OPTICAL ELEMENT WITH AN OXYGEN-IMPERMEABLE BARRIER LAYER

Description

[0001] The present invention relates to an optical element having a photochromic layer with improved UV and light stability, and to a method for producing such an optical element.

[0002] Optical elements with a photochromic layer are known in the prior art. A photochromic layer can also be described as a self-tinting layer. Depending on the intensity of the UV radiation striking the optical element, photochromic layers darken or lighten, and consequently, so does the optical element to which they are applied. The darkening or lightening of the photochromic layer or optical element is due to a photochromic dye that undergoes a reversible hue change as a result of UV irradiation. The UV irradiation alters the molecular structure of the photochromic dye and thus its absorption behavior. When the UV irradiation ceases, the photochromic dye returns to its original molecular structure and its original absorption behavior.A photochromic dye thus enables a reversible switching back and forth between a dark and a light tint.

[0003] Photochromic coatings with a thickness greater than 30 µm are typically applied to optical elements by casting or spin-coating processes, or by incorporation into the element via mass production. However, for quality reasons, applying photochromic coatings with a thickness of 30 µm or less, particularly 10 µm or less, is advantageous. When applying photochromic coatings with a thickness of 30 µm or less, especially 10 µm or less, media with a lower viscosity can be used in which the photochromic dye is dissolved or suspended. The lower viscosity of such a medium results in a more consistent distribution of the photochromic coatings and thus improved cosmetic appearance of the optical element.

[0004] However, photochromic layers, or more precisely the photochromic dye they contain, are damaged by the action of oxygen and UV radiation. Since UV radiation is necessary for the photochromic properties of the photochromic layers, damage to these layers can only be reduced by minimizing oxygen diffusion into the photochromic layer. In cases where a photochromic layer thicker than 30 µm is applied to an optical element, oxygen diffusion only occurs in the upper region of the photochromic layer. The underlying portion is protected from oxygen diffusion and cannot be damaged by oxygen and UV radiation. Photochromic layers thicker than 30 µm therefore generally exhibit low degradation due to oxygen and UV radiation.

[0005] However, in photochromic layers with a thickness of 30 µm or less, especially 10 µm or less, oxygen diffusion occurs across the entire layer, leading to damage of the entire layer. Such photochromic layers therefore require at least one protective layer to shield them from degradation by oxygen and UV radiation.

[0006] DE 10 2006 048338 A1 discloses such a photochromic layer of low thickness, which is protected from degradation by an additional oxygen-impermeable barrier layer.

[0007] Hard coatings, commonly applied to optical elements to protect them from scratches, do not provide a barrier to oxygen diffusion. Therefore, they cannot protect an underlying photochromic layer from degradation. Antireflection coatings, which can also be applied to optical elements to prevent reflections, can, however, reduce oxygen diffusion. These coatings are highly susceptible to scratches, which can lead to a local loss of protection for the photochromic layer against oxygen diffusion in areas where the antireflection layer is damaged. The resulting local degradation of the photochromic layer is then visible as a bright line in a darkened state of the optical element.

[0008] The present invention is therefore based on the objective of providing an optical element in which the photochromic layer is protected from degradation by oxygen and UV radiation.

[0009] This problem is solved by the embodiments of the present invention characterized in the claims.

[0010] In particular, according to the invention an optical element in the form of a spectacle lens is provided, comprising in the following order a substrate, a photochromic layer and an oxygen-impermeable barrier layer, wherein the oxygen-impermeable barrier layer comprises at least one polymer selected from the group consisting of ethylene-vinyl alcohol copolymer, cellulose hydrate, polyvinyl alcohol, polyacrylonitrile, polyvinyl dichloride, polyurethane and polyethylene terephthalate.

[0011] The optical element according to the invention, which comprises, in the following order, a photochromic layer and an oxygen-impermeable barrier layer comprising at least one polymer selected from the group consisting of ethylene-vinyl alcohol copolymer, cellulose hydrate, polyvinyl alcohol, polyacrylonitrile, polyvinyl dichloride, polyurethane, and polyethylene terephthalate, enables the protection of the photochromic layer from degradation by oxygen and UV radiation. This significantly increases the service life of the photochromic layer and thus the service life of the photochromic properties of the optical element. Furthermore, unlike antireflective coatings, the oxygen-impermeable barrier layer can also be arranged beneath a hard lacquer, thereby protecting it from scratches.Local damage to the oxygen-impermeable barrier layer can therefore be avoided by placing it beneath the hard coating. Otherwise, such damage would lead to local diffusion of oxygen into the photochromic layer, resulting in damage from oxygen and UV radiation. Such damage to the photochromic layer is perceived as bright areas when the optical element is darkened. Since antireflection layers cannot be placed beneath the hard coating and therefore cannot be protected from scratches or other damage, using scratch-prone antireflection layers as the oxygen barrier can lead to local degradation of the photochromic layer, which is easily visible when the optical element is darkened.Such local degradation of the photochromic layer can be prevented by the oxygen-impermeable barrier layer. Furthermore, the protection of the photochromic layer from degradation by oxygen and UV radiation does not rely on expensive antireflection coatings. Consequently, optical elements with thinner photochromic layers can be manufactured without an antireflection layer.

