Multi-layer adhesive bond with axial gradients of the coefficients of thermal expansion

Abstract

The present invention relates to an optical system, comprising a first and a second optical element and at least two polymer layers, to a method for producing an optical system, and to the use of the optical system for reality systems.

Description

[0001] Description

[0002] Multilayer adhesive bond with axial gradient of

[0003] Thermal expansion coefficients

[0004] The present invention relates to an optical system comprising a first and a second optical element and at least two polymer layers, a method for producing an optical system and the use of the optical system for augmented reality systems, virtual reality systems, smart glasses, head-mounted displays, mixed reality systems, extended reality systems and cross reality systems.

[0005] Glued lens systems are known in the art and describe an optical configuration in which two lenses are glued together with their flat or curved sides to perform an optical and mechanical function. The way light is guided through the system depends on the optical properties and arrangement of the two lenses. These systems are often used in applications such as microscopes, cameras, and projectors.

[0006] US 2020 / 0412923 A1 describes an image pickup assembly and a manufacturing method for an image pickup assembly. The image pickup assembly comprises an image pickup element, an adhesive layer, and an optical layer. The adhesive layer comprises a plurality of stacked adhesive sublayers.

[0007] In general, optical elements, such as lenses, which have a particularly large diameter-to-thickness ratio (usually an aspect ratio, for example, of the diameter of a lens to its thickness at the center, in a range greater than 10) and also significantly different coefficients of thermal expansion, are bonded with a low-stiffness adhesive. The thermal expansion of the optical elements (adherents) and the adhesive differs greatly, which can lead to optically significant deformations of the adherends or failure of the adhesive bond. To reduce these problems while maintaining the stiffness of the polymerized adhesive, a large bond gap depth and / or a low-stiffness adhesive must be selected. It is also known that in optical design for precision optics, a differential thermal expansion of the adherends of 0.1 pm / K should not be exceeded.Adhesives generally exhibit low stiffness, meaning stiffness depends on the material, temperature, and, especially at high Poisson's ratios, the geometry. The glass transition temperature is also relevant in this context. The elastic modulus is generally also given as a measure of stiffness. Elastic moduli of a few MPa, for example, <10 MPa, are considered less stiff.

[0008] Therefore, reliable adhesion (to adherends and adjacent adhesives) and cohesion of the adhesive bond across the relevant transport, storage, and operating temperature ranges and other environmental influences are desirable, resulting in improved resistance to cleaning and mechanical stress, resulting in more reliable optical function. In particular, differences in refractive index must not impair the optical function. Low undesired reflectance and absorbance, as well as low scattering and positional stability of the adherends (long-term and during vibrations), are therefore always desirable. Reduced strength of the adhesive bond can lead to insufficient cohesive strength and / or insufficient positional and dimensional stability, especially under cyclically changing thermal loads. In addition, low stiffness during vibrations can lead to disruptive optical effects, such as oscillation of the adherends relative to one another.

[0009] The object of the present invention is therefore to reduce undesirable stresses and deformation in a joining group in such a way that optical and mechanical functions are sufficiently fulfilled for all environmental conditions.

[0010] The object is achieved by an optical system comprising i) at least one first optical element (01) and ii) at least one second optical element (02), wherein the optical elements (01) and (02) are arranged on top of one another and between the mutually arranged surfaces of the optical elements (01) and (02) iii) at least two polymer layers with different thermal expansion coefficients, selected from the group of polymer layers consisting of polymer layer (P1), polymer layer (P2), polymer layer (P3), polymer layer (P4), polymer layer (P5) and polymer layer (P6), are arranged, wherein the optical system comprises at least one beam path which successively penetrates an optical element, the polymer layers and the further optical element, and wherein total reflection can take place at an interface to at least one polymer layer,when an electromagnetic wave propagates through the polymer layer from one optical element to the other optical element and wherein the thermal expansion coefficient of the polymer layers from the optical element (02) to the optical element (01) comprises a gradient.,

[0011] "Total internal reflection" refers to the well-known physical phenomenon of total internal reflection of electromagnetic radiation, particularly light (light beams), during the transition from an optically dense to an optically thin medium. This means that if the angle of incidence reaches a certain value, the refracted beam runs parallel to the interface. If the angle of incidence becomes even larger, the light is completely reflected, and only an evanescent field of the incident light penetrates the optically thinner medium. This phenomenon is called total internal reflection.

[0012] An "optical system" in the sense of the present invention preferably refers to a combination of optical elements that work together to shape, control, or manipulate electromagnetic radiation fields, in particular directed fields or light beams, in order to achieve a specific goal. This can be, for example, the magnification of objects in a microscope, the transmission of light images, or the collection of light from distant objects. Optical systems can consist of one or more lenses, mirrors, prisms, and other optical elements and can also include light sources such as LEDs or lasers. Light beams are directed electromagnetic fields that describe the propagation of electromagnetic radiation in space and time, in particular visible and near-infrared light. They can be refracted or redirected by optical elements such as lenses, mirrors, or prisms.

[0013] In the present invention, an "optical element" is preferably understood to mean a part or component that is used in an optical system to shape, control, or manipulate electromagnetic radiation, in particular light beams. Optical elements therefore preferably include lenses, mirrors, prisms, filters, and many other types of optical components. They can be used in a variety of applications such as cameras, telescopes, microscopes, and other optical devices. Unless otherwise stated, the terms "optical element" and "waveguide" are used synonymously. In the present invention, a "polymer layer" is preferably understood to mean a layer composed of a polymer material. Polymers are used in a variety of applications, including plastics, coatings, adhesives, and other materials.A polymer layer can be applied to a surface to form a barrier, to provide protection, insulation, or another function.

