Method for the replication of a hologram by means of an optical adhesive film

Abstract

The invention relates to a method for the replication of a hologram into a light-sensitive 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 light-sensitive composite web to a surface of the master element, exposing the master element in order to replicate the at least one master hologram into the light-sensitive composite web, and detaching the exposed composite web from the master element. The method furthermore comprises temporarily applying an optical adhesive film between the light-sensitive composite web and the surface of the master element. The optical adhesive film mediates an optical contact between the master element and the light-sensitive composite web during the exposure. In a further aspect, the invention relates to a method for the replication of a hologram into a light-sensitive composite web using a coupling-in element, wherein an optical adhesive film is introduced between composite web and coupling-in element.

Description

[0001] METHOD FOR REPLICATION OF A HOLOGRAM USING AN OPTICAL ADHESIVE FILM

[0002] DESCRIPTION

[0003] 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 to a surface of the master element, exposing the master element to replicate the at least one master hologram in the photosensitive composite web, and detaching the exposed composite web from the master element. The method further comprises temporarily applying an optical adhesive film between the photosensitive composite web and the surface of the master element. The optical adhesive film mediates optical contact between the master element and the photosensitive composite web during exposure.In a further aspect, the invention relates to a method for replicating a hologram in a light-sensitive composite web using a coupling element, wherein an optical adhesive film is introduced between the composite web and the coupling element.

[0004] Background and state of the art

[0005] The invention relates to the field of hologram replication.

[0006] HOEs (Holographic Optical Elements) typically refer to optical components in which holographic properties are used to achieve a specific light beam path, such as transmission, reflection, diffraction, scattering, and / or deflection, etc. This allows desired optical functionalities to be implemented compactly in any substrate. The holographic properties preferably exploit the wave nature of light, particularly coherence and interference effects. Both the intensity and phase of the light are taken into account.

[0007] Such holographic elements are used in many areas, such as in transparent displays (e.g. in shop windows, refrigerated cabinets, vehicle windows), for lighting applications such as information or warning signals in glass surfaces, light-sensitive detection systems, for example for interior monitoring (eye tracking in vehicles or presence status tracking of people indoors).

[0008] Holograms are created by the interference of a reference beam with light reflected or diffracted from the surface of an object (object rays). Traditionally, three-dimensional objects were used to create unique, customized holograms. Commercially available HOEs, on the other hand, are often mass-produced using duplication processes. Such duplication processes typically use a master hologram containing the image to be copied. The master holograms used are often stored in a substrate body that carries the master hologram. The substrate body is preferably transparent and can have various shapes, such as a cuboid, a plate, or a cylinder. The combination of the master hologram and the substrate body forms a master element.

[0009] The master element is exposed to a coherent light source to replicate the image from the master hologram into a photosensitive composite. For mass production, the photosensitive composite can be provided in the form of a flowing web comprising a photosensitive material and one or more carrier or protective layers. For this purpose, the photosensitive web is preferably transported through various workstations to produce the HOEs.

[0010] During exposure, the composite sheet is placed onto a surface of the master element. To create a reflection hologram, the coherent light can traverse the composite sheet before reaching the master hologram, where it is reflected back into the composite sheet. Alternatively, to create a transmission hologram, the coherent light can first be directed onto the master hologram, where it is diffracted before reaching the composite sheet. In both cases, the object and reference beams interfere with each other in the light-sensitive material to form the replicated hologram. The replication process is sensitive to unwanted stray light, which can also interfere with the object and / or reference beams. If, for example, irregularities or gaps occur at the interface between the composite sheet and the surface of the master element, the reference and / or object beams can be internally reflected.This can lead to either light loss or unwanted interference, which impairs the quality of the replicated hologram. Providing sufficient optical contact between the master element and the composite web is therefore highly relevant for the quality of the replicated hologram.

[0011] This also applies to the possible use of coupling elements in the exposure process, which are used in certain configurations to replicate the holograms. Coupling elements can, for example, be used preferentially to adjust an exposure angle. The exposure angle, i.e., the angle at which the object and reference beams strike the light-sensitive material, also determines the angle at which the hologram can be reconstructed. Varying the exposure angle thus enables the production of different types of holograms, for example: edge-lit, backlit, at eye level, or only visible from below, etc.

[0012] By passing the coherent light used to expose the hologram through a coupling element, the exposure angle can be varied or adjusted. The coupling element is transparent at least to the wavelength of the exposure beam and can take on various shapes, such as a cuboid, a plate, a pyramid, a cylinder, etc. The coupling element can also be placed on the composite sheet so that the light is first refracted by the material of the coupling element to achieve a desired approach angle on the composite sheet. However, if small gaps exist at the interface or boundary between the coupling element and the composite sheet, the light can be internally reflected. This also leads to unwanted interference or losses.Therefore, in such constellations, a nearly perfect optical contact between the coupling element and the composite track is also desirable in order to produce high-quality replicated holograms.

[0013] To improve the optical contact between the composite web and adjacent components (such as master elements or coupling elements) in an exposure process, the use of index-matching liquids has been proposed. WO 9619754 A1 teaches a method for replicating a master hologram from a hollow, drum-shaped master element into a composite web. The composite web flows over a curved surface of the rotating master element. It was found that image artifacts caused by internal reflections at air / glass or air / substrate interfaces were caused when the optical contact between the components was insufficient. To improve the optical contact between the composite web and the master element, an index-matching liquid such as xylene is continuously applied to the surface of the master element. The liquid fills gaps between the master element and the composite web.Additionally, the composite web is immersed in an index match fluid before exposure. After exposure, the fluid must be removed from the composite web before it can be rolled up or further processed.

[0014] A disadvantage of the proposed process, however, is that xylene is a highly flammable irritant and suspected of being carcinogenic, so its use requires greater plant complexity to ensure explosion protection, environmental protection, and occupational safety. Furthermore, the necessary removal of the index match fluid increases the complexity and effort of the HOE production process.

[0015] JP2000250386A also discloses the use of an index match liquid to improve the optical contact between a master element and a light-sensitive composite web. The index match liquid must not be too volatile, as it must remain in a liquid state for the duration of the coating and exposure. However, the index match liquid is dried from the exposed composite web before further processing. This, in turn, significantly increases the complexity of the system. In addition, a liquid index match must be very thin so that molecular movement in the liquid film does not change the phase position of the passing light, which would, in turn, negatively impact the quality of the holograms. The index match liquid is also usually lost upon removal, meaning it cannot be reused. This further increases the costs of the entire process.

[0016] Low-volatility index match fluids that do not dry quickly may remain on the surfaces of the master hologram or other components for longer. This may require cleaning the master hologram to prevent the accumulation of fluids and contaminants. This cleaning step can be laborious, especially if the master hologram has a non-smooth surface (e.g., a relief pattern). Current technology offers only limited solutions for protecting the surfaces of master holograms when they come into contact with liquid or resinous materials.

[0017] The use of optically transparent layers is known to protect a master hologram from contamination during an exposure process. DE 10 2006 016 139 A1 discloses the use of a transparent release layer between a resinous (non-solid) photosensitive layer and a master hologram. The release layer is intended to facilitate removal of the resinous photosensitive layer from the master hologram. To minimize the optical influence of the release layer, the difference in refractive index between the photosensitive layer and the release layer is intended to be minimized or completely eliminated. The release layer should therefore have no optical effect.

[0018] In addition, the release layer can serve as a cover layer for the relief structure of the master hologram. Despite the release layer being depicted as very thin, the relief structure of the master hologram remains sharp and can be pressed into the photosensitive layer. DE 10 2006 016 139 A1 suggests that the release layer is a coating that is permanently applied to a surface of the master hologram.

[0019] To integrate the exposed hologram into a product, DE 102006 016 139 A1 also describes the use of an adhesive layer that bonds the replicated hologram to a substrate. Unlike the release layer, the adhesive layer remains a permanent component of the product, from which the hologram can no longer be removed. In the field of optical displays, optical clearance adhesives (OCAs) are also known to be used to bond a backlight to a screen.

[0020] KR20150001411A teaches an example of such an OCA for use in an LCD screen. The OCA comprises an adhesive and prevents the formation of an air layer between the backlight and the LCD screen. Similarly, US10611937B2 teaches an adhesive layer used to firmly bond a glass layer to a sensor film of a screen. The adhesive layer comprises an OCA to ensure good optical performance of the screen. Such an adhesive layer is intended to permanently bond the screen layers together to ensure a long product life. Removal of the adhesive layer is not intended.

[0021] Furthermore, a transparent multilayer microfluidic arrangement is known from DE 10 2019 112 254 A1. The different layers of the arrangement are bonded together with a transparent adhesive. Microfluidic channels are created by clamping a wall structure between a transparent, flexible cover layer and a base layer. The optical refractive indices of the layer materials are selected to make the layer structure imperceptible. This is intended to facilitate the reading of the microfluidic results. A hot-melt adhesive is proposed to create the adhesive layer. In some embodiments, the adhesive layer is exposed to UV radiation to adjust its local adhesive properties. This adhesive layer is also configured for a permanent bond.

[0022] In light of the state of the art, there is therefore a need to improve processes for replicating holograms in a light-sensitive material with regard to efficiency, cost-effectiveness, and the optical quality of the replicated holograms. In particular, there is a need to improve the optical contact between the light-sensitive composite web and the adjacent optical components, such as the master element or the coupling elements, which reliably ensures exposure without interference, does not require hazardous chemicals or excessive cleaning, can be removed without residue, and is easy to handle.

[0023] Object of the invention

[0024] The object of the invention is to provide a method for replicating a hologram from a master element into a light-sensitive composite web without the disadvantages of the prior art. In particular, it was an object of the invention to provide a method suitable for material-friendly replication of holograms on a light-sensitive composite web with high optical precision and quality. Summary of the Invention

[0025] The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

[0026] In a first aspect, the invention relates to a method for replicating a hologram in a photosensitive composite web, comprising the following steps: a. providing a master element comprising a substrate body and at least one master hologram, b. applying a photosensitive composite web to a surface of the master element, c. exposing the master element to replicate the at least one master hologram in the photosensitive composite web, and d. detaching the exposed composite web from the master element.

[0027] Furthermore, the method according to the invention comprises a temporary application of an optical adhesive film between the photosensitive composite web and the surface of the master element, which preferably provides an optical contact between the master element and the photosensitive composite web during the exposure of the master element.

[0028] In a further aspect, the invention relates to a method for replicating a hologram in a photosensitive composite web, comprising the following steps: a. providing a master element comprising a substrate body and at least one master hologram, b. applying a photosensitive composite web to a surface of the master element, c. applying a coupling element to the photosensitive composite web such that the photosensitive composite web is positioned between a surface of the coupling element and the surface of the master element, d. exposing the master element using the coupling element to replicate the at least one master hologram in the photosensitive composite web, e. detaching the coupling element from the exposed composite web and f. detaching the exposed composite web from the master element.Furthermore, the method comprises a temporary application of an optical adhesive film between the light-sensitive composite web and the surface of the coupling element, which preferably provides an optical contact between the coupling element and the light-sensitive composite web during the exposure of the master element.

[0029] The inventive method has the advantage of ensuring virtually flawless optical contact between a master element (or a coupling element) and the light-sensitive composite sheet without requiring additional steps for cleaning or evaporating an index-matching liquid. Instead, a residue-free removable optical adhesive film can create a smooth, gap-free transition between the master element (or the coupling element) and the composite sheet, so that essentially no unwanted reflections or scattering occur at the component interfaces. This reduces optical losses and minimizes the potential occurrence of optical interference that could leave undesirable patterns in the replicated hologram.Another particularly advantageous feature is that the optical adhesive film adheres sufficiently to both the master element and the light-sensitive composite sheet, preventing the formation of bubbles or air gaps. At the same time, the optical adhesive film is only temporarily applied to the master element, so the surface of the master element does not exhibit any adhesion to any contamination.

