TITLE

Method for producing a three-dimensional optical structure and three-dimensional optical structure

BACKGROUND

The present invention relates to a method for producing a three-dimensional optical structure, in particular an ophthalmic lens, wherein in a first step a base structure is printed by depositing droplets of a first printing ink at least partially side by side and preferably at least partially on top of each other.

Printed three-dimensional optical structures such as ophthalmic lenses are well known from the prior art. In recent years, with the rise of rapid prototyping and in particular additive manufacturing, it has become clear that such optical structures can easily be produced by three-dimensional printing. An advantage of three-dimensionally printed optical structures and in particular ophthalmic lenses is their variability and versatility, especially with regard to individual customizability and the possibilities of special uses. Not only is it easy to customize optical functions of the optical structures during their production, but the optical structures may also be specially adapted for the integration of functional components. For example, it is conceivable that the three-dimensional optical structure is used as the lens in a pair of glasses through which information is displayed to the user, which is the case in so-called augmented reality glasses.

For reasons of safety and/or comfort, it is desirable that the lens comprises anti-reflective properties. Typically, such properties are obtained by means of a coating step in a separate production step after printing (and curing) of the optical structure is finished. The optical structure, e.g. the lens, is transferred to another apparatus and the anti-reflective coating is applied e.g. by means of spin coating, dip coating, physical vapor deposition or chemical vapor deposition. These are all well-known techniques.

Due to the underlying principles of physics of anti-reflective coatings, their thickness is usually very small, i.e. in the order of 100 nm to 200 nm. Yet, due to technical limitations, in particular due to the droplet size of printing ink, a three-dimensionally printed layer comprises a thickness which is usually rather in the order of pm.

Hence, with currently known techniques, three-dimensional printing of an anti-reflective coating is not possible.

SUMMARY

It is therefore a purpose of the present invention to provide a method for producing a three- dimensional optical structure, in particular an ophthalmic lens, by means of three- dimensional printing comprising anti-reflective properties.

According to the present invention, this object is achieved by a method for producing a three- dimensional optical structure, in particular an ophthalmic lens, wherein in a first step a base structure is printed by depositing droplets of a first printing ink at least partially side by side and preferably at least partially on top of each other, wherein in a second step at least one layer is printed in at least a region of a surface of the base structure by depositing droplets of a second printing ink at least partially side by side, wherein the second printing ink is different from the first printing ink and comprises at least a first component and a second component, wherein the first component comprises a higher refractive index than the second component, wherein after printing, a separation between the first component and the second component of the second printing ink is established such that the layer, in particular the second component, forms an anti-reflective coating.

The method according to the invention advantageously allows for a particularly easy way to produce an optical structure, such as an ophthalmic lens, comprising an anti-reflective coating by means of three-dimensional printing. Thus, the production of the optical structure is quick, easy and less prone to damage due to transport between apparatus. Due to the separation between the first and the second component and their respective properties, the relevant interface for reflections is not the interface between the printed layer and the base structure, but the interface between the first component and the second component. The effective thickness of the anti-reflective coating is substantially determined by the amount of the second component. Furthermore, by adjusting the amount and the refractive index of the second component, the properties of the anti-reflective coating may advantageously be tuned. Additionally, the thickness of the layer, in particular the second component, is adjustable in order to obtain predetermined properties. Preferably, the thickness of the layer is adjustable while keeping the relative shares of the first component and the second component, i.e. in particular the composition of the second printing ink, constant. More preferably, the separation between the first component and the second component is a phase separation.

The embodiments and advantages described in conjunction with this subject matter of the present invention also apply to the further subject matter of the present invention and vice versa.

Preferably, the second printing ink comprises, at least prior to printing and/or curing at least one further component. This may be an additive, a suspension fluid and/or a color component.

According to a preferred embodiment of the present invention, the layer, in particular the first component of the second printing ink, is configured such that it forms a hard coating. This is particularly advantageous, because this way the layer acts as an anti-reflective coating and a hard coating at the same time, thus preventing damage to the optical structure from external influences. Preferably, the printed layer, in particular the second component, comprises a uniform thickness, in particular a constant thickness over its entire lateral extension. Even more preferably, the printed layer comprises a lower thickness than the base structure. This is particularly advantageous, because in this way, the layer does not substantially influence the optical properties of the optical structure. Additionally or alternatively, the printed layer of the second printing ink provides shielding of the optical structure against radiation - such as ultraviolet light, blue light and/or (near) infrared light - and/or color correction. It is herewith advantageously possible to protect the optical structure from external damaging and/or deteriorating influences, in particular mechanical, chemical or radiation influences. It is herewith advantageously possible to create a relatively thin optical structure with additional protective properties without having to print an additional layer.

