Additive manufacturing of transparent optical articles

Abstract

An optical composition for vat photopolymerization including a photocurable monomer or blend of monomers; a photoinitiator; a UV absorber; and a hindered amine light stabilizer. A method of forming an optical article including printing the optical article using vat photopolymerization and the optical composition, wherein an optical surface of the optical article extends in a z-axis, the z-axis being perpendicular to a print surface that the optical article is printed on.

Description

ADDITIVE MANUFACTURING OF TRANSPARENT OPTICAL ARTICLESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 63 / 558,684 entitled “ADDITIVE MANUFACTURING OF TRANSPARENT OPTICAL ARTICLES”, filed on February 28, 2024, the entire disclosure of which is incorporated by reference in its entirety.GOVERNMENT LICENSE RIGHTS

[0002] This invention was made with government support under Government Contract No. W91 INF-17-2-0227 awarded by the U.S. Army Contracting Command on behalf of the U.S. Army Research Laboratory (ARL). The government may have certain rights in the invention.FIELD

[0003] The present disclosure relates to an optical composition and method of additive manufacturing an object using vat photopolymerization.BACKGROUND

[0004] Photopolymers are widely used in additive manufacturing processes such as vat photopolymerization and material jetting. Vat photopolymerization allows for fine print resolution. However, due to printing parameters, hardware limitations, and / or support structures, the printed object may have surface defects, such as layer stepping and surface roughness.

[0005] In the context of optical lenses, surface roughness and material composition may obstruct the clarity of the lens and reduce the lens’s functionality. Therefore, a composition and method of use to produce a smooth and clear object printed using vat photopolymerization and a post-process method is needed.SUMMARY

[0006] The present disclosure provides an optical composition for vat photopolymerization, including a monomer or monomer blend, including at least one of a (meth)acrylate and thio-(meth)acrylate functional group; 0.20 mass % to 3.0 mass % of aphotoinitiator; 0.40 mass % to 2.2 mass % of a UV absorber; and 0.40 mass % to 2.2 mass % of a hindered amine light stabilizer (HALS), based on a total mass of the optical composition.

[0007] The present disclosure further provides a method of forming an optical article, the optical article comprising an optical surface that defines an optical geometry, including printing the optical article of a predetermined curved or flat boundary using vat photopolymerization. The curved or flat boundary defining the optical geometry. The optical article is printed such that the optical surface of the optical article extends in a z-axis, the z-axis being perpendicular to a print surface the optical article is printed on. The vat photopolymerization comprises an optical composition. The optical composition includes a monomer or a blend of monomers including at least one of a (meth) acrylate and thio-(meth)acrylate functional group; 0.20 mass % to 3.0 mass % of a photoinitiator; 0.40 mass % to 2.2 mass % of a UV absorber; and 0.40 mass % to 2.2 mass % of a hindered amine light stabilizer (HALS), based on a total mass of the optical composition.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The above-mentioned and other features and advantages of this disclosure, and the manner of attaining them, will become more apparent and the disclosure itself will be better understood by reference to the following description taken in conjunction with the accompanying drawings. These above-mentioned and other features of the disclosure may be used in any combination or permutation.

[0009] FIG. 1 A is an illustration of the orientation of a lens in a vat photopolymerization printing process of the present disclosure;

[0010] FIG. IB is an illustration of two view of the lens printed using the vat photopolymerization process of FIG. 1 A;

[0011] FIG. 2 is an illustration of different printing orientations in the Z axis of a -4 lens geometry on a build platform according to the present disclosure;

[0012] FIG. 3A is an image of a -4 lens printed using the method of the present disclosure;

[0013] FIG. 3B is an image of the -4 lens of FIG. 3A with the lens between a mold and additional monomer added to smooth the lens during curing;

[0014] FIG. 4 is flow chart of a method of printing an object using vat photopolymerization according to the present disclosure; and

[0015] FIG. 5 is an image showing the birefringence of an optical article comprising the optical composition of the present disclosure.

[0016] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate the disclosure, and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner.DETAILED DESCRIPTION

[0017] The present disclosure provides an optical monomer composition and method of additively manufacturing a 3D object comprising the optical monomer composition using vat photopolymerization.I. Definitions

[0018] For purposes of the following detailed description, it is to be understood that the disclosure may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about." For example, numerical ranges provided for weight percentages of components or amounts of components added should be construed as being modified by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0019] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.

[0020] Whereas particular examples of this disclosure have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variationsof the details of the present disclosure may be made without departing from what is defined in the appended claims.

[0021] Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges from (and including) the recited minimum value of 1 to the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

[0022] The use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, the use of "or" means "and / or" unless specifically stated otherwise, even though "and / or" may be explicitly used in certain instances.

[0023] “Bottom exposure time” as used herein refers to the length of time a first set of layers of a 3D printed object is exposed to UV light to ensure e a polymerized base is adhered to the build plate. The bottom exposure time may be multiple times more than regular exposure time needed to print subsequent layers.

[0024] ‘Bottom layers” as used herein refers to the number of base layers adhered to the build plate and that follow the bottom exposure time.

[0025] “Exposure time” as used herein refers to the UV light exposure time on each layer as the object is 3D printed, with may be different from the “bottom exposure time”.

[0026] “Off time” as used herein refers to the amount of time between every motion of an elevator that moves the build plate up and down that allows material to reflow between the membrane and the build plate.

[0027] “Ultraviolet light” or “UV light” as used herein refers to any light with a wavelength of 100-405 nm and including each of UVA (e.g., 315-405 nm), UVB (e.g., 280-315 nm) and UVC (e.g., 100-280 nm) Ultraviolet (UV) light.

[0028] “Vertical orientation” as used herein describes the position of a three-dimensional article where the optical and / or flat surface of the object is oriented in a substantially perpendicular position (e.g., in a substantially normal direction) relative to the print bed / print surface of the additive manufacturing deice (e.g., 3D printer).II. Optical Composition for Vat photopolymerization Printing

[0029] The present disclosure provides an optical composition for printing an optical article, such as a lens, disc, or any other suitable three-dimensional (3D) additivelymanufactured object with low haze, high transmissivity, and low color using vat photopolymerization additive manufacturing. The composition may comprise a photocurable monomer / monomer blend, a UV absorber, a photoinitiator, and hindered amine light stabilizers (HALS).

[0030] The type of, and relative proportions of (e.g., mass %, weight %, and / or PPM) the photocurable monomer / monomer blend, UV absorber, photoinitiator, HALS component, and / or additional additives may be selected and / or tuned, such that the object is additively manufacturable by the methods described herein, and particularly, relating to vat photopolymerization-type additive manufacturing where the object is printed such that an optical surface of the ophthalmic object is oriented in a substantially vertical orientation. For instance, the weight percent of each of the photocurable monomer / monomer blend, UV absorber, photoinitiator, and HALS component may be adjusted in combination such that ophthalmic object is printable via vat polymerization where the optical surface of the object is oriented in a vertical direction (e.g., normal to / perpendicular to the print bed / print surface of the vat polymerization 3D printer). The vertical orientation printing results in an additive manufactured object that exhibits optical performance similar to ophthalmic objects manufactured via casting / molding methods, as well as superior optical performance to ophthalmic objects printed in a horizontal orientation relative to the print bed / print surface, as to be described in further detail herein.A. Photocurable Monomers and Monomer Blends

[0031] The optical composition may comprise a photocurable monomer or blends of photocurable monomers. The monomer(s) may comprise any suitable UV curable ophthalmic monomer complex including an ethylenically unsaturated monomer combinations of ethylenically unsaturated monomers.

