Insert for injection-molding of an ophthalmic lens and manufacturing method using the same

Abstract

An insert (10) which is suitable for injection-molding of an ophthalmic lens from a polymer-based material, is modified for the ophthalmic lens to be devoid of weld line and optical distortions. Part of the insert is comprised of a metal foam or metal alloy foam (13; 13') having a thermal conductivity of less than 20 W∙m-1 ∙K-1. The insert may be provided with a surface pattern suitable for generating a microstructure in an optical surface of the ophthalmic lens. The microstructure may comprise a set of separated bulges (24) each forming a convex optical surface portion of a positive microlens included in the optical surface of the ophthalmic lens. In this way, the ophthalmic lens has a myopia control function, additionally to compensating for a myopia of a wearer of the ophthalmic lens.

Description

[0001] INSERT FOR INJECTION-MOLDING OF AN OPHTHALMIC LENS AND MANUFACTURING METHOD USING THE SAME

[0002] The invention relates to an insert suitable for injection-molding of an ophthalmic lens, and to a manufacturing method using such insert.

[0003] - BACKGROUND OF THE INVENTION -

[0004] Injection-molding is commonly used for manufacturing ophthalmic lenses, including eyeglasses and contact lenses. Such process implements limiting a mold cavity between two inserts which define opposed optical surfaces of an ophthalmic lens to be manufactured, and injecting a melt polymer-based material into the cavity for forming the ophthalmic lens. However, at least three issues arise when manufacturing ophthalmic lenses in this way.

[0005] A first issue relates to progression of a front edge of the melt material penetrating into the mold cavity until complete filling. Indeed, parts of the mold cavity where it is thinner exhibit higher flow resistance for the melt material, so that the front edge of the melt material slows down from such parts whereas it moves with higher speed elsewhere in the mold cavity. For a minus ophthalmic lens being manufactured, the location with smallest thickness is at the center of the mold cavity, such that the melt material splits before reaching the drain gate of the mold, curls from the cavity center and meets at the end, thus forming a weld line. Such weld line results in an optical defect for the final ophthalmic lens product.

[0006] A second issue relates to optical distortions existing in the final ophthalmic lens product, due to uneven cooling speed throughout the ophthalmic lens. Indeed, because thermal conductivity of the inserts is higher than that of the melt material which has been injected into the mold cavity, lens parts that are thinnest cool down first, resulting in non-uniform shrinkage of the lens material which produces the optical distortions. A third issue relates to manufacturing of ophthalmic lenses which are provided with microstructures in at least one of their optical surfaces, using injection-molding. Indeed, at least one of the inserts has then to be provided with a surface pattern that corresponds to the desired microstructure, through machining of its insert surface, for example using diamond-turning for accuracy of the obtained surface pattern.

[0007] US 6,576,162 B2 teaches that the preceding first and second issues can be addressed and solved by using an insert material that has low thermal conductivity. To this end, using inserts made of glass material such as borosilicate crown glass has been proposed for yielding ophthalmic lenses free of weld lines.

[0008] But inserts made of glass are not appropriate for producing insert surface patterns such as required for ophthalmic lenses provided with microstructures. Indeed, glass material is prone to severe fatigue when being machined and submitted to rapid temperature time-variations, and breaks after a reduced number of thermal cycles involved for lens mass production.

[0009] Therefore, injection-molded ophthalmic lenses with surface microstructures have been produced by combining a concave insert of stainless steel plated with nickel-phosphorous (NiP) with a convex glass insert. The surface pattern was machined in the NiP-plating of the concave insert. But using a glass insert requires implementing compression-injection to achieve defect-free lenses, and also increases the cycling time to avoid glass breakage.

[0010] Starting from this situation, one object of the present invention consists in providing inserts that solve at least one of the three above-mentioned issues. More specifically, the invention aims at providing inserts that make it possible producing ophthalmic lenses free of weld lines and optical distortions, and that may be provided with surface microstructures.

[0011] Another object of the invention consists in providing such inserts which allow reducing cycling time for successive lens injection cycles.

