Replication method for copying holograms into liquid photopolymers

Abstract

The invention preferably relates to a method for continuously replicating holograms, preferably by means of a device comprising a coating module, a lamination module, an exposure module and a fixing module, wherein the method comprises the following steps: coating a first carrier film with a liquid photopolymer by means of the coating module; applying a second carrier film onto the coated first carrier film by means of a lamination module in order to obtain a photopolymer composite comprising a liquid photopolymer layer between the two carrier films; 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 by means of a light source such that the master hologram is replicated into the photopolymer composite; and curing the replicated hologram present in the liquid photopolymer in the stationary module.

Description

[0001] The present invention relates to a method for continuously replicating a master hologram into a liquid photopolymer.

[0002] The method of the invention comprises: coating a first carrier film with a liquid photopolymer by means of a coating module; and applying a second carrier film to the coated first carrier film by means of a laminating module in order to obtain a photopolymer composite. The photopolymer composite comprises a layer of liquid photopolymer between the two carrier films. The method 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 this region of the photopolymer composite by means of a light source, so that the master hologram is replicated in the photopolymer composite. The replicated hologram present in the liquid photopolymer is cured in a fixing module. Background Art

[0003] The invention relates to the field of hologram replication.

[0004] Modern micro-optical methods allow functions such as imaging or optical monitoring to be inconspicuously integrated into large-format glass surfaces by means of holographic optical elements (HOEs).

[0005] HOE typically refers to an optical component that uses holographic properties to achieve a specific beam path of light (e.g., transmission, reflection, diffraction, scattering and / or deflection, etc.). As a result, the desired optical function can be implemented in a compact manner on any desired substrate. The holographic properties preferably utilize the wave properties of light, in particular coherence effects and interference effects. Here, both the intensity and phase of the light are taken into account.

[0006] Such holographic elements are used in many areas, for example in transparent displays (e.g. in display windows, refrigeration equipment, vehicle window panes), for lighting applications (such as information or warning signals in glass surfaces), in photosensitive detection systems (e.g. for interior monitoring (eye tracking in vehicles or presence tracking of people inside)).

[0007] WO 2020157312 A1 discloses an example of a HOE that has been integrated into a vehicle window pane. The hologram incorporated in the window pane can be used as a waveguide to guide the incident light to the detector. The hologram is produced from a photosensitive material, such as photosensitive glass, dichromated gelatin or a photopolymer. For example, these can be applied to a polycarbonate film and exposed accordingly thereon. The film can then be laminated to a substrate for waveguides in order to produce a waveguide, which is then laminated to the vehicle window pane.

[0008] WO 2018054985 A1 discloses a volume hologram integrated in a vehicle taillight to give the taillight a unique appearance. For this purpose, the volume hologram can be exposed into a holographic layer (for example comprising a photopolymer) and applied directly to the taillight as a film. The volume hologram can have both a color filtering function and a beam shaping function. To achieve this, a suitable composition of the photosensitive material can be selected. The thickness of the hologram can also be selected so that it works as a white light reflection hologram, where the wavelength for reconstruction is selected from a provided spectrum.

[0009] WO 2016202595 A1 discloses a holographic element produced as a HOE layer in eyeglass lenses. By integrating the HOE in the glasses, relevant data can be displayed to the user, or optical functions can be implemented. For this purpose, a liquid photopolymer is applied to the surface of a glass substrate and then exposed. In order to make a sufficient contribution to the optical function, such as the strength of the glasses, it is preferred to use a photopolymer thickness between 50 μm and 100 μm. The addition of dyes to the photopolymer also allows the layer to be configured so that it implements a color filtering function. In some embodiments, the photopolymer layer is disposed on a carrier film before being applied to the glass, for example using a TECHNOLOGY INC. from Covestro AG. HX film. The holographic layer is sealed by applying an additional layer. Thus, the overall thickness of the glasses can be kept low.

[0010] As is clear from the examples, HOEs can be used for numerous applications due to their space-saving design and various functionalities. Therefore, there is a need for replication methods for holograms that are suitable for mass production and can preferably be integrated into a wide variety of different components, in particular glass surfaces. However, the produced holographic elements must here have different properties depending on the application, such as photosensitivity, layer thickness or material selection composition. With regard to the above examples, it may be necessary, for example, that different properties of the holographic element are required between eyeglass lenses of different colors or intensities or between taillights of different makes or models. Therefore, there is a need for efficient mass production of holographic elements with different properties, preferably without the need to use a plurality of different devices to produce the holograms or to adjust the holograms in a complex manner.

[0011] The production of holographic optical elements as insert parts usually requires the use of a carrier substrate and a photosensitive layer. The photosensitive layer conventionally used is dichromated gelatin. A preferred alternative is the use of photopolymers, which are usually available in a film composite in dry form with specific sizes, thicknesses and compositions that are optimized for different purposes, for example for exposure to light of a specific wavelength.

[0012] EP 3065002 B1 discloses a method for producing a holographic security element. Each holographic security element is constructed step by step, wherein a carrier film with a replication layer is provided. The application layer has a concave-convex structure produced by embossing. A photopolymer in liquid form is applied to the replication layer to fill the valleys of the concave-convex structure. A scraper is used to partially remove the photopolymer from the area of ​​the concave-convex structure so that the photopolymer layer can have a variable thickness. Then, the layer structure is guided through the side surface of a cylindrical master element so that the liquid photopolymer layer contacts the side surface. In some embodiments, the side surface has an additional concave-convex structure, which is transferred to the liquid photopolymer layer by means of pressure. At the same time, the master element is exposed to write a volume hologram in the liquid photopolymer layer. The formability of the photopolymer is used to produce a security element with both a concave-convex structure and a volume hologram. After the photopolymer layer has been cured in an exposure station, an adhesive film is applied to its surface.

[0013] DE 102006016139 A1 discloses another method for mass production of holographic security elements. Here, too, the holographic security element is built up stepwise and comprises a liquid photopolymer layer. The liquid photopolymer layer is brought into contact with the relief structure of the master element in order to emboss the relief structure into the security element. At the same time, the master hologram is replicated by exposure into the liquid photopolymer layer.

[0014] In EP 3065002 B1 and DE 102006016139 A1, a liquid photopolymer layer is provided during contact with a master element in order to achieve the desired transfer of the relief structure.

[0015] However, exposed photopolymer layers are also associated with disadvantages. Firstly, these methods are more sensitive to mechanical influences. Secondly, the nature and properties of the photopolymers used are limited, since the viscosity or consistency of the liquid photopolymer may need to be adjusted in order to achieve a stable layer thickness, a stable relief structure and / or low adhesion to the master element. Furthermore, it is necessary to clean the master element thoroughly or to use an antifouling coating on the master element in order to prevent the accumulation of photopolymer residues.

[0016] WO 2019 / 215272 A1 discloses another method for mass production of holographic security elements. The starting material for producing the holographic element is a photosensitive film. The photosensitive film is preferably in the form of a composite composed of a dried, heat-stable photopolymer sandwiched between two polymer films. The photopolymer is then subsequently exposed by conventional methods. In particular, without an embossing method, the starting material for exposing the volume hologram is more mechanically robust than a deformable alternative comprising a liquid photopolymer in contact with a master element, and photopolymer residues are avoided.

[0017] Holographic films comprising a film substrate and a photosensitive photopolymer layer are available, for example, from Covestro Deutschland AG as The invention is commercially available in the form of a product series. WO 2018 / 206503A1 discloses, by way of example, a method for producing a film-bound photopolymer film for exposure with a hologram. The photosensitive film comprises a layer structure comprising a curable protective layer C, a dried photopolymer layer B and a carrier layer A. This is said to provide a stable photopolymer film into which a hologram can also be copied in a simple manner.

[0018] However, since the production of photosensitive films is usually separated from exposure and fixing, these film composites with the desired properties must be mass-produced in advance. Disadvantageously, the properties of film composites comprising photopolymers cannot be adjusted directly. Instead, new developments of photosensitive films are required every time changes are made to the layer thickness, the carrier substrate or the sensitivity of the photopolymer.

[0019] Especially in the case of holograms in preliminary and small-scale series production, this is extremely disadvantageous if, for example, special adjustments of the film-bound photopolymer are required for a specific holographic system and the additional requirement for development work increases 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] EP 0896260 A2 discloses an example of a method and a device for copying a hologram. For this purpose, a master hologram in the form of a frosted glass screen is arranged parallel to a photosensitive film. Depending on the type of hologram, a laser is positioned which scans the master hologram line by line. During the method, it is important that the position of the film relative to the master hologram remains stable. Figure 1 The exposures are performed one after the other, and interruptions slow down the process. Similar to WO 2019 / 215272 A1, EP0896260 A2 also uses a prefabricated photosensitive film as starting material. Due to processing reasons, the properties of this film can no longer be adjusted later, but must be developed and manufactured individually with changed properties. Even if it were possible, it would be difficult for preliminary or small-scale batch production to be economically viable.

[0022] As an alternative to prefabricated photosensitive films, there are already some proposals in the prior art to apply liquid photopolymers directly to the product to be integrated with the HOE. The method for integrating holograms into glazing composites with curved geometries according to DE 102019130022 A1 and the above-mentioned eyeglass production method in WO 2016202595 A1 are examples of such in-situ coating operations.

[0023] However, the proposed method is complex and not procedurally efficient, since the coating cannot be carried out continuously. The method is also slowed down, since each substrate must be cleaned and activated by plasma pretreatment before coating. Furthermore, it is difficult to precisely establish the desired layer thickness of the photopolymer layer in this method.

[0024] There is therefore a need for a faster and higher-quality method for the continuous replication of holograms, which replicated holograms can then be integrated in a simple manner into various components depending on the application and in which time-consuming and inexpensive adjustments can be made for the establishment of desired properties of the replicated holograms.

[0025] Purpose of the Invention

[0026] The object of the present invention is to provide a method for continuously replicating holograms without the disadvantages of the prior art. In particular, the object of the present invention is to provide a method capable of replicating holograms with high precision and high speed, wherein the method is simultaneously characterized by a high flexibility in establishing the desired properties of the replicated holograms. Summary of the invention

[0027] This problem is solved by the features of the independent claim. Advantageous configurations of the invention are described in the dependent claims.

[0028] The present invention relates to a method for continuously replicating holograms, preferably by means of an apparatus comprising a coating module, a laminating module, an exposure module and a fixing module. The method comprises the following steps:

[0029] a. coating the first carrier film with a liquid photopolymer by means of a coating module,

[0030] b. applying a second carrier film to the coated first carrier film by means of a laminating module in order to obtain a photopolymer composite comprising a liquid photopolymer layer between the two carrier films,

[0031] c. bringing a region of the photopolymer composite into contact with an axially rotatable master element comprising the master hologram to be replicated in an exposure module and exposing the region of the photopolymer composite by means of a light source so that the master hologram is replicated in the photopolymer composite, and

[0032] d. Curing of the replicated hologram in the liquid photopolymer in a fixing module.

[0033] The method of the invention provided with the above-mentioned method steps allows the liquid photopolymer itself to be advantageously used directly as the starting material for the replication. Preferably, the photopolymer can also be mixed in situ and the finished mixture can be supplied to the coating module (also synonymously referred to as "application module" in the context of the present invention). Alternatively, the coating module is supplied with the aid of a finished liquid photopolymer mixture which is preferably stored in the dark. Therefore, the liquid photopolymer can be changed or provided with different additives between successive batches. Therefore, a wide range of liquid photopolymers can be used in the same device and adjusted according to the desired properties of the resulting polymer composite. In contrast, the procedures known so far in the prior art are to replicate in an already completed polymer composite, the properties of which cannot be easily changed.

[0034] The ability to copy holograms into still liquid photopolymers by means of the method according to the invention opens up even greater process flexibility. By means of the method according to the invention, in particular process parameters such as the layer thickness of the photopolymer composite, its photosensitivity or the properties of the carrier film can be adjusted in a simple manner to suit the respective desired application. The ability to quickly change these properties without the provision of prefabricated photosensitive films allows the production of holograms in small-scale operations to become economically viable.

[0035] Advantageously, for this purpose, coating of the liquid photopolymer onto the first carrier film, lamination of the first carrier film with the second carrier film, exposure for writing the hologram into the liquid photopolymer and fixing for curing the liquid photopolymer are covered in the same process. Advantageously, the process can be supplied with different compositions of the liquid photopolymer designed specifically for the desired exposure conditions. The desired layer thickness of the photopolymer composite can also be defined with the aid of the coating module. Subsequent process sequences, such as exposure or curing of the photopolymer, can be adjusted with the aid of corresponding downstream modules in a single device.

[0036] Providing a method with the above steps enables continuous duplication of holograms in roll-to-roll mode. This is particularly fast and accurate, since all operating conditions can be easily automated and controlled. No operator intervention is required during a run. Adjustments are preferably only made between runs. This is particularly advantageous compared to the known prior art, in which the master hologram above the liquid photopolymer layer must be positioned and adjusted not only between runs but also between individual duplications.

[0037] With the help of in-situ lamination, film thickness and carrier film properties can be easily adjusted between runs. The liquid photopolymer can be sealed between two films by lamination in order to ensure high stability and avoid contamination. Lamination also protects the liquid photopolymer from adverse deformations caused by shear forces. This reduces the tendency to errors in hologram production.

[0038] Another notable feature of the method is that the photopolymer composite is brought into contact with a master element mounted in an axially rotatable manner, while a light source exposes the master hologram onto areas of the photopolymer composite to obtain a replicated hologram. In this sense, the "contact" is based on optical contact, but additional mechanical contact may also be preferred. The master element mounted in an axially rotatable manner allows in particular to continuously incorporate the exposure process into a roll-to-roll process. Interruptions of the process, as occur in conventional methods using a frosted glass screen as master hologram, are avoided.

[0039] By means of the rotation of the master element, one or more master holograms can be repeatedly exposed at a speed which is also synchronized in a simple manner and extremely precisely with the process flow of the photopolymer composite. The exposure method can be carried out quickly and continuously by means of the axially rotatable master element without having to pause between the individual replication steps. It can also be advantageous to adjust the position of the light-sensitive object relative to the master hologram. The increased exposure speed also reduces faults caused by light from the outside, thus making the replication process more accurate.

[0040] Fixing also allows for increased precision in the replication operation. Since liquid photopolymers are sensitive to mechanical disturbances, providing a fixing module in the same device facilitates the transfer of the exposed liquid photopolymer from the master hologram to the fixing agent in a particularly fast and non-disruptive manner, thus avoiding possible mechanical or electromagnetic distortions.

[0041] Due to the rapidity and precision of the equipment, no drying station is required between the coating module and the exposure module. Therefore, small batch production can be carried out in a more economical way.

[0042] Due to the high processing speed, liquid photopolymers with low storage stability of days, hours or minutes can be used. These liquid photopolymers should preferably be handled carefully due to their photosensitivity. Therefore, the coating module is preferably optically insulated from ambient light. The high-speed processing of photopolymers reduces the risk of interference caused by reflections and ambient light, so that the final product has high precision and high quality.

[0043] In the context of the present invention, a "module" preferably refers to a workstation in a continuous manufacturing method, preferably equipped with the technical means required for performing the method steps. Different modules can, but need not, be separated from each other by housings or partitions.

[0044] In the context of the present invention, "lamination" is preferably a cohesive thermal bonding method without auxiliary materials such as adhesives. The lamination module preferably comprises at least one lamination roller, which is heated to 5° C. to 300° C., preferably 15° C. to 200° C. or 20° C. to 100° C. At these preferred temperatures, particularly effective lamination can be performed and the liquid photopolymer can additionally be cooled quickly before exposure. The lamination is preferably designed to establish a permanent bond between the first carrier film and the second carrier film, preferably by melting along one or both uncoated edge portions of the carrier films. The liquid photopolymer is then preferably sealed between the carrier films.

[0045] It is particularly preferred to cool the liquid photopolymer to a temperature of less than 40°C prior to exposure in order to ensure the best replication quality of the master hologram in the liquid photopolymer. Exposing the liquid photopolymer at a lower temperature facilitates the writing of a diffraction pattern in the material that remains stable.

[0046] In the context of the present invention, a "composite" is preferably a multilayer material consisting of two or more different components with different physical properties, which are bonded to each other at the interface. Preferably, the bond between the components is such that it will not separate under the action of a small force and is therefore considered permanent.

[0047] In the context of the present invention, "exposure" should preferably be understood to mean the controlled steering of an electromagnetic beam towards a corresponding sensitive surface, preferably for forming a hologram. Different methods of exposing holograms are known; these methods include transmission or reflection techniques for producing volume holograms. Examples thereof will be explained in detail later in this text.

[0048] In the context of the present invention, a "light source" (or "radiation source") is preferably a device for releasing electromagnetic radiation, in particular for exposure. The emitted electromagnetic radiation may include visible light and / or radiation having a wavelength outside the visible range of the electromagnetic spectrum. The light source preferably emits a coherent light beam.

[0049] A "master element" is preferably a three-dimensional unit comprising a master hologram, the form of which ensures that any movement of the master element directly results in a corresponding movement of the master hologram. When a "master element" is referred to as "axially rotatable", this preferably means that the master element in the exposure module is mounted so as to be rotatable along an axis. Thus, an axially rotatable mounting characterizes a mounting that enables the master element to be rotated around its axis. The axis is preferably in the middle of the cross section of the master element so that the master element can be rotated in a space-saving manner. The master element is preferably prismatic, which means that it has a constant cross section of any desired shape, such as a square, polygon, ellipse or circle. The ends of the master element having the cross-sectional shape may be referred to as "main surfaces". The elongated faces of the master element between the two ends may be referred to as "sides".

[0050] In the context of the present invention, a "master hologram" is preferably a holographic optical element comprising at least one hologram to be replicated. The master hologram is designed for optical functions (e.g. diffraction, reflection, transmission and / or refraction) for one or more wavelengths. For this purpose, for example, multiple holograms each diffracting light of one wavelength and / or multiple holograms diffracting light of multiple wavelengths can be arranged as a hologram stack. For example, the master hologram can be a diffractive optical element (DOE). The diffractive optical element (DOE) uses a surface concave-convex profile with a microstructure to achieve its optical function. Alternatively, the microstructure can also exist in the volume of the element in the form of local differences in refractive index. The light transmitted by the DOE can be converted into almost any desired distribution by diffraction and subsequent propagation. This can involve images, logos, texts, light refraction patterns, etc.

[0051] The process for producing a master hologram may preferably be referred to as "hologram origination" or "hologram mastering". A master hologram may be produced by analog or digital methods. In an illustrative analog method, a first coherent light beam (object beam) is reflected from an object onto a recording material, which is simultaneously subjected to a second coherent light beam (reference beam). On the recording material, the object beam and the reference beam interfere, producing an interference pattern. This interference pattern or fringe pattern is recorded by a photosensitive material and, after processing, takes the shape of a surface relief pattern on the surface of the material or a shape of a spatially varying refractive index of only a few microns below the surface. In order to view the image of the original object, the master hologram may be illuminated with light diffracted by the recorded surface relief pattern or refractive index pattern. The diffracted light beam contains the image of the original object. Then, when additional copies with the same image are produced, the master hologram may be used as a new object.

[0052] The master hologram can preferably be computer generated. The microscopic grating that generates the diffraction effect can be produced, for example, by laser interference lithography. In this technology, two or more coherent light beams are configured so that they interfere at the surface of the recording material. The position of the light beam relative to the recording material can be controlled by a computer. Depending on the intensity of the laser, the recording material can be made of almost any material. Other techniques such as electron beam lithography can also be used for the digital production of master holograms. The master hologram can preferably include glass, silicon, quartz, UV paint, photopolymer composites and / or metals such as nickel.

[0053] In the context of the present invention, the term "liquid" or liquid photopolymer is preferably defined as a substance that undergoes continuous deformation when subjected to shear stress of any magnitude (Munson et al., Fundamentals of Fluid Mechanics, Wiley: 2010, p. 13).

[0054] Liquids may preferably also be characterized by their viscosity and may be distinguished from other semisolid substances.

[0055] The dynamic viscosity of the liquid photopolymer used as raw material at 300K is preferably between 0.2 mPas (milliPascal seconds) and 200 Pas (Pascal seconds), more preferably between 1 mPas and 10 000 mPas. The dynamic viscosity of the liquid photopolymer during exposure is preferably between 0.2 mPas and 200 Pas. It may be preferred that the liquid photopolymer is pre-crosslinked after application to the carrier film and before exposure, converting it into a viscoelastic state.

[0056] The viscoelastic state of the liquid photopolymer can be characterized here by its complex viscosity. The real part η' of the complex viscosity is related to the viscous properties or liquid characteristics (and the so-called loss modulus G"), while the imaginary part η" is related to the elastic properties or solid content (and the storage modulus G'). In a preferred embodiment, the material properties of the liquid photopolymer during exposure are such that the ratio between the storage component (solid-state characteristics) or storage modulus G' and the loss component (liquid characteristics) or loss modulus G" is at least 1:10. The higher the storage component in the ratio, the more favorable the effect on the exposeability during the replication process. In a preferred embodiment, the ratio of the storage modulus G' to the loss modulus G" is at least 1:5, at least 1:2, 1:1, 2:1, 5:1 or more. The ratio between the storage modulus G' and the loss modulus G" preferably does not exceed 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 reproduced hologram. The ratio can be established by adjusting the composition of the photopolymer, for example by adding thixotropic agents, pre-crosslinking the photopolymer or evaporating the solvent after applying the liquid photopolymer to a first carrier film and before laminating the liquid photopolymer with a second carrier film. The viscoelastic properties of the liquid photopolymer can also be optimized by cooling the liquid photopolymer before or during exposure.

[0057] "Fixing" preferably refers to a process step for curing a liquid material, in particular a liquid photopolymer, preferably by introducing electromagnetic energy and / or thermal energy into the material. The energy can preferably be applied uniformly to the surface of the sensitive material in order to ensure simultaneous curing. Preferably, all layers of the photopolymer composite, in particular including the photopolymer layer, are cured at this stage.

[0058] Preferred steps of the method are explained in detail here. The order of the following explanation may but does not necessarily correspond to the order of the method steps.