[0032] The ophthalmic monomer(s) may be ethylenically unsaturated monomer(s) and may include one or more of, or combination of, a (meth) acrylate functional group, and / or a thio-(meth)acrylate functional group. Suitable monomers may include acrylic acid, methacrylic acid, esters of acrylic acid such as methyl acrylate, butyl acrylate and 2-hydroxyethyl acrylate, esters of methacrylic acid, such as methyl methacrylate, phenoxyethyl methacrylate, isobomyl methacrylate, cyclohexyl methacrylate, butyl methacrylate, 2-hydroxyethyl methacrylate, and blends thereof.

[0033] Suitable polyfunctional (meth)acrylate monomers may include commercially available dimethacrylates such as 1,6-hexanediol di(meth)acrylate, bisphenol A di(meth)acrylate, polyethylene glycol di(meth)acrylates and polycaprolactonedi(meth) acrylates .

[0034] Further, (meth) acrylate functional monomers may be prepared by the reaction of a polyol precursor with an acrylating agent by art-recognized means. Suitable acrylating agents include (meth) acryloyl chloride and (meth)acryloyl anhydride. Transesterification using methyl(meth)acrylate may also be performed. Suitable polyol precursors may include straight chain alkylene glycols such as ethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, or diethylene glycol, triethylene glycol; branched chain alkylene glycols such as 1,2-propanediol, 2-methy 1-1, 3 -propanediol, 1 ,2-butanediol, 1,3-butanediol, 2, 3 -butanediol; phenylene diols such as ortho, meta and para dihydroxy benzene; alkyl substituted phenylene diols such as 2, 6-dihydroxy toluene, 3-methylcatechol, 4-methylcatechol, 2-hydroxybenzyl alcohol, 3-hydroxybenzyl alcohol, 4-hydroxybenzyl alcohol, and 3,5-bis(l,l-dimethylethyl)-4-hydroxy-benzenemethanol; dihydroxybiphenyls such as 4,4’ -dihydroxybiphenyl and 2,2’dihydroxybiphenyl; bisphenols such as 4,4’-isopropylidenediphenol; 4,4’ -oxybisphenol; 4,4’ -dihydroxybenzenephenone; 4,4’-thiobisphenol; phenolphthlalein; bis(4-hydroxyphenyl)methane; 4, 4’ -(1,2-ethenediyl)bisphenol; and 4,4’ -sulfonylbisphenol; halogenated bisphenols such as 4,4’-isopropylidenebis(2,6-dibromophenol), 4,4’-isopropylidenebis(2,6-dichlorophenol) and 4,4’-isopropylidenebis(2,3,5,6-tetrachlorophenol); and biscyclohexanols, which can be prepared by hydrogenating the corresponding bisphenols, such as 4,4’-isopropylidenebiscyclohexanol; 4,4’-oxybiscyclohexanol; 4,4’-thiobiscyclohexanol; and bis(4-hydroxycyclohexanol)methane.

[0035] Ethoxylated versions of any of the aforementioned polyols may be first prepared, such as by reaction of the alcohol groups with an ethoxylating agent such as ethylene oxide under art-recognized conditions. A polyol, e.g., trimethylolpropane , is reacted with an oxirane containing substance, such as ethylene oxide, propylene oxide, a-butylene oxide or P-butylene oxide, to form what is commonly referred to as an ethoxylated, propoxylated or butoxylated polyol having hydroxy functionality. The average number of alkoxylated groups per alcohol groups of the starting polyol can range from 1 to 9. These may be used to prepare the corresponding poly(meth)acrylates by reaction with an acrylating agent as mentioned above.

[0036] Any of the aforementioned polyol precursors may form the corresponding (meth)acrylate by reaction with an acrylating agent as described above.

[0037] Suitable monomers having thio(meth) acrylate functional groups include bis(2-methacryloylthioethyl)sulfide, bis(2-acryloylthioethyl)sulfide, 2,5-bis(methacryloylthiomethyl)l,4-dithiane, 2-ethyl-2-((meth)acryloylthiomethyl)-l,3-bis[(meth)acryloylthio]propane, l,2,3-tris[(meth)acryloylthio]propane, 2,2-bis[(meth)acryloylthiomethyl]-l,3-bis[(meth)acryloylthio]propane, 4-(meth)acryloylthiomethyl-3,6-dithia-l,8-bis[(meth)acryloylthio]octane, 7-[2-(meth)acryloyloxyethyl]-3,6,8,ll-tetrathia-l,13-bis[(meth)acryloylthio]tridecane, 4,8-bis[(meth)acryloylthiomethyl]-3,6,9-trithia- 1, 1 l-bis[(meth)acryloylthio]undecane or regioisomers thereof, such as the 4,7- or 5,7- regioisomers, 2,5-bis(methacryloylthiomethyl)l,4-dithiane.

[0038] Suitable monomers comprising (meth) acrylate and thio(meth)acrylate functional groups include: 2-acryloyloxyethyl-2’ -acryloylthioethyl sulfide, 2-methacryloyloxyethyl-2’-methacryloylthioethyl sulfide, l,3-bis[(meth)acryloylthio]-2-(meth) aery loy loxypropane, 1 -(meth) aery loy lthio-2, 3 -bi s [ (meth) acryloyloxy ]propane, 1,2-bis[(meth)acryloylthio]-3-(meth)acryloyloxypropane, and 7-(meth)acryloyloxymethyl-3,6,9,12-tetrathia-l,14-bis[(meth)acryloylthio]tetradecane.

[0039] Mixtures of any of the above-mentioned (meth)acrylates and / or thio(meth) acrylate functional monomers may be used to achieve the desired refractive index and hardness of the polymerizate.

[0040] As with the above-mentioned polyols, polythiols and polythio-alcohols may be (meth)acrylated by reaction with an excess of an acrylating agent such as those mentioned above.

[0041] The optical composition may comprise a mass percent of photocurable monomers / monomer blend, including one or more (meth)acrylate or thio-(meth)acrylate functional groups, from 95 %, 96 %, 97 % to 98 %, 98.5 %, or 99 % or any range using any of the foregoing values as endpoints, such as 95 % to 99 %, 96 % to 98.5 %, or 97 % to 98 %, based on the total mass of the composition.B. Photoinitiator

[0042] The optical composition may include a photoinitiator or combination of photoinitiators. A photoinitiator can be activated by actinic radiation that can apply energyeffective in generating an initiating species from the photopolymerization initiator upon irradiation such as ultraviolet (UV) light including UVA, UVB, and UVC spectra), visible light, and blue light. A photoinitiator can be a UV photoinitiator that is activated by UV light in the UVA, UVB, and / or UVC spectrum. Activation wavelengths may range from 300-450 nm.