[0012] - SUMMARY OF THE INVENTION - For meeting at least one of these objects or others, a first aspect of the present invention proposes a new insert suitable for injection-molding of an ophthalmic lens from a polymer-based material. This insert comprises a rigid main portion and a surface defining portion which is connected to the rigid main portion and designed for defining an optical surface of the ophthalmic lens when the material is injected into a mold cavity that is partly bound by the surface defining portion of the insert. At least part of the rigid main portion is comprised of a metal foam or metal alloy foam which has a thermal conductivity of less than 20 W nr1K-1(watt per meter and per Kelvin), preferably less than 10 W m-1K-1.

[0013] Thanks to the low value of the thermal conductivity, as allowed by using the metal foam or metal alloy foam for the at least part of the rigid main portion of the insert, ophthalmic lenses which are free of wedge line and optical distortions can be produced using injection-molding.

[0014] In addition, because the metal foam or metal alloy foam has features similar to those of the involved metal or metal alloy, the insert can withstand rapid temperature time-variations and uneven temperature distributions, so that short cycling time can be implemented for successive lens injection cycles, leading to high production yield values.

[0015] Possibly, the rigid main portion may form at least 80%, preferably more than 90%, of the volume of the insert, whereas the surface defining portion forms the remainder of the insert volume.

[0016] Also possibly, the metal foam or metal alloy foam may form at least 30%, preferably 50%, even more preferably 80%, of the volume of the rigid main portion.

[0017] Furthermore, the surface defining portion of the insert may be provided with a surface pattern suitable for generating a microstructure in the optical surface of the ophthalmic lens when the material is injected into the mold cavity. In particular, such surface pattern may be designed so that the microstructure comprises a set of separated bulges each forming a convex optical surface portion of a positive microlens included in the optical surface of the ophthalmic lens. Such microstructure with convex microlens surface portions suits for obtaining myopia-control lenses. Alternatively, the surface pattern may be designed so that the microstructure comprises a Fresnel structure, for example for reducing a thickness and / or weight of the ophthalmic lens while achieving a high optical power value.

[0018] In various embodiments, the metal foam or metal alloy foam may be based on aluminium (Al), or based on nickel (Ni), or based on titanium (Ti), or based on a titanium-nickel (Ti-Ni) alloy, or based on a titanium-aluminium- nickel (Ti-AI-Ni) alloy, or based on a titanium-aluminium-vanadium (Ti-AI-V) alloy, or based on a blend of several of them.

[0019] In preferred embodiments, the rigid main portion of the insert may further comprise a metal coating or metal alloy coating which covers at least part of the metal foam or metal alloy foam. The surface defining portion may be then a plating which is connected to the metal foam or metal alloy foam through the metal coating or metal alloy coating. Preferably, a thickness of the plating may be between 5 pm (micrometer) and 1 mm (millimeter), preferably between 200 pm and 500 pm. Possibly, the plating may be based on nickelphosphorous (NiP). The metal coating or metal alloy coating is preferably of dense material. In the present description, dense material or dense metal or dense metal alloy means material or metal or metal alloy with porosity of less than 10%-volume.

[0020] Alternatively, the rigid main portion of the insert may comprise a casing composed of a not-foam rigid material, i.e. a dense rigid material, which surrounds the metal foam or metal alloy foam. For example, the not-foam rigid material may be a dense metal material or dense metal alloy material, in particular dense stainless steel. In such case, the part of the rigid main portion that is composed of the metal foam or metal alloy foam may be preferably closer to a useful face of the surface defining portion that matches the optical surface of the ophthalmic lens, compared to a back face of the insert opposite the surface defining portion.

[0021] Possibly, the surface defining portion of the insert may be designed for defining a convex optical surface of the ophthalmic lens. To this end, the surface defining portion of the insert may be concave, corresponding to the optical front surface of the ophthalmic lens being convex.

[0022] A second aspect of the invention proposes a method for manufacturing an ophthalmic lens using injection-molding, which method comprises:

[0023] / 1 / providing an insert according to the first invention aspect;

[0024] 121 using the insert for forming a mold cavity, the mold cavity being partly bound by the surface defining portion of the insert;

[0025] / 3 / injecting a polymer-based material into the mold cavity; and

[0026] / 4 / retrieving the ophthalmic lens after cooling of the polymer-based material contained in the mold cavity.