Preferably, the anti-reflective coating, formed by the second component of the second type printing layer, comprises a minimal layer thickness. It is hence advantageously possible that the coating does not or at least not significantly contribute to the optical properties of the base structure and therefore the optical structure.

Preferably, the refractive indices of the first component and the second component are significantly different. More preferably, the difference between the refractive indices comprises between 2% and 30% and in particular at least 5%, at least 10%, at least 20%, or at least 25%. While a relatively high refractive index preferably allows for a thinner lens, a relatively low refractive index preferably yields a broader spectrum with regard to anti- reflective properties. By choosing the first and second component of the second printing ink such as described above, it is advantageously possible to provide a layer which is at the same time relatively thin and comprises anti-reflective properties over a broad range of wavelengths. Preferably, the second component comprises a reflective index whose numerical value is substantially the root square of the reflective index of the first component. This advantageously yields a maximum in efficiency for the anti-reflective properties. More preferably, the first component comprises a reflective index between 1.45 and 1.75 and/or the second component comprises a reflective index less than 1.4, in particular between 1.2 and 1.4.

According to a preferred embodiment of the present invention, the second printing ink comprises between 85% and 99% of the first component and/or between 1% and 15% of the second component.

The optical structure is a three-dimensional structure preferably intended to at least partially transmit light. The optical structure is more preferably intended for use with the visible spectrum. Preferably, in order to serve an optical purpose, the optical structure is at least partially optically transparent, in particular at least for a predetermined range of wavelengths, such as the visible spectrum. In particular, the optical structure may be a lens and even more preferably an ophthalmic lens. Ophthalmic lenses comprise concave, convex, biconcave, biconvex, plano-concave, plano-convex and meniscus lenses. Ophthalmic lenses in the sense of the present invention also comprise multifocal lenses as well as gradient-index lenses. Ophthalmic lenses comprise in particular spectacle lenses or other lenses that are used in eyewear.

In the context of the present invention, printing of an optical structure comprises building up the structure from layers of printing ink. These are obtained through a targeted placement of droplets of printing ink at least partially side by side. The droplets of printing ink are preferably ejected from nozzles of a print head, typically in a substantially vertical direction towards a substrate or another suitable surface, though ejecting at an angle is possible as well, wherein the print head is controlled by a controller according to predetermined print data. The print data preferably comprises slicing data, wherein in particular, a predetermined shape of the optical structure is converted into print data by dividing it into a plurality of layers, i.e. slices, which are at least partially stacked upon each other. Droplets of layers constituting the following layer are at least partly ejected towards the previously deposited layer, such that the three-dimensional structure is built up layer by layer. Preferably, the three-dimensional printer used for the method according to the present invention is a multi-jet printer.

According to a preferred embodiment of the present invention, the optical structure, in particular the base structure and/or the layer, are at least partially printed in a multi-pass printing mode, wherein preferably a layer printed in a multi-pass printing mode comprises multiple sublayers which are printed in subsequent sublayer printing steps, wherein at least one sublayer printing step is followed by an at least partial curing step. This allows in a very advantageous manner for a highly flexible and customizable production of an optical structure. A multi-pass printing mode preferably comprises the printing head making several passes, in particular back and/or forth, wherein during each pass, a sublayer of the layer is printed. Each sublayer may be subjected to a separate curing step, only the completed layer may be subjected to a curing step or a curing step is performed in regular or irregular intervals, e.g. as soon as a predetermined amount of sublayers are printed and/or after a predetermined time after printing has passed. Alternatively or additionally, at least one layer of the base structure and/or the layer is printed in a multi-pass printing mode, wherein at least one further layer is printed in a non-multi-pass printing mode. By including a multi-pass printing mode, it is advantageously possible to correct errors in the optical structure. This process is detailed in the previous application EP 3722073 A1 of the present applicant. The disclosure of the aforementioned application, at least regarding the application of a multipass printing mode for approximation error reduction, is incorporated in the present disclosure.

