WO2024192695A1

WO2024192695A1 - Method for applying a marking structure to a casting mold for manufacturing a spectacle lens blank

Info

Publication number: WO2024192695A1
Application number: PCT/CN2023/082940
Authority: WO
Inventors: Jun Zhou
Original assignee: Carl Zeiss Vision International Gmbh; Carl Zeiss Vision Technical Services (Guangzhou) Ltd.
Priority date: 2023-03-22
Filing date: 2023-03-22
Publication date: 2024-09-26
Also published as: WO2024194412A1

Abstract

Provided is a method (300) for applying a marking structure (22) to a casting mold (10) for manufacturing a spectacle lens blank (12). The method (300) comprises generating (302) the marking structure (22) at an inner surface of at least one part of the casting mold (10) by selectively applying a laser radiation to an intended position of the marking structure (22). The method (300) is characterized in that the laser radiation is selectively applied such as to generate the marking structure (22) as one or more protrusions (24, 32) of the inner surface of the at least one part of the casting mold (10) by laser-induced swelling of the casting mold (10) at the intended position of the marking structure (22).

Description

METHOD FOR APPLYING A MARKING STRUCTURE TO A CASTING MOLD FOR MANUFACTURING A SPECTACLE LENS BLANK

Provided is a method for applying a marking structure to a casting mold for manufacturing a spectacle lens blank, a method for manufacturing a spectacle lens blank and a use of laser-induced swelling for applying a marking structure to an inner surface of a casting mold adapted for manufacturing a spectacle lens blank. The embodiments are, thus, related to manufacturing techniques for spectacle lens blanks.

Spectacle lenses are often made by machining spectacle lens blanks, which are also known as “pucks” . Such spectacle lens blanks are typically manufactured by casting the spectacle lens blanks in respective casting molds. The casting process may comprise providing a suitable casting mold providing a void for casting, filling the void of the casting mold with a casting material, curing the casting material inside the casting mold and mechanically opening and removing the casting mold from the casted spectacle lens blank.

In some cases it may be desirable to provide symbols on the spectacle lens, such as one or more optical marks, which may serve for identifying and/or specifying the spectacle lens blank. The optical marks are often applied to the spectacle lens blank by providing a respective marking structure to the inside of the casting mold prior to casting the spectacle lens blank using said casting mold. For instance, the one or more optical marks applied to the spectacle lens blank may comprise or consist of a data matrix code for identifying the product and/or for creating a link between the casted spectacle lens blank and the used casting mold.

A commonly used material for casting spectacle lens blanks is CR39, which is a common term for a material with the chemical expression allyl diglycol carbonate (ADC) in its monomeric state and Poly (allyl diglycol carbonate) (PADC) in its polymeric state. When using CR39 as casting material, a process for manufacturing a spectacle lens blank or a semi-finished spectacle lens product by casting would comprise the steps of (i) providing a casting mold without marking structure, (ii) applying a marking structure to the casting mold, and (iii) casting the spectacle lens blank using the casting mold having the marking structure applied thereto.

The marking structures applied to the casting mold are to be made on the casting mold in such a manner that the marking structure generates an optical mark transferred to the spectacle lens blank during the casting process. The optical mark is typically intended to be visible to respective machines, such as code readers, and to the human eye. Moreover, applying the marking structure to the casting mold shall avoid any damages or impairments to the casting mold and the casted spectacle lens blanks and last for a lifetime of the casting mold, which is typically in the range of up to 1.300 cycles.

Conventionally, two different techniques for applying a marking structure to the casting mold are available, which are (i) acid etching and (ii) laser engraving resulting in material removal of the casting mold.

Acid etching for applying the marking structure to the casting mold uses an acid to etch a pre-coated inner surface of the casting mold to the effect that the exposed area corresponding to the intended marking structure is etched. However, acid etching comes along with various disadvantages, which include (i) the process being complicated and requiring the operator to carry out a large number of different steps, (ii) the process requiring resin and acid, which may both be undesirable from an ecological point of view, (iii) the process requiring the operator to wear protective gear against the acid, and (iv) the resulting marking structure is prone to mold sticking, which may result in the casting form and/or the cast spectacle lens blank partly disintegrating when removing the casting mold from the spectacle lens blank.

On the other hand, using laser engraving resulting in material removal from the casting mold is based on using laser irradiation for sublimating a part of the material. The sublimated material leaves behind one or more recesses at the inner surface of the casting mold forming the marking structure. Laser engraving resulting in material removal comes along with various disadvantages, which include (i) the formation of micro cracks in the casting mold, typically at the edge of the engraving area, which tend to expand when removing the casting mold from the cast spectacle lens blank often resulting in the casting mold breaking in an early stage of its intended life time, (ii) monomeric casting material remaining on the casting mold after removing the casting mold from the spectacle lens blank, and (iii) the resulting marking structure being prone to mold sticking, which may result in the casting form and/or the cast spectacle lens blank partly disintegrating when removing the casting mold from the spectacle lens blank.

US 2002/0003605 A1 describes a method for making inversion marks for a contact lens. The method includes projecting one or more laser beam pulses through a laser beam mask to etch an array of recessed spots in a surface of a contact lens mold insert and then scanning the insert and mask synchronously with respect to the laser beam pulses thereby forming the inversion mark on the mold insert. The mold insert is used to make casting cups for cast-molding contact lenses, through which the inversion marks are reproduced on the contact lenses. The described method uses a metal mold.