[0014] The polymer layer is preferably an adhesive layer. An "adhesive" within the meaning of the present invention is an organic or inorganic substance or a silicone compound that can bond adherends through surface adhesion and internal strength (cohesion) without surface or structural changes. Depending on the hardening mechanism, a distinction is made between physically setting and chemically curing adhesives.

[0015] Preferably, the adhesive is a physically setting adhesive, for example a hot melt adhesive, solvent-based wet adhesive, contact adhesive, dispersion adhesive, water-based adhesive, pressure-sensitive adhesive or plastisol.

[0016] Preferably, the adhesive is a chemically curing adhesive, for example a polymerization adhesive (such as instant adhesives (cyanoacrylates), methyl methacrylates (MMA), unsaturated polyesters, anaerobic curing adhesives or radiation-curable adhesives), a polycondensation adhesive (such as phenolic resins, silicones, polyimides, bismaleimides, MS polymers) or a polyaddition adhesive (such as epoxy resins or polyurethanes).

[0017] In the present invention, the term “beam path” is preferably understood to mean the geometric course of electromagnetic radiation, in particular light rays, through optical systems.

[0018] In the present invention, the term "electromagnetic wave" or "electromagnetic radiation" is preferably understood to mean a wave of coupled electric and magnetic fields. Depending on the frequency, an electromagnetic wave can generally be radio waves, microwaves, infrared radiation, light in the visible spectrum, UV radiation, X-rays and gamma radiation, whereby in the context of the present invention the term preferably refers to electromagnetic radiation in the visible and IR-A range. In the present invention, the "thermal expansion coefficient" is preferably understood to be a measure of the relative change in the length of a body in a defined spatial direction when its temperature changes. It is expressed as the quotient of the change in length (e.g. pm) per unit length (e.g. m) and per temperature change interval, e.g. degrees Celsius or Kelvin.Each material type has a characteristic coefficient of thermal expansion, which depends on the material properties such as the atomic structure and bond types, and thus also on temperature, for example. Taking the coefficient of thermal expansion into account during design can prevent distortions and dimensional errors caused by temperature changes.

[0019] The optical system comprises at least one beam path, which thus successively penetrates an optical element, the polymer layers and the further optical element, in particular the optical element (02), the polymer layers and the optical element (01), in particular a further or the first beam path which optionally penetrates the optical element (03), the polymer layers, the optical element (02), the polymer layers and the optical element (01). The optical system is therefore preferably optically transparent, so that the transmittance of light visible to humans ("VIS") and of IR-A radiation is advantageously more than 85%, preferably more than 90%. A high transmittance of IR-A radiation is particularly advantageous for AR / VR / MR systems in which IR-A radiation is used for sensors, for example for measuring the direction of gaze or eye pupil position and size.

[0020] Preferably, the value of the gradient of the thermal expansion coefficient increases from the optical element (02) to the optical element (01) or increases in sections. The section-wise increase is understood to mean a change in sign of the gradient of the thermal expansion coefficient, ie it first increases and then decreases again in one polymer layer, before continuing to increase or decrease in another polymer layer. In other words, the use of different polymer layers with different thermal expansion coefficients results in a discrete or continuous gradient of the thermal expansion coefficients. Preferably, the individual polymer layers each have a thermal expansion coefficient in the range from 10 to 400 ppm / K, particularly preferably in a range from 15 to 375 ppm / K.

[0021] Advantageously, by using several polymer layers, which particularly preferably act as adhesives (for example, curable liquids or solid films), with different thermal expansion, an optically functional connection is achieved which leads to fewer undesirable stresses and / or deformations in the optical system.

[0022] The difference in the thermal expansion coefficients of the polymer layers is therefore advantageously adapted to one another step by step or continuously over several polymer layers, and the layer thickness can preferably be selected such that the stresses on the polymer layers / optical elements, i.e. on the adhesion surfaces, are significantly reduced compared to bonding with a single adhesive layer. In the present invention, adhesion surfaces or adhesion zone are preferably understood to mean the pure contact surface between the polymer layer (adhesive) and the joining part (optical element). In this region, the polymer layer has a modified chemical structure and composition due to the adhesion to the surface of the joining part compared to more distant regions (cohesion zone). In the transition zone between the adhesion and transition zones, the structure, composition, and macroscopic structure of the polymer layer change continuously.The material stiffness of the polymer layer changes depending on the thickness.

[0023] For example, this depends on the Poisson's ratio and the local chemical structure. Therefore, the thickness of the individual polymer layers is preferably in the range of 10 to 100 pm.

[0024] To ensure better adhesion of the polymer layers to each other or to the optical element, the corresponding surfaces can preferably be subjected to a surface treatment before they are brought into contact with each other. This can be done, for example, with primers, surface functionalization with plasma or laser, or similar technical measures.

[0025] The thickness of a polymer layer is preferably in the range of 15 to 65 pm, very preferably 20 to 55 pm, and especially preferably 25 to 45 pm. The polymer layers can each have different thicknesses.Preferably, the polymer layer (P1) can have a layer thickness in a range from 15 to 65 pm, particularly preferably 20 to 55 pm and especially preferably 25 to 45 pm, the polymer layer (P2) can have a layer thickness in a range from 15 to 65 pm, particularly preferably 20 to 55 pm and especially preferably 25 to 45 pm, the polymer layer (P3) can have a layer thickness in a range from 15 to 65 pm, particularly preferably 20 to 55 pm and especially preferably 25 to 45 pm, the polymer layer (P4) can have a layer thickness in a range from 15 to 65 pm, particularly preferably 20 to 55 pm and especially preferably 25 to 45 pm, the polymer layer (P5) can have a layer thickness in a range from 15 to 65 pm, particularly preferably 20 to 55 pm and especially preferably 25 to 45 pm, and the polymer layer (P6) can have a Layer thickness in a range of 15 to 65 pm, particularly preferably 20 to 55 pm and especially preferably 25 to 45 pm.

