In preferred embodiments, the coherence length of the light source is preferably at least 150 pm, more preferably at least 500 pm, and even more preferably at least 2 mm. The coherence length is preferably at least twice the distance between the photopolymer and the master hologram. However, the coherence length is preferably not so long that parasitic microstructures, such as interference grids, appear in the hologram. The maximum preferred coherence depends on the hologram type and the geometric dimensions of the exposure module. In preferred embodiments, the coherence length of the light source is less than 1 m.

[0068] The light source may comprise multiple light sources. These may preferably be configured to scan a line or region of the photopolymer composite in optical contact with the master element.

[0069] A device for shaping and / or guiding the light beam can optionally be provided between the light source and the master element or the photopolymer composite. This can comprise any number or type of lenses, prisms, mirrors, etc. The means for shaping and / or guiding the light beam can distribute the light such that it essentially covers, for example, a point, a line, or an expanded area. Scanning can additionally be provided by means of a corresponding scanning unit. The light source can preferably be configured to generate one or more beams that illuminate the entire length of the lateral surface of the master element, or preferably at least a length corresponding to the coated part of the photopolymer composite, by means of an expanded beam and / or by scanning.

[0070] The master element preferably has a prismatic shape, in particular a cylindrical shape. The axial rotatability allows the master element to preferably function as a roller. This enables synchronous movement between the master and the light-sensitive photopolymer composite, so that the likelihood of positioning errors can be reduced. Depending on the materials used, a frictional force between the photopolymer composite and the master element may be sufficient to cause the movement of the master element. In this case, the master element advantageously does not require its own drive, and the movement occurs essentially passively through the movement of the photopolymer composite. Alternatively or additionally, a rotation speed of the master element can be controlled separately via a suitable drive, whereby the drive ensures synchronous movement of the surface of the master element with the photopolymer composite.

[0071] In a further preferred embodiment of the invention, the master element is driven either by power transmission from a functional roller, a flanged gear ring, a cardan drive, or a belt drive. The master element is preferably provided with its own drive. With a functional roller, the power transmission can preferably take place through friction, wherein the functional roller preferably comprises a rubber material. The drive mechanism is preferably designed so that the surfaces of the master element are maximally accessible to an exposure beam. Advantageously, with these drive technologies, essentially all surfaces of the master element can remain free for optical functions. This enables a more efficient exposure process and the use of the same master element for copying different hologram types, depending on the positioning of the light source.

[0072] In a further preferred embodiment of the invention, the master element is rotated in synchronism with the web speed of the photopolymer composite web. "Rotation of the master element in synchronism with the web speed" of the photopolymer composite web preferably means that the peripheral speed of the outer surface of the master element is identical to the web speed of the photopolymer composite web. This prevents unwanted slippage between the photopolymer composite web and the outer surface of the master element or excessive web tension of the photopolymer composite web, allowing the master hologram to be replicated in the photopolymer layer in a precise position and without distortion.

[0073] The web speed with respect to the photopolymer composite web preferably refers to the speed of the photopolymer composite web or carrier film in the longitudinal direction through the device. The longitudinal direction is preferably defined by the longest dimension of the photopolymer composite web and preferably corresponds to the main direction in which the photopolymer composite web is moved through the device. The web speed can be the speed of a point on the carrier film or photopolymer composite web. The peripheral speed preferably refers to the speed of a point on the outer surface of the master element, which performs a circular movement due to its rotation, and can also be referred to as the unwind speed.

[0074] In a further preferred embodiment of the invention, the drive of the master element is controlled by a control unit, in particular in order to obtain a desired circumferential speed of the lateral surface of the master element.

[0075] In a preferred embodiment of the invention, the control unit is configured to maintain a desired web tension in the photopolymer composite web. This can be a web tension before and / or after the master element. This can ensure that the photopolymer composite does not overstretch, e.g., due to an excessively low web speed of the photopolymer web before the master element. It can also ensure that the photopolymer composite does not buckle, e.g., due to an excessively low web speed of the photopolymer web after the master element. The mechanical introduction of defects into the photopolymer layer can thus be avoided.

[0076] In a particularly preferred embodiment of the invention, the control unit is configured to control drives of transport rollers (also referred to as “transport rollers” in the sense of the invention) for moving the photopolymer composite web to and from the master element in order to maintain a desired web tension in the photopolymer composite web, in particular before and after the master element.

[0077] For this purpose, the web tension is preferably monitored by suitable sensors. Should the web tension lie outside a permissible range, it is preferred that the control unit is configured to adjust the rotational speed of one or more transport rollers (instead of the master element). For this purpose, the control unit can send a signal to the drives of one or more transport rollers to bring the web tension back within the permissible range. The master element thus also plays the role of a "master" on the control side with regard to the web tension of the photopolymer composite web. The control unit is thus preferably designed to maintain a desired rotational speed of the master element constant, while drives of transport rollers or other components of the device that influence the web speed of the photopolymer web are readjusted.

[0078] For the purposes of the invention, "web tension" is preferably a measure of the tensile load to which the photopolymer composite web is subjected in the longitudinal direction, in particular in the direction of its movement through the device. It can be defined by the force acting on the photopolymer composite web in the longitudinal direction compared to the cross-section of the photopolymer composite web and can be expressed, for example, in N / mm 2 be measured.

[0079] The rotation of the master element in synchronization with the flow rate or web speed of the photopolymer composite web enables a continuous and rapid replication process. This is particularly advantageous for processing the highly sensitive liquid photopolymer layer, as the still-liquid photopolymers are sensitive to ambient light, stray light, or shear forces. The liquid photopolymers are fixed after a short exposure period, and the continuous process also prevents mechanical influences that cause distortion.

[0080] The device according to the invention further comprises a fixation module configured to cure the replicated hologram in the photopolymer composite. With the fixation module, the composite web can be transferred from the exposure module, preferably quickly and with minimal deflections. The fixation module can preferably comprise a light source, preferably UV radiation, and / or a heat treatment source. In the case of fixation with a UV lamp (also referred to as a "UV radiator" within the meaning of the invention), this is preferably set to radiate intense UV radiation between 315 and 400 nm onto the photopolymer layer.

[0081] The fixing module can be located in the same housing as the exposure module. In a preferred embodiment, the device is designed such that fixing occurs immediately after exposure on the master element. Preferably, the distance between an incident electromagnetic beam from the exposure light source and a fixing beam is less than 50 cm, preferably less than 10 cm, preferably less than 5 cm, even more preferably less than 1 cm. The fixing beam can be an expanded beam or consist of one or more optionally scanning beams and can preferably be arranged such that it is directed onto the master element and passes through the photopolymer layer arranged between the fixing beam source and the master element.

[0082] The device preferably also comprises a control unit for controlling the components of the device, for example the coating module, the lamination module, the exposure module and / or the fixing module.

[0083] The term "control unit" preferably refers to any computer unit with a processor, a processor chip, a microprocessor, or a microcontroller that enables automatic control of the components of the device, e.g., a rotation speed of an unwind roll, a take-up roll, a lamination roll, a transport roll, a master element, or an adjustment of a photopolymer composition, a coating thickness, a lamination temperature, a lamination pressure, a lamination pressure force, an orientation and / or scanning speed of a light source, a fixation intensity, etc. The components of the control unit can be conventional or individually configured for the respective implementation. Preferably, the control unit comprises a processor, a memory, and computer code (software / firmware) for controlling the components of the device.