Moreover, in prior art methods for preparing textured molds are known. For instance, CN114573217A describes a method for preparing a texture mold with fine lines and complex and diverse textures without the need for acid etching and UV transfer printing. The described technique uses multiple rounds of laser processing on the mold according to a preset program to shape the texture on the mold. The laser power is 5 W to 8 W, the scanning speed is 400 mm/s to 600 mm/s and the number of scans is 25 to 35 times. The minimum distance between the laser beams of the laser treatment in different rounds is 1 mm to 7 mm. The laser may be an ultraviolet nanosecond laser or an infrared picosecond laser. The mold is made of ceramics or graphite.

Furthermore, in prior art the physical process of laser-induced swelling of transparent glasses is known and described for instance in the following scientific publications.

S. Logunov et al.: “Laser-induced swelling of transparent glasses” , Applied Surface Science 257 (2011) 8883-8886.

S. Logunov et al. describe a process of forming bumps on the surface of transparent glasses such as display glasses with moderate thermal expansion ～3.2 × 10-6 K-1 and high coefficient of thermal expansion (CTE) glasses, e.g. soda-lime glasses with CTE～9×10-6 K-1 using high-power ultra-violet (UV) lasers at a wavelength where glass is transparent. The effect is characterized with optical dynamic measurements. The process relies on increased glass absorption from color-center generation and leads to glass swelling with the formation of bumps. The bump height may constitute more than 10%of the thickness of the glass sample. The required exposure time is relatively short～1 s, and depends on the glass properties, laser power, its repetition rate, and focusing conditions. A brief review of the potential applications for these bumps is provided.

A method for laser texturing of doped borosilicate glasses is described in the following scientific publication:

A. Streltsov et al.: “Laser texturing of doped borosilicate glasses” Proc. SPIE 7584, Laser Applications in Microelectronic and Optoelectronic Manufacturing XV, 75840S (17 February 2010) .

A. Streltsov et al. describe a novel process of laser-assisted fabrication of surface structures on doped oxide glasses with heights reaching 10-13%of the glass thickness. This effect manifests itself as a swelling of the irradiated portion of the glass, and occurs in a wide range of glass compositions. The extent of such swelling depends on the glass base composition. Doping with Fe, Ti, Co, Ce, and other transition metals allows for adjusting the absorption of the glass and maximizing the feature size. In the case of bumps grown on borosilicate glasses, reversible glass swelling is observed, and the bump height increases or decreases depending on whether the consecutive laser pulse has higher or lower energy compared to the previous one. Density, refractive index, fictive temperature, and phase separation dynamics are explored to understand the hypothetical mechanism, which includes laser heating of glass, glass melting, and directional flow.

It is, thus, desirable to provide a method for applying a marking structure to a casting form for manufacturing spectacle lens blanks and a method for manufacturing a spectacle lens blank having an optical mark without the disadvantages described above of conventional techniques based on acid etching or laser engraving resulting in material removal. Moreover, when regarding CN114573217A as closest prior art, though being related to a different technical field, the objective technical may be more specifically regarded as applying a marking structure to a casting mold enhancing the expected lifetime of the casting mold.

This problem is solved by a method for applying a marking structure to a casting mold for manufacturing a spectacle lens blank and a use of laser-induced swelling for applying a marking structure to an inner surface of a casting mold adapted for manufacturing a spectacle lens blank having the features of the respective independent claim. Optional features and embodiments are provided in the dependent claims and the description.

In one aspect, a method for applying a marking structure to a casting mold for manufacturing a spectacle lens blank is provided. The method comprises generating the marking structure at an inner surface of at least one part of the casting mold by selectively applying a laser radiation to an intended position of the marking structure. The method is characterized in that the laser radiation is selectively applied such as to generate the marking structure as one or more protrusions of the inner surface of the at least one part of the casting mold by laser-induced swelling of the casting mold at the intended position of the marking structure.

In another aspect a use of laser-induced swelling for applying a marking structure to an inner surface of a casting mold adapted for manufacturing a spectacle lens blank is provided.

A spectacle lens blank may relate to a piece of optical material manufactured in a casting process. The spectacle lens blank may optionally have one optically finished surface for the making of a lens, as specified in section 3.8.1 of ISO 13666: 2019 (E) . The spectacle lens blank may be a blank, a semi-finished blank, a lens blank, a semi-finished lens and/or a semi-finished lens blank according to section 3.8.1 of ISO 13666: 2019 (E) . Moreover, the spectacle lens blank may be rough blank corresponding to a piece of optical material according to section 3.3.1 of ISO 13666: 2019 (E) with neither side having finished surfaces. The optical material may be a transparent material capable of being manufactured into optical components, as specified in section 3.3.1 of ISO 13666: 2019 (E) .

A spectacle lens may satisfy the specifications of section 3.5.2 of ISO 13666: 2019 (E) ) . In particular, a spectacle lens may be an ophthalmic lens according to section 3.5.1 of ISO 13666: 2019 (E) worn in front of, but not in contact with, the eyeball.

The back surface of the spectacle lens blank may relate to the surface of the spectacle lens blank from which a back surface of a resulting spectacle lens is made during further manufacturing steps based on the spectacle lens blank. The back surface of the resulting spectacle lens may be the surface of the spectacle lens intended to be fitted nearer to the eye according to section 3.2.14 of ISO 13666 (E) .

Manufacturing the spectacle lens may consist of or comprise casting the spectacle lens using a suitable casting mold. The casting mold may be a casting form providing a void with suitable dimensions to create the predefined spectacle lens blank when filled with casting material and when curing (at least partly) the casting material within the casting mold. The inner surface may be referred to as a casting surface.

