Patent Application
20240316829
The present disclosure relates to a low thermal conductivity mold insert for reducing defects during fabrication of lenses, including lenses having microstructures thereon.
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Glass inserts can be used during injection molding to fabricate lenses that are free of defects, such as “weld line” and “center distortion” defects. Glass inserts are more adept at preventing such defects due to having lower thermal conductivity. This property helps preserve the heat of an injected polymer melt, which then helps “heal” weld line defects by prolonging the cooling of the polymer melt and preventing distortion due to uneven shrinkage.
However, injection molding of lenses can require glass inserts having microlenses on their surface that are difficult to produce on typical glass materials such as borosilicate. That is, forming microstructures on a glass surface can be expensive, difficult to produce, can lead to glass breakage during microstructure engraving, and are easily and often broken during handling, cleaning, and the production of lenses. Moreover, glass inserts break easily during injection molding, which leads significant equipment down time and thus reduces yields and productivity. Therefore, a mold insert that has similar thermal behavior (i.e. low thermal conductivity) to glass while providing a suitable functional surface to withstand the microstructure fabrication process on said surface is desired. The desired mold insert will also be durable and resist breakage during molding processes.
Aspects of the disclosure may address some of the above-described shortcomings in the art, particularly with the solutions set forth in the claims.
The present disclosure relates to a mold insert, including a plurality of microstructures along a surface of the mold insert and a metal alloy, wherein the metal alloy has a thermal conductivity between 1 and 50 W/m-K, and the metal alloy has a modulus of between 100 GPa and 1000 GPa.
The present disclosure additionally relates to a method of forming a mold insert, including coating a bulk portion of the mold insert with a first metal alloy, a material of the bulk portion being a second metal alloy; and machining the first metal alloy to form a functional surface including a plurality of microstructures along a surface of the mold insert and the first metal alloy, wherein the first and the second metal alloys have a thermal conductivity between 1 and 230 W/m-K, and wherein the first and second metal alloys have a modulus of between 100 GPa and 1000 GPa.
Note that this summary section does not specify every feature and/or incrementally novel aspect of the present disclosure or claimed invention. Instead, this summary only provides a preliminary discussion of different embodiments and corresponding points of novelty. For additional details and/or possible perspectives of the embodiments, the reader is directed to the Detailed Description section and corresponding figures of the present disclosure as further discussed below.
Various embodiments of this disclosure that are proposed as examples will be described in detail with reference to the following figures, wherein:
The following disclosure provides many different variations, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting nor inoperable together in any permutation. Unless indicated otherwise, the features and embodiments described herein are operable together in any permutation. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Further, spatially relative terms, such as “top,” “bottom,” “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. Inventive apparatuses may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.
The order of discussion of the different steps as described herein has been presented for clarity sake. In general, these steps can be performed in any suitable order. Additionally, although each of the different features, techniques, configurations, etc. herein may be discussed in different places of this disclosure, it is intended that each of the concepts can be executed independently of each other or in combination with each other. Accordingly, the present disclosure can be embodied and viewed in many different ways.
As previously mentioned, weld line and center distortion defects can occur during the molding process for lenses due to the increased cooling of an injected polymer melt. In general, weld lines can be formed during injection when an advancing polymer melt front meets another melt front, which can originate from filling a cavity of the mold from multiple gates. As such, this can lead to head-on impingement of separate flow fronts of the polymer melt, or splitting and converging of flow fronts due to presence of obstacles or excess transversal part thickness variation.
To this end,
In brief, a mold cavity for injection molding of a lens is formed by two opposite faced inserts. For example, one concave mold insert and one convex mold insert can be used. To address the weld line issue, inserts made of crown glass or other materials having a thermal diffusivity a that satisfies 1≤α/αg<11, where αg is the thermal diffusivity of a borosilicate crown glass being equal to 6.20E-7 m2/s can be used in conjunction with an injection-compression process. This was described in Essilor U.S. Pat. No. 6,576,162, incorporated herein by reference in its entirety.
In a useful scope, an injection-compression molding process can be characterized by forming the mold cavity having an initial opening that is larger than a desired part thickness at the beginning of an injection cycle. This enlarged cavity thickness can reduce the flow resistance of the injected polymer melt and thus the pressure requirement of filling the cavity. Subsequently, the mold cavity opening would close down through movement of the mold inserts and/or mold plates to the final desired part thickness before the end of injection phase. The injection speed, initial opening of the cavity, closing speed, and closing pressure, however, can be carefully determined not only to control the movement of the flow front to avoid weld line defects, but also to achieve good optics.
Notably, in a useful scope, the functional surface 105 can be formed of a first material, and the bulk portion 110 can be formed of a second material different from the first material. For example, the first material of the functional surface 105 can be a first metal alloy, and the second material of the bulk portion 110 can be a second metal alloy. The first material and the second material can have a thermal conductivity between 1 and 100 W/m-K, or between 1 and 50 W/m-K, or preferably between 5 and 12 W/m-K. The first material and the second material can have a modulus of, for example, between 10 and 2000 GPa, or between 50 and 1500 GPa, or preferably between 100 and 1000 GPa. The first material and the second material can have thermal diffusivity of, for example, less than or equal to 3.1E-6.
In a useful scope, the second material of the bulk portion 110 is titanium alloy Ti-Al6-V4 in place of stainless steel, then plated with NiP as the first material of the functional surface 105, followed by diamond turning of the plurality of microstructures 115 to make inserts for injection molding of defect free minus lenses. Plating of the NiP first material before diamond turning can facilitate achieving more defect-free mold insert surfaces of optical finish and to improve the scratch resistance of the first mold insert 198 for better durability. In addition, the thermal conductivity of NiP is lower than most metals and alloys, thus plating of the NiP reduces the overall thermal diffusivity of the first mold insert 198 and enhances its ability to achieve defect-free lenses. It is preferred to have the NiP plating thickness >=5 μm, more preferably >=100 μm, and most preferably >=300 μm not only to have enough thickness for re-fabrication of the plurality of microstructures 115 and the functional surface 105 if needed, but also to have extra thermal effects in preventing the formation of weld lines and center distortion defects. Other non-limiting examples of metals and metal alloys for the first material and the second material include stainless steel, nickel alloy hastelloy r-235, nickel alloy (hot rolled or forged), titanium, titanium alloy (Ti, Al6, V4), titanium alloy (Ti, Al8, Mo, V1), titanium alloy (Ti, Al4, V4, Cr10), and titanium alloy (Ti, Al2, Sn11, Zr5), among others.
The plurality of microstructures 115 can be used to mold, for example, refractive micro-structures or diffractive micro/nano-structures. The plurality of microstructures 115 can be an inversion of a desired final pattern be formed on the resulting lens after molding. The plurality of microstructures 115 can include microlenses or microlenslets or any other type of structure or elements having physical Z deformation/height or depth between 0.1 μm to 50 μm and width/length between 0.5 μm to 1.5 mm. These structures preferably have periodical or pseudo periodical layout, but may also have randomized positions. The preferred layout for microstructures is a grid with constant grid step, honeycomb layout, multiple concentric rings, contiguous e.g. no space in between microstructures. These structures may provide optical wave front modification in intensity, curvature, or light deviation, where the intensity of wave front is configured such that structures may be absorptive and may locally absorb wave front intensity with a range from 0% to 100%, where the curvature is configured such that the structure may locally modify wave front curvature with a range of +/−20 Diopters, and light deviation is configured such that the structure may locally scatter light with angle ranging from +/−1° to +/−30°. A distance between structures may range from 0 (contiguous) to 3 times the structure in “X” and/or “Y” size (separate microstructures).
In the sense of the disclosure, two optical elements located on a surface of a lens substrate are contiguous if there is a path supported by said surface that links the two optical elements and if along said path one does not reach the basis surface on which the optical elements are located. According to another scope, the optical elements are contiguous over a pupil when the optical lens over said pupil comprises no refraction area having a refractive power based on a prescription for said eye of the wearer or a refraction area having a refractive power based on a prescription for said eye of the wearer consisting in a plurality of respectively independent island-shaped areas. According to another scope, the two optical elements are contiguous if there is a path linking the two optical elements along part of said path one may not measure the refractive power based on a prescription for the eye of the person. According to another scope, optical elements being contiguous can also be defined in a surfacic or surface-oriented manner. A measured surface being between 3 mm2 and 10 mm2 is considered. The measured surface comprises a density of “W” optical elements per mm2. If in said measured surface, at least 95% of the surface, preferably 98%, has an optical power different from the surface onto which the optical elements are located, said optical elements are considered to be contiguous.
Furthermore, microstructures which form a microstructured main surface of an ophthalmic lens substrate may include lenslets. Lenslets may form bumps and/or cavities (i.e., raised or recessed lenslet structures) at the main surface they are arranged onto. The outline of the lenslets may be round or polygonal, for example hexagonal. More particularly, lenslets may be microlenses. A microlens may be spherical, toric, cylindrical, prismatic, or aspherical shapes or any combination to make a multi-element shape. A microlens may have a single focus point, or cylindrical power, or multi-focal power, or non-focusing point. Microlenses can be used to prevent progression of myopia or hyperopia. In that case, the base lens substrate comprises a base lens providing an optical power for correcting myopia or hyperopia, and the microlenses may provide respectively an optical power greater than the optical power of the base lens if the wearer has myopia, or an optical power lower than the optical power of the base lens if the wearer has hyperopia. Lenslets may also be Fresnel structures, diffractive structures such as microlenses defining each a Fresnel structure, permanent technical bumps (raised structures), or phase-shifting elements. It can also be a refractive optical element such as microprisms and a light-diffusing optical element such as small protuberances or cavities, or any type of element generating roughness on the substrate. It can also be π-Fresnel lenslets as described in US2021109379, i.e. Fresnel lenslets which phase function has π phase jumps at the nominal wavelength, as opposition to unifocal Fresnel lenses which phase jumps are multiple values of 2π. Such lenslets include structures that have a discontinuous shape. In other words, the shape of such structures may be described by an altitude function, in terms of distance from the base level of the main surface of the optical lens the lenslet belongs to, which exhibits a discontinuity, or which derivative exhibits a discontinuity. In a useful scope, the microstructure can be a branding mark, holographic mark, metasurface, or the like.
Lenslets may have a contour shape being inscribable in a circle having a diameter greater than or equal to 0.5 micrometers (μm) and smaller than or equal to 1.5 millimeters (mm). Lenslets may have a height, measured in a direction perpendicular to the main surface they are arranged onto, that is greater than or equal to 0.1 μm and less than or equal to 50 μm. Lenslets may have periodical or pseudo periodical layout but may also have randomized positions. One layout for lenslets is a grid with constant grid step, honeycomb layout, multiple concentric rings, contiguous e.g. no space in between microstructures. These structures may provide optical wave front modification in intensity, curvature, or light deviation, where the intensity of wave front is configured such that structures may be absorptive and may locally absorb wave front intensity with a range from 0% to 100%, where the curvature is configured such that the structure may locally modify wave front curvature with a range of +/−20, 500, or 1000 Diopters, and light deviation is configured such that the structure may locally scatter light with angle ranging from +/−1° to +/−30°. A distance between structures may range from 0 (contiguous) to 3 times the structure (separate microstructures).
The cavity can be connected to a hollow line formed by the coupling of the first and second mold sides 101, 102. The line can be configured to receive a polymer melt, for example, via a screw feeder or similar polymer injector device. The polymer injector can be attached to the mold device and configured to inject the polymer melt into the cavity when the first mold side 101 is coupled with the second mold side 102 to form a resulting lens from the polymer melt with surface features based on the plurality of microstructures 115 and a surface of the second mold insert 199 facing the cavity. For a semi-finished lens, a curvature along a convex side of the lens is fixed and the concave side of the lens can be modified after molding, for example via grinding and polishing. Note that multiple lines for receiving the polymer melt can be connected, such that an injection of the polymer from a source can fill multiple mold devices with a single injection and allow for parallel fabrication of multiple lenses.
As previously described, for a non-straight injection molding process, the first mold insert 198 and the second mold insert 199 can further adjust their displacement even after coupling and after the polymer melt is injected. For example, the first mold insert 198 and the second mold insert 199 can move closer together after the polymer melt is injected to compress the polymer melt before the polymer melt fully cools. The resulting lens can be removed upon uncoupling of the first mold side 101 and the second mold side 102.
Example 1-Injection molding experiments of producing minus lenses was conducted using NiP plated titanium alloy (Ti-Al6-V4) first mold inserts 198 on an injection-molding machine equipped with a 4-cavity injection-compression (V/C) mold using a Sabic Lexan polycarbonate resin.
The thickness of the NiP plating of the functional surface 105 on the first mold inserts 198 was approximately 300 μm. Tables I and II are the corresponding processing settings for −6.00 and −4.00 Diopter lenses, respectively. The conditions were set in accordance with those typically used for glass mold inserts except the injection velocity and the cooling time. As titanium alloy inserts can withstand much higher injection pressure than glass inserts, PC melt can be injected into the mold cavities at a higher speed. Further, the required cooling time for titanium alloy inserts was significantly shorter due to their better thermal conductivity than glass.
Based on the aforementioned processing conditions, the actual cycle time for molding −6.00 Diopter lenses with the titanium alloy as the second material in the bulk portion 110 of the first mold inserts 198 was 235 seconds, which demonstrated a 17% reduction in time compared with 284 seconds for glass first mold inserts 198. Furthermore, the cycle time for molding −4.00 Diopter lenses was reduced by 21%, from 266 seconds for glass first mold inserts 198 to 210 seconds with the titanium alloy as the second material in the bulk portion 110 of the first mold inserts 198. All of the resulting lenses were coated with a hard coating and inspected; all lenses were observed to be free of weld line and center distortion defects, and the through-powers and μ-lens global average powers were within manufacturing specifications.
In the preceding description, specific details have been set forth, such as a particular geometry of a processing system and descriptions of various components and processes used therein. It should be understood, however, that techniques herein may be practiced in other embodiments that depart from these specific details, and that such details are for purposes of explanation and not limitation. Embodiments disclosed herein have been described with reference to the accompanying drawings. Similarly, for purposes of explanation, specific numbers, materials, and configurations have been set forth in order to provide a thorough understanding. Nevertheless, embodiments may be practiced without such specific details. Components having substantially the same functional constructions are denoted by like reference characters, and thus any redundant descriptions may be omitted.
Various techniques have been described as multiple discrete operations to assist in understanding the various embodiments. The order of description should not be construed as to imply that these operations are necessarily order dependent. Indeed, these operations need not be performed in the order of presentation. Operations described may be performed in a different order than specifically described unless expressly indicated otherwise. Various additional operations may be performed and/or described operations may be omitted.
Those skilled in the art will also understand that there can be many variations made to the operations of the techniques explained above while still achieving the same objectives of the disclosure. Such variations are intended to be covered by the scope of this disclosure. As such, the foregoing descriptions of embodiments are not intended to be limiting. Rather, any limitations to embodiments are presented in the following claims.
Embodiments of the present disclosure may also be as set forth in the following parentheticals.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21306021.3 | Jul 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/070049 | 7/18/2022 | WO |
