METHOD FOR ADJUSTING THE REFRIGERATIVE INDEX

Description

TECHNICAL AREA

[0001] Several aspects of the disclosure relate to the manufacture of optical components for optical elements used in display devices, such as data glasses. BACKGROUND

[0002] Adhesives are known from the state of the art that are suitable as specialized optical cements for filling structures, such as those used in data glasses for embedding functional layers.

[0003] The key to developing such data glasses lies in the so-called smart glasses, which project virtual content into the field of vision. This typically involves an injection-molded optical component with various high-precision freeform surfaces, a so-called waveguide. An injection-molded Fresnel structure, coated with a semi-transparent layer, serves to project the virtual image to the eye while simultaneously allowing the wearer to perceive their surroundings through this structure without obstructing their view. Alternatively, this structure can also be partially coated with a 100% reflective layer. Provided the areas with 100% reflective coating are relatively small (e.g., diameter <1 mm) and the intervening areas have a sufficiently high transmission rate for ambient light, the wearer can also perceive a virtual image superimposed on their surroundings.

[0004] To ensure an unobstructed view in both horizontal and vertical directions through the prisms or mirror structures arranged in the smart glass, it is advantageous for the adhesive used to have a refractive index as close as possible to that of the base material. Furthermore, the adhesive can be part of the optical path for the virtual image. Manufacturing such devices requires precise refractive index matching of the adhesive to the optical components, a process also known as "index matching."

[0005] The optical elements used for this purpose are usually manufactured by gluing and joining optical components, such as transparent shells or overcrowded Fresnel structures.

[0006] According to WO 2015 / 121341 A1, adhesives with optically functional properties, such as a defined refractive index, can be produced by using adhesive components with optical properties. A desired refractive index or dispersion (Abbe number) of such adhesives can be adjusted to the intended purpose by selecting the components used, particularly their chemical structure. Refractive correction of adhesives for optical components (precision cements), especially refractive correction to a specific optical component to be bonded, can be achieved for defined wavelengths (e.g., in optical measuring systems) or, in polychromatic applications, for a specific wavelength range (e.g., 450 nm - 700 nm). In polychromatic refractive correction, it is important to match the dispersion (wavelength dependence of the refractive index) of the precision cement and the optical components as closely as possible.Typically, a center wavelength is defined in such cases, e.g., 546 nm (ne). The dispersion of fine putties can be controlled by the adhesive components used, since the chemical structure of the monomer substances has a significant influence on the refractive index and dispersion.

[0007] One specific application is the aforementioned cementing of optical components that exhibit diffractive, reflective, and / or other micro-optical elements on a component surface. If the refractive index is adjusted to Δn < 0.0005, diffractive structures embedded in the cement layer, for example, become virtually invisible.

[0008] Depending on the structure to be filled and its relative position to the direction of view, it may be necessary to adjust the refractive index between the adhesive and the base material to the fourth or fifth decimal place in order to ensure the least possible disturbance to the user's vision when looking through it.

[0009] Adhesives that meet the above requirements, such as a permanently constant value with the described accuracy for the refractive index, are hardly available commercially, since even with identical adhesives there is usually at least a slight variation between different batches.

[0010] Achieving this level of accuracy in the refractive index during synthesis is a complex task. Whether dealing with a two-component (2K) system of resin and hardener, or a mixture of several one-component (1K) systems, each component must be manufactured to extremely tight tolerances. If batches of resin and hardener with different production dates are to be used in daily production while adhering to the maximum permissible index deviation, the effort and tolerance management become even more demanding.

[0011] When optical components to be bonded or filled are manufactured using injection molding, variations in the refractive index of the base glass itself cannot be ruled out. These variations are due, for example, to the optical properties of the plastic granules used, which also exhibit, or can exhibit, manufacturing-related variations in their refractive index. Due to the process parameters of injection molding, different refractive indices result in the finished component for the exact same starting material, depending on the processing parameters. These indices can also differ locally within the component. Examples of process parameters that influence solidification behavior and thus also the local optical properties include temperature and shear conditions during melting in the cylindrical screw, injection speed, holding pressure profile, cooling time, and mold temperature control.Since these parameters also influence the geometric dimensions of the injection-molded part, they are typically used to compensate for environmental and manufacturing variations to ensure compliance with geometric component tolerances. The process-related coordination of dimensional accuracy and refractive index for the base glass and adhesive system therefore presents a particular challenge. BRIEF SUMMARY

[0012] Therefore, there is a need for improved techniques to manufacture optical elements with a precisely matched refractive index. This problem is solved by the features of the independent claims. The features of the dependent claims define embodiments.

[0013] A method for adjusting the refractive index of an adhesive for an optical element is disclosed, wherein the adhesive is optically transparent and is made from several starting materials, the method comprising: Producing at least one test specimen of the optical element using the adhesive, performing an optical analysis of the at least one test specimen of the optical element by measuring at least one parameter, adjusting a mixing ratio of the several starting materials of the adhesive based on a result of the optical analysis, and producing several series products of the optical element using the adhesive with the adjusted mixing ratio of the several starting materials.

[0014] Preferably, in the inventive method, several test specimens of the optical element can be produced successively, wherein the mixing ratio of the several starting materials is adjusted between the production of the several test specimens, based on the results of the preceding optical analyses of the several test specimens. The adjustment is preferably carried out progressively, linearly, or degressively.