[0012] A further advantage of the optical element according to the invention is that thinner photochromic layers, in particular with a thickness of 30 µm or less and preferably 10 µm or less, can be provided in the optical element. These thinner layers can be applied during the fabrication of the optical element using methods that are superior to those used for applying thicker layers. This superiority is evident, among other things, in reduced inventory and greater flexibility with regard to photochromic colors, pre-coloring, and darkening depths. Furthermore, thinner photochromic layers, in particular with a thickness of 30 µm or less and preferably 10 µm or less, can be produced using media in which the photochromic dye is dissolved or suspended and has a lower viscosity.The lower viscosity of the medium results in a consistent application of such thin layers of photochromic coatings, thus improving the cosmetic appearance of the optical element. In contrast, the use of media with a higher viscosity increases the risk of air inclusions or irregular application of the photochromic coating, which can lead to unsatisfactory cosmetic appearance of the optical element due to visible streaks or waves.

[0013] The optical element according to the invention, comprising in the following order a substrate, a photochromic layer, sometimes also referred to as a photoresist, and an oxygen-impermeable barrier layer, sometimes also referred to as an oxygen barrier layer, will be explained in more detail below.

[0014] According to the present invention, the substrate, the photochromic layer, and the oxygen-impermeable barrier layer are arranged in the optical element such that, starting from the surface of the substrate, the photochromic layer is arranged first, followed by the oxygen-impermeable barrier layer. The photochromic layer is therefore arranged between the substrate and the oxygen-impermeable barrier layer. In principle, at least one further layer can be arranged between the oxygen-impermeable barrier layer and the photochromic layer.

[0015] In a preferred embodiment of the present invention, the oxygen-impermeable barrier layer is arranged directly on the photochromic layer. This allows the photochromic layer to be better protected from oxygen diffusion than with additional intermediate layers.

[0016] The photochromic layer and the oxygen-impermeable barrier layer can be arranged on both sides or on one side of the substrate, preferably on both sides.

[0017] In addition to the photochromic layer and the oxygen-impermeable layer, the optical element in preferred embodiments of the present invention can comprise at least one further layer. The possible further layers can be selected from the group consisting of a primer layer, a hard layer, an anti-reflective layer, and an easy-clean layer.

[0018] The arrangement of the additional layers in the optical element is not further restricted, as long as it is suitable in principle for the optical element and the additional layers can perform their function.

[0019] In a preferred embodiment, the photochromic layer is applied directly to the substrate.

[0020] Preferred layer arrangements of the optical element according to the invention, starting from the surface of the substrate, are: Substrate / primer layer / photochromic layer / oxygen-impermeable barrier layer / hard layer / anti-reflective layer / easy-clean layer, substrate / primer layer / photochromic layer / oxygen-impermeable barrier layer / hard layer / easy-clean layer, substrate / photochromic layer / oxygen-impermeable barrier layer / hard layer / easy-clean layer, substrate / primer layer / photochromic layer / oxygen-impermeable barrier layer / hard layer, substrate / photochromic layer / oxygen-impermeable barrier layer / hard layer / anti-reflective layer / easy-clean layer, substrate / photochromic layer / oxygen-impermeable barrier layer / hard layer / anti-reflective layer, and substrate / photochromic layer / oxygen-impermeable barrier layer / hard layer, wherein the layer arrangement substrate / photochromic layer / oxygen-impermeable barrier layer / hard layer is particularly preferred.

[0021] Regardless of whether the photochromic layer and the oxygen-impermeable barrier layer are arranged on both sides or on one side of the substrate, the other layers, if present, can each be arranged independently of one another on both sides or on one side of the substrate. The primer layer, hard layer, and easy-clean layer are preferably arranged independently of one another on both sides of the substrate, while the anti-reflective layer is preferably arranged on one side for cost reasons.

[0022] According to the present invention, the substrate as such is not subject to any particular restrictions, as long as it is in principle suitable for use in an optical element and can be coated with at least one photochromic layer and an oxygen-impermeable barrier layer. An optical element is defined as a spectacle lens.

[0023] Regarding the base material, the substrate is not further restricted. It can be made of mineral glass or plastic glass. Plastic glass has the advantage over mineral glass of being lower density and therefore lighter. Furthermore, substrates made of plastic glass offer increased break resistance. Suitable plastic materials include, for example, polythiourethane, polyurethane, polymethyl methacrylate, polycarbonate, polyacrylate, or polydiethylene glycol bisallyl carbonate, as well as combinations thereof; in principle, other transparent plastic materials can also be used.

