NL2022782B1

NL2022782B1 - Mould for casting an optical element and method for manufacturing

Info

Publication number: NL2022782B1
Application number: NL2022782A
Authority: NL
Inventors: Petrus Franciscus Biskop Gregorius; Klamer Lucas
Original assignee: Addoptics B V
Priority date: 2019-03-21
Filing date: 2019-03-21
Publication date: 2020-09-28
Also published as: WO2020190142A1

Abstract

Title: Mould for casting an optical element and method for manufacturing Abstract A first aspect provides a mould for casting an optical element, comprising at least a ﬁrst mould part comprising a cavity having a shape complementary to an intended shape of at least part of the optical element, wherein the ﬁrst mould part predominantly comprises a mould compound having a mould glass transition temperature lower than an optics melting point of an optics compound predominantly to be comprised by the optical element. Such mould allows for casting of the optical element at a temperature below the mould glass transition temperature. If the temperature of the mould is increased to a temperature above the mould glass transition temperature, below the optics melting point, the mould can be conveniently removed from the optical element by virtue of the ﬂexible nature of the mould. During the casting process, the mould may be kept below the mould glass transition temperature to provide a rigid mould.

Description

P122716NL00 Title: Mould for casting an optical element and method for manufacturing

TECHNICAL FIELD The various aspects and implementations thereof relate to manufacturing of a mould for casing an optical element and the casting of the optical element using the mould.

BACKGROUND Optical elements like lenses, mirrors and prisms are traditionally manufactured by sawing, cutting and grinding of materials like glass - lead glass, lime glass, other, or a combination thereof - quartz, diamond and sutable polymers like polycarbonate, acrylic resins, other, or a combination thereof. Such mechanical working of the material leaves mechanical irregularities at the surface of the optical element, which impact optical performance.

Alternatively, the material for the optical element is molten and cast in a mould. Moulds used are heavy and expensive, in particular for manufacturing of optical elements from mineral elements, like lead and lime glass.

Manufacturing of lenses by using drop on demand systems for constructing an optical element has been investigated, but this involves relatively poor material quality & geometrical limitations article manufactured.

SUMMARY It appears it is preferred to provide a mould and a method for manufacturing such mould that allows for flexible manufacturing of the mould as well as for the optical element.

A first aspect provides a mould for casting an optical element, comprising at least a first mould part comprising a cavity having a shape complementary to an intended shape of at least part of the optical element, wherein the first mould part predominantly comprises a mould compound having a mould glass transition temperature lower than an optics melting point of an optics compound predominantly to be comprised by the optical element.

Such mould allows for casting of the optical element at a temperature below the mould glass transition temperature. If the temperature of the mould is increased to a temperature above the mould glass transition temperature and below the optics melting point, the mould can be conveniently removed from the optical element by virtue of the flexible nature of the mould. Yet, during the casting process, the mould may be kept below the mould glass transition temperature to provide a rigid mould.

A compound may comprise a single material or a mixture of materials. It is noted that if a compound is a mixture of materials, such compound has a melting trajectory rather than a melting point. In such case, the start temperature of the melting trajectory is to be considered as the melting point.

Together with the intended compound for the optical material, an ensemble of the mould and the intended compound for the optical material may be considered.

In an embodiment, the optics melting point is determined after curing of the optics compound. The optics compound may be provided in the mould as two reactive components reacting as such, as monomers that may react to form polymers, which reactions take place spontaneously or by applying a reactive action like an additional chemical, thermal energy, photonic energy, other, or a combination thereof. Such compound, before reaction, may have a relatively low melting point, or, as a suspension, may be fluid at a low temperature. However, after reaction, the melting temperature may be significantly higher, having formed larger molecules.

In a further embodiment, the mould glass transition temperature is lower than an optics glass transition temperature of the optics compound.

In such embodiment, the mould and optical element may be separated at a temperature above the mould glass transition temperature and below the optics glass transition temperature, thus separating the rigid optical element from the flexible mould.