[0015] The method can further include the implementation of a control loop, whereby the control loop compares the at least one measured variable with a respective setpoint and adjusts the dosage of at least one of the several starting materials as the controlled variable when adapting the mixing ratio. The control loop can be implemented, for example, by software that is executed from memory on a processor-based system. A suitable controller can be used. In particular, the control tolerance of such a control loop can be defined as a deviation from a predetermined refractive index of less than 0.0005 or less than 0.0001.

[0016] The adhesive can be a two-component adhesive, wherein the multiple starting materials comprise a first starting material, a second starting material, a third starting material, and a fourth starting material, and a first component of the two-component adhesive is mixed from the first starting material and the second starting material, a second component of the two-component adhesive is mixed from the third starting material and the fourth starting material, and the adjustment of the mixing ratio of the multiple starting materials can include adjusting a first part mixing ratio of the first starting material relative to the second starting material when mixing the first component, and adjusting a second part mixing ratio of the third starting material relative to the fourth starting material when mixing the second component.Furthermore, adjusting the mixing ratio may include adjusting a third part of the mixing ratio of the first component relative to the second component.

[0017] In the process according to the invention, the mixing of the first component of the two-component adhesive from a first starting material and a second starting material can take place in a first mixer, and the mixing of the second component of the two-component adhesive from a third starting material and a fourth starting material can take place in a second mixer. The mixing of the first and second components of the two-component adhesive can take place in a third mixer downstream of the first and second mixers.

[0018] The mixing ratio of the several starting materials can be adjusted by changing the quantity of at least one of the several starting materials, by changing the weight of at least one of the several starting materials, by changing the volume of at least one of the several starting materials, and / or by changing the flow of at least one of the several starting materials from a storage container into a mixing container, for example via a metering pump.

[0019] In the method according to the invention, the at least one measured quantity can comprise color separation and / or an optical offset of the optical transmission of the optical element, which are determined based on the optical transmission of the test pattern. The at least one measured quantity can comprise the prismatic effect of the optical element, which is determined based on the optical transmission of the test pattern, and / or can comprise optical dispersion of the adhesive at a specific wavelength or in a wavelength range. The optical element can be any type of micro- and / or macrostructure which, due to its geometric configuration, leads to an optically measurable deviation in the test image in the event of a non-compliant refractive index of the adhesive.Typical geometries include: Fresnel structures, prism structures, pyramid structures, grooved or wavy structures, spherical, toric, or freeform curved surfaces – connected or segmented, arranged individually or as an array, etc. The optical element may preferably comprise a Fresnel structure, and the test pattern can be reflected laterally into the Fresnel structure or the optical element during the process. The Fresnel structure may, for example, have steps along a surface, and lateral reflection can then occur in the plane of this surface.

[0020] In the method according to the invention, the optical element can comprise several optical components, and the production of the at least one test specimen of the optical element comprises bonding several optical components with the adhesive and initiating a curing of the adhesive, wherein the optical analysis is carried out before, during or after the initiation of the curing.

[0021] The production of at least one test specimen of an optical element comprising multiple optical components can involve bonding these components with adhesive and initiating the curing of the adhesive. A first optical component of the multiple optical components of the optical element comprises a Fresnel structure, and a second optical component of the multiple optical components of the optical element comprises a shell. Alternatively, other structures, such as prismatic structures, are also conceivable. BRIEF DESCRIPTION OF THE FIGURES

[0022] FIG. 1 shows an exemplary arrangement for carrying out the optical analysis according to the method of the invention. FIG. 2 schematically shows the effect of the refractive index variance for an exemplary adhesive system in the optical analysis of an optical component. FIG. 3 This shows, by way of example, the effects of an insufficient adjustment of the refractive index, which can be used as a measurement parameter for adjusting the refractive index within the framework of optical analysis. FIG. 4 shows a scheme for the setup of a closed-loop controlled process as an embodiment of the method according to the invention. FIG. 5 shows another scheme for the construction of a closed-loop controlled process as an embodiment of the method according to the invention. FIG. 6 This is a flowchart of an exemplary procedure. DETAILED DESCRIPTION OF EXECUTION FORMS

[0023] The properties, features and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more easily understood in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings.

[0024] The present invention is now explained in more detail with reference to preferred embodiments and the drawings. In the figures, identical reference numerals denote identical or similar elements. The figures are schematic representations of various embodiments of the invention. Elements depicted in the figures are not necessarily shown to scale. Rather, the various elements shown in the figures are represented in such a way that their function and general purpose are understandable to a person skilled in the art.

[0025] The following describes techniques used in the manufacture of optical elements. The inventive method for adjusting the refractive index generally comprises the acquisition of at least one measurement parameter during an optical analysis. This enables the determination of the quality of the index match for determining the quantities and mixing ratios of the adhesive, so that the refractive index can be adjusted according to requirements. In the case of "index-matched" overfilling of Fresnel structures, a test pattern, such as a black-and-white test pattern (preferably a pattern of stripes, or a checkerboard pattern, etc.), can be viewed through a filled structure using a camera. The color separation or optical misalignment due to the prismatic effect, which is still present even with a suboptimal match, can then be evaluated and used as a measurement parameter.