[0084] The control unit may also comprise a programmable circuit board, a microcontroller, or other device for receiving and processing data signals from the components of the device, for example, from sensors relating to the speed of the first or second carrier films, the master element, or the photopolymer composite web, as well as other relevant sensory information. The control unit preferably further comprises a computer-usable or computer-readable medium, such as a hard disk, random access memory (RAM), read-only memory (ROM), flash memory, etc., on which computer software or code is installed. The computer code or software for controlling the components of the device may be written in any programming language or model-based development environment, e.g.in C / C++, C#, Objective-C, Java, Basic / VisualBasic, MATLAB, Python, Simulink, StateFlow, Lab View, or Assembler, but not limited to. The term "control unit configured to perform a specific operation, such as adapting the rotation speed of the master element to the web speed of a photopolymer composite web, or vice versa, by changing the speed of one or more drive motors, may include custom or standard software installed on the control unit that initiates and controls these operational steps.

[0085] In preferred embodiments, the device can comprise sensors, for example tension sensors for measuring the tension in the first and / or second carrier foil. In these cases, the control unit is preferably configured to receive data from the sensors, for example tension sensors, and optionally evaluate it, for example to compare detected tension values ​​with reference values. The control unit can preferably also be configured to adapt process parameters, for example the speed of one or more transport rollers, based on an evaluation of the data, for example by sending a signal to one or more drive motors in order to equalize the tension between the first and second carrier foils.

[0086] In a further preferred embodiment of the invention, the web tension of the photopolymer composite web is detected by suitable sensors and transmitted to the control unit. Preferably, the web tension in the device is controlled by tension separation, independent of the web speed. The web tension control is particularly designed to maintain a constant web tension between the coating module and the exposure module. A consistent web tension can prevent length changes in the relevant sections of the photopolymer composite web. Such length changes are undesirable, especially while the photopolymer is still liquid, since these length changes can lead to layer inhomogeneities such as fisheyes, sink marks, severe orange peel, etc.Maintaining a substantially constant web tension is therefore particularly preferred in the sections of the device following coating up to exposure, preferably up to fixation.

[0087] In preferred embodiments, the device can comprise a motor for driving the master element, wherein the rotational speed of the master element and / or the flow rate or web speed of the photopolymer composite and / or the web tension of the photopolymer composite web is detected by a sensor and transmitted to the control unit. In these cases, the control unit is preferably configured to compare the rotational speed of the master element with the web speed of the photopolymer composite and adjust the speed of one or both elements to maintain synchronous web travel. Alternatively or additionally, the rotational speed of the master element is controlled as a function of the measured web tension of the photopolymer composite web in order to maintain the web tension within a preferred range.

[0088] Particular preferred features of the device will now be explained in more detail. The order of explanations does not necessarily correspond to the order of arrangement in the device.

[0089] In a preferred embodiment of the invention, the exposure module is configured such that, while the photopolymer composite is guided through the exposure module, a region of the photopolymer composite to be exposed temporarily assumes the shape of a peripheral surface of the master element and is guided over the rotating master element, moving along with the peripheral surface. Therefore, there is preferably mechanical contact between a region of the master element and a region of the photopolymer composite. "Over the rotating master element" does not mean a specific direction of the photopolymer composite relative to the master element, but rather any direction that runs at least partially along the circumference of the master element. The film composite can thus run above, below, to the left, to the right, diagonally to the master element, etc.

[0090] The shape of a lateral surface of the master element can only be temporarily assumed over a very small area. For example, the area to be exposed can be formed as a thin line with a line width of less than 1 mm, e.g., if the composite runs essentially tangentially to the lateral surface of the master element.

[0091] Likewise, the area of ​​the photopolymer composite to be exposed can temporarily assume the shape of the outer surface of the master element over an extended area, for example, arcuately over a circular segment of a cylindrical master element with an aperture angle of more than 5° or more than 10°. This provides additional space for exposure and, optionally, fixation. Exposure can preferably occur on the exposed area along a line parallel to the rotation axis of the master element or simultaneously in several lines. Exposure is preferably carried out by an expanded constant light beam or by one or more continuously scanning light sources, preferably lasers.

[0092] In a preferred embodiment, the light source(s) of the exposure module and the light source(s) for fixing (e.g., a UV lamp) the photopolymer composite web are located in the same optically isolated housing. Fixing can preferably take place in the same extended area immediately after exposure. This allows for a minimal transport path between exposure and fixing, so that the exposed photopolymer spends particularly little time in a medium-viscosity state after exposure. This reduces the risk of distortions that can occur during transport of the composite, for example, if the tension in the first and second carrier films is not equal and shear forces occur along the composite web.

[0093] Distortions in the still medium-viscosity photopolymer lead to a reduction in the resolution of an exposed image and therefore to a reduction in the quality of the final product. These distortions are often caused by shear forces acting on the photopolymer, which can deform the exposed microstructures. This occurs, for example, when one of the first or second carrier films is pulled faster than the other. Therefore, it is preferred that the tension in each of the upper and lower carrier films be automatically measured and compared, preferably before lamination, to ensure that they are synchronized and any errors can be corrected.

[0094] In a preferred embodiment, the device comprises means for monitoring and controlling the tension in the films to further reduce the likelihood of distortions caused by shear forces. Preferably, the tension in the carrier films is measured by one or more sensors prior to lamination, and the data is fed to a control unit that compares the determined tensions. Preferably, the control unit initiates corrective action if the difference in tension exceeds a predetermined limit. Preferably, the adjustment measure comprises sending a signal to one or more drive motors to change the rotation speed of a driven roller.The control unit can also evaluate data from the sensors to determine whether one or more carrier foils are jammed (voltage increase) or torn (voltage drop) in order to bring the device to a safe stop in either case.

[0095] In a further preferred embodiment of the invention, the master element comprises a base body. The base body can be transparent, color-filtering, or opaque. At least the outer surface of the base body is preferably optically polished. A polishing degree of P3 is preferred, with a higher polishing degree of P4 being even more preferred.

[0096] In a further preferred embodiment of the invention, the base body has a surface fit of a maximum of A / 2, in particular with respect to the radiation generated by the light source. In the sense of the invention, the surface fit preferably corresponds to the difference between an actual shape of the base body and a desired shape. The surface fit is preferably determined using a test glass with a diameter of 50 mm. For example, a test glass with a known diameter and known curvature is placed on the surface of the base body. This arrangement is illuminated with a laser of a known wavelength so that interference fringes can be observed on the test glass. Conclusions can be drawn from the interference fringes about the curvature deviation of the base body from the known curvature of the test glass.

[0097] In a further preferred embodiment of the invention, the master element's deviation from an ideal cylindrical shape is no more than 0.2 mm, in particular no more than 0.01 mm. This enables very precise light deflection through the body or surface of the master element. At the same time, the rotation of the master element can be very precisely synchronized with the movement of the photopolymer composite web.

[0098] In the case of an opaque base body, a master hologram is preferably located on a lateral surface of the base body. Such a base body can be completely or partially absorbent for the wavelength of the light source of the exposure module. It is preferred that such a master element is configured for copying a volume hologram using a reflection method; i.e., the light source is arranged such that the light passes through the composite as a reference beam and then through the master hologram before being reflected by the master hologram back through the composite as an object beam. With an absorbent base body, it is advantageous that reflective interference can be kept to a minimum.