As second aspect provides a method of manufacturing of a mould part of a mould for casting of an optical element. The method comprises receiving manufacturing data suitable for controlling a liquid dispensing system, providing a liquid mould printing material having, after curing, a glass transition temperature lower than a melting point or a glass transition point of the optical element once cast and cured. and depositing droplets of the mould printing material for forming a first layer of the mould part on a substrate using a droplet on demand system. The deposition is followed by curing the first layer of mould printing material, depositing droplets of the mould printing material for forming a second layer of the mould part on top of the first layer using the droplet on demand system and curing the second layer of mould printing material.

This method may be continued or repeated, layer upon layer, until the full mould is ready. This method allows for a custom-made mould that may be re-used. In this way, a relatively low cost method is provided for providing limited series of identical optical elements.

The glass transition temperature of the cured mould is preferably lower than a glass transition temperature of an intended compound for forming the optical element and in any case lower than a melting point of the intended compound for forming the optical element.

Curing is to be understood as to solidify or harden, fully or at least partially, in order for the mould - or, in other implementation, the optical element - to be handled without losing shape due to the handling. In an embodiment, the substrate comprises a temperature control module arranged to control temperature of the substrate. This allows to keep the temperature of the mould below the glass transition temperature of the composition of the mould, thus maintaining rigid nature of the mould. Another embodiment comprises applying a release material to an outer surface of the mould forming a cavity having a shape complementary to an intended shape of the optical element. Such material may provide a surface to which an intended compound of the optical element does not stick or does not bind, either physically or chemically - or both -, making separation of the optical element and the mould more convenient. A third aspect provides a method of manufacturing an optical element. The method comprises providing the mould according to the fist aspect or manufactured according to the second aspect, controlling temperature of the mould below the mould glass transition temperature and providing an optical compound for forming the optical element having a melting temperature higher than the glass transition temperature of the mould material. The method further comprises casting the optical compound in the cavity of the mould, allowing the optical compound to settle for taking a shape complementary to the shape of the cavity, curing of the optical element compound. The method also comprises controlling temperature of the mould above the glass transition temperature of the mould compound and below the melting point of the optical compound and separating the mould and the optical element.

BRIEF DESCRIPTION OF THE DRAWINGS The various aspects and implementations thereof will now be further elucidated in conjunction with drawings. In the drawings:

Figure 1 A: shows a drop on demand dispensing system and a substrate; Figure 1 B: shows a stage in manufacturing of a mould; Figure 1 C: shows a manufactured mould; 5 Figure 2 A: shows a stage in manufacturing of an optical element; Figure 2 B: shows an optical element in a mould; Figure 2 C: shows a manufactured optical element; Figure 2 D: shows a compound mould; Figure 2 E: shows a further manufactured optical element; and Figure 3: shows a flowchart.

DETAILED DESCRIPTION Figure 1 A shows a drop on demand system 150 that 1s arranged to deploy a droplet 170 of a substance for forming a mould 102 or at least part thereof. The drop on demand system 150 comprises a dispensing head 160 comprising an dispensing actuator 162 for controlling ejection of a drop 170 of a liquid, suspension or emulsion supplied to the dispensing head 160 as indicated by the arrow. The drop on demand system 150 is applied to a positional actuator 154 for moving the dispensing head 160 relative to a substrate 100 on which the mould 102 in built up. The substrate 100 may form part of the mould 102 or not; it may comprise the same substance as that of the mould 102 or a different substance.

The positional actuator 154 is preferably arranged to move the dispensing head 160 in three dimensions in linear fashion in each dimension; two dimensions perpendicular to one another and parallel to the substrate 100 and a third dimension perpendicular to the other two. In another embodiment, the dispensing head 160 remains at a fix position and the substrate 100 is movable relative to the dispensing head by means of a positions actuator engaging with the substrate 100. The positional actuator 154 and the dispensing actuator 162 are controlled by a dispensing controller 152. The dispensing controller is controlled to manufacture, by means of the drop on demand system 150, a three-dimensional structure and the mould 100 for an optical element 200 (Figure 2 A) in particular. The drop on demand system 150 also comprises a UV lamp 164 as a curing module for curing a layer defined by the deployed drops. The UV-lamp 164 may provide a narrow spectrum, for example between 365 nm and 405 nm, or a broad spectrum. An implementation of a method for manufacturing of the mould 100 and the subsequent manufacturing of the optical element 200 will be discussed in conjunction with a flowchart 300 shown by Figure 3. In the table below, brief indications of the various elements of the flowchart 300 are provided.