[0026] Preferably, at least one refractive index of at least one polymer layer differs by a factor of 0.975 to 1.025, preferably 0.985 to 1.020, from the refractive index of the first optical element (01) or other polymer layers, or of the second optical element (02). For example, the polymer layer (P1) can have a refractive index that is up to a factor of 0.975 lower than the refractive index of the first optical element (01) or of the second optical element (02). Likewise, the polymer layer (P1) can have a refractive index that is up to a factor of 1.025 higher than the refractive index of the first optical element (01) or of the second optical element (02). By a suitable selection of the refractive indices, total reflection at the interfaces where it is not desired can be avoided, or the critical angle of total reflection can be achieved to be as high as possible.If the factor in the direction of light propagation is higher (greater than 1.025), total internal reflection does not occur, but refraction and Fresnel reflection do. If the factor is lower (less than 0.975), total internal reflection can occur, but at such high critical angles that this generally does not affect the application.

[0027] If the optical element O2 is a waveguide and total internal reflection occurs at the interface between O2 and one of the adjacent polymer layers (P3 and P7 in Fig. 1), these polymer layers (P3 and P7 in Fig. 1) must have a sufficiently lower refractive index (e.g., a factor of 0.5 to 0.9). Therefore, in a further preferred embodiment, the refractive index of a polymer layer, in particular the polymer layer following the second optical element (O2) in the direction of the beam path (polymer layer P3 in Fig. 1), can differ from that of the second optical element (O2) by at least a factor of 0.50, preferably at least a factor of 0.60, preferably at least a factor of 0.70, preferably at least a factor of 0.85, preferably at least a factor of 0.90, i.e., the refractive index of a polymer layer should be at least a factor of 0.9 lower than that of the second optical element (O2).Particularly preferably, the refractive index of a polymer layer differs from that of the second optical element (O2) by a factor in the range from 0.90 to 0.60, particularly preferably 0.85 to 0.70.

[0028] Preferably, the refractive index of the polymer layer following the second optical element (O2) in the direction of the beam path (polymer layer P3 in Fig. 1) differs from the refractive index of the second optical element (O2) by a factor of 0.90 to 0.60, particularly preferably 0.85 to 0.70. Thus, total internal reflection (TIR) ​​occurs between these two layers (between O2 and P3 in Fig. 1).

[0029] Preferably, total reflection occurs between (O2) and the polymer layer that follows (O2) in the direction of the beam path (polymer layer P3 in Fig. 1). Alternatively, total reflection occurs within the polymer stack, i.e., the polymer layers arranged on top of one another (e.g., at P2 and P3 or P7 and P8 in Fig. 1). In this case, the refractive index of a polymer layer preferably differs by a factor of 0.90 to 0.60, particularly preferably 0.85 to 0.70, from the refractive index of the polymer layer following in the direction of the beam path. Such an arrangement is shown in embodiments #3 and #4.

[0030] Alternatively, a low-index cladding coating can be applied to the surfaces of (O2). In this case, the TIR occurs at the interfaces between O2 and this low-index cladding coating. Low-index cladding coatings are polymer layers known to those skilled in the art and are described, for example, in "Low Refractive Index Adhesives and Coatings - Addison Clear Wave (addisoncw.com), R272 TDS (addisoncw.com)". The low-index cladding coating can be an adhesive, but it does not have to be an adhesive. Further examples are sol-gel coatings filled with nano- to micro-glass hollow spheres that are sintered (cf. Optical coatings - Inkron). The low-index cladding coating preferably has a thickness in the range of 1-10 μm, preferably 1-5 μm, for example 2 μm.The factor is calculated as the refractive index of the polymer layer / the refractive index of the waveguide, where the waveguide is preferably the second optical element (O2) and the polymer layer is the polymer layer adjacent to the waveguide. The arcsine of this quotient yields the critical angle of total internal reflection. The smaller the quotient, the smaller the critical angle of total internal reflection.

[0031] Preferably, the refractive index of the polymer layer at whose interface total reflection can occur is smaller than that of the further polymer layer adjacent to this interface or that of the optical element adjacent to this interface. Preferably, the refractive index of the polymer layer at whose interface total reflection can occur is smaller by a factor in the range from 0.90 to 0.60, particularly preferably 0.85 to 0.70, than the refractive index of the further polymer layer adjacent to this interface or that of the optical element adjacent to this interface. Preferably, the subsequent polymer layer of the polymer layer at whose interface total reflection can occur can have a greater or equal value to that of the previously adjacent polymer layer or that of the optical element adjacent to this interface.Particularly preferred critical angles for total reflection are between 58.5° and 44.4°, most preferably below 55° and in particular below 50°.

[0032] By preferably adjusting the difference in the thermal expansion coefficients of the polymer layers step by step or continuously over several layers and by selecting the layer thickness accordingly, stresses on the adhesion surfaces are significantly reduced compared to bonding with a single adhesive layer.

[0033] Preferably, the first optical element (01) has a first thermal expansion coefficient (L1), the second optical element (02) has a second thermal expansion coefficient (L2), and the first thermal expansion coefficient (L1) and the second thermal expansion coefficient (L2) are different from one another. Advantageously, the thermal expansion coefficient (L2) is in a range from 0.5 to 100 ppm / K, particularly preferably in a range from 3 to 12 ppm / K. Advantageously, the thermal expansion coefficient (L1) is in a range from 0.5 to 100 ppm / K, particularly preferably in a range from 35 to 75 ppm / K. Preferably, the difference between the thermal expansion coefficient of the first optical element (01) and that of the adjacent polymer layer is in a range from 0 to 400 ppm / K, in particular in a range from 5.0 to 135.0 ppm / K, particularly preferably in a range from 5.0 to 100.0 ppm / K.

