FDM 3D Printing of Optical Lens with High Clarity and Mechanical Strength

Abstract

The disclosure includes core-shell filament composition for additive manufacturing of ophthalmic lenses and ophthalmic lens components. The disclosure also includes a set of criteria for selecting core and shell thermoplastic combinations that exhibit high optical clarity, improved filament inter-strand diffusion, high inter-strand adhesion, and improved manufactured part strength when used in an additive manufacturing method like fused deposition modelling.

Claims

1. A core-shell filament for use in additive manufacturing of an ophthalmic lens, the core-shell filament comprising: an elongated core formed of a first thermoplastic material having a first refractive index; and a shell around the elongated core, wherein the shell is formed of a second thermoplastic material having a second refractive index; wherein the difference between the first refractive index and the second refractive index is equal to or less than 0.1.

2. The core-shell filament of claim 1, wherein adhesion between the first and second thermoplastic materials is at least 100 g/25 mm.

3. The core-shell filament of claim 1, wherein at least one of the first thermoplastic material and second thermoplastic material further comprises at least one or more of a flow improver, a near infra-red absorber, a plasticizer, and a compatibilizer.

4. The core-shell filament of claim 1, wherein the first thermoplastic material has a glass transition temperature that is within 100° C. of the second thermoplastic material glass transition temperature.

5. The core-shell filament of claim 1, wherein the first thermoplastic material has a flexural modulus that is within 3,000 MPa of the second thermoplastic material flexural modulus.

6. The core-shell filament of claim 1, wherein the core has a diameter ranging from 0.05 mm to 3.0 mm.

7. The core-shell filament of claim 1, wherein the shell has a thickness ranging from 0.05 mm to 3.0 mm.

8. The core-shell filament of claim 1, wherein the first thermoplastic material and the second thermoplastic material are each independently selected from the group consisting of polycarbonate, thermoplastic urethane, polyacrylate, polyester, copolyester, polymethacrylate, polystyrene, polyamide, polysulfone, polyphenylsulfone, polyetherimide, polypentene, polyolefin, ionomer, ethylene methacrylic acid, cyclic olefin copolymer, acrylonitrile, styrene maleic anhydride, a copolymer thereof, or a derivative or mixture thereof.

9. An additive manufacturing method for fabricating an ophthalmic lens comprising: feeding a first thermoplastic material having a first refractive index to a co-extrusion die; feeding a second thermoplastic material having a second refractive index to a co-extrusion die; co-extruding the first and second thermoplastic materials to produce a core-shell filament; and building up multiple voxels of co-extruded core-shell filament to fabricate the ophthalmic lens; wherein a difference between the first refractive index and the second refractive index is equal to or less than 0.1.

10. The method of claim 9, wherein the co-extruded core-shell filament comprises an elongated core formed of the first thermoplastic material and a shell around the elongated core formed of the second thermoplastic material.

11. The method of claim 9, wherein the first thermoplastic material has a glass transition temperature that is within 100° C. of the second thermoplastic material glass transition temperature.

12. The method of claim 9, wherein the first thermoplastic material has a flexural modulus that is within 3,000 MPa of the second thermoplastic material flexural modulus.

13. The method of claim 9, wherein at least one of the first thermoplastic material and the second thermoplastic material further comprises at least one of a flow improver, a near infra-red absorber, a plasticizer, and a compatibilizer.

14. The method of claim 9, wherein adhesion between deposited filament voxels is at least 100 g/25 mm.

15. An optical article comprising an ophthalmic lens obtained by the manufacturing method of claim 10.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0024] FIG. 1 is an illustration depicting a core-shell filament co-extrusion apparatus and process.

[0025] FIG. 2 is a diagram depicting an FDM 3D-printing apparatus and process.

DETAILED DESCRIPTION

[0026] 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.

[0027] 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.

[0028] “Ophthalmic lens,” according to the disclosure, is defined as a lens adapted, namely for mounting in eyeglasses, whose function is to protect the eye and/or to correct vision. This lens can be an afocal, unifocal, bifocal, trifocal, or progressive lens. The ophthalmic lens may be corrective or un-corrective. Eyeglasses wherein ophthalmic lenses will be mounted could be either a traditional frame comprising two distinctive ophthalmic lenses, one for the right eye and one for the left eye, or like mask, visor, helmet sight or goggle, wherein one ophthalmic lens faces simultaneously the right and the left eyes. Ophthalmic lenses may be produced with traditional geometry as a circle or may be produced to be fitted to an intended frame.