302 start 304 receive layer data 306 apply mould layer 308 cure 310 cavity surface? 312 apply surface layer 314 cure 316 end? 318 cool 320 apply further mould parts 322 control temperature 324 cast optical component 326 cure 328 separate element from mould 330 end

The procedure starts in a terminator 302, in which the drop on demand system 150 1s imtialised. In step 304, the dispensing controller receives data on one or more layers to be deployed. The received data comprises locations on the substrate 100 to which the positional actuator 154 can move the dispensing head 160 for deploying one or more droplets. By applying more droplets at one location, height of a layer of the mould 102 may be controlled or width of features may be controlled, in a dimension parallel to the upper surface of the substrate 100. Alternatively or additionally, a size of a droplet to be deployed may be controlled.

The substrate 100 may be provided with indentations or protrusions. Such indentations or protrusions may be used for alignment of the mould 102, for providing protrusions on the mould 102 - in case of indentations in the mould 102 - or holes or bores, either blind holes or through holes - in the mould 102, in case of protrusions on the substrate

100.

The deployed compound for forming the mould 102 preferably comprises acrylic, urethane, polyvinyl Alcohols, hot melt wax, polyolefins, like polyethylene, atactic polypropylene, polybutene, polyamides, polycaprolactone, styrene block copolymers, ethylene-vinyl acetate, other organic or inorganic polymers, or a combination thereof. Such substance has a glass-transition temperature preferably between 30°C and 60°C. It is preferred to use a material that may be re-used, like the hotmelt material referenced above.

In step 306, a layer of the mould is formed as a pattern for applied droplets. In one implementation, the layer may be manufactured as a continuous and preferably contiguous layer. In another implementation, droplets are applied in a staggered fashion, with voids between dots, for example in a checkerboard pattern. A subsequent layer may be formed by droplet applied in a complementary pattern, i.e. dots of the subsequent layer are applied at locations where the previous layer has voids. Hence, in such implementation, one full layer is formed by two sub-layers having complementary patterns of applied dots. In case the mould is to comprise a void or cavity, both sub-layers do not have droplets deployed at such locations.

In step 308, the UV light 164 is used for curing the layer formed by a deployed pattern of droplets. If one contiguous layer is to be formed by two complementary layers, the first sub-layer is preferably cured before the second sub-layer is applied. In one implementation, a light energy dose 1s provided for fully curing the deployed droplets. In another implementation, alight energy dose is provided for partially curing the deployed droplets. In such implementation, droplets of a lower layer is further cured while a higher layer is receiving an energy dose for the first time. An advantage is that droplets of subsequent layers may coalesce before being fully cured. In other implementations, other methods of curing may be used, using electromagnetic waves having different wavelengths, by supplying or withdrawing thermal energy, by providing certain substances - oxygen, nitrogen, water, other or a combination thereof - by other means or a combination thereof. The curing may optionally be executed under an inert atmosphere. Some part might remain uncured in order to produce a cavity.

In step 310, it is determined, based on data received by the dispensing controller 152 or by another controller controlling the dispensing controller 152, whether the top surface of the cured layer of the mould 102 1s a surface of a cavity 106 (Figure 1 B) of the mould 102. If this is the case, an optional liner 104 as a mould surface layer is applied in step 312. The liner 104 preferably comprises a material that does not bind with any material comprised by an optical element that is to be formed by means of the mould

102. The material of the liner 104 is preferably deployed by the drop on demand system 150 as well, preferably with a further dispensing head of the drop on demand system 150.