[0027] Possibly, the ophthalmic lens may be a negative ophthalmic lens, i.e. suitable for compensating for a myopia of a wearer of this ophthalmic lens. Indeed, the invention method allows in particular obtaining negative ophthalmic lenses that are free of weld lines and optical distortions although being thinner at center parts thereof compared to their peripheral parts. More specifically, an optical power value of the ophthalmic lens may be between 0 and -12 diopters, and preferably between -0.25 and -10 diopters, in signed values.

[0028] When the invention method is implemented for manufacturing an eyeglass with diameter of between 50 mm and 100 mm, step / 3 / may be executed at a mold cavity temperature (Tmoid) within 30°C (Celsius) below the glass transition temperature (Tg) of the polymer-based material, that is Tg> Tmoid Tg- 30°C, and preferably within 20°C below Tg, that is Tg> Tmoid Tg- 20°C, and step / 4 / may be executed after the ophthalmic lens sufficiently solidifies to avoid deformation during retrieving thereof.

[0029] - BRIEF DESCRIPTION OF THE DRAWINGS -

[0030] Figure 1 a is a perspective view of an ophthalmic lens to be manufactured using the invention.

[0031] Figure 1 b is a cross-sectional view of the ophthalmic lens of Figure 1 a. Figure 2 is a cross-sectional view of an insert according to a first embodiment of the present invention.

[0032] Figure 3 corresponds to Figure 2 for a second embodiment of the invention.

[0033] Figure 4 illustrates an implementation of an insert according to the invention for injection-manufacturing of an ophthalmic lens according to Figures 1 a and 1 b.

[0034] For clarity sake, element sizes which appear in these figures do not correspond to actual dimensions or dimension ratios. Also, same reference signs which are indicated in different ones of these figures denote identical elements of elements with identical function.

[0035] - DETAILED DESCRIPTION OF THE INVENTION -

[0036] Referring to Figures 1 a and 1 b, an ophthalmic lens 20 suitable for incorporation into an eyeglass equipment has a front optical surface S21, which is convex, and a rear optical surface S22, which is concave. The ophthalmic lens 20 may be a negative lens, i.e. it has a negative optical power value suitable for compensating for a wearer’s myopia. To this end, a curvature of the front optical surface S21 is less than another curvature of the rear optical surface S22. Due to this, a thickness of the ophthalmic lens 20 between both optical surfaces S21 and S22 is less in a center part of the lens compared to its thickness at a peripheral edge E23 of the lens 20. The peripheral edge E23 may be circular and 76 mm in diameter, when the ophthalmic lens 20 is an eyeglass. The ophthalmic lens 20 may be a finished single vision lens, where the shapes of both optical surfaces S21 and S22 are final, i.e. none of these optical surfaces is to be machined between injection-molding and use by the wearer.

[0037] The ophthalmic lens 20 may be comprised of a portion of a transparent polymer-based material, for example polycarbonate-based material, which is bounded by both optical surfaces S21 and S22 with the peripheral edge E23.

[0038] The front optical surface S21 may additionally be provided with separated projecting bulges 24 of several tens to a few hundreds of micrometers in diameter when measured parallel to a base shape of the front optical surface S21. Each bulge 24 forms a convex optical surface portion which acts as a positive microlens included in the front optical surface S21. Curvature of each bulge is higher than that of the base shape of the front optical surface S21 at the location in the bulge. In a known manner, the bulges 24 produce a myopia control efficiency to the wearer of the ophthalmic 20. The bulges 24 may be distributed in the front optical surface S21 along concentric circular tracks or a contiguous formation, as a not-limiting distribution example. Alternatively, the microstructure formed by the bulges 24 may be replaced with a Fresnel structure.

[0039] The insert 10 which is now described is suitable for forming the front optical surface S21 during an injection-molding process implemented for manufacturing the ophthalmic lens 20.

[0040] Referring to Figure 2, the insert 10 has a general shape of a cylinder segment with axis A-A and circular cross-section, and extending parallel to the axis A-A from a back face S12 to a useful face S11. The useful face S11 of the insert 10 has a surface that matches or substantially matches the front optical surface S21 of the ophthalmic lens 20, including the bulges 24 or Fresnel structure if any, but with relief inversion. For example, recesses 25 are provided in the useful face S11, that correspond to the bulges 24 with a one-to-one matching relationship. The recesses 25 are formed in addition to a curved base shape of the useful face S11. The insert 10 comprises a rigid main portion 12 and a surface defining portion 1 1 . The surface defining portion 11 forms the useful face S11 , whereas the rigid main portion 12 forms the back face S12 and may constitute a substrate to the surface defining portion 11 . The rigid main portion 12 and the surface defining portion 1 1 are connected to each other, preferably in a fixed manner, so that the useful face S11 and the back face S12 are oriented oppositely.

[0041] The rigid main portion 12 has a part thereof that is composed of a metal foam or metal alloy foam 13. In a known manner, a metal foam or metal alloy foam is a rigid skeleton of solid metal or solid metal alloy respectively, which defines a porosity structure. The porosity may be of open type or closed type, randomly or periodically distributed, and may form a main part of the total volume of the metal foam or metal alloy foam 13, in particular more than 50%, for example 80%. Processes for producing metal foam elements or metal alloy foam elements are known in the art and described in numerous articles with public access. The metal or metal alloy of the foam 13 and the foam density are selected so that the foam 13 has a thermal conductivity of less than 20 W ITT1K’1, preferably less than 10 W nr1K-1. For example, but not limitedly, the insert 10 may use a foam 13 that is an aluminium alloy 6101 foam having a density of 250 kg / m3and a thermal conductivity less than 4.65 W nr1K’1, or a titanium-nickel alloy foam having a density of 600 kg / m3and a thermal conductivity less than 0.8 W nr1K-1. The thermal conductivity can be finely tuned by changing the density and the porosity morphology of the foam 13.

[0042] In the embodiment of Figure 2, the foam 13 is coated externally with a thin layer of dense metal 14, so that both together form the rigid main portion 12 of the insert 10. Put another way, the layer 14, referred to as coating in the general part of the present description, coats the foam 13 at its peripheral limit on all sides. For example, the metal coating 14 may be a 10 pm-thick nickel layer, whereas the part of the rigid main portion 12 that is composed of the foam 13 may be of between 10 mm and 50 mm in thickness when measured along the axis A-A.

[0043] In the embodiment of Figure 3, the foam now with reference sign 13’ is enclosed within a casing 14’, for example of dense stainless steel, for forming together the rigid main portion 12. In such embodiment, the rigid main portion 12 may be preferably designed so that the foam 13’ is closer to the useful face S11 compared to the back face S12. For example, for measurements along the axis A-A, a thickness of the foam 13’ may be of about 10 mm, that of a front part of the casing 14’ intermediate between the foam 13’ and the useful face S11 may be of about 5 mm, and that of a back part of the casing 14’ intermediate between the foam 13’ and the back face S12 may be of about 15 mm. In embodiments that use a casing 14’, the surface defining portion 1 1 including the useful face S11 may be formed by a surface portion of such casing itself, or by a plating which is adhered to the casing 14’ opposite the back face S12 as shown in Figure 3, for example a NiP-based plating again.

[0044] Generally, the rigid main portion 12 may be plated with a metal or metal alloy that forms the surface defining portion 11 . For example, 300 pm (micrometer) of nickel phosphorous (NiP) may be plated on the coating 14 or casing 14’. The face of the rigid main portion 12 that receives the metal or metal alloy plating may be initially designed so as to roughly match the desired base shape of the useful face Sn. Then, the insert 10 is finely machined, preferably using diamond-turning, for forming first the base shape of the useful face S11 , and then the localized recesses 25 each corresponding to one of the bulges 24.

[0045] Figure 4 illustrates schematically an injection-molding sequence implemented for manufacturing the ophthalmic lens 20. The insert 10 is placed in a mold 100, facing another insert 30 that has a convex useful face S30 for defining the rear optical surface S22 of the lens 20, within a mold enclosure 40. Both inserts 10 and 30 are spaced apart from each other for forming a cavity C between their respective useful faces S11 and S30. The invention improvement to the injection-molding method especially suits ophthalmic lenses that have negative optical power values, for example from -4 diopters to -6 diopters, not limitedly. In such cases, the mold cavity C may be about or less than 2 mm- thick at a center point thereof, and about 7 mm to more than 10 mm in thickness at its circular peripheral limit. The useful face S11 is concave with base curvature radius of about 214 mm for manufacturing a lens with optical power value of -4 diopters and 261 mm for -6 diopters, optionally with the superimposed spherical recesses 25. The useful face S30 is convex and smooth with curvature radius of about 87 mm for -4 diopters and 71 mm for - 6 diopters. The mold enclosure 40 is provided with an injection gate I. A melt transparent polymer-based material, for example polycarbonate-based, is injected into the mold cavity C through the gate I until the mold cavity C is completely full. Injection time may be of about 30 s (second), and respective temperatures of the melt material and of the mold enclosure 40 may be of about 310°C and 138°C. Injection cycling time can be reduced by 21% for the case of -4 diopters and 7% for the case of -6 diopters, in particular thanks to the insert 10 being free of breakage risk as compared to a glass insert. Cooling time for the injected material to cool down and solidify sufficiently to avoid deformation of the ophthalmic lens during retrieval may be of about 230 s for - 4 diopters and about 250 s for -6 diopters. In addition, the ophthalmic lens 20 after recovering from the mold 100 does not exhibit weld line and optical distortions.

[0046] Several invention objects are:

[0047] An insert (10) suitable for injection-molding of an ophthalmic lens

[0048] (20) from a polymer-based material, the insert comprising a rigid main portion

[0049] (12) and a surface defining portion (1 1 ) which is connected to the rigid main portion and designed for defining an optical surface (S21) of the ophthalmic lens when the material is injected into a mold cavity (C) that is partly bound by the surface defining portion of the insert, characterized in that at least part of the rigid main portion (12) is comprised of a metal foam or metal alloy foam (13; 13’) having a thermal conductivity of less than 20 W nr1K-1.

[0050] The insert (10) of object 1 , wherein the thermal conductivity of the metal foam or metal alloy foam (13; 13’) is less than 10 W nr1K’1. The insert (10) of object 1 or 2, wherein the metal foam or metal alloy foam (13; 13’) is based on aluminium, or based on nickel, or based on titanium, or based on a titanium-nickel alloy, or based on a titanium-aluminium- nickel alloy, or based on a titanium-aluminium-vanadium alloy, or based on a blend of several of them.

[0051] The insert (10) of one of the objects 1 to 3, wherein the surface defining portion (1 1 ) of the insert is provided with a surface pattern suitable for generating a microstructure in the optical surface (S21) of the ophthalmic lens (20) when the material is injected into the mold cavity (C). The insert (10) of object 4, wherein the surface pattern is designed so that the microstructure comprises a set of separated bulges (24) each forming a convex optical surface portion of a positive microlens included in the optical surface (S21) of the ophthalmic lens (20), or the microstructure comprises a Fresnel structure.

[0052] The insert (10) of one of the objects 1 to 5, wherein the rigid main portion (12) of the insert further comprises a metal coating or metal alloy coating (14) which covers at least part of the metal foam or metal alloy foam (13), and wherein the surface defining portion (11 ) is a plating connected to said metal foam or metal alloy foam through the metal coating or metal alloy coating.

[0053] The insert (10) of object 6, wherein a thickness of the plating is between 5 pm and 1 mm, preferably between 200 pm and 500 pm.

[0054] The insert (10) of object 6 or 7, wherein the plating is based on nickel-phosphorous.

[0055] The insert (10) of one of the objects 1 to 5, wherein the rigid main portion (12) further comprises a casing (14’) composed of a not-foam rigid material, the casing surrounding the metal foam or metal alloy foam (13’).

[0056] 10: The insert (10) of object 9, wherein the part of the rigid main portion (12) that is composed of the metal foam or metal alloy foam (13’) is preferably closer to a useful face (S11) of the surface defining portion (11 ) that matches the optical surface (S21) of the ophthalmic lens (20), compared to a back face (S12) of the insert opposite the surface defining portion. The insert (10) of one of objects 1 to 10, wherein the surface defining portion (11 ) of said insert is designed for defining a convex optical surface (S21) of the ophthalmic lens (20).

[0057] 12: A method for manufacturing an ophthalmic lens (20) using injection-molding, that comprises: / 1 / providing an insert (10) according to one of the objects 1 to 11 ;

[0058] 121 using the insert (10) for forming a mold cavity (C), where the mold cavity is partly bound by the surface defining portion (11 ) of said insert;

[0059] / 3 / injecting a polymer-based material into the mold cavity (C); and / 4 / retrieving the ophthalmic lens (20) after cooling of the polymer-based material contained in the mold cavity (C).