[0034] Preferably, the difference between the thermal expansion coefficient of the second optical element (O2) and that of the adjacent polymer layer is in a range from 0 to 400 ppm / K, in particular in a range from 5.0 to 135.0 ppm / K, particularly preferably in a range from 5.0 to 30.0 ppm / K.

[0035] Preferably, the difference in the thermal expansion coefficient from one polymer layer to another polymer layer at the interface of which no total reflection with critical angles of less than 77° can take place is in a range from 0 to 250 ppm / K, in particular in a range from 5.0 to 85.0 ppm / K, particularly preferably in a range from 5.0 to 30.0 ppm / K. Preferably, the difference in the thermal expansion coefficient from one polymer layer to another polymer layer, wherein no total reflection, particularly preferably no total reflection with critical angles of less than 77°, can take place at the interface of these two polymer layers, is in this range.

[0036] Preferably, the glass transition temperature of the polymer layers lies outside the temperature range of -50°C to 115°C, preferably -40°C to 90°C, most preferably -30°C to 85°C. This advantageously allows for better transport and storage stability of the optical systems.

[0037] Preferred is an optical system comprising i) at least one first optical element (O1) constructed from a polymer (A1) or from a glass, in particular based on SiO2, and ii) at least one second optical element (O2) constructed from a glass, in particular based on SiO2, or constructed from a polymer (A2).

[0038] Particularly preferred is an optical system comprising i) at least one first optical element (01) constructed from a polymer (A1) and ii) at least one second optical element (02) constructed from a glass, in particular based on SiO2. Preferably, the optical element (01) is constructed from a polymer (A1) and / or the optical element (02) is constructed from a polymer (A2), wherein the polymer (A1) or (A2) is selected from the group consisting of polythiourethanes, polycarbonates, polycarbonate copolymers, polyesters, and cyclic olefin polymers (COP).

[0039] Preferably, the glass is selected from the group of optical glasses, consisting of optical flint glass, in particular heavy flint glass, lanthanum heavy flint glass, lanthanum flint glass, arsenic and lead-free flint glass (“N-glass”), heavy flint glass with a glass transition temperature < 600°C (“P-glass”) and optical crown glass, in particular heavy crown glass, heavy crown glass with a glass transition temperature < 600°C (GP-glass”).

[0040] Preferably, the optical element (01) and / or (02) is a refractive, reflective or diffractive optic or a lens selected from the group consisting of spherical lenses, aspherical lenses, freeform lenses, Fresnel lenses or metal lenses on wafers.

[0041] Any suitable polymer can be used in the polymer layers (P1) to (P6). Suitable polymers are known to those skilled in the art and are commercially available. The polymer layers preferably comprise at least one polymer selected from the group consisting of radiation-curable polymers, UV-curable polymers, UV-hybrid polymers, thermally curable polymers, moisture-curable polymers, anionically curable polymers, anaerobically curable polymers, two-component adhesives, and polymers cured with an activator, as well as mixtures thereof.

[0042] The polymer layers (P1) to (P6) preferably comprise UV-curable polymers or UV-hybrid polymers. UV-hybrid polymers are polymers that undergo further curing after UV curing, such as thermal curing, anaerobic curing, or moisture curing. Particularly preferred are UV-curable polymers and UV-hybrid polymers that do not require thermal curing after UV curing, meaning they are fully cured at room temperature.

[0043] The polymers, especially UV-curable polymers, preferably cure at a temperature in the range of 20-40°C, preferably at room temperature. The polymers can be one-component, two-component, or multi-component polymers. Two-component polymers or two-component adhesives are also known as reactive adhesives or structural adhesives. They are characterized by the fact that they do not cure through the evaporation of a substance such as a solvent or water, but rather through a chemical reaction. This requires that the two required components are metered in the correct mixing ratio and mixed homogeneously. Two-component adhesives are preferably solvent-free.

[0044] The polymers that are cured with an activator are preferably acrylate and silicone adhesives.

[0045] Preferred UV-curable polymers and UV-hybrid polymers are polymers based on (meth)acrylate monomers, epoxy monomers, vinyl monomers and allyl monomers, in particular epoxy-based polymers, acrylate-based polymers and fluorinated acrylate-based polymers, and silicone rubber-based polymers, as well as mixtures thereof.

[0046] The (meth)acrylate monomers can typically be monofunctional, difunctional, trifunctional, and / or tetrafunctional (meth)acrylate monomers. The epoxy monomers can typically be monofunctional, bifunctional, trifunctional, and / or tetrafunctional epoxy monomers. The vinyl monomers and allyl monomers can typically be monofunctional, bifunctional, trifunctional, and / or tetrafunctional vinyl monomers and allyl monomers.

[0047] Suitable polymers or monomer mixtures for producing these polymers are known to the person skilled in the art and are commercially available, for example the AC-L and AC-PR series (acrylates), AC-R series (fluorinated acrylates) and AC-A series (epoxies) from Addison Clear Wave Coatings Inc. or the adhesives, in particular the OK fine putties, from ZEISS.