In another implementation, the dispensing head 160 comprises additional nozzles for deploying droplets of material of the liner 104. In step 314, the droplets of the liner 104 are cured. If it is determined that the top of the deployed mould layer does not form a surface of the cavity 106, the process branches in step 310 to step 304 in which further layer data is received. If all layer data for the mould 102 has been received at once, the process branches back to step 306 from step 310. If part of the liner 104 has been deployed in step 314, the process proceeds to step 316 in which it is determined whether all layers of the mould have been deployed. If this is not the case, the procedure branches back to step 304 or step 306 as discussed above.

When applying a subsequent layer, the positional actuator 154 moves away from the substrate 100, preferably to maintain a distance between the dispensing head 160 and the layer on which subsequent droplets within a pre-determined ranged, preferably around 1 millimetre.

The drop on demand system 150 may comprise sensors for measuring locations and sizes of deployed droplets. With respect to size, width, diameter and/or height of individual droplets may be measured. Of a deployed layer, thickness and shape may be measured. The deployment process may be adjusted in accordance with the measured values. Also temperature of the deployed droplets may be measured.

If all layers have been deployed, the mould 102 may be provided as depicted by Figure 1 C, with the cavity 106 fully clad with the liner 104. At this point, the process continues to step 318 in which the mould 102 1s optionally cooled for moulding an optical element 200 as depicted by Figure 2 A. the optical element 200 may be manufactured using the mould 102 as a single piece mould. In another implementation, the optical element 200 may be manufactured using multiple mould parts as depicted by Figure 2 D.

In the implementation depicted by Figure 2 D, a further mould 102" is provided to from, with the mould 102, a compound mould. Between the mould 102 and the further mould 102', a washer 108 is provided. The washer 108 is preferably provided as a flexible material that may be conveniently and efficiently removed between the mould 102 and the further mould 102' after the optical element 200 has been manufactured. The further mould 102' and the washer 108 are applied to the mould 102 in step

320.

Instead of the washer 108, also a larger third part may be used for the compound mould. The third part may be used for further shaping of the optical element 200, for example by shaping an undercut. The washer 108 or other third may be made from the same material or materials as proposed above for the mould 102, other materials or a combination thereof.

In step 322, temperature of the mould 102 and, optionally, the further mould 102' is controlled. The temperature of the mould 102 - or compound mould - is controlled such that the temperature of the mould 102 1s below a glass-transition temperature of the compound of which the mould 102 is manufactured. Yet, the temperature should not be too low such that any material cast in the mould 102 settles, solidifies or otherwise cured too fast - or may not cure at all -, introducing internal strain that may lead to inhomogeneity of the optical element 200.

The temperature of the mould 102 may be controlled by means of a casting support 210 comprising a cooling element 212 as a temperature control module, as depicted by Figure 2 A and Figure 2 D. The cooling element 212 may be controlled using a feedback loop with a sensor. That may be by means of a thermocouple and/or another sensor, either mechanically, electrically or electronically, other, or a combination thereof.

While the temperature of the mould 102 - or the compound mould - 1s controlled, material for forming the optical component is provided in the mould 102 in step 324, thus casting the optical element 200. The cavity 106 of the mould 102 is preferably fully filled, as depicted by Figure 2 B. The filling of the mould 102 may be executed in a low-pressure or vacuum environment, to prevent any inclusion of gases as bubbles. In one implementation, different moulding substances are provided in the mould 102 or compound mould for manufacturing of multi-refractory index optical elements.

The compound for manufacturing the optical element 200 is preferably provided in a liquid state, yet at a temperature that still allows the temperature of the mould 102 to be controlled below the glass-transition temperature of the material of the mould 102. If forming part of the compound mould, the mould 102 and/or the further mould 102' is provided with one or more bores or other openings for receiving the substance for forming the optical element 200.