[0099] In the case of a transparent or color-filtering base body, a master hologram is preferably incorporated into or on a lateral surface of the base body. The base body preferably comprises optical glass, for example N-BK7, Borofloat glass, borosilicate glass, B270N-SF2, P-SF68, P-SK57Q1, P-SK58A, BK10, quartz glass and / or P-BK7, or optical plastic, for example polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin polymers (COP), or cycloolefin copolymers (COC). Such a base body can preferably be used for copying a volume hologram using a reflection or transmission method.

[0100] Regardless of the material of the base body, one or more master holograms can be present only in one or more specific areas of the lateral surface. To avoid reflection interference, it is preferable for the master hologram-free areas of the base body to be coated with a reflection-reducing material.

[0101] It may be preferred that an optical fluid be applied to a surface of the master element and / or the photopolymer composite. This fluid preferably has an optical refractive index close to that of the master element, in particular a cover of the master element, and / or the photopolymer composite in order to minimize reflections at the interfaces between the master element and the photopolymer composite. The optical fluid can also improve the optical contact between the elements, as any shape and / or surface defects of the optical elements are compensated.

[0102] In a further preferred embodiment of the invention, an optical adhesive film is temporarily introduced between the master element and the photopolymer composite.

[0103] In a further preferred embodiment of the invention, the exposure module comprises at least one unwinding and one winding roll for temporarily applying an optical adhesive film between the master element and the photopolymer composite. The unwinding roll is preferably used for unwinding the optical adhesive film, and the winding roll is used for winding the optical adhesive film after use. The optical adhesive film preferably temporarily bonds the composite (preferably at least for the duration of an exposure) to the master element and advantageously creates an optical bond between the two elements. This has the advantage of reducing unwanted reflections at the interfaces between the master element and the photopolymer composite, resulting in a higher-quality hologram. The optical adhesive film can also be referred to as OCA (Optical Clearance Adhesive).

[0104] The method preferably comprises a step of removing the optical adhesive film from the master element and / or from the photopolymer composite after exposure, wherein the device preferably comprises suitable means for the removal - for example a take-up roll.

[0105] For the purposes of the invention, an "optical adhesive film" is preferably a transparent film with a refractive index close to the refractive index of the master element and / or the photopolymer composite. The optical adhesive film is preferably designed to improve optical contact between the master element and the photopolymer composite, so that reflections at the interface between the master element and the photopolymer composite are reduced or eliminated.

[0106] The materials used for the optical adhesive film preferably have identical or similar optical properties to those materials used for the substrate of the master element, its cover, and / or the composite web. These similar or identical properties preferably include transparency, haze, stress birefringence properties, and / or the refractive index. The use of identical or similar materials enables a very close match of the refractive index of the optical adhesive film to the refractive indices of the adjacent master element and / or photopolymer composite, ensuring a transition between the adjacent refractive indices without refractive index jumps. Reflections at the interface between the master element, the optical adhesive film, and / or the photopolymer composite are thereby largely eliminated or significantly minimized.

[0107] Furthermore, the optical adhesive film is preferably a solid in which the Brownian motion is sufficiently small, preventing any "wobble" in the phase of the light and thus resulting in a more stable interference field in the hologram copy within the exposure time. This prevents the microstructures from blurring, maximizing the diffraction efficiency of the holograms. The sharpness and contrast of the resulting hologram are also significantly improved. The optical adhesive film improves the optical contact between exposed transparent components through which the exposure light is passed. This reduces unwanted reflections, scattering, or losses and increases the quality of the reproduced hologram.

[0108] The optical adhesive film can be formed analogously to the photopolymer composite—for example, as a web—and moved through the process in a similar manner, e.g., using rollers. This enables easy synchronization of the optical adhesive film with the photopolymer composite.

[0109] In contrast to the OCAs (optical clearance adhesives) commonly used in optical displays, the optical adhesive film preferably exhibits low adhesive strength in addition to its advantageous optical properties. This allows the optical adhesive film to be removed from a surface after use without leaving residue and with little force.

[0110] In a preferred embodiment of the invention, the optical adhesive film comprises at least one adhesive layer. The at least one adhesive layer preferably has a peel force relative to the surface of the master element and / or a surface of the photopolymer composite of less than 3 N / cm (Newton per centimeter), preferably less than 1 N / cm. In preferred embodiments, however, the peel force of the adhesive layer of the optical adhesive film relative to the surface of the master element and / or a surface of the photosensitive composite web is at least 0.01 N / cm, preferably at least 0.1 N / cm. The peel force of the optical adhesive film or one of its layers can be measured, for example, according to a 180-degree peel test. In preferred forms, the measurement is carried out according to ASTM D903.

[0111] In a preferred embodiment of the invention, the optical adhesive film has a single-layer structure, wherein the structure has precisely one adhesive layer. The precisely one adhesive layer is preferably adhesive on both sides to provide optical contact. In a preferred embodiment of the invention, the optical adhesive film comprises two adhesive layers, wherein each adhesive layer is preferably applied directly to a carrier layer, so that the optical adhesive film comprises three layers. Such an optical adhesive film can adhere to two surfaces simultaneously, thereby providing particularly good optical contact and reducing the risk of air gaps or unwanted reflections.

[0112] The optical adhesive film is preferably optically transparent. The optical adhesive film preferably comprises a material with a Fresnel-corrected transparency of at least 99%, a maximum haze of 0.5%, and a minimal polarization tendency. The material of the optical adhesive film is preferably colorless. It is particularly preferred that the optical adhesive film does not exhibit a yellow tinge or gray coloration. The adhesive strength of the optical adhesive film should be so low that no undesirable stresses arise in the photopolymer composite and no traces are left on the master element or the photopolymer composite. This means that the optical adhesive film can preferably be removed without leaving residue. A preferred adhesive strength is between 10 cN / cm and 3 N / cm for the optical adhesive film.

[0113] In preferred embodiments, the optical adhesive film comprises a carrier layer coated on both sides with an optically transparent adhesive material. The carrier layer is therefore preferably provided with adhesive layers on both sides, wherein the adhesive layers preferably consist of one adhesive material. The carrier layer preferably comprises one or more of the following materials: polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene, polypropylene, cellulose acetate triacetate (TAC), cellulose hydrate, cellulose nitrate, cycloolefin polymers, polystyrene, polyepoxides, polysulfone, cellulose triacetate (CTA), polyamide, polymethyl methacrylate (PMMA), polyvinyl chloride, polyvinyl butyral, perfluoroethylene propylene (FEP), or polydicyclopentadiene, or mixtures thereof.The optically transparent adhesive material preferably comprises an adhesive material based on silicone, acrylate, rubber or mixtures thereof, with rubber-based adhesive materials being particularly preferred.

[0114] It is preferred that the outer layers of the optical adhesive film are each protected by a protective film in the initial state. Suitable unwinding rollers can be provided for unwinding these protective films in the section between the unwinding roller of the optical adhesive film and the master element.

[0115] It is preferred that the refractive index difference between the master element and the optical adhesive film, and preferably also between the master element and the adjacent photopolymer composite, be no more than 0.2, more preferably no more than 0.1, and even more preferably no more than 0.05. This enables significantly improved control of the diffraction of the exposure light without the need for optical fluids, which require high maintenance and frequent cleaning of the device.

[0116] It is particularly preferred that the optical adhesive film has a refractive index that lies between the refractive index of the master element (or its cover) and the adjacent photopolymer composite (or its adjacent carrier film). In this context, the term "between" preferably also includes the values ​​of the refractive indices of the adjacent master element or photopolymer composite itself. This arrangement enables a smooth or interference-free transition of light rays between the master element and the photopolymer composite with minimal reflections and / or aberrations at interfaces.