[0026] Such techniques can be used to manufacture optical elements that can be used, for example, in connection with smart glasses. Such techniques could also be used, for example, for head-up displays. An exemplary arrangement with which the method according to the invention can be carried out is shown in FIG. 1 shown, wherein a test pattern is represented by a test specimen of an optical component or optical element, for example a test specimen made of a filled Fresnel structure G1 ( FIG. 1a ), G2 ( FIG. 1b ) or G3 ( FIG. 1c The test specimen is viewed using a camera K, and one or more measured parameters, such as color separation and / or optical offset, are recorded and evaluated. This then allows for a specific refractive index adjustment by changing the quantity of the adhesive components; that is, the index match can be made or improved. A further embodiment regarding the arrangement of the test specimen, camera, and test pattern is illustrated in [reference to be added]. FIG. 1(c) As shown: Here, the light emanating from the test pattern is guided within the waveguide until it is coupled out towards the camera. In special cases, this light path within the glass can correspond exactly to that of the application as smart glass.

[0027] The test pattern itself can also be a self-illuminating object, such as a display, or a non-self-illuminating object.

[0028] FIG. 2 This figure illustrates the effect of refractive index variation on an optical component using a sample adhesive system. Besides an offset from the original image and / or a shifted double image, a different (color) separation is a further measure of the match or mismatch of the refractive indices or Abbe numbers of the base material and adhesive, and thus also a measure of the refractive index adjustment required. This allows for direct characterization across the entire visible wavelength range.

[0029] In the FIG. 2 Image a) shows a possible test pattern, and images b) to e) show possible recordings as observed by a viewer or the camera. FIG. 2 Figure 1 shows (a) the target image, (b) a left image shift, (c) a right image shift, (d) a bilateral image shift, and (e) illustrates a color split, e.g., red on the right, blue on the left, or vice versa, etc. This observation can, in principle, be made before, during, or after the curing process. The fully cured state is decisive for the final assessment of sufficient refractive index matching. However, with sufficient experience with the respective adhesive system, the final component quality in the fully cured state can already be inferred from the image defects of the uncured, partially cured, or cured system. Especially with very long curing processes, an early indication of the expected result is particularly valuable in order to compensate for process variations by adjusting the mixing ratios in a timely manner.

[0030] Depending on the sign of the difference between the actual and target values ​​of the refractive index and the geometric relationships of the structures to be filled, the image captured by the camera may show an image shift, a widening of the test marks, or color splitting compared to the original. In the case that the values ​​in this example are FIG. 2 (b) - (e) The images shown represent the achieved final state of the curing process. The measurement of a parameter corresponding to the offset or color separation indicates that the desired index match has not been achieved, so that an improved match can be found by further application of the inventive method, i.e., by adjusting the mixing ratio and producing several series products of the optical element using the adhesive with the adjusted mixing ratio.

[0031] FIG. 3 shows in analogy to FIG. 2 An example is another test pattern as well as optical effects, such as those that occur according to the geometric relationships in the case of an insufficient index match and can be used as measured values. Accordingly, they show FIG. 3 (a) the target image, and FIG. 3 (b) bis (d) a corresponding image offset.

[0032] As can be seen from the above observations regarding FIG. 2 and FIG. 3 In accordance with the invention, the at least one measured parameter can comprise a color splitting and / or an optical offset of an optical transmission of the optical element, which are determined based on the optical transmission of the test pattern.

[0033] The procedure can also be implemented as a closed-loop controlled process. The example in the FIG. 4 The schematically depicted structure, which consists of the arrangement described below, will be explained.

[0034] As previously described, the transparent adhesive used is formed from several starting materials; it can be a two-component (2K) adhesive. For example, the first and second starting materials A1 and A2 can form the resin component A, and the third and fourth starting materials B1 and B2 can form the hardener component B.

[0035] In the FIG. 4 In the described example, a first component A of the two-component adhesive is mixed from a first starting material A1 and a second starting material A2, and a second component B of the two-component adhesive is mixed from a third starting material B1 and a fourth starting material B2. This involves adjusting the mixing ratio of the several starting materials, i.e., a first partial mixing ratio (A1):(A2) of the first starting material A1 relative to the second starting material A2, when mixing the first component A, and an adjustment of the mixing ratio of the several starting materials, a second partial mixing ratio (B1):(B2) of the third starting material B1 relative to the fourth starting material B2, when mixing the second component B.

[0036] In the FIG. 4 In the illustrated embodiment, the reservoirs for the starting materials A1 / A2 contain the starting materials for resin A, i.e., the first and second starting materials A1 and A2, which form resin A and, after mixing in mixer M1, enter reservoir A. The reservoirs B1 / B2 contain the aforementioned starting materials for component B of the adhesive, i.e., the third and fourth starting materials B1 and B2, which, after mixing in mixer M2, enter reservoir B. Components A and B together form the reactive system, which cures over time through thermal and / or photochemical / UV activation, with the components coming into contact in mixer M3 in the illustrated example. The reservoirs can be pressurized to p1 to p6 to ensure the desired feed to the metering pumps P1 to P6. The metering pumps are responsible for the precise adjustment of the mixing ratios in the subsequent mixing systems.Mixers M1 to M3 are responsible for the mixing process and can be controlled accordingly via a controller unit C. For example, mixer M1 can be configured to mix the starting materials A1 and A2, and mixer M2 can be configured to mix the starting materials B1 and B2, which are fed into mixer M3 via pumps P5 and P6, respectively. Mixer M3 is configured to mix components A (here: resin) and B (here: hardener). This results in the adhesive AB being obtained in reactive form. The inventive method can also include adjusting a third mixing ratio of the first component A relative to the second component B.