A marking structure may be a structure applied to the casting mold suitable to transfer a predefined structure from the casting mold to a spectacle lens blank casted using said casting mold. The marking structure may be applied to an inner surface of the casting mold being in direct contact with the casting material when casting the spectacle lens blank. The marking structure may correspond to the predefined optical mark to be applied to the spectacle lens blank during the casting process or to a negative structure of the predefined optical mark. “Negative structure” in the context of the disclosure means that the optical mark may represents a complementary or inverted structure of the marking structure.

“Selectively applying a laser radiation” means that the laser radiation is applied to pre-selected sections of the casting mold in order to create a pre-selected marking structure at the intended position of the marking structure on the casting mold. Hence, the laser radiation is not necessary applied in a homogeneous manner to the entire casting form or an entire surface of the casting form but may be restricted to these sections of the casting mold that are to be altered to generate the marking structure in the predefined manner.

A protrusion of the inner surface of the at least one part of the casting mold may be an alteration of the inner surface of the at least one part of the casting mold protruding from the non-altered parts of the inner surface of the at least one part of the casting mold. The protrusion may extend into a void at least partially defined by said inner surface of the at least one part of the casting mold when the casting mold is assembled.

“Generating the marking structure as one or more protrusions by laser-induced swelling” means, that the alteration of the inner surface of the at least one part of the casting mold generating the marking structure is at least partially or entirely a result of laser-induced swelling of the sections of the inner surface of the at least one part of the casting mold altered by the laser radiation. The laser-induced swelling is a physical process, as described above in an exemplary manner in the above-identified scientific publications by S. Logunov et al. and A. Streltsov et al.. The alteration of the material of the casting mold by laser swelling results in the affected material of the casting mold to extend in volume and, hence, create a protrusion. However, in contrast to techniques commonly used in prior art, as described in CN114573217A the laser-induced swelling does not result in a significant evaporation of material of the casting mold and, hence, does not come with a significant loss of material of the casting mold. Moreover, the laser induced swelling may alter the affected sections of the inner surface of the casting mold by providing material extensions resulting in protrusions, but may refrain from creating any recesses, such as indentations, at the inner surface of the casting mold.

An inner surface of the casting mold is a surface of the casting mold being in contact with the casting material during the casting process. Accordingly, the shape of an inner surface of the casting mold determines the shape of an outer surface of the cast spectacle lens blank. The inner surface of the casting mold may be referred to as a casting surface.

The casting mold may be usable multiple times, i.e., for sequentially casting multplie spectacle lens blanks using the same casting mold. The casting mold may be adapted to be usable at least 100 times, optionally at least several hundreds of times and optinally up to or at least 1300 times before the casting mold has to be replaced.

The method, in accordance with the disclosure, provides the advantage that a marking structure can be applied to the inner surface of the casting mold essentially without removing material from the inner surface of the casting mold. This allows generating a marking structure, showing solely protrusions and essentially no recesses. Due to this effect, no casting material penetrates the inner surface of the casting mold, as would be the case if the inner surface of the casting mold had one or more recesses. Due to the inner surface of the casting mold having only protrusions, a resulting optical mark in a spectacle lens blank cast with said casting mold solely will have only recesses, such as indentations, which form the optical mark. Accordingly, when removing the casting mold from a cast spectacle lens blank after the casting process no penetrated material has to be extracted from recesses at the inner surface of the casting mold, as no such recesses are present. This may result in the marking structure at the inner surface of the casting mold and, in the same manner, the optical mark at the cast spectacle lens blank having a smoother surface than when generated with conventional methods using acid etching or laser engraving based on material removal. In addition, the smooth marking structure provides the benefit of reducing the risk of monomer casting material remaining at the marking structure of the casting mold after the casting process, which may enhance the lifetime of the casting mold.

Moreover, the method according to the disclosure provides the advantage that the boundaries of the laser processing area, i.e. the boundaries of the generated marking structure and the resulting optical mark are smooth, which reduces or prevents the formation of micro-cracks as often observed with conventional methods of applying the marking structure. Furthermore, this provides the beneficial effect of reducing or avoiding damages to the casting mold and/or the cast spectacle lens blank (s) .

The method according to the disclosure may provide the advantage that it facilitates the casting of spectacle lens blanks using the material CR39. Conventional casting processes involving an application of a marking structure with conventional methods on the inner surface of the casting mold, such as acid etching or laser engraving based on material removal, often result in a lifetime of less than ten casting processes when using CR39 as casting material, and then the casting mold has to be replaced due to damages to the casting mold or the cast spectacle lens blank. This disadvantage may originate in the physical properties of CR39, which exhibits a strong tendency to stick to the casting mold, in particular to a casting mold made of glass. However, the advantages described above of the method according to the disclosure remedy the origins of such damages and, thus, allow a longer lifetime of the casting molds even when used with CR39 as casting material exceeding 14 casting processes. Therefore, the disclosure provides the advantage that the sustainability of the casting process can be increased and the waste and rejects as well as the manufacturing costs per cast spectacle lens blank can be reduced.

Furthermore, the disclosure provides the advantage that no application of acid, or otherwise hazardous or ecologically unfavorable materials have to be used. Therefore, the manufacturing effort can be reduced and the environmental friendliness can be improved.