[0048] Preferred polymers are low-outgassing (preferably with a CVCM < 0.1%, “Collectible Volatile Condensible Materials”) and resistant to color changes (e.g. thermal, humidity or radiation-induced) so that the optics remain cloud-free and transparent without color change over the product lifetime.The optical system preferably comprises iv) at least one third optical element (03) made of a polymer (A3), wherein the optical elements (01), (02) and (03) are arranged on top of one another and v) at least two polymer layers selected from the group of polymer layers consisting of polymer layer (P7), polymer layer (P8), polymer layer (P9), polymer layer (P10), polymer layer (P11) and polymer layer (P12) are arranged between the mutually arranged surfaces of the optical elements (02) and (03), wherein the optical system preferably comprises at least one (further) beam path, wherein total reflection can take place at an interface to at least one polymer layer from v) when an electromagnetic wave propagates through the polymer layer from one optical element to the other optical element and wherein the thermal expansion coefficient of the polymer layers from the optical element (03) to the optical element (02) comprises a gradient.

[0049] Preferably, the polymer (A3) is selected from the group consisting of polythiourethanes, polycarbonates, polycarbonate copolymers, polyesters and cyclic olefin polymers (COP).

[0050] Any suitable polymer can be used in the polymer layers (P7) to (P12). The polymers described above for the polymer layers (P1) to (P6) are particularly suitable. Such polymers are known to those skilled in the art and are commercially available. The thickness of the polymer layers (P7) to (P12) is preferably within the range described above for the polymer layers (P1) to (P6).

[0051] Preferably, the polymer layers contain at least one additive. This additive can advantageously modify the refractive index and / or the thermal expansion coefficient of the respective polymer layer. The additives can also be used to adjust the polymer thickness.

[0052] Additives that can modify the thermal expansion coefficient of a (transparent) polymer are: 1. Micro- or nanoparticles based on silicon dioxide or titanium dioxide, carbon nanotubes that are embedded in the polymer from which the polymer layer is made.

[0053] 2. Glass fragments or fibers added as reinforcing materials.

[0054] 3. Metals such as aluminum, copper or nickel, which are applied to the surface of the polymer in the form of nanoparticles.

[0055] 4. Composite materials consisting of polymer matrix and the above-mentioned additives.

[0056] 5. Polymer blends, in which two or more polymers are mixed together to influence the thermal expansion coefficient.

[0057] Most preferably, the additive consists of micro- or nanoparticles based on silicon dioxide.

[0058] Advantageously, the amount of the at least one further additive comprises 0.01 to 10 wt.%, preferably 0.1 to 5 wt.%, based on the total mass of the individual polymer layer. Most preferably, the at least one additive or at least two additives can form a gradient within the respective polymer layer in the direction of the beam path, i.e., in other words, an axial density gradient perpendicular to the lateral adhesion surface.

[0059] Preferably, the composition used to produce the polymer layer comprises at least one further additive selected from the group consisting of UV initiators, co-initiators, dyes, dispersants, anti-settling agents, wetting agents, including anti-crater or leveling additives, biocides, UV absorbers or mixtures thereof.

[0060] The polymer layers preferably contain additives selected from the group consisting of metal oxide nanoparticles, semimetal oxide nanoparticles, polycyclic aromatic hydrocarbons, hydroxy- and methoxy-substituted diaryl nitrones, polythiol (PSH), aromatic monomers, metal-containing monomers, metal-polymer composites, and metal-polymer nanocomposites. These additives can modify the refractive index of the respective polymer layer. The polymer layers are preferably free of halogens. This means that the corresponding polymers do not have chloride, fluoride, bromide, or iodide substituents.

[0061] A further aspect of the invention is a method for producing the optical system according to the invention, comprising the steps a) providing at least one first optical element (01) and at least one second optical element (02), b) applying a first polymer layer orthogonally to the surface of one of the optical elements that runs along the beam path, c) applying a second polymer layer orthogonally to the surface of the first polymer layer that runs along the beam path or applying a second polymer layer orthogonally to the surface of the other optical element that runs along the beam path, d) joining the optical elements so that at least two polymer layers are located between the two optical elements.

[0062] Preferably, in the method according to the invention, the optical elements and the polymer layers are at least partially bonded to one another in step d).

[0063] Application of polymer layers

[0064] The polymer layers in steps b) and c) can be applied using a conventional method known to the person skilled in the art. Preferably, in the process according to the invention, the polymer layers in steps b) and c) are applied using spin coating, 3D printing, adhesive films, thermal lamination, chemical diffusion, dip coating, spray coating, powder coating, doctor blade coating, or casting.

[0065] Preferably, a casting process is used. For this purpose, the first optical element (01) or the second optical element (02) can be mounted on a front-side mold shell and / or a rear-side mold shell of a casting mold. The mold shell used in each case typically has an identical radius of curvature to the first optical element (01) or second optical element (02) mounted in the mold shell. Suitable casting molds are disclosed, for example, in DE 102013222232 A1. The optical element (01) or (02) is typically fixed to the mold shell by vacuum. The optical element (01) or (02) typically has the same diameter as the mold shell.

[0066] During the casting process, the monomer mixture required to produce the respective polymer layer is poured directly onto the back of the optical element (01) or (02), which has optionally been provided with at least one functional layer. Typically, only a small amount of release agent, e.g., organic phosphonates or phosphoric acid esters, is added to this monomer mixture, if at all, so that a mechanically indetachable bond is created between the back of the optical element (01) or (02) and the front of the respective polymer layer. To prevent a mechanically indetachable bond from also forming between the back of the respective polymer layer and the further mold surface, the further mold shell is typically coated with a protective layer, for example, a protective film or a protective lacquer (e.g.,Illmar P4 optical coating, M-Lack 10 optical coating, PBJ 2002 protective coating, TLS blue / 2002 protective coating, from Pieplow & Brand) on the side facing the respective polymer layer to be cast. This protective layer can optionally be removed in a subsequent process step, e.g., during machining, turning, and / or polishing of the respective polymer layer.