[0024] In terms of its geometric shape, the substrate can basically be planar-parallel, biconcave, plano-concave, convex-concave, concave-convex, plano-convex or biconvex.

[0025] According to the present invention, the optical element is a spectacle lens.

[0026] The base material of a spectacle lens substrate is selected so that the lens typically has a refractive index in the range of 1.45 to 1.90, particularly in the range of 1.45 to 1.55, 1.59 to 1.68, or 1.70 to 1.76. Therefore, lenses can be made from standard glass with a refractive index of approximately 1.50, from quality glass with a refractive index of approximately 1.60 or 1.67, or from premium glass with a refractive index of approximately 1.74.

[0027] Typically, the front surface of a spectacle lens substrate is convex, while the back surface, facing the eye, is concave. This geometric shape is referred to as concave-convex for lenses with positive refractive power and convex-concave for lenses with negative refractive power. Progressive lenses are another example of a lens substrate with a similar geometric shape. These are also known as progressive lenses in the prior art.

[0028] The photochromic layer and the oxygen-impermeable barrier layer are preferably arranged only on the front surface of the substrate, i.e., the side facing away from the eye, in order to avoid adverse effects on the photochromic behavior of the lens caused by varying light intensities at different locations on the lens. The anti-reflective layer, if present, is preferably arranged on the front surface of the substrate, i.e., the side facing away from the eye.

[0029] According to the present application, the photochromic layer comprises at least one photochromic dye. Photochromic dyes are defined as dyes in which a change in absorption behavior is induced by light (visible light or UV radiation). Depending on the application, the person skilled in the art selects at least one suitable photochromic dye, whereby the combination of several photochromic dyes is also possible. One criterion here, besides the actual application, is the desired hue that the optical element should exhibit, for example, in the absence or presence of light of a certain intensity.

[0030] Various classes of photochromic dyes are known in the art. These often include benzopyrans or their higher fused ring systems, chromenes, viologens, fulgides and fulgimides, and especially spiro compounds such as spirooxazines or spiropyrans, though this is not the only category. Several of these photochromic dyes can also be combined.

[0031] The photochromic layer can also contain a matrix, comprising at least one transparent plastic material, for the photochromic dye(s) to be used. The transparent plastic materials used for this purpose are not further restricted and are known to those skilled in the art.For example, a transparent homo- or copolymer selected from the group consisting of polymethacrylates, such as poly(methyl methacrylate), poly(ethylene glycol bismethacrylate), polyacrylates, poly(ethoxylated bis-phenol A dimethacrylate), thermoplastic polycarbonate, polyvinyl acetate, polyvinyl butyral, polythiourethane, polyurethane, or a polymer selected from the group consisting of diethylene glycol bis(allyl carbonate) monomers, diethylene glycol dimethacrylate monomers, ethoxylated phenol methacrylate monomers, ethoxylated diisopropenylbenzene monomers, and ethoxylated trimethylolpropane triacrylate monomers, preferably polymethacrylates or polyacrylates, can be used as a transparent plastic material.

[0032] In a preferred embodiment of the present invention, the thickness of the photochromic layer is at least 1 µm, preferably at least 2 µm, and particularly preferably at least 3 µm. Furthermore, according to the invention, the thickness of the photochromic layer is at most 30 µm, and particularly preferably at most 10 µm. The specified thickness ranges can be freely combined. For example, the thickness of the photochromic layer can be from 2 µm to 30 µm, and particularly preferably from 3 µm to 10 µm.

[0033] Photochromic layers of reduced thickness, particularly 30 µm or less, preferably 10 µm or less, can be applied during the fabrication of the optical element using methods that are superior to those used for applying thicker layers in terms of process control. This superiority is evident, among other things, in reduced inventory and greater flexibility regarding photochromic colors, pre-coloring, and darkening depths.

[0034] Furthermore, in the case of thinner photochromic layers, particularly those with a thickness of 30 µm or less, and preferably 10 µm or less, the viscosity of the medium in which the photochromic dye is dissolved or suspended can be reduced in the optical element fabrication process. Using media with a lower viscosity reduces the risk of air inclusions or irregularities in the photochromic layer, thereby avoiding the negative cosmetic appearance of the optical element caused by visible streaks or waves. The thinner the photochromic layer, the lower the viscosity of the medium in which the photochromic dye is dissolved or suspended can be.Especially for photochromic layers with a thickness of 30 µm or less, preferably 10 µm or less, such a medium in which the photochromic dye is dissolved or suspended can be used with a sufficiently low viscosity to avoid negative cosmetic effects on the optical element by the appearance of streaks or waves.