[0117] As an illustrative, non-limiting example, the refractive indices, starting from the base body and radially outwards, can be chosen as follows.

[0118] Basic body (from N-BK7): n e = 1 .519

[0119] Adhesive layer: n e = 1 .51

[0120] Master hologram (photopolymer layer): n e = 1,500

[0121] Master hologram (carrier foil): n e = 1 .485

[0122] Optical adhesive film (OCA consisting of adhesive layer / carrier layer / adhesive layer): n e = 1 .47 / 1 .485 / 1 .47

[0123] Those skilled in the art are familiar with other materials that, based on the present teaching, enable the most continuous possible transition of the refractive index of the master element and the adjacent carrier film. For example, as an alternative, the base body can comprise Borofloat-33, which has a refractive index of 1.48. The materials of the additional layers can be selected to match this index. For all of the above-mentioned components (base body to optical adhesive film), it is generally preferred that the respective refractive index be between 1.4 and 1.6.

[0124] For all of the above-mentioned components, their materials preferably have a Fresnel-corrected transparency of at least 99%, a maximum haze of 0.5%, and a minimal polarization tendency. The stress-optical coefficient of the materials is preferably as low as possible. The stress birefringence of the materials is preferably minimized by appropriate annealing so that carrier films do not exhibit a zebra pattern when viewed through crossed polarizers. It is also preferred that the materials used exhibit minimal streaks, inclusions, and bubbles.

[0125] In a further preferred embodiment of the invention, the master element has a constant diameter of at least 50 mm, preferably at least 100 mm, more preferably at least 150 mm, and even more preferably at least 300 mm. Advantageously, corresponding shapes and dimensions of the master element cause particularly low distortions due to shear forces in the liquid photopolymer layer. The lower curvature caused by the larger diameter also enables increased flexibility and control in the alignment of the exposure light and positively influences any introduced tensile or shear forces in the photopolymer composite, i.e., they are lower.

[0126] Optionally, additional transport rollers can also be provided in the device between the exposure module and the fixing module. To protect the exposed liquid photopolymer layer, it is also preferred in such a case for such rollers to have a larger, constant diameter. Preferred diameters are at least 50 mm, preferably at least 100 mm, more preferably at least 150 mm, and even more preferably at least 300 mm. The optional transport rollers are preferably aligned such that a path between the exposure module and the fixing module has no or as few deflections as possible. This means that it is particularly preferred for the transport of the exposed liquid photopolymer to proceed essentially in a straight line.

[0127] In a further preferred embodiment of the invention, one or both base surfaces and / or the lateral surface of the master element are completely or partially provided with an anti-reflective coating. This advantageously reduces unwanted interference with the exposure caused by reflections.

[0128] In a further preferred embodiment of the invention, the coating module is configured to coat the liquid photopolymer onto the first carrier film using a roll-to-roll process. The coating module may comprise one or more coating elements, whereby the suitable coating element can be selected depending on the layer thickness and rheological properties. Preferred coating elements include, for example, an anilox roller, a wire doctor blade, a profile doctor blade, a slotted nozzle, a doctor blade, a chamber doctor blade, a comma doctor blade, and / or means for a doctor blade process.

[0129] The thickness of a photopolymer layer is preferably 1-200 μm. For photopolymer layers with thicknesses between 1-15 μm, it is preferable to use an anilox roller in a gravure printing process. For photopolymer layers with thicknesses between 7-40 μm, wire or profile doctor blades are preferred. For layer thicknesses between 40 and 100 μm, a slot die, a doctor blade, or a comma doctor is preferably used.

[0130] In a further preferred embodiment of the invention, the device comprises two coating modules, wherein a first coating module is configured to coat a first carrier film with a liquid photopolymer, and a second coating module is configured to coat a second carrier film with a liquid photopolymer. By separately coating two films and joining them together, thinner coating layers can be combined into a thicker photopolymer layer. Advantageously, thinner layers degas faster. The solvents in the coatings can also evaporate more quickly before the lamination process.

[0131] Furthermore, coating additional carrier films can enable the production of photopolymer stacks. For example, a stack of three liquid photopolymer layers, each separated by a carrier film, can comprise three different photopolymer compositions, each composition being sensitive to light of a specific wavelength (preferably RGB).

[0132] In a further preferred embodiment of the invention, the device comprises an unwinding station for unwinding a carrier film supplied as a roll. It is preferred that the device comprises unwinding stations for each of the first and second carrier films. It is also preferred that the carrier films are supplied to the device between two protective films. In this case, the device preferably comprises unwinding rollers for removing one or more protective films before the carrier films are further processed. It is particularly preferred that the protective films are removed from only one side of the carrier films.

[0133] In a further preferred embodiment, the device further comprises a surface pretreatment station, preferably based on the principle of a plasma pretreatment station, between at least one of the unwinding modules and a coating module, in particular between the unwinding modules and the coating modules. This advantageously improves the adhesion of the liquid photopolymer layer to the carrier films. The device preferably comprises a first surface pretreatment station for pretreating the first carrier film and a second surface pretreatment station for pretreating the second carrier film. If additional films are to be coated with a photopolymer or cover a photopolymer layer, the device can preferably also comprise a surface pretreatment station for each additional film that should come into contact with a photopolymer layer.

[0134] In a further preferred embodiment of the invention, the lamination module comprises at least one lamination roller (or "lamination roller"), in particular a pair of lamination rollers. The at least one lamination roller is preferably configured to exert a pressure of 0.02 - 200 N / cm 2 , especially 0.02 - 50 N / cm 2to the two carrier films and the photopolymer layer in between. The pressure application is preferably monitored by a suitable sensor and preferably serves to control the lamination module. A film coating can preferably be used as a sensor for the pressure exerted by the at least one lamination roller, with a pressure sensor distributed over the entire film (so-called "pressure measuring film"). This allows the pressure distribution along a lamination roller to be determined, so that any misalignment of the lamination roller can be detected and corrected.

[0135] In a further preferred embodiment of the invention, the lamination module comprises a pair of laminating rollers. It is preferred that the lamination module applies a compressive force of between 10 and 20,000 N to the two carrier films and the intermediate photopolymer layer. The required compressive force preferably depends on the width of the carrier films, the coating width, the target layer thickness, and / or the web speed. Alternatively or additionally, the lamination module can laminate the at least two carrier films at a temperature between 5 and 300°C, preferably 15 and 200°C, in particular 20 and 100°C. Depending on the materials of the two carrier films, the temperature is preferably selected so that one or both are brought to their melting point for a short period of time. The preferred temperature depends not only on the aforementioned parameters but also on the photopolymer formulation.The temperature and pressure should preferably be adjusted so that the photopolymer layer remains in a liquid state or maintains or adjusts a viscosity optimized for subsequent process steps. The lamination module preferably connects the first and second carrier films along two parallel uncoated edges, so that the liquid is enclosed between them.

