Injection Overmolding with Heat/Cool Cycling for Making Optical Lenses Using 3D-Printed Functional Wafers

Abstract

Disclosed herein is an injection molding method for making optical thermoplastic lenses using 3D—printed functional wafers. The method employs a variable injection molding cavity temperature that is heated to at least wafer Tg—10° C.

Claims

1. A method for producing an optical article, the method comprising over-molding an additive manufactured functional wafer having a functional wafer glass transition temperature onto a convex surface of a base lens to produce an ophthalmic lens, wherein the over-molding comprises: affixing the functional wafer to the concave surface of an injection molding cavity; filling the injection molding cavity with molten base lens material; and raising the injection molding cavity temperature from a first temperature to a second temperature that is at least 10° C. less than the functional wafer glass transition temperature, such that T.sub.cavity≥T.sub.g, wafer10° C.

2. The method of claim 1, wherein the over-molding viscoelastically deforms the functional wafer.

3. The method of claim 2, wherein the viscoelastic deformation templates the texture of the concave surface of the mold cavity onto the convex surface of the functional wafer.

4. The method of claim 3, wherein the templating produces an ophthalmic lens with an optically smooth convex surface having a roughness less than 20 nm RMS.

5. The method of claim 1, wherein the additive manufactured functional wafer is wafer of non-optical quality with a surface roughness greater than 50 nm RMS.

6. The method of claim 1, wherein the functional wafer includes at least one UV cut, blue cut, color enhancement, near infrared cut, chronocut, and/or photochromicity dye or filter.

7. The method of claim 1, wherein the functional wafer material is selected from the group consisting of polyamides, polyesters, polyester alloys, polyethylenes, polyethylene terephtalate, polysiloxanes, polyimides, polyurethanes, polypropylenes, polyetheretherketones, polyetherarylketones, perfluoroalkoxys, polychloro-trifluoroethylenes, polyolefins such as cyclo-olefin polymers, polyacrylics, polyacrylates such as polymethylmethacrylate (PMMA), poly(meth)acrylate, polyethyl(meth)acrylate, polybutyl(meth)acrylate, and polyisobutyl(meth)acrylate, polythiourethanes, polycarbonates (PC), ali-cyclic polycarbonates, polyallylics, polyphenylene sulfides, polyvinyls, polyarylenes, polyoxides, polysulfones, fluorinated ethylene propylenes, polytetrafluoroethylenes, ethylene-tetrafluoroethylenes, polyvinylidene fluorides, ethylene-chlorortifluoroethylenes, polystyrenes, polyacrylonitriles, styrene copolymers such as styrene acrylonitrile, styrene methyl methacrylate, styrene butadiene methyl methacrylate, acrylonitrile butadiene styrene, methyl methacrylate acrylonitrile butadiene styrene, and styrene maleic anhydride, polyimides, polyetherimides, polypentenes, cellulose triacetate, and copolymers, derivatives, and mixtures thereof.

8. The method of claim 1, further comprising raising the injection molding cavity molding temperature to at least 5° C. above a functional wafer glass transition temperature.

9. The method of claim 1, wherein the first temperature ranges from room temperature to 10° C. below the functional wafer glass transition temperature.

10. An optical article comprising an ophthalmic lens comprising a base lens and an additive-manufactured functional wafer affixed to the convex surface of the base lens, wherein the ophthalmic lens is produced by injection over-molding a molten base lens material over the additive-manufactured functional wafer and heating the injection molding cavity to a molding temperature at least 10 ° C. less than the functional wafer glass transition temperature, such that T.sub.cavity≥T.sub.g, wafer−10° C.

11. The optical article of claim 10, wherein the injection molding cavity is heated to a molding temperature at least 5° C. more than the functional wafer glass transition temperature.

12. The optical article of claim 10, wherein the functional wafer includes at least one UV cut, blue cut, color enhancement, near infrared cut, chronocut, and/or photochromicity dye or filter.