[0035] Various methods for applying photochromic layers are known to those skilled in the art. The photochromic dye can be applied to the substrate either as such or embedded in a polymer material. For example, the photochromic dye can be dissolved or dispersed in a polymer material, e.g., by adding the photochromic dye to a monomeric material or prepolymer before polymerization, and the polymer material containing the photochromic dye can then be applied to the substrate. In addition to a monomer or prepolymer to be polymerized, a fully polymerized polymer can also be dissolved together with the photochromic dye. This solution is applied to the substrate and hardens upon evaporation of the solvent. Optionally, the photochromic layer can be further hardened by chemical cross-linking of the matrix-forming polymer materials.Preferably, the photochromic layer is only dried and not additionally chemically cured. This allows for easier correction of defects occurring during application, such as blistering, by selectively removing the formed layer. The plastic material with the embedded photochromic dye can be applied, for example, by spin coating, dip coating, or spray coating, but these methods are not the only options. The spin coating process is particularly suitable for applying photochromic layers with a thickness greater than 30 µm. However, thicknesses of 30 µm or less are also possible using this method. Dip coating, also known as immersion coating, is particularly suitable for applying photochromic layers with a thickness of 10 µm or less. With this latter method, a surprisingly lower tendency for the photochromic dye to migrate into other layers can be achieved.In this process, a previously prepared substrate is immersed in a dye bath. This bath contains a photochromic dye dissolved or dispersed in a liquid medium. The medium also contains a solvent and, optionally, a matrix-forming polymer. As a result of immersion in the dye bath, the substrate is coated with a film consisting of the above medium and then withdrawn from the dye bath at a specific speed. The withdrawal speed is not further limited as long as a photochromic layer with the desired properties can be deposited. Preferably, the speed is 0.5 to 4 mm / s. By evaporating the solvent from the film that has formed on the surface of the withdrawn substrate, the photochromic layer is transformed into a solid. Optionally, the matrix-forming polymer contained therein can be chemically cured.The corresponding procedures are sufficiently known to those skilled in the art. Immersion in a dye bath should be carried out in such a way that the substrate obtained after post-processing, coated with a photochromic layer, exhibits a predetermined target transmission. The transmission also depends on the extent of dye uptake and can therefore be adjusted by the duration of immersion. In addition to immersion in a dye solution, a colored lacquer can also be applied, which releases the dyes to the substrate and is subsequently removed.

[0036] According to the present invention, the oxygen-impermeable barrier layer comprises at least one polymer selected from the group consisting of ethylene-vinyl alcohol copolymer, cellulose hydrate, polyvinyl alcohol, polyacrylonitrile, polyvinyl dichloride, polyurethane, and polyethylene terephthalate. In a preferred embodiment, the oxygen-impermeable barrier layer comprises at least one polymer selected from the group consisting of ethylene-vinyl alcohol copolymer, cellulose hydrate, polyvinyl alcohol, polyacrylonitrile, polyvinyl dichloride, and polyethylene terephthalate. The oxygen-impermeable barrier layer preferably comprises at least one polymer selected from ethylene-vinyl alcohol copolymer and polyvinyl alcohol; more preferably, it comprises an ethylene-vinyl alcohol copolymer. Such polymers are capable of forming a transparent film.The ethylene-vinyl alcohol copolymer can have a degree of hydrolysis of 92 mol% or more, preferably 95 mol% or more, and particularly preferably 99 mol% or more. If the oxygen-impermeable barrier layer comprises more than one polymer, all polymers, several polymers, or only one polymer can exhibit the properties described below. The oxygen-impermeable properties of the barrier layer result from the oxygen permeability of the polymer and the thickness of the oxygen-impermeable barrier layer. Preferably, an oxygen-impermeable barrier layer with a thickness of less than 2 µm, and particularly preferably less than 1 µm, is applied to avoid negatively affecting the adhesion, cosmetic properties, and optical characteristics of the optical element.

[0037] The at least one polymer preferably has an oxygen permeability ≤ 0.5 mL·m·m⁻² ·Tag⁻¹ ·Pa⁻¹ and particularly preferably ≤ 0.01 mL·m·m⁻² ·Tag⁻¹ ·Pa⁻¹. The oxygen permeability of the polymer is measured according to ISO 15105. Furthermore, the at least one polymer is generally selected such that a 4% aqueous solution thereof has a viscosity of 0.1 to 30 mPa·s at 20°C. The viscosity of the 4% aqueous solution is measured using a rotational viscometer at a shear rate of 23–30 mPa·s and a temperature of 20°C.

[0038] In a preferred embodiment of the present invention, the at least one polymer has a mass-weighted molar mass (Mw) in the range of 10,000 g / mol to 130,000 g / mol, preferably 80,000 g / mol to 110,000 g / mol, determined by gel permeation chromatography (GPC) with light scattering detection according to DIN EN ISO 16014-5.