[0136] In a further preferred embodiment of the invention, one or both laminating rollers comprise stainless steel. Stainless steel offers various advantages, such as the ability to withstand high pressures and easy cleaning. The laminating rollers can be rigid, e.g. without coating the stainless steel and / or by coating the stainless steel only with a protective layer and / or a pressure sensor. This is particularly advantageous when thin layers of liquid photopolymer are provided between the carrier films. However, with greater photopolymer layer thicknesses, it can also be advantageous if the laminating rollers have a less rigid coating. In some embodiments, it is therefore preferred for one or more of the laminating rollers to comprise a rubber coating, wherein the rubber coating can, for example, comprise a fluoroelastomer such as Viton or a nitrile rubber (acrylonitrile butadiene rubber, NBR).In a further preferred embodiment of the invention, the device comprises a degassing station arranged between the coating module and the lamination module. The degassing station is preferably configured to transmit vibration to the coated first and / or second carrier film. The vibration advantageously serves to eliminate any air bubbles in the liquid photopolymer layer. The degassing station is preferably also configured to be heatable to 30–300°C, in particular 100–200°C. The elevated temperature also serves to remove solvents. The degassing station can also be used to increase the viscosity of the photopolymer layer for subsequent process steps. This further reduces any influence of residual shear forces on the liquid photopolymer layer.

[0137] In all modules and stations of the device, it is preferred that a web width of the carrier films or the photopolymer composite can be accommodated between 150 and 1500 mm, with a coated width preferably being 100 and 1400 mm. For transporting the web-shaped carrier films or the photopolymer composite, the device preferably comprises web guide elements such as guide rollers and / or a tension roller or tension roller. The web guide elements and the modules are preferably configured for a web speed between 5 cm / min and 50 m / min.

[0138] All modules and stations of the device are preferably also multipliable. For example, the device can have three consecutive exposure modules for exposing three different color-sensitive components of the liquid photopolymer at different wavelengths. Alternatively or additionally, the device can comprise three parallel coating modules, lamination modules, and exposure modules, which process three different color-sensitive photopolymer composites to produce a stack of three composites, e.g., an RGB stack, after fixation.

[0139] The device according to the invention is preferably configured to carry out a method for the continuous replication of a hologram. The method preferably comprises the following steps: a. coating a first carrier film with a liquid photopolymer using a coating module, b. applying a second carrier film to the coated first carrier film using a lamination module to obtain a photopolymer composite comprising a liquid photopolymer layer between two carrier films, c. bringing a region of the photopolymer composite into contact with an axially rotatable master element comprising a master hologram to be replicated in an exposure module and exposing the region of the photopolymer composite using a light source so that the master hologram is replicated onto the photopolymer composite, and d. curing a replica hologram contained in the liquid photopolymer in a fixing module.

[0140] The average person skilled in the art recognizes that technical features, definitions and advantages of preferred embodiments of the device according to the invention also apply to the method, and vice versa.

[0141] The process is particularly characterized by bringing the photopolymer composite into contact with an axially rotatably mounted master element, while the light source exposes the master hologram to an area of ​​the photopolymer composite to obtain a replicated hologram. "Bringing into contact" in this sense refers to optical contact, although additional mechanical contact may also be preferred. The axially rotatably mounted master element allows, in particular, continuous integration of the exposure process into a roll-to-roll process. Process interruptions, as in conventional processes using ground glass screens, are avoided.

[0142] Due to the high processing speed, liquid photopolymers with a short storage life of just a few days, hours, or minutes can be used. Due to their light sensitivity, these liquid photopolymers should preferably be handled with care. Therefore, the coating module is preferably optically isolated from ambient light. High-speed processing of the photopolymers reduces the risk of interference from reflection and ambient light, ensuring the final product is highly precise and high-quality. Due to the speed and precision of the device, a drying station between the coating and the exposure modules is not required. This allows for even more cost-effective production of small batches.

[0143] The preferred steps of the procedure are explained in more detail here. The order of the following explanations may, but does not necessarily, correspond to the order of the procedural steps.

[0144] A first carrier film is preferably coated with a liquid photopolymer in a coating module. The thickness of a photopolymer layer is preferably 1-200 μm. For photopolymer layers with thicknesses between 1-15 μm, it is preferable to use an anilox roller in a gravure printing process. For photopolymer layers with thicknesses between 7-40 μm, wire or profile doctor blades are preferred. If the layer thickness is between 40 and 100 μm, a slot die, a doctor blade, or a comma doctor is preferably used. The process can optionally comprise the simultaneous coating of both the first and second carrier films using separate coating elements. By coating two films separately and joining them, thinner coating layers can be combined to form a thicker photopolymer layer. The advantage is that thinner layers degas more quickly.The solvents in the coatings can also evaporate more quickly before the lamination process.

[0145] The method preferably further comprises applying a second carrier film to the coated first carrier film using a lamination module to obtain a photopolymer composite comprising a liquid photopolymer layer between two carrier films. The lamination module preferably comprises two lamination rollers. It is preferred that the lamination module applies a compressive force of between 10 and 20,000 N to the two carrier films and the intermediate photopolymer layer. The required compressive force preferably depends on the width of the carrier films, the coating width, the target layer thickness, and / or the web speed. Alternatively or additionally, the lamination module can laminate the at least two carrier films at a temperature between 20 and 300°C. Depending on the materials of the two carrier films, the temperature is preferably selected so that one or both are brought to their melting point for a short period of time.In addition to the parameters mentioned above, the preferred temperature also depends on the photopolymer formulation.

[0146] The composition of the photopolymer as well as the pressure and temperature of the lamination are preferably selected so that the photopolymer remains in a liquid state during a lamination process or a viscosity optimized for the subsequent process steps is maintained or adjusted.

[0147] The first and second carrier films are preferably designed as a (randomly long) web, so that the lamination produces a (randomly long) photopolymer composite web comprising a liquid photopolymer layer.

[0148] The method preferably further comprises bringing a region of the photopolymer composite into contact with an axially rotatable master element comprising a master hologram to be replicated in an exposure module and exposing the region of the photopolymer composite using a light source, such that the master hologram is replicated onto the photopolymer composite. In this method step, a region of the photopolymer composite to be exposed preferably temporarily assumes the shape of a region of a lateral surface of the master element. The preferably web-shaped photopolymer composite is preferably guided over the rotating master element. The speed of the web and the master element are preferably synchronized with one another. The synchronization can be carried out by a control unit as described above. Therefore, there is preferably mechanical contact between a region of the master element and a region of the photopolymer composite.If the composite is guided tangentially to the master element, this area is a line with a line width of, for example, less than 1 mm. Likewise, the area of ​​the photopolymer composite to be exposed can temporarily assume the shape of the outer surface of the master element over an extended area, for example over an arc-shaped area over a circular segment of a cylindrical master element with an opening angle of more than 5° or more than 10°. This offers more space for exposure and optionally fixation. The exposure can preferably take place on the exposed area along a line parallel to the rotation axis of the master element or simultaneously in several lines. Preferably, the exposure is carried out by one or more continuously scanning light sources, preferably lasers.

[0149] Following exposure, fixation can preferably be performed on the master element. Due to the sensitivity of the exposed liquid photopolymer to distortion, it is particularly advantageous for fixation to occur immediately after exposure with minimal transport between the two process steps.

[0150] The method preferably comprises curing a replica hologram contained in the liquid photopolymer in a fixation module. The fixation module allows the composite web to be transferred from the exposure module, preferably quickly and with minimal deflections. The fixation module can preferably comprise a UV radiation and / or heat treatment source. The fixation module can be located in the same housing as the exposure module. In a preferred embodiment, the device is designed such that fixation takes place immediately after exposure to the master element.

[0151] In a preferred embodiment of the invention, the first and / or the second carrier film is based on a material or material composite selected from a group comprising polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene, polypropylene, cellulose acetate, triacetate (TAC), cellulose hydrate, cellulose nitrate, cycloolefin polymers, polystyrene, polyepoxides, polysulfone, cellulose triacetate (CTA), polyamide, polymethyl methacrylate (PMMA), polyvinyl chloride, polyvinyl butyral, polydicyclopentadiene, mixtures of two or more of the materials mentioned or coextrudates comprising one or more of the materials mentioned, with PC, PET and / or TAC being particularly preferred.

[0152] In particular, it has been found that the aforementioned materials, especially coextrudates of two or more of these materials, are extremely weather-resistant, preferably less prone to tearing, and exhibit fewer weak points in their expansion. This improves the service life of the resulting holograms. The materials and properties of the carrier films can be selected to ensure the most continuous transition of the refractive indices possible from the master hologram to the liquid photopolymer layer, taking into account the properties of any intermediate layers.

[0153] In a preferred embodiment of the invention, the liquid photopolymer comprises

[0154] (i) at least one writing monomer;

[0155] (ii) a photoinitiator system; and

[0156] (iii) comprises at least one organic component, wherein the liquid photopolymer optionally further comprises one or more of the following components: a catalyst, a dye, a radical stabilizer, a solvent, a non-polymerizable component, a reactive diluent, a dye oxidizing agent, a dye reducing agent, a bleaching agent, a thixotropic agent, a nucleating agent and / or auxiliaries or additives.

[0157] Suitable liquid photopolymers are known to those skilled in the art. For example, compositions for liquid photopolymers as disclosed in EP1779196B1 are suitable. In a preferred embodiment, the liquid photopolymer is binder-free. The writing monomer is preferably an ethylenically unsaturated monomer having the general formula:

[0158] Where n is 2 to 4, R' is hydrogen or CH3 and L

[0159] Is, wherein the phenyl rings are optionally substituted with one or more substituents selected from the group consisting of halogen, C-alkyl, alkoxy or hydroxy; L 1 a covalent bond of a straight-chain or branched C- alkyl group is:

[0160] L 2 a covalent bond, a straight-chain or branched C-alkyl group optionally substituted by hydroxy, or -[L 3 -O] m -, where L 3 is a CM alkylene group and m is 1 to 40;

[0161] Wherein the at least one organic component is selected from the group consisting of castor oil, palm kernel oil, coconut oil and combinations thereof.

[0162] The components of the liquid photopolymer can preferably be mixed in situ. The amounts of the various components and the inclusion of optional components can be adjusted from batch to batch as required.

[0163] In a preferred embodiment of the invention, the residence time of the liquid polymer during transport of the photopolymer composite from the exposure module to the fixing module is not more than 10 minutes, preferably not more than 5 minutes, more preferably not more than 3 minutes.

[0164] In a further preferred embodiment of the invention, a residence time of the liquid photopolymer between its coating on the first carrier film and its curing is not more than 15 minutes, preferably not more than 10 minutes, particularly preferably not more than 5 minutes.

[0165] The short residence time of the photopolymer between the operating modules is advantageous because in this way all work steps can be completed before distortions in the hologram (e.g. due to mechanical influences on the liquid photopolymer) or other disturbing effects (e.g. due to finite storage stability or optical stray light) can occur.

[0166] The device according to the invention and the preferred method provide a photopolymer composite, wherein the photopolymer composite comprises a photopolymer between two carrier films in which a hologram has been replicated by the method and / or device.

[0167] The average person skilled in the art recognizes that technical features, definitions and advantages of preferred embodiments of the device according to the invention and / or the preferred method also apply to the photopolymer composite that can be produced and vice versa.

[0168] Detailed description

[0169] The invention will be explained in more detail below using examples and illustrations, without being limited to them. Brief description of the illustrations

[0170] Fig. 1 Schematic representation of the device according to the invention and the preferred method according to a preferred embodiment

[0171] Fig. 2 Schematic representation of the exposure module according to another preferred embodiment

[0172] Fig. 3 Schematic representation of an arrangement of the exposure module for the duplication of a hologram by reflection

[0173] Fig 4 Schematic representation of an arrangement of the exposure module for the

[0174] Reproduction of a hologram by transmission, whereby the master element is exposed from a lateral surface

[0175] Fig. 5 Schematic representation of an arrangement of the exposure module for the duplication of a hologram by transmission, whereby the master element is exposed from a base surface

[0176] Detailed description of the illustrations

[0177] Figure 1 schematically shows a device according to a preferred embodiment of the invention. The device comprises two coating modules 16 and 17, a lamination module 14, an exposure module comprising a cylindrical master element 4 and a laser, and a fixation module 25. The device is preferably designed for a web-like flow of the carrier films 18, 19 or a photopolymer composite 1 in the illustrated arrangement from left to right. The entire device is preferably shielded from external light. The stations and processes through which the web passes will now be explained in more detail.

[0178] A first carrier film 18 is preferably supplied between protective films and in the form of a roll as starting material. The first carrier film preferably comprises polycarbonate and has a preferred thickness of between 50 and 125 μm. The width of the film is preferably up to 1500 mm, but more preferably up to 310 mm. In this way, the entire width can usually be covered in the later process with a single plasma pretreatment unit. An unwind roll 20 feeds the first carrier film 18 to a coating module. In a section of the path between the unwind roll and the coating module, a set of take-up rolls 22 for removing the protective films from the carrier film can be provided. Although it may be preferred that the protective film is removed only from the side of the carrier film 18 to be coated, in this exemplary embodiment it is removed from both sides.A plasma pretreatment station 23 can preferably be provided between the take-up rolls 22 and the coating module 17. This preferably prepares the side of the carrier film 18 to be coated in order to improve the adhesion of a liquid photopolymer 9 to its surface. The pretreated carrier film is then fed to a first coating module 17.

[0179] In the embodiment shown, analogous stations and process steps are also provided for a second carrier film 19. The second carrier film can preferably comprise polycarbonate and has a preferred thickness between 50 and 125 μm. This is also unrolled from an unwind roll 21, its protective films are removed by rollers 22, it is subjected to a plasma pretreatment, and then fed to a second coating module 16. The web speed through the pretreatment station is preferably 1 to 10 m / min.

[0180] In the embodiment shown, two coating modules are provided: the first coating module 17 comprises an anilox roller, which is particularly suitable for thin coatings (with a layer thickness between 1 - 15 μm). The second coating module 16 comprises a comma doctor blade, which is particularly suitable for thicker coatings (with a layer thickness between 40 - 100 μm). To cover further thickness ranges, the device can, for example, alternatively or additionally comprise a further wire doctor blade or profile doctor blade for coating the upper and / or lower carrier films (not shown). It is not necessary that both carrier films are coated. Depending on the requirements of the series to be produced, the desired coating module can be switched on. A liquid photopolymer 9 is preferably fed to the coating modules either from a storage container or a mixing unit (not shown).In preferred embodiments, these can also form part of the device to allow for particularly rapid adjustment of the photopolymer formulation. The coating of the films can preferably be designed in such a way that a coating-free edge is maintained on the sides of each film. This allows for easier handling and facilitates the subsequent lamination process.

[0181] After passing through the coating module, each carrier film is conveyed via a transport roller 3 to a degassing station 15. In the degassing station, the carrier films are preferably caused to vibrate by means of vibrating rollers, causing bubbles to escape from the viscous liquid layer. Since the liquid photopolymer 9 may also contain a solvent, this can also be removed in this station. For this purpose, it may be preferred for the degassing station to additionally heat the carrier films to a temperature between 30 and 300 °C. The degassing station can therefore simultaneously function as an evaporation unit (of solvents). The heating can be achieved, for example, by a heated transport roller or via a heatable transport section.The evaporation of all or part of the solvent component can also be designed to adjust the viscosity of the liquid photopolymer to facilitate further processing steps. Advantageously, a more viscous liquid photopolymer layer is less susceptible to deformation due to shear forces and reduces unwanted distortions in the replication process.

[0182] The two carrier films 18 and 19 are then transported to a lamination module 14. The lamination module 14 preferably comprises a pair of lamination rollers, one or both of which are adjustable in position to define a maximum thickness of the materials flowing between them. The lamination rollers preferably comprise silicone and can, for example, have a diameter of 50 to 200 mm. The lamination rollers can preferably be heated to a temperature between 5 and 300°C, preferably 15 to 200°C. If the target temperature of the heater is equal to or lower than the ambient temperature, active heating is of course not required. The lamination rollers are also preferably configured to exert a compressive force of between 10 and 20,000 N on the carrier films and the sandwiched photopolymer layer.The photopolymer composite is then optionally actively cooled to room temperature, preferably between 20 and 25 °C. The control unit preferably regulates the required heating and / or cooling based on the process requirements for the respective series and the ambient conditions.

[0183] The lamination module is preferably designed such that a photopolymer composite 1 is formed from the three layers 19, 9, and 18. The photopolymer composite 1 preferably flows continuously from the lamination module 14 into a closed housing 6, which contains at least the exposure module. The inlet 7 of the housing can itself have a pair of positionable rollers. The housing contains at least the master element 4 and a light source. Preferably, the housing is optically isolated. The degree of optical isolation can be determined by the exposure requirements. Particularly at high web speeds, ambient light does not tend to interfere with the exposure process, so complete light tightness is not required.

[0184] Input 7, master element 4, a transport roller 3, and output 8 are preferably arranged such that the photopolymer composite 1 is deflected by the master element 4. The master element is cylindrical here and mounted for rotation about a center point of its circular cross-section. The photopolymer composite 1 is guided, in particular, over a portion of the lateral surface on an underside of the master element, wherein an area of ​​the photopolymer composite to be exposed temporarily assumes the shape of a lateral surface of the master element, at least in some areas, and is guided over the rotating master element, moving along with the lateral surface.

[0185] In this embodiment, the region of the photopolymer composite 1 to be exposed temporarily assumes the shape of the lateral surface of the master element 4 over an extended region, wherein the extended region extends in an arc shape over a circular segment of a cylindrical master element with an opening angle of more than 5°, preferably more than 10°.

[0186] Advantageously, in this case, a dedicated drive for the master element can be dispensed with. Since the movement of the carrier film creates a frictional force across the surface of the mast element (possibly mediated by an adhesive layer), this can be sufficient to cause synchronous rotation of the mast element 4 with the photopolymer composite 1. This also ensures particularly good exposure conditions and enables process efficiency.

[0187] In the embodiment shown, an optical adhesive film 2 is also temporarily placed as a web between the master element and the photopolymer composite web. The optical adhesive film 2 preferably consists of a carrier layer provided with an adhesive layer on both sides. To facilitate handling, the optical adhesive film 2 is preferably supplied in the form of a roll with a protective film on each side. The optical adhesive film is first unwound, preferably from a supply roll 10. The protective films are then removed by take-up rolls 12. The optical adhesive film is guided through the master element and a take-up roll 13, which can optionally function as a pull roll. In this way, a flow of the optical adhesive film 2 is maintained synchronously with the flow of the photopolymer composite 1 over a surface of the lateral surface of the master element.

[0188] The optical adhesive film acts as an optical clearance adhesive (OCA) and ensures a smooth optical bond between a master hologram and the photopolymer composite 1. The master hologram is preferably applied as a layer to an outer surface of the master element.

[0189] The replication of the master hologram can preferably be carried out by a reflection or transmission process to form a volume hologram in the still-liquid photopolymer 9. The position of the light source and the light beam can be adjusted for the respective processes so that the light rays either transmit through the master element and a master hologram contained therein or thereon (transmission hologram) or are reflected by the master hologram back into the photopolymer composite (reflection hologram). In the example of Fig. 1, the laser source is arranged below the master element and configured to replicate the master hologram by reflection. The master element is opaque, and the optical adhesive film is adapted to the refractive index of the master hologram layer located on an outer surface of the master element.The carrier foils 18 and 19 are both transparent, allowing light to pass through them to the master hologram, which reflects the light back through all layers of the photopolymer composite. The laser can be configured to scan along an axial direction of the master element. The scanning speed can be adjusted to the path speed of the photopolymer composite 1.

[0190] Since the just-exposed liquid photopolymer 9 is mechanically sensitive, the rollers and guides over which it runs from the master element to the end of the fixing module are preferably designed so that they do not have tight deflections. The radii of these rollers 24 are preferably set to at least 100 mm, more preferably at least 200 mm, and even more preferably at least 300 mm.

[0191] To prevent unwanted shear forces from acting on the liquid photopolymer layer, the device also includes tension sensors to maintain an identical tension and strain state in the two carrier films 18 and 19. The exposed photopolymer composite leaves the light-tight housing 6 via an exit 8. However, the passing photopolymer composite preferably remains protected from outside light until it is completely fixed. The photopolymer composite is guided by guide rollers 24 to the fixing module 25.

[0192] The fixing module 25 preferably comprises one or two UV lamps and a heating device. The fixing process is designed to cure the liquid photopolymer layer to fix the hologram. This preferably occurs quickly, preferably within three minutes of photopolymer exposure, to prevent the quality of the final fixed hologram from being compromised. The air in the fixing module is preferably continuously exchanged by an airflow system.

[0193] After leaving the fixing module, the now cured photopolymer composite 1 with the hologram is preferably provided with a protective film 28 on both sides. If the outer protective film of the carrier films 18 and 19 has not yet been removed, it can be removed and replaced here. Unwinding rollers 26 feed the protective film to a workstation comprising a set of rollers with adjustable spacing. Finally, the finished photopolymer composite 1 is wound up by an unwinding roller 27. Alternatively, the finished product, which contains one or more repeating holograms, can be cut to size and stored in cassette form. Figure 2 shows an exposure module and method according to a further preferred embodiment of the invention. In the embodiment shown, the photopolymer composite 1 moves from right to left. The master element 4 is cylindrical with a constant diameter.The schematic representation shows the circular base area of ​​the master element. A region of the photopolymer composite 1 to be exposed temporarily takes on the shape of a region of the outer surface and moves with the outer surface while being guided over the rotating master element. An optical adhesive film 2 is arranged as an intermediate layer between the master element 4 and the photopolymer composite 1. In this embodiment, the region of the photopolymer composite that is in contact with the outer surface and is deformed by it is determined by the positioning of two lower transport rollers 3. The exposure module also comprises an upper transport roller 3 that is in contact with the outer surface of the master element. This roller is preferably made of rubber and has its own drive. The upper transport roller 3 transmits a rotational movement to the master element 4 through friction and determines its rotational speed.In this case, the movement of the mast element 4 can be actively controlled independently of that of the photopolymer composite 1. The control is preferably configured to ensure synchronous movement of the lateral surface and the photopolymer composite.

[0194] Alternatively, the master element 4 can also have a flange at one or both ends. The flange can, for example, be designed to interact with a gear ring or a belt mechanism to move the mast element. This has the advantage that both the outer surface and the base surfaces of the master element are almost completely optically accessible, allowing flexible positioning of the light beams.

[0195] Figure 3 schematically shows an arrangement of the light source with respect to the master element 4 for copying a master hologram 29 by reflection into a photopolymer composite 1. The light source is preferably arranged such that a light beam 5 is generated which acts as a reference beam and passes through the photopolymer composite 1 and an optical adhesive film 2 before being at least partially reflected by the master hologram 29. A reflected beam acts as an object beam and passes through the optical adhesive film 2 and the photopolymer composite 1. The reference beam and the object beam preferably interfere in the liquid photopolymer layer to inscribe the hologram. The angle at which the reference beam strikes the master hologram can preferably correspond to the angle at which the copied hologram is illuminated in order to reconstruct the hologram, e.g., in a head-up display.Figure 4 schematically shows an arrangement of the light source relative to the master element 4 for copying a master hologram 29 by transmission from a lateral surface into a photopolymer composite 1. The light source is preferably arranged such that a beam 5 generated by the light source passes through the master element 1, the master hologram 29, the optical adhesive film 2, and the photopolymer composite 1 as a reference beam. The reference beam 5 is preferably partially diffracted by the master hologram 29 to generate object beams with different angles of incidence to the photopolymer composite. The object beams preferably interfere with the undiffracted reference beam in the liquid photopolymer layer to replicate the hologram.

[0196] Figure 5 schematically shows another arrangement of the light source relative to the master element 4 for copying the master hologram 29 by transmission into a photopolymer composite 1. In this embodiment, the light source is arranged such that a light beam 5 generated by the light source strikes a base surface of the master element 4 (analogous to an edge-lit configuration). The base surface preferably does not include a master hologram 29, which instead is present on the lateral surface.

[0197] For this embodiment, the master element 4 is preferably provided as a light guide. As with other arrangements for transmission holography, the light is preferably split by the master element into a reference beam, which passes through the master hologram without diffraction or with less diffraction, and an object beam, which is diffracted by the master hologram. The object beam and the reference beam interfere with each other in the liquid photopolymer layer to change its refractive index accordingly and write the hologram.

[0198] The light beam propagates within the master element preferably by reflection, preferably total internal reflection. Light losses in the areas of the lateral surface that are not in optical contact with the photopolymer composite are preferably minimized.

[0199] List of reference symbols

[0200] 1 photopolymer composite

[0201] 2 Optical adhesive film

[0202] 3 Transport roller (or “transport roller”)

[0203] 4 Master element

[0204] 5 light beam

[0205] 6 Light-tight housing

[0206] 7 Entrance into light-tight housing

[0207] 8 Exit from light-tight housing

[0208] 9 Liquid photopolymer

[0209] 10 Optical adhesive film unwinding roll

[0210] 11 Winding roll for the protective film of the optical adhesive film

[0211] 12 winding roll for the protective film of the optical adhesive film

[0212] 13 Optical adhesive film winding roll

[0213] 14 Laminating roller (or “laminating roller”)

[0214] 15 Degassing station

[0215] 16 Coating module (or “application module”) - comma mark

[0216] 17 Coating module (or “application module”) - anilox roller

[0217] 18 First carrier film

[0218] 19 Second carrier film

[0219] 20 unwinding roll for the first carrier film

[0220] 21 Unwind roll for the second carrier film

[0221] 22 Protective film winding roll for the carrier films

[0222] 23 Pretreatment station (plasma)

[0223] 24 Guide roller

[0224] 25 Fixation module

[0225] 26 Unwinding roll protective film for the fixed hologram

[0226] 27 Take-up roll for the fixed hologram

[0227] 28 Protective film for the fixed hologram

[0228] 29 Master hologram

Claims

PATENT CLAIMS 1 . Device for the continuous replication of a hologram comprising a. a coating module (17) which is designed to coat a liquid photopolymer (9) onto a first carrier film (18), b. a lamination module (14) which is designed to apply a second carrier film (19) to the first carrier film (18) coated with the photopolymer in order to obtain a photopolymer composite (1) comprising a liquid photopolymer layer between two carrier films, c.an exposure module, wherein the exposure module has a light source (5) and a master element (4) comprising a master hologram to be replicated, wherein the master element is mounted so as to be axially rotatable and the exposure module is designed to bring the photopolymer composite (1) into optical contact with the master element, while the light source (5) exposes the master hologram to a region of the photopolymer composite (1) to obtain a replicated hologram, and d. a fixing module (25) which is designed to cure the replicated hologram in the photopolymer composite (1).

2. Device according to claim 1, characterized in that the exposure module is configured such that during the photopolymer composite (1 ) is guided through the exposure module, an area of ​​the photopolymer composite to be exposed temporarily assumes the shape of a lateral surface of the master element (4) in some areas and is guided over the rotating master element (4) moving along with the lateral surface.

3. Device according to one of the preceding claims, characterized in that the master element (4) comprises a base body, wherein the master hologram is introduced within the base body and / or applied to a lateral surface of the base body, wherein a reflection-reducing material is preferably applied to the areas of the master element (4) not covered by the master hologram.

4. Device according to one of the preceding claims, characterized in that the exposure module comprises at least one unwinding roller (10) and one winding roller (13) for temporarily applying an optical adhesive film (2) between the master element (4) and the photopolymer composite (1). Device according to claim 4, characterized in that the optical adhesive film (2) has a refractive index which lies between a refractive index of the master element and the carrier film, wherein a refractive index difference between the master element and the optical adhesive film, preferably also between the master element and the carrier film, is particularly preferably not more than 0.2, more preferably not more than 0.1, and even more preferably not more than 0.

05. Device according to one of the preceding claims, characterized in that the master element (4) has a constant diameter of at least 50 mm, preferably at least 100 mm, more preferably at least 150 mm, and even more preferably at least 300 mm.Device according to one of the preceding claims, characterized in that the master element is driven either by power transmission from a functional roller, a flanged sprocket, or a belt drive. Device according to one of the preceding claims, characterized in that one or both base surfaces and / or a lateral surface of the master element (4) is provided with an anti-reflective coating. Device according to one of the preceding claims, characterized in that the coating module (17) is configured to coat the liquid photopolymer (9) onto the first carrier film (18) by means of a roll-to-roll process, wherein the coating module preferably comprises an anilox roller, a wire doctor blade, a profile doctor blade, a slot nozzle, a doctor blade, and / or a comma doctor blade. Device according to one of the preceding claims. characterized in that the device comprises two coating modules (17, 16), wherein a first coating module (17) is configured to coat a first carrier film (18) with a liquid photopolymer (9) and a second coating module (16) is configured to coat a second carrier film (19) with a liquid photopolymer (9). Device according to one of the preceding claims, characterized in that the device comprises an unwinding station for unwinding a carrier film supplied as a roll, wherein the device preferably further comprises a plasma pretreatment station (23) between the unwinding station and the coating module. Device according to one of the preceding claims, characterized in that the lamination module (14) comprises a pair of lamination rollers, and preferably at a pressure between 0.02 - 200 N / cm 2 , especially 0.02 - 50 N / cm 2and / or at a temperature between 5 - 200 °C, in particular 15 - 200 °C, the second carrier film (19) is laminated to the coated first carrier film (18). Device according to one of the preceding claims, characterized in that a degassing station (15) is arranged between the coating module (17, 16) and the lamination module (14), wherein the degassing station (15) is preferably designed to transmit a vibration to the coated first and / or second carrier film (18, 19) and / or the degassing station (15) is preferably configured to be heatable to 30 - 300 °C, in particular 100 - 200 °C.

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