WO2014060098A1

WO2014060098A1 - Creation of microstructured casting moulds or punches

Info

Publication number: WO2014060098A1
Application number: PCT/EP2013/003112
Authority: WO
Inventors: Stephan Trumm; Werner Müller
Original assignee: Rodenstock Gmbh
Priority date: 2012-10-17
Filing date: 2013-10-16
Publication date: 2014-04-24
Also published as: DE102012020363A1; DE102012020363B4

Abstract

The present invention relates to a method for producing a lens, particularly an ophthalmic lens, with a microstructure on at least one curved lens surface. The method according to the invention comprises the following steps: provision of a substantially planar film (20); generation of a microstructure (18, 18') in or on the substantially planar film; deformation of the film to create a curved surface which determines the at least one curved lens surface of the lens (10) to be manufactured with the microstructure; and transfer of the microstructure from the shaped film onto the lens to be manufactured.

Description

Production of microstructured molds or stamps

description

The presented invention relates to a method for producing a lens, in particular a spectacle lens, which has a particularly diffractive microstructure on at least one side. In this case, the desired microstructure is produced in particular by use of a correspondingly structured casting mold during the production of the semi-finished product (blanks) or finished product (spectacle lens) by casting or the desired microstructure is produced in particular by the use of a suitably structured stamp in the semi-finished product (blank) or finished product (blank). Spectacle lens) introduced forming. Diffractive optics often use a combination of a refractive and a diffractive effect on at least one surface or interface. This makes it possible to achieve very good imaging qualities even in complex optics with high functional density even with comparatively few lens elements. Especially for applications in which only a single lens is used, a combination of refractive and diffractive effects can reduce aberrations which can otherwise only be suppressed by multilayer lenses or by refractive index gradient lenses. In particular, with lenses such as e.g. Spectacle lenses constructed of a dispersive material sometimes utilize diffractive microstructures on a lens surface, for example, to reduce color fringes due to chromatic aberrations of the lens. Some examples of a design of diffractive structures for color fringe correction are known, for example, from DE 10 2010 051 627 A1, DE 10 2010 051 637 A1, DE 10 2010 051 645 A1 and DE 10 2010 051 762 A1.

However, one of the challenges of using diffractive structures is theirs large production costs. In particular for the production of rotationally symmetric structures, machining processes (eg diamond turning) have become established. In this case, either the lens to be produced can be machined directly, or a casting mold or a punch is machined to form therein a negative of the microstructure to be provided on the lens, which is then cast by casting the lens or by stamping on the corresponding lens surface is transmitted. However, these machining methods have certain limits with respect to the achievable feature sizes and freedom from deviation from rotational symmetry.

Another approach is optical structuring by means of laser direct exposure, as described, for example, in "Diffractive Structures on Curved Surfaces for Hybrid Imaging Systems" by Rene Reichle et al., Photonik 4/2010, pages 36-40. Laser direct exposure on the one hand offers a relatively high structural resolution In the process, a substrate (eg, a lens to be patterned) is coated with photoresist, which is then locally exposed, in particular by means of a focused laser beam For the microstructuring of curved lens surfaces, for example of spectacle lenses, it is crucial that the surface to be structured remains always in the focus of the laser light during the exposure of the photoresist, for example by means of an autofocus system The uniform deposition of the photoresist on a curved surface also places certain demands on the deposition process. Overall, a very high structural quality for microstructures, even on curved surfaces and with a high degree of freedom with respect to the shape of the microstructures, can therefore be achieved by an optical method by means of laser direct exposure using a corresponding technological outlay. In this method, the curvature is (usually) limited.

Object of the present invention is the production of lenses, in particular of spectacle lenses, with a particular diffractive microstructure on at least to simplify a curved surface of the lens.

This object is achieved by a method having the features specified in claim 1. Preferred embodiments are subject of the dependent claims.

Thus, the invention provides a method for producing a lens, in particular a spectacle lens, with a microstructure on at least one curved lens surface. The at least one lens surface on which the desired microstructure is to be formed may in particular be a convex or a concave surface. It may thus be either the front surface or the back surface of a spectacle lens. In a further preferred embodiment, corresponding microstructures could also be provided both on the front surface and on the rear surface of a spectacle lens.