[0043] Suitable UV photoinitiators may include acylphosphine oxide type 1 photoinitiator. Further, suitable photoinitiator may include a-hydroxyketones, benzophenone, a, a.-diethoxyacetophenone, 4,4-diethylaminobenzophenone, 2,2-dimethoxy-2-phenylacetophenone, 4-isopropylphenyl 2-hydroxy-2-propyl ketone, 1 -hydroxy cyclohexyl phenyl ketone, isoamyl p-dimethylaminobenzoate, methyl 4-dimethylaminobenzoate, methyl O-benzoylbenzoate, benzoin, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2-hydroxy-2-methyl- 1 -phenylpropan- 1 -one, 2-isopropylthioxanthone, dibenzosuberone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bisacyclophosphine oxide, benzophenone photoinitiators, oxime photoinitiators, phosphine oxide photoinitiators, and combinations of any of the foregoing.

[0044] The photoinitiator concentration may be directly proportional to the speed of cure, with higher concentrations making faster cure speeds. However, the photoinitiator concentration may also negatively affect the haze percentage and increase yellowing color of the final article. Thus, the photoinitiator concentration may be optimized to control cure speed and reduce haze percent.

[0045] The optical composition may comprise a mass percent of a photoinitiator from 0.20 wt. %, 0.35 wt. %, 0.40 wt. %, 0.45 wt. % to 0.50 wt. %, 0.60 wt. %, 1 wt. %, 1.5 wt. %, 2.0 wt. %, 2.5 wt. %, or 3 wt. % or any range using any of the foregoing values as endpoints, such as 0.20 wt. % to 0.60 wt. %, 0.35 wt. % to 0.50 wt. %, 0.40 wt. % to 0.45 wt. %, 1.0 wt. % to 3.0 wt. %, 1.5 wt. % to 3.0 wt. %, or 2.0 wt. % to 3.0 wt. %, as based on the total mass of the composition.C. Ultraviolet (UV) Absorber

[0046] The optical composition may comprise a UV absorber (i.e., UVA). The UV absorber may limit the penetration of UV light in a composition by absorbing and dissipating the energy of the incoming UV radiation. This may prevent the UV light from reaching the deeper layers of the composition when additively manufactured, which can control or limit the polymerization of the composition. Specifically, as the optical composition is exposed toUV light, a portion of the UV radiation is absorbed by the UV absorber, preventing the absorbed light from penetrating the optical composition. This limited penetration may control the amount and reaction rate of polymerization in optical composition, allowing for controlled curing depths and surface properties.

[0047] Suitable UV Absorbers may absorb ultraviolet light in a range from 300 nm to 405 nm for vat photopolymerization systems with 405 nm wavelength. The UV absorber may be selected to absorb ultraviolet light to within 5 nm of the wavelength of the light source used to initiate photopolymerization for any other vat photopolymerization system with a different wavelength.

[0048] Suitable UV absorbers may include benzophenones such as 2-hydroxybenzophenone, benzotriazoles such as 2-hydroxyphenylbenzotriazole, triazines such as 2-hydroxyphenyltriazine, oxalanilide, 2-hydroxyphenyltriazine, cinnamates, salicylates, formamidine, and / or any suitable commercially available UV absorbers.

[0049] The UV absorber may protect a printed object, comprising the optical composition, from environmental conductions and prevent coloring changes, such as yellowing. The concentration of UV absorber in a composition may influence print speed, with higher concentrations of UV absorber leading to slower polymerization speed. Thus, the amount of UV absorber in the present composition may be optimized to reduce yellowing and adjust print speed.

[0050] The optical composition may comprise a mass percent of a UV absorber from 0.40 wt. %, 0.45 wt. %, 0.50 wt. % to 0.55 wt. %, 0.58 wt. %, 0.60 wt. %, or 2.2 wt.% or any range using any of the foregoing values as endpoints, such as 0.4 wt. % to 2.2 wt. %, 0.45 wt. % to 0.60 wt. %, 0.50 wt. % to 0.5 wt. %, or 0.50 wt. % to 0.58 wt. %, as based on the total mass of the composition.D. Hindered Amine Light Stabilizers

[0051] The optical composition may comprise a light stabilizer, such as a UV light stabilizer, which may include a hindered amine light stabilizer (HALS) component. HALS are a class of chemical compounds used in the protection of polymers against degradation caused by exposure to ultraviolet (UV) light. The HALS functions by scavenging free radicals generated during UV irradiation, thereby preventing the deterioration of the polymer's physical and mechanical properties. Specifically, the HALS component may include an amine functional group configured to inhibit the degradation of the blend ofpolymers by removing free radicals produced by photo-oxidation of the polymers. Suitable HALS components include the following: l-(Methyl)-8-(l,2,2,6,6-pentamethyl-4-piperidinyl)-sebacate, bis(l,2,2,6,6-pentamethyl-4-piperidyl) Sebacate bis(l,2,2,6,6-pentamethylpiperidin-4-yl) n-butyl 3,5-di-tert-butyl-4-hydroxybenzylmalonate; bis(l,2,2,6,6-pentamethylpiperidyl)-2-n-butyl-2-(2-hydroxy-3,5-di-tert-butylbenzyl)malonate; 2-chloro-4,6-bis(4-n-butylamino-l,2,2,6,6-pentamethylpiperidyl)-l,3,5-triazine; 3-dodecyl-l-(l,2,2,6,6-pentamethylpiperidin-4-yl)pyrrolidine-2,5-dione; N-( 1,2, 2,6,6-pentamethylpiperidin-4-yl)-n-dodecylsuccinimide; and combinations thereof.

[0052] High concentrations of HALS in a composition may impact print speed, haze percentage, and color of the cured composition. Therefore, the amount of HALS in the optical composition may be optimized to target such optical features.

[0053] The optical composition may comprise a mass percent of a HALS from 0.40 %, 0.45 %, 0.50 % to 0.55 %, 0.60 %, 0.85 wt. %, 2.0 wt. %, or 2.2 % or any range using any of the foregoing values as endpoints, such as 0.4 % to 2.2 %, 0.45 % to 0.60 %, 0.50 % to 0.55 %, or 0.85 wt. % to 2.0 wt. %, based on the total mass of the composition.E. Additional Additives

[0054] Additives, such as pigments or fixed tint dyes, may be added to the optical composition to achieve the correct color desired for the transparent application. Suitable pigments / dyes may include anthraquinone dyes derivatives such as the following commercial dyes: Morplas Blue 2R (solvent Blue 128) 9,10-anthracenedione-l,4-bis(2-bromo-4,6-dimethylphenyl) amino; Morplas Violet 3B (solvent Violet 38) 9,10-anthracenedione-l,4 { (2, 6-dibromo-4methyl phenyl) amino}; Morplas Yellow GS (solvent Yellow 163) 9,10-anthracenedione-l,4-bis (phenylthio); Morplas Violet 14 (solvent Violet 14) 9,10-anthracenedione-l,8-bis (methylphenyl) amino; Morplas Blue E (solvent Blue 101) 9,10-anthracenedione-l,4-bis (alkylphenyl)amino; Pylakrome Blue LX-9704 (solvent Blue 58) Undisclosed by manufacturer; Pyrazolone Derivatives; Pylakrome Yellow LX-10124 Undisclosed by manufacturer; Pylam Liquid Oil Yellow LO-2112 l-phenyl-3-methyl-4-(alkylphenylazo)-5(solvent Yellow) pyrazalone; and combinations thereof.

[0055] Other suitable additives may include antioxidants (such as triphonyphosphite), polymerization modifiers (chain transfer reagents), photosensitizers (such asisopry opylthioxanthone), and internal mold release agents (such as MOLDWIZ 4681, SELEC UN, etc).

[0056] The coating composition may comprise a mass percent of additives from 0.0001 wt. %, 0.0002 %, 0.00025 wt. % to 0.0003 %, 0.0004 wt. %, or 0.0005 wt. %, or any range using any of the foregoing values as endpoints, such as 0.0001 wt. % to 0.0005 wt. %, 0.0002 wt. % to 0.0004 wt. %, or 0.0003 wt. % to 0.0004 wt. %, based on the total mass of the composition.

[0057] As describe previously, the type of and relative weight % of (e.g., PPM of) each of the photocurable monomer / monomer blend, photoinitiator, UV absorber, and HALS component may be adjusted in combination in order to result in an ophthalmic object that is vat polymerization additively manufacturable (e.g., 3D printable) in a substantially vertical orientation, which optically performs similar to (e.g., as well as) optical articles manufactured via casting methods. For instance, 1) the type and relative weight % (e.g., PPM) of the photoinitiator may be selected to control cure speed and reduce haze percent, which may be selected in combination with 2) the type and relative weight % (e.g., PPM) of the UV absorber, which may be selected to absorb UV light in a given frequency range as well as reduce yellowing and adjust print speed, which may be selected in combination with 3) the type and relative weight % (e.g., PPM) of the HALS component, which may be selected to impact print speed, haze percentage, and color of the cured composition, each selected in view of 4) the optical monomer / monomer blend utilized for the ophthalmic composition.

[0058] Here, it has been surprisingly found that, as based upon the selection of an ophthalmic monomer / monomer blend including an ethylenically unsaturated functional group, that 1) a photoinitiator comprising from 0.20 wt. % to 3.0 wt. %, 2) a UV absorber comprising from 0.40 wt. % to 2.2 wt. % and 3) a HALS component from 0.40 wt. % to 2.2 wt. % , results in an additively manufactured object that performs as well as optical articles manufactured by casting methods, since the resulting optical composition is vat polymerization additively manufacturable where the optical surface of the object is oriented in a substantially vertical direction (e.g., substantially normal to the print bed / print surface of the vat polymerization 3D printer).III. Print Process and Post-Curing Process

[0059] The present disclosure provides a method for additively manufacturing an object using vat photopolymerization and a post-cure process.

[0060] Vat photopolymerization is an additive manufacturing process that uses a bottom-up, top-down or volumetric approach. A bottom-up approach is the most commonamong the vast majority of commercial desktop and industrial systems. This bottom-up approach performs the printing operation while the build platform moves up after each layer is light-cured to allow resin liquid to flow back and then moves down to prepare for the next layer. A detachment or peeling step is required between each layer to detach from the bottom of the vat.

[0061] Vat photopolymer system processes can include different light sources, such as lasers, LED’s with DLP chips, LED’s with LCD screens.

[0062] The resolution of vat photopolymerization in the XY plane is defined by the pixel size of the light source. In case of the laser light source, it can be the beam spot size the minimum pixel size. For LED light sources it can be the minimum DLP or LCD screen squared minimum light image.

[0063] As shown in FIG. 4, method 40 includes printing the object using vat photopolymerization 41, optionally, removing the support structures 42, enclosing the object in a mold 43, filling the mold with extra monomer and securing the mold 44, exposing the mold to light and heat 45, and removing the object form the mold with solvent 46. All steps 41-46 are further described below.

[0064] The printed object may be referred to as an optical article, lens, disc, or any suitable ophthalmic object additively manufactured using vat photopolymerization in step 41. Referring to FIGS. 1A, an elevator 17 may lower a build platform 18 into a vat 14 comprising the optical composition. A light source 16 may be projected into the bottom of the vat, opposite build platform 18, activating the optical composition such that an object 12 is printed onto build platform 18. Light source 16 may emit a UV light within a specific UV wavelength range, such as UV A light in the 315-405 nm range, and specifically an LED with a narrow and emission of 405 nm or 385 nm.

[0065] Light source 16 may emit a light of a specific wavelength such as 405 nm or 385 nm, with an irradiance from 3 mW / cm2, 5 mW / cm2, 7 mW / cm2to 9 mW / cm2, 11 mW / cm2, or 13 mW / cm2, or any range using any of the foregoing values as endpoints, such as 3 mW / cm2to 13 mW / cm2, 5 mW / cm2to 11 mW / cm2, or 7 mW / cm2to 9 mW / cm2.

[0066] Printing parameters for the vat photopolymerization may vary depending on the geometry of the object being printed and / or the printable composition. Printing parameters may include bottom exposure time, bottom layers, exposure time, off time and layer thickness.

[0067] Bottom exposure time in vat polymerization refers to the duration during which the optical composition at the bottom of the vat is exposed to the UV / curing light, determining the solidification and quality of the printed layers in the additive manufacturing process. Here, the bottom exposure time of the printed optical composition may be at least 20 seconds (sec.), at least 22 sec., at least 24 sec., at least 26 sec., at least 28 sec., at least 30 sec., or at least 32 sec., or any range using any of the foregoing values as endpoints, such as 20 sec. to 32 sec., 22 sec. to 30 sec., or 24 sec. to 28 sec..

[0068] Bottom / base layers in vat polymerization refers to the initial layers of the additively manufactured object that adhere to the build platform, serving as the foundation for subsequent layers and influencing the overall structural integrity and accuracy of the printed product. Here, the printed optical composition may comprise at least 2, at least 3, at least 4, at least 5, at least 6, or at least 7 bottom layers when forming the printed object.

[0069] Exposure time in vat polymerization refers to the duration for which each layer of liquid resin is exposed to the curing / UV light, determining the degree of solidification and intricacy in the additive manufacturing process, influencing the final quality of the printed object. Here, exposure time may vary depending on the thickness of the layer. Specifically, the thicker the layer desired, the longer the exposure time. In the case where the exposure time is too low for a large area within a thin layer, the polymerization will be insufficient, and the exposure time should be adjusted. Here, the printed optical composition may comprise an exposure time of at least 2 sec., 3 sec., 4 sec., 5 sec., 6 sec., 7 sec., 8 sec. 9 sec., 10 sec., or 11 sec. when forming the printed object.

[0070] Off time in vat polymerization refers to the duration during which the ultraviolet (UV) light source is deactivated or paused, allowing for the temporary interruption of the curing process, which may manage the layer-by-layer polymerization in vat photopolymerization. Off time may also be used to detach the printed layer from the membrane or film of the vat photopolymerization system in the case of bottom-up systems. For all SLA, DLP, and LCD vat photopolymerization systems, the off time may also serve as a time to allow reflow of the optical composition to cover the printed surface and allow the composition to further polymerize in the next layer. Here, the printed optical composition may comprise an off time of at least 0.5 sec., 1 sec., 1.5 sec., or 2 sec., or 3 sec. when forming the printed object.

[0071] The printed object may have a maximum layer thickness 10 pm or less. In some cases, a layer thickness of 10 pm or less may be considered “layerless, ” or“continuously printed”. Layer thickness is determined based upon partitioning of the object relative to the Z axis, where the material is polymerized on a layer-by layer basis, resulting in the given layer thickness. Here, during additive manufacturing, the additive manufacturing system stops and moves the printed layer away from the printing area after each layer is exposed with light to polymerize, allowing for the unpolymerized material to flow and cover the subsequent printing area. As an alternative, continuous printing relies on fine layer partitions, where the printing apparatus may not stop printing between added layers. A volumetric printing process may also utilize multiple projection planes and selective light curing. Depending on the build orientation of the object in a vat photopolymerization system, the layer thickness may be directly proportional to the surface roughness of the final article. This is due to the steps generated on any curved surface on the same plane surface as the build area.

[0072] The printed object may have a maximum layer thickness of 10 pm or less, such as a layer thickness of 0.1 pm, 1 pm, 4 pm to 6 pm, 8 pm, or 10 pm, or any range using any of the foregoing values as endpoints, such as 0.1 pm to 10 pm, 1 pm to 10 pm, or 4 pm to 10 pm. The small layer thickness results in increased hardness and reduced haziness and surface imperfections in the resulting optical article.

[0073] As described above, the type and weight percent of each of the photocurable monomer / monomer blend, UV absorber, photoinitiator, and HALS component of the optical composition may be adjusted in combination such that an ophthalmic object is printable via vat polymerization where the optical surface of the object is oriented in a vertical direction (e.g., normal to the print bed / print surface of the vat polymerization 3D printer). Here, the selection of printing parameters (e.g., bottom exposure time, bottom layers, exposure time, off time, layer thickness) may directly influence the optical composition, and the optical composition may directly influence the 3D vat polymerization printing behavior. In this case, it has been surprisingly found that the foregoing optical composition may be selected to be additively manufacturable via vat polymerization in a vertical orientation based upon the combined selection / optimization of each of the bottom exposure time from 20 sec. to 32 sec., the number of bottom layers from 2 to 7 layers, the exposure time from 2 sec. to 11 sec., the off time from 0.5 sec. to 3 sec. and the layer thickness of 10 pm or less.A. Vertical Orientation Printing

[0074] The printable object may be designed using a suitable computer aided design software. A vat photopolymerization printer may be used with a UV light and a z-axis pitch distance of 10 pm or less.

[0075] Referring to FIGS. 1A and IB, an object 12 may be printed using thin print layers (0.1 pm to 10 pm, as discussed previously) such that an optical surface 12d of the object is in the z-axis direction. Optical surface 12d of the printed object 12 refers to the curved or flat boundary that plays a role in the manipulation of light as it passes through object 12. The curvature of optical surface 12d defines an optical geometry of object 12, discussed further below. Optical surface 12d of printed object 12 may define a height of object 12. Object 12 extends from a build platform 18 in the z-direction as each thin layer of object 12 is printed using the vat photopolymerization process such that object 12 is supported by support structures 13 onto build platform 18 along a bottom / periphery edge 12c of object 12. Once the object is printed, any existing support structures 13 may be removed. In some cases, object 12 may be printed at an angle relative to the z-axis, such as, and with reference to FIG. 2, angles between 1 and 65 degrees. Printing at an angle allows for the additive manufacturing of larger object diameters in the build diameter, as compared to object printed in the normal direction.

[0076] Traditional additive manufacturing of objects similar to object 12 were limited to printing optical articles on top of a prefabricated surface (e.g., a substrate), which were further limited to being printed in a substantially horizontal orientation (e.g., printed across a build platform) such that the width of the object extends in the z direction. Specifically, a prefabricated lens, such as a precursor lens, may serve as a substrate upon which subsequent layers of material are deposited / built, resulting in a three-dimensional optical article that can be post-processed into an optical lens. Due to the limitations of vat-polymerization-type additive manufacturing, the additive manufacturing process must occur while the substrate is oriented in a substantially horizontal orientation (e.g., across the build platform) when building the successive layers.

[0077] The use of a substrate and / or printing horizontally presents numerous drawbacks which detrimentally affect the optical performance of the resulting lens.Specifically, when printing an object in the horizontal orientation (e.g., the optical surface being horizontal to the print surface / bed of the 3D printer), the layer thickness of the composition is directly proportional to the height of concentric circle defects present withinthe lens. Concentric circle defects refer to optical imperfections that manifest as a series of circular or ring-shaped patterns on the lens surface. Such defects induce birefringent effects, and in some cases, circular birefringent effects, due to the multiple layers of material splitting light into different wavelengths and generating a rainbow effect. Specifically, circular birefringence effects may occur when the materials of the lens introduce a phase difference between the two circularly polarized components of light. Such defects may directly relate to the layer by layer lines of the printed object, showing a rainbow effect when tilting the optical article against a light source. Optical articles additively manufactured in a horizontal orientation, such as those reliant on a substrate, therefore include numerous concentric circles (e.g., due to the method of horizontal deposition), which result in relatively high, if not very high birefringent effects (e.g., birefringent defects). These birefringent defects negatively impact the optical performance of the lens, affecting the visual quality and clarity of the lens, which potentially impacts the wearer's vision.

[0078] Furthermore, the limitations of vat polymerization-type additive manufacturing requires the use of a support structure to secure the substrate to the build platform, which based upon the horizontal orientation of the additive manufacturing process, must be attached to the article across a front surface or back surface of the printed object in order to build the subsequent layers. For instance, in the scenario where a lens precursor (e.g., a substrate) is used, the substrate must be secured to the build platform by support structures, where support structures are attached to the flat / optical surface of the lens precursor.Alternatively, if no substrate is used, support structures are required to attach the object to the build platform during formation, which is also attached to the flat / optical surface in the horizontal orientation. Such support structures adversely affect the overall quality of the object since the support structures were attached to the flat surface, which in the case of an ophthalmic article, is the optical surface, leaving a multitude of surface defects or ridges after the support structures were removed, resulting in undesirable imperfections in the object. For instance, the front and back optical surfaces may be obstructed due to surface defects caused from support structures, rendering the lens unusable / flawed. The surface roughness of the resulting object may also increase due to the support structure attachments.

[0079] Vertically additive manufacturing the optical article does not rely on a substrate (e.g., is substrate-less). Accordingly, vertical orientation printing greatly reduces the effect of circular defects, as compared with horizontal printing. Specifically, any circular defects of objects printed in the vertical orientation relate to the pixel size of the projectedimage or the vector traced by the 3D printer. Therefore, such variables can be adjusted to minimize the circular defects, depending on their orientation in the Z axis, resulting in ophthalmic articles outperforming articles additively manufactured in the horizontal orientation.

[0080] Furthermore, vertically additive manufacturing the optical article avoids the support structures 13 from being in contact with front surface 12a and / or rear surface 12b, and instead, only contacts an outer periphery of object 12, such as along bottom surface 12c. In this case, any defects or ridges can be easily removed from the outer periphery (e.g., as compared to front surface 12a and / or rear surface 12b), and in the context of ophthalmic lenses / objects, avoids adversely affecting the optical surface(s) of the lens, as also shown in FIG. 4 step 42.B. Post Curing Process

[0081] In vat photopolymerization, the post curing process is done to enhance the structural and functional properties of the printed object. The post curing cycle is performed with UV light at the same, or substantially similar irradiance as was used during the vat photopolymerization printing process. Some post curing systems / processes utilized post heating (e.g., via heating elements) which provides, prior or during the post curing cycle, a thermal cycle to enhance mechanical properties and drying of the printed parts.

[0082] Referring to FIGS. 3A and 3B, the post-curing process 30 is shown. A mold 34 may be placed on either side of lens 12, also described in FIG. 4 step 43. The mold 34 may be a rigid, semi-rigid, or flexible mold. Mold 34 may be made of a material such as plastic, glass, or any other suitable material. Mold 34 may have a hollow area of substantially similar geometry as the desired geometry of the printed object. In step 44 of FIG. 4, extra monomer 32 may be added to printed lens 12 and mold 34 such that the total volume of the hollow area of mold 34 is filled with lens 12 and extra monomer 32. The amount of extra monomer added may be directly related to the surface area needed to cover and the pressure put against the monomer to find the optimum amount. Lens 12 may be sandwiched by mold 34 and mold 34 is secured together by a fastener, such as transparent tape, clamps, or other suitable devices, such that the position and pressure on lens 12 are held constant (FIG. 4 step 44). The amount of extra monomer 32 added may be selected to fill the volume created by the gaps between printed surfaces of lens 12 and mold 34.

[0083] Once the mold is closed with the lens and extra monomer within the mold, the mold may be exposed to the UV light, such as for 1 hour, 2 hours, 3 hours at a temperature between 60 °C and 120°C (FIG. 4 step 45). The amount of time and temperature of curing may be directly proportional to the UV light source irradiance. The optical composition in a post cure oven with LED UV light sources and an irradiance of 9.1 mW / cm2may cure for 2 hours at 80°C. However, the optical composition in a post cure oven with a mercury light bulb and an irradiance of 964 mW / cm2may cure for 1 minute at 80°C. In the case where grooves and / or other surface defects are present on the surface of lens 12 (e.g., during 3D printing) monomer 32 infills such features, and once cured, results in a lens 12 with smooth optical surfaces.

[0084] After the thermal and UV exposure, the fastener is removed and mold 34 may be opened. To detach printed lens 12 from mold 34, a solvent may be used to rise lens 12 and loosen lens 12 from mold 34 (FIG. 4 step 46). Lens 12 does not require a cleaning solvent to remove haziness (e.g., the process is substantially solvent free).IV. Properties of Additively Manufactured Object Using Vat photopolymerization

[0085] A variety of different objects may be printed using the composition and method described herein. For instance, and as described above, ophthalmic objects (e.g., ophthalmic lenses) comprising the optical composition may be formed via the present vat polymerization-based additive manufacturing and curing process, which may result in ophthalmic objects exhibiting surprisingly high-performance properties and / or characteristics, as compared to analogous additive manufacturing techniques. Specifically, the type and weight percent of each of the photocurable monomer / monomer blend, UV absorber, photoinitiator, and HALS component of the optical composition may be adjusted in combination such that the ophthalmic object is printable via vat polymerization where the optical surface of the object is oriented in a vertical direction (e.g., normal to the print bed / print surface of the vat polymerization 3D printer), as based upon the selection / tuning of various printing parameters including bottom exposure time, bottom layers, exposure time, off time, and layer thickness. Post curing, the optical article may exhibit surprisingly high-performance characteristics as compared with articles resulting from other additive manufacturing techniques (e.g., vat polymerization with a substrate / horizontal orientation). The performance characteristics directly result from the selection of any one of each of the components of the optical composition and printing parameters utilized. Therefore, and inview of the foregoing discussion, the printing process and optical composition may be regard as optimized, resulting in additively manufactured objects, and particularly ophthalmic objects, that exhibit performance comparable to molded lenses, which is a marked improvement over similar additive manufacturing techniques.A. Layer Thickness

[0086] As described previously, the printed object may have a minimum layer thickness of 0.1 pm, 1 pm, 4 pm to 6 pm, 8 pm, or 10 pm, or any range using any of the foregoing values as endpoints, such as 0.1 pm to 10 pm, 1 pm to 8 pm, or 4 pm to 6 pm. as described previously, the layer thickness might be directly influence (e.g., be proportional to) the surface roughness of the printed article. The small layer thickness increases hardness and reduces haziness and surface imperfections in the resulting optical article.B. Optical Geometry

[0087] An optical article printed using the composition and the method of the present disclosure may have a planar, plano-convex, double-convex, plano-concave, double-concave, positive achromatic, and / or aspheric geometry. Alternatively, the optical article may have a square, round, or oval geometry.

[0088] The optical article may have an optical lens geometry of -1, -2 to -3, or -4, or any range using any of the foregoing values as endpoints, such as -1 to -4 or -2 to -3.C. Total Optical Article Thickness

[0089] The optical article may have a total thickness of at least 1 mm, at least 2 mm, at least 2.5 mm, at least 3 mm, at least 3.5 mm, or at least 4 mm, or any range using any of the foregoing values as endpoints, such as 1 mm to 4 mm, 2 mm to 3.5 mm, or 2.5 mm to 3 mm.D. Surface Roughness

[0090] Surface roughness of a printed object, such as an ophthalmic lens, refers to the microscopic irregularities on its outer surface, influencing factors such as visual clarity, comfort, and the potential for light scattering; a lower surface roughness is associated with smoother lenses that contribute to improved optical performance and wearer satisfaction. The surface of the printed object may be determined by the printing variables including, but not limited to, the illumination pixel size. The printed object may have a roughness measured using a confocal laser scanning microscope. The object printed, before adding the object to a mold and adding extra monomer, according to the method of the present disclosure may have a surface roughness root mean square height (Sq) less than 0.250 pm, less than 0.200 pm,less than 0.150 pm, less than 0.100, less than 0.080 pm, less than 0.060 pm, less than 0.040, or less than 0.020 pm, or any range using any of the foregoing values as endpoints, such as 0.020 pm to 0.250 pm, 0.040 pm to 0.200 pm, 0.060 pm to 0.150 pm, or 0.080 pm to 0.100 pm.

[0091] Objects printed horizontally may have a surface roughness root mean square height greater than 0.250 pm generated by a stair-stepping effect in the optical surface that lays onto the print surface.E. Micro hardness

[0092] The microhardness of a additively manufactured object, such as an ophthalmic lens, describes its resistance to indentation or surface deformation at a microscopic level, providing insights into the lens's durability and ability to withstand external forces without compromising optical performance. The object additively manufactured according to the method of the present disclosure may have a microhardness of at least 90 N / mm2, at least 100 N / mm2, at least 110 N / mm2, at least 120 N / mm2, at least 130 N / mm2, or at least 180 N / mm2, or any range using any of the foregoing values as endpoints, such as 90 N / mm2to 180 N / mm2, 100 N / mm2to 130 N / mm2, or 110 N / mm2to 120 N / mm2, as determined by DIN EN ISO 14577-1.F. Refractive Index

[0093] The Refractive Index (RI) of an additively manufactured object, such as an ophthalmic lens, refers to how much the lens can bend and slow down light, influencing its optical power; a higher refractive index indicates a more efficient bending of light, enabling the creation of thinner and lighter lenses with enhanced vision correction capabilities. The object additively manufactured according to the method of the present disclosure may have a refractive index of 1.0, 1.1, 1.3 to 1.5, 1.6, or 1.7, or any range using any of the foregoing values as endpoints, such as 1.0 to 1.7, 1.1 to 1.6, or 1.3 to 1.5, as measured according to ASTM C1648.G. Abbe Value

[0094] The Abbe value of an additively manufactured object, such as an ophthalmic lens refers to its ability to disperse light, indicating how much chromatic aberration or color distortion occurs as light passes through the lens; a higher Abbe value implies lower chromatic aberration and better optical quality. The object additively manufactured according to the method of the present disclosure may have an Abbe value of 28, 30, 32 to 35, 36, or 38,or any range using any of the foregoing values as endpoints, such as 28 to 38, 30 to 36, or 32 to 35, as measured according to ASTM Cl 648.H. Percent (%) Transmittance

[0095] The Percent (%) Transmittance of an additively manufactured object, such as an ophthalmic lens, represents the percentage of light that passes through the lens, indicating its optical transparency; a higher % transmittance value corresponds to a greater amount of light transmission, contributing to clear vision and visual comfort for the lens. The object additively manufactured according to the method of the present disclosure may have a % transmittance of 86%, 88%, 90% to 92%, 94%, to 95%, or any range using any of the foregoing values as endpoints, such as 86% to 95%, 88% to 94%, or 90% to 92%, as measured according to ASTM D1003-9.I. Percent Haze Value

[0096] The percent (%) haze value of an additively manufactured object, such as an ophthalmic lens, describes the cloudiness of a lens caused by the scattering of light. The greater the value, the more cloudiness may be visible in the object. The object additively manufactured according to the method of the present disclosure may have a percent haze of less than 10 %, less than 8 %, less than 6 %, less than 4%, less than 2%, or less than 1%, or any range using any of the foregoing values as endpoints, such as 1-10 %, 2-8 %, or 4-6 %, as determined by ASTM D1003.J. Yellowness Index

[0097] Yellowness Index at a wavelength of 313 nanometers, also referred to as the YI E313, of an additively manufactured object, such as an ophthalmic lens, is a measure that quantifies the degree of yellow tint in the lens material when exposed to ultraviolet light, offering insight into its potential to filter harmful UV rays and enhancing visual comfort by reducing glare and improving contrast. The object additively manufactured according to the method of the present disclosure may have a YI E313 value of greater than 6, greater than 8, greater than 10, greater than 12, greater than 14, or greater than 16, as measured according to ASTM E313.K. Birefringence

[0098] As described previously, the birefringence of an additively manufactured object, such as an ophthalmic lens, is an optical property of the lens that occurs when a beam of light passes through an optical material and splits into different wavelengths, generating a rainbow effect. Circular birefringence specifically may occur when the materials of the lensintroduce a phase difference between the two circularly polarized components of light. As described previously, the object additively manufactured according to the method of the present disclosure may significantly reduce the birefringent effects, and in some cases, circular birefringent effects, as compared to similar articles manufactured by comparable techniques (e.g., horizontally / with a substrate), since the present ophthalmic article is additively manufactured in a substantially vertical orientation. Accordingly, the object additively manufactured according to the method of the present disclosure may have low (e.g., 2, as relating to Working Example 6) or no (e.g., 1, as relating to Working Example 6) birefringent effects.EXAMPLES

[0099] Aspects of the present disclosure are further illustrated by reference to the following examples. It will be apparent to those skilled in the art that many modifications, both to materials, and methods, may be practiced without departing from the scope of the disclosure.Example 1: A Monomer Optical Composition Formulation For A Vat Photopolymerization Technology

[0100] In this example, a first additively manufacturable (e.g., 3D printable), optical composition was mixed for optimal printing. The components of the formulation were constructed using the compositions below.Table 1: First Formulation of Medium Refractive Index Monomer Optical Composition'A mixture of monofunctional methacrylates and difunctional methacrylates formulated to give a polymerizate with 1.56 refractive index.Example 2: An Optical Composition Formulation For A Vat Photopolvmerization Technology

[0101] In this example, a second additively manufacturable (e.g., 3D printable), optical composition was mixed for optimal printing. The components of the formulation were constructed using the compositions below by the same method described in relation to Example 1.Table 2: Formulation of High Refractive Index Monomer Optical Composition2A mixture of 40% difunctional methacrylate and 60% di- and tri- functional thiomethacrylates (by weight) formulated to give a polymerizate with a 1.60 refractive index.Example 3: An Optical Composition Formulation For A Vat Photopolymerization Technology

[0102] In this example, a third additively manufacturable (e.g., 3D printable), optical composition was mixed for optimal printing. The components of the formulation wereconstructed using the compositions below by the same method described in relation to Example 1.Table 3: Formulation of Medium Refractive Index Monomer Optical Composition3A mixture of monofunctional methacrylates and difunctional methacrylates formulated to give a polymerizate with 1.56 refractive index.Example 4: An Optical Composition Formulation For A Vat Photopolymerization Technology

[0103] In this example, a fourth additively manufacturable (e.g., 3D printable), optical composition was mixed for optimal printing. The components of the formulation were constructed using the compositions below by the same method described in relation to Example 1.Table 4: Formulation of Medium Refractive Index Monomer Optical Composition4A mixture of monofunctional methacrylates and difunctional methacrylates formulated to give a polymerizate with 1.56 refractive index.Example 5; Printing of Medium and High Refractive Index Monomer Composition Formulation for a Vat Photopolymerization Technology

[0104] For the additive manufacturing (e.g., 3D printing) process, a computed aided design was generated to be 3D printed and properly oriented, so that slices can be digitally generated and transfer all this information including other parameters to generate the physical object in the 3D printer. A variety of lenses comprising the optical composition of Example 1 were printed using different layer thicknesses.