[0039] In addition to at least one polymer, the oxygen-impermeable barrier layer may contain other components that improve the flow behavior of the medium for forming the oxygen-impermeable barrier layer during production, the adhesion of the oxygen-impermeable barrier layer to the adjacent layers of the optical element, or the wetting of the oxygen-impermeable barrier layer, as well as resulting in a smoother surface of the oxygen-impermeable barrier layer.

[0040] According to the present invention, the oxygen-impermeable barrier layer has a thickness of 0.1 µm to 4 µm, particularly preferably 0.3 µm to 2 µm. In this thickness range, the diffusion of oxygen into the photochromic layer is sufficiently prevented without negatively affecting the properties of the optical element.

[0041] The application of the oxygen-impermeable barrier layer is not subject to any particular restrictions, provided that the oxygen-impermeable barrier layer adequately protects the photochromic layer from oxygen diffusion and does not impair the properties of the optical element. Various suitable methods for this purpose are known to those skilled in the art. For example, the oxygen-impermeable barrier layer can be applied to the substrate by a dipping, spraying, or spin-coating process. Such processes involve dissolving or suspending the polymers forming the oxygen-impermeable barrier layer, and optionally other components, in a solvent or combination of solvents, applying the solution or suspension to the substrate, and converting the oxygen-impermeable barrier layer into a solid form by drying.Suitable solvents for sufficiently suspending or dissolving the polymers forming the oxygen-impermeable barrier layer and, if applicable, other components, as well as suitable concentrations of the solution or suspension, are known to those skilled in the art.

[0042] To promote adhesion of the layers arranged on the substrate, the substrate can be provided with a primer layer for this purpose. Preferably, however, no primer layer is applied to the substrate. In such an optical element, there is then no primer layer between the substrate and the photochromic layer.

[0043] The primer layer can increase not only the adhesion strength of the coating but also the fracture toughness of the substrate. To further enhance adhesion between the barrier layer and other layers, a primer layer can also be applied below and / or above the barrier layer. Layer thicknesses, materials, and methods for applying such a primer layer are well known to those skilled in the art. For example, the substrate can be primed using dipping, spraying, or spincoating processes.

[0044] As mentioned earlier, a hard coating can be applied to the substrate to protect the oxygen-impermeable barrier layer from damage. This is also advisable if the substrate is made of plastic glass, as this is a relatively soft material and therefore an optical element made from it is more susceptible to scratches than one made from mineral glass. The hard coating is preferably applied to the side of the oxygen-impermeable barrier layer facing away from the photochromic layer.

[0045] The hard coating can have a single-layer or multi-layer structure. Various materials and processes can be used to produce the hard coating, which a person skilled in the art will select appropriately. Typically, the hard coating is applied in the form of a hard lacquer or an inorganic material, particularly quartz-based. However, it is preferred to use a hard coating based on an acrylic polymer, a urethane polymer, a melamine polymer, a silicone resin, or an inorganic material, particularly quartz-based. The hard coating can be located completely or partially above the oxygen-impermeable layer and on one or both sides of the substrate.A hard layer arranged over the oxygen-impermeable barrier layer protects the underlying oxygen-impermeable barrier layer from scratches or other mechanical damage, thereby maintaining the protection of the photochromic layer from degradation by oxygen diffusion. Preferably, a silicone resin, for example based on siloxanes, is applied as the hard layer to the surface of the optical element.

[0046] A suitable layer thickness for the hard coating is not further limited and can be readily determined by a person skilled in the art. Preferably, the hard coating has a layer thickness of 20 µm or less, more preferably 1 to 15 µm, and most preferably 1 to 5 µm.

[0047] The application of a hard coating is generally carried out using conventional methods such as dipping, spraying, or spin coating. However, if the hard coating is an inorganic material, such as a quartz-based material, it can be applied to the substrate using physical or chemical vapor deposition. Suitable methods for this are well known to those skilled in the art.

[0048] Furthermore, the optical element can have an antireflective coating. In one embodiment of the present invention, the optical element does not contain an antireflective coating. In such cases, a more cost-effective optical element with improved UV and light stability can be obtained. Like the hard coating, the antireflective coating can also have a single- or multi-layer structure. Such single- or multi-layer antireflective coatings are known to those skilled in the art, and in the case of a multi-layer antireflective coating, the number of layers is not fundamentally limited. In a multi-layer antireflective coating, the layer sequence is usually chosen such that a layer with a low refractive index of a certain thickness is adjacent to a layer with a high refractive index of a certain thickness.In other words, for such a structure, it is preferred that layers with a low refractive index and layers with a high refractive index are arranged alternately.

[0049] Suitable materials and layer thicknesses for realizing such a structure are known to those skilled in the art. The antireflection layer can, for example, comprise a sequence of various transparent materials, including, but not limited to, SiO₂, SiO₂, Ta₂O₅, TiO₂, ZrO₂, Al₂O₃, Nd₂O₅, Pr₂O₃, PrTiO₃, La₂O₃, Nb₂O₅, Y₂O₃, HfO₂, InSn oxide (ITO), Si₃N₄, MgO, MgF₂, CeO₂, and ZnS. Some of these materials, such as SiO₂, have a comparatively low refractive index, while others, such as Ta₂O₅, have a comparatively high refractive index.

[0050] The thickness of the antireflective coating, whether single-layer or multi-layered, is not subject to any particular limitation. However, it preferably has a thickness of 2000 nm or less, more preferably 1500 nm or less, and most preferably 300 nm or less. The thickness of the antireflective coating itself is simultaneously 100 nm or more. In a multi-layered antireflective coating, the thickness of each individual layer is adjusted appropriately as described above. Additional layers, such as adhesive layers (e.g., with a thickness in the range of approximately 5 nm to 5 µm), which do not necessarily have an optical function but can be advantageous for durability, adhesion properties, climate resistance, etc., can also be incorporated into the antireflective coating.

[0051] The individual layers of the antireflective coating can be applied by immersion, spraying, or spin coating processes, as well as by physical or chemical vapor deposition, all of which are sufficiently known to those skilled in the art. Examples of methods for application by physical vapor deposition include electron beam evaporation from a crucible, resistance evaporation from a boat, and plasma assistance during evaporation, but these are not the only possibilities.

[0052] Furthermore, if required, an easy-care layer, sometimes also referred to as a "topcoat," "cleancoat," or hydrophobic and / or oleophobic coating, which serves to repel dirt and water droplets, can be applied to the substrate. This easy-care layer preferably comprises a silane, siloxane, or silazane with at least one fluorine-containing group, preferably having more than 20 carbon atoms. The silane, siloxane, or silazane with at least one fluorine-containing group is preferably based on a silane, siloxane, or silazane with at least one hydrolyzable group. Suitable hydrolyzable groups are not subject to any particular restrictions and are known to those skilled in the art.

[0053] The thickness of the easy-care layer is not subject to any particular limitation. However, it preferably has a thickness of 50 nm or less, and more preferably 20 nm or less.

[0054] The expert is familiar with the appropriate materials and measures for applying such an easy-care layer.

[0055] In another aspect, the present invention relates to a method for manufacturing an optical element in the form of a spectacle lens, comprising, in the following order, the steps: (a) Providing a substrate, (b) applying a photochromic layer with a thickness of 30 µm or less, and (c) applying an oxygen-impermeable barrier layer with a thickness of 0.1 µm to 4 µm, preferably directly onto the photochromic layer.

[0056] The manufacturing process according to the invention, by which the optical element according to the invention can be obtained, is explained in more detail below: In the first step, a substrate is provided. As already explained in more detail above, the substrate itself is not subject to any particular restrictions. The above statements, as made in connection with the optical element according to the invention, apply accordingly to the manufacturing process according to the invention.

[0057] In a subsequent step, a photochromic layer is applied to the substrate. In a preferred embodiment of the method according to the invention, the photochromic layer is applied directly to the substrate. As mentioned above, the application of photochromic layers is known to those skilled in the art from the prior art, and the preceding descriptions, as they have been made for the optical element according to the invention, apply accordingly to the step of applying the photochromic layer.

[0058] In a further step, an oxygen-impermeable barrier layer is applied to the substrate.

[0059] In the step of applying an oxygen-impermeable barrier layer, the person skilled in the art may refer to methods known from the prior art. In a preferred embodiment of the inventive method for producing an optical element, the step of applying the oxygen-impermeable barrier layer comprises an immersion process, a spraying process, or a spincoat process. Such processes may initially include dissolving or suspending the at least one polymer forming the oxygen-impermeable barrier layer and optionally further components in a solvent. The preceding descriptions, as given for the optical element according to the invention, apply accordingly to the polymer forming the oxygen-impermeable barrier layer.The solution or suspension is then applied according to the immersion, spraying, or spincoat process by immersing the substrate in a bath filled with the solution or suspension and withdrawing it at a speed of 0.5 to 4 mm / s, preferably 0.57 to 2 mm / s; spraying the solution or suspension onto the substrate; or applying the suspension or solution to the substrate and subsequently rotating the substrate. In a spincoat process, the substrate can be rotated at a speed of 50 to 200 revolutions per minute during the application of the medium from which the oxygen-impermeable barrier layer is formed. After application of the medium, the substrate is rotated for 5 to 30 seconds, preferably 10 to 20 seconds, at a speed of 200 to 700 revolutions per minute, preferably 300 to 600 revolutions per minute, and particularly preferably 400 to 500 revolutions per minute.Preferably, the oxygen-impermeable layer is applied using dipping or spincoat methods.

[0060] The oxygen-impermeable barrier layer is subsequently solidified by removing the solvent from the solution or suspension applied to the substrate, for example, by drying or evaporating the solvent. Drying can be carried out at room temperature up to 200°C, preferably 40°C to 150°C, and particularly preferably 60°C to 90°C. It is known to those skilled in the art that the drying time depends on the temperature and the boiling point of the solvent. For example, drying can be carried out for 2 to 25 minutes, preferably 5 to 10 minutes.

[0061] If further layers are provided in the optical element to be manufactured, the manufacturing process according to the invention can be supplemented in the appropriate sequence by the corresponding steps for applying the further layers. Among other things, a hard layer, an anti-reflective layer, and / or an easy-clean layer can optionally be applied. As mentioned above, the hard layer and the anti-reflective layer, if provided, can be applied by dipping, spraying, or spin coating processes, or by physical or chemical vapor deposition. The substrate can also be pre-coated with a primer layer. The above descriptions, as they have been made for the optical element according to the invention, apply accordingly.

[0062] In another aspect, the present application concerns the use of an optical element. The optical element can be used for ophthalmic purposes, as lenses for all types of eyewear, such as sunglasses, safety glasses, ski goggles, and helmet visors. Character description

[0063] Figure 1 shows the degradation behavior of the photochromic layer of an optical element comprising an oxygen-impermeable barrier layer applied by spin coating, compared to a photochromic layer of an optical element not comprising an oxygen-impermeable barrier layer, after accelerated aging by irradiation with a xenon lamp, with both optical elements not including an additional hard layer. Figure 2shows the different degradation of a photochromic layer in optical elements with and without an oxygen-impermeable barrier layer applied by a dipping process after accelerated aging by irradiation with a xenon lamp, with both optical elements additionally including a hard layer. Examples

[0064] The following examples serve to further illustrate the present invention, without, however, being limited thereto.

[0065] In a first exemplary embodiment, an optical element with an oxygen-impermeable barrier layer and an identical element without an oxygen-impermeable barrier layer are produced as follows: A substrate consisting of a thermally cross-linked acrylate polymer, in the form of a flat disk with a thickness of 3 mm, a diameter of 60 mm, and an optical refractive index of 1.5, is provided. The substrate comprises a photochromic layer with a thickness of 5 µm. The photochromic layer contains a photochromic dye and an acrylate polymer. The photochromic layer was applied as a solution with 1-methoxy-2-propanol as the solvent and cured by drying. An oxygen-impermeable barrier layer is applied by spin coating using an aqueous 5% ethylene-vinyl alcohol copolymer solution, which has an n-propanol:water mixture in a ratio of 3:7.One mL of the solution is applied to the substrate, which is rotated at 100 revolutions per minute. The ethylene-vinyl alcohol copolymer used has a hydrolysis level of 99–99.4 mol%. The substrate is then rotated for a further 12 seconds at 450 revolutions per minute. The applied film is then dried for 5 minutes at 90 °C, resulting in a solid, oxygen-impermeable barrier layer with a thickness of 1.7 µm.

[0066] In a second exemplary embodiment, an optical element with an oxygen-impermeable barrier layer and a hard coating, as well as an identical element without an oxygen-impermeable barrier layer, are produced as follows: A substrate consisting of polythiourethane, in the form of a glass element with a thickness of 2 mm, a diameter of 60 mm, an optical refractive index of 1.6, and a refractive power of -2.25 diopters, is provided. A photochromic layer with a thickness of 7 µm is applied to the substrate. The photochromic layer contains a photochromic dye and an acrylate polymer. The photochromic layer was applied as a solution in 1-methoxy-2-propanol as a solvent by spin coating and cured by drying.The substrate is immersed in a tank containing a 2.5% aqueous ethylene-vinyl alcohol copolymer solution, based on a 3:7 n-propanol:water mixture, and withdrawn at a speed of 1 mm / s. The ethylene-vinyl alcohol copolymer has a hydrolysis degree of 99–99.4 mol%. The applied film is then dried for 10 minutes at 60°C, resulting in a solid, oxygen-impermeable barrier layer. After cooling, the substrate is immersed in a hard-film forming solution containing water, methanol, ethanol, isopropanol, and 1-methoxypropanol as solvents and withdrawn at a speed of 1 mm / s. A hard film is formed on the substrate by pre-drying at 60°C for 10 minutes and subsequent curing at 110°C for 3 hours. The hard coating is a polysiloxane-based thermally cured layer.