In this case, the method according to the invention comprises providing a substantially planar foil and generating a microstructure in or on the substantially planar foil. In other words, a microstructure is produced on at least one surface of the substantially planar film. Depending on how exactly the production process proceeds, ie, in particular depending on how many intermediate steps of a subsequent transfer of the microstructure still take place, the microstructure produced on the at least one surface of the essentially planar film substantially forms a positive or negative copy of the final, is to be formed on the curved lens surface microstructure.

The production of a microstructure on the at least one surface of the film is preferably carried out by means of lithographic technology. In this case, in a preferred embodiment, the lithography can be carried out directly on the film. In another preferred embodiment, lithography is carried out on a substantially planar structure transfer substrate, and the microstructure produced in this case is subsequently transferred, in particular mechanically, to the planar film. After the microstructure has been formed on the surface of the substantially planar film, the method comprises reshaping the film to create a curved surface which defines or replicates the at least one curved lens surface of the lens to be fabricated having the microstructure. The resulting after production of the microstructure in at least one surface of the film planar product is thus brought by transformation in the desired global shape (eg sector of a sphere). The result can then preferably be used directly as a casting mold or stamp for the lens to be produced (in particular a spectacle lens) or used as a master for one or more consecutive replication steps. According to the invention, the method thus comprises transferring the microstructure from the formed film to the lens to be produced (in particular by casting and / or by a stamping or stamping process). The invention presented here is a method for providing lenses, in particular spectacle lenses, which have a microstructure on at least one side. In this case, the structure is produced in particular by use of a correspondingly microstructured casting mold in the production of the semi-finished product (blanks) or finished product (spectacle lens) by casting. Alternatively, the structure can also be introduced into the semifinished product (blank) or finished product (spectacle lens) by the use of a correspondingly microstructured stamp.

Although it is possible to produce microstructures on curved surfaces of molds and dies with high accuracy even with conventional mechanical methods, the structures naturally have dead zones due to the expansion of the tool, which may be disadvantageous for the application. On the other hand, this disadvantage does not have a lithographic representation. However, lithographic processes (such as single and multi-level mask exposure, laser direct exposure) on curved substrates are possible only with the comparatively high technological complexity described above, and even then lithography is technical only on slightly curved substrates reliably realizable. Particularly in the field of spectacle lenses, however, it is desirable to apply a microstructure to a surface (preferably front surface) of the spectacle lens which, however, is typically so strongly curved that the generation of the necessary mold or the necessary stamp by conventional lithographic methods alone is often insufficient or not sufficient is possible.

On the other hand, with the aid of the present invention, it is even possible to use a whole-area lithographic process with very simple means and with high precision and reproducibility in order to define the desired microstructure. After the microstructure according to the invention is first generated on a substantially planar surface of a deformable film, there occur neither "dead" (inaccessible) zones, as is known for example in the conventional machining of curved surfaces, nor has a complex, very fast autofocus control Rather, the substantially planar film can be lithographically patterned with very simple means, preferably even over the entire surface (that is to say over the entire surface to be structured simultaneously), before the film is then formed, to introduce the required global surface curvature.

As can be seen, it is not absolutely necessary that the provided film (or its surface to be structured) is completely planar. Instead, the improvement according to the invention is already achieved if the global curvature of the film during the production of the microstructure is significantly smaller than the global curvature of the lens surface to be produced (eg spectacle lens surface), which should have the desired microstructure. As a global curvature, an average curvature is preferably considered, which disregards in particular the microstructures. In particular, the curvature of a sphere or the mean curvature of a tom can be regarded as the global curvature, and the foil or the lens surface to be produced, in particular on the basis of average square squares, is the best approach.

In this sense, in a method according to the invention, the film is considered to be "substantially planar" in particular if the curvature of the film provided (ie before forming) is not more than about one-fifth, preferably not more than about one-tenth, more preferably not more than about one-twentieth, more preferably not more than about one-fiftieth, most preferably not more than about one-hundredth of the curvature of the lens surface to be made, most preferably not deviating the area of the film to be patterned from a plane prior to forming greater than about 1 mm, more preferably no greater than about 0.5 mm, even more preferably no greater than about 0.2 mm, more preferably no greater than about 0.1 mm, even more preferably no greater than about 50 μm or even not even greater than about 10 μιη, more preferably not greater than about 1 μηη, most preferably not large he μιη than about 0.1 μιη or not even greater than about 0.05 or even not even greater than about 10 nm.