[0037] The control parameters for the dosing pumps can be generated using the aforementioned optical analysis, i.e., an optical performance analysis, and a control loop can be established in this way. Changing the mixing ratios results in altered reactivity between the components, for example, between the resin and hardener of a two-component adhesive. The quantities of at least one of the starting materials can be adjusted by changing the initial weight, by changing the volume, and / or by changing the flow rate of at least one of the multiple starting materials into a storage container.

[0038] The mixing ratio can be adjusted by a controlled system, whereby the controlled system uses the amount of adhesive components or starting materials being mixed with another adhesive component or starting material as the control variable.

[0039] The components themselves can be composed of several components, constituents, or starting materials. The aforementioned first and second starting materials A1 and A2 for component A can be variants of the same chemical material, in this case, for example, the resin, and differ, for instance, in their refractive index in the range of the third or fourth decimal place. As mentioned above, this difference can be due to the manufacturing process or deliberately adjusted so that one of the two variants is below and the other above the target value of the refractive index for component A. Metering pumps can be used to adjust the mixing ratio of A1 and A2, allowing A to be precisely adjusted to the required refractive index. As mentioned at the beginning, components A1 and A2 can also be different adhesives, for example, two different one-component adhesives.

[0040] The way in which the refractive index for component A is controlled can also be applied to component B, which can be, in particular, the hardener of a two-component adhesive. If the starting materials B1 and B2 differ, for example, in viscosity and / or reactivity, then a precise and needs-based adjustment of the hardener component B is also possible here.

[0041] In combination with the second component B of the reactive system, here the hardener, which in the above example is mixed from the third and fourth starting materials B1 and B2, the final refractive index adapted to the optical component or the component is then obtained by mixing components A and B.

[0042] Especially with thermally curing systems, two opposing effects often occur. Higher temperatures decrease viscosity, which is often desirable to create a thin, uniform adhesive gap. However, this also accelerates the curing process, which, depending on the temperature gradient within the component or adhesive gap, can lead to stresses and distortion. This, in turn, can negatively affect the optical performance of the component or optical element. Therefore, the ability to adjust viscosity and / or reactivity during processing is desirable. Such changes also affect the refractive index of the overall A+B system, which is then compensated for by adjusting the mixing ratio of the starting materials (referred to above as A1 and A2) as described previously.For example, the resin component (referred to above as A) can influence the optical properties, and the hardener component B can influence the processing properties. The components, with their various properties such as batch-by-batch (i.e., production-related) variations in the refractive index of the starting material (referred to above as A1 and A2, respectively), can be mixed as needed.

[0043] Here, the procedure can be used to assess the quality of the index match in order to determine the (for example, in the exemplary arrangements in FIG. 4 and 5The controller C shown includes the individual volume flows and mixing ratios to be set. Such a design can further include the implementation of a control loop, wherein the control loop compares the at least one measured variable with a respective setpoint and, as the controlled variable, adjusts the dosage of at least one of the several starting materials when adapting the mixing ratio.

[0044] As described above, in the "index-matched" overfilling of Fresnel structures, a black-and-white test pattern (stripes, checkerboard pattern, etc.) can be viewed as a test object (designated G1, G2, and G3 in the figures) using a camera. The color separation or optical offset due to the prismatic effect, which is still present even with a suboptimal match, is evaluated and used as a measurement for the index match. An exemplary setup for optical analysis is shown in FIG. 1 , 4 and 5 shown.

[0045] Different analytical methods can also be used to design the control system compared to the analytical methods described above.

[0046] The method of the invention can advantageously be implemented as a process in which a control loop is established. The method can thus include the implementation of a control loop in which the control loop compares the at least one measured variable with a respective setpoint and adjusts the dosage of at least one of the several starting materials as the controlled variable when adapting the mixing ratio. This is applicable both to the mixture of components such as resin and hardener, and to the starting materials of the resin or hardener component.

[0047] Further subconfigurations based on the structure described above are also conceivable, as illustrated by the following example: The structure described so far for a 2-component system also includes its application to a 1-component system, such as UV-curing 1-component adhesives, or mixtures thereof. Here, too, it is extremely difficult, yet necessary, to ensure a perfect index match and to also compensate for process-related index fluctuations (for example, of the plastic used for the base material). According to a FIG. 5 The shown variant of the invention is omitted in comparison to FIG. 4 The starting materials A1 and A2 are mixed to form A, and B1 with B2 to form B. All components A1, A2, B1, and B2 are directly dosed into a single, shared mixer unit M1. The refractive index of the overall system is controlled by varying the volumetric flow rate of the starting materials A1, A2, B1, and / or B2 individually or collectively, according to the required volume ratios. Similarly, the first and second starting materials A1 and A2 can be fed directly into the mixer M1 via pumps P1 and P2, as can starting materials B1 and B2 via pumps P3 and P4. The filled optical component G2, which can be a Fresnel structure, is obtained after mixing A and B.