At least the inner surface of the casting mold comprises or is made of an inorganic glass. Alternatively, at least the inner surface of the casting mold comprises or is made of a silicate glass. This may allow the inner surface of the casting mold to have particularly suitable material properties for applying the marking structure based on laser-induced swelling of the material of the inner surface of the casting mold. Moreover, this provides the advantage that the cast mold is made of a material having suitable properties for casting spectacle lens blanks when using CR39 as casting material. However, also other casting materials may be used, such as high index materials. The advantages of the disclosure when used with CR39 as casting material may entirely or partially apply when using a high index material as casting material. A high index material may for instance comprise or consist of MR7 and/or MR8 and/or MR10.

The laser radiation may comprise ultraviolet laser (UV) radiation and/or infrared (IR) laser radiation. In particular, the laser radiation may be pulsed UV laser radiation, for instance nanosecond or picosecond laser pulses. This provides the advantage that many glasses commonly used for manufacturing casting molds for manufacturing spectacle lens blanks having a suitable transmittance and absorbance in the UV spectral range and in particular at 355 nm. For instance, fused silica offers a transmittance of about 90%at a wavelength of 355 nm and consequently a low absorption, which appears favorable for laser-induced swelling to achieve a significant bump height (compare the above-cited publication of S Logunov et al. reporting an ideal absorption between 15%and 70%for achieving a maximum bump height) . The infrared laser radiation may be provided by a CO₂ laser source. Optionally, the CO₂ laser source may comprise a CO₂ laser having a central emission wavelength of 10, 6μm and optionally a maximum power of 20 W.

Generating the marking structure as one or more protrusions of the inner surface of the at least one part of the casting mold by laser-induced swelling may include selectively melting at least a part of the casting mold at the intended position of the marking structure. This allows generating the one or more protrusions without a need of forming recesses and indentations. Therefore, selectively melting at least a part of the casting mold at the intended position of the marking structure allows generating the marking structure having a smooth surface. In the context of the disclosure, “selectively melting” means that the material of the inner surface of the casting mold is selectively molten at these positions and sections only, which are to be altered for generating the protrusions forming the marking structure, while the material of the casting mold is not molten in other positions and sections which are not to be altered for generating the protrusions forming the marking structure.

The one or more protrusions may extend 500μm or less from the inner surface of the at least one part of the casting mold into a void provided by the casting mold. The one or more protrusions may optionally extend 200μm or less, or 100μm or less. This may allow a moderate penetration depth of the marking protrusion into the bulk casting material forming the cast spectacle lens blank and, hence, may facilitate the removal of the casting mold from the cured spectacle lens blank without damaging the spectacle lens blank and/or the casting mold.

The created marking structure may solely consists of one or more protrusions. In particular, the marking structure may optionally not comprise any recesses, such as indentations. This may prevent casting material penetrating the inner surface of the casting mold into the recesses. Thus, this feature may reduce a risk of damaging the spectacle lens blank and/or the casting mold when removing the casting mold from the cast spectacle lens blank.

The one or more protrusions may comprise at least one selected from the group comprising one or more spot-like bumps and one or more linear beadings. The spot-like bumps may be protrusions having a circular or polygonal cross-sectional shape (in a plane parallel to the inner surface of the casting mold) . The linear beadings may be protrusions having a significantly larger extension in a first direction along the inner surface of the casting mold than in a second direction along the inner surface of the casting mold perpendicular to the first direction. Alinear beading may have a shape representing a straight line. Alternatively, alinear beading may have a shape representing free-form line deviating from a straight line, i.e., the linear beading may have bends and/or curves.

In another aspect, a method for manufacturing a spectacle lens blank is provided. The method comprises providing a casting mold having an inner surface, applying a marking structure to the inner surface of the casting mold using a method according to the disclosure as described above, casting the spectacle lens blank using the casting mold, wherein the marking structure applied to the inner surface of the casting mold creates an optical mark at the casted spectacle lens blank, and curing the cast spectacle lens blank in the casting mold and removing the spectacle lens blank from the casting mold.

The disclosure presented with reference to the method for applying a marking structure to a casting mold shall be considered as disclosed in the same way for the method of manufacturing a spectacle lens and vice versa.

The optical mark created at the casted spectacle lens blank may correspond to a negative structure of the marking structure applied to the inner surface of the casting mold. Accordingly, the optical mark may relate to a direct imprint created by the marking structure when casting the spectacle lens blank using the casting mold.

The marking structure may be applied to the inner surface of the casting mold so that the optical mark is created at a back surface of the cast spectacle lens blank. This provides the advantage that the optical mark may be used to identify the spectacle lens blank during a manufacturing process for manufacturing a spectacle lens from the cast spectacle lens blank. However, as typically the back surface of the spectacle lens blank is processed further in a grinding and/or polishing process to provide the final spectacle lens, the optical mark at the back surface is removed during the manufacturing process and does not impede the back surface of the finished spectacle lens. Moreover, this provides the advantages that the removal of the optical mark from the back surface occurs as a side effect of the regular grinding and/or polishing process and, hence, does not require an additional and separate step for the removal of the optical mark.

Casting the spectacle lens blank comprises filling a void provided by the casting mold at least partly with CR39. This provides the advantage that spectacle lens blanks may be cast from the material CR39, which may offer advantageous properties for the cast spectacle lens cast, while avoiding or reducing a risk of damaging the cast spectacle lens blank and/or the casting mold when removing the casting mold form the spectacle lens blank, as is frequently observed when applying the marking structure using a conventional technique.