In particular structures are provided as a microstructure, which serve as diffractive gratings for visible light. In a preferred embodiment, the microstructure is produced by means of lithography directly in or on the film. For this purpose, a layer of photoresist is preferably applied directly to the film, which is exposed for example by means of a focused laser and / or by means of a lithographic shadow mask and / or by means of holographic interference structures and then developed. Thereafter, an etching step is preferably carried out, which transfers the microstructure produced in the photoresist to the film. In particular, after removal of the remaining photoresist, the film can be subjected to further forming.

In another preferred embodiment, the lithography is not carried out directly on the film to be formed, but on a substantially planar substrate, from which the microstructure is then transferred directly or indirectly, for example by an embossing or stamping process on the substantially planar film. This substrate thus serves to transfer the microstructure from the planar lithography to the film. The substrate should therefore be referred to below as a structure transfer substrate. In this embodiment, the production of a microstructure in or on the film thus preferably comprises producing a microstructure by means of lithography in or on a structure transfer substrate and transferring the microstructure generated on the structure transfer substrate into or onto the substantially planar film. As already mentioned, in particular an embossing or stamping method can be used. In this case, in particular by mechanical pressure, the microstructure produced in the structure transfer substrate is embossed into the substantially planar film. For this it is necessary that the film can deform much easier than the structure transfer substrate. The structure transfer substrate must therefore have a mechanical stability which ensures that the microstructure produced therein is not significantly deformed during the embossing process. In turn, the film should be plastically deformable so that the embossed microstructure is retained on at least one surface of the film after the embossing process.

The preferred embodiment by means of a substantially planar structure transfer substrate offers a greater choice in the materials to be used, in particular for the film to be formed, since the lithography and the forming into the curved shape are decoupled from one another. This makes it possible on the one hand, in the lithography (ie for the Strukturtransfersubstrat) non-deformable materials (such as relatively thick substrates of nickel, aluminum or the like) to use while for forming (ie as a film) on the other hand, lithographically non-workable materials (eg special organic compounds such as PMMA or PC) can be used.

Particularly preferably, a plurality of films are embossed by means of a single, lithographically structured structure transfer substrate, which are then used in each case for forming. This can be done directly or again via one or more intermediate steps ("fathers") .The later remarks on possible downstream down- and forming steps apply here analogously. Regardless of this intermediate step by means of a structure transfer substrate, the respective products (ie the results of the first step or the intermediate step) can be subjected to processes for optimizing certain properties. Examples of this are chemical or thermal curing steps or special coatings before use as a casting mold or stamp in the forming or forming, as well as plasticization before forming.

Overall, therefore, first the microstructure is introduced, in particular by lithographic processes, into a plane (or only moderately curved) film. In this case, a film is understood as meaning a substrate which is sufficiently flexible for the deformation in the subsequent step. Examples include thin sheets of organic material or (semi-) metals (e.g., silicon, aluminum, nickel) having a preferred thickness of up to about 200 microns (more preferably 10-50pm).

The resulting planar (or only moderately curved) product is reshaped into the desired global shape (e.g., base curve of the desired spectacle lens area) in a subsequent step. A suitable possibility for this is, for example, a forming process under thermal action. Thus, by appropriate heating of the film, a wrinkle-free and crack-free deformation can be promoted.

In a preferred embodiment, the provided film has a thickness of not more than about 0.5 mm, preferably not more than about 0.2 mm, more preferably not more than about 0.1 mm, most preferably in the range of about 10 pm up to about 50 pm. At these thicknesses, on the one hand, in particular a good formation of diffractive microstructures and, on the other hand, a good, damage-free deformation of the film is possible in a particularly efficient manner. For example, when using soft metals for the film but also for some organic films, it would certainly also be possible to use significantly thicker films down to a few millimeters. In a preferred embodiment, the film provided comprises organic material, in particular PMMA and / or PC, and / or metal, in particular aluminum and / or nickel, and / or a semimetal and / or a semiconductor, in particular silicon. In these materials, on the one hand, the formation of diffractive microstructures with high precision and, on the other hand, a good, damage-free deformation of the film is possible in a particularly efficient manner.

In the simplest case, the film is used after forming directly as (at least part of) a mold or as (at least part of) a stamp (s). However, since this film is preferably relatively thin, it is particularly preferred to apply it to a stronger substrate having a corresponding curvature or shape. This substrate (also referred to below as the carrier substrate) can not only be used to strengthen the mechanical stability, but also serve, for example, to improve the thermal properties during the casting or molding process. In this case, the carrier substrate may already be part of the casting mold or the punch, which is used to specify the curvature or the shape of the lens to be produced. Such a procedure has the additional advantage that a corresponding demolding after forming the film is eliminated. Thus, the forming of the film preferably comprises arranging the film on a carrier substrate with a curved carrier surface. In this case, the film with the surface facing away from the at least one microstructured surface of the film is arranged on the curved carrier surface of the carrier substrate, so that it adheres to it in particular. The at least one microstructured surface of the film is thus remote from the carrier substrate, so that the exposed microstructure can be transferred to the lens to be produced. In a preferred embodiment, the carrier substrate provided with the film thus serves directly as a casting mold or as a stamp for the lens to be produced. In a preferred embodiment, transferring the microstructure from the curved foil to a lens thus comprises casting the lens by means of a mold such that it is shaped to produce a curved surface Film forms an inner surface of the mold, which defines the at least one curved lens surface of the lens to be produced with the microstructure. Thus, the carrier substrate with the film adhering thereto is particularly preferably used directly as a casting shell. In a further preferred embodiment, the second surface of the lens to be produced can also be formed by means of an analogous manufactured mold shell. In a preferred embodiment, only one of the two lens surfaces, in particular the front surface of a spectacle lens, has a corresponding diffractive microstructure, while the other surface (in particular the rear surface of a spectacle lens) is subjected to further processing after casting by appropriate grinding processes.

In another preferred embodiment, transferring the microstructure from the curved sheet to a lens comprises stamping such that the sheet formed to create the curved surface forms a stamp face of the stamp containing the at least one curved lens surface of the lens to be produced Microstructure determines. It is thus particularly preferred to use directly the carrier substrate with the film adhering thereto as a stamp for forming the desired microstructure in the lens to be produced.

Regardless of the use of said back substrate, one or more additional processing steps (eg, chemical or thermal curing, coating) may be performed prior to use as a mold or stamp. Notwithstanding a direct use of the formed film as part of a casting mold or a stamp but also further Ab- and / or forming steps can be stored. Thus, it may be advantageous for a number of reasons not to use the film after its forming directly as (part of) a mold or as (part of) a stamp (s) as described above, but rather the mold or the stamp by additional Ab- or Forming steps to produce from the formed film. Thus, the reshaped film (possibly together with a corresponding carrier substrate) preferably serves as a master. This master can then serve to directly mold a casting mold or a stamp from it (master -> casting mold or stamp) or one or more molding steps are interposed (master -> father -> casting mold or stamp or master -> father -> .. -> casting mold or stamp).

In a preferred embodiment, transferring the microstructure from the curved foil to a lens thus involves directly or indirectly transferring the microstructure from the curved foil to a casting mold (optionally via one or more intermediate steps) and casting the lens by means of the casting die. Similarly, in another preferred embodiment, transferring the microstructure from the curved foil to a lens involves directly or indirectly transferring the microstructure from the curved foil to a punch (optionally via one or more intermediate steps and embossing the lens by means of the punch.

In a preferred embodiment, the method comprises molding the mold (or the stamp) or a father by electroplating. A technical advantage of this procedure is the decoupling of the deformation of the film from the actual casting or embossing process. This material can be used, which are particularly suitable for the individual process steps (durable, stable, better to clean, ...). Thus, non- or poorly formable materials (such as thick substrates of nickel, aluminum, or the like) can act as molds for the lenses (spectacle lenses or blanks) which are particularly suitable. On the other hand, for forming the film, materials (e.g., organic compounds such as PMMA or PC) which are less suitable for the molding of spectacles or blanks can be used.