Preferably, the first printing ink and/or the second printing ink comprises a translucent or transparent component. More preferably, the first and/or second printing ink comprises at least one polymerizable component, in particular a photo-polymerizable and/or thermo- polymerizable component. The at least one polymerizable component is most preferably a monomer and/or an initiator that polymerizes upon exposure to radiation, e.g. ultra-violet (UV) and/or infrared (IR) light, and/or upon exposure to heat. The deposited droplets are preferably pin cured, i.e. partially cured, after deposition. More preferably, the viscosity of the at least one deposited droplet of the (first and/or second) printing ink is increased. Pin curing is most preferably carried out after deposition of the respective droplet or after deposition of an entire (sub)layer or only part of a layer. Alternatively, pin curing is carried out at certain intervals, e.g. after printing of every second (sub)layer. In particular for an optical structure, it is desirable that the structure is at least partly translucent and/or transparent. Preferably, curing may comprise actively and/or passively curing, wherein in particular passively curing includes letting the droplets dry or cure over time, whereas actively curing includes acting upon the deposited droplets, e.g. submitting the droplets to additional energy such as electromagnetic radiation, in particular UV and/or IR light, and/or thermal energy, in particular heat.

According to a preferred embodiment of the present invention, the base structure is printed on a substrate, a lens blank and/or a three-dimensionally printed structure. In particular, the base structure is printed upon a base layer, wherein the base layer is (three- dimensionally)printed upon a substrate. This is particularly advantageous as the resulting surface, upon which the base structure is printed, may be produced such as to comprise a very smooth surface, which is of particular importance for high-quality optical structures. Furthermore, the material of the base layer may be chosen such as to allow for an optimal bonding to both the substrate on the one side and the base structure on the other side. Preferably, the substrate, the lens blank and/or the base layer comprises glass and/or a polymer, in particular trivex, cellulose triacetate (TAC), cyclic olefin copolymer (COC), polyethylene terephthalate (PET), polycarbonate (PC), thiourethane and/or Polymethyl methacrylate (PMMA), which is also known as acrylic glass or plexiglass. Those materials are well-known and tested materials for optical purposes and therefore particularly suited for the production of the optical structure according to the present invention. Preferably, within the context of the present invention, it is assumed and preferred that the bottom of the base structure is generally flat and therefore comprises a substantially flat surface area. Of course, the base structure may as well comprise a curved surface at its bottom. All features and explanations apply equivalently in this case.

According to a preferred embodiment of the present invention, prior to printing, the first component and the second component of the second printing ink are provided as a homogenous or heterogenous mixture, in particular in an emulsion and/or in a suspension. It is thus advantageously possible to provide a second printing ink with fluid properties close to that of the first printing ink, in particular in a state suitable for use in a three-dimensional printing system, i.e. ejectable as droplets from the nozzles of a print head.

According to a preferred embodiment of the present invention, in a third step, after the separation is established, the layer is at least partially cured, wherein preferably the base structure is at least partially cured before the second step. It is herewith advantageously possible to further fine tune the anti-reflective properties of the layer by determining exactly when the layer is cured and hence fixed. According to a preferred embodiment of the present invention, during the separation, the first component migrates to a bottom of the layer and/or the second component migrates to a top of the layer. The person skilled in the art understands that “top” and “bottom” as all other directional indications refer to a production scenario, in which a downward direction is parallel to the gravitational direction. In particular, if the layer is applied on a top, in particular an outermost, surface of the base structure, the bottom of the layer is adjacent to a top of the base structure and forms an interface therewith, and/or the top of the layer is an uppermost surface of the layer, e.g. an interface surface to ambient air. Preferably, the separation is established by sedimentation of the first component and/or floating of the second component. In particular, the migration of the first component is a sedimentation, i.e. its movement is due to gravitational forces in a suspension and/or emulsion. It is herewith advantageously possible to obtain a separation between the first component and the second component of the second printing ink by waiting a predetermined time after deposition, i.e. printing, by means of gravitational forces. The person skilled in the art understands that preferably materials of different refractive index comprise different masses, which determines if a component will migrate, in particular sink, to the bottom of the layer or float to the top. More preferably, the speed of the migration process is adjustable. Even more preferably, the migration process is accelerated by the application of vibrational forces and/or by increasing the temperature of the materials, e.g. the first and/or second printing i nk[Ai] . It is thus advantageously possible to provide a faster printing process, thus leading to reduced production costs.

Preferably, the first component comprises a higher mass than the second component. More preferably, the first component comprises TiC>2, ZnO, CeC>2, ZnS and/or ZrC>2 particles. This means that the first component preferably is a high refractive index particle. Even more preferably, the second component comprises MgF2, CaF2, AIF3, SiC>2, polyhedral oligomeric silsesquioxane (POSS) and/or hollow SiO2 (silica) particles, i.e. in particular hollow silica gel spheres or pellets and/or nanoporous particles. This means that the second component preferably is a low refractive index particle.

According to a preferred embodiment of the present invention, the surface tensions of the first component and the second component are chosen such that the separation will occur at at least one interface surface within the layer. This is particularly advantageous if the layer comprises an (outer) interface surface to air (or another suitable surrounding medium). The first and/or second component will then advantageously separate depending on their respective surface tensions. According to a preferred embodiment of the present invention, the first component is at least partially fluorophile and the second component is at least partially hydrophile or hydrophobe, and/or wherein the first component is at least partially hydrophile and the second component is at least partially hydrophobe, such that the separation is established by self-migration of the first component and/or the second component. It is hence advantageously possible to replace and/or supplement a migration due to gravitational forces by a migration which is due to a repulsion between the first component and the second component. An example of a fluorophile component would be a perfluorocarbon (PFC) and/or a monomer with a polymerizable group and at least one perfluorocarbon side chain, such as hexafluoroisopropyl (meth)acrylate, trifluoroethyl (meth)acrylate, bis-(1 , 1 ,1, 3,3,3- hexafluoroisopropyl) itaconate, nonafluorohexyl (meth)acrylate, bis (meth)acrylate and/or dodecafluorooctane.

According to a preferred embodiment of the present invention, the reactivity, in particular the polymerization reactivity, of the first component and the second component are chosen such that the first component reacts prior to the second component. In particular, the materials for the first and second component are chosen such that they react differently during photopolymerization, e.g. radical polymerization or cationic polymerization. Preferably, the first component is configured to initiate photo-polymerization earlier and/or react quicker than the second component. More preferably, the first component will react according to a faster chemical mechanism by the use of a monomer containing at least one polymerizable group such as thiol and alkene/alkyne, acrylate and/or maleimide. Even more preferably, the second component will react according to slower chemical mechanism by the use of a monomer containing at least one polymerizable group such as methacrylate, epoxy and/or allyl/vinyl. It is hence advantageously possible that the separation is in particular initiated by curing and fine tunable.

Preferably, at least one of the above-described approaches is used to obtain the separation between the first component and the second component. More preferably, a combination of two or more approaches is used. Thus, the production of the anti-reflective coating may advantageously be precisely controlled. In particular, the separation between the first component and the second component is established within the thickness of layer.

According to a preferred embodiment of the present invention, the second step is performed such that the thickness of the layer, in particular the part of the layer formed by the second component after separation, is an uneven multiple of one quarter of a predetermined wavelength, wherein the predetermined wavelength is preferably within a range of 400 nm to 800 nm. The person skilled in the art understands that this wavelength substantially corresponds to the visible spectrum and/or that due to the thickness of one quarter of the wavelength, destructive interferences are created which advantageously cancel reflections. The person skilled in the art further acknowledges that the resulting thickness of the anti- reflective coating comprises ca. 100 nm to 200 nm, which is lower than the thickness of a typical three-dimensionally printed layer. Hence, the idea according to the present invention to use two components and create a separation after depositing or printing is the only way to create a layer thin enough to act as or form an anti-reflective coating.

According to a preferred embodiment of the present invention, during the second step, an interface between the first component and the second component is created with regard to their respective refraction indices. This means in particular that there is a non-contiguous change in refractive index along a direction, preferably in a vertical and/or radial direction, depending on the symmetry of the optical structure. Alternatively or additionally, during the second step, a gradient of refractive index is created within the layer, wherein in particular the gradient is directed from a top to a bottom of the layer. Such a gradient preferably comprises a contiguous change in refractive index along a predetermined direction. In particular, a gradient represents the maximum rate of increase and its direction.

According to a preferred embodiment of the present invention, the first component, in particular the composition of the first component, of the second printing ink substantially corresponds to the first printing ink, in particular the composition of the first printing ink. Hence, preferably, the second printing ink corresponds to the first printing ink with at least one further component, i.e. the second component. It is hence advantageously possible to simply use the first printing ink together with an additional component as a second printing ink. Furthermore, this advantageously allows for better optical properties of the optical structure since there is only one interface between two different refractive indices, i.e. between the first component (and the base structure, which comprises the same refractive index as the first component) and the second component. Reflections may only occur at that interface.

According to a preferred embodiment of the present invention, the surface of the base structure on which the layer is printed is a boundary surface to air, in particular to ambient air and/or to an air gap within the optical structure. This means in particular that an outermost surface of the optical structure, such as the outer face of an ophthalmic lens, is at least partially covered with the anti-reflective coating. Alternatively or additionally, an inner surface of the optical structure is at least partially covered with the anti-reflective coating, wherein the inner surface is adjacent to an air-gap within the optical structure. This is particularly advantageous for printing lenses with embedded functional components, in particular waveguides.

According to a preferred embodiment of the present invention, the first step is performed such that the base structure comprises a diffraction grating, wherein the second step is performed such that a region of the surface of the base structure in which the diffraction grating is located is free of the anti-reflective coating. It is herewith advantageously possible to create an optical structure comprising both a diffraction grating for optical purposes and an anti-reflective coating in areas in which a high transmittance is desirable.

According to another preferred embodiment of the present invention, the first step and the at least one second step are carried out without transferring the base structure from a first device to a second device. This advantageously significantly increases the efficiency of the optical structure production process. A transfer which is prone to errors and time consuming is no longer necessary. The optical structure can remain in the same device during the entire manufacturing process. Preferably, the first and/or second device is a three-dimensional printer, more preferably a three-dimensional inkjet printer, in particular a multi-jet printer.

A further subject matter of the present invention is a three-dimensional optical structure, in particular an ophthalmic lens, in particular produced by a method according to any one of the preceding claims, with a base structure comprising a cured first printing ink, wherein at least one region of a surface of the base structure comprises at least one printed layer, wherein the printed layer comprises a cured second printing ink, wherein the second printing ink is different from the first printing ink, wherein the second printing ink comprises at least a first component and a second component, wherein the first component comprises a higher refractive index than the second component, wherein the first component and the second component are separated such that the layer, in particular the second component, forms an anti-reflective coating.

The embodiments and advantages described in conjunction with this subject matter of the present invention also apply to the further subject matter of the present invention and vice versa.

The optical structure according to the present invention is particularly advantageous as it allows a quick and easy production of the optical structure completely by means of three- dimensional printing and including the production of the anti-reflective coating. Such an anti- reflective coating may hence in the context of the present invention also be called an anti- reflective coating layer and/or anti-reflective layer. Preferably, the amount of the second component, in particular the relative amount compared to the amount of the first component, predominantly or completely determined the (total) thickness of the anti-reflective coating layer.

According to a preferred embodiment of this subject matter of the present invention, the thickness of the printed layer, in particular the part of the layer formed by the second component, is an uneven multiple of one quarter of a predetermined wavelength, wherein the predetermined wavelength is preferably within a range of 400 nm to 800 nm. It is hence advantageously possible to print an anti-reflective coating which is suitable for visible light. This is particularly important for ophthalmic lenses.

According to a preferred embodiment of this subject matter of the present invention, the surface of the base structure on which layer is printed is a boundary surface to air, in particular to ambient air and/or to an air gap within the optical structure. This is particularly advantageous for printing lenses with embedded functional components, in particular waveguides.

According to a preferred embodiment of this subject matter of the present invention, the base structure comprises a diffraction grating, wherein a region of the surface of the base structure in which the diffraction grating is located is free of the anti-reflective coating. It is herewith advantageously possible to create an optical structure comprising both a diffraction grating for optical purposes and an anti-reflective coating in areas in which a high transmittance is desirable.

According to preferred embodiment of this subject matter of the present invention, the optical structure comprises an optical waveguide comprised of the plurality of microstructures. In particular, a plurality of microstructures creates a diffraction grating which may be used as an optical waveguide. It is hence advantageously possible to use the method according to the present invention to create an optical structure comprising an optical waveguide. It is hence advantageously possible to create optical structures such as lenses for augmented reality eyewear. A waveguide is e.g. implemented in an air-gap embedded within an optical structure, in particular a lens. Preferably, all surfaces facing the air gap are configured such as to act as total-internal-reflection layers for the light conducted by the waveguide. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an optical structure produced by a method according to an advantageous embodiment of the present invention immediately after the second step but before separation between the first component and the second component has occurred.

Figure 2 shows the optical structure produced by a method according to the advantageous embodiment of the present invention after separation between the first component and the second component has occurred.

DETAILED DESCRIPTION

The present invention will be described with respect to a particular embodiment and with reference to the drawing, but the invention is not limited thereto but only limited by the claims. The drawing described herein is only schematic and are non-limiting. In the drawing, the sizes may be exaggerated and non-proportional and may not be drawn to scale for illustrative purposes.

Where an indefinite or definite article is used when referring to a singular noun, e.g. “a”, “an”, “the”, this includes a plural of that noun unless something else is specifically stated.

In Fig. 1, an optical structure 1 produced by a method according to an advantageous embodiment of the present invention is depicted immediately after the second step but before separation between the first component 4 and the second component 5 has occurred. The optical structure 1 described herein is a three-dimensional structure preferably intended to at least partially transmit light. The optical structure 1 is more preferably intended for use with the visible spectrum. In particular, the optical structure 1 produced by the method further described below is an ophthalmic lens, e.g. a prescription lens, such as inserted into a pair of glasses.

The method according to the present invention is an additive manufacturing technique called three-dimensional printing. In the context of the present invention, printing of an optical structure 1 comprises building up the structure from layers of printing ink. These are obtained through a targeted placement of droplets of printing ink at least partially side by side. The droplets of printing ink are preferably ejected from nozzles of a print head towards a substrate or another suitable surface, wherein the print head is controlled by a controller according to predetermined print data representing the desired final shape of the optical structure 1. Preferably, after deposition, after finishing a layer or after finishing printing a predetermined part of the optical structure 1 , a curing step is performed, in which photo- polymerizable and/or thermo-polymerizable components of the printing ink are e.g. irradiated with UV light, IR light and/or visible light, and/or may be subjected to heat, upon which the components of the printing ink polymerize and are hence solidified.

The optical structure 1 may at least partially be printed in a multi-pass printing mode. A layer printed in a multi-pass printing mode comprises multiple sublayers which are printed in subsequent sublayer printing steps, wherein at least one sublayer printing step is followed by an at least partial curing step. This allows in a very advantageous manner for a highly flexible and customizable production of an optical structure 1. A multi-pass printing mode preferably comprises the printing head making several passes, in particular back and/or forth, wherein during each pass, a sublayer of the layer is printed. Each sublayer may be subjected to a separate curing step, only the completed layer may be subjected to a curing step or a curing step is performed in regular or irregular intervals, e.g. as soon as a predetermined amount of sublayers are printed and/or after a predetermined time after printing has passed.

Here, the optical structure 1 comprises at least a base structure 2, e.g. the lens corpus itself, and an additional layer 3 printed on the base structure 2. According to the present invention, at least partially different printing inks are used for the base structure 2 and the (additional) layer 3. A first printing ink is used for the base structure 2 and a second printing ink is used for the additional layer 3. Because only the additional layer comprises the second printing ink, it is subsequently only referred to as the layer 3. The layer 3 (printed with the second printing ink) may thus be differentiated from the layers of the base structure 2, which are printed with the first printing ink. Preferably, the first printing ink and/or the second printing ink comprises a component which is and/or becomes translucent or transparent after curing. More preferably, the first and/or second printing ink comprises at least one photo- polymerizable component and/or at least one thermo-polymerizable component. The at least one polymerizable component is most preferably a monomer and/or an initiator that polymerizes upon exposure to radiation, e.g. UV or IR light, and/or upon exposure to heat. The deposited droplets are preferably pin cured, i.e. partially cured, after deposition. Pin curing is most preferably carried out after deposition of the respective droplet or after deposition of an entire (sub)layer or only part of a layer. Preferably, the base structure 2 is printed on a substrate, a lens blank and/or a three- dimensionally printed structure itself. More preferably, the substrate, the lens blank and/or the base layer comprises glass and/or a polymer, in particular cellulose triacetate (TAC), cyclic olefin copolymer (COC), polyethylene terephthalate (PET), polycarbonate (PC) and/or Polymethyl methacrylate (PMMA), which is also known as acrylic glass or plexiglass. Those materials are well-known and tested materials for optical purposes and therefore particularly suited for the production of the optical structure 1 according to the present invention.