[0067] For thermoplastic polymers processed by injection molding, the molding process must be adapted to produce the respective polymer layer. In this case, the injection mold is typically equipped with an additional vacuum port on the side where the optical element is to be applied. Before the injection mold is closed, the optical element is secured using vacuum. This adaptation of the molding process is particularly suitable for systems based on polymethyl methacrylates, polycarbonates, or cycloolefin copolymers.

[0068] In an optical system comprising at least a third optical element (03), the application of a polymer layer to the third optical element (03) can be carried out in the same way as described for the optical elements (01) and (02). 3D printing

[0069] Preferably, a printing process, in particular a 3D printing process, is used, which is an additive manufacturing process in which the desired surface topography of one of the surfaces of the polymer layers is created exclusively by material deposition. The three-dimensional shape of a polymer layer to be printed is first digitally cut into two-dimensional horizontal sections.

[0070] The respective polymer layer produced by means of a printing process, in particular a 3D printing process, may require at least one further mechanical processing step, for example, polishing. Typically, the respective polymer layer produced by means of a printing process, in particular a 3D printing process, does not require any further mechanical processing step, for example, machining and / or grinding and / or turning and / or polishing.

[0071] For the layered buildup of the respective polymer layer, a printing ink that can be used in a 3D printing process is preferably used. The "layered buildup" involves the successive application of the printing ink, typically the 3D printing ink. The successive deposition can take place in an area next to each other or vertically one above the other. For example, if a first application of the printing ink, typically 3D printing ink, is made in one area, another layer can be printed over the entire area of ​​the first application or a portion of the area of ​​the first application. Typically, the successive deposition of the printing ink, typically the 3D printing ink, first takes place in an adjacent area before a further successive deposition of the printing ink, typically the 3D printing ink, takes place in the overlying layer.

[0072] The printing ink, in particular 3D printing ink, typically comprises at least one UV-curable polymer, optionally at least one colorant, optionally at least one UV initiator, optionally at least one solvent, and optionally at least one additive. The UV-curable polymer, the colorant, the UV initiator, and other additives are described in this application in connection with the polymer layers.

[0073] The optional at least one solvent in the printing ink, typically 3D printing ink, can be selected from the group consisting of alcohols, ketones, esters, ethers, thioethers, amides, hydrocarbons, amines, and mixtures thereof. Typically, the optional at least one solvent is selected from the group consisting of alcohols, ketones, esters, and mixtures thereof. In the context of this invention, a solvent can be, firstly, one type of solvent and, secondly, a solvent mixture.

[0074] A further aspect of the invention is the use of the optical system according to the invention for AR (Augmented Reality) systems, VR (Virtual Reality) systems, smart glasses, head-mounted displays (HMD), mixed reality systems, extended reality systems and XR (Cross Reality) systems.

[0075] Figure 1 :

[0076] Figure 1 shows a multilayer adhesive bond with a discrete axial thermal expansion coefficient.

[0077] Figure 2:

[0078] Figure 2 shows a multi-layer adhesive bond with a continuous axial thermal expansion coefficient.

[0079] Figure 1 shows the multilayer adhesive bond with a discrete axial thermal expansion coefficient for an optical system comprising a first optical element (01), a second optical element (02), and a third optical element (03). The optical element (02) is a glass lens and is shown in the center of the arrangement. The three polymer layers (P7), (P8), and (P9) are arranged below it. The polymer layer (P7) is arranged on the lower surface of the optical element (02), and the polymer layer (P8) is arranged in the middle of (P7) and (P9). (P9) is arranged on the upper surface of the optical element (03). The optical element (03) consists of a polymer (A3). The optical element (01) consists of a polymer (A1). The individual polymer layers can be applied one after the other using spin coating, adhesive films, or thermal lamination, allowing the discrete layers to form.The corresponding polymer layers (P1) to (P3) are arranged between the optical element (O1) and (O2). Figure 2 shows the multilayer adhesive bond with a continuous axial thermal expansion coefficient for an optical system. The structure corresponds to the structure shown in Figure 1. The individual polymer layers can be applied, for example, by chemical diffusion. The multilayer adhesive bond in Figure 2 also comprises several discrete polymer layers between (O1) and (O2), as well as between (O2) and (O3). To illustrate the continuous gradient of the thermal expansion coefficients across the polymer layers, however, this figure does not show the individual polymer layers, but rather the continuous gradient of the thermal expansion coefficients across several polymer layers.

[0080] Materials

[0081] In the examples according to the invention, the following materials are used, among others:

[0082] The following polymers were used for the optical elements:

[0083] ZEON 350R 2017: cyclic olefin polymer (COP)

[0084] Mitsui MR8 and Mitsui MR10: Polymers based on thiourethane

[0085] Sabic Lexan CXT 19: polycarbonate copolymer resin

[0086] OKP4HT: Polyester

[0087] The following glasses were used for the optical elements:

[0088] Schott N-LASF46B Glass: Lanthanum Heavy Flint, N-Glass

[0089] Schott P-SF68 Glass: Heavy Flint, P-Glass

[0090] Schott P-SF8 Glass: Heavy Flint, P-Glass

[0091] Schott P-SK60 Glass: Heavy Crown, P-Glass

[0092] Schott N-LAF33 Glass: Lanthanum flint, N-glass

[0093] The following polymers were used for the polymer layers:

[0094] Zeiss OK 2405 SILICONE: Silicone rubber

[0095] ZEISS OK 2030: UV-curable epoxy resin

[0096] ACWAC A535-A UV-curable epoxy resin

[0097] ACWAC A1432 UV-curable epoxy resin ACW AC A535-AN EPOXY UV-curable epoxy resin