13. The optical article of claim 10, wherein a functional wafer material is selected from the group consisting of polyamides, polyesters, polyester alloys, polyethylenes, polyethylene terephtalate, polysiloxanes, polyimides, polyurethanes, polypropylenes, polyetheretherketones, polyetherarylketones, perfluoroalkoxys, polychloro-trifluoroethylenes, polyolefins such as cyclo-olefin polymers, polyacrylics, polyacrylates such as polymethylmethacrylate (PMMA), poly(meth)acrylate, polyethyl(meth)acrylate, polybutyl(meth)acrylate, and polyisobutyl(meth)acrylate, polythiourethanes, polycarbonates (PC), ali-cyclic polycarbonates, polyallylics, polyphenylene sulfides, polyvinyls, polyarylenes, polyoxides, polysulfones, fluorinated ethylene propylenes, polytetrafluoroethylenes, ethylene-tetrafluoroethylenes, polyvinylidene fluorides, ethylene-chlorortifluoroethylenes, polystyrenes, polyacrylonitriles, styrene copolymers such as styrene acrylonitrile, styrene methyl methacrylate, styrene butadiene methyl methacrylate, acrylonitrile butadiene styrene, methyl methacrylate acrylonitrile butadiene styrene, and styrene maleic anhydride, polyimides, polyetherimides, polypentenes, cellulose triacetate, and copolymers, derivatives, and mixtures thereof.

14. The optical article of claim 10, wherein the ophthalmic lens comprises a surface roughness less than 20 nm RMS.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0021] FIG. 1 is a schematic of an FDM 3D printing apparatus.

[0022] FIG. 2 is a schematic that depicts a conventional injection over-molding method in which the cavity temperature is maintained below the wafer glass transition temperature.

[0023] FIG. 3 is an illustration that represents an FDM 3D-printed functional wafer. The wafer has rough surfaces that inherently results from the FDM 3D-printing process.

[0024] FIG. 4 is a schematic illustrating an injection over-molding process as disclosed herein. The process includes the step of raising the cavity temperature to at least 10 ° C. below the wafer glass transition temperature

DETAILED DESCRIPTION

[0025] Various features and advantageous details are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments, are given by way of illustration only, and not by way of limitation. Various substitutions, modifications, additions, and/or rearrangements will be apparent to those of ordinary skill in the art from this disclosure.

[0026] In the following description, numerous specific details are provided to provide a thorough understanding of the disclosed embodiments. One of ordinary skill in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0027] A wafer is defined as a structure that possesses particular desired optical attributes, e.g., selective light transmittance, reflectance or absorbance, polarization properties, color, photochromism, electrochromism, and the like. The wafer structure is produced by an additive manufacturing process. The process involves deposition of multiple filament voxels adhered, or otherwise secured, to each other. An optically smooth surface refers to a transparent object surface that has a roughness of less than 20 nm RMS, preferably less than 17 nm RMS. Non-optical quality refers to a transparent object having a surface roughness that is greater than 50 nm RMS.

[0028] As used herein, “inter-diffuse” and derivatives, means movement of at least an ion, molecule, portion of a molecule, or portion of a polymer chain, from the space occupied by one voxel into the space occupied by a juxtaposed, physically contacting, voxel. Inter-diffusion can occur spontaneously or be induced by mechanical, physical, or chemical treatment. For example, a mechanical treatment includes agitation, such as by exposure to ultra-sonic energy, high-frequency vibratory device, etc., which promote mixing at the voxel boundaries. Macro-diffusion is a mechanical method wherein the voxels are blended or “smeared” by table vibrations, especially where such vibrations occur at the time of deposition, resulting in intimate voxel-to-voxel contact. An exemplary physical treatment includes a thermal treatment by exposure to heat, infrared, microwave, etc., radiation. A thermal treatment increases temperature above the glass-liquid transition point (Tg) of the high viscosity domain in the voxels and promotes inter-diffusion. An exemplary chemical treatment includes a chemical reaction between reactive species of composition. The molecular mass of the polymers present in the voxels can be reduced, such as by two-pathway chemistries or reversible reactions, to promote inter-diffusion.