Furthermore, this method can offer an economic advantage. Thus, the additional molding steps are often cheaper than the direct production by means of lithographic processes and a deformation of the film.

Analogous to the procedure described above can also be here or several additional processing steps (eg chemical or thermal curing, coating) are performed before the respective Ab- or forming steps.

In order to obtain the desired structure in the lens to be manufactured (e.g., spectacle glass or blank), the following points should particularly be considered in the design of the structure for lithography. Depending on the number of Ab- or forming processes (to create the microstructure on the film and transfer of the microstructure from the film to the lens surface), the lithographically generated structure is provided for the lens to be produced structure as a negative (no or an even number Impression steps) or as a positive (odd number) play.

Preferably, the influence of the deformation of the film on the geometry of the microstructure is already taken into account in the generation of the microstructure on the planar film by already precompensating the deformation of the microstructure caused by the deformation. Thus, the original plane structure is curved by the deformation. The effects of this distortion as well as the expansion or compression of the surface associated with the forming are likewise already taken into account in the structure produced in particular by lithography. Since diffractive microstructures, in particular in the case of spectacle lenses, generally run substantially in the tangential direction (ie micro-ribs and micro-trenches of such diffractive structures generally run essentially transversely to the radial direction of a spectacle lens), the reshaping of the film can in any case take place such that the mutual distances of the diffractive structures are present hardly change when forming. Thus, the method according to the invention is particularly well suited, above all, to produce spectacle lenses with diffractive structures (in particular for color fringe correction) very efficiently.

Preferably, also possible influences of further, optional process steps (eg intermediate steps in the impression), which lead to changes in the structure (eg casting shrinkage, slight changes to the structure during casting or stamping, deformation in coating steps) are already considered in advance. Thus, the invention makes it possible in the last consequence, in particular spectacle lenses which have a desired diffractive microstructure, to provide very efficiently and precisely with simple means. Accordingly, changes in the structure which can occur during the production steps of the spectacle lens can also be taken into account. Such deformations can already occur, for example, during casting or stamping of the spectacle lens or blanks, during further processing (eg delays due to the blocking or generation (grinding, cutting, polishing, etc.) of the prescription surface on the side facing away from the microstructure) and the finishing (eg deformations during the application of coatings). Since these influences can depend on the materials and processes used for the spectacle lens, these corrections can also be selected in terms of product, material (eg with different shrinkage coefficients) or process-specific (eg temperatures during coating steps).

The invention will be described below with reference to preferred embodiments with reference to the accompanying drawings. Showing:

1 schematic representations of lenses (eyeglass lenses or

Lens blanks) having a diffractive microstructure on a first surface of the respective lens; and

2A-2D are schematic representations of individual method steps in one

Manufacturing method according to a preferred embodiment of the present invention.

Fig. 1 illustrates examples of spectacle lenses 10 of different effect and surface curvature. In this case, a spectacle glass body 12 in each case has a front surface 14 and a rear surface 16 (eye-side surface). On the front surface 14, a diffractive microstructure 18 is formed in each case. The representation of the diffractive microstructure 18 should be regarded as purely schematic. In particular, the respective microstructure 18 is not shown to scale. Usually that is Microstructure 18 compared to the lens body 12 is much smaller. Typical dimensions of diffractive microstructures are approximately 0.3 to 5 μm in the axial direction (ie in the thickness direction of the spectacle lens) and approximately 1 to 500 μm in the lateral direction.

From left to right, in Fig. 1, one after the other, a plus lens with a convex base curve (front surface 14), a minus lens with a convex base curve (front surface 14), a plus lens with a flat base curve (front surface 14) and a minus lens with a flat base curve (front surface 14) shown. The production of spectacle lenses with a curved (for example convex) base curve and diffractive structures 18 is made particularly efficient by a method according to the invention.