[0048] FIG. 5 Figure 1 shows a simplified arrangement as an example for carrying out the method of the invention. G1 illustrates a test specimen that may comprise a filled structure of an optical component, e.g., a filled Fresnel structure as an optical component or part of an optical element. The test specimen G1 is subjected to optical analysis with camera K, recording at least one measured quantity, whereby, optionally, as mentioned above, a pattern may also be used for the optical analysis. In the FIG. 5 In the variant shown, the components (for example, resin and hardener, referred to above as A and B) are fed directly to the mixer M1, and are not held as separate components A and B via separate streams in the mixers M1 and M2 (cf. FIG. 4 ). In analogy to the one in FIG. 4 In the arrangement shown, the first and second starting materials A1 and A2 (which, when mixed, yield resin A, for example) are fed to mixer M1 by pumps P1 and P2, optionally subjected to pressures p1 and p2, as determined by the analysis result from test specimen G1. The third and fourth starting materials B1 and B2 (which, when mixed, yield hardener B, for example) are fed to mixer M1 by pumps P3 and P4, optionally subjected to pressures p3 and p4, where they are mixed to form adhesive AB, which is then processed into the filled structure G2. If necessary, structure G2 can then be subjected to optical analysis in parallel or sequentially compared with structure G1 to perform index matching.Structures G1 and G2 can be any type of micro- and / or macrostructure which, due to its geometric shape, leads to an optically measurable deviation in the test image if the adhesive's refractive index does not meet the specifications. Typical geometries include: Fresnel structures, prism structures, pyramid structures, grooved or wavy structures, spherical, toric, or freeform curved surfaces – connected or segmented, arranged individually or as an array, etc.

[0049] As mentioned above, the refractive index can be adjusted by varying the weight or flow or volume of the adhesive components.

[0050] In this way, the refractive index can be adjusted during the manufacturing process, and precise adaptation and tracking can be achieved according to the inventive method. Preferably, this control is effected via a controller (control unit) C, as shown in FIG. 4 and 5 depicted.

[0051] For example, an adhesive in the process according to the invention can be a composition based on epoxy resins and thiols, which can be polymerized by amine catalysis.

[0052] For adhesives, especially structural adhesives used in precision mechanics and optics, there is an increasing need for short curing times. Reactive adhesives with short curing times typically also have short working times. However, from a technological perspective, sufficiently long working times are often required, for example, to precisely align the workpieces to be bonded. Polyurethane adhesives and amine-cured epoxy resins are commonly known as commercially available adhesives that cure at room temperature. With a working time of approximately one hour, the curing time at room temperature until final strength is reached is in the range of one to two days.

[0053] The inventive method for adjusting the refractive index is particularly suitable for an optical element in which optical components and their parts are bonded together by the aforementioned adhesive and the adhesive becomes part of the optical system.

[0054] In the inventive method, an adhesive or composition with a short curing time and a sufficiently long processing time can be used, so that complete curing occurs at room temperature and the micro-putty exhibits excellent adhesive strengths.

[0055] An adhesive that can be used in the method according to the invention can, for example, be taken from DE 10 2012 210 185 A1, WO 2009 / 056196 A1, or WO 2015 / 121341 A1. In this way, the individual parts of an optical component, or optical components, can be joined together by means of an adhesive or adhesive system based on an amine-catalyzed thiol curing of epoxy resins analogous to WO 2015 / 121341 A1, in particular those analogous to claims 1 to 9, and especially preferably analogous to claim 1 of WO 2015 / 121341 A1. The processing can, for example, be carried out at a temperature in the range of 20°C to 80°C, preferably in the range of 40°C to 70°C, and particularly preferably in the range of 45°C to 65°C.

[0056] A tertiary amine can be used as a starting material for an adhesive that can be used in the process according to the invention, analogous to WO 2015 / 121341 A1.

[0057] An adhesive composition usable in the process of the invention can be UV-curable and contain a photolatent base, as described, for example, in claim 9 of WO 2015 / 121341 A1. The photolatent base used in the invention is understood to be the photolatent base compound according to claim 1 of EP 2 145 231 B1, to which reference is made hereforth. A photoinitiator used in the invention is a chemical compound that decomposes into reactive fragments upon absorption of light. These reactive fragments then detach the protecting group from the photolatent base in the composition, resulting in a strongly basic amidine structure from the photolatent base, which, as a base, catalyzes the polymerization reaction between the epoxide and the SH group of the thiol ester.In this way, the amine-catalyzed thiol reaction with the epoxide is locally accelerated in the area exposed to UV light, thereby greatly reducing the curing time of the composition.

[0058] In addition to the photoinitiator, a dye may be included.

[0059] When using the composition according to WO 2015 / 121341 A1 as an embedding medium or for bonding glasses, it is advantageous if the composition additionally contains an alkoxysilane, which may also have a polymerizable group.

[0060] Furthermore, the composition according to WO 2015 / 121341 A1 may additionally contain plasticizers, solid plasticizers, synthetic resins; and / or polymers such as ethylene vinyl acetate copolymers (EVA). Fillers such as quartz flour (Silbond) and highly dispersed silica may also be used as additives.