[0060] Object 13: The method of object 12, wherein the ophthalmic lens (20) is a negative ophthalmic lens.

[0061] Object 14: The method of object 13, wherein an optical power value of the ophthalmic lens (20) is between 0 and -12 diopters, and preferably between - 0.25 and -10 diopters, in signed values.

[0062] Object 15: The method of one of the objects 12 to 14, implemented for manufacturing an eyeglass with diameter of between 50 mm and 100 mm, and wherein step / 3 / is executed at a mold cavity temperature within 30°C below the glass transition temperature of the polymer-based material, and preferably within 20°C below said glass transition temperature, and step / 4 / is executed after the ophthalmic lens sufficiently solidifies to avoid deformation during retrieving of said ophthalmic lens.

Claims

CLAIMS1. An insert (10) suitable for injection-molding of an ophthalmic lens (20) from a polymer-based material, the insert comprising a rigid main portion (12) and a surface defining portion (11 ) which is connected to the rigid main portion and designed for defining an optical surface (S21) of the ophthalmic lens when the material is injected into a mold cavity (C) that is partly bound by the surface defining portion of the insert, wherein at least part of the rigid main portion (12) is comprised of a metal foam or metal alloy foam (13; 13’) having a thermal conductivity of less than 20 W ar1K1, and wherein the rigid main portion (12) of the insert further comprises a metal coating or metal alloy coating (14) which covers at least part of the metal foam or metal alloy foam (13), and wherein the surface defining portion (11 ) is a plating connected to said metal foam or metal alloy foam through the metal coating or metal alloy coating.

2. The insert (10) of claim 1 , wherein the thermal conductivity of the metal foam or metal alloy foam (13; 13’) is less than 10 W nr1K-1.

3. The insert (10) of claim 1 or 2, wherein the metal foam or metal alloy foam (13; 13’) is based on aluminium, or based on nickel, or based on titanium, or based on a titanium-nickel alloy, or based on a titanium-aluminium-nickel alloy, or based on a titanium-aluminium-vanadium alloy, or based on a blend of several of them.

4. The insert (10) of one of the preceding claims, wherein the surface defining portion (11 ) of the insert is provided with a surface pattern suitable for generating a microstructure in the optical surface (S21) of the ophthalmic lens (20) when the material is injected into the mold cavity (C).

5. The insert (10) of claim 4, wherein the surface pattern is designed so that the microstructure comprises a set of separated bulges (24) each forming a convex optical surface portion of a positive microlens included in the opticalsurface (S21) of the ophthalmic lens (20), or the microstructure comprises a Fresnel structure.

6. The insert (10) of one of the preceding claims, wherein a thickness of the plating is between 5 pm and 1 mm, preferably between 200 pm and 500 pm.

7. The insert (10) of claim 6, wherein the plating is based on nickelphosphorous.

8. The insert (10) of one of the preceding claims, wherein the surface defining portion (11 ) of said insert is designed for defining a convex optical surface (S21) of the ophthalmic lens (20).

9. A method for manufacturing an ophthalmic lens (20) using injectionmolding, that comprises: / 1 / providing an insert (10) according to one of the preceding claims;121 using the insert (10) for forming a mold cavity (C), where the mold cavity is partly bound by the surface defining portion (11 ) of said insert; / 3 / injecting a polymer-based material into the mold cavity (C); and / 4 / retrieving the ophthalmic lens (20) after cooling of the polymer-based material contained in the mold cavity (C).

10. The method of claim 9, wherein the ophthalmic lens (20) is a negative ophthalmic lens.

11. The method of claim 10, wherein an optical power value of the ophthalmic lens (20) is between 0 and -12 diopters, and preferably between - 0.25 and -10 diopters, in signed values.

12. The method of one of claims 9 to 11 , implemented for manufacturing an eyeglass with diameter of between 50 mm and 100 mm, and wherein step / 3 / is executed at a mold cavity temperature within 30°C below the glass transition temperature of the polymer-based material, and preferably within20°C below said glass transition temperature, and step / 4 / is executed after the ophthalmic lens sufficiently solidifies to avoid deformation during retrieving of said ophthalmic lens.

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