[0030] Furthermore, the "optical adhesive film" is preferably a solid in which the Brownian motion is sufficiently small, thereby preventing any "wobble" in the phase of the light and thus resulting in a more stable interference field in the hologram copy within the exposure time. This prevents the microstructures from blurring, thus maximizing the diffraction efficiency of the holograms. The sharpness and contrast of the generated hologram are also significantly improved. The optical adhesive film is preferably designed to adhere to a surface of the composite sheet and an adjacent surface of the master element and / or coupling element. The strength of the adhesion is preferably so high that a seamless bond can be achieved between the composite sheet and the adjacent component without requiring more pressure to be exerted on the composite sheet than would otherwise be the case to bring it into contact with these elements.It is particularly preferred that the composite web does not have to be pressed so strongly onto the master element or coupling element that material deformation occurs. Thus, the method according to the invention also differs in this respect from that of DE 10 2006 016 139 A1 , which requires printing a deformable layer onto the release / cover layer of a master hologram. At the same time, the strength of the adhesion of the optical adhesive film to 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 invention preferably further differs from the adhesive layers of the prior art such as DE 10 2006 016 139 A1 , KR20150001411A, US10611937B2 and DE 10 2019 112 254 A1 , which are designed for permanent bonding.

[0031] Furthermore, it is preferred that the optical adhesive film is provided in the form of a film or foil. This means that the material of the optical adhesive film does not only form a film or foil when it is applied (e.g. by spraying) to the surface of a process component. Instead, the optical adhesive film preferably already has a defined width and thickness before it is applied to or between process components. The optical adhesive film according to the invention thus differs from protective or release layers as known from DE 10 2006 016 139 A1, which are permanently applied to a surface of the master hologram by means of coating. The optical adhesive film is preferably provided in roll form, although other embodiments such as a loop or a series of individual stickers are also possible.

[0032] A further advantage of the method according to the invention is that the materials used for the optical adhesive film can have identical or similar optical properties to those used for the substrate of the master element (or the coupling element) and / or the composite web. Preferably, the similar or identical properties include transparency, haze, stress birefringence properties, and / or the refractive index. The use of identical or similar materials enables a very close adaptation of the refractive index of the optical adhesive film to the refractive indices of the adjacent process components, ensuring a transition between the adjacent refractive indices without refractive index jumps.Reflections at the interface between the master element (or the coupling element), the optical adhesive film and / or the light-sensitive composite sheet are thereby largely eliminated or significantly minimized.

[0033] By making optical contact using an optical adhesive film, the exposure can also be easily integrated into a continuous manufacturing process, preferably into a roll-to-roll process. The optical adhesive film can be shaped analogously to the composite web and moved through the process in a similar way, e.g. using rollers. This enables simple synchronization of the optical adhesive film with the composite web. It is also possible and may be preferred for the optical adhesive film and / or the light-sensitive composite web to be applied to the surface of the master element or the surface of the coupling element by a laminating roller. During exposure, the optical adhesive film is preferably in mechanical contact with the light-sensitive composite web and the master element and / or coupling element.Preferably, the optical adhesive film is removed after exposure from both the light-sensitive composite web and the master element and / or coupling element. Therefore, the optical adhesive film is preferably not a permanent component of the light-sensitive composite web, the master element, or the coupling element.

[0034] Optical adhesive films can be precisely specified with regard to their layer thickness, layer thickness homogeneity, 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 remains uniform throughout. In contrast, when using index-match liquids, the dosage can vary over time, and there is no guarantee that the liquid will be evenly distributed over the desired surfaces. A similar problem can arise when applying hot-melt adhesives, as these are also dispensed in liquid form. When applying an optical adhesive film according to the invention, a distance between a composite web and a master element and / or coupling element can be bridged particularly precisely.The use of an optical adhesive film with a correspondingly specified layer thickness, layer thickness homogeneity, and waviness also leads to high process stability in the copying process. In particular, the surfaces of the optical adhesive film can be designed to be essentially waviness-free. This avoids fluctuations in the thickness of the adhesive film, which could blur the interference field of the object and reference beams and lead to deviations in the optical function of the replicated hologram from the master hologram.

[0035] Compared to the prior art processes based on index match fluids, the use of optical adhesive film can also be made safer for the user. This is because such an adhesive film generally does not contain highly toxic substances and is non-volatile, thus eliminating the need for special safety measures (such as gas extraction or insulation).

[0036] Furthermore, volatile index match liquids generally cannot be recovered after use. This means that they either evaporate or lack the required degree of purity, which allows reuse only after complex redistillation. This increases the material or equipment requirements and makes the process more expensive. In contrast, the optical adhesive film can be reused for a variety of applications. For example, a single loop of the adhesive film can advantageously undergo the process. A loop preferably represents a closed arrangement of the optical adhesive film in which the same optical adhesive film is used multiple times for exposure. Alternatively, an optical adhesive film can also be continuously supplied from a provided unwinding roller to an exposure station.If there is no more adhesive film on the unwinding roller, it can be refilled or replaced. It may also be preferred for a used optical adhesive film to be rewound after exposure using a rewinding roll for reuse or recycling. The method according to the invention can therefore advantageously be designed to save resources in various ways.

[0037] The process according to the invention is also extremely gentle on materials, clean, and leaves no residues on the process components, such as the master element or the coupling element. This is primarily due to the relatively weak adhesive force of the optical adhesive film and the fact that it can be continuously or intermittently removed from the surfaces of the process components. In this way, fresh optical adhesive film can also be applied to the surfaces continuously or intermittently. The optical adhesive film therefore preferably does not represent a sticky, permanent process component that could accumulate dust or residues. Residues on the exposed composite web are also avoided, so that the produced hologram can be seamlessly integrated into a final product - preferably without a further cleaning step. This improves the efficiency of the process and eliminates unnecessary work steps.

[0038] A further advantage of the process according to the invention is that the photosensitive composite web, or at least an outer layer thereof, can be configured either as a solid or as a non-solid material. The photosensitive material can, for example, be solid and / or enclosed between solid carrier layers such as polycarbonate films. The solid carrier layers can be applied to the surface of a process component, which can also be completely smooth (without relief patterns). It is generally difficult to bring two smooth, solid surfaces into good optical contact with each other because the intermolecular forces acting between the surfaces are not strong enough to bring them into continuous contact, and the surfaces can even electrostatically repel each other.By temporarily placing the optical adhesive film between the solid surfaces, sufficient attractive electrostatic forces can be generated between them to ensure stable contact and no relative movement between the composite sheet and the adjacent component. This significantly improves the quality of the replication process.

[0039] If an outer layer of the photosensitive composite web comprises a non-solid material, such as a semi-solid or resinous material, it can still be used with the optical adhesive film. For example, a solid support layer of the composite web can be brought into contact with the optical adhesive film. Alternatively, the optical adhesive film is used to bring the non-solid surface into contact with a process component and is subsequently removed from the non-solid surface after it has been fused and / or cured. The optical adhesive film is thus versatile and suitable for a number of different embodiments of the photosensitive composite web.

[0040] As can be seen from the above-mentioned advantages, a method in which the optical adhesive film is applied between the light-sensitive composite web and the coupling element solves the same technical problem as a method in which the optical adhesive film is applied between the light-sensitive composite web and the master element. The optical adhesive film primarily improves the optical contact between exposed transparent components through which the exposure light is passed. This reduces unwanted reflections, scattering, or losses and improves the quality of the reproduced hologram. Both methods are therefore linked in such a way that they implement a single general inventive concept.

[0041] A person skilled in the art will also recognize that preferred features or advantages of embodiments of the method in which the optical adhesive film is applied to the master element also apply to embodiments of the method in which the optical adhesive film is applied to the coupling element, and vice versa. A combination of the methods is also clearly particularly preferred. This means that when using a coupling element in the exposure process, it is particularly preferred to introduce an optical adhesive film both temporarily between the master element and the light-sensitive composite web, and also between the coupling element and the light-sensitive composite web. However, it may also be preferred to introduce an optical adhesive film, for example temporarily only between a coupling element and the light-sensitive composite web, and not between a master element and the light-sensitive composite web.In such an embodiment, the photosensitive composite web can thus also be exposed while in direct contact with a surface of the master element, wherein the contact is not mediated by an optical adhesive film.

[0042] For the purposes of the invention, "application" preferably means that one process component (e.g., master element, coupling element, and / or photosensitive composite web) is brought into direct or indirect contact with another. For example, when applying a composite web to a master element or coupling element, a protective layer and / or optical adhesive film may be present between the process components. For the purposes of the invention, "application" is also preferably used to indicate that one process component exerts a mechanical force on another, e.g., by resting on it and applying its weight (as in the case of a coupling element resting on a photosensitive composite web) or exerting a frictional force, as in the case of a rotating cylindrical master element that causes a photosensitive composite web to move in tandem with the master element.The force transmission can also take place the other way around, so that the light-sensitive composite track causes a movement or rotation of the master element.

[0043] A "process component" within the meaning of the invention is preferably a stationary, movable, or consumable component or material used in the exposure process. The process component is preferably configured to interact with the light in the exposure process, for example, through reflection, transmission, or diffraction, in order to adjust the exposure process. For example, optical components such as a master element or coupling element, as well as a light-sensitive composite web, represent a process component within the meaning of the invention.

[0044] For the purposes of the invention, the "surface" of a process component may refer to the surface of the process component that is brought into contact with another process component. The "surface" of a process component may preferably also refer to its outermost layer, particularly in the case of a layered process component. For example, the surface of the photosensitive composite web may be an upper carrier film, while the surface of a master element may refer to an upper cover used to protect the master hologram.

[0045] For the purposes of the invention, "detachment" is a separation, preferably the separation of the process components so that they are no longer in contact with each other, preferably neither directly nor indirectly. During a "detachment," an increasing air gap is preferably introduced between the process components, for example, when the composite web detaches from a master element or coupling element.

[0046] An "optical contact" should preferably allow a beam of light to pass between process components without experiencing significant reflections or even total internal reflection. Direct material contact between the process components is possible, but not necessary. To mediate optical contact between the master element and the composite web, an optical adhesive film, for example, is provided to mediate contact. However, direct optical contact is preferably present between the optical adhesive film and the adjacent process components. If a gap is present between the surfaces of the optical adhesive film and the adjacent process component, it is preferably smaller than half a wavelength of the light so that no interference fields form at the interface between the surfaces.Preferably, neither reflection (especially total internal reflection) nor scattering occurs at the interface between the surfaces. The optical contact between the light-sensitive composite web and another process component (master element, coupling element) is mediated by an optical adhesive film. This preferably means that the light-sensitive composite web and the other component are in mechanical contact with the optical adhesive film. This preferably means that the optical adhesive film adheres physically, chemically, or electrostatically to a surface of the light-sensitive composite web or the other component.

[0047] Adhesion of the optical adhesive film to the photosensitive composite web and / or the further process component preferably comprises the presence of attractive forces between the optical adhesive film and the respective component. When the optical adhesive film is placed between two process components to mediate optical contact between them, stronger attractive forces are preferably present between each process component and the optical adhesive film compared to 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. Furthermore, the adhesion is preferably sufficient to prevent movement between the process components between which the optical contact is mediated.

[0048] A "composite" within the meaning of the invention is preferably a multilayer material consisting of two or more different components with different physical properties that are bonded together at an interface. Preferably, the bond between the individual components is such that it cannot be separated by the influence of slight force and is therefore considered permanent. Preferably, the layers of the composite web must not be separated by a force of less than 10 N / cm, preferably less than 50 N / cm, even more preferably less than 100 N / cm. The composite can, for example, consist of a material enclosed between two transparent carrier films. The photosensitive composite can be provided with one or more protective films that are present during exposure or removed before exposure.Alternatively or additionally, the composite sheet may comprise a stack of layers, each of which is light-sensitive to different spectral ranges.

[0049] A “composite web” within the meaning of the invention is preferably a composite material with a length that is at least twice, preferably at least five times, and even more preferably at least twenty times its width. The thickness of the composite web is preferably set such that it has a certain flexibility so that it can, for example, be partially wound around a roller. The composite web preferably 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. The composite web preferably encloses the photosensitive material between two transparent carrier films that have a similar refractive index to the photosensitive material. The refractive index of the carrier films and the photosensitive material is preferably between 1.4 and 1.6.In some preferred embodiments, the photosensitive composite web comprises a photosensitive material on a single carrier film, such that one surface of the photosensitive material is exposed. The photosensitive material can be, for example, a photosensitive photopolymer or a dichroic gelatin with a preferred layer thickness between 1 and 500 μm. The photosensitive material can be photosensitive to the entire visible spectrum or wavelength-selective.

[0050] For the purposes of the invention, "light sensitivity" preferably refers to a material's holographic suitability. A material is preferably considered holographically suitable if, upon exposure to sufficiently coherent light, the interference fields of the light can be stored as microstructures in the material. Holographic suitability is preferably related to the size of the resulting microstructures. The resulting microstructures are preferably no larger than the light / dark structures of an interference field.

[0051] For the purposes of the invention, "exposure" preferably refers to the targeted directing of electromagnetic radiation, preferably in the wavelength range between 400 and 1600 nm, onto a correspondingly sensitive surface, preferably to form a hologram. Various methods for exposing a hologram are known, including transmissive or reflective techniques for producing volume holograms. Examples of these will be explained in more detail later in this text.

[0052] A "master element" is preferably a three-dimensional unit comprising at least one master hologram in a shape that ensures that a movement of the master element directly leads to a corresponding movement of the master hologram. A master element can also comprise a plurality of master holograms, for example, 2, 3, 5, or more. The master element preferably has a length and width approximately equal to that of the master hologram. The master element is preferably at least twice, preferably five times, and particularly preferably at least twenty times as high as the master hologram.

[0053] The master element preferably comprises a substrate body that either encloses or supports the at least one master hologram. In embodiments, the master element may, for example, comprise a transparent top cover for protecting a master hologram located between the cover and the substrate body. Preferably, the top cover has a refractive index selected to allow light to pass through it, the master hologram, and the substrate body without significant diffraction. The top cover may, for example, be a transparent film or a glass layer.

[0054] The master element may preferably have the shape of a cuboid block, a plate, a pyramid, a prism, or a cylinder. The substrate body may be shaped accordingly.

[0055] Preferably, the substrate body of the master elements can be formed from a material which is an optical plastic, preferably selected from the group: polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin polymers (COP) and cycloolefin copolymers (COC) and / or an optical glass, preferably selected from the group: borosilicate glass, quartz glass, B270, N-BK7, N-SF2, P-SF68, P-SK57Q1, P-SK58A and P-BK7.

[0056] Preferably, both the substrate body and any cover of the master element have a refractive index between 1.4 and 1.6.

[0057] The choice of material for the substrate body may depend on the desired exposure angle or refractive index. It may also be preferable for a substrate body to be colored, for example, to filter light wavelength-selectively to create a hologram with a specific wavelength. In this way, a broadband light source can be used to expose various master holograms.

[0058] It is preferred that the surface of the master element comprises glass, PC, TAC, or PMMA. The surface material can be in the form of a foil or plate to protect the master hologram. However, the surface material can also be the material of the substrate body itself and, for example, have a cuboid or cylindrical shape.

[0059] Whether an optical adhesive film is placed on a substrate or on a cover of a master element can depend on the direction from which the master hologram is to be exposed. In some cases, the optical adhesive film can be applied to a side or base of the master element. Preferably, the affected surface of the master element is smooth, which means in particular that it does not comprise a relief pattern. The master hologram preferably comprises a volume hologram. For the replication of the volume hologram, the quality of the reproduction depends primarily on the optical rather than the mechanical contact between the master hologram and the photosensitive material used. If the surface of the master element is smooth, the optical adhesive film can also be applied and removed more easily without leaving residues, e.g. in the recesses of a relief pattern.Preferably, the "width" refers to a dimension in a horizontal plane transverse to a composite web flow direction. Preferably, the "length" refers to a dimension in a horizontal plane along a composite web flow direction. Preferably, the "height" refers to a dimension in a vertical plane orthogonal to the plane formed by the width and length.

[0060] A “substrate body” within the meaning of the invention is preferably a three-dimensional block of material which carries or encloses the master hologram. The substrate body is preferably transparent. In some embodiments, the substrate body has a plurality of surfaces, including a flat surface which can be horizontally oriented. In some embodiments, the substrate body is prismatic, i.e. it has a constant cross-section of any shape, e.g. square, polygonal, elliptical or circular. The ends of the substrate body which have the shape of the cross-section can be referred to as the “base surface”. The elongated surface of the substrate body which lies between the two ends can be referred to as the “lateral surface”. In some embodiments, the shape of an axially rotatable cylinder is preferred. Within the meaning of the invention, the shape of a rotatable prismatic substrate body orMaster element, preferably a cylinder, also referred to as a “roller”.

[0061] For the purposes of the invention, the term "transparent" or "transparency" preferably refers to a property of a material whereby it is essentially permeable to light. A transparent material within the meaning of the invention is preferably transmissive for at least part of the electromagnetic spectrum, preferably with a wavelength between 300 nm and 25 pm, particularly preferably between 400 nm and 780 nm. A transparent material, for example a transparent substrate body, is particularly preferably permeable to light in a wavelength range with which the master holograms are exposed. A transparent material can also be colored to select light radiation of a specific wavelength.

[0062] A "master hologram" within the meaning of the invention is preferably a holographic-optical element comprising at least one hologram to be replicated. The master hologram is designed for an optical function (e.g. diffraction, reflection, transmission and / or refraction) for one or a plurality of wavelengths. For this purpose, for example, several holograms, each diffracting light of one wavelength and / or multiplex holograms diffracting light of several wavelengths, can be arranged as hologram stacks. The master hologram can, for example, be a diffractive optical element (DOE). Diffractive optical elements (DOEs) use a surface relief profile with a microstructure for their optical function. Alternatively, the microstructure can also be present in the volume of the element, e.g. in the form of a local difference in the refractive index.The light transmitted through a DOE can be converted into almost any desired distribution through diffraction and subsequent propagation. This can be an image, a logo, text, a refraction pattern, or similar. The master hologram preferably comprises a volume hologram.

[0063] The process for producing the master hologram can preferably be referred to as "hologram origination" or "hologram mastering." The master hologram can be created using an analog or digital process. In an exemplary analog process, a first coherent beam, the object beam, is reflected from an object and onto a recording material, which is simultaneously exposed to a second coherent beam, the reference beam. The object beam and the reference beam interfere, creating an interference pattern on or in the recording material. This interference pattern is recorded by light-sensitive material, so that after processing, the shape of a surface relief pattern on a surface of the material or a spatially varying refractive index is created in the material, which is usually only a few micrometers thick.To view an image of the original object, the master hologram can be illuminated with light diffracted by the recorded surface relief pattern or refractive index pattern. This diffracted beam contains the image of the original object. The master hologram can then be used as a new object when creating further copies with the same image.

[0064] The master hologram can preferably also be computer-generated. The microscopic gratings that produce the diffraction effects can be produced, for example, by laser interference lithography. In this technique, two or more coherent light beams are configured to interfere at the surface of a recording material. The positions of the light beams relative to the recording material can be controlled by a computer. Depending on the strength of the laser, the recording material can be made of almost any material. Other techniques such as electron beam lithography can also be used to digitally produce the master hologram. The master hologram can preferably comprise glass, silicon, quartz, UV varnish, a photopolymer composite, and / or a metal such as nickel.

[0065] For the purposes of the invention, a "coupling element" is preferably a three-dimensional block of transparent material with a refractive index and dimensions configured to direct the exposure beams toward and / or away from the master holograms. The coupling element can preferably have various optically accessible surfaces. Preferably, at least one side surface and one bottom surface of the coupling element are optically accessible. In some embodiments, the coupling element can have the shape of a cuboid block, a (flat) plate, a pyramid, or a prism. In some embodiments, the coupling element is prismatic, i.e., it has a constant cross-section of any shape, e.g., square, polygonal, elliptical, or circular. The ends of the coupling element that have the shape of the cross-section can be referred to as the "base surface."The elongated surface of the coupling element, located between the two ends, can be referred to as the "surface surface." In some embodiments, the shape of an axially rotatable cylinder is preferred. For the purposes of the invention, the shape of a rotatable prismatic coupling element, preferably a cylinder, can also be referred to as a "roller."

[0066] Preferably, the coupling element can be formed from an optical plastic or optical glass, wherein in preferred forms, preferred materials mentioned above with regard to the substrate body of the master element can be used.

[0067] It is preferred that the surface of the coupling element comprises glass, PC, TAC, or PMMA. The surface material can be in the form of a foil or a plate in the case of a multilayer coupling element. However, the surface material can also be the material of a monolithic coupling element and, for example, have a cuboid or cylindrical shape.

[0068] In a preferred embodiment of the invention, the surface of the coupling element has an anti-reflective coating. This allows reflection losses on the surface of the coupling element to be largely eliminated.

[0069] The coupling element can be arranged in various orientations with respect to the master element, with the light-sensitive composite track preferably being positioned between the coupling element and the master element during exposure. Assuming a cuboid-shaped coupling element and master element with top, bottom, and side surfaces, the coupling element can, for example, be arranged above the master element. In this case, it may be preferable for the composite track to be guided between a top side of the master element and a bottom side of the coupling element. A reference beam can be directed obliquely downwards onto a side surface of the coupling element, which is present as a block or cuboid above the master element. The reference beam is refracted by the coupling element, and the refracted reference beam travels through the composite track to the master hologram.The refraction caused by the coupling element can be used, for example, to achieve the acute angle of incidence required for an edge-lit hologram. A master hologram can reflect the refracted reference beam, allowing an object beam from the master hologram to pass through the composite sheet. The object beam and reference beam interfere in the light-sensitive material of the composite sheet to create a reflection hologram. By providing an optical adhesive film on both sides of the composite sheet, optical losses or unwanted reflections at the interfaces can be effectively prevented.

[0070] In a preferred embodiment of the invention, the optical adhesive film and / or the light-sensitive composite web is applied to the surface of the master element and / or the coupling element by means of lamination.

[0071] A “lamination” in the sense of the invention is preferably a method for joining two components, wherein the bond is preferably not 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 flow during lamination. The lamination is preferably designed such that the photosensitive composite web and / or the optical adhesive film continuously covers a rigid surface, preferably of a master element and / or coupling element, so that no gaps, bubbles or wrinkles are present. Optionally, the lamination is carried out using a laminating roller, which can preferably exert pressure. The lamination can take place at room temperature (20°C).Optionally, the lamination roller can also be heated to a lamination temperature above room temperature, for example, selected from a range of 20°C - 200°C, preferably 40°C - 100°C. The lamination (for example, a lamination pressure or a lamination temperature) is preferably designed to create a gap-free, but detachable (temporary) bond between the light-sensitive composite web and / or the optical adhesive film and a relevant surface (for example, a master element and / or coupling element).

[0072] In a preferred embodiment of the invention, the optical adhesive film and / or the photosensitive composite web are applied to the surface of the master element and / or the coupling element by bringing a flowing photosensitive composite web into contact with a partial circle of a curved surface. Preferably, the curved surface is part of the lateral surface of a rotatable cylinder, with the partial circle preferably having an opening angle between 1° and 45°, more preferably between 2° and 20°. Preferably, the photosensitive composite web and / or the optical adhesive film temporarily assumes the shape of the lateral surface during exposure.

[0073] In a preferred embodiment of the invention, the method comprises the step of detaching the optical adhesive film from the master element, the coupling element and / or from the photosensitive composite web. The detachment preferably takes place continuously or intermittently. In a roll-to-roll process, the optical adhesive film can be continuously moved through a device in sync with the composite web. If, instead, the composite web is held stationary for each exposure step and only moved after complete exposure of a master hologram (e.g., if the master element is a plate rather than a roller), the optical adhesive film is preferably also held stationary during the exposure step and detached after complete exposure of the master hologram.In a preferred embodiment of the invention, a refractive index difference between the surface of the master element and the optical adhesive film and / or between the optical adhesive film and a surface of the photosensitive composite web is not more than 0.2, preferably not more than 0.1, and more preferably not more than 0.05.

[0074] By adjusting the refractive index of the optical adhesive film to match or closely match the refractive index of the adjacent process component, it is possible to achieve excellent optical contact without internal reflections at the interfaces. The quality of the reproduced hologram can be improved by minimizing losses and optical interference.

[0075] Likewise, in the case where the optical adhesive film is placed between the photosensitive composite sheet and a coupling element, the difference between the refractive index of the optical adhesive film and an adjacent surface of the coupling element is preferably not more than 0.2, more preferably not more than 0.1, and even more preferably not more than 0.05.

[0076] In a further preferred embodiment of the invention, the refractive index of the optical adhesive film lies between the refractive index of the surface of the master element and the refractive index of a surface of the photosensitive composite web. If the optical adhesive film is arranged between the photosensitive composite web and a coupling element, the refractive index of the optical adhesive film is preferably between that of the photosensitive composite web and that of the coupling element. In this context, the term "between" preferably also includes the values ​​of the refractive indices of the adjacent process components themselves. This arrangement enables a smooth or interference-free transition of light rays between the various process components with minimal reflections and / or aberrations at interfaces.

[0077] As an illustrative example, the refractive indices, starting from a substrate body of a master element, can be chosen, for example, as follows.

[0078] Substrate body (from N-BK7): n e = 1 .519

[0079] Adhesive layer: n e = 1 ,51 Master hologram (photopolymer layer): n e = 1,500

[0080] Master hologram (protective film): n e = 1 .485

[0081] Optical adhesive film (adhesive layer / carrier layer / adhesive layer): n e = 1 .47 / 1 .485 / 1 .47

[0082] Composite sheet (carrier film / photopolymer layer / carrier film) n e = 1.48 / 1.50 / 1.48

[0083] In the above example, the light-sensitive composite sheet may, for example, comprise a carrier film made of triacetate (TAC), which has a refractive index of 1.48. Unless otherwise stated, the refractive indices mentioned in this text are measured according to ISO 489.

[0084] If the light-sensitive composite web comprises photopolymers 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-mentioned values ​​allow a particularly smooth optical transition.

[0085] If the light-sensitive composite web comprises photopolymers and, for example, a PC carrier film, the optical adhesive film can 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.

[0086] In a further example, in which the photosensitive composite sheet comprises a PC carrier film and is in contact with the optical adhesive film, which in turn is in contact with a TAC protective layer of a master element, it may also be preferred that the refractive index of the optical adhesive film is between that of PC and TAC, that is, the optical adhesive film preferably has a refractive index between 1.48 and 1.58.

[0087] Those skilled in the art are familiar with materials that, based on the present teaching, enable the most continuous possible transition between the refractive index of the master element / coupling element and the adjacent surface of the light-sensitive composite web. For example, as an alternative, the substrate body can comprise Borofloat-33, which has a refractive index of 1.48. The materials of the additional layers can be selected to match this index. For all of the above-mentioned components (substrate body to optical adhesive film), it is generally preferred that the respective refractive index be between 1.4 and 1.6.

[0088] 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 preferred embodiments, the photosensitive material is soft and / or deformable, particularly in liquid or resinous form. Thus, the photosensitive material can adhere to a solid surface and optionally be deformed, for example, to replicate a surface relief pattern.

[0089] Preferably, during exposure, the uncovered side of the photosensitive material is brought into contact with the surface of the master element. Preferably, no optical adhesive film is used between the photosensitive material and the master element. Instead, the optical adhesive film can be inserted between the side of the carrier film facing away from the master element and a coupling element. By bringing the photosensitive material into contact with the surface of the master element, the material deformability of the photosensitive material can be exploited to achieve seamless contact with the surface of the master element. For example, the photosensitive composite web can be printed onto the surface of the master element to eliminate air gaps. Alternatively or additionally, the photosensitive material can have adhesive properties analogous to the properties of the optical adhesive film.This can prevent unwanted reflections at the interface between the photosensitive material and the master element. This arrangement can offer additional advantages if the master element has a surface relief that can be transferred into the photosensitive composite web through contact. Optionally, additional layers, such as a second carrier film or a protective coating, can then be applied to the exposed and preferably cured photosensitive material to enclose the photosensitive material.

[0090] In a further preferred embodiment of the invention, the optical adhesive film comprises at least one adhesive layer. The at least one adhesive layer preferably has a peel force relative to the surface of the master element and / or the coupling element and / or a surface of the light-sensitive composite web of less than 3 N / cm (Newton per centimeter), preferably less than 1 N / cm. In preferred embodiments, however, the peel force of the adhesive layer of the optical adhesive film relative to the surface of the master element and / or the coupling element and / or a surface of the light-sensitive composite web is at least 0.01 N / cm, preferably at least 0.1 N / cm. It has been proven that the aforementioned parameters for the peel force represent an optimum between easy, residue-free removal of the optical adhesive film from the respective component and the simultaneous elimination of an optical interface between the components.Furthermore, it has been found that these peel forces sufficiently suppress relative movements such as vibrations between the components. While the transparent adhesives of the prior art can help improve the quality of hologram reconstruction, the optical adhesive film of the present invention improves the quality of replication. It is sufficiently adhesive to reduce optical losses at the interface between the components, but can also be removed, allowing the composite web to be moved from a master element to another processing station.

[0091] The material and design of the adhesive layer are preferably selected such that it adheres to the material of the composite web, the master element, and / or the coupling element with which it is to be brought into contact and does not repel it. Thus, the adhesive layer preferably adheres to all transparent polymers and glasses, in particular to the above-mentioned preferred materials for a master element, coupling element, or a composite web. Additionally or alternatively, the adhesive layer preferably adheres to a solid and / or resinous light-sensitive material, particularly preferably a photopolymer. In particular, the optical adhesive film does not serve to facilitate the detachment of the composite web from the respective process component, but rather to improve the optical contact. This can also include an additional improvement in mechanical or electrostatic contact.

[0092] The peel force of the optical adhesive film or one of its layers can be measured, for example, using a 180-degree peel test. The preferred method is ASTM D903, in which six inches of adhesive tape is applied to a clean substrate surface. The substrate is clamped. One free end of the adhesive tape is folded back 180 degrees and pulled with a force gauge. The force in Newtons required to detach each inch of the adhesive tape from the substrate is the peel force.

[0093] The peel strength of an adhesive material with respect to a substrate surface preferably depends not only on the material composition of the adhesive material and the substrate, but also on the process conditions under which the adhesive material was applied to its carrier, if present, and to the substrate surface. For pressure-sensitive adhesive materials, for example, a stronger bond to a carrier layer can be achieved if high pressure, temperature, and / or additional crosslinking of the adhesive material to the carrier layer is applied during application of the carrier layer. Preferably, an additional primer layer can be incorporated to specifically increase the adhesion of the adhesive material to the carrier layer.This effect can be exploited to improve the integrity of a multilayer optical adhesive film and, at the same time, to minimize peel forces of the multilayer adhesive film with respect to process components such as a composite web, a coupling element or a master element.

[0094] In contrast to the OCAs used in the prior art finished products to create permanent adhesion, the preferred peel force is low. This means that the optical adhesive film adheres sufficiently to ensure optical contact during exposure, but at the same time can be easily removed without tearing or leaving residue on the composite web or adjacent process components. Furthermore, the optical adhesive film can advantageously be provided extremely thin. High mechanical strength is not necessary to prevent damage or tearing upon removal from the respective surface. Furthermore, a relatively low adhesive or peel force of the optical adhesive film facilitates reuse of the optical adhesive film, for example, by providing a loop, as explained above.

[0095] In a further preferred embodiment of the invention, the optical adhesive film comprises at least one adhesive layer, wherein the at least one adhesive layer has a modulus of elasticity of up to 50 MPa. The modulus of elasticity can be determined, for example, by a test based on DIN EN ISO 725, ASTM D5026 or ASTM D882 or DIN EN 15870. This means that the optical adhesive film preferably has a certain degree of elasticity. This is particularly useful for wrapping the optical adhesive film around transport rollers and the surfaces of the optical components with which it is used. The sufficiently elastic optical adhesive film is less likely to be pinched, damaged and / or torn during transport through the process. Furthermore, plastic deformations, which can lead to irregularities in the optical contact, can be avoided.

[0096] The adhesive layer preferably has a transmittance of at least 80%, whereby the transmittance is preferably measured without Fresnel correction. This preferably means that the measured transmittance is reduced by the amount of the two Fresnel reflections on the front and back of the material. The transmittance without Fresnel reflections is preferably approximately 8% higher than with an uncorrected method. Alternatively, the transmittance measurement can be carried out at the Brewster angle using p-polarized light, since there is no interfacial reflection for p-polarized light at the Brewster angle. The transmittance preferably refers to the permeability of a medium to light waves without changing the wavelength. The percentage transmittance is preferably the percentage of the intensity of the transmitted light compared to the light incident on the medium. The transmittance can be measured, for example, according to DIN EN ISO 13468.The adhesive layer is therefore preferably transparent to light across the wavelength spectrum 400–780 nm and exhibits minimal light scattering. Preferably, the adhesive layer is colorless. However, a yellowish or grayish appearance is also acceptable. Such an adhesive layer can be used for a variety of applications and is therefore preferable to a color-filtering adhesive layer that is red, blue, green, etc. Preferably, the adhesive layer has a haze of up to 2%. It is desirable that the degree of haze be minimized. This leads to a reduction in the losses of the light used for exposure as well as a reduction in unwanted reflections.

[0097] For the purposes of the invention, the term "haze" preferably refers to transmission haze, measured according to ASTM D1003. Haze preferably refers to the scattering of light upon passing through a transparent material, which can lead to the creation of additional interfering interference fields and thus to additional but undesirable micro-optical structures in the replicated hologram. Haze can be inherent in the material, a result of the molding process, a consequence of the surface structure, or the result of environmental factors such as surface abrasion.

[0098] Preferably, the adhesive layer exhibits a brightness variation of up to 20% across its width between crossed polarizers. This reduces the optical losses caused by the adhesive layer and increases the quality of the replicated hologram.

