Casting mould for spectacle lenses

Abstract

The invention relates to a method for producing a casting mould, preferably for casting an optical element, in particular for casting a spectacle lens semi-finished product, the method comprising at least one of the following steps: - providing a casting mould semi-finished product having a casting mould surface; - applying pulsed laser radiation to at least one location on the casting mould surface, which laser radiation is designed to form at least one cavity in the casting mould surface; - polishing the surfaces of the at least one formed cavity.

Description

[0001] Casting mold for spectacle lenses

[0002] The present invention relates to a casting mold, in particular for producing spectacle lenses, the production of the casting mold, in particular a functional surface of the casting mold, and the use of the casting mold.

[0003] In the manufacturing process of an ophthalmic lens, semi-finished glass products are often prefabricated and stored. These are then selected based on the desired optical properties of the lens to be manufactured and subjected to further processing steps. Functional features are developed during processing steps such as machining, polishing, additive processes, etc.

[0004] It is an object of the invention to provide a casting mold, a method for producing the casting mold and a use of the casting mold, which can already form functional features in the glass semi-finished product.

[0005] This object is achieved by the method having the features of claim 1, the casting mold having the features of claim 9, and by the use having the features of claim 10.

[0006] One aspect relates to a method for producing a casting mold, preferably for casting an optical element, in particular a spectacle lens semi-finished product, comprising at least one of the following steps:

[0007] Providing a casting mold semi-finished product with a casting mold surface which is preferably convex or concave, but can also be flat,

[0008] Applying pulsed laser radiation and / or focused ion radiation to the casting mold surface at at least one location, which is designed to form at least one cavity in the casting mold surface, polishing the surfaces of the at least one formed cavity, applying laser radiation, in one embodiment or optionally a further laser radiation, and / or focused ion radiation, in one embodiment or optionally a further focused ion radiation, which is designed to reduce a roughness of the surface of the at least one cavity,

[0009] Applying a polishing agent to the surfaces of the at least one formed cavity, which polishing agent is designed to reduce a roughness of the surface of the at least one cavity,

[0010] Hardening the mold surface.

[0011] In one embodiment, polishing comprises applying laser radiation to the surfaces of the at least one formed cavity. In a further development of an embodiment, which comprises applying pulsed laser radiation to the casting mold surface at at least one location, which is designed to form at least one cavity in the casting mold surface, applying further laser radiation to the surfaces of the at least one formed cavity, and / or applying focused ion radiation to the surfaces of the at least one formed cavity. In a further development of an embodiment, which comprises applying focused ion radiation to the casting mold surface at at least one location, which is designed to form at least one cavity in the casting mold surface, applying further focused ion radiation to the surfaces of the at least one formed cavity.wherein this (further) laser radiation and / or ion radiation is designed to reduce a roughness of the surface of the at least one cavity, in a further development the polishing is carried out wholly or partly by this application.

[0012] Additionally or alternatively, in one embodiment, the polishing comprises applying a polishing agent to the surfaces of the at least one formed cavity, which is designed to reduce the roughness of the surface of the at least one cavity. In a further development, the polishing is carried out entirely or partially by applying the polishing agent. A further aspect relates to a casting mold, in particular for producing an optical element, preferably a spectacle lens or a spectacle lens semi-finished product, wherein the casting mold was produced according to a method according to the invention.

[0013] A further aspect relates to a use of the casting mold according to the invention in a method for producing an optical element, in particular a spectacle lens or a spectacle lens semi-finished product.

[0014] Advantageously, the casting mold enables the process for producing the ophthalmic lens (or semi-finished product) to be designed with minimal technical complexity and particularly cost-effectively to solve the complex manufacturing task, namely the provision of microelements that are complementary in shape to the at least one cavity of the casting mold. If the microelements are advantageously already produced during the casting of the ophthalmic lenses or semi-finished products (blanks), for example by providing at least one casting mold surface with corresponding cavities, a large number of ophthalmic lenses or semi-finished products (blanks) can be produced.

[0015] Semi-finished ophthalmic lenses or optical lenses can be manufactured in a simple manner. Furthermore, the method for producing the mold allows for precise design of the cavities while forming a particularly smooth surface on the mold surface, which enables particularly high quality and easy removal of the cast optical element from the mold.