The method may further comprise a step of mechanically removing the casting mold from the cast spectacle lens blank. This may ensure a reusability of the casting mold for casting further spectacle lens blanks with the very same casting mold. This may improve the ecological sustainability of the process for manufacturing spectacle lenses and reduce the manufacturing costs.

The optical mark may include at least one selected from the group comprising one or more characters readable by a human eye, a machine-readable code, and a data matrix code. This may allow or facilitate identifying the spectacle lens blank based on the optical mark during the casting process. Moreover, this may allow the optical mark to be readable by a human operator as well as by a machine, such as a machine code reader. Therefore, as soon as the spectacle lens blank is removed from the casting mold, the spectacle lens may be identified based on the optical mark and a seamless traceability of the spectacle lens blank may be achieved.

Optionally a commercially available UV laser marking instrument may be used for providing the laser radiation, such as the system UV MD-U1000 provided by the manufacturer KEYENCE. Optionally a commercially available casting mold may be used.

Different spectacle lens blank designs may have different curvatures at the front surface and at the back surface and suitable casting molds may be provided for casting spectacle lens blanks having the predefined curvatures at the front surface and the back surface. The casting molds may have a curvature at their inner surfaces corresponding to the predetermined curvatures of the front surface and the back surface of the spectacle lens blank to be cast. Throughout the disclosure the inner surface of a casting mold may be referred to as a casting surface.

For instance, a first type of casting mold may have a curvature of the casting surface providing an optical power of 4, 14 D and a diameter of 80 mm. The marking structure to be applied may be adapted to imprint an optical mark in the shape of a data matrix code into the spectacle lens cast having a symbol size of 20x20 cells, wherein each cell has a rectangular and optionally a quadratic shape with a side length of 0, 4 mm. Accordingly, the marking structure may have a width of 8 mm and a height of 8 mm at the casting surface. When using the above-mentioned device UV MD-U1000, a relative laser power may be adjusted to 80%, at a scan speed of 15 mm/s and a pulse frequency of the pulsed laser radiation of 40 kHz. The marking structure may be applied by one single exposure only. Alternatively or additionally, the marking structure may be adapted to imprint an optical mark comprising one or more letters readable by humans. The letters may for instance be specified by the true type font “Arial” , have a height of 3 mm, awidth of 100%, a character layout spacing of 0%. This may be applied using the above-mentioned device UV MD-U1000 at a relative laser power of 80%, a scan speed of 3 mm/s and a pulse frequency of 40 kHz. The spot variable may be chosen as “0” , the fill type as “Boundary” and the shrink boundary may be 0 mm. The laser radiation may be focused directly at the inner surface of the casting mold at the intended position of the marking structure, i.e. the focal plane of the laser radiation may be positioned at the intended position of the marking structure (Spot Variable=0) .

For instance, a second type of casting mold may have a curvature of the casting surface providing a power of 6, 03 D and having a diameter of 80 mm. The marking structure to be applied may be adapted to imprint an optical mark in the shape of a data matrix code into the spectacle lens cast having a symbol size of 20x20 cells, wherein each cell has a rectangular and optionally quadratic shape with a side length of 0, 4 mm. Accordingly, the marking structure may have a width of 8 mm and a height of 8 mm at the casting surface. When using the above-mentioned device UV MD-U1000, a relative laser power may be adjusted to 80%, at a scan speed of 9 mm/s and a pulse frequency of the pulsed laser radiation of 40 kHz. The marking structure may be applied by only one single exposure. Alternatively or additionally, the marking structure may be adapted to imprint an optical mark comprising one or more letters readable by humans. The letters may for instance be specified by the true type font “Arial” , have a height of 3 mm, a width of 100%, a character layout spacing of 0%. This may be applied using the above-mentioned device UV MD-U1000 at a relative laser power of 80%, a scan speed of 2 mm/s and a pulse frequency of 40 kHz. The marking structure may be applied by only one single exposure. The spot variable may be chosen as “0” , the fill type as “Boundary” and the shrink boundary may be 0 mm. The laser radiation may be focused directly at the inner surface of the casting mold at the intended position of the marking structure, i.e. the focal plane of the laser radiation may be positioned at the intended position of the marking structure (Spot Variable=0) .

The used laser source providing the laser radiation may be a 3-axis UV laser marker of the MD-U1000 series of the manufacturer KEYENCE, as described in MD-U1000 Series User’s Manual provided by the manufacturer KEYENCE under the document number 96M14647. According to this document, the emitted laser radiation has a wavelength of 355 nm and a power of 2, 5 W in the focus at a repetition rate of 40 kHz. Therefore, a power of 100%may relate to a power of 2, 5 W in the focus. Accordingly, a power of 80%may relate to a power of 2, 0 W in the focus. The focus may be positioned directly at the inner surface of the casting mold at the intended position of the marking structure. Alternatively, the focus may be positioned before or after the inner surface of the casting mold along the optical axis of the laser radiation. Optionally, the focus may be positioned within a distance range of±5 mm around the inner surface of the casting mold along the optical axis of the laser radiation.

The method for applying a marking structure to a casting mold for manufacturing a spectacle lens blank may further comprise a process of annealing the casting mold. This may provide the advantage that an internal mechanical stress within the casting mold and in particular in the area of the marking structure, which may originate in the process of generating the marking structure, may be reduced. As a consequence thereof, a risk of cracks in the casting mold occurring in the area of the marking structure can be reduced and, hence, the reject of casting molds can be reduced and the lifetime of the casting mold may be enhanced.