[0029] As used herein, “voxel” means a volume element. A voxel is a distinguishable, geometric shape which is part of a three-dimensional space. The diameter, width, or thickness of a voxel is typically in the range of 0.1 to 500 μm. A voxel includes elongated shapes, such as strands, therefore, the length of a voxel does not necessarily include an upper limit. A voxel length can be 0.1 μm, 100 μm, 0.1 cm, 100 cm, greater than 100 cm, or any length therebetween. “Voxel” can refer to an individual element which, in combination with other voxels, can define a line or a layer or other predetermined shape or pattern within the three-dimensional space. Constituted voxels can be any desired shape, depending on the technology and manufacturing process conditions used. A plurality or collection of adjacent voxels, when arranged, can create or define a line or layer and can constitute an optical element. A particular voxel may be identified by x, y, and z coordinates of a selected point of geometry of the shape, such as a corner, center, or by other means known in the art. The boundary of a voxel is defined by the outer surface of the voxel. Such boundaries may be in close proximity to, with or without contacting.

[0030] As used herein, “Additive Manufacturing” means manufacturing technology as defined in the international standard ASTM 2792-12, describing a process of joining materials to make 3-D solid objects from a 3-D digital model. The process is referred to as “3-D printing” or “materials printing” since successive layers are laid down atop one another. Printing materials include liquids, powders, filaments, and sheet materials, from which series of cross-sectional layers are built. The layers, which correspond to the virtual cross sections from the CAD (Computer Aided Design) model, are joined or automatically fused to create the solid 3-D object. Additive Manufacturing includes, but is not limited to, manufacturing methods such as stereolithography, mask stereolithography, mask projection stereolithography, polymer jetting, scanning laser sintering (SLS), scanning laser melting (SLM), and fused deposition modelling (FDM). Additive Manufacturing technologies comprise processes which create 3-D solid objects by juxtaposition of volume elements or particles according to a pre-determined arrangement, typically defined in a CAD file. Juxtaposition is understood as sequential operations including building one material layer on top of a previously built material layer, and/or positioning a material volume element next to a previously deposited material volume element. The term “part” refers to any part built using a layer-based additive manufacturing technique, and includes 3D parts and support structures built using layer-based additive manufacturing techniques. An exemplary part disclosed herein is a functional wafer.

[0031] The term “polymer” refers to a polymeric material having one or more monomer species, including homopolymers, copolymers, terpolymers, and the like. As used herein, “thermoplastic” is understood to be a polymer resin that can melt when exposed to heat, and preferably is optically clear and of optical grade.

[0032] Fused deposition modeling is the most widely used 3D printing technology for producing thermoplastic parts. An FDM 3D printer (FIG. 1) builds parts by extruding a thermoplastic filament through a heated nozzle. Generally, the filament 12 is fed to extruder 14, which includes heater block 16 and heated nozzle 18. The melted filament is delivered through the heated nozzle 18 onto a printing bed 20. The melted filament is applied on the X-Y plane to produce the first layer. Once first layer is complete, the platform is lowered along the Z-axis direction and a second layer is then printed. The above steps are repeated till the part is manufactured. The hot strands weld to one another to form a solid part.

[0033] FDM is one of the most cost-effective methods for producing custom thermoplastic parts and prototypes. One major disadvantage of FDM 3D printing is its inability to deposit filament at a resolution that is high enough to achieve optical quality. The layering method of FDM results in rough edges on the surface of the 3D-printed part that scatter light and lead to a non-transparent appearance.