[0067] The resulting optical elements are subjected to accelerated aging by irradiation with a xenon lamp without additional temperature control or manipulation and are examined for degradation of the photochromic layer after 25 and 50 hours (xenon test). The xenon lamp has a solar-like emission spectrum. The distance between the optical elements and the xenon lamp is calibrated so that the optical elements are exposed to an irradiation intensity of < 700 W / m². This distance is kept constant throughout the aging process.

[0068] The degradation of the photochromic layer of optical elements, with and without an oxygen-impermeable layer, is assessed visually in both the bright and darkened states. The darkened state is achieved by irradiation with a solar simulator at an effective power of 4 mW / cm² for UVA radiation emission over 0.5 minutes. In the darkened state, an optical element with an undamaged photochromic layer exhibits a total transmission of 10%, while in the undarkened state, it exhibits a total transmission of 86%. The total transmission is measured in accordance with DIN EN ISO 8980-3.

[0069] As can be seen from Figure 1As can be seen, after accelerated aging for over 50 hours using a xenon lamp, a significant darkening can be observed for the optical element with an oxygen-impermeable layer and without an additional hard coating. The photochromic layer can be protected from degradation by oxygen and UV radiation by the oxygen-impermeable barrier layer. The optical element retains its photochromic properties. Thus, in transmission measurements of the optical element with an oxygen-impermeable layer, no increase in overall transmission can be detected after accelerated aging for over 25 hours.

[0070] For the corresponding optical element without an oxygen-impermeable barrier layer, no darkening of the photochromic layer can be observed after accelerated aging over 50 hours under identical conditions. Complete degradation of the photochromic layer occurs over 50 hours, and the element completely loses its photochromic properties. Furthermore, after accelerated aging over 25 hours, an increase in overall transmission from 10% to 21% can be observed.

[0071] From the Figure 2For optical elements that also contain a hard coating, it can be concluded that, without an oxygen-impermeable barrier layer, the optical element exhibits deteriorated optical properties after accelerated aging for over 50 hours in the non-darkened state, which is visually recognizable by the distinct yellowing of the element. Yellowing cannot be observed in the corresponding optical element with an oxygen-impermeable barrier layer in the non-darkened state after 50 hours of accelerated aging.

[0072] From the comparison of both photochromic elements, which are subjected to accelerated aging over 50 hours, it can be deduced that the degradation of the photochromic layer in an optical element according to the invention can be avoided by applying an oxygen-impermeable barrier layer and the service life of the photochromic layer or the photochromic properties of the optical element according to the invention can be extended.

Claims

1. An optical element comprising, in the following order, a substrate, a photochromic layer, and an oxygen-impermeable barrier layer, wherein the oxygen-impermeable barrier layer comprises at least one polymer selected from the group consisting of ethylene-vinyl alcohol copolymer, cellulose hydrate, polyvinyl alcohol, polyacrylonitrile, polyvinyl chloride, polyurethane, and polyethylene terephthalate, wherein the optical element is a spectacle lens, the photochromic layer has a thickness of 30 µm or less, characterized in that the layer thickness of the oxygen-impermeable layer is 0.1 µm to 4 µm .

2. An optical element according to claim 1, wherein the photochromic layer is disposed directly on the substrate.

3. An optical element according to any one of claims 1 or 2, wherein the at least one polymer is selected from the group consisting of ethylene-vinyl alcohol copolymer, cellulose hydrate, polyvinyl alcohol, polyacrylonitrile, polyvinyl chloride, and polyethylene terephthalate.

4. An optical element according to any one of claims 1 to 3, wherein the oxygen-impermeable barrier layer is disposed directly on the photochromic layer.

5. An optical element according to any one of claims 1 to 4, wherein the photochromic layer has a thickness of 10 µm or less.

6. An optical element according to any one of claims 1 to 5, wherein the thickness of the oxygen-impermeable layer is 0.3 µm to 2 µm.

7. An optical element according to any one of claims 1 through 6, wherein the at least one polymer has a weight-average molecular weight (Mw) of 10,000 g / mol to 130,000 g / mol.

8. An optical element according to any one of claims 1 to 7, wherein the optical element further comprises at least one layer selected from a hard coating and an antireflective coating, which is disposed on the side of the oxygen-impermeable barrier layer facing away from the photochromic layer.

9. A method for manufacturing an optical element, comprising the following steps in the order listed below: (a) providing a substrate, (b) applying a photochromic layer, and (c) applying an oxygen-impermeable barrier layer, preferably directly onto the photochromic layer, wherein the optical element is a spectacle lens wherein the photochromic layer has a thickness of 30 µm or less , characterized in that the layer thickness of the oxygen-impermeable layer is 0.1 µm to 4 µm .

10. The method according to claim 9, wherein the photochromic layer is applied directly to the substrate.

11. Use of the optical element according to any one of claims 1 to 8 for ophthalmic purposes as lenses for eyeglasses of all kinds, such as sunglasses, safety glasses, and visors for helmets.