[0099] The adhesive layer preferably further comprises an adhesive material based on acrylic, EVOH, rubber, silicone, or mixtures thereof. In particular, such materials can advantageously achieve a preferably low peel force, high transparency, sufficient elasticity, and mechanical strength. Furthermore, these materials can be easily formed into adhesive films of suitable thicknesses. Methods for producing adhesive materials based on the aforementioned materials are known to those skilled in the art. Such methods are described in the specialist literature, for example, in "Haftklebebänder, selbstklebende Folien und Etiketten" (H-adhesive Tapes, Self-Adhesive Films and Labels) by Georg Krüger, ISBN 3446422811.

[0100] The adhesive material preferably comprises at least one polymerizable resin, the polymerizable resin preferably being based on acrylic, EVOH, rubber, silicone, or mixtures thereof, and at least one polymerization agent. The polymerization agent is preferably selected to initiate the polymerization of the monomers present in the polymerizable resin. The polymerization agent preferably comprises a crosslinker and / or a crosslinking catalyst. Examples of monomers of a first type that are present in the polymerizable resin (e.g., acrylic resin) and can be polymerized by the polymerization agent are (meth)acrylic acid ester monomers. The polymerizable resin may also comprise monomers of a second type that have crosslinkable functional groups so that they can react with the monomers of the first type.Examples of such crosslinkable functional groups include hydroxyl groups, carboxyl groups, glycidyl groups, isocyanate groups, or a nitrogen-containing functional group, and the like. The crosslinker and / or crosslinking catalyst is preferably selected taking into account the crosslinkable functional groups present in the polymerizable resin. The adhesive strength of the composition can be adjusted by adding a crosslinker of a suitable type and amount. Suitable components and methods for producing an adhesive material with the preferred optical and mechanical properties are known to those skilled in the art.

[0101] In preferred embodiments, the adhesive layer has a thickness of 50 μm to 250 μm. The thickness can be adjusted depending on the desired properties of the optical adhesive film. For example, a lower thickness can increase the transparency of the optical adhesive film, while higher thicknesses can provide better compensation for any irregularities in the surfaces to be bonded and ensure increased mechanical strength. The aforementioned parameter range has proven particularly advantageous for a wide variety of applications.

[0102] In preferred embodiments, the adhesive material comprises a crosslinker. A crosslinker can advantageously reduce the peel force required to detach the optical adhesive film from the relevant surfaces. The crosslinker preferably also prevents adhesive residues from remaining on the surfaces. A small amount of a crosslinker in an adhesive composition can increase the adhesive strength of the adhesive up to a certain concentration. Above such a threshold concentration, for example, 0.2%, an increase in the crosslinker can reduce the adhesive strength. The proportion of crosslinker used can therefore advantageously adjust the adhesive properties of the adhesive material.

[0103] A "crosslink" is preferably a bond or a short sequence of bonds that connects one polymer chain to another. These bonds can be covalent or ionic, and the polymers can be either synthetic polymers or natural polymers (such as proteins). A "crosslinker" is preferably an additive that promotes the formation of such crosslinks between the polymers present in the adhesive material.

[0104] Examples of crosslinkers include isocyanate crosslinkers, epoxy crosslinkers, aziridine crosslinkers, metal chelate crosslinkers, or modified silanes such as aminobissilane. For example, a silane compound can be used as a crosslinker for acrylic resins.

[0105] Preferably, a crosslinker is present in the adhesive material at a concentration of at least 0.1 wt.%, preferably at least 0.2 wt.%, particularly preferably 0.2-0.9 wt.%. For the aforementioned concentrations, preferred peel forces of the optical adhesive film on different surfaces could be achieved in a preferred range of 0.3-1.6 N / cm. These preferred crosslinker concentrations are particularly advantageous for an acrylate-based crosslinker. However, the preferred concentration of a crosslinker can depend on its crosslinking activity, the base material, or the surface, as will be explained in more detail later in this text.

[0106] In a further preferred embodiment of the invention, the optical adhesive film has a single-layer structure, wherein the structure has precisely one adhesive layer. The precisely one adhesive layer is preferably adhesive on both sides to facilitate 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 1 MPa, more preferably at least 2 MPa. The tensile strength is preferably determined by a test method according to ASTM D882 or DIN EN ISO 725.Such an optical adhesive film can, on the one hand, be kept extremely thin and transparent, while, on the other hand, it has sufficient strength for various processes such as transport, application, and / or lamination and can be removed without residue without risk of damage. In a further preferred embodiment of the invention, the optical adhesive film has at least one carrier layer. Such an optical adhesive film has a multilayer structure, wherein the carrier layer is coated on at least one side with an adhesive layer. The carrier layer is preferably non-adhesive. In some embodiments, the carrier layer can be coated with an adhesive layer on only one side.

[0107] In a further preferred embodiment of the invention, the optical adhesive film comprises two adhesive layers, wherein each adhesive layer is preferably applied directly to the carrier layer. It is particularly preferred that the carrier layer is coated on both sides with an adhesive layer, so that the optical adhesive film comprises three layers. Such an optical adhesive film can adhere to two surfaces simultaneously, whereby particularly good optical contact can be achieved and the risk of air gaps or unwanted reflections is reduced. In the case of a multi-layer (e.g. two-layer and / or three-layer) optical adhesive film, it is preferred that one or all adhesive layers have a tensile strength of at least 1 MPa, preferably up to 2 MPa.This ensures sufficient force transfer so that shear forces within the multi-layer structure do not lead to relative movements between the layers.

[0108] In a further preferred embodiment of the invention, the at least one adhesive layer is applied directly to the carrier layer. Preferably, the peel force of the adhesive layer relative to the carrier layer is greater than the peel force of the adhesive layer relative to the surface of the master element and / or the coupling element and / or a surface of the photosensitive composite web and / or a protective film. This ensures that the adhesive layer adheres to the carrier layer throughout the entire process and prevents the leaving of adhesive residues on process components.

[0109] The different peel forces of the adhesive layer relative to a carrier layer of the adhesive film or surface of process components (e.g. a master element, a coupling element and / or a composite web) can preferably be influenced by the selection of materials and / or process conditions under which the adhesive layer can be applied to a carrier layer. In preferred embodiments, the carrier layer is prepared on the side to which the adhesive layer is applied by applying a primer. In this way, the adhesive material can be applied to the carrier film and, in addition to crosslinking the adhesive material, a bond to a primer layer of the carrier film can be created. As a result, the adhesive layer adheres more firmly to the carrier layer than to a material laminated to the adhesive layer after crosslinking, even if this material consists of the same material as the carrier film.

[0110] In a further preferred embodiment of the invention, the surface of the carrier film to be coated with the adhesive layer is treated prior to coating, for example, by plasma treatment or corona treatment. Such a surface treatment can also advantageously increase the adhesion between the carrier film and the adhesive layer.

[0111] In another preferred embodiment of the invention, the process conditions under which the adhesive layer is applied to the carrier layer are selected to increase the adhesion of the adhesive layer to the carrier layer. Preferably, the temporary application of the optical adhesive film to the surface of the master or coupling element takes place under different process conditions that ensure a lower peel force on the surface of the process components. In this way, the effect of process conditions such as pressure, temperature, and light can be exploited to ensure the integrity of a multilayer optical adhesive film during use.

[0112] The carrier layer preferably 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 force or subjected to greater friction without tearing. With such a carrier layer in a multilayer structure, the tear resistance and thus the processability of the optical adhesive film as a web product can be reliably increased, significantly minimizing the risk of leaving residues on the relevant surfaces. This enables particularly reliable elimination of air gaps at the interface between the relevant surface and the optical adhesive film and improved optical contact.

[0113] Preferably, the carrier layer - analogous to the at least one adhesive layer - has a transmission of at least 80%, wherein the transmission is preferably measured without Fresnel correction. The optical adhesive film can be transparent to light - in particular in a wavelength range of 400-780 nm - and have minimal light scattering. It can also be preferred for the carrier layer to have a haze of up to 1.5% in order to reduce light losses and desired reflections. In particular, it is preferred for the carrier layer to have a brightness fluctuation between crossed polarizers of up to 30% across the width of the carrier layer in order to reduce the optical losses caused by the carrier layer.

[0114] The carrier layer preferably comprises one or more of the following materials: polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene, polypropylene, cellulose acetate, triacetate (TAC), cellulose hydrate, cellulose nitrate, cycloolefin polymers, polystyrene, polyepoxides, polysulfone, cellulose triacetate (CTA), polyamide, polymethyl methacrylate, polyvinyl chloride, polyvinyl butyral, polydicyclopentadiene, or mixtures thereof. The carrier layer particularly preferably comprises polycarbonate (PC), polyethylene terephthalate (PET), cellulose acetate, triacetate (TAC), polymethyl methacrylate, or mixtures thereof.

[0115] The thickness of the carrier layer is preferably between 6 μm and 100 μm. It has been found that a thickness of at least 6 μm can provide the preferred tensile strength of at least 5 MPa for a wide variety of materials, while maintaining high transparency. The use of thinner carrier layers also results in an overall thinner optical adhesive film. At greater thicknesses, however, the carrier film is even more tear-resistant. Up to a thickness of approximately 100 μm, particularly high transmission and low haze can still be ensured. The aforementioned parameter range has therefore proven particularly advantageous for a wide variety of applications.

[0116] In a further preferred embodiment of the invention, the optical adhesive film is provided with at least one protective film. Preferably, the 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, maintaining its smoothness and low haze. The protective film also protects the adhesive layer from particles that may be present during the replication process and enables the optical adhesive film to be delivered in roll form. It can also simplify handling of the optical adhesive layer, particularly during winding, unwinding, and transport.The protective film preferably comprises one or more of the following materials: polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene, polypropylene, cellulose acetate, triacetate (TAC), cellulose hydrate, cellulose nitrate, cycloolefin polymers, polystyrene, polyepoxides, polysulfone, cellulose triacetate (CTA), polyamide, polymethyl methacrylate, polyvinyl chloride, polyvinyl butyral, polydicyclopentadiene, silicone paper, or mixtures thereof. Particularly preferably, the protective film comprises polyethylene, polypropylene, silicone paper, or mixtures thereof. The thickness of the protective film is preferably 10 μm to 50 μm.

[0117] In a further preferred embodiment of the invention, the at least one protective film is present directly on the at least one adhesive layer. The peel force required to remove the protective film from the adhesive layer is preferably no more than 0.2 N / cm, particularly preferably no more than 0.1 N / cm.

[0118] In a further preferred embodiment of the invention, the optical adhesive film is provided with protective films on both sides. It may be preferable for only one or both protective films to be removed before exposure. For example, it may be preferable for the protective film to be removed on the side facing the master element and / or coupling element.

[0119] It is preferable to remove the protective films from both sides of the optical adhesive film so that the adhesive properties of the optical adhesive film can contribute to improving the optical contact at both its interfaces with the adjacent process component. This improves the optical contact between the light-sensitive composite web and the coupling element and / or master element.

[0120] In a further preferred embodiment of the invention, the optical adhesive film is temporarily applied between the light-sensitive composite web and the surface of the master element or the coupling element by means of at least one roller. The at least one roller is preferably selected from the group comprising: unwinding roller, transport roller, winding roller, and / or lamination roller. The optical adhesive film can, for example, circulate between two transport rollers arranged such that the path of the optical adhesive film contacts the surface of a master element. Alternatively, the optical adhesive film can flow between an unwinding and a winding roller so that its path contacts the surface of a master element.

[0121] In the case of a rotatable master element, the master element can be placed in a path of the optical adhesive film between an unwinding and a winding roller, so that the optical adhesive film comes into contact with a portion of the surface of the master element. In this case, the optical adhesive film (as well as the composite web) preferably temporarily assumes the shape of a portion of a lateral surface of the master element. The optical adhesive film is preferably guided over the rotating master element, and the speed of the optical adhesive film, the composite web, and the master element are preferably synchronized. Such an arrangement is particularly advantageous in the context of a roll-to-roll hologram duplication process, wherein the rotational speed of the various rollers can be adjusted. Such a process is fast, economical, and preferably suitable for the continuous mass production of HOEs.

[0122] With a stationary, cuboid-shaped master element, a lamination roller can roll over an extended optical adhesive film and, for example, bring it into contact with the flat top surface of a master element. By applying appropriate pressure, air gaps can be eliminated and a particularly seamless application can be achieved.

[0123] In a further preferred embodiment of the invention, the optical adhesive film is introduced between the photosensitive composite web and the surface of the master element during the exposure step by means of a coupling element. Preferably, a second optical adhesive film is introduced between the photosensitive composite web and the coupling element during exposure, as shown, for example, in Figures 5, 6, and 8.

[0124] In a further preferred embodiment of the invention, the surface of the master element and / or the surface of the coupling element is curved, wherein preferably the master element and / or the coupling element is designed as an axially rotatable cylinder or roller.

[0125] If the surface of the master element and / or coupling element is curved, as in the case of a cylinder, the optical adhesive film preferably adheres temporarily over a relatively short length to the surface of the master element, for example to the lateral surface of a cylindrical master element and / or coupling element. The temporary adhesion of the optical adhesive film preferably occurs over a length between 1 and 20 mm, particularly preferably between 2 and 10 mm. This length can depend on the radius of the cross-section of the cylinder. The area of ​​adhesive and optical contact between the optical adhesive film and the master element and / or coupling element can also be measured in terms of the opening angle of the cross-section of the cylinder around whose arc the optical adhesive film is applied. This angle is preferably between 1° and 45°, more preferably between 2° and 20°.With such a length and / or opening angle, the risk of the optical adhesive film tearing is significantly reduced, and air gaps are sufficiently eliminated. A particularly low force is required to move the optical adhesive film through a continuous process, including the continuous detachment of the adhesive film from the curved surface.

[0126] In a further preferred embodiment of the invention, the steps of the method are controlled by a control unit. Preferably, the control unit controls the transport speed of the optical adhesive film and the photosensitive composite web so that they are synchronized with each other during exposure.

[0127] The term "control unit" preferably refers to any computer unit with a processor, a processor chip, a microprocessor, or a microcontroller that enables automatic control of the components of the device, e.g., the rotation speed of an unwinding roller, a rewinding roller, a lamination roller, a transport roller, the movements / rotation of a master element, the movements / rotation of a coupling element, a lamination temperature, a lamination pressure, an orientation and / or scanning speed of a light source, a wavelength of the light source, a fixation intensity, etc. The components of the control unit can be conventional or individually configured for the respective implementation. Preferably, the control unit comprises a processor, a memory, and computer code (software / firmware) for controlling the components of the device.

[0128] The control unit may also comprise a programmable circuit board, a microcontroller, or other device for receiving and processing data signals from the components of the device, for example, from sensors relating to the identity or type of a master element, as well as other relevant sensory information. The control unit preferably further comprises a computer-usable or computer-readable medium, such as a hard disk, random access memory (RAM), read-only memory (ROM), flash memory, etc., on which computer software or code is installed. The computer code or software for controlling the components of the device may be written in any programming language or model-based development environment, e.g., without limitation, C / C++, C#, Objective-C, Java, Basic / VisualBasic, MATLAB, Python, Simulink, StateFlow, Lab View, or Assembler.

[0129] The term "control unit is configured to" perform a specific process step, such as exposing a master element at a specific angle by changing the speed of one or more drive motors, may include custom or standard software installed on the control unit that initiates and controls these operational steps.

[0130] The exposure for replicating a master hologram using the method according to the invention can be carried out using various techniques. Hologram replication processes can be divided into relief holograms and volume holograms.

[0131] Relief holograms are formed by physical contact between a deformable sensitive layer and a master hologram, so that the diffraction pattern of the master hologram is imprinted into the sensitive layer.

[0132] A volume hologram is preferably written into a sensitive layer by the interference of two light beams (a so-called reference beam and an object beam). Preferably, a volume hologram is written into the composite web. This can preferably be done using a transmission or reflection technique. Interference of object and reference beams within the hologram volume preferably creates a sequence of Bragg planes. A volume hologram therefore preferably has a non-negligible extension in the propagation direction of the light beams, whereby the Bragg condition applies during reconstruction on a volume hologram. For this reason, volume holograms exhibit wavelength and / or angular selectivity. The ability of volume holograms to store multiple images simultaneously enables, among other things, the production of colored holograms or white holograms.Light sources that emit the three primary colors blue, green, and red can be used to record holograms. These three beams preferably simultaneously illuminate a portion of the composite web. After exposure, three holograms are stored simultaneously in the volume hologram. To reproduce the color hologram, it can be exploited that each partial hologram can be reconstructed using only the color with which it was recorded. Thus, the three reconstructed color separations overlap to create a color, true-to-original image, provided the color components are correctly weighted.

[0133] Reflection holograms are reflective holograms that reflect incoming light from a light source, thus acting like a mirror. Preferably, the incident direction of the reference beam (preferably an incoming light beam from the light source) and the object (in this case, the master hologram) are arranged on opposite sides of the composite sheet. A reference beam penetrates the composite sheet and is then reflected by the master hologram back into the light-sensitive layer of the composite sheet. In the light-sensitive layer of the composite sheet, the reference beam and object beam overlap in different beam directions to create the replicated hologram. The master hologram can preferably be applied to a surface of the master element or integrated into the substrate body.

[0134] A light source for exposing a reflection hologram can be arranged such that the reference beam is incident on the composite path in a desired direction, preferably in a direction that is desired for later reconstruction. In a preferred embodiment, the light source is oriented with respect to the master element such that the composite path is located between the light source and the master element. The light source can, for example, be aligned above the master element such that the reference beam is incident downwards on the composite path in a predetermined direction. The angle at which the reference beam strikes the master hologram can be adjusted by a transparent coupling element that diffracts the light at a desired angle. The reference beam is preferably at least partially reflected by the master element in the form of an object beam back into the composite path.The reference beam and the object beam enter the photopolymer composite from opposite sides and interfere in its light-sensitive layer to replicate the hologram.

[0135] Transmission holograms are transmissive holograms, where the light from a light source is transmitted and diffracted by it. Preferably, the incident direction of the reference beam (preferably an incident light beam from the light source) and the object (in this case, the master hologram) are arranged on the same side of the composite sheet. An incident beam penetrates the master hologram and is separated into an (undiffracted) reference beam and an object beam. In the light-sensitive layer of the composite sheet, the reference beam and object beam overlap with the same beam direction to create the replicated hologram.

[0136] In the case of a transmission hologram, it may be preferable to arrange the light source such that the composite path can be illuminated by a reference beam and an object beam from the same side. The light source is preferably oriented with respect to the master element such that a light beam first passes through the master element and the master hologram before reaching the composite path. The light source can preferably be arranged such that it passes through a transparent master element from a side surface. The light source can also preferably be arranged such that it falls onto the composite path through an upper and / or lower surface of the master element. The incident light beam is preferably refracted by the master element such that a reference beam and an object beam are created, wherein the object beam preferably corresponds to the portion of the light that is diffracted by the master hologram.The object beam preferentially interferes with the undiffracted reference beam in the compound path to replicate the hologram.

[0137] In preferred embodiments of the invention, one or more master elements can be used to expose the composite web to replicate a transmission hologram therein. Preferably, the replicated transmission hologram can be configured to be edge-lit, so that the holographic image can be reconstructed by light from a substantially lateral direction. The replicated transmission hologram can also be configured to be back-illuminated, so that the holographic image can be reconstructed by light incident substantially from back to front. It may also be preferred that one or more master elements are used to expose the composite web and replicate a reflection hologram therein. Likewise, it may be desirable for the replicated reflection hologram to be edge-lit.Such a hologram can, for example, be used in a glass pane with concealed light sources arranged along its edges. The replicated reflection hologram can also be configured to be front-illuminated. Such a hologram can advantageously produce a holographic image when illuminated by ambient light and viewed relatively orthogonally at eye level. Multiple such holograms can also be used in a glass pane, for example of the type disclosed in WO2020157312A1, to produce a holographic image when viewed orthogonally by reflecting light from concealed light sources along a predetermined path. It can also be advantageous to use one or more master elements to expose the composite sheet to produce a hologram comprising both a reflection and a transmission hologram.

[0138] The process components can be arranged in various ways to produce high-quality reflection and transmission holograms as desired. The optical adhesive film is therefore versatile. Various techniques for exposing the composite web with a master element and optionally a coupling element using different reference beam angles and for producing various types of holograms are explained below and in the detailed description with reference to the figures. The techniques can be combined with one another and with other embodiments of the method. An important advantage is that an optical adhesive film according to the invention ensures almost perfect optical contact between the composite web and optical components such as a master element and / or coupling element in the most diverse constellations for replicating a hologram.

[0139] In a preferred embodiment of the invention, an optical adhesive film is inserted between a portion of a lateral surface of a cylindrical master element and a light-sensitive composite web. It may be preferred that no coupling element be used during exposure. In a preferred embodiment, a cylindrical coupling element is used in combination with the cylindrical master element in a roll-to-roll process for exposure. Preferably, the master element and the coupling element are rotatably mounted, with their rotation preferably being synchronized. The optical adhesive film and the light-sensitive composite web can run synchronously between the master element and the coupling element.It is further preferred that a second optical adhesive film is placed between the light-sensitive composite web and the coupling element, so that an arrangement consisting of: cylindrical coupling element / second optical adhesive film / light-sensitive composite web / first optical adhesive film / cylindrical master element is formed. The exposure of such an arrangement can take place from a lateral surface or base surface of the coupling element, so that a reference beam is refracted towards the master hologram. Such an exposure method can be suitable, for example, for producing a reflection hologram. Alternatively, the exposure can also take place, for example, from a lateral surface or base surface of the master element in order to generate a transmission hologram. Since both the master element and the coupling element are designed as rotatable cylinders or rollers, the exposure process can be rapid and continuous.

[0140] In a further preferred embodiment of the invention, a master element, but no coupling element, is used during exposure, wherein the master element has a flat surface and is preferably cuboid or plate-shaped. Preferably, an optical adhesive film is applied to the flat surface of the master element, for example by lamination with a laminating roller. Preferably, the photosensitive composite web is applied to the optical adhesive film, for example by lamination with the same or a further laminating roller. The lamination ensures good optical contact between the photosensitive composite web and the surface of the master element. Such an arrangement can offer a larger contact area compared to an arc-shaped contact over a circular segment of a cylindrical master element.Such an arrangement can therefore be advantageous for the production of series in which, for example, a plurality of holograms are replicated from a plate-shaped master element.

[0141] In a further preferred embodiment of the invention, both a master element and a coupling element are used during exposure, wherein preferably only the master element or the coupling element is cylindrical. The non-cylindrical component can preferably have a flat surface and be, for example, cuboid- or plate-shaped. In such an embodiment, the cylindrical component can be used to laminate the optical adhesive film and / or the photosensitive composite web to the flat surface of the master element or the coupling element.

[0142] As a simple example, the master element can have the shape of a cuboid. A first optical adhesive film can be applied to the upper flat surface of the master element, preferably by lamination. A light-sensitive composite web can be applied to the top side of the first optical adhesive film, preferably also by lamination. Furthermore, a second optical adhesive film can be applied to the top side of the light-sensitive composite web, preferably by lamination. A cylindrical coupling element - which is preferably used for the lamination of one or more of the aforementioned layers - is arranged above the second optical adhesive film, so that optical contact is established between the lateral surface of the coupling element and all of the aforementioned process components up to and including the master element.

[0143] Exposure can be achieved, for example, by directing a reference beam onto the lateral surface or the base surface of the coupling element. The reference beam is refracted within the coupling element such that it exits along the optical contact line and is reflected by a master hologram in the master element. Alternatively, exposure can also be achieved from the master element, with the light then being guided away from the composite web by the coupling element. In another example, the functions of the cuboid and cylindrical components can be reversed, i.e., the coupling element can be cuboid-shaped while the master element is cylindrical.

[0144] In a further preferred embodiment of the invention, a master element and a coupling element are used during exposure, wherein preferably both the master element and the coupling element have a flat surface and are preferably in the form of a cuboid, block, plate, or pyramid. In a preferred embodiment of the invention, the exposure process is carried out with a block-shaped master element, a first optical adhesive film, a light-sensitive composite web, a second optical adhesive film, and a block-shaped coupling element, which are in optical contact with one another in the order mentioned. The coupling element is preferably also in optical contact with the master element, mediated by intermediate layers (first optical adhesive film, light-sensitive composite web, second optical adhesive film).Preferably, the intermediate layers are applied to the respective surface of the master element or coupling element by lamination, for example using a separate laminating roller.

[0145] Detailed description

[0146] In the following, the invention will be explained in more detail using examples and illustrations, without being limited to these.

[0147] Short description of the figures

[0148] Fig. 1 is a schematic representation of a single-layer optical adhesive film provided with protective films on both sides. Fig. 2 is a schematic representation of a three-layer optical adhesive film comprising a carrier layer and two adhesive layers, which is provided with protective films on both sides.

[0149] Fig. 3 shows an example of the peel strength of preferred adhesive layers with different crosslinker concentrations against different surface materials.

[0150] Fig. 4 shows schematically a preferred arrangement for replicating a hologram in which an optical adhesive film is inserted between a cylindrical master element and a light-sensitive composite web.

[0151] Fig. 5 shows schematically a preferred arrangement for replicating a hologram by means of a cylindrical master element and cylindrical coupling element, in which an optical adhesive film is inserted both between the master element and the light-sensitive composite web and between the coupling element and the light-sensitive composite web.

[0152] Fig. 6 shows schematically a preferred arrangement for replicating a hologram by means of a cuboid master element and cylindrical coupling element, in which an optical adhesive film is inserted both between the master element and the light-sensitive composite web and between the coupling element and the light-sensitive composite web.

[0153] Fig. 7 shows schematically a preferred arrangement for replicating a hologram by means of a cuboid master element without a coupling element, in which an optical adhesive film is inserted between the master element and the light-sensitive composite web.

[0154] Fig. 8 shows schematically a preferred arrangement for replicating a hologram by means of a cuboid master element and cuboid coupling element, in which an optical adhesive film is inserted both between the master element and the light-sensitive composite web and between the coupling element and the light-sensitive composite web.

[0155] Fig. 9 shows schematically a preferred arrangement for replicating a reflection hologram by means of a cylindrical master element by exposure to a lateral surface, in which an optical adhesive film is introduced between the master element and the light-sensitive composite web.

[0156] Fig. 10 shows schematically an arrangement for replicating an edge-lit hologram using a cylindrical master element by exposure to a base surface, in which an optical adhesive film is introduced between the master element and the light-sensitive composite web.

[0157] Fig. 11 shows schematically an arrangement for replicating a plurality of holograms which are integrated in a plate-shaped master element and a cylindrical coupling element, wherein an optical adhesive film is introduced between the coupling element and the composite web.

[0158] Fig. 11A is a schematic representation of the application of the photosensitive composite sheet to the surface of the master element.

[0159] Fig. 11B is a schematic representation of the application of the optical adhesive film between the cylindrical coupling element and the photosensitive composite sheet applied to the master element in order to establish an optical contact between the coupling element and the photosensitive composite sheet.

[0160] Fig. 11C is a schematic representation of the detachment of the coupling element from the exposed composite web.

[0161] Detailed description of the illustrations

[0162] Figure 1 shows a single-layer optical adhesive layer 2 for use in a method according to the invention. The optical adhesive layer 2 comprises precisely 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, it is preferred that the material of the adhesive layer 15 is a weakly adhesive adhesive. Such an adhesive can preferably be peeled off from the surface of a respective process component with a peel force of no more than 3 N / cm, preferably 1 N / cm. It is preferred that the tensile strength of the adhesive layer 15 is at least 1 MPa, preferably at least 2 MPa, and that the single-layer optical adhesive film 2 has a modulus of elasticity of less than 50 MPa.Such an optical adhesive film 2 can, on the one hand, be kept extremely thin and transparent, while, on the other hand, it has sufficient mechanical strength and elasticity for various processes such as transport, application and / or lamination and can be removed without residue without risk of damage.

[0163] The thickness of the single-layer optical adhesive film 2 is preferably between 50 and 250 μm, so that any irregularities or gaps between the light-sensitive composite web and the surface of the respective process component in the area of ​​optical contact are reliably filled to enable optimal exposure. The refractive index of the single-layer adhesive film 2 is preferably close to that of the adjacent layer of the light-sensitive composite web and / or the adjacent layer or surface of the respective process component.

[0164] Figure 2 shows a three-layer optical adhesive film with a carrier layer 14 coated with a first adhesive layer 15 on a first side and a second adhesive layer 16 on an opposite side. Together, these three layers form the optical adhesive film 2. The adhesive layers 15 and 16 preferably have properties similar to those of the single-layer optical adhesive film of Figure 1. However, it may be preferred that the adhesive material used in these layers be more adhesive than the adhesive material of the single-layer optical adhesive film. In addition, these adhesive layers may have a lower tensile strength of up to 1 MPa.

[0165] Preferably, the adhesive materials of the adhesive layers 15 and 16 of these embodiments require a greater peel force to be removed from the carrier layer 14 than from the surface of the respective process component and / or the photosensitive composite web 1.

[0166] It may be preferred that the adhesive material used in the adhesive layers 15, 16 of Figs. 1 and 2 comprises a crosslinker. Fig. 3 shows the results of a study of the effect of a crosslinker on the adhesive strength of an adhesive material. The adhesive material studied was made on the basis of acrylate. However, similar results were also achieved with adhesive materials based on silicone or rubber. The adhesive layers 15 were prepared with different concentrations of crosslinker. The adhesive layers 15 were applied to surfaces made of various materials such as glass, PC, TAC and PMMA and then peeled off the corresponding surfaces at an angle of 180° at a speed of 300 mm / min. The peel force required to detach the adhesive layers from the corresponding surfaces was measured per cm of the adhesive layers.

[0167] The results show that increasing the crosslinker concentration reduces the peel force required to detach the adhesive layers from the various surfaces. For example, at a crosslinker concentration of 0.4%, the adhesive layer 15 required a peel force of approximately 1.5 N / cm to be removed from a polycarbonate (PC) surface. This is slightly higher than the preferred maximum peel force of 1 N / cm for a low-tack adhesive preferred for use in the single-layer optical adhesive film. However, the peel force can be reduced to less than 1 N / cm, for example, by increasing the crosslinker concentration to 0.6%.

[0168] The low peel forces achieved by the adhesive layers shown as examples are ideally suited for the temporary application and residue-free removal of an optical adhesive film to improve optical contact between different process components.

[0169] According to the invention, the optical adhesive film 2 can be used in a variety of arrangements to optimize the optical contact between different elements in an exposure process. Figures 4-8 are merely illustrative examples of the application of the optical adhesive film 2 according to the invention.

[0170] Fig. 4 shows the use of an optical adhesive film 2 between a cylindrical master element 4 and a light-sensitive composite web 1. The master element 4 can preferably comprise a master hologram on its outer surface and is preferably mounted so as to be rotatable. The light-sensitive composite web 1 is guided over a section of the outer surface on an underside of the master element 4, wherein an area of ​​the composite web 1 to be exposed temporarily assumes the shape of a outer surface of the master element 4, at least in some areas, and is guided over the rotating master element 4, moving along with the outer surface. During exposure, an optical adhesive film 2 is introduced between the composite web 1 and the circumference of the outer surface of the master element 4.In the area of ​​optical contact, the optical adhesive film 2 is substantially parallel to the light-sensitive composite web 1, with its movement being synchronized with the movement of the light-sensitive composite web 1.

[0171] In this arrangement, the light can be directed, for example, from below onto the photosensitive composite sheet to form a reflection hologram. For such exposure, the master element 4 can be transparent or opaque, preferably apart from a transparent cover layer that protects the master hologram. The reference beam can pass essentially undeflected through the photosensitive composite sheet 1, the optical adhesive film 2, and the transparent cover before being reflected by the master hologram. In the photosensitive layer of the composite sheet, the reference beam and object beam overlap in different beam directions to create the replicated hologram.

[0172] The optical adhesive film 2 advantageously prevents unwanted reflections and / or light losses from occurring at the interfaces between the optical adhesive film 2 and the light-sensitive composite web 1 and / or the cover of the master element 4.

[0173] The arrangement can also be used to expose a transmission hologram in the light-sensitive composite web 1. In this case, the master element 4 preferably comprises a transparent substrate body and a transparent cover layer. A reference beam can, for example, be directed from above through the lateral surface of the master element 4 so that it is transmitted through a master hologram, the optical adhesive film 2, and the composite web 1. Alternatively, a reference beam can be directed onto a base surface of the master element 4 so that it is refracted by the substrate body of the master element 4, and the refracted beam is transmitted through a master hologram 6, the optical adhesive film 2, and the composite web 1. In both cases, the reference beam is partially transmitted undiffracted by the master hologram and partially diffracted to generate an object beam that also passes through the optical adhesive film 2 and composite web 3.In the light-sensitive layer of the composite sheet 3, the reference beam and object beam overlap with the same beam direction to create the replicated hologram. The optical adhesive film 2 also prevents unwanted optical losses and internal reflections at the interfaces, resulting in a high-quality transmission hologram.

[0174] Fig. 5 schematically shows another exemplary arrangement for replicating a hologram using optical adhesive films according to the invention. In this example, two optical adhesive films 2 are used. A first optical adhesive film 2 is arranged between a rotatably mounted cylindrical master element 4 and a light-sensitive composite web 1. A second optical adhesive film 2 is arranged between the light-sensitive composite web 1 and a cylindrical coupling element 9. This arrangement can be used, for example, for exposing a reflection hologram into the light-sensitive composite web 1. The reference beam can be directed by the coupling element 9—either through its lateral surface or base surface—such that it strikes the master hologram on the lateral surface of the master element 4 at a desired angle.A reflection hologram can then be exposed into the photosensitive composite web 1 in a similar manner as described above for Fig. 4. The coupling element 9 can advantageously adjust 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. It is therefore particularly advantageous to apply optical adhesive films 2 to the two interfaces between the various exposed process components (coupling element 9, composite web 1, and master element 4) to avoid unwanted optical losses and reflections.

[0175] Fig. 6 shows a further arrangement of the process components for replicating a hologram, in which the master element 4 has the shape of a cuboid block. The upper 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) that protects the master hologram. The master element 4 can be used to expose a reflection hologram into the photosensitive composite web 1 with the aid of the coupling element 9, as explained above for Fig. 5, for example.