[0098] ACWAC A586 UV-curable epoxy resin

[0099] ACW AC L2002-C56 UV curable acrylic resin

[0100] ACWAC L2002-C42 UV curable acrylic resin

[0101] NTT-AT #18165 ACRYLATE UV-curable acrylic resin

[0102] ACW PR-1600-CA ACRYLATE UV-curable acrylic resin

[0103] ACWAC L2061-B ACRYLATE UV-curable acrylic resin

[0104] ACWAC L2007 UV curable acrylic resin

[0105] ACWAC R272 UV curable fluorinated acrylic resin

[0106] ACWAC R262-MOD-5 UV curable fluorinated acrylic resin

[0107] Examples

[0108] The adhesive layer thicknesses depend, among other things, on the processability (especially viscosity) of the adhesive, the extent of the adhesion edge zones (minimum layer thicknesses), the size of the adherends, and the required temperature ranges. Layer thicknesses are generally minimized. The adhesive thickness can be adjusted for a product through structural optimization so that it is minimal and does not exceed a specific shape deviation of one or all adherends over the desired temperature range.

[0109] The application example chosen is the bonding of plastic lenses, for example, for vision correction, to glass optics, such as waveguides for AR / VR / XR systems. The operating temperature range is assumed to be -10°C to +45°C, and the storage and transport temperature ranges are -30°C to +85°C. In addition to the properties mentioned above, it is important that the adhesive / coating in contact with the waveguide has a low refractive index so that the critical angle for total internal reflection meets the requirements of the AR / VR / XR system. Furthermore, the subsequent adhesive layers should have the same or higher refractive index to prevent the creation of a "parasitic" waveguide, which applies across the entire operating temperature range (the temperature dependence of all relevant optical and mechanical material properties must be considered). Thermal expansion coefficient

[0110] The coefficient of thermal expansion (GTE) can be determined using standard methods. For example, the coefficient of thermal expansion can be determined according to ASTM E831 or ISO 11359-2.

[0111] refractive index

[0112] The refractive index can be determined using standard methods, for example ASTM D542.

[0113] Glass transition temperature (Tg)

[0114] The glass transition temperature (Tg) can be determined using standard methods, for example JIS K7121.

[0115] For #1 and #2) Simple examples with two layers, one for acrylates and one for epoxies

[0116] For #3 and #4) Examples with total reflection at adhesive layer in adhesive layer stack

[0117] To #5, #6 and #7) Further examples

[0118] In the examples, the first optical element (01) is shown in the top row, and the second optical element (02) is shown in the bottom row, with the polymer layers in between. The beam path runs from the second optical element (02) toward the first optical element (01).

[0119] Nomenclature: CTE = Coefficient of Thermal Expansion (ppm / K); RI = Refractive Index (@ 589 nm); TG = Glass Transition Temperature; gray indicates the material at which total internal reflection occurs. All values ​​are exemplary nominal values ​​from technical data sheets. #1 Acrylate (halogen-free)

[0120] CTE CTE difference RI TG

[0121] ZEON 350R 2017 - Cyclo Olefin 70.00 1.51 121.00

[0122] polymer

[0123] ACWAC L2002-C56 59.00 11.00 1.51 145.00

[0124] Schott N-LASF46B Gias 6.00 18.00 1.90 611.00 critical angle 52.88

[0125] #2 Epoxy (halogen-free)

[0126] CTE CTE difference RI TG

[0127] Mitsui MR8 - Thiourethane 65.00 1.60 118.00

[0128] ACWAC A535-A 42.00 23.00 1.57 145.00

[0129] Schott P-SF68 Gias 8.40 12.60 2.00 428.00 critical angle 52.19

[0130] #3 Acrylate + Silicone (halogen-free) - Total reflection in the adhesive stack (one

[0131] adaptation layer)

[0132] CTE CTE difference Rl TG

[0133] Mitsui MR10 - Thiourethane 65 1.67 100.00

[0134] NTT-AT #18165 ACRYLATE 144.00 -79.00 1.68 113.00

[0135] NTT-AT #18165 ACRYLATE 144.00 206.00 1.68 113.00

[0136] Schott P-SF8 Gias 9.40 134.60 1.69 524.00 critical angle 56.55 #4 Epoxy + Acrylate + Silicone (halogen-free) - Total reflection in the adhesive stack

[0137] (many customization layers)

[0138] CTE CTE difference Rl TG

[0139] Mitsui MR10 - Thiourethan 65 1.67 100.00

[0140] NTT-AT #18165 ACRYLAT 144.00 -79.00 1.68 113.00

[0141] NTT-AT #18165 ACRYLAT 144.00 206.00 1.68 113.00

[0142] ACW PR-1600-CA ACRYLAT 60.00 84.00 1.60 89.00

[0143] ACWAC L2061-B ACRYLAT 35.00 25.00 1.60 130.00

[0144] ACWAC A535-AN EPOXY 28.00 7.00 1.59 170.00

[0145] Schott P-SK60 Gias 7.10 20.9 1.61 507.00 krit. Winkel 61.14

[0146] #5 Acrylat Variante 2

[0147] CTE CTE-Differenz Rl TG

[0148] Sabie Lexan CXT19 - Polycarbonat 60.00 1.61 195.00

[0149] ACWAC L2007 37.00 23.00 1.57 109.00

[0150] Schott P-SK60 Glas 7.10 10.90 1.61 507.00 krit. Winkel 61.14

[0151] #6 Acrylat Variante 3

[0152] CTE CTE-Differenz Rl TG

[0153] Sabie Lexan CXT19 - Polycarbonat 60.00 1.61 195.00

[0154] ACWAC L2007 37.00 23.00 1.57 109.00

[0155] Schott N-LAF33 Price 5.60 12.40 1.79 600.00 krit. Winkel 54.65 #7 Epoxy + Acrylates