[0016] The term mold surface describes the surface or area of ​​the mold that comes into contact at least partially, in particular completely, with the casting material to determine the shape of the cast element. Other surfaces or areas of the mold can be provided to hold or handle the mold before, after and / or during casting. The term mold cavity refers to a hollow space into which the liquid casting material flows to form the optical element. It is understood that the cavities should preferably not have any undercuts to prevent the cast element from being removed from the mold or to prevent the element from being damaged. The mold is used to cast at least one optical element, preferably by casting a polymer. The optical element is characterized in that it is transparent to part or all of the visible spectrum of light.An optical element can be an optical lens, a spectacle lens, a contact lens, etc., or corresponding semi-finished products thereof.

[0017] The cavities preferably have a diameter of about 0.05 mm to about 3 mm, preferably from about 0.05 mm to about 0.3 mm or from about 0.3 mm to about 3 mm. The cavities could have a lateral extension in a direction along the mold surface, which is preferably in the range of about 0.3 mm to about 3 mm, preferably from about 0.5 mm to about 2.5 mm.

[0018] Preferably, the cavities can have an extension perpendicular to the lateral extension (depth) of approximately 0.1 pm to approximately 10 pm, preferably from approximately 1 pm to approximately 5 pm, more preferably from approximately 0.3 pm to approximately 2 pm, in particular less than approximately 1 pm. The cavities can have a substantially spherical shape or an aspherical shape.

[0019] The cavities can preferably have an elongated shape, wherein a lateral extent in a first direction is preferably greater by a factor of two or more than a lateral extent along a second direction which is oriented perpendicular to the first direction. The extent in the second direction or width direction can be between approximately 1 μm and approximately 50 μm. A multiplicity of cavities can be arranged in such a way as to form, for example, a unit cell, wherein the casting mold surface is covered at least in regions with one or more unit cells. Analogous to tiling, the unit cells can be arranged in a periodically repeating pattern. Tiling here refers to the gap-free and overlap-free covering of the casting mold surface by uniform partial areas, here unit cells.There can be exactly one unit cell shape or two, three, or more different unit cell shapes. For example, the unit cells can exhibit rotational symmetry with a twofold, threefold, fourfold, or sixfold axis of rotation. In this application, the diameter is defined as the maximum length of a straight line that can be drawn from edge to edge of the cavity. For spherical cavities, the diameter corresponds to twice the sphere's radius. For squares, the diameter corresponds to 1.41 times the edge length.

[0020] Preferably, the pulsed laser radiation has an energy (density) of about 10 J / m 2 up to about 100 kJ / m 2 , preferably of about 20 J / m 2 up to about 20 kJ / m 2The energy input into the material causes laser ablation, or laser vaporization, whereby material is removed from the surface of the mold by bombardment with (pulsed) laser radiation. The high-power laser radiation used in this process leads to rapid heating of the material and the formation of a plasma on its surface.

[0021] With femtosecond pulses, the material's electrons can reach high temperatures, exciting thermal oscillations of the atomic nuclei for a few picoseconds. These high-energy electrons can lead to the breaking of chemical bonds. With glass, the preferred material for the mold, such short laser pulses can also cause a Coulomb explosion, in which the electrons leave the solid, and some of the remaining positive ions are ejected from the surface by Coulomb repulsion.

[0022] With laser pulses in the nanosecond range, the laser energy leads to heating of the surface (in the sense of thermal motion of the atoms) during the laser pulse. Since heat conduction only allows for a slow energy transfer into the bulk, the radiated energy is concentrated on a very thin layer, causing the surface of the material to reach very high temperatures, which leads to the sudden evaporation of the material.