Suitable materials or compound are preferably poly(methyl methacrylate); polycarbonate; silicones, urethanes, high refractive index polymers, other, or a combination thereof; the compound may be thermosetting or thermoharding. The glass-transition temperature of the compound is preferably at least 5°C, more preferably at least 10°C higher and most preferably 20°C higher than the glass-transition temperature of the compound of the mould 102. This allows separation of the optical element 200 and the mould 102 at a temperature below the glass-transition temperature of the compound of the optical element 200 and above the glass-transition temperature the compound of the mould 102.

In another embodiment, the melting point of the compound for manufacturing of the optical element 200 is at least 5°C, more preferably at least 10°C and most preferably 20°C higher than the glass-transition temperature of the compound of the mould 102.

Once the mould has been filled, as depicted by Figure 2 B, the optical element 200 is cured in step 326. The curing may be executed as indicated above for the mould, by using electromagnetic waves having different wavelengths, by supplying or withdrawing thermal energy, by providing certain substances - oxygen, nitrogen, water, other or a combination thereof - by other means or a combination thereof.

After curing the optical element 200, the optical element 200 is separated from the mould 102 or the compound mould comprising the mould 102, the further mould 102' and the washer 108 in step 328. For separating the mould 102 and the optical element 200, the mould 102 is preferably brought at a temperature above the glass-transition temperature of the substance forming the mould 102, yet below the glass-transition temperature of the substance forming the optical element. In another implementation, the mould 102 is preferably brought at a temperature above the glass-transition temperature of the substance forming the mould 102, yet below the melting point of the substance forming the optical element. The separation yields the optical element as depicted by Figure 2 C or Figure 2 E.

The description above may be, without limitations, be summarised by means of the following examples:

1. Mould for casting an optical element, comprising at least a first mould part comprising a cavity having a shape complementary to an intended shape of at least part of the optical element; Wherein the first mould part predominantly comprises a mould compound having a mould glass transition temperature lower than an optics melting point of an optics compound predominantly to be comprised by the optical element.

2. Mould according to example 1, wherein the optics melting point is at least 5°C, preferably 10°C, more preferably 20°C higher than the mould compound glass-transition temperature.

3. Mould according to example 1 or example 2, wherein the optics melting point is determined after curing of the optics compound.

4. Mould according to any of the preceding examples, wherein the mould glass transition temperature is lower than an optics glass transition temperature of the optics compound.

5. Mould according to example 4, wherein the optics glass transition temperature is at least 5°C, preferably 10°C, more preferably 20°C higher than the mould glass-transition temperature.

6. Mould according to example 4 or example 5, wherein the optics melting point is determined after curing of the optics compound.

7. Method of manufacturing of a mould part of a mould for casting of an optical element, the method comprising: - Receiving manufacturing data suitable for controlling a Liquid dispensing system; - Providing a liquid mould dispensing material having, after curing, a glass transition temperature lower than a melting point or a glass-transition temperature of the optical element; - Depositing droplets of the mould dispensing material for forming a first layer of the mould part on a substrate using a droplet on demand system; - Curing the first layer of mould dispensing material; - Depositing droplets of the mould dispensing material for forming a second layer of the mould part on top of the first layer using the droplet on demand system; - Curing the second layer of mould dispensing material.

8. Method according to example 7, wherein the substrate comprises a temperature control module arranged to control temperature of the substrate and/or the mould.

9. Method according to example 7 or example 8, wherein the substrate is provided with at least one alignment module provided by a recessed portion of the substrate.

10. Method according to any of the examples 7 to 9, wherein the droplets for forming the first layer form a first pattern complementary to a second pattern of droplets forming the second layer.

11. Method according to any of the examples 7 to 10, further comprising applying a release material to an outer surface of the mould forming a cavity having a shape complementary to an intended shape of the optical element.

12. Method according to example 11. Wherein the release material is applied using the droplet on demand system.

13. Method of manufacturing an optical element, the method comprising: - Providing the mould according to any of the example 1 to 6 or manufactured according to any of the examples 7 to 12; - Controlling temperature of the mould below the mould glass transition temperature; - Providing an optical compound for forming the optical element having a melting temperature higher than the glass transition temperature of the mould material; - Casting the optical compound in the cavity of the mould; - Allowing the optical compound to settle for taking a shape complementary to the shape of the cavity; - Curing of the optical element compound; - Controlling temperature of the mould above the glass transition temperature of the mould compound and below the melting point of the optical compound; - Separating the mould and the optical element.

14. Mould for an optical element manufactured according to the method according to any of the example 7 to 12.

15. Optical element manufactured according to the method of example 13.

In the description above, it will be understood that when an element such as layer, region or substrate is referred to as being “on” or “onto” another element, the element is either directly on the other element, or intervening elements may also be present. Also, it will be understood that the values given in the description above, are given by way of example and that other values may be possible and/or may be strived for.

Furthermore, the invention may also be embodied with less components than provided in the embodiments described here, wherein one component carries out multiple functions. Just as well may the invention be embodied using more elements than depicted in the Figures, wherein functions carried out by one component in the embodiment provided are distributed over multiple components.

It is to be noted that the figures are only schematic representations of embodiments of the invention that are given by way of non-limiting examples. For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. The word ‘comprising’ does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words 'a' and 'an' shall not be construed as limited to 'only one’, but instead are used to mean 'at least one’, and do not exclude a plurality.

Claims

Conclusions

A mold for casting an optical element, comprising at least a first mold portion having a cavity in a shape complementary to the intended shape of at least a portion of the optical element; In which the first mold half mainly comprises a mold material composition having a glass transition temperature lower than the melting point of an optical material composition which is mainly comprised by the optical component.

A mold according to claim 1, where the optical melting point is at least 5 degrees Celsius, preferably 10 degrees Celsius, more preferably 20 degrees Celsius higher than the glass transition temperature of the mold material composition.

Mold according to claim 1 or 2, wherein the optical melting point is determined after curing of the optical material composition.

A mold according to any one of the preceding claims, wherein the mold glass transition temperature is lower than an optical glass transition temperature of the optical material composition.

Mold according to claim 4, where the optical glass transition temperature is at least 5 degrees Celsius, preferably 10 degrees Celsius, more preferably 20 degrees Celsius higher than the mold glass transition temperature.

A mold according to claim 4 or claim 5 wherein the optical melting point is determined after curing the optical material composition.

A method for manufacturing a mold part of a mold for casting an optical element, the method comprising: - receiving manufacturing data suitable for controlling a liquid dispensing system; - provided with a liquid mold-dispensable material having, after curing, a glass transition temperature lower than a melting point or glass transition temperature of an optical element; depositing droplets of the mold-dispensable material to form the first layer of the mold part on a substrate using the droplet on demand system; - curing of the first layer of the dispensed material; depositing droplets of the mold-dispensable material to form the second layer of the mold part on the first layer using the droplet on demand system; - curing of the second layer of the dispensed material.

The method of claim 7, wherein the substrate comprises a temperature control module that can control the temperature of the substrate and / or the mold.

The method of claim 7 or claim 8, wherein the substrate includes at least one alignment module through a recessed portion of the substrate.

A method according to any one of claims 7 to 9, wherein the droplets form a pattern complementary to a second pattern forming the second layer to form the first layer.

A method according to any one of claims 7 to 10, including applying a release material to one of the outer surfaces of the mold forming cavity with a shape complimenting the intended shape of the optical element.

A method according to claim 11 wherein the release material is applied via a droplet on demand system.

A method of manufacturing an optical element, the method comprising: - provided with a mold, according to any one of claims 1 to 6 or manufactured according to claims 7 to 12; - controlling the temperature of the mold below the glass transition temperature; - provided with an optical material composition for forming the optical element with a melting temperature higher than the glass transition temperature of the mold material; pouring the optical material composition into the cavity of the mold; - allowing the optical material composition to assume a shape complementary to the shape of the cavity; - curing the optical material composition; - controlling the temperature of the mold above the glass transition temperature of the mold material composition and below the melting point of the optical material composition; and - separating the mold and the optical element.

A mold for an optical element manufactured according to the method defined in any one of claims 7 to 12.

Optical element manufactured according to the method of claim

13.