[0034] Because 3D printing is more cost-effective for small volumes and quick prototyping tasks, FDM can be used to produce functional wafers from a thermoplastic filament having specific dyes and/or filters. Examples include UV cut, blue cut, NIR cut, color enhancement, chronocut, and photochromic filters. The resulting functional wafer can then be integrated onto the front surface of an ophthalmic lens by injection over-molding process (or film insert molding process).

[0035] Conventional injection over-molding process were examined, however, these failed to produce lenses of optical quality, despite the high heat and pressure provided by the injection molding apparatus. In the conventional injection over-molding process, the entire injection over-molding cycle takes place at a constant cavity temperature (T.sub.cavity) that is substantially lower than the glass transition temperature of the wafer material (T.sub.g, wafer). The glass transition temperature characterizes a second order transition of amorphous polymers from brittle, glassy solids to viscous or rubber-like substances. T.sub.cavity must be lower than T.sub.g, wafer so that the functional wafer holds its shape when being inserted into the cavity. Further, T.sub.cavity must be lower than the glass transition temperature of the lens material (T.sub.g, lens) so the resulting lens is in a solid form that is rigid enough to be ejected without deformation. Most commonly, T.sub.cavity≤T.sub.g, lens−20° C. The wafer and the lens are typically made of the same material in order to provide compatibility between the wafer and the lens for good bonding. In this case, T.sub.g, wafer=T.sub.g, lens.

[0036] The diagram in FIG. 2 represents a conventional injection over-molding process. The injection molding apparatus consists of two mold halves and two opposite facing inserts. The concave and convex insert each reside in a mold half, forming a cavity. In a conventional injection molding process, the cavity temperature T.sub.cavity is maintained at a constant temperature. In step I, the mold is opened to provide access to the insert surfaces. In step II, a functional wafer is inserted. The wafer is affixed to the concave insert surface. In step III, the two mold halves are joined to close the mold and form the injection molding cavity. The cavity space is a template that represents the shape of the lens to be molded. In step IV, molten lens material is injected into the mold cavity, and the molten lens material becomes fuse-bonded to the wafer. In step V, the mold halves are separated and the lens is ejected.

[0037] One reason conventional injection over-molding processes are not able to produce lenses of optical quality using 3D-printed functional wafers is because the convex surface of the wafer is kept at a temperature well below its T.sub.g. The convex surface remains solid throughout the injection over-molding process and retains the surface ridges resulting from voxel deposition (FIG. 3). This problem can be overcome by increasing the cavity temperature to a temperature that is at least 10° C. below the wafer thermoplastic Tg (T.sub.cavity≥T.sub.g.wafer−10° C.), preferably to a temperature that is at least 5° C. above the functional wafer glass transition temperature (T.sub.cavity≥T.sub.g.wafer+5° C.). At these cavity temperature ranges, the wafer material is able to undergo viscoelastic deformation. The wafer material's convex surface undergoes viscoelastic deformation under the high heat and high injection pressure to replicate the surface of the concave insert. A lens manufactured according to the criteria set forth above has an optically smooth front surface, with the wafer's original surface roughness having been reduced.

[0038] The injection over-molding process disclosed herein employs a variable cavity temperature (FIG. 4). The process involves increasing the cavity temperature to a temperature that is at least 10° C. below the wafer thermoplastic Tg, preferably to a temperature that is at least 5° C. above the wafer thermoplastic Tg. At this temperature, the wafer material softens enough to undergo viscoelastic deformation under the high injection pressure to replicate the surface of the concave insert. This results in the production of a wafer-over-molded lens with an optically smooth front surface.