The process of annealing the casting mold may comprise the following steps after applying the marking structure to the casting mold:

(i) heating the casting mold to a temperature of about 550℃, wherein the temperature may be in increased in a slow fashion, such as for example by 20℃ per minute;

(ii) keep the casting mold at a temperature of about 550℃ for about 30 minutes; and

(iii) letting the casting mold cool down to room temperature, which may be at 20℃; The cooling down may be carried out by allowing the casting mold to rest at room temperature.

It is understood by a person skilled in the art that the features described above and the features in the following description and figures are not only disclosed in the explicitly disclosed embodiments and combinations, but that also other technically feasible combinations as well as the isolated features are comprised by the disclosure. In the following, several optional embodiments and specific examples are described with reference to the figures to illustrate the disclosure without limiting the disclosure to the described embodiments.

Further optional embodiments will be illustrated in the following with reference to the drawings. The figures show:

Figures 1A to 1C a casting mold for manufacturing a spectacle lens blank according to an optional embodiment of the disclosure;

Figure 2 a part of a spectacle lens blank according to an optional embodiment cast with the casting mold shown in Figures 1A to 1C;

Figure 3 a method according to an optional embodiment for applying a marking structure to a casting mold;

Figure 4 a method for manufacturing a spectacle lens blank according to an optional embodiment;

Figures 5A to 5C exemplary results of conventional optical marks at spectacle lens blanks generated with conventional methods deviating from the disclosure presented above and damages occurring at spectacle lens blanks treated with these conventional methods;

Figure 6 photographs of a part of a conventional glass mold suffering a damage from a mold sticking defect.

Figure 7 a casting mold comprising a front glass mold and a back glass mold.

The same reference signs are used for corresponding or similar features in different drawings.

Figures 1A to 1C show a casting mold 10 for manufacturing a spectacle lens blank 12 (see Figure 2) according to an optional embodiment of the disclosure. Figure 1A depicts the casting mold 10 in a perspective view revealing several parts of the casting mold 10, comprising a front glass mold 14 and a back glass mold 16, which when assembled together form a cavity or void 18 to be filled with casting material. The casting mold 10 further comprises a gasket 17 for fixating the assembly of front glass mold 14 and back glass mold 16 and a sprue 20 for filling the casting material into the void 18. The casting material may comprise or consist of monomeric CR39, which after curding in the void 18 forms the spectacle lens blank 12 from polymeric CR39. The shape and structure of the front glass mold 14 determines the shape and texture of the front surface of the spectacle lens blank 12 cast using the casting mold 10. Likewise, the shape and structure of the back glass mold 16 determines the shape and texture of a back surface 36 of the spectacle lens blank 12 cast using the casting mold 10. Figure 1B depicts the casting mold 10 in a side view showing the relative arrangement of the front glass mold 14, the back glass mold 16 and the void 18 fillable with casting material. The casting mold 10, in particular the back glass mold 16 and the front glass mold 14, may be made of an inorganic glass and/or a silicate glass. For instance, the back glass mold 16 and the front glass mold 14 may be made of fused silica. These materials may provide the advantage that they are suitable for applying a marking structure 22 based on laser-induced swelling.

Figure 1C presents a detailed and enlarged view of a part of the back glass mold 16 having a marking structure 22 applied to it using a method according to the disclosure. As can be seen, the marking structure 22 comprises an arrangement of spot-like protrusions 24 forming a data matrix code 26 and several letters 28 and digits 30 provided by protrusions in the shape of linear beadings 32. The enlarged sections presented on the right-hand side of Figure 1C provide a detailed view at a magnification of about 1.000 times on the spot-like protrusions 24 and the linear beadings 32 forming the data matrix code 26 and the letters 28 and digits 30 of the marking structure 22, respectively. The spot-like protrusions 24 and the protrusions having the shape of linear beadings 32 are generated by laser-induced swelling due to selective laser radiation. The spot-like protrusions 24 may be referred to as spot-like bumps. It is emphasized that the spot-like protrusions 24 and the linear beadings 32 solely consist of protrusions and do not exhibit any recesses extending into the bulk material of the back glass mold 16. Consequently, the marking structure 22 formed by the spot-like protrusions 24 and the protrusions having the shape of linear beadings 32 is adjusted to imprint a respective optical mark 34 (see Figure 2) into a spectacle lens blank 12 cast using the casting mold 10, without casting material penetrating the inner surface of the casting mold 10, i.e., the surface of the back glass mold 16 being in contact with the casting material. This reduces or prevents the risk of casting material sticking to the casting mold 10, which may be particularly important when using the highly sticky material CR39 as casting material. Therefore, the casting mold 10 according to this embodiment reduces the risk of damaging the casting mold 10 and/or the cast spectacle lens blank 12 when disassembling the casting mold 10 and removing the casting mold 10 from the cast spectacle lens blank 12. The letters and digits of the marking structure 22 applied to the back glass mold 16 have regular orientation. This will result in an optical mark 34 formed at the back surface of the spectacle lens blank 12 cast with this casting mold corresponding to a mirror image of the marking structure 22, i.e. the letters and digits being reverted (see Figure 2) . This will result in the optical mark 22 being properly readable when viewed from the front surface of the spectacle lens blank 12, i.e., through the volume of the spectacle lens blank 12.