[0029] Ophthalmic lenses manufactured in accordance with any of the methods of the invention can furthermore be functionalized, in a further step of optionally post-treating the lens, by adding at least a functional coating and/or a functional film. Functionalities may be added on one face of the ophthalmic lens, or on both faces of the ophthalmic lens, and on each face, the functionalities may be identical or different. The functionality can be, but is not limited to, impact-resistance, anti-abrasion, anti-soiling, anti-static, anti-reflective, anti-fog, anti-rain, self-healing, polarization, tint, photochromic, and selective wavelength filter which could be obtained through an absorption filter or reflective filter. Such selective wavelength filters are particularly useful for filtering ultra-violet radiation, blue light radiation, or infra-red radiation, for example. The functionality may be added by at least one process selected from dip-coating, spin-coating, spray-coating, vacuum deposition, transfer processes, or lamination processes. By transfer process it is understood that functionality is firstly constituted on a support like a carrier, and then is transferred from the carrier to the ophthalmic lens through an adhesive layer constituted between the two elements. Lamination is defined as obtaining a permanent contact between a film which comprises at least one functionality as disclosed herein and the surface of the ophthalmic lens to be treated, the permanent contact being obtained by the establishment of a contact between said film and the lens, followed optionally by a polymerization step or a heating step, in order to finalize the adhesion and adherence between the two entities. At the end of this lamination process the assembled film and the optical lens form one single entity. During the lamination process, an adhesive is used to laminate the interface of the film and the ophthalmic lens.

[0030] 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.

[0031] The terms “core” and “shell” of a filament refer to relative locations of the portions along a cross-section of the filament that is orthogonal to a longitudinal length of the filament, where the core portion is an inner portion relative to the shell portion. Unless otherwise stated, these terms are not intended to imply any further limitations on the cross-sectional characteristics of the portions. The composite filament core may have a diameter ranging from 0.05 mm to 3.0 mm, or more particularly may be 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 1.5, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.55, 2.6, 2.65, 2.7, 2.75, 2.8, 2.85, 2.9, 2.95, 3.0, and all diameters therein. The composite filament shell may have a thickness ranging from 0.05 mm to 3.0 mm, or more particularly may be 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 1.5, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.55, 2.6, 2.65, 2.7, 2.75, 2.8, 2.85, 2.9, 2.95, 3.0, and all thicknesses therein. The composite filament diameter ranges in size from 0.15 mm to 9.0 mm.

[0032] 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, and sheet materials, from which series of cross-sectional layers are built. The layers, which correspond to the virtual cross sections from the CAD 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 (Computer Aided Design) 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. Exemplary parts include, but are not limited to, wafers and lenses.

[0033] As used herein, “voxel” means a volume element. A voxel is a distinguishable, geometric shape which is part of a three-dimensional space. The size of a voxel is typically in the range of 0.1 to 500 μm for one dimension. “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.

[0034] 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.

[0035] 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, infra-red, 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.

[0036] It is an object of the present disclosure to provide a composite core-shell filament material for additive manufacturing optical lenses having high clarity and mechanical strength. In some embodiments, the additive manufacturing method is fused deposition modeling. The composite core-shell filament material improves inter-diffusion and adhesion between deposited filament layers. The composite filament includes a core thermoplastic and a shell thermoplastic having refractive indices that are within 0.1 of each other. The core and shell thermoplastics are selected based on their refractive indices, and optional selection criteria, including glass transition temperature, flexural modulus, compatibility, and thermoplastic functional group. The resulting improvements in diffusability, inter-layer adhesion, and light propagation make the composite core-shell filaments disclosed herein attractive building blocks for fused deposition modeling.

[0037] In general, the compatibility between thermoplastic (polymer) phases determines the properties of a heterogeneous polymer blend. The interface between the polymer phases in a polymer system is characterized by the interfacial tension. If there are strong interactions between the phases then the polymer blend will be miscible in nature. Polymer molecular mass, architecture (degrees of branching), and the chemical nature of side chains contribute to compatibility between different polymers. Existing methods known to those of skill in the art may be used to predict or calculate polymer compatibility. For example, Polymer Science Series A, March 2015, Volume 57, Issue 2, pages 186-199 describes methods for assessing polymer compatibility. The methods include, but are not limited to, rheological measurements, nuclear magnetic resonance (NMR) spectroscopy, transmission electron microscopy (TEM), and small angle scattering.

Examples

Core-Shell Structured Filament Extrusion Process

[0038] The filament extrusion apparatus and process is shown in FIG. 1. Core thermoplastic is loaded into hopper A 2 and a shell thermoplastic loaded into a hopper B 4. The core thermoplastic hopper feeds a core material extruder 10 and the shell thermoplastic hopper feeds a shell material extruder 12. In each extruder, the respective thermoplastic material travels through multiple extrusion and/or temperature zones. Upon exiting the extruder, the extruded thermoplastic are passed through melt pumps 6 and 8. The core thermoplastic 18 and shell thermoplastic 16 are then passed through spinning head 14 to produce composite core-shell filament 20. The composite core-shell filament is wound up and collected by winder 22. The filament diameter can be adjusted by adjusting the melt pump volume flowrate and winding speed ratio. The core diameter and shell thickness may each be independently varied by adjusting the respective thermoplastic extrusion rate.

[0039] FDM 3D Printing Process

[0040] An exemplary FDM 3D-printing process is shown in FIG. 2. A 3D computer-aided design (CAD) model is converted into standard triangulation language (STL) format. This is followed by virtually slicing the virtual part into thin horizontal layers, which are approximately 100 μm height along the Z-axis (vertical). The FDM apparatus then takes the STL virtual part instructions and builds up a part by adding filament that corresponds to the virtual layers. Generally, the filament 24 is fed to extruder 26, which includes heater block 28 and heated nozzle 30. The melted filament is delivered through the heated nozzle 30 onto a printing bed 32. 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.

[0041] The examples included in the tables below examine various filamentous combinations of core and shell thermoplastics. The examples included in Tables 5 and 6 include one or more additives. Abbreviations: polycarbonate=PC; thermoplastic urethane=TPU; polyamide=PA. Core and shell combinations are not limited to the combinations disclosed below. As discussed above, the c ore and shell combination selection criteria include a refractive index difference of 0.1 or less, and optionally, additional criteria including Tg, flexural modulus, and polymer compatibility. These parameters are included in the tables below, along with observations and results.

TABLE-US-00001 TABLE 1 Example 1: PC/TPU Flexural TP Grade RI Tg Modulus Observations/results Core PC Sabic Lexan 1.59 150° C. 2350 MPa 1. Matched RI between core OQ3820 and shell. Shell TPU Lubrizol 1.60  90° C. 2206 MPa 2. PC and TPU exhibit good VSN 2000 compatibility. 3. TPU shell layers could be easily diffused due to low Tg and adhered together due to —NH—COO— functional groups.

TABLE-US-00002 TABLE 2 Example 2: PC/PA TP Grade RI Tg Observations/results Core PC Sabic Lexan 1.59 150° C. 1. Matched RI between core OQ3820 and shell. Shell PA Evonik 1.59 130° C. 2. PC and PA has good com- Trogamid patibility. A4100 3. PA shell could be easily diffused due its lower Tg and better adhered due to —NH—CO— functional groups.

TABLE-US-00003 TABLE 3 Example 3: PC/Copolyester Modulus TP Grade RI Tg (Flexural) Observations/results Core PC Sabic Lexan 1.59 150° C. 2350 MPa 1. Matched RI between core OQ3820 and shell. Shell Copolyester Eastman Tritan 1.57 103° C. 1575 MPa 2. PC and copolyester exhibit VX351 HF good compatibility. 3. Copolyester shell could be diffused easily due to low Tg and modulus.

TABLE-US-00004 TABLE 4 Example 4: PC/PC TP Grade RI MFI* Observations/results Core PC Sabic Lexan 1.59 7.4 1. Same RI between core OQ3820 and shell. Shell PC Sabic Lexan 1.59 25 2. PC shell layer has lower OQ3120 viscosity and can readily diffuse into PC core layer. *MFI—melt flow index (g/10 min)

TABLE-US-00005 TABLE 5 Example 5: PC/PC TP Grade Filter/additive Observations/results Core PC Sabic Lexan None 1. Same RI between core OQ3820 and shell. Shell PC Sabic Lexan NIR filter 2. PC shell layer includes OQ3820 (Epolight 4831) NIR filter and remains at higher temperature under IR heater. This assists in core-shell inter-diffusion.

TABLE-US-00006 TABLE 6 Example 6: PC/PC TP Grade Filter/additive Observations/results Core PC Sabic Lexan None 1. Same RI between core OQ3820 and shell. Shell PC Sabic Lexan Flow improver 2. Shell layer has lower OQ3820 (MF-11) viscosity due to flow improver. This assists in core-shell inter-diffusion.

[0042] Table 7 below includes extrusion temperatures used for Examples 1-6 above.

TABLE-US-00007 TABLE 7 Filament component extrusion temperatures Core filament Shell filament Example extrusion temp. Range extrusion temp. range 1 PC 230-330° C. TPU 200-300° C. 2 PC 230-330° C. PA 260-330° C. 3 PC 230-330° C. Copolyester 240-300° C. 4 PC 230-330° C. PC-high MI 200-300° C. 5 PC 230-330° C. PC + NIR 230-330° C. 6 PC 230-330° C. PC + MF 230-330° C.

[0043] 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.