FIGS. 2A to 2D illustrate an example of a manufacturing method according to a preferred embodiment of the invention. Thus, in this preferred embodiment, initially a substantially planar foil 20 is provided which has a substantially planar front surface 22 and a rear surface 24. At least on the front surface 22, a microstructure 18 'is preferably formed by means of a planar lithography, which essentially already defines a microstructure 18 to be formed in the spectacle lens to be produced. The microstructure 18 'in the axial direction (thickness direction of the film 20) is preferably significantly smaller than the thickness of the film 20, which is why it is not shown in FIG. 2A to 2D as a visible structure. In addition, the microstructure 18 'is preferably generated substantially only at the front surface 22 but not at the rear surface 24 of the film 20. Depending on how many intermediate steps are to take place during a subsequent transfer of the microstructure to the spectacle lens, the microstructure 18 'constitutes a positive or a negative of the microstructure 18 to be formed in the spectacle lens. In the example of the preferred method shown schematically here, it is a negative, since In this example, the transmission of the microstructure is done directly.

After creating the microstructure 18 'in or on the substantially planar Film 20, in particular on its front surface 22, the foil 20 is reshaped so that it substantially follows the base curve of the spectacle lens to be produced, as illustrated in FIG. 2C. In the embodiment shown here, the deformation preferably takes place by arranging the film 20 on a carrier substrate 26 with a curved carrier surface, which essentially defines the base curve of the spectacle lens to be produced. In this case, the film 20 is arranged with its rear surface 24 to the carrier substrate 26, so that the microstructure 18 'is exposed. The carrier substrate 26 with the film 20 arranged thereon is then preferably used as a casting shell for a lens blank or a spectacle lens 10. In this case, the front surface 22 of the film 20 with the microstructure 18 'forms the casting surface for the front surface (base curve) 14 of the produced spectacle lens 10. After curing of the lens blank 10 this is again taken out of the mold, preferably (but not necessarily) Film 20 is removed again from the front surface 14 of the lens blank 10.

In another preferred embodiment, not shown here, the carrier substrate 26 is used together with the foil 20 arranged thereon as a stamp for an embossing process.

Reference numeral 10 spectacle lens (blank)

12 spectacle glass body

14 front surface (base curve) of the spectacle lens

16 rear surface of the spectacle lens

18, 18 'microstructure

20 foil

22 front surface of the film

24 back surface of the film

26 carrier substrate

Claims

Claims. A method of manufacturing a lens having a microstructure on at least one curved lens surface, comprising:

Providing a substantially planar film;

Creating a microstructure in or on the substantially planar film;

Deforming the curved surface forming film defining the at least one curved lens surface of the microstructured lens to be made;

Transferring the microstructure from the formed film to the lens to be produced.

2. The method of claim 1, wherein the microstructure is produced by means of lithography directly in or on the film.

3. The method of claim 1, wherein creating a microstructure in or on the film comprises:

Generating a microstructure by means of lithography in or on a pattern transfer substrate; and

Transferring the microstructure created on the pattern transfer substrate into or onto the substantially planar film.

4. The method according to any one of the preceding claims, wherein the forming of the film comprises arranging the film on a carrier substrate having a curved support surface.

5. The method of claim 1, wherein transferring the microstructure from the curved foil to a lens comprises casting the lens by means of a casting mold such that the foil formed to create a curved surface forms an inner surface of the casting mold comprising the at least one Defines curved lens surface of the lens to be produced with the microstructure.

6. The method of claim 1, wherein transferring the microstructure from the curved foil to a lens comprises:

Transferring the microstructure from the curved film to a mold; and

Pour the lens through the mold.

7. The method of claim 1, wherein transferring the microstructure from the curved film to a lens comprises embossing by means of a stamp such that the film formed to create the curved surface forms a stamp surface of the stamp comprising the at least one stamp Defines curved lens surface of the lens to be produced with the microstructure.

8. The method of claim 1, wherein transferring the microstructure from the curved foil to a lens comprises:

Transferring the microstructure from the curved film to a stamp; and

Embossing of the lens by means of the punch.

A method according to any one of the preceding claims, wherein the provided film has a thickness of not more than about 0.5 mm, preferably not more than about 0.2 mm, more preferably not more than about 0.1 mm, most preferably ranging from about 10 m to about 50 pm.

10. The method according to any one of the preceding claims, wherein the film provided organic material, in particular PM A and / or PC, and / or metal, in particular aluminum and / or nickel, and / or a semi-metal and / or a semiconductor, in particular silicon, includes.