[0023] The pulsed laser radiation preferably has a wavelength of approximately 190 nm to approximately 12,000 nm. The wavelength can preferably be in the UV range, i.e. wavelengths of approximately 200 nm to approximately 400 nm, particularly preferably in the range of approximately 250 nm to approximately 380 nm, in particular approximately 193 nm, approximately 266 nm or 355 nm. The wavelength can preferably be in the IR range, i.e. wavelengths of approximately 780 nm to approximately 12,000 nm, particularly preferably in the range of approximately 800 nm to approximately 5,000 nm, in particular approximately 1064 nm, approximately 1500 nm, approximately 2,000 nm or 10.6 nm. The laser radiation is expediently generated by one or more laser sources, which can optionally be bundled together. Such a laser source can be, for example, an excimer laser, an NdYAG laser, a CO2 laser or similar.Preferably, the laser radiation generated by the at least one laser source can be converted by a frequency doubler into laser radiation with half the wavelength, for example, for the above-mentioned preferred wavelengths, to wavelengths of approximately 97 nm, 133 nm, 178 nm, 532 nm, 750 nm, 1000 nm, or 5300 nm. Preferably, the frequency doubler can be optionally connected so that two different wavelengths of laser radiation can be provided.

[0024] Alternatively or additionally (instead of pulsed laser radiation), focused ion radiation can be used. Depending on the strength of the ion current, the focus is on material removal or the scanning of the surface of the object to be examined by the ion beam as an imaging process. In the latter case, one also speaks of a focused ion beam microscope. The focused ion radiation is preferably generated by ions, preferably gallium, neon or helium ions, whereby the ions are accelerated with voltages of approximately 0.5 kV to approximately 50 kV, preferably from approximately 2 kV to approximately 50 kV. The beam current can be regulated by apertures of various sizes, preferably to a value of approximately 1 pA to approximately 1.3 pA, particularly preferably from approximately 1.5 pA to approximately 25 nA. High currents are used for coarse material removal to form the cavities, while small currents are used for polishing and imaging due to the better resolution.Particularly preferably, the possibility of imaging the machined surface by operating a corresponding device as a focused ion beam microscope can be used to carry out immediate quality control and, if necessary, post-processing.

[0025] Advantageously, glass, as the preferred material for the mold, is partially opaque to these wavelengths and absorbs this radiation well, allowing for good energy transfer to the material to be removed. However, it is understood that wavelengths in the visible light range—i.e., from approximately 380 nm or 400 nm to approximately 780 nm or 800 nm—can also be used, such as 532 nm. Coloring or doping the glass of the mold can preferably increase the energy transfer to the material or the absorption.

[0026] More preferably, the laser radiation used to reduce the roughness of the cavities' surfaces can be pulsed or non-pulsed laser radiation. In particular, a CO2 laser can be used for laser polishing, especially with a wavelength of 10.6 pm. It is understood that a different wavelength can also be used for laser polishing. Particularly preferably, the wavelength used for laser polishing is twice as long as the laser radiation used to form the cavities, which can be achieved in particular by deactivating the frequency doubler.

[0027] Polishing glass with CO2 laser radiation is based on the absorption of laser radiation in a thin surface layer of the mold material, preferably so that near-surface temperatures just below the evaporation temperature of the material are reached. This reduces the viscosity of the material and smooths the roughness due to surface tension. In other words, remelting takes place instead of material removal. By selecting the appropriate process parameters, such as temperature, speed, and intensity distribution, the polishing can be adapted to the surface shape of the mold. Advantageously, a high process speed, preferably of up to 1 cm 2 / s for quartz glass.

[0028] The pulsed laser radiation preferably has a pulse length of approximately 10 fs to approximately 10 ps, ​​more preferably approximately 20 fs to approximately 2 ns. The method can be used with lasers of various wavelengths and various pulse durations, particularly high-power lasers, such as continuous wave, modulated continuous wave, and pulsed lasers, Q-switched, and other pulsed lasers. Laser pulse durations, such as, but not limited to, lasers with pulses that can be measured in femtoseconds, picoseconds, nanoseconds, or microseconds, modulated continuous wave, and continuous wave lasers, can be used. The individual pulses can act on the material to be ablated at a repetition rate of approximately 100 Hz to approximately 10 kHz, preferably approximately 250 Hz to approximately 2500 Hz.

[0029] Alternatively or additionally, the roughness of the cavities can be reduced using a polishing agent. Preferably, the cavities can be polished using a chemical polishing agent, in particular an acidic or fluorine-containing polishing agent. Preferably, polishing can be performed by immersing the mold surface in and / or spraying it with the polishing agent, with additional mechanical processing of the surface to be polished being possible. The mechanical processing can be performed using cylindrical or flat polishing discs or brushes. More preferably, immersing in and / or spraying with the polishing agent can alternate with immersing in or spraying with water.