[0039] In the injection over-molding process disclosed herein, the process starts at Step I “Open mold” at time 0, at which the cavity temperature T.sub.cavity(0) is at a temperature substantially lower than T.sub.g, wafer and T.sub.g, lens (T.sub.cavity(0)<T.sub.g, wafer and T.sub.cavity(0)<T.sub.g, lens). In some embodiments, T.sub.cavity(0) ranges from room temperature to 10° C. below the functional wafer glass transition temperature. Heating of the cavity including the 2 mold halves and inserts commences. In Step II, the functional wafer is inserted into the cavity abutting the concave insert. The cavity temperature at this time T.sub.cavity(t) is still substantially lower than T.sub.g, wafer. Heating of the cavity continues and the 2 mold halves close to form the final cavity at Step III. In Step IV, injection of the molten lens materials begins while the cavity is being heated to a temperature that is 10° C. below the glass transition temperature of the wafer material (T.sub.cavity(t)≥T.sub.g, wafer10° C.). After the cavity is completely filled and packed under pressure, heating is discontinued and the temperature begins to drop back to T.sub.cavity(0). In Step V, the mold is opened to eject the solidified lens and the injection over-molding cycle is completed. At this time, the cavity temperature is holding at T.sub.cavity(0). In embodiments where dissimilar wafer and lens materials are used, T.sub.cavity(0) is lower than both T.sub.g, lens and T.sub.g, .sub.wafer to prevent deformation of the resulting lens.

EXAMPLES

Example 1

[0040] Base lens material 1—A UV-stabilized polycarbonate (Sabic Lexan® OQ3820) was employed as the base lens material. This PC resin has a glass transition temperature of 150° C. and a UV-cut at about 380 nm, as measured through a 2 mm thick lens.

[0041] Functional wafer 1—The same polycarbonate used in base lens material 1 was compounded with 1.0% of a UV absorber (Tinuvin® 326) and extruded into 1.75 mm filaments. A 4-base plano wafer, 76 mm in diameter and 1.0 mm in thickness, was FDM 3D-printed using the filaments. 3D-printed functional wafer 1 was non-transparent with a rough surface.

[0042] Functional wafer 1 was applied onto base lens material 1 employing the key parameters listed in Table 1 below.

TABLE-US-00001 TABLE 1 Concave insert Steel, 76 mm, and R132.5 mm Convex insert Steel, 76 mm, and R88.3 mm Lens material Base lens material 1 (PC) Wafer material Functional wafer 1 material (PC + UV absorber) FDM printed wafer 4-base, 76 mm, R132.5 mm, thickness 1 mm geometry T.sub.g, lens 150° C. T.sub.g, wafer 150° C. Melt temperature (T.sub.melt) 260° C. T.sub.cavity(0) at Step I 120° C. T.sub.cavity(t) at end of Step IV 150° C.

[0043] The resulting semi-finished (SF) lens, 10 mm in thickness, was optically transparent with a smooth front surface and exhibited a UV-cut at about 402 nm after surfacing to 2 mm plano. In addition, the blue cut performance BVC B′ was determined to be about 30%.

Example 2

[0044] Base lens material 2—A PMMA resin (Evonik ACRYLITE® hw55) was employed as base lens material 2.

[0045] Functional wafer 2—The same 3D-printed functional wafer as used in Example 1 above. Functional wafer 2 was applied to base lens material 2 using the key parameters listed in Table 2 below.

TABLE-US-00002 TABLE 2 Concave insert Steel, 76 mm, and R132.5 mm Convex insert Steel, 76 mm, and R88.3 mm Lens material Base lens material 2 (PMMA) Wafer material Functional wafer 1 material (PC + UV resin) FDM printed wafer 4-base, 76 mm, R132.5 mm, thickness 1 mm geometry T.sub.g, lens 120° C. T.sub.g, wafer 150° C. Melt temperature (T.sub.melt) 245° C. T.sub.cavity(0) at Step I 100° C. T.sub.cavity(t) at end of Step IV 150° C.

[0046] The resulting 10 mm thick SF lens was optically transparent with a smooth front surface and exhibited a UV-cut at about 402 nm after surfacing to 2 mm plano. The blue cut performance BVC B′ was measured to be about 30%.

[0047] The claims are not to be interpreted as including means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively.