Method for replicating holograms by optical adhesive film

Abstract

The invention relates to a method for replicating a hologram in a photosensitive composite web. The method according to the invention preferably comprises providing a master element comprising a substrate body and at least one master hologram, applying a photosensitive composite web on a surface of the master element, exposing the master element to copy the at least one master hologram into the photosensitive composite web, and separating the exposed composite web from the master element. The method further includes temporarily applying an optical adhesive film between the photosensitive composite web and a surface of the master element. The optical adhesive film enables optical contact between the master element and the photosensitive composite web during exposure. In another aspect, the invention relates to a method of replicating a hologram in a photosensitive composite web using an input coupling element wherein an optical adhesive film is introduced between the composite web and the input coupling element.

Description

[0001] The present invention relates to a method for replicating a hologram in a photosensitive composite web. The method according to the present invention preferably comprises providing a master element comprising a substrate body and at least one master hologram, applying a photosensitive composite web on the surface of the master element, exposing the master element so as to replicate at least one master hologram into the photosensitive composite web, and separating the exposed composite web from the master element. The method also comprises temporarily applying an optical adhesive film between the photosensitive composite web and the surface of the master element. The optical adhesive film enables optical contact between the master element and the photosensitive composite web during exposure. On the other hand, the present invention relates to a method for replicating a hologram in a photosensitive composite web using an input coupling element, wherein an optical adhesive film is introduced between the composite web and the input coupling element.

[0002] Background and Prior Art

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

[0004] A holographic optical element (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 on an arbitrary substrate in a compact manner. 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.

[0005] Such holographic elements have applications 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), photosensitive detection systems (e.g. for interior monitoring (eye tracking in vehicles or presence tracking of people inside)).

[0006] Holograms are generated by the interference of a reference beam with light (object beam) reflected or diffracted by the surface of an object. Three-dimensional objects have traditionally been used to produce unique custom holograms. In contrast, commercially available HOEs are usually mass-produced by means of replication methods. Such replication methods usually use a master hologram with the image to be copied. The master hologram used is usually stored in a substrate body that carries the master hologram. The substrate body is preferably transparent and can have various shapes, such as a parallelepiped shape, a sheet or a roll. The combination of the master hologram and the substrate body forms a master element.

[0007] The master element is exposed using a coherent light source in order to copy the image from the master hologram into the photosensitive composite. For mass production, the photosensitive composite can be provided in the form of a traveling web comprising the photosensitive material and one or more carriers or protective layers. For this purpose, the photosensitive web is preferably conveyed through various workstations in order to produce the HOE.

[0008] During exposure, the composite web is placed on the surface of the master element. To produce a reflection hologram, the coherent light can pass through the composite web to reach the master hologram and then be reflected back to the composite web by the master hologram. To produce a transmission hologram, the coherent light can alternatively be first directed to the master hologram, with the help of which the coherent light is diffracted before reaching the composite web. In both cases, the object beam and the reference beam interfere with each other in the photosensitive material and form a replicated hologram. The replication process is sensitive to unfavorable interference light, which can also interfere with the object and / or reference beams. For example, if irregularities or gaps appear at the interface between the composite web and the surface of the master element, internal reflections may occur in the reference beam and / or the object beam. This may result in light loss or cause unfavorable interference, affecting the quality of the replicated hologram. Therefore, providing sufficient optical contact between the master element and the composite web is closely related to the quality of the replicated hologram.

[0009] This also applies to possible use of input coupling elements during the exposure process, which in certain configurations are used for hologram replication. For example, the input coupling elements can preferably be used to adjust the exposure angle. The exposure angle (i.e. the angle at which the object beam and the reference beam are incident on the photosensitive material) also determines the angle at which the hologram can be reconstructed. Thus, varying the exposure angle allows the generation of different types of holograms, such as: side-lit holograms, back-lit holograms, holograms at eye level or holograms that are only visible from below, etc.

[0010] The exposure angle can be changed or adjusted by directing the coherent light used to expose the hologram through an input coupling element. The input coupling element is transparent to at least the wavelength of the exposure beam and can take different shapes, such as a cuboid, a sheet, a pyramid, a roller, etc. Moreover, the input coupling element can be placed on the composite web so that the light is initially diffracted by the input coupling element material in order to obtain the desired approach angle on the composite web. However, if there is a small gap at the interface or boundary between the input coupling element and the composite web, there may be internal reflection of the light. This also leads to unfavorable interference or losses. Therefore, in this arrangement, almost perfect optical contact between the input coupling element and the composite web is also desirable in order to produce high-quality replicated holograms.

[0011] The use of a refractive index matching liquid has been proposed in order to improve the optical contact between a composite web and an adjacent component (e.g. a master element or an input coupling element) during exposure. WO 9619754 A1 teaches a method for replicating a master hologram from a hollow drum-shaped master element in a composite web. The composite web travels simultaneously on the curved surface of a rotating master element. In this case it is established that in the case of insufficient optical contact between the components, image artifacts are generated by internal reflections at the air / glass or air / substrate interface. In order to improve the optical contact between the composite web and the master element, a refractive index matching liquid (such as xylene) is continuously directed onto the surface of the master element. The liquid fills the gap between the master element and the composite web. Furthermore, before exposure, the composite web is immersed in the refractive index matching liquid. After exposure, the liquid is removed from the composite web, which can then be rolled up or further processed.

[0012] However, a disadvantage of the proposed method is that xylene is a readily flammable irritant and suspected to be carcinogenic, so its use requires greater system complexity in order to ensure explosion protection, environmental protection and industrial safety. Moreover, the complexity and expense of the HOE production process are increased by the required removal of the refractive index matching liquid.

[0013] JP 2000250386 A also discloses the use of a refractive index matching liquid for improving the optical contact between the master element and the photosensitive composite web. The refractive index matching liquid must not be too volatile, since it must remain in the liquid phase for the duration of the coating and exposure process. However, the refractive index matching liquid is dried before the exposed composite web is further processed. Again, this is accompanied by a significant increase in system complexity. Moreover, the liquid refractive index matching device must be very thin so that the molecular motion in the liquid film does not change the phase angle of the light passing through, as this would in turn have a negative impact on the hologram quality. Typically, the refractive index matching liquid is lost even when it is removed, and therefore it cannot be used again. This further increases the overall process costs.

[0014] Semi-volatile index matching liquids that do not dry quickly can remain on the surface of a master hologram or other component for a longer period of time. This may require cleaning the master hologram in order to avoid accumulation of liquid and contaminants. This cleaning step may be complicated, especially if the master hologram has a non-smooth surface (e.g., a concave-convex pattern). The prior art provides only limited solutions regarding the protection of the surfaces of master holograms in the event that the surfaces of these master holograms come into contact with liquid or resin materials.

[0015] It is known to use an optically transparent layer to protect the master hologram from contamination during the exposure method. DE 10 2006 016 139 A1 has disclosed the use of a transparent separation layer between the resin (non-solid) photosensitive layer and the master hologram. The separation layer should facilitate the removal of the resin photosensitive layer from the master hologram. In order to keep the optical influence of the separation layer small, it is provided that the refractive index difference between the photosensitive layer and the separation layer is kept small or completely avoided. Therefore, the separation layer should not have any optical power.

[0016] Furthermore, the separation layer can be used as a covering layer for the relief structure of the master hologram. Despite the separation layer (which is shown to be very thin), the relief structure of the master hologram is still sharp and may be pressed into the photosensitive layer. DE 102006 016 139 A1 proposes a separation layer as a coating permanently applied to the surface of the master hologram.

[0017] In order to integrate the exposed hologram in the product, DE 10 2006 016 139 A1 furthermore describes the use of an adhesive layer which bonds the replicated hologram to the substrate. In contrast to the separating layer, the adhesive layer remains a permanent component of the product from which the hologram can no longer be removed.

[0018] In the field of optical displays, it is also known to use "optical gap adhesives" (OCAs) for the purpose of bonding backlighting to the screen.

[0019] KR 20150001411 A teaches an example of such an OCA for use in an LCD screen. The OCA includes an adhesive and prevents the formation of an air layer between the background lighting and the LCD screen. Similarly, US10611937B2 teaches an adhesive layer for firmly bonding a glass layer to a sensing film of the screen. The adhesive layer includes an OCA in order to ensure good optical properties of the screen. The purpose is to have such an adhesive layer permanently bond the layers of the screen to each other in order to ensure a long service life of the product. Removal of the adhesive layer is not provided.

[0020] In addition, DE 10 2019 112 254 A1 has disclosed a transparent multilayer microfluidic arrangement. The different layers of the arrangement are bonded to each other by a transparent adhesive. The microfluidic channel is produced by clamping a wall structure between a transparent flexible cover layer and a base layer. The optical refractive index of these layer materials is selected so that the layer structure is imperceptible. This should facilitate the readout of the microfluidic results. Regarding the production of the adhesive layer, a hot melt adhesive is proposed. In some embodiments, in order to set its local adhesion properties, the adhesive layer is exposed to UV radiation. The adhesive layer is also configured for permanent bonding.

[0021] In view of the prior art, there is a need for improved methods for reproducing holograms in photosensitive materials, taking into account efficiency, economy and optical quality of the replicated holograms. In particular, there is a need for improved optical contact between a photosensitive composite web and adjacent optical components, such as a master element or an input coupling element, which reliably ensures interference-free exposure, which does not require hazardous chemicals or excessive cleaning, which can be removed without residue and is easily removable.

[0022] Purpose of the Invention

[0023] The problem solved by the present invention is to provide a method for replicating a hologram from a master element in a photosensitive composite web which does not have the disadvantages of the prior art. In particular, one problem solved by the present invention is to provide an optically very precise and high-quality method which is suitable for user-friendly replication of holographic material on a photosensitive composite web. Summary of the invention

[0024] This problem is solved by the features of the independent claim. Advantageous configurations of the invention are described in the dependent claims.

[0025] In a first aspect, the invention relates to a method for replicating a hologram in a photosensitive composite web, the method comprising the following steps:

[0026] a. providing a master element, the master element comprising a substrate body and at least one master hologram,

[0027] b. applying a photosensitive composite web to the surface of a master element,

[0028] c. exposing the master element to replicate at least one master hologram in a photosensitive composite web, and

[0029] d. Separating the exposed composite web from the master element.

[0030] Further, the method according to the invention comprises temporarily applying an optical adhesive film between the photosensitive composite web and the surface of the master element, preferably while the master element is exposed, said optical adhesive film achieving optical contact between the master element and the photosensitive composite web.

[0031] In another aspect, the invention relates to a method for replicating a hologram in a photosensitive composite web, the method comprising the following steps:

[0032] a. providing a master element, the master element comprising a substrate body and at least one master hologram,

[0033] b. applying a photosensitive composite web to the surface of a master element,

[0034] c. applying an input coupling element to the photosensitive composite web such that the photosensitive composite web is positioned between a surface of the input coupling element and a surface of the master element,

[0035] d. exposing the master element by means of an input coupling element in order to replicate at least one master hologram in a photosensitive composite web,

[0036] e. separating the input coupling element from the exposed composite web, and

[0037] f. Separating the exposed composite web from the master element.

[0038] Further, the method comprises temporarily applying an optical adhesive film between the photosensitive composite web and the surface of the input coupling element, preferably while the master element is exposed, said optical adhesive film achieving optical contact between the input coupling element and the photosensitive composite web.

[0039] An advantage of the method according to the invention is that the optical contact between the master element (or input coupling element) and the photosensitive composite web is ensured to be almost flawless, without the need for additional steps for purging or evaporating the refractive index matching liquid. Instead, the optical adhesive film, which can be removed without residue, can establish a smooth gapless transition between the master element (or input coupling element) and the composite web, and thus there are essentially no unfavorable reflections or scattering at the interface between the components. This reduces optical losses and minimizes the possible occurrence of optical interferences that could leave unfavorable patterns in the replicated hologram. It is also particularly advantageous that the optical adhesive film can be fully adhered to the master element and the photosensitive composite web at the same time to prevent the occurrence of bubbles or air gaps. At the same time, the optical adhesive film is only temporarily applied to the master element, so that the surface of the master element is not allowed to adhere to potential contaminants.

[0040] 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; this therefore produces a more stable interference field in the hologram copy during the exposure time. In this way, these microstructures do not get dirty, whereby the diffraction efficiency of the hologram is maximized. The sharpness and contrast of the produced hologram are also substantially improved. Preferably, the optical adhesive film is configured so that the optical adhesive film adheres to the surface of the composite web and to the adjacent surfaces of the master element and / or the input coupling element. The adhesion strength is preferably so high that a gap-free bond can be obtained between the composite web and the adjacent components without applying a greater pressure on the composite web than would otherwise be the case if the composite web were in contact with these elements. It is particularly preferred that the composite web does not need to be pressed so strongly on the master element or the input coupling element that a material deformation occurs. Therefore, the method according to the invention also differs in this respect from the method of DE 10 2006 016 139 A1, in which a deformable layer needs to be laminated on a separation layer / covering layer of the master hologram. At the same time, the adhesion strength of the optical adhesive film on these components should preferably be so low that the optical adhesive film can be removed without damage or residue. In this sense, the optical adhesive film of the present invention is preferably further different from adhesive layers in the prior art such as DE 10 2006 016 139 A1, KR 20150001411 A, US10611937 B2 and DE 102019 112 254 A1, which are designed for permanent adhesive bonding.

[0041] Furthermore, the optical adhesive film is preferably provided in the form of a foil or a film. That is to say, it is not the case that the material of the optical adhesive film forms a film or a foil only when it is applied (for example by spraying) onto the surface of a process component. Instead, the optical adhesive film preferably already has a defined width and thickness before it is applied onto or between process components. The optical adhesive film according to the invention thus differs from the protective layers or separation layers known from DE 10 2006 016 139 A1, which are permanently applied to the surface of the master hologram by coating. Preferably, the optical adhesive film is provided in the form of a roll, although other embodiments (for example a ring or a plurality of individual stickers) are also possible.

[0042] Another advantage of the method according to the invention lies in the fact that the material used for the optical adhesive film can have the same or similar optical properties as the material used for the substrate of the master element (or for the input coupling element) and / or the composite web. Preferably, the 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 matched very closely to the refractive index of the adjacent process parts, so that it can be ensured that the transition between adjacent refractive indices is free of refractive index jumps. This largely eliminates or significantly minimizes reflections at the interface between the master element (or input coupling element), the optical adhesive film and / or the photosensitive composite web.

[0043] Moreover, the optical contact by the optical adhesive film allows the exposure to be easily integrated in a continuous production process, preferably in a roll-to-roll process. The optical adhesive film can be formed in a manner similar to the composite web and can be moved through the process in a similar manner (e.g. by means of rollers). This enables simple synchronization of the optical adhesive film with the composite web. It is also possible and preferred that the optical adhesive film and / or the photosensitive composite web is applied to the surface of the master element or the surface of the input coupling element by means of a laminating roller. During exposure, the optical adhesive film is preferably in mechanical contact with the photosensitive composite web and the master element and / or the input coupling element. Preferably, the optical adhesive film is removed from the photosensitive composite web and the master element and / or from the input coupling element simultaneously after exposure. Therefore, the optical adhesive film is preferably not a permanent component of the photosensitive composite web, the master element or the input coupling element.

[0044] The optical adhesive film can be precisely specified in terms of its layer thickness, layer thickness uniformity and waviness. For example, the optical adhesive film can advantageously be provided with a desired constant thickness so that the intensity of the light used to expose the composite web always remains uniform. In contrast, if a refractive index matching liquid is used, the dosage can vary over time and it cannot be guaranteed that the liquid is evenly distributed on the desired surface. Similar problems may arise in the application of hot melt adhesives, since these are also metered in liquid form. The application of the optical adhesive film according to the present invention allows particularly precise bridging of the distance between the composite web and the master element and / or the input coupling element. Further, the use of an optical adhesive film with a correspondingly specifiable layer thickness, layer thickness uniformity and waviness results in high process stability during replication. In particular, the surface of the optical adhesive film can be configured to be substantially free of waviness. This avoids variations in the thickness of the adhesive film, which may contaminate the interference field of the object beam and the reference beam and may cause the replicated hologram to deviate from the master hologram in optical function.

[0045] Compared to methods based on index matching liquids as known from the prior art, the use of optical adhesive films can also be designed to be safer for the user. This is because such adhesive films generally do not contain very toxic substances and are non-volatile, so no separate safety measures (e.g. gas extraction or isolation) are required.

[0046] Moreover, volatile refractive index matching liquids are usually not recyclable after use. That is, they either evaporate or do not have the required purity, which means that reuse is only possible after complex redistillation. This increases material expenditure or technical system expenditure and makes the method more expensive. In contrast, the optical adhesive film can be reused for multiple applications. Advantageously, for example, a single ring of adhesive film can run through the process. Preferably, the ring represents a closed arrangement of the optical adhesive film, in which case the same optical adhesive film is used multiple times for exposure purposes. In an alternative, for example, the optical adhesive film can also be continuously supplied to the exposure station from a provided unwinding roller. If there is no longer adhesive film available on the unwinding roller, the unwinding roller can be filled or replaced. It can also be preferred that the used optical adhesive film is wound again by a rewinding roller after exposure for reuse or recycling. Therefore, the method according to the present invention can advantageously be configured to save resources in different ways.

[0047] Furthermore, the method according to the invention is very material-friendly, clean and does not leave residues on process parts, such as master elements or input coupling elements. This is preferably due to the relatively weak adhesive forces of the optical adhesive film and to the fact that the optical adhesive film can be removed from the surface of the process part continuously or intermittently. In this way, a fresh optical adhesive film can also be applied to the surface in a continuous or intermittent manner. Therefore, the optical adhesive film preferably does not represent a sticky, permanent process part on which dust or residues may accumulate. Residues on the exposed composite web are also avoided, so that the produced hologram can be seamlessly integrated in the final product, preferably without further cleaning steps. This increases the efficiency of the method and avoids unnecessary work steps.

[0048] Another advantage of the method according to the present invention is that the photosensitive composite web or at least its outer layer can be configured as a solid or non-solid. For example, the photosensitive material can be solid and / or enclosed between solid carrier layers (such as polycarbonate films). These solid carrier layers can be applied to the surface of the process parts that can even be completely smooth (without concave-convex patterns). Generally, it is difficult to make two smooth solid surfaces in good optical contact with each other because the intermolecular forces acting between these surfaces are not enough to make these surfaces contact each other uninterruptedly, and these surfaces may even electrostatically repel each other. By temporarily bringing the optical adhesive film between the solid surfaces, an electrostatic force with a sufficiently large attraction can be generated between them to ensure stable contact and no relative movement between the composite web and adjacent parts. This significantly improves the quality of the replication method.

[0049] Even if the outer layer of the photosensitive composite web should include a non-solid, such as a semi-solid or resin material, it can still be used with an optical adhesive film. For example, a solid support layer of the composite web can be brought into contact with the optical adhesive film. In an alternative, the optical adhesive film is used to bring the non-solid surface into contact with the process component and is subsequently removed from the non-solid surface after the non-solid surface is fixed and / or cured. Therefore, the optical adhesive film is versatile and suitable for many different embodiments of the photosensitive composite web.

[0050] As is apparent from the above advantages, the method of applying an optical adhesive film between a photosensitive composite web and an input coupling element solves the same technical problems as the method of applying an optical adhesive film between a photosensitive composite web and a master element. Specifically, the optical adhesive film improves the optical contact between the exposed transparent components through which the exposure light is directed. This reduces undesirable reflections, scattering or losses, and the quality of the reconstructed hologram is improved. Therefore, the two methods are associated with each other so as to form a single overall inventive concept.

[0051] It is also obvious to a person skilled in the art that preferred features or advantages of embodiments of the method in which an optical adhesive film is applied to a master element are equally applicable to embodiments of the method in which an optical adhesive film is applied to an input coupling element, and vice versa. Moreover, a combination of these methods is obviously particularly preferred. That is, if an input coupling element is used during the exposure process, it is particularly preferred to temporarily introduce an optical adhesive film between the master element and the photosensitive composite web and between the input coupling element and the photosensitive composite web. However, it may also be preferred to temporarily introduce an optical adhesive film only between, for example, the input coupling element and the photosensitive composite web, rather than between the master element and the photosensitive composite web. In such an embodiment, the photosensitive composite web can therefore also be exposed when it is in direct contact with the surface of the master element, wherein the contact is not achieved by the optical adhesive film.

[0052] Within the meaning of the present invention, "applying" preferably means that one process component (e.g. a master element, an input coupling element and / or a photosensitive composite web) is in indirect or direct contact with another process component. For example, when the composite web is applied to the master element or the input coupling element, a protective layer and / or an optical adhesive film may be present between the process components. Within the meaning of the present invention, "applying" is also preferably used to indicate that one process component exerts a mechanical force on another process component, for example by resting on the latter and pressing down on it (like the case where the input coupling element rests on the photosensitive composite web) or applying a friction force, like the case of a rotating cylindrical master element, which causes the photosensitive composite web to move simultaneously with the master element. The force transmission can also be reversed, with the result that the photosensitive composite web causes a movement or rotation of the master element.

[0053] A "process component" within the meaning of the present invention is preferably a fixed, movable or consumable component or material used in an exposure method. Preferably, the process component is configured such that it interacts with the light during the exposure method, e.g. by reflection, transmission or diffraction, in order to adjust the exposure method. For example, optical components, such as master elements or input coupling elements, represent process components within the meaning of the present invention, as does a photosensitive composite web.

[0054] Within the meaning of the present invention, the "surface" of a process component may relate to the surface of the process component that is in contact with another process component. Preferably, the "surface" of a process component may also relate to its outermost layer, especially in the case of a process component with a layer structure. For example, the surface of a photosensitive composite web may be an upper carrier film, while the surface of a master element may relate to an upper cover for protecting a master hologram.

[0055] "Separation" within the meaning of the present invention is separation, preferably separation of process components such that these components are no longer in contact with each other, preferably neither directly nor indirectly. Preferably, "separation" thus introduces an increased air gap between process components, for example when separating the composite web from the master element or the input coupling element.

[0056] "Optical contact" should preferably allow the beam path of light to pass between the process components without experiencing substantial reflection or even total internal reflection. Direct integral connection contact between these process components is possible but not mandatory. For example, an optical adhesive film that enables contact is provided for achieving optical contact between the master element and the composite web. However, there is preferably direct optical contact between the optical adhesive film and the adjacent process components. If there is a gap between the surface of the optical adhesive film and the surface of the adjacent process component, the gap is preferably less than half the wavelength of the light, so that no interference field is formed at the interface between the surfaces. Preferably, neither reflection (especially total internal reflection) nor scattering occurs at the interface between the surfaces.

[0057] The optical contact between the photosensitive composite web and another process component (master element, input coupling element) is achieved by the optical adhesive film. Preferably, this means that the photosensitive composite web and the other component are in mechanical contact with the optical adhesive film. Preferably, this means that the optical adhesive film is physically, chemically or electrostatically adhered to the surface of the photosensitive composite web or of the other component.

[0058] Preferably, the "attachment" or "adhesion" of the optical adhesive film to the photosensitive composite web and / or another process component includes the presence of attractive forces between the optical adhesive film and the relevant components. If the optical adhesive film is introduced between two process components in order to achieve optical contact between them, the attractive forces that exist between each process component and the optical adhesive film are preferably stronger than the attractive forces that would exist between the surfaces of the process components without the optical adhesive film. In other words: the process components preferably adhere more strongly to the optical adhesive film than to each other. Moreover, the adhesion is preferably sufficient to prevent movement between the process components between which the optical contact is achieved.

[0059] Within the meaning of the present invention, a "composite" is preferably a multilayer material consisting of two or more different components with different physical properties, which components are bonded to each other at the interface. Preferably, the bond between the individual components is constructed so that it cannot be separated by the influence of slight forces and is therefore considered permanent. Preferably, the layers of the composite web must not be separated by a force of less than 10N / cm, preferably less than 50N / cm, even more preferably less than 100N / cm. For example, the composite may consist of a material enclosed between two transparent carrier films. The photosensitive composite may be provided with one or more protective films, which are present during exposure or are removed before exposure. Alternatively or in addition, the composite web may comprise a stack of layers, each layer being photosensitive to a different spectral range.

[0060] Within the meaning of the present invention, a "composite web" is preferably a composite material whose length is at least twice, preferably at least five times, even more preferably at least twenty times, greater than its width. For example, the thickness of the composite web is preferably set so that it has a certain flexibility so that it can be partially wound on a roll. Preferably, the composite web has a thickness of up to 1000 μm, preferably up to 500 μm, particularly preferably up to 100 μm. The composite web comprises a photosensitive material. Preferably, the composite web encloses the photosensitive material between two transparent carrier films, the refractive index of which is similar to that of the photosensitive material. Preferably, the refractive index of the carrier film and the photosensitive material is between 1.4 and 1.6. In some preferred embodiments, the photosensitive composite web comprises the photosensitive material on a single carrier film, as a result of which there is one surface of the photosensitive material that is not covered. For example, the photosensitive material can be a photosensitive photopolymer or a dichromated gelatin with a preferred layer thickness of between 1 and 500 μm. The photosensitive material can be photosensitive to the entire visible spectrum or wavelength selective.

[0061] Within the meaning of the present invention, "light sensitivity" preferably relates to the suitability of a material for holography. Preferably, a material is considered suitable for holography if, under exposure to sufficiently coherent light, the interference field of the light can be stored as a microstructure in the material. Preferably, the suitability for holography is related to the size of the generated microstructure. Preferably, the generated microstructure is no larger than the light / dark structure of the interference field.

[0062] Within the meaning of the present invention, "exposure" is preferably understood to mean the targeted steering of an electromagnetic beam in a wavelength range preferably between 400 nm and 1600 nm onto a suitably sensitive surface, preferably for forming a hologram. Different methods of exposing holograms are known; these include transmission or reflection techniques for producing volume holograms. Examples thereof are explained in detail below within this document.

[0063] A "master element" is preferably a three-dimensional unit comprising at least one master hologram, whose form ensures that a movement of the master element directly leads to a corresponding movement of the master hologram. The master element may also comprise a plurality of master holograms, for example 2, 3, 5 or more. Preferably, the length and width of the master element correspond approximately to the length and width of the master hologram. Preferably, the height of the master element is at least twice, preferably five times, particularly preferably at least twenty times the height of the master hologram.

[0064] The master element preferably comprises a substrate body enclosing or carrying at least one master hologram. In an embodiment, the master element may comprise, for example, a transparent upper cover for protecting the master hologram present between the cover and the substrate body. Preferably, the upper cover has a refractive index that has been selected so that light passes through the upper cover, the master hologram and the substrate body substantially without being diffracted. For example, the upper cover may be a transparent film or a glass layer.

[0065] The master element can preferably have the shape of a parallelepiped block, a plate, a pyramid or a prism or a cylinder. The shape of the substrate body can be set accordingly.

[0066] Preferably, the substrate body of the master element can be formed of a material which is an optical plastic, preferably selected from the group consisting of: polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin polymer (COP) and cycloolefin copolymer (COC), and / or an optical glass, preferably selected from the group consisting of: borosilicate glass, quartz glass, B270, N-BK7, N-SF2, P-SF68, P-SK57Q1, P-SK58A and P-BK7.

[0067] Preferably, the refractive index of both the base body and any covering of the master element is between 1.4 and 1.6.

[0068] The material of the substrate can be selected according to the desired exposure angle or refractive index. In addition, it can be preferred that the substrate is colored so that, for example, wavelength selectivity filters light, thereby producing a hologram with a specific wavelength. In this way, a broadband light source can be used to expose different master holograms.

[0069] Preferably, the surface of the master element comprises glass, PC, TAC or PMMA. The material of the surface may be in the form of a film or sheet for protecting the master hologram. However, the material of the surface may also be the material of the substrate itself, and for example have a parallelepiped shape or a cylindrical shape.

[0070] Whether the optical adhesive film is placed on a substrate or on a cover of the master element may depend on the direction in which the master hologram is intended to be exposed. In some cases, the optical adhesive film may be applied to the side or base of the master element. Preferably, the relevant surface of the master element is smooth; in particular, this means that it does not comprise a concave-convex pattern. Preferably, the master hologram comprises a volume hologram. In order to replicate a volume hologram, the quality of the reproduction depends primarily on the optical contact rather than the mechanical contact between the master hologram and the photosensitive material utilized. Moreover, if the surface of the master element is smooth, the optical adhesive film can be applied and removed more easily without, for example, leaving residues in the recesses of the concave-convex pattern.

[0071] Preferably, "width" relates to the dimension in a horizontal plane transverse to the direction of travel of the composite web. Preferably, "length" relates to the dimension in a horizontal plane along the direction of travel of the composite web. Preferably, "height" relates to the dimension in a vertical plane, which is orthogonal to the plane formed by the width and the length.

[0072] Within the meaning of the present invention, a "substrate body" is preferably a three-dimensional block of material that carries or encloses a master hologram. Preferably, the substrate body is transparent. In some embodiments, the substrate body has multiple faces, including a flat surface that can be oriented horizontally. In some embodiments, the substrate body is prismatic, that is, it has a constant cross-section of any desired shape (for example, square, polygonal, elliptical or circular). The end of the substrate body with the cross-sectional shape can be referred to as a "base". The elongated face of the substrate body located between these two ends can be referred to as a "lateral face". In some embodiments, the shape of an axially rotatable cylinder is preferred. Within the meaning of the present invention, the form of a rotatable prismatic substrate body or a master element, preferably a cylindrical form, can also be referred to as a "roller".

[0073] Within the meaning of the present invention, the term "transparent" or "transparency" preferably relates to the property of a material, whereby it is substantially transmissive to light. Preferably, within the meaning of the present invention, a transparent material is transmissive at least to a portion of the electromagnetic spectrum preferably having a wavelength between 300 nm and 25 μm, particularly preferably between 400 nm and 780 nm. Particularly preferably, the transparent material (e.g. a transparent substrate body) is transmissive to light in the wavelength range used when exposing the master hologram. The transparent material can also be colored in such a way that it selects for light radiation of a specific wavelength.

[0074] Within the meaning 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. In an alternative, the microstructure can also be present in the volume of the element, for example 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. Preferably, the master hologram comprises a volume hologram.

[0075] The process for producing a master hologram may preferably be referred to as "hologram origination" or "hologram mastering". A master hologram may be created by analog or digital methods. In an exemplary 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 or in the recording material, the object beam and the reference beam interfere, producing an interference pattern. The interference pattern is recorded by a photosensitive material, so that after processing, this produces the shape of a surface relief pattern on the surface of the material, or a spatially varying refractive index in a material that is typically only a few microns thick. 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. Subsequently, when additional copies with the same image are created, the master hologram may be used as a new object.

[0076] The master hologram can also preferably be computer generated. Microscopic gratings that generate diffraction effects 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 composed 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.

[0077] Within the meaning of the present invention, an "input coupling element" is preferably a three-dimensional block made of a transparent material having a refractive index and dimensions configured such that they direct an exposure beam to a master hologram and / or direct said exposure beam away from said master hologram. Preferably, the input coupling element may have different optically accessible faces. Preferably, at least one side face and the underside of the input coupling element are optically accessible. In some embodiments, the input coupling element may have the shape of a parallelepiped block, a (flat) plate, a pyramid or a prism. In some embodiments, the input coupling element is prismatic, i.e. it has a constant cross-section of any desired shape, such as square, polygonal, elliptical or circular. The end of the input coupling element having the cross-sectional shape may be referred to as a "base". The elongated face of the input coupling element located between the two ends may be referred to as a "lateral face". In some embodiments, the shape of an axially rotatable cylinder is preferred. The form of a rotatable prismatic input coupling element, preferably a cylinder, may also be referred to as a "roller" within the meaning of the present invention.

[0078] Preferably, the input coupling element may be formed from optical plastic or optical glass, wherein in a preferred embodiment the preferred materials mentioned above in connection with the substrate body of the master element may be used.

[0079] Preferably, the surface of the input coupling element comprises glass, PC, TAC or PMMA. In the case of a multilayer input coupling element, the material of the surface may be in the form of a film or sheet. However, the material of the surface may also be the material of the integral input coupling element and have, for example, a parallelepiped shape or a cylindrical shape.

[0080] In a preferred embodiment of the invention, the surface of the input coupling element comprises an anti-reflection coating. This can largely eliminate reflection losses at the surface of the input coupling element.

[0081] The input coupling element can be arranged in different alignments relative to the master element, wherein the photosensitive composite web is preferably positioned between the input coupling element and the master element during exposure. If a parallelepiped input coupling element and a master element having a top surface, a bottom surface and side surfaces are used, the input coupling element can be arranged, for example, above the master element. In this case, it can be preferred that the composite web is directed between the top side of the master element and the bottom side of the input coupling element. The reference beam can be directed obliquely downward to the side of the input coupling element that is present as a block or parallelepiped above the master element. The reference beam is refracted by the input coupling element, and the refracted reference beam reaches the master hologram through the composite web. For example, the refraction caused by the input coupling element can be used to obtain the required acute angle of incidence for a side-lit hologram. The master hologram can reflect and refract the reference beam so that the object beam passes from the master hologram through the composite web. The object beam and the reference beam interfere in the photosensitive material of the composite web to produce a reflection hologram. By providing optical adhesive films on both sides of the composite web, optical loss or unfavorable reflection at the interface can be effectively avoided.

[0082] In a preferred embodiment of the invention, an optical adhesive film and / or a photosensitive composite web is applied to the surface of the master element and / or to the surface of the in-coupling element by lamination.

[0083] Within the meaning of the present invention, "lamination" is preferably a method for connecting two components, wherein the connection is preferably non-permanent. One of the two components preferably comprises a rigid flat surface and is preferably firmly attached. The other of the two components is preferably flexible and can travel during the lamination process. Lamination is preferably configured so that the photosensitive composite web and / or the optical adhesive film covers the rigid surface of the preferably entire master element and / or the input coupling element in such a way that there are no gaps, bubbles or wrinkles. Optionally, the lamination is implemented by a lamination roller, which is preferably capable of applying pressure. Lamination can be implemented at room temperature (20°C). Optionally, the lamination roller can also be heated to a lamination temperature above room temperature, for example a temperature selected from the range of 20°C-200°C, preferably 40°C-100°C. Lamination (eg lamination pressure or lamination temperature) is preferably designed such that a gap-free but separable (temporary) connection is established between the photosensitive composite web and / or optical adhesive film and the relevant surfaces (eg of the master element and / or input coupling element).

[0084] In a preferred embodiment of the invention, the optical adhesive film and / or the photosensitive composite web is applied to the surface of the master element and / or the surface of the input coupling element by contacting the advancing photosensitive composite web with a partial circle of a curved surface. Preferably, the curved surface is a portion of a lateral face of a rotatable cylinder, wherein the partial circle preferably has an aperture angle between 1° and 45°, more preferably between 2° and 20°. Preferably, the photosensitive composite web and / or the optical adhesive film temporarily adopts the shape of the lateral face during exposure.

[0085] In a preferred embodiment of the invention, the method comprises a step of separating the optical adhesive film from the master element, the input coupling element and / or the photosensitive composite web. Preferably, the separation is carried out continuously or intermittently. In the case of a roll-to-roll method, the optical adhesive film can be continuously moved through the device in synchronization with the composite web. In contrast, if the composite web remains fixed for each exposure step and moves only after the master hologram is fully exposed (for example, if the master element is a sheet instead of a roller), the optical adhesive film is preferably also kept fixed during the exposure step and separated after the master hologram is fully exposed. In a preferred embodiment of the invention, the refractive index difference between the surface of the master element and the optical adhesive film and / or between the optical adhesive film and the surface of the photosensitive composite web is not greater than 0.2, preferably not greater than 0.1, more preferably not greater than 0.05.

[0086] By setting the refractive index of the optical adhesive film so that it is the same as or very close to the refractive index of the adjacent process component, excellent optical contact can be obtained without internal reflections at the interface. This can improve the quality of the reconstructed hologram because losses and optical interference are minimized.

[0087] Likewise, where an optical adhesive film is introduced between the photosensitive composite web and the input coupling element, the difference between the refractive index of the optical adhesive film and the refractive index of the adjacent surface of the input coupling element is preferably no greater than 0.2, more preferably no greater than 0.1, more preferably no greater than 0.05.

[0088] In another preferred embodiment of the invention, the refractive index of the optical adhesive film is between the refractive index of the surface of the master element and the refractive index of the surface of the photosensitive composite web. If the optical adhesive film is arranged between the photosensitive composite web and the input coupling element, the refractive index of the optical adhesive film is preferably between the refractive index of the photosensitive composite web and the refractive index of the input coupling element. In this context, the term "between" preferably also includes the refractive index value of the adjacent process components themselves. This arrangement allows a smooth or interference-free transition of the light beam between different process components with minimal reflections and / or aberrations at the interface.

[0089] As an illustrative example, the refractive index may be selected, for example, as described below, using the substrate body of the master element as a starting point.

[0090] -Base body (made of N-BK7): n e =1.519

[0091] - Adhesive layer: n e =1.51

[0092] -Master hologram (photopolymer layer): n e =1.500

[0093] -Master hologram (protective film): n e =1.485

[0094] -Optical adhesive film (adhesive layer / carrier layer / adhesive layer): n e =1.47 / 1.485 / 1.47

[0095] - Composite web (carrier film / photopolymer layer / carrier film) e =1.48 / 1.50 / 1.48

[0096] In the above example, the photosensitive composite web may, for example, include a carrier film made of triacetate (TAC) having a refractive index of 1.48. The refractive indices specified in this document are measured according to ISO 489, unless otherwise stated.

[0097] If the photosensitive composite web comprises a photopolymer and one or more TAC carrier films, the optical adhesive film preferably has a refractive index of 1.48 + / - 0.2, preferably + / - 0.1, more preferably + / - 0.05, so that the above values ​​allow particularly smooth optical transitions.

[0098] For example, if the photosensitive composite web comprises a photopolymer and a PC carrier film, the optical adhesive film may preferably have a refractive index of 1.58+ / -0.2, preferably + / -0.1, more preferably + / -0.05, so that a particularly smooth optical transition is also ensured.

[0099] In another example in which the photosensitive composite web includes a PC carrier film and is in contact with an optical adhesive film, which in turn is in contact with a TAC protective layer of a master element, it is also preferred that the refractive index of the optical adhesive film is between the refractive index of PC and the refractive index of TAC, that is, the optical adhesive film preferably has a refractive index between 1.48 and 1.58.

[0100] The skilled person knows materials that allow a refractive index transition that is as continuous as possible between the adjacent surfaces of the master element / input coupling element and the photosensitive composite web using the present teaching as a starting point. For example, as an alternative, the substrate body may comprise Borofloat-33, which has a refractive index of 1.48. The materials of the further layers may be selected so as to match this refractive index. In general, a corresponding refractive index of between 1.4 and 1.6 is preferred for all the above-mentioned components (substrate body to optical adhesive film).

[0101] In a preferred embodiment of the invention, the photosensitive composite web comprises a carrier film and a photosensitive material, wherein the photosensitive material is present as a layer on the carrier film. Preferably, one side of the photosensitive material remains uncovered. In a preferred embodiment, the photosensitive material is soft and / or deformable, especially in the form of a liquid or resin. Thus, the photosensitive material can be adhered to a solid surface and optionally deformed, for example for replicating a surface relief pattern.

[0102] Preferably, the uncovered side of the photosensitive material is brought into contact with the surface of the master element during exposure. Preferably, no optical adhesive film is inserted between the photosensitive material and the master element. Instead, the optical adhesive film can be introduced between the side of the carrier film facing away from the master element and the input coupling element. By bringing the photosensitive material into contact with the surface of the master element, the physical deformability of the photosensitive material can be utilized so as to obtain a gapless contact with the surface of the master element. For example, the photosensitive composite web can be pressed onto the surface of the master element in order to eliminate air gaps. In an alternative or in addition thereto, the photosensitive material can have adhesive properties similar to those of the optical adhesive film. This can suppress unfavorable reflections at the interface between the photosensitive material and the master element. If the master element includes surface reliefs, this arrangement can have additional advantages, which surface reliefs can be transferred into the photosensitive composite web due to contact. Optionally, a further layer (e.g. a second carrier film or a protective coating) can then be applied to the exposed, preferably cured photosensitive material in order to enclose the photosensitive material.

[0103] In another preferred embodiment of the present invention, the optical adhesive film comprises at least one adhesive layer. The at least one adhesive layer preferably has a peeling force of less than 3 N / cm (Newtons per centimeter), preferably less than 1 N / cm, relative to the surface of the master element and / or the surface of the input coupling element and / or the surface of the photosensitive composite web. However, in a preferred embodiment, the peeling force of the adhesive layer of the optical adhesive film relative to the surface of the master element and / or the surface of the input coupling element and / or the surface of the photosensitive composite web is at least 0.01 N / cm, preferably at least 0.1 N / cm. It has been found that the above parameters of the peeling force represent the optimal conditions between the simple and residue-free removal of the optical adhesive film from the corresponding component and the simultaneous elimination of the optical interface between the components. Moreover, it has been established that these peeling forces fully suppress relative movement between the components, such as vibration. Although transparent prior art adhesives can help improve the quality of hologram reconstruction, the optical adhesive film of the present invention improves the quality of replication. This is because the viscosity of the adhesive is large enough to reduce the optical losses at the interface between the components; however, it can also be removed so that the composite web can be moved from the master element to another process station.

[0104] Preferably, the material and configuration of the adhesive layer have been selected so that the adhesive layer adheres to the material of the composite web, the material of the master element and / or the material of the input coupling element and is not repelled therefrom, the material of the adhesive layer being brought into contact with these materials. Thus, preferably, the adhesive layer adheres to all transparent polymers and glass, in particular to the above-mentioned preferred materials for the master element, the input coupling element or the composite web. In addition or in the alternative, the adhesive layer is preferably adhered to a solid and / or resinous photosensitive material, particularly preferably a photopolymer. In particular, the optical adhesive film is not used to facilitate the separation of the composite web from the corresponding process part; instead, the optical adhesive film is used to improve the optical contact. This may also include additional improvements in mechanical or electrostatic contact.

[0105] For example, the peel force of an optical adhesive film or one of its layers can be measured according to a 180 degree peel test. In a preferred embodiment, the measurement is performed according to ASTM D903, wherein a six inch adhesive tape is applied to a clean substrate surface. The substrate is clamped. The free end of the adhesive tape is folded back 180 degrees and pulled with a dynamometer. The force (in Newtons) required to separate each centimeter of the adhesive tape from the substrate corresponds to the peel force.

[0106] The peel force of the adhesive material relative to the substrate surface preferably depends not only on the material composition of the adhesive material and the material composition of the substrate, but also on the process conditions under which the adhesive material is applied to its carrier (if any) and to the substrate surface. For example, in the case of a pressure-sensitive adhesive material, a stronger bond to the carrier layer can be obtained if high pressure, temperature and / or additional crosslinking of the adhesive material on the carrier layer is applied during application to the carrier layer. Preferably, an additional adhesion promoter layer can be introduced in order to specifically increase the adhesion of the adhesive material on the carrier layer. This effect can be exploited in order to first improve the integrity of the multilayer optical adhesive film and at the same time keep the peel force of the multilayer adhesive film low relative to process components such as composite webs, input coupling elements or master elements.

[0107] Compared to the OCA used in the finished product of the prior art to produce permanent adhesion, the preferred peel force is low. This means that although the optical adhesive film is fully adhered to ensure optical contact during exposure, the optical adhesive film can be easily removed at the same time without tearing or leaving residues on the composite web or adjacent process parts. Moreover, the optical adhesive film can advantageously be provided in a very thin form. No large mechanical strength is required to prevent damage or tearing during separation from the corresponding surface. Moreover, the relatively low adhesion or peel force of the optical adhesive film facilitates the reuse of the optical adhesive film, for example by providing a ring as explained above.

[0108] In another preferred embodiment of the present invention, the optical adhesive film comprises at least one adhesive layer, wherein the Young's modulus of at least one adhesive layer is at most 50 MPa. For example, the Young's modulus can be determined by testing according to DIN EN ISO 725, ASTM D5026 and / or ASTM D882 or DIN EN 15870. That is, the optical adhesive film preferably has a certain degree of elasticity. This is particularly useful for winding the optical adhesive film on the surface of a conveying roller and an optical component used therewith. Due to the method, an optical adhesive film with sufficient elasticity is not easily stuck, damaged and / or torn during conveying. Moreover, plastic deformation can be avoided, which may cause irregularities in the optical contact.

[0109] Preferably, the adhesive layer has a transmittance of at least 80%, wherein the transmittance is preferably measured without Fresnel correction. Preferably, this means that the measured transmittance reduces the absolute value of the two Fresnel reflections at the front and rear sides of the material. The transmittance without Fresnel reflection is preferably about 8% higher than the uncorrected method. Alternatively, the transmittance measurement can be implemented with p-polarized light at the Brewster angle, because there is no interface reflection at the p-polarized light at the Brewster angle. Preferably, the transmittance relates to the transmittance of the medium to the light wave without changing the wavelength. The transmittance percentage is preferably the percentage of the intensity of the transmitted light compared to the light incident on the medium. For example, the transmittance can be measured according to DIN EN ISO13468. Therefore, the adhesive layer is preferably transparent to light within the 400nm-780nm wavelength spectrum and has minimal light scattering. The adhesive layer is preferably colorless. However, a yellow tint or a gray appearance is also permissible. This adhesive layer can be used for a variety of applications, and should therefore be preferred over a color filter adhesive layer of red, blue, green, etc.

[0110] Preferably, the adhesive layer has a haze of up to 2%. It is desirable to minimize the degree of haze. This results in less loss of light for exposure and less undesirable reflections.

[0111] Within the meaning of the present invention, the term "haze" preferably relates to the transmission haze measured according to ASTM D1003. Haze preferably denotes the scattering of light during its passage through a transparent material, which may lead to the generation of additional disturbing interference fields and thus additional but unfavorable micro-optical structures in the replicated hologram. Haze may be an intrinsic property of the material, a result of the forming process, a result of the surface structure, or a result of environmental factors such as surface abrasion.

[0112] Preferably, the adhesive layer has a brightness variation of up to 20% across its width between crossed polarisers. This reduces optical losses caused by the adhesive layer and improves the quality of the replicated hologram.

[0113] Preferably, the adhesive layer also comprises an adhesive material based on acryl, EVOH, rubber, silicone or a mixture thereof. Advantageously, in particular, preferably low peel forces, high transparency, sufficient elasticity and mechanical strength can be achieved by such materials. Moreover, the shape of these materials can be easily set to an adhesive film with a suitable thickness. Methods for producing adhesive materials based on the above materials are known to those skilled in the art. Such methods are described in the professional literature, for example in Georg Krüger's " selbstklebende Folien und Etiketten”, ISBN3446422811.

[0114] Preferably, the adhesive material comprises at least one polymerizable resin, wherein the polymerizable resin is preferably based on acryl, EVOH, rubber, silicone or a mixture thereof, and at least one polymerizing agent. The polymerizing agent is preferably selected so that it triggers the polymerization of the monomers present in the polymerizable resin. The polymerizing agent preferably comprises a crosslinking agent and / or a crosslinking catalyst. An example of a first type of monomer present in a polymerizable resin (e.g., an acrylic resin) and polymerizable by a polymerizing agent is a (meth) acrylate monomer. The polymerizable resin may also comprise a second type of monomer containing a crosslinkable functional group capable of reacting with the first type of monomer. Examples of such crosslinkable functional groups include hydroxyl, carboxyl, glycidyl, isocyanate or nitrogen-containing functional groups, etc. Preferably, the crosslinking agent and / or the crosslinking catalyst are selected with respect to the crosslinkable functional groups present in the polymerizable resin.

[0115] The adhesion of the composition can be adjusted by adding a suitable cross-linking agent in a suitable amount. Those skilled in the art are aware of suitable components and methods for producing adhesive materials having preferred optical and mechanical properties.

[0116] In a preferred embodiment, the adhesive layer has a thickness of 50 μm to 250 μm. The thickness can be adapted according to the desired properties of the optical adhesive film. In the case of smaller thicknesses, for example, the transparency of the optical adhesive film can be increased, while greater thicknesses can ensure improved compensation of possible inhomogeneities of the surfaces to be bonded and ensure increased mechanical strength. The above parameter range has been found to be particularly advantageous for a variety of applications.

[0117] In a preferred embodiment, the adhesive material includes a crosslinking agent. Advantageously, the peel force required to separate the optical adhesive film from the relevant surface can be reduced by the crosslinking agent. The crosslinking agent also advantageously prevents adhesive residue from being left on these surfaces. A small amount of crosslinking agent in the adhesive composition can increase the adhesive ability of the adhesive up to a certain concentration. Above this threshold concentration, such as 0.2%, the increase of crosslinking agent can reduce the adhesion. The proportion of crosslinking agent used can therefore advantageously adjust the adhesive properties of the adhesive material.

[0118] "Crosslinks" are preferably bonds or short sequences of bonds that link polymers to each other. These connections can be in the form of covalent bonds or ionic bonds, and the polymers can be synthetic polymers or natural polymers (such as proteins). "Crosslinkers" are preferably additives that promote the formation of such crosslinks between polymers present in the adhesive material.

[0119] Examples of the crosslinking agent include an isocyanate crosslinking agent, an epoxy crosslinking agent, an aziridine crosslinking agent, a metal chelate crosslinking agent, or a modified silane such as aminobissilane. As an example, a silane compound may be used as a crosslinking agent for an acrylic resin.

[0120] Preferably, the crosslinker is present in the adhesive material in a concentration of at least 0.1% by weight, preferably at least 0.2% by weight, particularly preferably 0.2% to 0.9% by weight. For the above concentrations, preferred peel forces of the optical adhesive film in the preferred range of 0.3 N / cm to 1.6 N / cm can be achieved on different surfaces. These preferred crosslinker concentrations are particularly advantageous for acrylate-based crosslinkers. However, the preferred concentration of the crosslinker may depend on its crosslinking activity, the base material or the surface, as will be explained in detail below in this document.

[0121] In another preferred embodiment of the present invention, the optical adhesive film has a single-layer structure, wherein the layer structure includes exactly one adhesive layer. Exactly one adhesive layer is preferably adhesive on both sides to achieve optical contact. In this way, the optical adhesive film can be kept particularly thin and possible optical interfaces within the optical adhesive film can be avoided. In the case of a single-layer structure, the optical adhesive film preferably has a tensile strength of at least 1MPa, more preferably at least 2MPa. Preferably, the tensile strength is determined by a test method according to ASTM D882 or DIN EN ISO 725. On the one hand, such an optical adhesive film can remain very thin and transparent, while on the other hand, such an optical adhesive film has sufficient strength for different processes (such as conveying, applying and / or laminating) and can be removed without residue and risk of damage. In another preferred embodiment of the present invention, the optical adhesive film includes at least one carrier layer. Such an optical adhesive film has a multilayer structure, wherein the carrier layer is coated with an adhesive layer at least on one side. The carrier layer is preferably not sticky. In some embodiments, the carrier layer can be coated with an adhesive layer only on one side.

[0122] In another preferred embodiment of the present invention, the optical adhesive film comprises two adhesive layers, wherein each adhesive layer is preferably present in a manner directly applied to the carrier layer. It is particularly preferred that the carrier layer is coated with adhesive layers on both sides, so that the optical adhesive film comprises three layers. Such an optical adhesive film can be adhered to two surfaces at the same time, thereby achieving particularly good optical contact and reducing the risk of air gaps or even adverse reflections. In the case of a multilayer (e.g. two-layer and / or three-layer) optical adhesive film, preferably one or all adhesive layers have a tensile strength of at least 1 MPa, preferably up to 2 MPa. This ensures sufficient force transmission and therefore shear forces within the multilayer structure do not lead to relative movement between the layers.

[0123] In another preferred embodiment of the invention, the at least one adhesive layer is present in a manner applied directly to the carrier layer. Preferably, the peeling force of the adhesive layer relative to the carrier layer is greater than the peeling force of the adhesive layer relative to the surface of the master element and / or the surface of the input coupling element and / or the surface of the photosensitive composite web and / or the surface of the protective film. This ensures that the adhesive layer remains adhered to the carrier layer during the entire process and this avoids adhesive residues being left on the process parts.

[0124] The different peeling forces of the adhesive layer relative to the surface of the carrier layer of the adhesive film or of a process component (e.g. a master element, an input coupling element and / or a composite web) can preferably be influenced by the choice of material and / or the process conditions under which the adhesive layer can be applied to the carrier layer. In a preferred embodiment, the carrier layer is prepared by applying an adhesion promoter (primer) to the side to which the adhesive layer is applied. In this way, the adhesive material can be applied to the carrier film and, in addition to the crosslinking of the adhesive material, a bond to the primer layer of the carrier film can also be established. As a result, the adhesive layer adheres more firmly to the carrier layer than a material laminated to the adhesive layer after crosslinking, even if the latter material consists of the same material as the carrier film.

[0125] In another preferred embodiment of the present invention, the surface of the carrier film intended to be coated with the adhesive layer is treated before coating, for example, by plasma treatment or corona treatment. Advantageously, such surface treatment can also increase the adhesion between the carrier film and the adhesive layer.

[0126] In a further preferred embodiment of the invention, the process conditions for applying the adhesive layer to the carrier layer are selected such that the adhesion of the adhesive layer to the carrier layer is increased. Preferably, the temporary application of the optical adhesive film to the surface of the master element or the input coupling element is carried out under different process conditions, which allows for lower peel forces from the surface of the process part. In this way, the influence of process conditions (such as pressure, temperature and light) can be used to maintain the integrity of the multilayer optical adhesive film during its use.

[0127] Preferably, the carrier layer has a tensile strength of at least 5 MPa. Such a carrier layer is particularly suitable as a stabilizer for the optical adhesive film and can be pulled with greater forces or exposed to greater frictional forces without tearing. By means of such a carrier layer in a multilayer structure, the tear resistance and thus the process capability of the optical adhesive film as a web can be reliably increased, thereby significantly minimizing the risk of leaving residues on the relevant surface. This allows particularly reliable elimination of air gaps at the interface between the relevant surface and the optical adhesive film and improved optical contact.

[0128] Preferably, the carrier layer has a transmittance of at least 80% in a manner similar to the at least one adhesive layer, wherein the transmittance is preferably measured without Fresnel correction. The optical adhesive film may be transparent to light, in particular light in the wavelength range of 400 nm to 780 nm, and may exhibit minimal light scattering. It may also be preferred that the carrier layer has a haze of up to 1.5% in order to reduce light losses and desired reflections. In particular, it is preferred that the carrier layer has a brightness variation of up to 30% over the width of the carrier layer between crossed polarizers in order to reduce optical losses caused by the carrier layer.

[0129] Preferably, the carrier layer 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, polyvinyl chloride, polyvinyl butyral, polydicyclopentadiene or a mixture thereof. Particularly preferably, the carrier layer comprises polycarbonate (PC), polyethylene terephthalate (PET), cellulose acetate, cellulose triacetate (TAC), polymethyl methacrylate or a mixture thereof.

[0130] The thickness of the carrier layer is preferably 6 μm to 100 μm. It has been established that for a variety of materials, a thickness of at least 6 μm can provide a preferred tensile strength of at least 5 MPa while being highly transparent. The use of a thinner carrier layer also ensures an overall thinner optical adhesive film. In contrast, the carrier film is even more tear-resistant at a greater thickness. In addition, particularly high transmittance and low haze can be ensured up to a thickness of about 100 μm. Therefore, the above parameter range has been found to be particularly advantageous for a variety of applications.

[0131] In another preferred embodiment of the present invention, the optical adhesive film is provided with at least one protective film. Preferably, at least one protective film is removed before the step of temporarily applying the optical adhesive film between the photosensitive composite web and the surface of the master element. The protective film can protect the surface quality of the optical adhesive layer and maintain the smoothness and low haze of the optical adhesive layer. Moreover, the protective film protects the adhesive layer from particles that may be present during the replication process and allows the optical adhesive film to be supplied in the form of a roll. The protective film can also facilitate the handling of the optical adhesive layer, especially during winding, unwinding and transportation.

[0132] Preferably, the protective film 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, polyvinyl chloride, polyvinyl butyral, polydicyclopentadiene, silica gel paper or a mixture thereof. Particularly preferably, the protective film comprises polyethylene, polypropylene, silica gel paper or a mixture thereof. The thickness of the protective film is preferably 10 μm to 50 μm.

[0133] In another preferred embodiment of the present invention, at least one protective film is directly present on at least one adhesive layer. Preferably, the peeling force required to remove the protective film from the adhesive layer is no greater than 0.2 N / cm, particularly preferably no greater than 0.1 N / cm.

[0134] In another preferred embodiment of the invention, the optical adhesive film is provided with protective films on both sides. It may be preferred to remove only one or both protective films before exposure. For example, it may be preferred to remove the protective film from the side facing the master element and / or the input coupling element.

[0135] It is preferred to remove the protective film from both sides of the optical adhesive film so that the adhesive properties of the optical adhesive film can help improve the optical contact of its two interfaces with adjacent process components. This improves the optical contact between the photosensitive composite web and the input coupling element and / or the master element.

[0136] In another preferred embodiment of the invention, the optical adhesive film is temporarily applied between the photosensitive composite web and the surface of the master element or the surface of the input coupling element by means of at least one roller. Wherein, at least one roller is preferably selected from the group comprising: an unwinding roller, a conveying roller, a rewinding roller and / or a laminating roller. For example, the optical adhesive film can circulate between two conveying rollers, which are arranged so that the path of the optical adhesive film comes into contact with the surface of the master element. In an alternative, the optical adhesive film can travel between an unwinding roller and a rewinding roller so that its path comes into contact with the surface of the master element.

[0137] In the case of a rotatable master element, the master element can be brought into the path of the optical adhesive film between the unwinding roller and the rewinding roller such that the optical adhesive film contacts a portion of the surface of the master element. In this case, the optical adhesive film (and the composite web) preferably temporarily adopts the shape of a region of the lateral face of the master element. In the process, the optical adhesive film is preferably guided on the rotating master element and the speeds of the optical adhesive film, the composite web and the master element are preferably synchronized with each other. This arrangement is particularly advantageous within the scope of a roll-to-roll hologram replication method, wherein the rotation speeds of different rollers can be set. This method is fast, economical and preferably suitable for continuous mass production of HOEs.

[0138] In the case of a fixed parallelepiped master element, the laminating roller can roll over the stretched optical adhesive film and, for example, bring the optical adhesive film into contact with the flat top side of the master element. Appropriate application of pressure allows the air gaps to be removed and a particularly gap-free application to be obtained.

[0139] In another preferred embodiment of the invention, during the exposure step, an optical adhesive film is introduced between the photosensitive composite web and the surface of the master element by means of an input coupling element. Preferably, during the exposure process, a second optical adhesive film is introduced between the photosensitive composite web and the input coupling element, for example Figure 5 , Figure 6 and Figure 8 as shown in .

[0140] In a further preferred embodiment of the invention, the surface of the master element and / or the surface of the input coupling element is curved, wherein preferably the master element and / or the input coupling element are configured as an axially rotatable cylinder or roller.

[0141] If the surface of the master element and / or the input coupling element is curved, like in the case of a cylinder, the optical adhesive film is preferably temporarily adhered to the surface of the master element over a relatively short length, for example to the lateral surface of the cylindrical master element and / or the input coupling element. Preferably, the optical adhesive film is temporarily adhered over a length between 1 mm and 20 mm, particularly preferably between 2 mm and 10 mm. The length can depend on the radius of the cross section of the cylinder. The adhesive optical contact area between the optical adhesive film and the master element and / or the input coupling element can also be measured in the form of the aperture angle of the cross section of the cylinder, over the arc length of which the optical adhesive film is applied. Preferably, the angle is between 1° and 45°, more preferably between 2° and 20°. With such a length and / or aperture angle, the risk of tearing of the optical adhesive film is significantly reduced, and air gaps are fully eliminated. The force required to move the optical adhesive film by continuous displacement (including continuous separation of the adhesive film from the curved surface) is particularly small.

[0142] In another preferred embodiment of the present invention, the steps of the method are controlled by a control unit. Preferably, the control unit controls the conveying speeds of the optical adhesive film and the photosensitive composite web so that these optical adhesive film and the photosensitive composite web are synchronized with each other during exposure.

[0143] Preferably, the term "control unit" relates to any desired computer unit with a processor, processor chip, microprocessor or microcontroller which allows automatic control of components of the device, such as unwinding rollers, rewinding rollers, laminating rollers, rotation speed of the conveyor rollers, movement / rotation of the master element, movement / rotation of the input coupling element, lamination temperature, lamination pressure, orientation and / or scanning speed of the light source, wavelength of the light source, fixing intensity, etc. The components of the control unit may be configured conventionally or may be configured individually for the respective embodiment. Preferably, the control unit comprises a processor, a memory and a computer code (software / firmware) for controlling the components of the device.

[0144] 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 identity or type of the motherboard element), and other related sensor-based information. The control unit preferably further includes a computer-usable or computer-readable medium, such as a hard disk, random access memory (RAM), read-only memory (ROM), flash memory, etc., on which computer software or code is installed. The computer code or software for controlling the components of the device 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.

[0145] The phrase "the control unit is configured to" perform specific method steps, for example, exposing the master element at a specific angle by varying the speed of one or more drive motors, may include customer-specific software or standard software installed on the control unit and initiating and controlling these operating steps.

[0146] The exposure of the master hologram for replication by the method according to the invention can be carried out based on different techniques.Hologram replication methods can be divided into relief holograms and volume holograms.

[0147] 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.

[0148] The volume hologram is preferably written into the sensitive layer by interference of two light beams, a so-called reference beam and an object beam. Preferably, the volume hologram is written into a composite web. Preferably, this can be implemented by transmission or reflection techniques. 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 beams, wherein the Bragg conditions apply in the case of reconstruction at the volume hologram. It is for this reason that the volume hologram has wavelength and / or angle selectivity. The ability of a volume hologram to store multiple images simultaneously allows in particular the generation of color holograms or white holograms. Light sources emitting the three primary colors of blue, green and red can be used to record the hologram. Preferably, the three light beams illuminate a portion of the composite web simultaneously. 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 fragments can be superimposed to form a faithful color image.

[0149] A reflection hologram is a reflection hologram that reflects light incident from a light source and thus works like a mirror. The directions of incidence of the reference beam (preferably the beam incident from the light source) and the object (in this case the master hologram) are preferably arranged on opposite sides of the composite web. The reference beam passes through the composite web and is then reflected by the master hologram back into the photosensitive layer of the composite web. Thus, the reference beam and the object beam are superimposed in the photosensitive layer of the composite web in different beam directions in order to produce a replicated hologram. Preferably, the master hologram can be applied to the surface of the master element or be present in a manner integrated in the substrate body.

[0150] The light source used to expose the reflection hologram can be arranged so that the reference beam is incident on the composite web in a desired direction, preferably in a direction required in a subsequent reconstruction process. In a preferred embodiment, the light source is oriented relative to the master element in such a way that the composite web is located between the light source and the master element. For example, the light source can be aligned above the master element in such a way that the reference beam is incident on the composite web downwardly in a predetermined direction. The angle at which the reference beam is incident on the master hologram can be set by a transparent input coupling element that diffracts the light at the desired angle. Preferably, at least a portion of the reference beam is reflected by the master element back into the composite web as an object beam. Therefore, the reference beam and the object beam enter the photopolymer composite from opposite sides and interfere in the photosensitive layer of the photopolymer composite in order to replicate the hologram.

[0151] A transmission hologram is a transmissive hologram in which light from a light source passes through the transmission hologram and is diffracted by it. The incident directions of the reference beam (preferably the incident beam from the light source) and the object (in this case the master hologram) can preferably be present in such a way that they are arranged on the same side of the composite web. The incident beam passes through the master hologram and is split into (undiffracted) reference beam and object beam. The reference beam and the object beam are thus superimposed in the photosensitive layer of the composite web with the same beam direction in order to produce a replicated hologram.

[0152] In a transmission hologram, it may be preferred to arrange the light source so that the composite web can be exposed from the same side by the reference beam and the object beam. Preferably, the light source is oriented relative to the master element so that the light beam first passes through the master element and the master hologram and then reaches the composite web. Preferably, the light source can be arranged so that the light passes through the transparent master element from the side. Preferably, the light source can also be arranged so that the light is incident on the composite web through the upper surface and / or the lower surface of the master element. Preferably, the incident light beam is refracted by the master element so that a reference beam and an object beam are generated, wherein the object beam preferably corresponds to the component of the light diffracted by the master hologram. Preferably, the object beam interferes with the undiffracted reference beam in the composite web so as to replicate the hologram.

[0153] In a preferred embodiment of the invention, one or more master elements may be used to expose a composite web so as to replicate a transmission hologram therein. Preferably, the replicated transmission hologram may be designed so that it is side-lit, and thus the holographic image representation may be reconstructed by light from a substantially lateral direction. The replicated transmission hologram may also be configured so that it is illuminated from behind, and thus the holographic image representation may be reconstructed by light incident in a substantially back-to-front manner. It may also be preferred to use one or more master elements to expose a composite web and replicate a reflection hologram therein. It may also be desirable that the replicated reflection hologram is side-lit. For example, such a hologram may be used in a glass sheet, with the light source being arranged at the edge of the glass sheet in a hidden manner. The replicated reflection hologram may also be configured so that it is illuminated from the front. Advantageously, such a hologram may produce a holographic image representation when illuminated by ambient light and viewed relatively orthogonally at eye height. A plurality of such holograms may also be used in a glass sheet, for example in a manner as disclosed in WO 2020157312A1, to produce a holographic image representation when viewed orthogonally by reflection of light from a hidden light source along a predetermined path. It may also be advantageous to use one or more master elements to expose the composite web in order to produce a hologram comprising both a reflection hologram and a transmission hologram.

[0154] These process components can be arranged in different ways in order to produce high-quality reflection holograms and transmission holograms as required. Therefore, the optical adhesive film is universal. Different techniques for exposing composite webs and master elements and optionally input coupling elements using different reference beam angles and for producing different types of holograms are explained below by way of example and in a detailed description based on the drawings. These techniques can be combined with each other and with further embodiments of the method. An important advantage is that in different settings for replicating holograms, the optical adhesive film according to the invention ensures almost perfect optical contact between the composite web and optical components (such as master elements and / or input coupling elements).

[0155] In a preferred embodiment of the invention, an optical adhesive film is introduced between a portion of the lateral face of the cylindrical master element and the photosensitive composite web. It may be preferred that no input coupling element is used during exposure. In a preferred embodiment, a cylindrical input coupling element is used in combination with a cylindrical master element in a roll-to-roll method for exposure. Preferably, the master element and the input coupling element are mounted in a rotatable manner, wherein their rotation is preferably synchronized. The optical adhesive film and the photosensitive composite web may act synchronously between the master element and the input coupling element. It is further preferred that a second optical adhesive film is introduced between the photosensitive composite web and the input coupling element, so that an arrangement is formed by the following: cylindrical input coupling element / second optical adhesive film / photosensitive composite web / first optical adhesive film / cylindrical master element. This arrangement may be exposed from the lateral face or base of the input coupling element so that the reference beam is refracted toward the master hologram. For example, this exposure method may be suitable for producing a reflection hologram. In an alternative, the exposure may also be implemented from the lateral face or base of the master element, for example, in order to produce a transmission hologram. By configuring both the master element and the input coupling element as rotatable cylinders or rollers, the exposure method can be carried out quickly and continuously.

[0156] In another preferred embodiment of the invention, a master element is used during exposure but no input coupling element is used, wherein the master element has a flat surface and is preferably in the form of a parallelepiped or a sheet. Preferably, the optical adhesive film is applied to the flat surface of the master element, for example by lamination using a laminating roller. Preferably, the photosensitive composite web is applied to the optical adhesive film, for example by lamination with the aid of the same or another laminating roller. Lamination ensures good optical contact between the photosensitive composite web and the surface of the master element. This arrangement can provide a larger contact area compared to an arc-shaped contact by a circular segment of a cylindrical master element. Therefore, this arrangement can be advantageous for producing, for example, batches in which a plurality of holograms are replicated by a sheet-like master element.

[0157] In another preferred embodiment of the invention, a master element and an input coupling element are used simultaneously during exposure, wherein preferably only one of the master element and the input coupling element is cylindrical. The non-cylindrical component may preferably have a flat surface and be in the form of a parallelepiped or a sheet, for example. In such an embodiment, the cylindrical component may be used to laminate the optical adhesive film and / or the photosensitive composite web onto the flat surface of the master element or of the input coupling element.

[0158] As a simple example, the master element may have the shape of a parallelepiped. A first optical adhesive film may be applied to the upper flat surface of the master element, preferably by lamination. A photosensitive composite web may be applied to the top side of the first optical adhesive film, preferably also by lamination. Further, a second optical adhesive film may be applied to the top side of the photosensitive composite web, preferably by lamination. A cylindrical input coupling element, preferably for laminating one or more of the above-mentioned layers, is arranged above the second optical adhesive film, so that optical contact is established between the lateral faces of the input coupling element and all the above-mentioned process components up to and including the master element.

[0159] For example, the exposure can be carried out by directing the reference beam to a lateral face or base of the input coupling element. In this case, the reference beam is refracted inside the input coupling element so that the reference beam exits along the optical contact line and is reflected by the master hologram in the master element. In an alternative, the exposure can also be carried out from the master element, wherein the light is then directed through the input coupling element away from the composite web. In another example, the functions of the parallelepiped component and the cylindrical component can be interchanged, i.e., the input coupling element can be a parallelepiped, while the master element is shaped as a cylinder.

[0160] In another preferred embodiment of the invention, a master element and an input coupling element are used simultaneously during exposure, wherein, preferably, both the master element and the input coupling element have a flat surface and are preferably present in the form of a parallelepiped, a block, a sheet or a pyramid. In a preferred embodiment of the invention, the exposure process is performed using a block-shaped master element, a first optical adhesive film, a photosensitive composite web, a second optical adhesive film and a block-shaped input coupling element that are in optical contact with each other in a specified order. The input coupling element is preferably also in optical contact with the master element via an intermediate layer (first optical adhesive film, photosensitive composite web, second optical adhesive film). Preferably, the intermediate layer is applied to the respective surface of the master element or the input coupling element by lamination (for example with the aid of a separate lamination roller). DETAILED DESCRIPTION

[0161] In the following, the invention will be explained in more detail with the aid of examples and drawings, but without being restricted thereto. BRIEF DESCRIPTION OF THE DRAWINGS

[0162] Figure 1 is a schematic diagram of a single-layer optical adhesive film with protective films on both sides.

[0163] Figure 2 is a schematic diagram of a three-layer optical adhesive film, including a carrier layer and two adhesive layers, with protective films disposed on both sides.

[0164] Figure 3 The peel forces of preferred adhesive layers having different crosslinker concentrations for different surface materials are shown by way of example.

[0165] Figure 4 A preferred arrangement for replicating a hologram is schematically shown, wherein an optical adhesive film is introduced between a cylindrical master element and a photosensitive composite web.

[0166] Figure 5 A preferred arrangement for replicating a hologram by means of a cylindrical master element and a cylindrical in-coupling element is schematically shown, wherein respective optical adhesive films are introduced both between the master element and the photosensitive composite web and between the in-coupling element and the photosensitive composite web.

[0167] Figure 6 A preferred arrangement for replicating a hologram by means of a parallelepiped-shaped master element and a cylindrical in-coupling element is schematically shown, wherein corresponding optical adhesive films are introduced both between the master element and the photosensitive composite web and between the in-coupling element and the photosensitive composite web.

[0168] Figure 7 A preferred arrangement for replicating a hologram by means of a parallelepiped-shaped master element without an in-coupling element is schematically shown, wherein an optical adhesive film is introduced between the master element and the photosensitive composite web.

[0169] Figure 8 A preferred arrangement for replicating a hologram by means of a parallelepiped-shaped master element and a parallelepiped-shaped in-coupling element is schematically shown, wherein corresponding optical adhesive films are introduced both between the master element and the photosensitive composite web and between the in-coupling element and the photosensitive composite web.

[0170] Fig. 9 A preferred arrangement for replicating a reflection hologram through a cylindrical master element by exposure on the lateral side is schematically shown, wherein an optical adhesive film is introduced between the master element and the photosensitive composite web.

[0171] Fig.10 An arrangement for replicating a side-lit hologram by means of a cylindrical master element by exposure on a substrate is schematically shown, wherein an optical adhesive film is introduced between the master element and the photosensitive composite web.

[0172] Fig. 11 schematically shows an arrangement for replicating a plurality of holograms integrated in a sheet-like master element, and a cylindrical input coupling element, wherein an optical adhesive film is introduced between the input coupling element and the composite web.

[0173] Fig.11A is a schematic diagram of applying a photosensitive composite web to a surface of a master element.

[0174] Fig. 11B is a schematic diagram of applying an optical adhesive film between a cylindrical input coupling element and a photosensitive composite web applied to a master element in order to establish optical contact between the input coupling element and the photosensitive composite web.

[0175] Fig. 11C is a schematic diagram of the separation of the input coupling element from the exposed composite web.

[0176] Detailed description with drawings

[0177] Figure 1 A single-layer optical adhesive layer 2 for use in the method according to the present invention is shown. The optical adhesive layer 2 comprises exactly one adhesive layer 15. The adhesive layer 15 is provided with protective films 6 and 7 on both sides. In this embodiment of the optical adhesive film, the material of the adhesive layer 15 is preferably a weakly adhesive adhesive. Preferably, such an adhesive can be pulled off the surface of the relevant process part with a peeling force of not more than 3N / cm, preferably 1N / cm. Preferably, the tensile strength of the adhesive layer 15 is at least 1MPa, preferably at least 2MPa, and preferably the single-layer optical adhesive film 2 has a Young's modulus of less than 50MPa. On the one hand, such an optical adhesive film 2 can remain very thin and transparent, while on the other hand, such an optical adhesive film has sufficient mechanical strength and elasticity for different processes (such as conveying, applying and / or laminating) and can be removed without residue and risk of damage.

[0178] The thickness of the single-layer optical adhesive film 2 is preferably between 50 μm and 250 μm, so that in the optical contact area, all possible inhomogeneities or all possible gaps between the photosensitive composite web and the surface of the relevant process component are reliably filled to enable optimal exposure. The refractive index of the single-layer adhesive film 2 is preferably close to the refractive index of the adjacent layers of the photosensitive composite web and / or the adjacent layers or surfaces of the relevant process component.

[0179] Figure 2A three-layer optical adhesive film is shown having a carrier layer 14 coated on a first side with a first adhesive layer 15 and on an opposite side with a second adhesive layer 16. These three layers together form the optical adhesive film 2. The adhesive layers 15 and 16 preferably have Figure 1 The single-layer optical adhesive film shown in FIG. 1 shows a similar performance. However, it may be preferred that the adhesive material used in these layers is more adhesive than the adhesive material of the single-layer optical adhesive film. Moreover, these adhesive layers may have a lower tensile strength of up to 1 MPa.

[0180] Preferably, the adhesive material in the adhesive layers 15 and 16 of these embodiments requires a greater peel force to be pulled away from the carrier layer 14 than from the surface of the associated process component and / or the photosensitive composite web 1 .

[0181] Preferably, in Figure 1 and Figure 2 The adhesive material used in the adhesive layers 15 and 16 in the embodiment of the present invention contains a cross-linking agent. Figure 3 The research results of the influence of the crosslinking agent on the bonding force of adhesive materials are shown. The adhesive material examined is based on acrylate production. However, similar results are also obtained using adhesive materials based on silicone resin or rubber. Adhesive layer 15 is generated to have different crosslinking agent concentrations. Adhesive layer 15 is applied to the surface made of different materials (such as glass, PC, TAC and PMMA), and then pulled away from the corresponding surface at a speed of 300mm / min at an angle of 180 °. The peeling force required for separating the adhesive layer from the corresponding surface is measured for each centimeter of adhesive layer.

[0182] The results show that high concentrations of crosslinker reduce the peel force required to separate the adhesive layer from different surfaces. For example, for removal from a polycarbonate (PC) surface, adhesive layer 15 requires a peel force of approximately 1.5 N / cm for a crosslinker concentration of 0.4%. This is slightly higher than the preferred maximum peel force of 1 N / cm for weak bonding adhesives, which is also preferred for use in single-layer optical adhesive films. However, the peel force can be reduced to less than 1 N / cm, for example, by increasing the crosslinker concentration to 0.6%.

[0183] The low peel forces exhibited by the exemplary adhesive layers are well suited for temporary application and residue-free removal of optical adhesive films to improve optical contact between different process components.

[0184] According to the present invention, the optical adhesive film 2 can be used in a variety of arrangements to optimize the optical contact between the different elements of the exposure process. Figures 4 to 8 This is merely an illustrative example of applying the optical adhesive film 2 according to the present invention.

[0185] Figure 4 The use of an optical adhesive film 2 between a cylindrical master element 4 and a photosensitive composite web 1 is shown. The master element 4, which is preferably rotatably mounted, can preferably comprise a master hologram on its lateral face. The photosensitive composite web 1 is guided on a portion of the lateral face on the bottom side of the master element 4, wherein the area of ​​the composite web 1 to be temporarily exposed adopts the shape of the lateral face of the master element 4 at least in a plurality of areas and is guided on the rotating master element 4 in such a way as to move with the lateral face. During exposure, the optical adhesive film 2 is introduced between the composite web 1 and the circumference of the lateral face of the master element 4. In the optical contact area, the optical adhesive film 2 is present substantially parallel to the photosensitive composite web 1, its movement being synchronized with the movement of the photosensitive composite web 1.

[0186] In this arrangement, light can be directed to the photosensitive composite web, for example, from below, in order to form a reflection hologram. For this exposure, the master element 4 can be configured to be transparent or opaque, preferably with the exception of a transparent cover layer protecting the master hologram. The reference beam can travel substantially without being refracted through the photosensitive composite web 1, the optical adhesive film 2 and the transparent cover and then be reflected by the master hologram. The reference beam and the object beam are superimposed in the photosensitive layer of the composite web in different beam directions in order to produce a replicated hologram.

[0187] The optical adhesive film 2 advantageously prevents undesirable reflections and / or light losses at the interface between the optical adhesive film 2 and the photosensitive composite web 1 and / or the cover of the master element 4 .

[0188] This arrangement can also be used to expose a transmission hologram into the photosensitive composite web 1. In this case, the master element 4 preferably comprises a transparent substrate body and a transparent cover layer. For example, the reference beam can be directed from above through the lateral face of the master element 4 so that the reference beam is transmitted through the master hologram, the optical adhesive film 2 and the composite web 1. In an alternative, the reference beam can be directed to the base of the master element 4 so that the reference beam is refracted by the substrate body of the master element 4 and the refracted beam is transmitted through the master hologram. Figure 6 , optical adhesive film 2 and composite web 1. In both cases, the reference beam is transmitted through the master hologram in a partially undiffracted manner and is partially diffracted to generate an object beam that also passes through the optical adhesive film 2 and composite web 3. Therefore, the reference beam and the object beam are superimposed in the photosensitive layer of the composite web 3 with the same beam direction to generate a replicated hologram. In addition, the optical adhesive film 2 prevents unfavorable optical losses and internal reflections at the interface to obtain a high-quality transmission hologram.

[0189] Figure 5Another exemplary arrangement for replicating holograms using optical adhesive films according to the present invention is schematically shown. In this example, two optical adhesive films 2 are used. The first optical adhesive film 2 is arranged between a rotatably mounted cylindrical master element 4 and a photosensitive composite web 1. The second optical adhesive film 2 is arranged between the photosensitive composite web 1 and a cylindrical input coupling element 9. For example, such an arrangement can be used to expose a reflection hologram into the photosensitive composite web 1. The reference beam can be deflected through the input coupling element 9 (or through its lateral surface or base) so that the reference beam is incident on the master hologram on the lateral surface of the master element 4 at a desired angle. Then, as for Figure 4 As described, a reflection hologram can be exposed in a similar manner in a photosensitive composite web 1. The input coupling element 9 can advantageously set the angle at which the photosensitive composite web 1 is exposed. However, this arrangement increases the number of different interfaces that the light must traverse for exposure. Therefore, it is particularly advantageous to apply an optical adhesive film 2 to both interfaces between the different exposed process components (input coupling element 9, composite web 1 and master element 4) to avoid disadvantageous optical losses and reflections.

[0190] Figure 6 Another arrangement of process components for replicating a hologram is shown, wherein a master element 4 has the shape of a parallelepiped block. The top side of the master element 4 is laminated with a first optical adhesive film 2, a photosensitive composite web 1, and a second optical adhesive film 2. Preferably, the master element 4 comprises a substrate body, a master hologram, and a transparent upper cover layer (not shown) for protecting the master hologram. For example, as described above for Figure 5 As described, the master element 4 can be used to expose a reflection hologram into the photosensitive composite web 1 by means of the incoupling element 9 .

[0191] Figure 7 Another arrangement is shown in which the master element 4 has the shape of a parallelepiped block. An optical adhesive layer 2 is laminated onto the top side of the master element 4, and a photosensitive composite web 1 is also laminated onto the top side of the optical adhesive layer 2. The master element 4 can preferably be exposed from above (i.e. in the direction of its top side) to a reference beam, which travels through the photosensitive composite web 1, the optical adhesive layer 2 and a transparent cover layer (not shown) before being reflected back into the photosensitive composite web 1 by the master hologram, so as to form a reflection hologram. In an alternative to transmission hologram replication, the master element 4 can be exposed on its underside or side, while its transparent block-shaped substrate refracts the reference beam so that the reference beam is incident on the master hologram at the desired angle. The reference beam can then be diffracted by the master hologram so as to form an object beam that interferes with the reference beam in the photosensitive composite web 1.

[0192] Figure 8 Shows something like Figure 7 An arrangement in which a block-shaped input coupling element 9 is placed above the second optical adhesive film 2. For example, the input coupling element 9 can be used to refract the reference beam so that the reference beam is incident on the master hologram at a desired angle in order to expose the reflection hologram in the photosensitive composite web 1.

[0193] Fig. 9 and Fig.10 is similar to Figure 4 A more detailed illustration of the arrangement of the exposure method.

[0194] Fig. 9 The exposure of a reflection hologram from a lateral face of a cylindrical master element 4 is shown. The transport rollers 3 are used to position the photosensitive composite web 1 around an arc of the circumference of the master element 4 so that a large part of the photosensitive composite web 1 is in optical contact with the master element 4. Preferably, the optical contact area corresponds to an arc of the circumference of the master element 4 having an angle of at least 1°, preferably at least 2°. One or more of the transport rollers 3 can also be used to control the rotation of the master element 4 and / or the movement of the photosensitive composite web 1 on the lateral face of said master element. In an alternative, the rotation of the master element 4 can also be caused by the friction generated by the movement of the optical adhesive film 2 on the lateral face of said master element. During exposure, the photosensitive composite web 1 moves from right to left.

[0195] An unwinding roller 10 is provided for unwinding the optical adhesive film 2. A rewinding roller 13 is provided for rewinding the used optical adhesive film 2. The rewinding roller 13 may be an active roller, which pulls the optical adhesive film 2 and thus controls its movement during the method. The optical adhesive film 2 is arranged between the photosensitive composite web 1 and the lateral surface of the master element 4, so that the optical adhesive film achieves optical contact between the lateral surface of the master element 4 and the surface of the photosensitive composite web 1.

[0196] The optical adhesive film 2 is provided on both sides with protective layers 6, 7. Rewinding rollers 11 and 12 are used to remove the protective layers 6 and 7 before the optical adhesive film 2 reaches the optical contact area between the master element 4 and the photosensitive composite web 1 .

[0197] The reference beam 5 is directed from below to the master element 4 so that it passes through the photosensitive composite web 1, the optical adhesive film 2 and the cover layer (not shown) of the master element before being reflected by the master hologram. The reflected object beam once again passes through the cover layer, the optical adhesive film 2 and the photosensitive composite web 1, where it interferes with the reference beam to expose a reflection hologram into the photosensitive composite web 1.

[0198] Fig.10 Shows something like Fig. 9However, the reference beam 5 is directed to the base of the transparent master element 4, wherein it is refracted so that it exits from the lower lateral face at the desired angle through the master hologram. The reference beam is transmitted through the master hologram in a partially undiffracted manner and is partially diffracted in order to produce an object beam which also passes through the optical adhesive film 2 and the composite web 3. The undiffracted reference beam and the diffracted object beam interfere with each other in the photosensitive composite web 1 in order to form a transmission hologram.

[0199] FIG. 11A to FIG. 11C A method for replicating a hologram in a photosensitive composite web 1 according to a preferred embodiment of the invention is shown. Fig.11A The step of applying a photosensitive composite web 1 to the surface of a master element 4 is shown. The master element 4 is a parallelepiped-shaped continuous sheet that accommodates a plurality of master holograms A, B, C, etc. Preferably, all master holograms are protected by a single transparent cover, and the surface of the master element is therefore continuous. A laminating roller 8 rolls on the stretched photosensitive composite web 1 and presses the photosensitive composite web against the continuous surface of the master element 4 in order to eliminate possible air bubbles.

[0200] like Fig.11A As depicted in , the laminating roller 8 moves on the photosensitive composite web 1, for example from right to left. At the same time, a transparent cylindrical input coupling element 9 descends in the direction of laminating the photosensitive composite web 1. The optical adhesive film 2 is positioned on an arc of the circumference of the input coupling element 9 by means of different rollers. The unwinding roller 11 supplies the optical adhesive film 2, while the rewinding roller 13 rewinds the optical adhesive film 2 after exposure. The rewinding roller 13 can be an active roller, that is, provided with an actuator, which pulls the optical adhesive film 2 and thus controls its travel during the method. The transport roller 3 is used to set the position of the optical adhesive film 2 relative to the lateral face of the input coupling element 9. The movement of the optical adhesive film 2 from right to left can cause a rotation of the input coupling element 9. The optical adhesive film 2 is provided with protective films 6 and 7 on both sides. These protective films are removed and rolled up by means of the unwinding rollers 11 and 12 before the exposure step.

[0201] Fig. 11BIt is schematically shown that an optical adhesive film 2 is applied between a cylindrical input coupling element 9 and a photosensitive composite web 1 in order to establish an optical contact between the input coupling element 9 and the photosensitive composite web 1. The input coupling element 9 is rolled from right to left on the top side of the photosensitive composite web 1, thereby creating a seamless optical contact between the master element 4 and the input coupling element 9. The optical adhesive film 2 is applied synchronously with the movement of the input coupling element 9. The optical contact area here moves from right to left together with the input coupling element 9. During the application of the input coupling element 9, light is used to expose the photosensitive composite web 1 in the optical contact area. A light source (not depicted), such as a laser, can be moved synchronously with the input coupling element 9. Such a synchronous movement of the light source can preferably include scanning over the width of the photosensitive composite web 1.

[0202] Fig. 11C The separation of the input coupling element 9 from the exposed composite web 1 is shown. The cylindrical input coupling element 9 is lifted and carries the optical adhesive film 2, which continues to adhere to its surface. The laminating roller 8 then rolls back from left to right so that the exposed composite web 1 can be lifted and separated from the top side of the master element 4. Suitable means (such as additional rollers) that enable the composite web 1 to be separated from the top side of the master element 4 are known to those skilled in the art.

[0203] Although in FIG. 11A to FIG. 11C In the example of , the parallelepiped-shaped lower sheet serves as the master element 4 and the larger transparent roller serves as the input coupling element 9, but the functions of these process components can also be reversed. For example, the lower sheet can be configured as the input coupling element, while the larger transparent roller is the master element. The light source can then be arranged accordingly and illuminate the input coupling element, for example from the bottom or from the side.

[0204] Reference numerals list

[0205] 1 Photosensitive composite web

[0206] 2 Optical Adhesive Film

[0207] 3 Conveyor rollers

[0208] 4 Master Components

[0209] 5 Light

[0210] 6. First protective film

[0211] 7 Second protective film

[0212] 8 Lamination Rollers

[0213] 9 Input coupling element

[0214] 10 Unwinding roller for optical adhesive film

[0215] 11 Rewinding roller for the first protective film

[0216] 12 Rewinding roller for second protective film

[0217] 13 Rewind Roll for Optical Adhesive Film

[0218] 14 Carrier layer

[0219] 15 First adhesive layer

[0220] 16 Second adhesive layer

Claims

1. A method for replicating a hologram in a photosensitive composite web (1), the method comprising the following steps: a. providing a master element (4), the master element comprising a substrate body and at least one master hologram, b. applying the photosensitive composite web (1) to the surface of the master element (4), c. exposing the master element (4) so ​​as to replicate the at least one master hologram in the photosensitive composite web (1), and d. separating the exposed composite web (1) from the master element (4), It is characterized in that The method further includes temporarily applying an optical adhesive film (2) between the photosensitive composite web (1) and the surface of the master element (4), wherein the optical adhesive film achieves optical contact between the master element (4) and the photosensitive composite web (1) while the master element (4) is exposed.

2. A method for replicating a hologram in a photosensitive composite web (1), the method comprising the following steps: a. providing a master element (4), the master element comprising a substrate body and at least one master hologram, b. applying the photosensitive composite web (1) to the surface of the master element (4), c. applying an input coupling element (9) to the photosensitive composite web (1) such that the photosensitive composite web (1) is positioned between the surface of the input coupling element (9) and the surface of the master element (4), d. exposing the master element (4) by means of the incoupling element (9) in order to replicate the at least one master hologram in the photosensitive composite web (1), e. separating the input coupling element (9) from the exposed composite web (1), and f. separating the exposed composite web (1) from the master element (4), It is characterized in that The method further comprises temporarily applying an optical adhesive film (2) between the photosensitive composite web (1) and the surface of the input coupling element (9), wherein the optical adhesive film achieves optical contact between the input coupling element (9) and the photosensitive composite web (1) while the master element (4) is exposed.

3. The method according to claim 1, It is characterized in that The refractive index difference between the surface of the master element (4) and the optical adhesive film (2) and / or between the optical adhesive film (2) and the surface of the photosensitive composite web (1) is not greater than 0.2, preferably not greater than 0.1, more preferably not greater than 0.

05.

4. The method according to claim 1 or 3, It is characterized in that The refractive index of the optical adhesive film (2) is between the refractive index of the surface of the master element (4) and the refractive index of the surface of the photosensitive composite web (2).

5. The method according to one or more of claims 1 or 3 and 4, It is characterized in that The optical adhesive film comprises at least one adhesive layer (15), wherein the at least one adhesive layer (15) has a peel force of less than 3 N / cm, preferably less than 1 N / cm relative to the surface of the master element (4) and / or the surface of the photosensitive composite web (1).

6. The method according to one or more of the preceding claims, It is characterized in that The optical adhesive film (2) comprises at least one adhesive layer (15), wherein the at least one adhesive layer (15) has a Young's modulus of up to 50 MPa across the width of the adhesive layer (15) and preferably a transmittance of at least 80%, a haze of up to 2% and / or a brightness variation of up to 30% between orthogonal polarizers.

7. The method according to one or more of the preceding claims, It is characterized in that The optical adhesive film (2) comprises at least one adhesive layer (15), wherein the at least one adhesive layer (15) comprises an adhesive material based on acryl, EVOH, rubber or silicone resin, and wherein the adhesive layer (15) preferably has a thickness of 50 μm to 250 μm.

8. The method according to one or more of the preceding claims, It is characterized in that The optical adhesive film (2) has a single-layer structure including exactly one adhesive layer (15), wherein the adhesive layer (15) preferably has a tensile strength of at least 1 MPa, preferably at least 2 MPa.

9. The method according to one or more of the preceding claims, It is characterized in that The optical adhesive film (2) comprises a carrier layer (14) and has at least one adhesive layer (15), wherein preferably the at least one adhesive layer (15) has a tensile strength of up to 2 MPa, preferably at least 1 MPa.

10. The method according to claim 9, It is characterized in that The at least one adhesive layer (15) is directly applied to the carrier layer (14), and the peeling force of the adhesive layer (15) relative to the carrier layer (14) is greater than the peeling force of the adhesive layer (15) relative to the surface of the master element (4) and / or the surface of the photosensitive composite web (1) and / or the surface of the protective film (6, 7).

11. The method according to any one of claims 9 and 10, It is characterized in that The optical adhesive film (2) comprises two adhesive layers (15, 16), wherein each adhesive layer (15, 16) is preferably applied directly onto the carrier layer (14).

12. The method according to one or more of claims 9 to 11, It is characterized in that The carrier layer (14) has a tensile strength of at least 5 MPa, wherein the carrier layer (14) preferably has a transmittance of at least 80%, a haze of up to 1.5% and / or a brightness variation of up to 30% between crossed polarizers over the width of the carrier layer (14).

13. The method according to one or more of claims 9 to 12, It is characterized in that The carrier layer (14) comprises one or more of the following materials: polycarbonate (PC), polyethylene terephthalate (PET), cellulose acetate, cellulose triacetate (TAC), polymethyl methacrylate or a mixture thereof, wherein the carrier layer (14) preferably has a thickness of 6 μm to 100 μm.

14. The method according to one or more of the preceding claims, It is characterized in that At least one protective film (6), preferably two protective films (6, 7) are arranged on the optical adhesive film, wherein the at least one protective film (6) is removed before the step of temporarily applying the optical adhesive film between the photosensitive composite web (1) and the surface of the master element (4).

15. The method according to the preceding claim, It is characterized in that The at least one protective film (6) comprises one or more of the following materials: polyethylene, polypropylene, silicone paper or a mixture thereof, Therein, the at least one protective film has a preferred thickness between 10 μm and 50 μm.

16. The method according to one or both of the two preceding claims, It is characterized in that The at least one protective film (6) is directly present on the at least one adhesive layer (15), wherein the peel force required to remove the protective film (6) from the adhesive layer (15) is not greater than 0.2 N / cm, preferably not greater than 0.1 N / cm.

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