Figure 2 shows a part of a spectacle lens blank 12 according to an optional embodiment cast with the casting mold 10 shown in Figures 1A to 1C. The cast spectacle lens blank 12 exhibits an optical mark 34 applied to the back surface 36 of the spectacle lens blank 12 during the casting process. The optical mark 34 originates in the marking structure 22 applied to the back glass mold 16 of the casting mold 10 prior to the casting process and, thus, corresponds in its structure to the marking structure 22 applied to the casting mold 10. In particular, the optical mark 34 may represent a negative structure of the marking structure 22 applied to the casting mold 10. Therefore, the optical mark 34 according to the presented optional embodiment comprises a data matrix code 26, letters 28 and digits 30. Due to the marking structure 22 having only protrusions, the optical mark 34 may solely be formed of recesses, such as indentations, at the back surface 36 of the spectacle lens blank 12. As the optical mark 34 is generated at the spectacle lens blank 12 during the casting process, no further process steps may be required for applying the optical mark 34 to the spectacle lens blank 12 after the casting process. The optical mark 34 may be usable for identifying and/or tracing the spectacle lens blank 12, and/or for assigning the spectacle lens blank 12 to the casting mold 10, with which the spectacle lens blank 12 was cast.

With reference to Figure 3 a method 300 according to an optional embodiment for applying a marking structure 22 to a casting mold 10 for manufacturing a spectacle lens blank 12 is described. The method may be suitable for providing a casting mold 10 as detailed above with reference to Figures 1A to 1C.

The method 300 may comprise a step 302 of generating the marking structure 22 at an inner surface of at least one part of the casting mold 10 by selectively applying a laser radiation to an intended position of the marking structure 22. The inner surface may be a surface of a front glass mold 14 or a surface of a back glass mold 16. In particular, the inner surface may be the surface of the front glass mold 14 or the surface of the back glass mold 16 being in contact with the casting material during the casting process. Generating the marking structure 22 as one or more protrusions of the inner surface of the at least one part of the casting mold 10 by laser-induced swelling may include selectively melting at least a part of the casting mold 10 at the intended position of the marking structure 22. The one or more protrusions may extend 500μm or less from the inner surface of the at least one part of the casting mold 10 into a void 18 provided by the casting mold 10. Optionally, the created marking structure 22 may solely consist of one or more protrusions 24, 32 and, hence, may not exhibit any recesses, such as indentations. The one or more protrusions 24, 32 may comprise at least one selected from the group comprising one or more spot-like bumps 24 and one or more linear beadings 32.

The method 300 is characterized in that the laser radiation is selectively applied to generate the marking structure 22 as one or more protrusions of the inner surface of the at least one part of the casting mold 10 by laser-induced swelling of the casting mold 10 at the intended position of the marking structure 22.

At least the inner surface of the casting mold 10 may comprise or may be made of an inorganic glass. Alternatively, at least the inner surface of the casting mold comprises or is made of a silicate glass. The laser radiation may be ultraviolet and/or infrared and optionally pulsed laser radiation.

In the following, a method 400 for manufacturing a spectacle lens blank 12 according to an optional embodiment will be described with reference to Figure 4.

In step 402 the method 400 comprises providing a casting mold 10 having an inner surface. The inner surface may be a surface of a front glass mold 14 or a surface of a back glass mold 16. In particular, the inner surface may be the surface of the front glass mold 14 or the surface of the back glass mold 16 being in contact with the casting material during the casting process.

In step 404 the method 400 comprises applying a marking structure 22 to the inner surface of the casting mold 10 using a method 300 as discussed above with reference to Figure 3.

In step 406 the method 400 comprises casting the spectacle lens blank 12 using the casting mold 10, wherein the marking structure 22 applied to the inner surface of the casting mold 10 creates an optical mark 34 at the casted spectacle lens blank12. Casting the spectacle lens blank 12 may comprise filling a void 18 of the casting mold 10 at least partly with a casting material comprising or consisting of CR39.

In step 408 the method 400 comprises curing the cast spectacle lens blank 12 in the casting mold 10.

In step 410 the method 400 may comprise mechanically removing the casting mold 10 from the cast spectacle lens blank 12.

The optical mark 34 created at the casted spectacle lens blank 12 may correspond to a negative structure of the marking structure 22 applied to the inner surface of the casting mold 10. The marking structure 22 may be applied to the inner surface of the casting mold 10 such that the optical mark 34 is created at a back surface 36 of the cast spectacle lens blank 12.

The optical mark 34 may include at least one selected from the group comprising one or more characters, such as letters 28 and/or digits 30, readable by a human eye, a machine-readable code, such as a bar code and/or a QR code and/or a data matrix code 26.

For the sake of comparison, Figures 5A to 5C show exemplary results of optical marks at spectacle lens blanks 12 generated with conventional methods deviating from the above-presented disclosure and damages occurring at spectacle lens blanks treated with these conventional methods.

Figure 5A depicts a conventional spectacle lens blank having generated thereon an optical mark in the form of a bar code, wherein a respective marking structure was applied using conventional acid etching at a conventional pre-coated glass mold used for casting said spectacle lens blank. As clearly visible in the enlarged section on the right hand side of Figure 5A, each line of the bar code suffers from filigree structures generated around the line, which increase the risk of the spectacle lens blank getting stuck at the casting mold resulting in damages when attempting a removal of the cast spectacle lens blank after the casting process.