After printing of the base structure 2, preferably the entire, here upper, surface of the base structure 2 is covered with a layer 3, which at least partially comprises anti-reflective properties in order to avoid or at least minimize reflections occurring at the surface of the lens. Now, according to the present invention, the layer 3 is produced by three-dimensional printing as well. It may therefore advantageously be applied in the same production sequence and/or in the same device, in particular in the same printer, in which the base structure 2 is produced as well.

Typically, an anti-reflective coating makes use of the physical concept of destructive interference. Therefore, preferably, the layer 3 and in particular the part of the layer 3 formed by the second component 5 comprises a thickness after separation which corresponds to a quarter of the wavelength of the light whose reflection is to be avoided or minimized. In the case of ophthalmic lenses, this is usually the visible spectrum, i.e. in particular a range of wavelengths of ca. 400-800 nm. Hence, the thickness of the anti-reflective coating formed by the second component 5 after separation is preferably between 100-200 nm.

Since typically layers produced by means of three-dimensional printings comprise a thickness in the order of micrometres, a new concept needed to be found to be able to print such an anti-reflective coating.

The present invention proposes to solve this problem by using a second printing ink for the printing of the layer 3, wherein the second printing ink comprises a first component 4 and a second component 5. The first component 4 comprises a material with a higher refractive index than that of the (material of the) second component 5. The first component 4 and the second component 5 may e.g. be provided in a suspension or an emulsion.

Immediately after printing of the layer 3, the first component 4 and the second component 5 are preferably homogenously distributed within the printed layer, as is schematically indicated in Fig. 1. It is noted that the relative thicknesses and/or heights of the base structure, the layer 3, the first component 4 and/or the second component 5 are not necessarily drawn to scale.

The first component 4 and the second component 5 are chosen such that after deposition, a separation sets in. This may be achieved in a variety of ways. E.g., the first component 4 is heavier and will migrate to the bottom of the layer 3, whereas the second component 5 will migrate to the top of the layer 3, i.e. in a vertical direction. In the drawing, this is parallel to the vertical direction z. Preferably, this migration is predominantly due to gravitation, as the first component 4 preferably comprises a higher mass than the second component 5. Additionally or alternatively, the first component 4 and the second component 5 may comprise different surface tensions, which promote a separation due to the surface tension at the outer boundary of the layer 3. Still further additionally or alternatively, chemical behavior of the first component 4 and the second component 5 may be tuned such that a separation occurs. E.g., repulsion between a fluorophile component and a hydrophile/hydrophobe component may be used and/or repulsion between a hydrophile and a hydrophobe component. Another example of a suitable chemical behavior would be a difference in reactivity of polymerization between the first component 4 and the second component 5. Preferably, the first component 4 is chosen such that it reacts first and polymerizes, while the second component 5 remains longer in liquid form and therefore migrates to the top of the coating layer 3. At least one of the above-described mechanism or any combination thereof may be used to obtain the separation between both components.

In Fig. 2, the optical structure 1 produced by a method according to the advantageous embodiment of the present invention is depicted after separation between the first component 4 and the second component 5 has occurred. The second component 5 has migrated to the top in a direction parallel to the vertical direction z.

Now, that a (complete) separation between the first component 4 and the second component 5 has occurred, the layer 3 may be cured and comprises an interface of refractive index between the first component 4 and the second component 5.

As detailed above, the anti-reflective properties, in particular the range of wavelengths for which the layer 3 exhibits anti-reflective properties, depend mainly on the thickness of the part of the layer 3 formed by the second component 5 and the reflective index of second component 5 after curing. It is conceivable to tune the thickness of the second component 5 after separation and curing directly by adjusting the amount and/or properties of the second component 5, but for practical reasons, it is preferable to maintain a constant composition of the second printing ink and instead print a thinner layer 3. It is hence advantageously possible to tune the anti-reflective properties of the optical structure 1 by adjusting the thickness of the layer 3 and thus adjusting the thickness of the part of the layer 3 formed by the second component 5 after separation and curing.

REFERENCE SIGN LIST

1 optical structure

2 base structure 3 (printed) layer

4 first component

5 second component z vertical direction