[0030] The polishing agent may contain mineral and / or organic acids or mixtures thereof. In particular, the polishing agent may contain hydrofluoric acid or

[0031] Hydrogen fluoride or salts thereof, since these chemical fluorine compounds can attack the surface of silicates. The polishing agent can preferably contain sulfuric acid, phosphoric acid, hydrochloric acid, or a mixture thereof as preferred inorganic acids. Further preferably, the polishing agent can contain formic acid, acetic acid, aqueous solutions of oxalic acid and propionic acid, or mixtures thereof, as preferred organic acids.

[0032] Advantageously, polishing the mold surface with an acid mixture as the preferred polishing agent enables a very smooth result. The effect can be adjusted by lengthening or shortening the immersion or spraying time, as well as by adjusting the acid concentration. The result can also be influenced by adjusting the ratio of hydrofluoric acid to the other acids. Spraying can be carried out using compressed air. The mold surface can also be wetted using polishing wheels or brushes wetted or soaked with the polishing agent. Polishing using the polishing agent can take place at temperatures from approximately 15°C to approximately 50°C. In particular, the appropriate polishing temperature can be achieved by tempering the polishing agent. The pH of the polishing agent can preferably be set between approximately 5 and approximately 6.5, particularly preferably between approximately 5.5 and 6.

[0033] The surfaces of the at least one formed cavity can be polished by means of the laser radiation and / or the polishing agent.

[0034] Preferably, the mold surface can be washed with a washing solution prior to polishing to perform a pre-cleaning step, which advantageously removes particles or deposits that could otherwise adversely affect the polishing process. The washing solution can be water or water-based, for example, and preferably contains a surfactant. Washing can be performed in an immersion bath or by spraying.

[0035] The semi-finished casting mold is preferably made of glass, in particular of a chemically hardenable glass. Advantageously, glass is stable and rigid, durable, inexpensive, and essentially chemically inert. The material of the casting mold or semi-finished casting mold is glass, particularly preferably float glass, quartz glass, or borosilicate glass. In principle, however, it can also be other similar glasses or glass materials, such as glass ceramics or other corresponding brittle, laser-transparent materials.

[0036] Preferably, the method for producing the casting mold comprises the step of: chemically hardening the casting mold surface.

[0037] The chemical hardening of glass is based on a process of ion exchange between the alkaline ions (mainly sodium, in some cases lithium) of the surface layers of the glass and the potassium ions (or sodium) of salt solutions with which the surfaces are wetted or in which they are immersed. Hardening preferably takes place at temperatures between approximately 400°C and approximately 500°C. Preferably, a plurality of cavities arranged according to a predeterminable structure are formed on the mold surface. The structure can, for example, be designed to provide a microstructure on a surface, in particular the front surface, of a spectacle lens or a spectacle lens body. This microstructure can serve, in particular, as a diffractive grating for visible light, preferably for color fringing correction or myopia control in the spectacle lens.

[0038] The optical element cast in the mold can preferably be formed from a polymer, in particular a thermoset or thermoplastic, preferably from polyethylene glycol bisallyl carbonate; copolymers containing polyethylene glycol dimethacrylate; polycarbonate; polythiourethane; or polyapisulfide.

[0039] The invention will be described below using preferred embodiments with reference to the accompanying drawings.

[0040] Fig. 1 schematic representations of casting mold semi-finished product and laser irradiation using pulsed laser radiation;

[0041] Fig. 2 Casting mold semi-finished product with cavity;

[0042] Fig. 3 Arrangement of a plurality of cavities to form a microstructure;

[0043] Fig. 4 schematic representations of casting mold semi-finished product and laser irradiation for polishing;

[0044] Fig. 5 schematic representations of casting mold semi-finished product and a device for polishing with acid-containing polishing agents by means of an immersion bath;

[0045] Fig. 6 schematic representations of casting mold semi-finished product and a device for polishing with acidic polishing agents by spraying;

[0046] Fig. 7 Arrangement of a plurality of cavities to form a spatially repeating microstructure.

[0047] Figure 1 shows a schematic representation of a semi-finished casting mold 2 and laser irradiation using pulsed laser radiation 4. In the method according to the invention for producing a casting mold, a semi-finished casting mold 2 can be provided with a casting mold surface 4. The casting mold surface 4 can be convex, concave, or flat. At least one location, the casting mold surface 4 can be exposed to pulsed, first laser radiation 6, which is designed to form at least one cavity 8 in the casting mold surface 4.

[0048] Alternatively, the laser radiation 4 shown in Figure 1 can also be replaced by focused ion radiation to form the cavity 8. For this purpose, a beam current of preferably more than about 1 nA up to about 25 nA or in particular up to 1.3 pA can be used to achieve a corresponding material removal.

[0049] Figure 2 shows a casting mold semi-finished product 4 with a cavity 8 with a diameter D. Depending on the physiological requirements of the spectacle lens, the cavity 8 can be incorporated into the casting mold semi-finished product 2 as a spherical, toric or any desired free-form surface element.

[0050] Figure 3 shows an arrangement of cavities 8 corresponding to a microstructure 12. The arrangement of the cavities 8 can be designed as desired depending on the physiological requirements, whether round, rectangular, in a parallelogram lattice, or in any other arrangement.

[0051] Figure 4 shows a planar laser beam 10 that can be moved in controlled paths over the semi-finished casting mold 2 or irradiates the entire surface of the semi-finished casting mold 2. The application of the further, second laser radiation 10 to the surfaces of the at least one formed cavity 8 is designed to reduce the roughness of the surface of the at least one cavity 8. The laser radiation 10 can differ in wavelength, pulse duration, and / or energy density from the laser radiation 6 used to form the cavities.

[0052] Alternatively, the laser radiation 10 shown in Figure 4 can also be replaced by focused ion radiation to polish the cavity 8. For this purpose, a beam current of preferably more than approximately 1 nA up to approximately 25 nA can be used in order to achieve a correspondingly low material removal suitable for polishing. Figure 5 shows an exemplary arrangement 100 for polishing the casting mold surface 4 using an acidic polishing agent 102 with an immersion bath 104 as a preferred embodiment. With an aqueous, hydrogen fluoride-containing solution, smoothing of the cavities 8 can advantageously be achieved at sufficient speed even at room temperature of approximately 20°C. Due to the low temperature, the casting mold semi-finished product is not thermally stressed, thereby avoiding thermal distortion.The polishing agent 102 can be continuously or intermittently mixed within the immersion bath, for example by stirring, whereby a uniform acid concentration can advantageously be maintained on the surface of the mold surface.

[0053] The use of so-called buffer solutions as polishing agents, with a pH value in the range of approximately 5.0 to approximately 6.5, has proven particularly beneficial. Additions to the polishing agent of substances that form compounds with the glass components, such as sodium chromate, sodium sulfate, sodium ferrocyanide, etc., also have a beneficial effect.

[0054] The polishing agent is preferably an acidic solution containing fluoride ions capable of attacking the glass in the region of the cavities 8 and forming a silicofluoride precipitate. The treated surface is preferably continuously mechanically treated to remove the precipitate and expose it to further attack by the polishing agent. Advantageously, spraying the mold surface 4 with the polishing agent can both easily meter the polishing agent and flush away the precipitate, so that further mechanical treatment (e.g., by brushing) is no longer necessary, but can still be performed optionally.

[0055] For example, the polishing agent 102 may have a sulfuric acid concentration of about 70 to about 78 weight percent and a hydrofluoric acid concentration of about 4 to about 6 weight percent and a temperature between 20°C and 50°C.

[0056] After polishing, the mold can be placed in another immersion bath to rinse off the polishing agent. This immersion bath can preferably contain a buffer solution with a neutral pH or a slightly alkaline pH of up to approximately 9, which neutralizes the polishing agent. The mold surface can also be sprayed with water or a buffer solution to remove the polishing agent from the surface.

[0057] Figure 6 shows a further exemplary arrangement 100 for polishing the casting mold surface 4 using an acid-containing polishing agent 102, wherein the polishing agent 102 is sprayed onto the casting mold surface 4 using a nozzle 106. The polishing agent 102 can have the same properties as described with reference to Figure 5. The polishing agent 102 can be applied to the casting mold surface 4 through the nozzle 106 at a predetermined pressure or a predetermined speed. By using fresh or reprocessed polishing agent, a uniform acid concentration can advantageously be sprayed onto the surface of the casting mold surface.

[0058] In addition to spraying the casting mold surface 4 with the polishing agent, mechanical polishing can also be performed, preferably by a polishing disk 108 rotating about a rotational axis R. More preferably, spraying with the polishing agent can alternate with spraying with water. In particular, polished particles can be washed away from the casting mold surface by a flow of polishing agent or water generated by the spraying.

[0059] Figure 7 shows an arrangement of cavities 8 corresponding to a microstructure 12. The arrangement of the cavities 8 can be designed as desired, depending on the physiological requirements. Whether round, rectangular, in a parallelogram lattice, or in any other arrangement.

[0060] Reference symbol

[0061] 2 semi-finished casting molds

[0062] 4 mold surface

[0063] 6 first laser radiation

[0064] 8 Cavity

[0065] 10 second laser radiation

[0066] 12 Microstructure

[0067] 100 arrangement

[0068] 102 polishes

[0069] 104 Immersion bath

[0070] 106 nozzle

[0071] 108 polishing disc

[0072] R rotation axis

Claims

Patent claims Method for producing a casting mold, preferably for casting an optical element, in particular a spectacle lens semi-finished product, comprising the following steps: Providing a casting mold semi-finished product (2) with a casting mold surface (4), which is preferably convex or concave, Applying pulsed laser radiation (6) and / or focused ion radiation to the casting mold surface (4) at least at one point, which is designed to form at least one cavity (8) in the casting mold surface (4), and Polishing the surfaces of the at least one formed cavity. Method according to claim 1, wherein the cavities (8) have a diameter (D) of approximately 0.3 mm to approximately 3 mm and / or wherein the cavities (8) have a depth (T) of approximately 0.1 μm to approximately 5 μm. Method according to claim 1 or 2, wherein the polishing comprises exposing the surfaces of the at least one formed cavity (8) to laser radiation (10) and / or focused ion radiation, which is designed to reduce a roughness of the surface of the at least one cavity (8). Method according to one of the preceding claims, wherein the pulsed laser radiation (6) has an energy (density) of approximately 10 J / m 2 up to about 100 kJ / m 2 , preferably of about 20 J / m 2 up to about 20 kJ / m 2 Method according to one of the preceding claims, wherein the pulsed laser radiation (6) has a wavelength of approximately 190 nm to approximately 12,000 nm. Method according to one of the preceding claims, wherein the pulsed laser radiation (6) has a pulse length of approximately 10 fs to approximately 10 ps. Method according to one of the preceding claims, wherein the ions of the focused ion radiation are accelerated with voltages of approximately 0.5 kV to approximately 50 kV and / or the beam current of the focused ion radiation has a magnitude of approximately 1 pA to approximately 1.3 pA. Method according to one of the preceding claims, wherein the polishing comprises applying a polishing agent to the surfaces of the at least one formed cavity, which polishing agent is designed to reduce a roughness of the surface of the at least one cavity. Method according to claim 8, wherein the polishing agent contains a fluorine compound, preferably hydrogen fluoride. Method according to claim 8 or 9, wherein the polishing agent contains an inorganic and / or an organic acid. Method according to one of the preceding claims, wherein the casting mold semi-finished product (2) is made of glass.Method according to one of the preceding claims, wherein the method for producing the casting mold comprises the step:. Hardening, preferably chemical hardening, of the casting mold surface (4). Method according to one of the preceding claims, wherein a plurality of cavities (8) arranged according to a predeterminable structure (12) are formed on the casting mold surface (4). Casting mold, in particular for producing an optical element, wherein the casting mold was produced by a method according to one of claims 1 to 13. Use of the casting mold according to claim 14 in a method for producing an optical element, in particular a spectacle lens or a spectacle lens semi-finished product.

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