[0156] CTE CTE-Differenz RI TG

[0157] OKP4HT - Polyester 63.00 1.63 142.00

[0158] ZEISS OK 2030 (Epoxy) 48.00 15.00 1.62 57.00

[0159] ACWAC L2007 37.00 11.00 1.57 109.00

[0160] ACWAC A586 28.00 9.00 1.56 107.00

[0161] Schott P-SF8 Glas 9.40 8.60 1.69 524.00 krit. Winkel 56.55

[0162] By appropriately adjusting the thermal expansion coefficients of the first optical element, the second optical element, and the polymer layers in the examples according to the invention, optical systems are obtained in which undesirable stresses and deformations are reduced. At the same time, by appropriately adjusting the refractive indices of the first optical element, the second optical element, and the polymer layers, reliable optical function is ensured.

Claims

Patent claims 1. An optical system comprising: i) at least one first optical element (01) and ii) at least one second optical element (02), wherein the optical elements (01) and (02) are arranged one on top of the other and between the mutually arranged surfaces of the optical elements (01) and (02) iii) at least two polymer layers with different thermal expansion coefficients, selected from the group of polymer layers consisting of polymer layer (P1), polymer layer (P2), polymer layer (P3), polymer layer (P4), polymer layer (P5) and polymer layer (P6), are arranged, wherein the optical system comprises at least one beam path which successively penetrates an optical element, the polymer layers and the further optical element, and wherein total reflection can take place at an interface to at least one polymer layer,when an electromagnetic wave propagates through the polymer layer from one optical element to the other optical element and wherein the thermal expansion coefficient of the polymer layers from the optical element (02) to the optical element (01) comprises a gradient., 2. Optical system according to claim 1, wherein the optical system is optically transparent.

3. Optical system according to claim 1 or 2, wherein the value of the gradient of the thermal expansion coefficient increases from the optical element (02) to the optical element (01) or increases in sections.

4. Optical system according to one of claims 1 to 3, wherein at least one refractive index of at least one polymer layer differs by a factor of 0.975 to 1.025 from the refractive index of the first optical element (01) or other polymer layers or of the second optical element (02).

5. Optical system according to one of claims 1 to 4, wherein the refractive index of the polymer layer at the interface of which total reflection can take place is smaller than that of the further polymer layer adjacent to this interface or that of the optical element adjacent to this interface, preferably smaller by a factor in the range of 0.90 to 0.60, particularly preferably 0.85 to 0.

70.

6. Optical system according to one of claims 1 to 5, wherein: the first optical element (01) has a first thermal expansion coefficient (L1), the second optical element (02) has a second thermal expansion coefficient (L2), and the first thermal expansion coefficient (L1) and the second thermal expansion coefficient (L2) are different from each other.

7. Optical system according to one of claims 1 to 6, wherein the glass transition temperature of the polymer layers is outside the temperature range of -50°C to 115°C, preferably -30°C to 85°C.

8. Optical system according to one of claims 1 to 7, wherein the difference between the thermal expansion coefficient of the first optical element (01) and that of the adjacent polymer layer is in a range of 0 to 400 ppm / K, preferably 5.0 to 135.0 ppm / K.

9. Optical system according to one of claims 1 to 8, wherein the difference in the thermal expansion coefficient of the second optical element (02) to the adjacent polymer layer is in a range of 0 to 400 ppm / K, preferably 5.0 to 135.0 ppm / K.

10. Optical system according to one of claims 1 to 9, wherein the difference in the thermal expansion coefficient from one polymer layer to another polymer layer at whose interface no total reflection with critical angles of less than 77° can take place lies in a range of 0 to 250 ppm / K, preferably 5.0 to 30.0 ppm / K.

11. Optical system according to one of claims 1 to 10, wherein the optical element (01) and / or (02) is a refractive, reflective or diffractive optic or is a lens selected from the group consisting of spherical lenses, aspheric lenses, freeform lenses, Fresnel lenses or metal lenses on wafers.

12. Optical system according to one of claims 1 to 11, comprising iv) at least one third optical element (03) constructed from a polymer (A3), wherein the optical elements (01), (02) and (03) are arranged on top of one another and between the mutually arranged surfaces of the optical elements (02) and (03) v) at least two polymer layers selected from the group of polymer layers consisting of polymer layer (P7), polymer layer (P8), polymer layer (P9), polymer layer (P10), polymer layer (P11) and polymer layer (P12) are arranged.

13. Optical system according to one of claims 1 to 12, wherein the polymer layers are free of halogens.

14. A method for producing an optical system according to one of claims 1 to 13, comprising the steps: a) providing at least one first optical element (01) and at least one second optical element (02), b) applying a first polymer layer orthogonally to the surface of one of the optical elements running to the beam path, c) applying a second polymer layer orthogonally to the surface of the first polymer layer running to the beam path or applying a second polymer layer orthogonally to the surface of the other optical element running to the beam path, d) joining the optical elements so that at least two polymer layers are located between the two optical elements.

15. A method for producing an optical system according to claim 14, wherein in step d) the optical elements and the polymer layers are at least partially bonded to one another.

16. A method for producing an optical system according to any one of claims 14 to 15, wherein the polymer layers in steps b) and c) are applied by means of spin coating, 3D printing, adhesive films, thermal lamination, chemical diffusion, dip coating, spray coating, powder coating, doctor blade coating, or casting processes.

7. Use of the optical system of one of claims 1 to 13 for AR (Augmented Reality) systems, VR (Virtual Reality systems), smart glasses, head-mounted displays (HMD), mixed reality systems, extended reality systems, and XR (Cross Reality) systems.

Images