[0059] According to the present invention, the first carrier film is coated with a liquid photopolymer in a coating module. The thickness of the photopolymer layer is preferably 1 μm to 200 μm. For a photopolymer layer with a thickness between 1 μm and 15 μm, an anilox roller is preferably used in a gravure printing method. For a photopolymer layer with a thickness between 7 μm and 40 μm, a wire doctor or a profile rod is preferred. If the layer thickness is between 40 μm and 100 μm, it is preferred to use a slit die, a doctor blade or a comma doctor blade. The method may optionally include coating both the first carrier film and the second carrier film simultaneously by a separate coating element. Coating the two films separately and joining them allows relatively thin coatings to be combined to give a thicker photopolymer layer. It is advantageous that thinner layers are degassed faster. The solvent in the coating can also evaporate faster before the lamination process.

[0060] The method of the present invention further comprises applying a second carrier film to the coated first carrier film by means of a laminating module so as to obtain a photopolymer composite comprising a liquid photopolymer layer between the two carrier films. The laminating module preferably comprises two laminating rollers. Preferably, the laminating module applies a compressive force between 10N and 20 000N to the two carrier films and the photopolymer layer therebetween. The required compressive force preferably depends on the width of the carrier film, the coating width, the target layer thickness and / or the web speed. Alternatively or additionally, the laminating module can laminate at least two carrier films at a temperature between 20°C and 300°C. The temperature is preferably selected depending on the material of the two carrier films so that one or both of the carrier films reaches its melting point in a short time. The preferred temperature depends not only on the above parameters but also on the photopolymer formulation.

[0061] The composition of the photopolymer and the pressure and temperature of the lamination are preferably selected such that the photopolymer remains in the liquid state during the lamination operation or acquires or establishes a viscosity which is optimized for further process steps.

[0062] The first carrier film and the second carrier film are preferably configured as a web (of any length), so that lamination completes a photopolymer composite web (of any length) comprising a liquid photopolymer layer.

[0063] The method of the invention further comprises bringing an area of ​​the photopolymer composite into contact with an axially rotatable master element comprising the master hologram to be copied in an exposure module, and exposing this area of ​​the photopolymer composite by means of a light source, so that the master hologram is copied into the photopolymer composite. In this method step, the area of ​​the photopolymer composite to be exposed preferably temporarily adopts the shape of an area of ​​the side surface of the master element. Preferably, the photopolymer composite, which is preferably in the form of a coil, is guided here over the rotating master element. The speeds of the coil and the master element are preferably synchronized with each other. The synchronization can be achieved by a control unit as further described below.

[0064] Thus, there is preferably mechanical contact between an area of ​​the master element and an area of ​​the photopolymer composite. For example, if the composite is guided tangentially to the master element, the area is a line with a line width of less than 1 mm. The area of ​​the photopolymer composite to be exposed can also temporarily adopt the shape of the side surface of the master element over an extended area, for example over an arc-shaped area of ​​a circle segment with an opening angle of more than 5° or more than 10° across the cylindrical master element. This provides more space for exposure and optional fixing. The exposure can preferably be achieved in the exposure area along a line parallel to the axis of rotation of the master element, or simultaneously on several lines. The exposure is preferably achieved with the aid of one or more continuously scanning light sources, preferably lasers.

[0065] After exposure, fixing can be performed, preferably on a master element. Since the exposed liquid photopolymer is sensitive to distortion, it is particularly advantageous if fixing is performed immediately after exposure, so that transport between these two method steps is minimized.

[0066] The method of the invention comprises curing a replicated hologram present in a liquid photopolymer in a fixing module. The fixing module can preferably receive the composite web from the exposure module quickly and with minimal deflection. The fixing module can preferably include a UV radiation and / or heat treatment source. The fixing module can be in the same housing as the exposure module. In a preferred embodiment, the apparatus for performing the method is configured so that fixing is performed immediately after the exposure of the master element.

[0067] The carrier film to which the liquid photopolymer is applied is preferably optically clear, especially for use in transparent displays. Polycarbonate materials are preferred, but numerous other materials as disclosed in detail herein may also be used. At least one of the first carrier film and the second carrier film is preferably glass clear, transparent and substantially colorless.

[0068] In a preferred embodiment of the present invention, the first carrier film and / or the second carrier film is based on a material or a material composite selected from the group comprising: polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene, polypropylene, cellulose acetate, cellulose triacetate (TAC), hydrated cellulose, cellulose nitrate, cycloolefin polymers, polystyrene, polyepoxide, polysulfone, cellulose triacetate (CTA), polyamide, polymethyl methacrylate (PMMA), polyvinyl chloride, polyvinyl butyral, polydicyclopentadiene, perfluoroethylene propylene (FEP), a mixture of two or more of the mentioned materials or a co-extrudate comprising one or more of the mentioned materials, more preferably PC, PET and / or TAC.

[0069] In particular, it has been found that the above-mentioned materials, in particular also coextrudates consisting of two or more of these materials, are extremely weather-resistant and preferably less prone to tearing and have fewer weak points within their scope. This increases the lifetime of the hologram produced. The materials and properties of the carrier film can be selected so that, taking into account the properties of any intermediate layers, a very continuous transition of the refractive index from the master hologram to the liquid photopolymer layer is ensured.

[0070] In a preferred embodiment of the present invention, the liquid photopolymer comprises:

[0071] (i) at least one writing monomer;

[0072] (ii) a photoinitiator system; and

[0073] (iii) at least one organic ingredient,

[0074] The liquid photopolymer may optionally further include one or more of the following ingredients: a catalyst, a dye, a free 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 an auxiliary or additive.

[0075] Suitable liquid photopolymers are known to those skilled in the art. For example, compositions for liquid photopolymers as disclosed in EP 1779196B1 are suitable. In a preferred embodiment, the liquid photopolymer is binder-free. The writing monomer is preferably an ethylenically unsaturated monomer having the following general formula:

[0076]

[0077] wherein n is 2 to 4, R' is hydrogen or CH3, and L is

[0078]

[0079] wherein the benzene ring is optionally selected from halogen, C 1-4 -substituted with one or more substituents from the group consisting of alkyl, alkoxy or hydroxy;

[0080] L 1 Is it a straight chain or branched chain C 1-4 - covalent bond of an alkyl group;

[0081] L 2 is a covalently bonded, optionally hydroxy-substituted, straight or branched chain C 1-4 -alkyl, or -[L 3 -O] m -, where L 3 It is C 1-4 -alkyl and m is 1 to 40;

[0082] The at least one organic ingredient is selected from the group consisting of castor oil, palm kernel oil, coconut oil, and combinations thereof.

[0083] The liquid photopolymer components can preferably be mixed in situ. The amounts of the different components and the incorporation of optional components can be adjusted in each run as required.

[0084] In a preferred embodiment of the present invention, the residence time of the liquid polymer during the transport of the photopolymer composite from the exposure module to the fixing module is no more than 10 minutes, preferably no more than 5 minutes, more preferably no more than 3 minutes.

[0085] In another preferred embodiment of the present invention, the residence time of the liquid photopolymer from coating on the first carrier film to curing is no more than 15 minutes, preferably no more than 10 minutes, more preferably no more than 5 minutes.

[0086] A short residence time of the photopolymer between the operating modules is advantageous because in this way all operating steps can be completed before distortions (e.g. due to mechanical influences on the liquid photopolymer) or other disturbing effects (e.g. due to limited storage stability or optical interfering light) can occur in the hologram.

[0087] The viscosity of the liquid photopolymer is preferably adjusted by mixing and / or by heating before it is supplied to the coating module. The photosensitivity, color sensitivity and any increase in the refractive index of the liquid photopolymer are preferably also adjusted before it is supplied to the coating module. The coating module preferably enables the thickness of the applied liquid photopolymer layer to be adjusted. This can be achieved in various ways, for example by adjusting the flow rate out of the slit die or by adjusting the distance between adjacent rollers. The coating module can be configured differently depending on the rheological properties and the desired thickness of the liquid photopolymer layer, as will be explained in detail later. The equipment used preferably includes several coating mechanisms arranged in succession, so that only a specific coating mode is adopted for the run. This has the advantage that a larger range of possible photopolymer layer thicknesses is possible, which can be adjusted between runs.

[0088] The exposure for replicating the master hologram in the exposure module can be based on various techniques.Hologram replication methods can be divided into concave-convex holograms and volume holograms.

[0089] The relief hologram is formed by physical contact between the deformable sensitive layer and the master hologram so that the diffraction pattern of the master hologram is imprinted in the sensitive layer.

[0090] The volume hologram is preferably written into the sensitive layer by the interference of two light beams, the so-called reference beam and the object beam. The volume hologram is preferably written into a liquid photopolymer layer. This can preferably be achieved by a transmission or reflection method. Due to the interference of the object beam and the reference beam within the hologram volume, a series of Bragg planes are preferably generated. Therefore, the volume hologram preferably has a non-negligible range in the propagation direction of the light, where the Bragg conditions apply to the reconstruction using the volume hologram. It is for this reason that the volume hologram has wavelength selectivity and / or angle selectivity. The ability of the volume hologram to store multiple images simultaneously allows in particular the generation of color holograms. A light source emitting the three primary colors of blue, green and red can be used to record the hologram. These three beams of light preferably expose the photopolymer layer at the same angle at the same time. After exposure, the three holograms are stored simultaneously in the volume hologram. The reproduction of the color hologram can make use of the fact that each partial hologram can only be reconstructed by the color used to record it. Therefore, if the color components are correctly weighted, the three reconstructed color sectors can be superimposed to form a realistic color image.

[0091] In the case of a reflection hologram, the directions of incidence of the reference beam (preferably an incident beam from a light source) and the object (in this case the master hologram) can be arranged on opposite sides of the liquid photopolymer layer. The reference beam penetrates the liquid photopolymer (preferably enclosed between two transparent carrier films in this case) and is then reflected by the master hologram back into the liquid photopolymer layer. The master hologram can preferably be applied to the surface of a master element, which is preferably not completely transparent, but at least partially reflective. Transparent master elements can also be used.

[0092] The light source for reflecting the hologram can be arranged so that the reference beam is incident on the liquid photopolymer layer in a desired direction, preferably in a direction desired in a subsequent reconstruction. In a preferred embodiment, the light source is oriented relative to the master element in such a way that the photopolymer composite is arranged between the light source and the master element. For example, the light source can be aligned below the master element so that the reference beam is incident on its side surface upwards in a specific direction. The reference beam is preferably at least partially reflected by the master element back into the photopolymer composite in the form of an object beam. Therefore, the reference beam and the object beam enter the photopolymer composite from opposite sides and interfere in the photopolymer layer of the photopolymer composite to replicate the hologram.

[0093] For transmission holograms, the liquid photopolymer layer is preferably arranged in such a way that it can be exposed by the reference beam and the object beam from the same side. The light source is preferably oriented relative to the master element so that the light beam first passes through the master element and the master hologram before reaching the photopolymer composite. This arrangement is illustrative and other arrangements are also conceivable. The light can preferably be arranged so that it passes through the preferably transparent master element from the side of the side surface opposite to the photopolymer composite. The incident light beam is preferably refracted by the master element so as to form a reference beam and an object beam, wherein the object beam preferably corresponds to the component of the light diffracted by the master hologram. The object beam preferably interferes with the undiffracted reference beam in the liquid photopolymer layer in order to replicate the hologram.

[0094] In another embodiment of the invention, the method may comprise edge-illuminated exposure, wherein the exposure module is arranged to replicate the master hologram (edge-illuminated hologram) by edge illumination. For this purpose, the master element is preferably provided in the form of an optical fiber and the light source is preferably arranged to direct light onto a main surface of the master element. As in the case of other arrangements for transmission holography, the light is preferably divided 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 is preferably propagated by reflection, preferably total reflection. Light losses in areas of the side surface that are not in optical contact with the photopolymer composite are preferably reduced to a minimum. Most of the light can preferably leave the master element via the master hologram arranged on the side surface in order to replicate the hologram into the photopolymer layer.

[0095] By aligning the light source onto the main surface, the apparatus for the method can be arranged in a particularly space-saving manner around the side surface, with maximum useful space. This space can be used to accommodate the master hologram, further optical layers and greater contact between the master element and the photopolymer composite. Aligning the light onto a flat area of ​​the master element additionally allows the apparatus used to be made less sensitive to small variations in the laser alignment (e.g. due to vibrations).

[0096] In a preferred embodiment, the light source emits a coherent light beam. Coherence preferably refers to the property of a light wave whereby a fixed phase relationship exists between two wave trains. Due to the fixed phase relationship between the two wave trains, a spatially stable interference pattern can be generated. With regard to coherence, a distinction can be made between temporal coherence and spatial coherence. Spatial coherence preferably constitutes a measure of the fixed phase relationship between wave trains perpendicular to the propagation and exists, for example, for parallel light beams. Temporal coherence preferably constitutes a fixed phase relationship between wave trains along the propagation direction and exists in particular for narrow-band, preferably monochromatic light beams.

[0097] The coherence length preferably denotes the maximum path length difference or flight time difference between two beams starting from a starting point such that when they are superimposed they still produce a (spatially and temporally) stable interference pattern. The coherence time preferably refers to the time required for light to travel the coherence length.

[0098] In a preferred embodiment, the light source is a laser. More preferably, the light source is a narrowband (preferably monochromatic) laser, with a preferred wavelength in the visible range (preferably 400nm to 780nm). A laser preferably refers to a light source that emits laser radiation. Non-limiting examples include solid-state lasers (preferably semiconductor lasers or laser diodes), gas lasers, or dye lasers.

[0099] Other light sources, preferably coherent light sources, may also be used.Preferred are narrow-band light sources, preferably monochromatic light sources, for example comprising light emitting diodes (LEDs), optionally in combination with a monochromator.

[0100] The coherence of the light beam is relatively less relevant to the generation of a relief hologram. In contrast, especially for the replication of a volume hologram, it is preferred that the light beam used for replication has sufficient coherence.

[0101] In a preferred embodiment, the coherence length of the light source is preferably at least 150 μm, more preferably at least 500 μm, 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, preferably, the coherence length is not too long to avoid the presence of parasitic microstructures in the hologram, such as interference gratings. The maximum preferred coherence depends on the type of hologram and the geometrical dimensions of the exposure module. In a preferred embodiment, the coherence length of the light source is less than 1 m.

[0102] The light source may comprise two or more light sources. The two or more light sources may preferably be configured such that they scan a line or area of ​​the photopolymer composite in optical contact with the master element.

[0103] Optionally, a device for forming and / or guiding a light beam in a device used between the light source and the master element or the photopolymer composite may be provided. The device may comprise any number or type of lenses, prisms, reflectors etc. The means for forming and / or guiding the light beam may distribute the light in such a way that the light substantially covers, for example, a point, a line or an extended area. With the aid of a suitable scanning unit, scanning may additionally be provided. The light source may preferably be configured such that it generates one or more light beams which illuminate the entire length of the side surface of the master element or preferably at least the length corresponding to the coated portion of the photopolymer composite by means of an expanded beam and / or by scanning.

[0104] The master element preferably has a prismatic shape, in particular a cylindrical shape. The axial rotatability allows the master element to preferably act as a roller. This enables a synchronous movement between the master and the light-sensitive photopolymer composite, so that the possibility of positioning errors can be reduced. Depending on the material used, the friction between the photopolymer composite and the master element can be sufficient to drive the master element to move. In this case, the master element advantageously does not require a dedicated drive, and the movement is essentially passive via the movement of the photopolymer composite. Alternatively or additionally, the rotation speed of the master element can be controlled separately via a suitable drive, wherein the drive ensures that the surface of the master element moves synchronously with the photopolymer composite.

[0105] In another preferred embodiment of the invention, the master element is driven by transmitting force by a functional roller, a flange-attached ring gear, a universal joint drive or a belt drive. The master element is preferably provided with a dedicated drive. In the case of a functional roller, the force can preferably be transmitted by friction, wherein the functional roller preferably comprises a rubber material. The drive mechanism is preferably designed so that the surface of the master element has maximum accessibility to the exposure light beam. Advantageously, in the case of these drive technologies, substantially all surfaces of the master element can remain transparent for optical functions. This makes the exposure method more efficient and enables the same master element to be used to replicate different hologram types depending on the positioning of the light source.

[0106] In another preferred embodiment of the present invention, the master element rotates synchronously with the web speed of the photopolymer composite web. "The master element rotates synchronously with the web speed of the photopolymer composite web" preferably means that the circumferential speed of the side surface of the master element is the same as the web speed of the photopolymer composite web. In this way, it is possible to prevent unfavorable slippage between the photopolymer composite web and the side surface of the master element or to prevent excessive web tension of the photopolymer composite web, so that the master hologram can be copied into the photopolymer layer in a precise position and without distortion.

[0107] The web speed with respect to the photopolymer composite web preferably refers to the speed of the photopolymer composite web or the carrier film in the longitudinal direction as it passes 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 moves through the device. The web speed may be the speed of a point on the carrier film or the photopolymer composite web. The circumferential speed preferably refers to the speed of a point on the side surface of the master element that performs a circular motion by means of its rotation and may also be referred to as the unwinding speed.

[0108] In a further preferred embodiment of the invention, the wear of the master element is controlled by a control unit, in particular in order to obtain a desired peripheral speed of the side surface of the master element.

[0109] In a preferred embodiment of the invention, the control unit is configured to maintain a desired web tension in the photopolymer composite web. This may be a web tension upstream of the master element and / or beyond the master element. This may ensure that the photopolymer composite does not overstretch, for example due to too low a web speed of the photopolymer web upstream of the master element. It may also ensure that the photopolymer composite does not bend, for example due to too low a web speed of the photopolymer web downstream of the master element. Thus, mechanical introduction of defects into the photopolymer layer may be avoided.

[0110] In a particularly preferred embodiment of the present invention, the control unit is configured to control the drive of a transport roller (also referred to as a "transport roller" in the context of the present invention) to move the photopolymer composite web to and from the master element so as to maintain the desired web tension in the photopolymer composite web, in particular upstream and downstream of the master element.

[0111] For this purpose, the web tension is preferably monitored by suitable sensors. If the web tension is outside the permissible range, it is preferred that the control unit is configured to adjust the rotation speed of one or more conveyor rollers (rather than the master element). For this purpose, the control unit can send a signal to the drive of one or more conveyor rollers in order to bring the web tension back into the permissible range. Therefore, the master element also plays a "master" role with respect to the web tension of the photopolymer composite web on the control side. Therefore, the control unit is preferably designed to keep the desired rotation speed of the master element constant, while correspondingly adjusting the drives of the conveyor rollers or other parts of the device that influence the web speed of the photopolymer web.

[0112] In the context of the present invention, "web tension" is preferably a measure of the tensile stress to which the photopolymer composite web is subjected in the longitudinal direction, in particular in the direction of its movement through the apparatus. Web tension may be defined by the ratio of the force acting on the photopolymer composite web in the longitudinal direction to the cross-section of the photopolymer composite web and may be measured, for example, in N / mm2.

[0113] The synchronous rotation of the master element with the flow rate or web speed of the photopolymer composite web enables a continuous and fast replication method. This is particularly advantageous for the processing of highly sensitive liquid photopolymer layers, since the still liquid photopolymer is sensitive to ambient light, disturbing light or shear forces. The liquid photopolymer is fixed after a short exposure time, and the continuous process can additionally avoid mechanical effects that lead to warping.

[0114] It may be preferred that an optical liquid is applied on the surface of the master element and / or the photopolymer composite. The optical refractive index of the optical liquid is preferably close to the optical refractive index of the master element (especially the cover of the master element) and / or the photopolymer composite, so as to minimize reflections at the interface between the master element and the photopolymer composite. Furthermore, the optical fluid may improve the optical contact between the elements, since any imperfections in the shape and / or surface of the optical element are equalized.

[0115] In another preferred embodiment of the invention, an optical adhesive film is temporarily introduced between the master element and the photopolymer composite.

[0116] In another preferred embodiment of the present invention, the exposure module comprises at least one unwinding roller and a winding roller for temporarily applying an optical adhesive film between the master element and the photopolymer composite. The unwinding roller is preferably used to unwind the optical adhesive film, and the winding roller is used to wind up the optical adhesive film after use. The optical adhesive film preferably temporarily bonds the composite to the master element (preferably at least for the exposure period), and advantageously forms an optical bond between the two elements. This has the advantage that unfavorable reflections at the interface between the master element and the photopolymer composite are reduced, thereby producing a higher quality hologram. The optical adhesive film may also be referred to as an OCA (optically clear adhesive).

[0117] 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 apparatus preferably comprises suitable means for the removal, such as a take-up roller.

[0118] In the context of the present invention, an "optical adhesive film" is preferably a transparent film having a refractive index close to that of the master element and / or the photopolymer composite. The optical adhesive film is preferably arranged to improve the optical contact between the master element and the photopolymer composite so as to reduce or eliminate reflections at the interface between the master element and the photopolymer composite.

[0119] The optical properties of the material used for the optical adhesive film are preferably the same or similar to those of the substrate, its cover and / or photopolymer composite used for the master element. Preferably, similar or identical properties include transparency, haze, stress birefringence properties and / or refractive index. The use of the same or similar materials allows the refractive index of the optical adhesive film to be very closely matched to the refractive index of the adjacent master element and / or photopolymer composite, so that it can be ensured that there is no refractive index jump in the transition between adjacent refractive indices. In this way, reflections at the interface between the master element, the optical adhesive film and / or the photopolymer composite can be largely eliminated or significantly minimized.

[0120] In addition, the optical adhesive film is preferably a solid in which the Brownian motion of the molecules is sufficiently small, thereby preventing "wobbling" of the light phase, so that the interference field in the hologram copy is more stable during the exposure time. In this way, the microstructure is not blurred, thereby maximizing the diffraction efficiency of the hologram. The clarity and contrast of the resulting hologram are also significantly improved. The optical adhesive film improves the optical contact between the exposed transparent parts through which the exposure light is directed. This reduces adverse reflections, scattering or losses, and the quality of the reproduced hologram is improved.

[0121] The optical adhesive film can be formed similarly to the photopolymer composite (eg as a web) and moved through the process in a similar manner (eg by means of rollers). This enables simple synchronization of the optical adhesive film and the photopolymer composite.

[0122] In addition to having favorable optical properties, the optical adhesive film preferably has a lower adhesive force than the OCAs (optically clear adhesives) known from the field of optical displays. As a result, the optical adhesive film can be easily removed from the surface without residue after use.

[0123] In a preferred embodiment of the present invention, the optical adhesive film comprises at least one adhesive layer. At least one adhesive layer preferably has a peel force of less than 3N / cm (Newtons per centimeter), preferably less than 1N / cm, relative to the surface of the master element and / or the surface of the photopolymer composite. However, in a preferred embodiment, the peel force of the adhesive layer of the optical adhesive film relative to the surface of the master element and / or the surface of the photopolymer composite is at least 0.01N / cm, preferably at least 0.1N / cm. For example, the peel force of the optical adhesive film or one of its layers can be measured according to a 180 degree peel test. In a preferred embodiment, the measurement complies with ASTM D903.

[0124] In a preferred embodiment of the present invention, the optical adhesive film has a single-layer structure, wherein the layer structure comprises exactly one adhesive layer. The exactly one adhesive layer is preferably adhesive on both sides in order to achieve optical contact.

[0125] 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 be adhered to two surfaces at the same time, so that particularly good optical contact can be achieved and any risk of air gaps or unfavorable reflections is reduced.

[0126] The optical adhesive film is preferably optically transparent. The material of the optical adhesive film preferably has a Fresnel-corrected transparency of at least 99%, a maximum haze of 0.5% and a minimum polarization tendency. The material of the optical adhesive film is preferably colorless. It is particularly preferred that the optical adhesive film has no yellow tint and no gray. The bonding strength of the optical adhesive film should be small enough so that no unfavorable tensions occur in the photopolymer composite and no marks are left on the master element or the photopolymer composite. This means that the optical adhesive film is preferably removable without residue. The preferred bonding strength of the optical adhesive film is between 10 cN / cm and 3 N / cm.

[0127] In a preferred embodiment, the optical adhesive film comprises a carrier layer, and both sides of the carrier layer are coated with an optically transparent adhesive material. Therefore, preferably, adhesive layers are arranged on both sides of the carrier layer, wherein the adhesive layers are preferably composed of adhesive materials. The carrier layer preferably comprises one or more of the following materials: polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene, polypropylene, cellulose acetate, cellulose triacetate (TAC), hydrated cellulose, cellulose nitrate, cycloolefin polymer, polystyrene, polyepoxide, polysulfone, cellulose triacetate (CTA), polyamide, polymethyl methacrylate (PMMA), polyvinyl chloride, polyvinyl butyral, perfluoroethylene propylene (FEP) or polydicyclopentadiene or a mixture thereof. The optically transparent adhesive material preferably comprises an adhesive material based on silicone, acrylate, rubber or a mixture thereof, and a rubber-based adhesive material is particularly preferred.

[0128] Preferably, the outer layers of the optical adhesive film are each protected in their original state with a protective film. Suitable unwinding rollers may be provided so as to unwind these protective films within the distance between the unwinding roller of the optical adhesive film and the master element.

[0129] Preferably, the difference in refractive index between the master element and the optical adhesive film, preferably also between the master element and the adjoining photopolymer composite, does not exceed 0.2, even more preferably does not exceed 0.1, still more preferably does not exceed 0.05. This enables a significantly improved control of the light diffraction of the exposure light without the need for optical fluids, the use of which requires intensive maintenance and frequent cleaning of the equipment.

[0130] It is particularly preferred that the refractive index of the optical adhesive film is between the refractive index of the master element (or its cover) and the refractive index of the adjacent photopolymer composite (or its adjacent carrier film). In this context, the word "between" preferably also includes the refractive index values ​​of the adjacent process components themselves. This arrangement allows a smooth or undisturbed transition of the light beam between the different process components with minimal reflections and / or aberrations at the interface.

[0131] As an illustrative, non-limiting example, in a radially outward direction from the body, the refractive index may be selected, for example, as follows:

[0132] - Body (made of N-BK7): n e =1.519

[0133] - Adhesive layer: n e =1.51

[0134] -Master hologram (photopolymer layer): n e =1.500

[0135] -Master hologram (carrier film): n e =1.485

[0136] -Optical adhesive film (OCA consisting of adhesive layer / carrier layer / adhesive layer): n e =1.47 / 1.485 / 1.47

[0137] The skilled person is aware of further materials which, starting from the present teaching, allow a substantially continuous transition of the refractive index of the master element and the adjoining carrier film. For example, in an alternative, the body may comprise Borofloat-33, which has a refractive index of 1.48. The materials of the further layers may be selected to match this refractive index. For all of the above components (body to optical adhesive film), it is generally preferred that the corresponding refractive index is between 1.4 and 1.6.

[0138] For all the above components, the material preferably has a Fresnel-corrected transparency of at least 99%, a maximum haze of 0.5%, and a minimum polarization tendency. The stress-optical coefficient of the material is preferably as small as possible. The stress birefringence of the material is preferably minimized by appropriate heat treatment so that the carrier film does not show zebra patterns when viewed through crossed polarizers. It is also preferred that the material used has a low level of streaks, inclusions, and bubbles.

[0139] In another 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, even more preferably at least 300 mm. Advantageously, the corresponding shape and size of the master element is such that distortions in the liquid photopolymer layer due to shear stresses are particularly small. The smaller curvature resulting from the larger diameter also enables greater flexibility and control in the alignment of the exposure light and has a positive effect on any input or shear forces introduced in the photopolymer composite, meaning that these forces are smaller.

[0140] Optionally, additional transport rollers can also be arranged in the device between the exposure module and the fixing module. The method preferably comprises a corresponding transport step. In order to protect the exposed liquid photopolymer layer, it is also preferred in this case that such rollers have a larger constant diameter. The preferred diameter is at least 50 mm, preferably at least 100 mm, more preferably at least 150 mm, even more preferably at least 300 mm. These optional transport rollers are preferably aligned so that the web has very little deflection, if any, between the exposure module and the fixing module. This means that it is particularly preferred that the transport of the exposed liquid photopolymer takes place essentially along a straight line.

[0141] In another preferred embodiment of the invention, one or both main surfaces and / or side surfaces of the master element are completely or partially provided with an anti-reflection coating. This can advantageously reduce adverse interferences in the exposure due to reflections.

[0142] In another preferred embodiment of the invention, the coating module is configured to coat the liquid photopolymer onto the first carrier film by means of a roll-to-roll process. The coating module may comprise one or more coating elements, wherein a suitable coating element may be selected depending on the layer thickness and the rheological properties. Preferred coating elements may advantageously be the following: anilox roller, wire doctor blade, profiled rod, slot die, doctor blade, chamber doctor blade, comma doctor blade and / or equipment for doctor blade process.

[0143] The thickness of the photopolymer layer is preferably 1 μm to 200 μm. For photopolymer layers with a thickness between 1 μm and 15 μm, an anilox roller is preferably used in a gravure printing process. For photopolymer layers with a thickness between 7 μm and 40 μm, a wire doctor blade or a profiled rod is preferred. If the layer thickness is between 40 μm and 100 μm, it is preferred to use a slot die, a doctor blade or a comma doctor blade.

[0144] In another preferred embodiment of the invention, the apparatus for the method comprises two coating modules, wherein the first coating module is arranged to coat the first carrier film with the liquid photopolymer and the second coating module is arranged to coat the second carrier film with the liquid photopolymer. The method preferably comprises corresponding coating steps. Coating the two films separately and joining them allows combining relatively thin coatings to give thicker photopolymer layers. Advantageously, the thinner layers are degassed faster. The solvent in the coating can also evaporate faster before the lamination process.

[0145] Furthermore, the application of further 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, wherein each composition is sensitive to a specific wavelength of light (preferably RGB), for example.

[0146] In another preferred embodiment of the invention, the device used comprises an unwinding station for unwinding the carrier film supplied as a roll. Preferably, the device comprises an unwinding station for the respective first and second carrier films. The method preferably comprises a corresponding unwinding step. It is also preferred that the carrier film is supplied to the device between two protective films. In this case, the device preferably comprises an unwinding roller for removing one or more protective films before the carrier film is further processed. It is particularly preferred that the protective film is removed only from one side of the carrier film.

[0147] In another preferred embodiment, the device used further comprises a surface pretreatment station (preferably following the principle of a plasma pretreatment station) between at least one of the unfolding modules and the coating module, in particular between each unfolding module and each coating module. This advantageously improves the adhesion of the liquid photopolymer layer to the carrier film. The method preferably comprises a corresponding plasma pretreatment. 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 there are further films to be coated with photopolymer or covered with a photopolymer layer, the device preferably can also include a surface pretreatment station for each further film to be in contact with the photopolymer layer.

[0148] In another preferred embodiment of the present invention, the laminating module comprises at least one laminating roller, in particular a pair of laminating rollers. The at least one laminating roller is preferably configured to apply 0.02 N / cm 2 Up to 200N / cm 2 , especially 0.02N / cm 2 Up to 50N / cm 2 The application of pressure is preferably monitored by suitable sensors and is preferably used to control the laminating module. The sensor for the pressure applied by the at least one laminating roller can preferably be a film coating, wherein the pressure sensors are distributed over the entire film (referred to as a "pressure measuring membrane"). In this way, the distribution of the pressure along the laminating roller can be determined, so that any incorrect alignment of the laminating roller can be identified and corrected.

[0149] In another preferred embodiment of the present invention, the laminating module comprises a pair of laminating rollers. Preferably, the laminating module applies a compressive force between 10N and 20 000N to the two carrier films and the photopolymer layer therebetween. The required compressive force preferably depends on the width of the carrier film, the coating width, the target layer thickness and / or the web speed. Alternatively or additionally, the laminating module can laminate at least two carrier films at a temperature between 5°C and 300°C, preferably between 15°C and 200°C, and especially between 20°C and 100°C. The temperature is preferably selected depending on the materials of the two carrier films so that one or both of the carrier films reaches its melting point in a short time. The preferred temperature depends not only on the above 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 a viscosity optimized for additional process steps is obtained or established. The laminating module preferably connects the first carrier film and the second carrier film along two parallel uncoated edges so that the liquid is trapped between the two.

[0150] In another preferred embodiment of the present invention, one or two laminating rollers include stainless steel. Stainless steel provides various benefits, such as the ability to withstand high pressure and easy cleaning. The laminating roller can be rigid, for example, without a stainless steel coating and / or only coated with a protective layer and / or a pressure sensor on the stainless steel. It is particularly advantageous to provide a thin liquid photopolymer layer between the carrier films. However, in the case of a relatively thick photopolymer layer, it may also be advantageous that the laminating roller has a coating with less rigidity. Therefore, in some embodiments, it is preferred that one or more of the laminating rollers have a rubber coating, wherein the rubber coating may include, for example, a fluoroelastomer (such as fluororubber (Viton)) or a nitrile rubber (acrylonitrile-butadiene rubber, NBR).

[0151] In another preferred embodiment of the invention, the apparatus comprises a degassing station arranged between the coating module and the laminating module. The method preferably comprises a corresponding degassing step. The degassing station is preferably arranged to transmit vibrations to the coated first carrier film and / or the second carrier film. The vibration is advantageously used to eliminate any bubbles in the liquid photopolymer layer. The degassing station is preferably also configured to be heatable to 30° C. to 300° C., in particular 100° C. to 200° C. The increased temperature is also used to remove the solvent. The degassing station can additionally 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.

[0152] The invention further relates to a photopolymer composite comprising a photopolymer between two carrier films, into which a hologram has been replicated by means of the method according to the invention or a preferred embodiment thereof.

[0153] One of ordinary skill in the art will recognize that the technical features, definitions and advantages of the preferred embodiments of the method of the present invention also apply to the photopolymer composites that may be produced, and vice versa.

[0154] The method is preferably carried out with the aid of an apparatus for continuously replicating holograms. The apparatus preferably comprises:

[0155] a. a coating module, the coating module being arranged to coat the liquid photopolymer onto the first carrier film,

[0156] b. a lamination module arranged to apply a second carrier film to the first carrier film coated with a photopolymer in order to obtain a photopolymer composite comprising a layer of liquid photopolymer between the two carrier films,

[0157] c. an exposure module, wherein the exposure module has a light source and a master element comprising a master hologram to be replicated,

[0158] wherein the master element is mounted for axial rotation and the exposure module is arranged to bring the photopolymer composite into optical contact with the master element, while the light source exposes the master hologram onto areas of the photopolymer composite to obtain a replicated hologram, and

[0159] d. A fixing module, which is configured to cure the replicated hologram in the photopolymer composite.

[0160] Those skilled in the art will recognize that the technical features, definitions and advantages of the preferred embodiments of the method of the present invention are also applicable to the device, and vice versa.

[0161] Before discussing the specific details of the preferred embodiment, the general working manner of some components of the device will now be explained in detail one by one.

[0162] The apparatus comprises a laminating module arranged to apply a second carrier film to a first carrier film coated with a photopolymer so as to obtain a photopolymer composite comprising a layer of liquid photopolymer between the two carrier films. The composition of the photopolymer is preferably arranged such that it does not solidify during the laminating operation. The first carrier film and the second carrier film are preferably arranged as a roll (of any length), such that the laminating module is arranged to complete a roll of the composite (of any length) comprising the layer of liquid photopolymer.

[0163] The device 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 arranged to bring the photopolymer composite into optical contact with the master element, while the light source exposes the master hologram onto an area of ​​the photopolymer composite to obtain a replicated hologram.

[0164] "Optical contact" should preferably allow the light beam path to pass between the photopolymer layer and the master hologram without experiencing substantial interference or absorption. Direct cohesive contact between the photopolymer composite and the master element is possible, but not mandatory. Instead, an intermediate layer may be arranged between the master element and the photopolymer composite, which intermediate layer is preferably transparent to the light from the light source of the exposure module, for example in the form of a transparent film.

[0165] The device further comprises a fixing module, which is arranged to cure the replicated hologram in the photopolymer composite. The fixing module can preferably receive the composite web from the exposure module quickly and with minimal deflection. The fixing module can preferably include a light source (preferably UV radiation) and / or a heat treatment source. In the case of fixing with a UV lamp (also referred to as a "UV source" in the context of the present invention), the UV lamp is preferably adjusted so that it emits strong UV radiation between 315nm and 400nm to the photopolymer layer.

[0166] The fixing module may be in the same housing as the exposure module. In a preferred embodiment, the device is configured such that fixing is performed immediately after the exposure of the master element. Preferably, the distance between the incident electromagnetic beam from the exposure source and the 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 may be an expanded beam or may consist of one or more optionally scanned beams and may 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.

[0167] The apparatus preferably further comprises a control unit for controlling components of the apparatus (eg a coating module, a laminating module, an exposure module and / or a fixing module).

[0168] The term "control unit" preferably relates to any computing unit with a processor, a processor chip, a microprocessor or a microcontroller, which is capable of automatically controlling components of the device, such as the rotation speed of the unwinding roller, the winding roller, the laminating roller, the conveying roller, the rotation speed of the master element, or the adjustment of the photopolymer composition, the coating thickness, the lamination temperature, the lamination pressure, the compression lamination pressure, the orientation of the light source and / or the scanning speed, the fixing intensity, etc. The components of the control unit can be configured conventionally or can be configured individually for the corresponding embodiment. Preferably, the control unit comprises a processor, a memory and a computer code (software / firmware) for controlling the components of the device.

[0169] The control unit may also include a programmable printed circuit board, a microcontroller or any other device for receiving and processing data signals from components of the device (e.g., from sensors related to the speed of the first carrier film or the second carrier film, the master element or the photopolymer composite web) and other related sensory information. The control unit preferably further includes a computer-usable or computer-readable medium, such as a hard disk, a random access memory (RAM), a read-only memory (ROM), a flash memory, etc., on which computer software or code is installed. The computer code or software for controlling the components of the device can be written in any desired programming language or model-based development environment, such as C / C++, C#, Objective-C, Java, Basic / VisualBasic, MATLAB, Python, Simulink, StateFlow, Lab View or assembler, but is not limited thereto.

[0170] The phrase "the controller is configured to" perform specific operating steps, such as adjusting the rotational speed of the master element to the web speed of the photopolymer composite web by changing the speed of one or more drive motors, or vice versa, may include customer-specific or standard software installed on the controller and initiating and controlling these operating steps.

[0171] In a preferred embodiment, the device may have a sensor, such as a tension sensor for measuring the tension in the first carrier film and / or the second carrier film. In these cases, the control unit is preferably arranged to receive and optionally evaluate data from the sensor, such as the tension sensor, for example in order to compare the detected tension value with a reference value. The control unit may preferably be further configured to adjust the speed of the one or more transport rollers by means of the evaluation of the data processing parameters by reference, for example by sending a signal to the one or more drive motors, in order to balance the tension between the first carrier film and the second carrier film.

[0172] In another preferred embodiment of the invention, the web tension of the photopolymer composite web is detected by a suitable sensor and transmitted to the control unit. The web tension in the device is preferably controlled by separating the tensile stress independently of the web speed. The control of the web tension is particularly arranged to maintain a constant web tension between the coating module and the exposure module. With the aid of a constant web tension, length variations in the sections of the photopolymer composite web in question can be avoided. Such length variations are undesirable, especially when the photopolymer is still liquid, because these length variations may lead to layer inhomogeneities, such as "fish eyes", shrinkage marks, pronounced orange peel patterns, etc. Therefore, it is particularly preferred to maintain a substantially constant web tension in the device after coating until exposure, preferably until the fixed section.

[0173] In a preferred embodiment, the device may comprise a motor for driving a 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 are detected by sensors and transmitted to the control unit. In these cases, the control unit is preferably configured such that it compares the rotational speed of the master element with the web speed of the photopolymer composite and adjusts the speed of one or both elements so that they maintain synchronous movement of the webs. Alternatively or additionally, the rotational speed of the master element is controlled in dependence on the measured web speed of the photopolymer composite layer so as to keep the web tension within a preferred range.

[0174] Particularly preferred features of the device will now be explained in detail. The order of explanation does not necessarily correspond to the order of arrangement in the device.

[0175] In a preferred embodiment of the invention, the exposure module is configured such that, when the photopolymer composite is guided through the exposure module, the areas of the photopolymer composite to be exposed temporarily adopt the shape of the side surface of the master element in some areas and are guided through the rotating master element as the side surface moves. Thus, there is preferably mechanical contact between areas of the master element and areas of the photopolymer composite. "Through a rotated master element" does not refer to a specific orientation of the photopolymer composite relative to the master element, but to any orientation running at least partially along the extent of the master element. Thus, the film composite can run above, below, to the left, to the right or diagonally, etc. relative to the master element.

[0176] The shape of the side surface of the master element may only be temporarily present in very small areas. For example, the area to be exposed may take the form of a thin line with a line width of less than 1 mm, for example when the composite runs substantially tangentially to the side surface of the master element.

[0177] The region of the photopolymer composite to be exposed can likewise temporarily adopt the shape of the side surface of the master element in an extended region, which extends, for example, in the form of an arc over a circle segment of a cylindrical master element having an opening angle of more than 5° or more than 10°. This provides additional space for exposure and optional fixation. Exposure can preferably be effected in the exposure region along a line parallel to the axis of rotation of the master element, or simultaneously on several lines. Exposure is preferably effected by means of an extended constant light beam or by means of one or more continuously scanning light sources, preferably lasers.

[0178] In a preferred embodiment, the light source of the exposure module and the light source for fixing the web of the photopolymer composite (e.g. a UV lamp or a UV source) are in the same optically insulating housing. Fixing can preferably be achieved directly in the same stretching area after exposure. This minimizes the transport distance between exposure and fixing, so that the amount of time that the exposed photopolymer is in a medium viscosity state after exposure is particularly short. This reduces the risk that the composite may be distorted during transport, for example when the tensions in the first and second carrier films are unequal and shear forces are generated along the composite web.

[0179] Distortions of the still medium-viscosity photopolymer result in a reduction in the resolution of the exposed image and thus in the quality of the final product. These distortions are often caused by shear forces acting on the photopolymer and possibly deforming the exposed microstructures. This can occur when, for example, one of the first or second carrier films is pulled faster than the other. It is therefore preferred to measure and compare the tension of each of the upper and lower carrier films, preferably automatically, before lamination, in order to ensure that the carrier films are synchronized and any errors can be corrected.

[0180] In a preferred embodiment, the apparatus comprises means for monitoring and controlling the tension of the film in order to further reduce the possibility of distortion caused by shear forces. The tension of the carrier film before lamination is preferably measured by one or more sensors and the data are sent to a control unit which compares the determined tensions. When the tension difference exceeds a defined value, the control unit preferably initiates corrective measures. The adjustment measures preferably include sending a signal to one or more drive motors in order to change the rotation speed of the driven rollers. The control unit can also evaluate the data from the sensors in order to determine whether one or more carrier films have become stuck (tension increase) or torn (tension decrease) in order to safely shut down the apparatus in either case.

[0181] In another preferred embodiment of the invention, the master element comprises a body. The body may be transparent, color-filtered or opaque. At least the side surface of the body is preferably optically polished. A P3 polishing grade is preferred, although an even higher P4 polishing grade is even more preferred.

[0182] In another preferred embodiment of the invention, the surface figure deviation of the subject does not exceed λ / 2, in particular with respect to the radiation generated by the light source. In the context of the present invention, the surface figure deviation corresponds to the difference between the actual shape of the subject and the target shape. The surface figure deviation is preferably determined with the aid of a test glass with a diameter of 50 mm. For example, a test glass with a known diameter and a known curvature is placed on the surface of the subject. This arrangement is exposed to a laser of a known wavelength so that interference fringes can be observed on the test glass. These interference fringes can be used to infer the deviation of the curvature of the subject from the known curvature of the test glass.

[0183] In another preferred embodiment of the invention, the master element deviates from the ideal cylindrical shape by no more than 0.2 mm, in particular by no more than 0.01 mm. This enables a very precise deflection of light through the body or surface of the master element. At the same time, the rotation of the master element can be very accurately synchronized with the movement of the photopolymer composite web.

[0184] In the case of an opaque body, the master hologram is preferably located on a side surface of the body. Such a body can be completely or partially absorptive for the wavelength of the light source of the exposure module. It is preferred here that such a master element is configured to replicate the volume hologram by a reflection method; in other words, the light source is arranged in such a way that the light as a reference beam passes through the composite, then through the master hologram, and then is reflected from the master hologram and passes through the composite again as an object beam. In the case of an absorbing body, it is advantageous that reflection interferences can be limited to a minimum.

[0185] In the case of a transparent or color-filtered body, the master hologram is preferably introduced into or onto a side surface of the body. The body preferably comprises optical glass (e.g. N-BK7, Borofloat glass, borosilicate glass, B270N-SF2, P-SF68, P-SK57Q1, P-SK58A, BK10, quartz glass and / or P-BK7) or optical plastic (e.g. polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin polymer (COP) or cycloolefin copolymer (COC)). Such a body can preferably be used to copy a volume hologram by reflection or transmission methods.

[0186] Regardless of the material of the body, there may be one or more master holograms that are present only in one or more specific areas of the side surface. To avoid reflection interference, it is preferred that the master hologram-free areas of the body are coated with a material that reduces reflections.

[0187] In all modules and stations of the system, roll widths of carrier film or photopolymer composites of between 150 mm and 1500 mm can preferably be accommodated, wherein the coating width is preferably 100 mm to 1400 mm. For the transport of carrier film or photopolymer composites in roll form, the system preferably has roll guide elements, such as guide rollers and / or tension rollers or tension rollers. The roll guide elements and modules are preferably configured for roll speeds of between 5 cm / min and 50 m / min.

[0188] All modules and stations of the device can preferably also be replicated. 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 include three coating modules, three laminating modules and three exposure modules arranged in parallel, wherein these three coating modules, three laminating modules and three exposure modules process different color-sensitive photopolymer compounds in order to create a stack consisting of the three compounds after fixing, for example an RGB stack. DETAILED DESCRIPTION

[0189] The present invention will be explained in detail hereinafter by means of examples and drawings, but is not limited thereto. BRIEF DESCRIPTION OF THE DRAWINGS

[0190] Figure 1 Schematic diagram of an apparatus for executing a method according to a preferred embodiment of the present invention

[0191] Figure 2 Schematic diagram of an exposure module in another preferred embodiment

[0192] Figure 3 Schematic diagram of an arrangement of an exposure module for replicating a hologram by reflection

[0193] Figure 4 Schematic diagram of an arrangement of an exposure module for replicating holograms by transmission, wherein the master element is exposed from the side surface

[0194] Figure 5 Schematic diagram of an arrangement of an exposure module for replicating holograms by transmission, wherein the master element is exposed from a main surface

[0195] Detailed description with drawings

[0196] Figure 1A schematic diagram of an apparatus for carrying out a method according to a preferred embodiment of the invention is shown. The apparatus comprises two coating modules 16 and 17, a laminating module 14, an exposure module comprising a cylindrical master element 4 and a laser, and a fixing module 25. The apparatus is preferably designed to flow a carrier film 18, 19 or a photopolymer composite 1 in web form from left to right in the arrangement shown. The entire apparatus is preferably shielded from external light. The stations and processes that the web undergoes will now be explained in detail.

[0197] Preferably, a first carrier film 18 is supplied as starting material between the protective films and in the form of a roll. The first carrier film preferably comprises polycarbonate and has a preferred thickness between 50 μm and 125 μm. The width of the film is preferably up to 1500 mm, but more preferably up to 310 mm. In this way, in the continuation of the method, the entire width can usually be covered by a single plasma pretreatment unit. An unwinding roller 20 guides the first carrier film 18 to the coating module. In the section of the coil between the unwinding roller and the coating module, a set of winding rollers 22 can be provided for removing the protective film from the carrier film. Although the protective film can preferably be removed only from the side of the carrier film 18 to be coated, in this illustrative embodiment the protective film is removed from both sides.

[0198] Preferably, a plasma pretreatment station 23 can be provided between the winding roll 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 the liquid photopolymer 9 on its surface. The pretreated carrier film is then supplied to the first coating module 17.

[0199] In the embodiment shown, similar stations and method steps are also provided for the second carrier film 19. The second carrier film can preferably include polycarbonate and have a preferred thickness between 50 μm and 125 μm. The second carrier film is also unwound from the unwinding roll 21, its protective film is removed by the roller 22, and it is subjected to plasma pretreatment and then supplied to the second coating module 16. The web speed through the pretreatment station is preferably 1 m / min to 10 m / min.

[0200] In the embodiment shown, two coating modules are provided, the first coating module 17 being an anilox roller particularly suitable for thin coatings (layer thickness between 1 μm and 15 μm). The second coating module 16 comprises a comma scraper, particularly suitable for thicker coatings (layer thickness between 40 μm and 100 μm). In order to cover a wider range of thicknesses, alternatively or additionally, the device may, for example, comprise an additional wire scraper or a profiled rod (not shown) for coating the upper carrier film and / or the lower carrier film. It is not necessary to coat both carrier films. Depending on the requirements of the production run, the desired coating module may be opened. Liquid photopolymer 9 is preferably supplied to the coating module from a storage container or a mixing unit (not shown). In a preferred embodiment, the storage container or the mixing unit may also form part of the device so as to allow particularly rapid adjustment of the photopolymer formulation. The coating of the film may preferably be configured so that an uncoated edge is left at the side of each film. This enables easier handling and facilitates subsequent lamination operations.

[0201] After passing through the coating module, each carrier film is conveyed to a degassing station 15 via a conveyor roller 3. In the degassing station, the carrier film is preferably vibrated by means of a vibrating roller so that air bubbles escape from the viscous liquid layer. Since the liquid photopolymer 9 may additionally contain a solvent, the solvent can also be discharged at this station. For this purpose, it can be preferred that the carrier film is additionally heated to a temperature between 30° C. and 300° C. in the degassing station. Thus, the degassing station can simultaneously serve as an evaporation unit (for the solvent). The heating can be achieved, for example, by means of a heated conveyor roller or by means of a heatable conveying zone. The evaporation of all or part of the solvent components can also be configured so that the viscosity of the liquid photopolymer is adjusted in order to facilitate further processing steps. Advantageously, a more viscous liquid photopolymer layer is less easily deformed by shear forces, thereby reducing unfavorable distortions during replication.

[0202] Subsequently, the two carrier films 18 and 19 are conveyed to the laminating module 14. The laminating module 14 preferably comprises a pair of laminating rollers, wherein the position of one or both rollers is adjustable so as to define the maximum thickness of the material flowing between the two. The laminating roller preferably comprises silicone and may have a diameter of, for example, up to 50 mm to 200 mm. The laminating roller may preferably be heated to a temperature between 5°C and 300°C, preferably 15°C to 200°C. If the target temperature for heating should be equal to or less than the ambient temperature, active heating is of course not required. The laminating roller is preferably also configured such that the laminating roller applies a compressive force between 10N and 20 000N on the carrier film and the photopolymer layer arranged in a sandwich shape. Then, the photopolymer composite is optionally actively cooled to room temperature, preferably to 20°C to 25°C. The control unit preferably controls the required heating and / or cooling based on the process requirements of the respective operation and the ambient conditions.

[0203] The laminating module is preferably configured to form a photopolymer composite 1 from these three layers 19, 9 and 18. The photopolymer composite 1 preferably flows continuously from the laminating module 14 into a closed housing 6 which at least accommodates the exposure module. The inlet 7 of the housing itself can have a pair of positionable rollers. The housing accommodates at least the master element 4 and the light source. The housing is preferably optically insulating. Here, the degree of optical insulation can be determined by the requirements for exposure. Especially at high web speeds, ambient light is unlikely to interfere with the exposure process, so that complete darkness is not required.

[0204] The inlet 7, the master element 4, the conveying rollers 3 and the outlet 8 are preferably arranged such that the photopolymer composite 1 is deflected by the master element 4. Here, the master element is cylindrical and is mounted so as to be rotatable about the center of its circular cross section. In particular, the photopolymer composite 1 is guided over a section of the side surface of the master element on the bottom side, wherein the areas of the photopolymer composite to be exposed temporarily adopt the shape of the side surface of the master element at least in some areas and are guided past the rotating master element as the side surface moves.

[0205] In this embodiment, the area of ​​the photopolymer composite 1 to be exposed temporarily adopts the shape of the side surface of the master element 4 in an extended area, wherein the extended area extends in the form of an arc across a circular segment of the cylindrical master element with an opening angle greater than 5°, preferably greater than 10°.

[0206] Advantageously, in this case, a dedicated drive for the master element can be dispensed with. Since the movement of the carrier film induces friction forces on the surface of the master element (optionally applied by an adhesive layer), this can be sufficient to rotate the master element 4 synchronously with the photopolymer composite 1. In this way, particularly good exposure conditions can also be ensured and a procedurally efficient implementation can be achieved.

[0207] In the embodiment shown, the optical adhesive film 2 is also temporarily introduced as a roll between the master element and the photopolymer composite roll. The optical adhesive film 2 is preferably composed of a carrier layer provided with adhesive layers on both sides. In order 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 preferably unwound from a unwinding roller 10. The protective film is then removed by a winding roller 12. The optical adhesive film is guided by the master element and a winding roller 13, which can optionally act as a tension roller. In this way, the flow of the optical adhesive film 2 can be maintained synchronously with the flow of the photopolymer composite 1 on the surface of the side surface of the master element.

[0208] The optical adhesive film acts as an optically clear adhesive (OCA) and ensures a smooth optical bond between the master hologram and the photopolymer composite 1. The master hologram is preferably mounted as a layer on the outer face of the master element.

[0209] Preferably, the master hologram can be replicated by means of a reflection or transmission process in order 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 process so that the light beam is transmitted through the master element and the master hologram present therein or thereon (transmission hologram) or is reflected by the master hologram back into the photopolymer composite (reflection hologram).

[0210] exist Figure 1 In the example of , the laser source is arranged below the master element and is configured so that the master hologram is replicated by reflection. The master element is opaque and the optical adhesive film matches the refractive index of the master hologram layer present on the outer surface of the master element. Both carrier films 18 and 19 are transparent so that light can pass through them to the master hologram and the master hologram reflects the light back through all layers of the photopolymer composite. The laser can be configured so that it scans in the axial direction of the master element. The scanning speed can be matched to the web speed of the photopolymer composite 1.

[0211] Since the just exposed liquid photopolymer 9 is mechanically sensitive, the rollers and guides through which it runs from the master element to the end of the fixing module are preferably configured so that they do not have any narrow angle deflection. The radius of these rollers 24 is preferably set to at least 100 mm, more preferably at least 200 mm, even more preferably at least 300 mm.

[0212] In order to prevent adverse shear forces from acting on the liquid photopolymer layer, the device further comprises a tension sensor for maintaining the same stress and strain state in the two carrier films 18 and 19. The exposed photopolymer composite leaves the opaque housing 6 via the outlet 8. However, the photopolymer composite that has passed this process is preferably kept free from the influence of external light until it is completely fixed. The photopolymer composite is guided by guide rollers 24 to a fixing module 25.

[0213] The fixing module 25 preferably comprises one or two UV sources and heating means. The fixing process is configured so that the liquid photopolymer layer is cured in order to fix the hologram. This is preferably done quickly, preferably within three minutes after exposing the photopolymer, in order to prevent the quality of the final fixed hologram from being impaired. The air in the fixing module is preferably continuously replaced by an air flow system.

[0214] After leaving the fixing module, a protective film 28 is preferably provided on both sides of the now cured photopolymer composite 1 with the hologram. If the outer protective films of the carrier films 18 and 19 have not been removed, they can be removed and replaced here. The unwinding roller 26 feeds the protective film to a workstation, which comprises a set of rollers with adjustable spacing. Finally, the finished photopolymer composite 1 is rolled up by the unwinding roller 27. Alternatively, the finished product containing one or more repeating holograms can be cut to size and stored in box form.

[0215] Figure 2 An exposure module and method in another preferred embodiment of the present invention are shown. In the embodiment shown, the photopolymer composite 1 moves from right to left. The master element 4 is a cylindrical configuration with a constant diameter. The schematic diagram shows the circular main surface of the master element. The area of ​​the photopolymer composite 1 to be exposed temporarily takes the form of an area of ​​the side surface and moves with the side surface when it is guided through the rotating master element. The optical adhesive film 2 is arranged as an intermediate layer between the master element 4 and the photopolymer composite 1. In this embodiment, the area of ​​the photopolymer composite that is in contact with the side surface and deformed thereby is fixed by positioning two lower conveying rollers 3. The exposure module further includes an upper conveying roller 3 that is in contact with the side surface of the master element. The roller is preferably made of rubber and has a dedicated drive. The upper conveying roller 3 transmits the rotational movement to the master element 4 by friction and determines its rotational speed. In this case, the movement of the master element 4 can be actively and independently controlled from the movement of the photopolymer composite 1. The controller is preferably arranged so as to ensure the synchronous movement of the side surface and the photopolymer composite.

[0216] Alternatively, the master element 4 may also have a flange at one or both ends. The flange may be configured, for example, so that it interacts with a ring gear or belt mechanism in order to move the master element. This has the advantage that both the side surface and the main surface of the master element are optically almost completely accessible and the light beam can be positioned flexibly.

[0217] Figure 3 A schematic diagram of the arrangement of a light source relative to a master element 4 is shown in order to copy a master hologram 29 into a photopolymer composite 1 by reflection. The light source is preferably arranged so that a light beam 5 is generated, which acts as a reference beam and passes through the photopolymer composite 1 and the optical adhesive film 2 and is then at least partially reflected by the master hologram 29. The reflected light 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 in order to write the hologram. The angle at which the reference beam strikes the master hologram may preferably correspond to the angle at which the copied hologram is illuminated in order to reconstruct the hologram, for example in a head-up display.

[0218] Figure 4 A schematic diagram of the arrangement of a light source relative to a master element 4 is shown in order to copy a master hologram 29 into a photopolymer composite 1 by transmission from a side surface. The light source is preferably arranged so that a light 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 in order to generate an object beam with a different angle of incidence on the photopolymer composite. The object beam preferably interferes with the undiffracted reference beam in the liquid photopolymer layer in order to replicate the hologram.

[0219] Figure 5 A schematic diagram of another arrangement of a light source relative to a master element 4 is shown in order to copy a master hologram 29 by transmission into a photopolymer composite 1. In this embodiment, the light source is arranged so that the light beam 5 generated by the light source encounters a major surface of the master element 4 (similar to an edge-lit configuration). The major surface preferably does not comprise a master hologram 29, but rather the master hologram is present on a side surface.

[0220] For this embodiment, the master element 4 is preferably provided in the form of an optical fiber. As in the case of 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 or with a small amount of 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 so as to change its refractive index correspondingly and write a hologram.

[0221] The light beam preferably propagates within the master element by reflection, preferably total reflection.Light losses in areas of the side surface that are not in optical contact with the photopolymer composite are preferably reduced to a minimum.

[0222] List of Reference Numerals

[0223] 1 Photopolymer composites

[0224] 2 Optical Adhesive Film

[0225] 3 Conveyor rollers (or "conveyor rollers")

[0226] 4 Master Components

[0227] 5 Beam

[0228] 6 Opaque shell

[0229] 7 Entrance to the opaque shell

[0230] 8 Opaque shell outlet

[0231] 9 Liquid Photopolymer

[0232] 10 Optical Adhesive Film Unwinding Roll

[0233] 11 Winding roll of protective film for optical adhesive film

[0234] 12 Winding roll of protective film for optical adhesive film

[0235] 13 Optical Adhesive Film Winding Roll

[0236] 14 Lamination rollers

[0237] 15 Degassing station

[0238] 16 Coating module (or "applying module") – Comma scraper

[0239] 17 Coating module (or "application module") - anilox roller

[0240] 18. First carrier film

[0241] 19. Second carrier film

[0242] 20 Unwinding roller for first carrier film

[0243] 21 Unwinding roller for second carrier film

[0244] 22 Protective film winding roll for carrier film

[0245] 23 Pretreatment station (plasma)

[0246] 24 Guide roller

[0247] 25 Fixed module

[0248] 26 Protective film unwinding roll for fixed hologram

[0249] 27 Take-up roll for fixed hologram

[0250] 28 Protective film for fixed holograms

[0251] 29 Master Hologram

Claims

1. A method for continuously replicating a hologram, preferably by means of an apparatus comprising a coating module, a laminating module, an exposure module and a fixing module, It is characterized in that The method comprises the following steps: a. coating the first carrier film (18) with a liquid photopolymer (9) by means of a coating module (17), b. applying a second carrier film (19) to the coated first carrier film (18) by means of a laminating module (14) in order to obtain a photopolymer composite (1) comprising a liquid photopolymer layer (9) between the two carrier films (18, 19), c. bringing a region of the photopolymer composite (1) into contact with an axially rotatable master element (4) comprising the master hologram to be replicated in an exposure module and exposing the region of the photopolymer composite (1) by means of a light source (5) so that the master hologram is replicated on the photopolymer composite (1), and d. Curing the replicated hologram present in the liquid photopolymer (9) in the fixing module (25).

2. The method according to claim 1, It is characterized in that The exposure module is configured so that, when the photopolymer composite (1) is guided through the exposure module, the areas of the photopolymer composite to be exposed temporarily adopt the shape of the side surface of the master element (4) in some areas and are guided through the rotating master element (4) as the side surface moves.

3. A method according to any one of the preceding claims, It is characterized in that The master element (4) comprises a body, wherein the master hologram has been inserted into the body and / or applied to a side surface of the body, wherein areas of the master element (4) not covered by the master hologram preferably have been applied with a reflection-reducing material.

4. A method as claimed in any one of the preceding claims, It is characterized in that The exposure module comprises at least one unwinding roller (10) and a winding roller (13) for temporarily applying an optical adhesive film (2) between the master element (4) and the photopolymer composite (1).

5. The method according to the preceding claim, It is characterized in that The refractive index of the optical adhesive film (2) is between the refractive index of the master element and the refractive index of the carrier film, Therein, more preferably, the refractive index difference between the master element and the optical adhesive film, preferably also between the master element and the carrier film, does not exceed 0.2, even more preferably does not exceed 0.1, still more preferably does not exceed 0.

05.

6. A method as claimed in any one of the preceding claims, It is 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, still more preferably at least 300 mm.

7. A method as claimed in any one of the preceding claims, It is characterized in that The master element is driven by force transmission via a functional roller, a flange-attached ring gear or a belt drive.

8. A method as claimed in any one of the preceding claims, It is characterized in that One or both main surfaces and / or side surfaces of the master element (4) have been provided with an anti-reflection coating.

9. A method as claimed in any one of the preceding claims, It is characterized in that The coating module (17) is arranged to coat the liquid photopolymer (9) onto the first carrier film (18) by a roll-to-roll method, wherein the coating module preferably comprises an anilox roller, a wire blade, a profiled rod, a slot die, a doctor blade and / or a comma blade.

10. The method according to any one of the preceding claims, It is characterized in that The method is carried out with the aid of an apparatus comprising two coating modules (17, 16), wherein a first coating module (17) is arranged to coat a first carrier film (18) with a liquid photopolymer (9) and a second coating module (16) is arranged to coat a second carrier film (19) with a liquid photopolymer (9).

11. A method as claimed in any one of the preceding claims, It is characterized in that The method is carried out by means of an apparatus comprising an unwinding station for unwinding a carrier film supplied in roll form, wherein the apparatus preferably further comprises a plasma pretreatment station (23) between the unwinding station and the coating module.

12. A method as claimed in any one of the preceding claims, It is characterized in that The laminating module (14) comprises a pair of laminating rollers, and the second carrier film (19) preferably has a pressure of 0.02 N / cm2 to 200 N / cm 2 Between, especially 0.02N / cm 2 Up to 50N / cm 2 and / or at a temperature between 5° C. and 200° C., in particular between 15° C. and 200° C., laminated onto the coated first carrier film ( 18 ).

13. A method as claimed in any one of the preceding claims, It is characterized in that The method is carried out with the aid of a degassing station (15) between the coating module (17, 16) and the laminating module (14), wherein the degassing station (15) is preferably arranged to transmit vibrations to the coated first carrier film and / or the second carrier film (18, 19), and / or the degassing station (15) is preferably configured to be heatable to 30°C to 300°C, in particular 100°C to 200°C.

14. A method as claimed in any one of the preceding claims, It is characterized in that The first carrier film (18) is based on a material or a material composite selected from the group comprising: polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene, polypropylene, cellulose acetate, cellulose triacetate (TAC), hydrated cellulose, cellulose nitrate, cycloolefin polymers, polystyrene, polyepoxide, polysulfone, cellulose triacetate (CTA), polyamide, polymethyl methacrylate (PMMA), polyvinyl chloride, polyvinyl butyral, polydicyclopentadiene, perfluoroethylene propylene (FEP), a mixture of two or more of the mentioned materials or a co-extrudate comprising one or more of the mentioned materials, more preferably PC, PET and / or TAC.

15. A method as claimed in any one of the preceding claims, It is characterized in that The liquid photopolymer (9) comprises: (i) at least one writing monomer; (ii) a photoinitiator system; and (iii) at least one organic ingredient, The liquid photopolymer (9) may further include one or more of the following components: a catalyst, a dye, a free radical stabilizer, a solvent, a non-polymerizable component, a reactive diluent, a dye oxidant, a dye reducing agent, a bleaching agent, a thixotropic agent, a nucleating agent and / or an auxiliary agent or additive.

16. A method as claimed in any one of the preceding claims, It is characterized in that The residence time of the photopolymer composite (1) during the transport of the photopolymer composite (1) from the exposure module to the fixing module (25) does not exceed 10 minutes, preferably does not exceed 5 minutes, more preferably does not exceed 3 minutes, and / or The residence time of the liquid photopolymer (9) from coating on the first carrier film (18) to curing is no more than 15 minutes, preferably no more than 10 minutes, more preferably no more than 5 minutes.

17. A photopolymer composite (1) comprising a photopolymer between two carrier films (18, 19), into which a hologram has been replicated by a method as claimed in any one of the preceding claims.

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