Figure 5B depicts a spectacle lens blank having generated thereon an optical mark in the form of a data matrix code, wherein a respective marking structure was applied by conventional laser engraving based on sublimation of material of the conventional glass mold used for casting said spectacle lens blank. The enlarged view on the right hand side of Figure 5B shows recesses formed by the conventional laser engraving, which exhibit a rough surface. As shown in Figure 5C, these recesses favor the generation of undesired micro-cracks 500 at the edges of the recesses. The micro-cracks 500 typically expand when opening the glass mold for removing the spectacle lens blank, which often results in the conventional glass mold breaking or a part of the material breaking away from the glass mold (see indicators 502 in Figure 5C) in an early stage of a desired lifetime of the glass mold. Moreover, the micro-cracks may enable left-over monomeric cast material sticking to the glass mold (see indicators 502 in Figure 5C) during the casting process and remaining at the casting mold after removal of the spectacle lens blank, which may render the glass mold unusable.

Figure 6 shows photographs of a part of a conventional glass mold suffering a damage from a mold sticking defect. The glass mold got broken due to remains of the monomeric casting material sticking to the glass mold, which resulted in the glass mold breaking during removal of the cast spectacle lens blank.

Figure 7 schematically depicts a casting mold 10 according to an optional embodiment comprising a front glass mold 14 and a back glass mold 16. The front glass mold 14 and the back glass mold 16 are assembled such that an inner surface 14a of the front glass mold 14 and an inner surface 16a of the back glass mold 16 form a void 18 for casting a spectacle lens blank 12. The inner surfaces 14a, 16a may be referred to as casting surfaces as they determine the shape of the front surface and the back surface of the spectacle lens blank 12 to be cast, respectively. In particular, the inner surface 14a of the front glass mold 14 may define the front surface of the spectacle lens blank 12. The inner surface 16a of the back glass mold 16 may determine the back surface 36 of the spectacle lens blank 12. The void 18 may be sealed by one or more gaskets 30.

List of reference signs
10                  Casting mold
12                  spectacle lens blank
14                  front glass mold
14a                 inner surface of front glass mold
16                  back glass mold
16a                 inner surface of back glass mold
17                  gasket
18                  void
20                  sprue
22                  marking structure
24                  spot-like protrusion
26                  data matrix code
28                  letter
30                  digit
32                  linear beading
34                  optical mark
36                  back surface of spectacle lens blank
300                 Method for applying a marking structure to a casting mold
302                 Method step
400                 Method for manufacturing a spectacle lens blank
402–410            Method steps
500                 micro crack
502                 material breaking away from glass mold

Claims

Method (300) for applying a marking structure (22) to a casting mold (10) for manufacturing a spectacle lens blank (12) , the method (300) comprising:

- generating (302) the marking structure (22) at an inner surface of at least one part of the casting mold (10) by selectively applying a laser radiation to an intended position of the marking structure (22) ;

characterized in that

the laser radiation is selectively applied such as to generate the marking structure (22) as one or more protrusions (24, 32) of the inner surface of the at least one part of the casting mold (10) by laser-induced swelling of the casting mold (10) at the intended position of the marking structure (22) .
Method (300) according to claim 1, wherein at least the inner surface of the casting mold (10) comprises or is made of an inorganic glass.
Method (300) according to claim 1 or 2, wherein at least the inner surface of the casting mold (10) comprises or is made of a silicate glass.
Method (300) according to any one of the preceding claims, wherein the laser radiation comprises at least one selected from the group comprising ultraviolet laser radiation and infrared laser radiation.
Method (300) according to any one of the preceding claims, wherein generating the marking structure (22) as one or more protrusions (24, 32) of the inner surface of the at least one part of the casting mold (10) by laser-induced swelling includes selectively melting at least a part of the casting mold (10) at the intended position of the marking structure (22) .
Method (300) according to any one of the preceding claims, wherein the one or more protrusions (24, 32) extend 500μm or less from the inner surface of the at least one part of the casting mold (10) into a void (18) provided by the casting mold (10) .
Method (300) according to any one of the preceding claims, wherein the created marking structure (22) solely consists of one or more protrusions (24, 32) .
Method (300) according to any one of the preceding claims, wherein the one or more protrusions (24, 32) comprise at least one selected from the group comprising one or more spot-like bumps (24) and one or more linear beadings (32) .
Method (400) for manufacturing a spectacle lens blank (12) , the method (400) comprising:

- providing (402) acasting mold (10) having an inner surface;

- applying (404) amarking structure (22) to the inner surface of the casting mold (10) using a method (300) according to any one of the preceding claims;

- casting (406) the spectacle lens blank (12) using the casting mold (10) , wherein the marking structure (22) applied to the inner surface of the casting mold (10) creates an optical mark (34) at the casted spectacle lens blank (12) ; and

- curing (408) the cast spectacle lens blank (12) in the casting mold (10) .
Method (400) according to claim 9, wherein the optical mark (34) created at the casted spectacle lens blank (12) corresponds to a negative structure of the marking structure (22) applied to the inner surface of the casting mold (10) .
Method (400) according to claim 9 or 10, wherein the marking structure (22) is applied to the inner surface of the casting mold (10) such that the optical mark (34) is created at a back surface of the cast spectacle lens blank (10) .
Method (400) according to any one of claims 9 to 11, wherein casting (406) the spectacle lens blank (12) comprises filling a void (18) provided by the casting mold (10) at least partly with CR39.
Method (400) according to any one of claim 9 to 12, further comprising the step:

- mechanically removing (410) the casting mold (10) from the cast spectacle lens blank (12) .
Method (400) according to any one of the claims 9 to 13, wherein the optical mark (34) includes at least one selected from the group comprising one or more characters (28, 30) readable by a human eye, amachine-readable code, and a data matrix code (26) .
Use of laser-induced swelling for applying a marking structure (22) to an inner surface of a casting mold (10) adapted for manufacturing a spectacle lens blank (12) .