[0176] Fig. 7 shows a further arrangement in which the master element 4 has the shape of a cuboid block. An optical adhesive layer 2 is laminated to the top of the master element 4, while a photosensitive composite sheet 1 is also laminated to the top of the optical adhesive layer 2. The master element 4 can preferably be exposed from above (i.e., toward its top side) with a reference beam, which passes through the photosensitive composite sheet 1, the optical adhesive layer 2, and a transparent cover layer (not shown) before being reflected by the master hologram back into the photosensitive composite sheet 1 to form a reflection hologram.As an alternative to replicating a transmission hologram, the master element 4 can be illuminated from its underside or from a side surface, while its transparent block-shaped substrate body refracts the reference beam so that it impinges on the master hologram at a desired angle. The reference beam can then be diffracted by the master hologram to form an object beam that interferes with the reference beam in the light-sensitive composite track 1.

[0177] Fig. 8 shows an arrangement analogous to Fig. 7, in which a block-shaped coupling element 9 is placed over the second optical adhesive film 2. The coupling element 9 can be used, for example, to refract a reference beam such that it strikes the master hologram at a desired angle in order to expose a reflection hologram in the light-sensitive composite web 1.

[0178] Figs. 9 and 10 are a more detailed illustration of an exposure process with an arrangement analogous to that of Fig. 4.

[0179] Fig. 9 shows the exposure of a reflection hologram from the outer surface of a cylindrical master element 4. Transport rollers 3 are used to position a photosensitive composite web 1 around a circular arc of the circumference of the master element 4 such that a significant part of the photosensitive composite web 1 is in optical contact with the master element 4. Preferably, an area of ​​optical contact corresponds to a circular arc of the circumference of the master element 4 having an angle of at least 1°, preferably of 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 flow of the photosensitive composite web 1 over its outer surface. Alternatively, the rotation of the master element 4 can also be caused by the friction resulting from the movement of the optical adhesive film 2 over its outer surface.The photosensitive composite web 1 moves from right to left during exposure. An unwind roller 10 is provided for unwinding an optical adhesive film 2. A take-up roller 13 is provided for winding the used optical adhesive film 2. The take-up roller 13 can be an active roller that pulls the optical adhesive film 2 and thus controls its flow during the process. The optical adhesive film 2 is arranged between the photosensitive composite web 1 and the outer surface of the master element 4 in such a way that it mediates optical contact between the outer surface of the master element 4 and a surface of the photosensitive composite web 1.

[0180] The optical adhesive film 2 is provided with a protective layer 6, 7 on both sides. Winding rollers 11 and 12 are used to remove the protective layers 6 and 7 before the optical adhesive film 2 reaches the area of ​​optical contact between the mast element 4 and the photosensitive composite web 1.

[0181] A reference beam 5 is directed from below onto the master element 4, passing through the photosensitive composite sheet 1, the optical adhesive film 2, and the cover layer of the master element (not shown) before being reflected by the master hologram. The reflected object beam passes again through the cover layer, the optical adhesive film 2, and the photosensitive composite sheet 1, where it interferes with the reference beam to imprint a reflection hologram onto the photosensitive composite sheet 1.

[0182] Fig. 10 shows an embodiment analogous to Fig. 9. However, the reference beam 5 is directed onto a base surface of the transparent master element 4, where it is refracted such that it exits a lower surface through the master hologram at a desired angle. The reference beam is partially transmitted undiffracted through the master hologram and partially diffracted to generate an object beam, which also passes through the optical adhesive film 2 and composite sheet 3. The undiffracted reference beam and a diffracted object beam interfere with each other in the light-sensitive composite sheet 1 to form a transmission hologram.

[0183] Fig. 11A-11C show a method for replicating a hologram in a photosensitive composite web 1 according to a preferred embodiment of the invention. Fig. 11A shows the step of applying a photosensitive composite web 1 to the surface of a master element 4. The master element 4 is a cuboid-shaped, continuous plate that houses several master holograms A, B, C, etc. Preferably, all master holograms are protected with a single transparent cover so that the surface of the master element is continuous. A laminating roller 8 rolls over the extended photosensitive composite web 1 and presses it against the continuous surface of the master element 4 to eliminate any air bubbles. As shown in Fig. 11A, the laminating roller 8 moves, for example, from right to left over the photosensitive composite web 1.At the same time, a transparent cylindrical coupling element 9 is lowered towards the laminated photosensitive composite web 1. An optical adhesive film 2 is positioned over a circular arc of the circumference of the coupling element 9 with the help of various rollers. An unwinding roller 11 supplies the optical adhesive film 2, while a take-up roller 13 winds up the optical adhesive film 2 after exposure. The take-up roller 13 can be an active roller - i.e., provided with an actuator - that pulls the optical adhesive film 2 and thus controls its flow during the process. Transport rollers 3 are used to adjust the position of the optical adhesive film 2 relative to the outer surface of the coupling element 9. The movement of the optical adhesive film 2 from right to left can cause a rotation of the 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 unrolled before the exposure step using the unwind rollers 11 and 12.

[0184] Fig. 11 B schematically shows an application of the optical adhesive film 2 between the cylindrical coupling element 9 and the photosensitive composite web 1 in order to establish an optical contact between the coupling element 9 and the photosensitive composite web 1. The coupling element 9 is rolled from right to left over the upper side of the photosensitive composite web 1, whereby a seamless optical contact is created between the master element 4 and the coupling element 9. The optical adhesive film 2 is applied synchronously with the movement of the coupling element 9. The area of ​​the optical contact moves together with the coupling element 9 from right to left. During the application of the coupling element 9, light is used to expose the photosensitive composite web 1 in the area of ​​the optical contact. The light source (not shown), for example a laser, can move synchronously with the coupling element 9.This synchronous movement of the light source may preferably involve scanning across the width of the light-sensitive composite web 1.

[0185] Fig. 11C shows the detachment of the coupling element 9 from the exposed composite web 1. The cylindrical coupling element 9 is lifted and carries the optical adhesive film 2, which remains adhered to its surface. The lamination roller 8 is then rolled back from left to right so that the exposed composite web 1 can be lifted and detached from the upper side of the master element 4. Suitable means (such as additional rollers) that can effect the detachment of the composite web 1 from the upper side of the master element 4 are known to those skilled in the art.

[0186] While in the example of Figures 11A-11C, the lower cuboid plate functions as the master element 4 and the larger transparent roller as the coupling element 9, the functions of these process components can also be reversed. For example, the lower plate can be configured as the coupling element, while the larger transparent roller is a master element. The light source can then be arranged accordingly, for example, illuminating the coupling element from a lower surface or side surface.

[0187] List of reference symbols

[0188] 1 Light-sensitive composite sheet

[0189] 2 Optical adhesive film

[0190] 3 Transport roller

[0191] 4 Master element

[0192] 5 light

[0193] 6 First protective film

[0194] 7 Second protective film

[0195] 8 Laminating roller

[0196] 9 Coupling element

[0197] 10 Unwinding roller for optical adhesive film

[0198] 11 Winding roller for first protective film

[0199] 12 Winding roller for second protective film

[0200] 13 Winding roller for optical adhesive film

[0201] 14 Carrier layer

[0202] 15 First adhesive layer

[0203] 16 Second adhesive layer

Claims

PATENT CLAIMS 1. Method for replicating a hologram into a photosensitive composite web (1), comprising the following steps: a. providing a master element (4) comprising a substrate body and at least one master hologram, b. applying a photosensitive composite web (1) to a surface of the master element (4), c. exposing the master element (4) to replicate the at least one master hologram into the photosensitive composite web (1), and d. removing the exposed composite web (1) from the master element (4), characterized in that the method further comprises a temporary application of an optical adhesive film (2) between the photosensitive composite web (1) and the surface of the master element (4), which provides optical contact between the master element (4) and the photosensitive composite web (1) during the exposure of the master element (4).

2. Method for replicating a hologram into a photosensitive composite (1), comprising the following steps: a. providing a master element (4) comprising a substrate body and at least one master hologram, b. applying a photosensitive composite (1) to a surface of the master element (4), c. applying a coupling element (9) to the photosensitive composite (1) such that the photosensitive composite (1) is positioned between a surface of the coupling element (9) and the surface of the master element (4), d. exposing the master element (4) using the coupling element (9) to replicate the at least one master hologram into the photosensitive composite (1), e. detaching the coupling element (9) from the exposed composite (1), and f.Detachment of the exposed composite web (1 ) from the master element (4), characterized in that the method further includes a temporary application of an optical adhesive film (2) between the photosensitive composite web (1 ) and the surface of the. The coupling element (9) comprises an optical contact between the coupling element (9) and the photosensitive composite film (1) during exposure of the master element (4). The method according to claim 1 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 a surface of the photosensitive composite film (1) is no more than 0.2, preferably no more than 0.1, and more preferably no more than 0.

05. The method according to claim 1 or 3 is characterized in that the refractive index of the optical adhesive film (2) lies between the refractive index of the surface of the master element (4) and the refractive index of a surface of the photosensitive composite film (2).A method according to one or more of claims 1 or 3-4, 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 strength against the surface of the master element (4) and / or a surface of the photosensitive composite web (1) of less than 3 N / cm, preferably less than 1 N / cm. A method according to one or more of the preceding claims, 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 and preferably a transmission of at least 80%, a haze of up to 2%, and / or a brightness variation between crossed polarizers of up to 30% across a width of the adhesive layer (15).Method according to one or more of the preceding claims 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 acrylic, EVOH, rubber or silicone and wherein the adhesive layer (15) preferably has a thickness of 50 pm to 250 pm. A method according to one or more of the preceding claims, characterized in that the optical adhesive film (2) has a single-layer structure comprising 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. A method according to one or more of the preceding claims, 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.A method according to claim 9, characterized in that the at least one adhesive layer (15) is applied directly to the carrier layer (14) and the peel strength of the adhesive layer (15) against the carrier layer (14) is greater than the peel strength of the adhesive layer (15) against the surface of the master element (4) and / or a surface of the photosensitive composite web (1) and / or a protective film (6, 7). A method according to any one of the preceding claims 9 or 10, characterized in that the optical adhesive film (2) comprises two adhesive layers (15, 16), wherein preferably each adhesive layer (15, 16) is applied directly to the carrier layer (14).A method according to one or more of claims 9-11, characterized in that the support layer (14) has a tensile strength of at least 5 MPa, wherein the support layer (14) preferably has a transmission of at least 80%, a haze of up to 1.5%, and / or a brightness variation between crossed polarizers of up to 30% across a width of the support layer (14). A method according to one or more of claims 9-12, characterized in that the support layer (14) comprises one or more of the following materials: polycarbonate (PC), polyethylene terephthalate (PET), cellulose acetate, triacetate (TAC). Polymethyl methacrylate or mixtures thereof, wherein the carrier layer (14) preferably has a thickness of 6 pm to 100 pm. A method according to one or more of the preceding claims, characterized in that the optical adhesive film is provided with at least one protective film (6), preferably with two protective films (6, 7) on both sides, wherein the at least one protective film (6) is removed before the step of temporarily applying the optical adhesive film between the photosensitive composite layer (1) and the surface of the master element (4). A method according to the preceding claim, characterized in that the at least one protective film (6) comprises one or more of the following materials: polyethylene, polypropylene, silicone paper, or mixtures thereof, wherein the at least one protective film preferably has a thickness between 10 and 50 pm.Method according to one or both of the two preceding claims characterized in that the at least one protective film (6) is located directly on the at least one adhesive layer (15), wherein the necessary peel force for removing the protective film (6) from the adhesive layer (15) is no more than 0.2 N / cm, preferably no more than 0.1 N / cm.

Images