[0061] Preferably, the resin component of the fine cement, as well as the hardener, should be produced reproducibly with the aforementioned accuracy. To achieve this accuracy, the process according to the invention preferably uses at least two main components, e.g., thiol esters or thiourethanes, with different refractive indices for the resin component (for example, an epoxy compound, component (A)) and / or for the hardener component (for example, a thiol ester (B) or oligomeric thiourethane).

[0062] The compositions for fine putties with high refractive index matching described in WO 2015 / 121341 A1 have proven particularly suitable. It is advantageous to use the oligomers described above or in this publication, especially the oligomeric thiourethanes (reduced volume shrinkage, low stresses during curing, viscosity adapted to the resin component – ​​resulting in better miscibility of resin and hardener).

[0063] The method according to the invention can, for example, be implemented in a method for manufacturing an optical element that is transparent for a predetermined wavelength range and in which an optically effective structure is embedded, comprising the following steps: a) Providing a first shell, transparent to the predetermined wavelength range, formed in one piece and having a structured section on its upper surface; b) Applying an optically active coating to the structured section to form the optically active structure; c) Providing a second shell, transparent to the predetermined wavelength range, formed in one piece and having a bottom surface with a shape complementary to the shape of the upper surface of the first shell, with or without a complementary structure to the first shell; d) Applying a composition transparent to the predetermined wavelength range as an adhesive to the upper surface of the first shell and / or the bottom surface of the second shell; and e) Joining the upper surface of the first shell to the bottom surface of the second shell by means of the adhesive. wherein the refractive index of the optical element is adjusted by the method according to the invention, so that a two-shell optical element is produced in which the optically effective structure is embedded.

[0064] As described above, the optically effective structure can be a Fresnel structure. As mentioned at the outset, the optically effective structures can be any type of micro- and / or macrostructure which, due to its geometric shape, leads to an optically measurable deviation in the test image if the adhesive's refractive index does not meet the specifications. Typical geometries include: Fresnel structures, prism structures, pyramid structures, grooved or wavy structures, spherical, toric, or freeform curved surfaces – connected or segmented, arranged individually or as an array, etc.

[0065] Using such a method, an optical element with two or more shells (especially with exactly two shells) can be manufactured with the desired accuracy in large quantities and with suitable optical properties. The optical element can also have more than two shells and two or more parts that are bonded or joined together with the adhesive.

[0066] The first shell can be provided in step a) such that the top surface, with the exception of the structured section, is formed as a smooth surface.

[0067] Furthermore, after step b), at least one depression formed by the structured section can be filled with material up to the top. Preferably, the same material used to form the first shell is used for this purpose. Alternatively, the described composition can be used for filling.

[0068] The filling process can be carried out in one step or in several steps. Specifically, the filling is performed in such a way that a smooth, continuous surface is achieved. The filled, textured section thus forms a continuous surface together with the rest of the surface.

[0069] In the aforementioned method based on WO 2015 / 121341 A1, in step d) the adhesive, the refractive index of which has been adjusted using the inventive method, can be applied as an adhesive layer to the entire top surface of the first shell and / or the entire bottom surface of the second shell. In particular, the structured section (preferably when it is filled with material up to the top surface) can also be provided with the adhesive layer.

[0070] The first shell can be made from a first polymer material and the second shell can each be selected from one or more thermoplastic materials, thermosetting materials, mineral materials and a combination of polymer material and mineral glasses.

[0071] The optically active structure can be configured, as described in WO 2015 / 121341 A1, for example, as a reflective and / or diffractive structure. In particular, the optically active structure can be configured as a partially reflective structure and / or a wavelength-dependent reflective structure. The formation of the first and / or second shell can, in particular, be carried out in at least two successive steps. This results in reduced shrinkage during the production of the first and second shells, respectively. In the described structure, for example, materials are used as the first and second polymer materials whose refractive indices differ by no more than 0.005, preferably no more than 0.002, more preferably no more than 0.0005, and even more preferably no more than 0.0001 for at least one wavelength from the predetermined wavelength range.In particular, the refractive indices can differ by no more than 0.00005. With such a small difference in refractive index, the interface between the two polymer materials virtually disappears optically for the predetermined wavelength range.

[0072] The polymer materials can be selected to exhibit the same dispersion within a predetermined wavelength range. This predetermined wavelength range can be the visible wavelength range, the near-infrared range, the infrared range, and / or the UV range.

[0073] Using the method according to the present invention, for example, an optical element can be produced according to the procedure described in WO 2015 / 121341 A1 such that, for example, in a first step, a first semi-finished product is produced by injection molding from a thermoplastic polymer. The first semi-finished product has a first side and a second side. A microstructure is formed on the second side, which defines the shape of the desired reflective facets.

[0074] Different materials can be used for the two semi-finished products. However, it is preferred that the same material be used for both. In particular, the aforementioned thermoplastic and / or thermosetting materials are suitable.

[0075] The adhesives described in WO 2015 / 121341 A1 allow sufficiently long working times of approximately 60 - 120 min with complete curing within approximately 4 - 6 hours (at room temperature), achieving excellent bond strengths.

[0076] FIG. 6 This is a flowchart of an exemplary procedure for adjusting the refractive index of an adhesive for an optical element.

[0077] In Box 3005, a test specimen of the optical element is produced. Several optical components of the optical element can be bonded together for this purpose. An optically transparent adhesive, as described above, is used. This optically transparent adhesive comprises several starting materials that are mixed together. In the first iteration of Box 3005, an initial mixing ratio of the several starting materials is used.

[0078] For example, in box 3005 a technique such as that related to FIG. 4 The following steps are carried out to perform the mixing, wherein, as mentioned above, the first and second starting materials A1 and A2, which form the resin A, enter the reservoir A after mixing in mixer M1, and the third and fourth starting materials B1 and B2 enter the reservoir B after mixing in mixer M2. Components A and B together form the reactive system, which cures over time through thermal and / or photochemical / UV activation, with the components coming into contact in mixer M3 in the example shown.

[0079] Furthermore, Box 3005 can contain a technique such as that related to FIG. 5 are carried out, in comparison to FIG. 4 As mentioned above, the components (for example, resin and hardener, referred to above as A and B) are fed directly to mixer M1 and are not held as separate components A and B via separate streams in mixers M1 and M2. By analogy to the FIG. 4 In the arrangement shown, the first and second starting materials A1 and A2 (which, when mixed, yield resin A, for example) are fed to mixer M1 by pumps P1 and P2, optionally subjected to pressures p1 and p2, as determined by the analysis result from test specimen G1. The third and fourth starting materials B1 and B2 (which, when mixed, yield hardener B, for example) are fed to mixer M1 by pumps P3 and P4, optionally subjected to pressures p3 and p4, as well as by pumps P3 and P4. The mixture then forms adhesive AB, which is processed into the filled structure G2.

[0080] The mixing ratio of the starting materials determines the refractive index. In particular, the refractive index at the initial mixing ratio may differ from the refractive index of the substrate material used for one or more of the optical elements. This can occur due to batch variations in the substrate material and / or variations in the mixing ratio of the starting materials. Environmental conditions can also influence the quality of the refractive index match.

[0081] In Box 3010, an optical analysis of the test specimen, which was produced in the current iteration of Box 3005, is performed. The purpose of the optical analysis is to determine the quality of the refractive index matching between the adhesive and the optical components. For example, as mentioned above, an optical analysis can be performed in Box 3010 by recording at least one measured parameter, such as in FIG. 1 ,4 and 5 shown. In particular, in box 3010, as in FIG. 4 and 5 As shown, an optical analysis of the test specimen G1, which may, for example, include a filled Fresnel structure as an optical component, is performed with camera K, recording at least one measurement parameter. If necessary, as mentioned above, the transmission of a pattern by a camera can be used for the optical analysis. The verification technique described in Box 3010 can also be used to verify the result of the optical analysis, such as the one described in FIG. 2 and FIG. 3 Evaluate the displayed color splitting or optical offset.

[0082] Box 3015 then checks whether an index match exists, that is, whether the refractive index of the adhesive differs from the refractive index of the optical components that form the optical element. For example, it can be checked whether a deviation exists within a specified tolerance range, so that the mixing ratio of the several starting materials can be adjusted between the production of the multiple test specimens—preferably progressively, linearly, or degressively—based on the results of the evaluation of the preceding optical analyses of the multiple test specimens, such as the optical misalignment or color separation, as described in FIG. 2 and FIG. 3 depicted.

[0083] If the check in Box 3015 reveals that the refractive index of the adhesive differs significantly from the refractive index of the optical components, the mixing ratio of the starting materials can be adjusted in Box 3020. This could be done in a controlled manner. For example, such a controlled adjustment could take into account the sign and / or magnitude of the deviation and translate it, using a predefined model, into an adjustment of the mixing ratio of one or more starting materials relative to one or more other starting materials. For instance, a tendency might be that a larger deviation in the refractive indices necessitates a larger adjustment of the mixing ratio. The specific implementation of the mixing ratio adjustment depends on the type of adhesive used and / or the starting materials employed.For example, such a dependency could be determined through empirical experiments. Such logic could be implemented by a controller that, based on program code from memory executed by the controller, controls, for example, a metering pump. This allows, in particular, the implementation of a control loop that minimizes the refractive index mismatch and uses the mixing ratio of the starting materials as the control variable. Such a control loop can operate with a particularly high latency because, for example, the optical analysis must wait for a stable state after the adhesive has begun to cure.

[0084] However, if the curing behavior is known, adjustments can be made based on the deviation observed in the uncured state. In this case, the target value would be a specific offset or a specific color separation immediately after application of the adhesive system or in a defined partially cured state.

[0085] With the adjusted mixing ratio, a further iteration of boxes 3005, 3010, and 3015 checks whether an index match exists. This means that the production of multiple test specimens (e.g., progressively, linearly, or degressively) can be carried out, whereby the adjustment of the mixing ratio of the multiple starting materials between the production of two test specimens (in successive iterations of boxes 3005, 3010, and 3015) is based on the result of a corresponding optical analysis from the preceding iteration.

[0086] If the check in Box 3015 finally shows that the refractive index of the adhesive does not deviate, or does not deviate significantly, from the refractive index of the optical components, i.e., a successful index match has been achieved, then finished series products with the desired optical properties can be manufactured in Box 3025.

[0087] Using the above-described method according to the invention, an optical element for a display device or data glasses can be produced, comprising several optical components, and being transparent or partially transparent for a predetermined wavelength range, and in which an optically effective structure is embedded, wherein the method according to the invention enables an adjustment of the refractive index so that interference-free vision through the optical element is possible.

Claims

1. Method of adjusting the refractive index of an adhesive for an optical element, wherein the adhesive is optically transparent and is produced from multiple starting materials, wherein the method comprises: - producing at least one specimen of the optical element using the adhesive, - conducting an optical analysis of the at least one specimen of the optical element with recording of at least one measurement parameter, - adjusting a mixing ratio of the multiple starting materials of the adhesive based on a result of the optical analysis, and - producing multiple repeat products of the optical element using the adhesive with the adjusted mixing ratio of the multiple starting materials.

2. Method according to Claim 1, wherein multiple specimens of the optical element are produced successively, wherein the mixing ratio of the multiple starting materials is adjusted between the producing of the multiple specimens, based on the result of the preceding optical analyses of the multiple specimens.

3. Method according to Claim 2, wherein the method further comprises: implementing a closed-loop control circuit, wherein the closed-loop control circuit compares the at least one measurement parameter with a respective target value and sets a dosage of at least one of the multiple starting materials as controlled variable in the adjusting of the mixing ratio.

4. Method according to Claim 3, wherein a closed-loop control tolerance of the closed-loop control circuit as variance from a defined refractive index is less than 0.0005 or less than 0.0001.

5. Method according to any of the preceding claims, wherein the multiple starting materials comprise a first starting material, a second starting material, a third starting material and a fourth starting material, wherein the adhesive is a two-component adhesive, wherein a first component of the two-component adhesive is mixed from the first starting material and the second starting material, wherein a second component of the two-component adhesive is mixed from the third starting material and the fourth starting material, wherein the adjusting of the mixing ratio of the multiple starting materials comprises the adjusting of a first partial mixing ratio of the first starting material relative to the second starting material in the mixing of the first component, wherein the adjusting of the mixing ratio of the multiple starting materials comprises the adjusting of a second partial mixing ratio of the third starting material relative to the fourth starting material in the mixing of the second component, wherein optionally the adjusting of the mixing ratio comprises the adjusting of a third partial mixing ratio of the first component relative to the second component.

6. Method according to any of the preceding claims, wherein the multiple starting materials comprise a first starting material, a second starting material, a third starting material and a fourth starting material, wherein the adhesive is a two-component adhesive, wherein the first component of the two-component adhesive is mixed from the first starting material and the second starting material in a first mixer, and wherein the second component of the two-component adhesive is mixed from the third starting material and the fourth starting material in a second mixer, and wherein the first and second components of the two-component adhesive are mixed in a third mixer downstream of the first and second mixers.

7. Method according to any of the preceding claims, wherein the mixing ratio of the multiple starting materials is adjusted by varying an amount of at least one starting material of the multiple starting materials, by varying a weight of at least one starting material of the multiple starting materials, by varying a volume of at least one starting material of the multiple starting materials, and / or by varying a flow rate of at least one starting material of the multiple starting materials from a reservoir vessel into a mixing vessel, for example via a metering pump.

8. Method according to any of the preceding claims, wherein the performing of the optical analysis comprises the recording of a temporal evolution of the at least one measurement parameter over a period of at least 24 hours, and / or wherein the performing of the optical analysis comprises the detecting of an optical transmission of a test pattern through the optical element by means of a camera, wherein optionally the at least one measurement parameter comprises a colour splitting and / or an optical displacement of an optical transmission of the optical element, which are determined based on the optical transmission of the test pattern, and / or wherein the at least one measurement parameter comprises the prismatic effect of the optical element which is determined based on the optical transmission of the test pattern.

9. Method according to Claim 8, wherein the optical element comprises a Fresnel structure, and wherein the test pattern is reflected laterally into the Fresnel structure.

10. Method according to any of the preceding claims, wherein the at least one measurement parameter comprises an optical dispersion of the adhesive at a particular wavelength or within a wavelength range.

11. Method according to any of the preceding claims, wherein the optical element comprises multiple optical components, wherein the producing of the at least one specimen of the optical element comprises the bonding of the multiple optical components with the adhesive and the initiating of curing of the adhesive, wherein the performing of the optical analysis commences after the initiation of curing.

12. Method according to any of the preceding claims, wherein the optical element comprises multiple optical components, wherein the producing of the at least one specimen of the optical element comprises the bonding of multiple optical components with the adhesive and the initiating of curing of the adhesive, wherein a first optical component of the multiple optical components of the optical element comprises a Fresnel structure, and wherein a second optical component of the multiple optical components of the optical element comprises a shell, wherein optionally the first optical component is a shell comprising the Fresnel structure.

13. Method according to either of Claims 11 and 12, wherein one or more of the optical components have been produced by the injection moulding method.

14. Method according to any of the preceding claims, wherein a curing reaction of the adhesive is initiated by means of UV light and / or thermally.

15. Method according to any of the preceding claims, wherein the adhesive is a thermally curing or photochemically curing such as, for example, UV-curing adhesive, and / or wherein the adhesive is produced from multiple 1-component adhesives as starting materials, and / or wherein the adhesive comprises an epoxy resin that cures via amine-catalysed thiol, or a polycarbonate resin.