[0105] A computer aided design (CAD) lens geometry should be finely exported from a CAD software package and imported into an additive manufacturing slicer software package to orient the part, generate the support structure geometry, and set the manufacturing parameters described as follows:Table 5: Printing Parameters (Irradiance = 3.2 nW / cm2)

[0106] The orientation of the lens geometry was important when establishing the surface roughness outcome directly from the additive manufacturing apparatus. Therefore, avertical orientation with the optical surfaces not facing the bottom or top of the printed area are important design aspects to achieving best printability of these functional surfaces.Example 6: Smoothing the Outer Surface of the 3D Printed -4 Lens

[0107] A comparative lens (sample comparative C) was casted using traditional methods and the same optical composition as Example 1. This included the use of glass molds for a piano lens which was assembled using tape to generate a gap of around 2 mm thick. Liquid monomer composition was then poured into the cavity of the mold lenses and finally closed with the aid of the same tape holding the molds. The cased lens (comparative C) did not undergo the post-cure process described in Example 7.Example 7 : Smoothing the Outer Surface of the 3D Printed -4 Lens

[0108] Each of the printed lenses were placed in between two glass molds pieces that correspond to the exact same geometry as each surface is placed upon. Additionally, in between the glass mold and printed surfaces, additional 3D printing formulation (e.g., monomer) was added in between the mold and the lens to further aid in the smoothing of the printed surfaces. Transparent tape was used to hold the glass mold with the printed object together. The transparent tape held the assembly in place and to added pressure between the mold surfaces and the printed surfaces to assure a full contact of the liquid formulation with all surfaces while being cured.

[0109] The printed lenses in the mold were exposed to both thermal energy and UV light to cure the added monomer into any grooves on the object created from the vat photopolymerization process. The post-curing cycles included exposure to UV light with an irradiance of 9.12 mW / cm2for 2 hours at 80°C.

[0110] The post-cured lenses appeared fully transparent. However, when backlit, three main defects are still possible to be seen. The first defect was the presence of concentric circles, which were barely visible to the naked eye, but noticeable with under backlight. The same figure A shows a diagonal line or birefringence across the center of the backlit lens. This birefringence was likely caused by the multiple irradiations during the layer-by-layer process. The birefringence location varied depending on the viewing angle of the lens, which reflected the multiple layer lines during the additive process. The last defect present was the incomplete filling of sections of the lens with extra monomer during post curing, as shown onthe B section of the same picture, resulting in less transparent surfaces. This defect was influenced by the pressure applied to the molds and the amount of extra monomer used.Example 8: Properties of the 3D Printed Lens

[0111] The data in Table 6 show the comparison of typical optical properties and hardness of the optical composition. Table 7 shows similar information but for a dyed version of the optical composition. Table 8 shows similar information but for a higher refractive index composition. In both cases, the properties showed that for printed examples, particularly at lower layer thickness, the properties such as hardness, RI, transmittance and color are identical as the casted sample (comparative C). Table 9 shows optical properties from formulations with a different photoinitiator setting the example of a higher loading of this element and its effect. There are only small differences in percent haze that keeps getting shorter with smaller layer thicknesses. For birefringence a qualitative evaluation was made for all the samples tested. The criteria followed was that every sample was placed over a white background at a certain height with a light shining through the top. If a rainbow set of lines were perceived on the white paper, a birefringence effect would be recorded. If this rainbow effect was relatively thin, it would be recorded as low birefringence, but it was thicker it would be recorded as high birefringence. An example is shown in FIG. 5.Table 6: Properties of Printed Lenses (with composition 1)Table 7: Properties of Printed Lenses (with dye) with Medium Refractive Index FormulationTable 8: Properties of Printed Lenses with Higher Refractive Index FormulationTable 9: Properties of Printed Lenses with Medium Refractive Index Formulation

[0112] Casted samples were the baseline to compare against for any printed sample. All samples at or below 25 pm layer thickness showed consistent property performance with percentage of haze being the most changing when moving down in layer thickness.

[0113] The lenses following the post-cure process had a smoother surface than the same lenses immediately following printing and the comparative casted lens (Sample I). The casted sample was made with a disc or piano lens, while the printed and post-processed lenses were -4 geometry lenses. The lenses were measured on the stage of a Keyence VK-X260K / X250K confocal scanning laser microscope The samples were imaged with a 20x magnification lens. Once the images were captured, they were taken to a VK file analyzer program where surface roughness was acquired with the generic software parameters. The height maps were normalized so the center region would be 0 microns for each sample.

[0114] Table 10 shows the smoothness properties of post-cure lens sample F versus a lens casted, and the sample F lens printed without the post-cure process. These results show how the post-process method provides as good a surface as good as a casted or traditional manufacturing method.Table 10: Surface Roughness of LensSample B 2.40 + 0.615 3.45 + 0.961PrintedSample B 0.046 + 0.007 0.062 + 0.012Postprocessed

[0115] Wherein particular examples of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims. This disclosure is therefore intended to cover any variations, uses, or adaptations of the disclosure using its general principles. Further, this disclosure is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this disclosure pertains and which fall within the limits of the appended claims.ASPECTS

[0116] Aspect 1 is an optical composition for vat photopolymerization, comprising:_a monomer or a blend of monomers comprising at least one of a (meth)acrylate and / or a thio-(meth) acrylate functional group; 0.20 mass % to 3 mass % of a photoinitiator; 0.40 mass % to 2.2 mass % of a UV absorber; and 0.40 mass % to 2.2 mass % of a hindered amine light stabilizer (HALS), based on a total mass of the optical composition.

[0117] Aspect 2 is the optical composition of Aspect 1, wherein the monomer or the blend of monomers comprises two or more (meth)acrylate and / or thio-(meth)acrylate functional groups.

[0118] Aspect 3 is the optical composition of either Aspect 1 or Aspect 2, wherein the UV absorber comprises at least one of a benzophenone and a triazine.

[0119] Aspect 4 is the optical composition of any one of Aspects 1-3, wherein the photoinitiator comprises an acylphosphine oxide type 1 photoinitiator.

[0120] Aspect 5 is the optical composition of any one of Aspects 1-4, wherein the UV absorber comprises an absorption range from 300 nm to 405 nm.

[0121] Aspect 6 is the optical composition of any one of Aspects 1-5, further comprising 0.0001 wt. % to 0.0005 wt. % of at least one additive; wherein the at least one additive is one of a pigment, a fixed tint dye, an antioxidant, a polymerization modifier, a photosensitizers, and an internal mold release agent.

[0122] Aspect 7 a method of forming an optical article, the optical article comprising an optical surface that defines an optical geometry, comprising: printing the optical article of a predetermined curved or flat boundary using vat photopolymerization, the curved or flat boundary defining the optical geometry; wherein the optical article is printed such that the optical surface of the optical article extends in a z-axis, the z-axis being perpendicular to a print surface the optical article is printed on; and wherein the vat photopolymerization comprises an optical composition, the optical composition comprising: a monomer or a blend of monomers comprising at least one of a (meth)acrylate and thio-(meth)acrylate functional group; 0.20 mass % to 3 mass % of a photoinitiator; 0.40 mass % to 2.2 mass % of a UV absorber; and 0.40 mass % to 2.2 mass % of a hindered amine light stabilizer (HALS), based on a total mass of the optical composition.

[0123] Aspect 8 is the method of Aspect 7, further comprising printing support structures for the optical article, the support structures anchoring the optical article along a periphery edge of the optical article to the print surface.

[0124] Aspect 9 is the method of Aspect 8, further comprising removing the support structures from the optical article.

[0125] Aspect 10 is the method of any one of Aspect 7-9, further comprising: enclosing the optical article in a mold, the mold having a hollow portion defining a mold optical geometry, wherein the mold optical geometry is substantially similar to the optical geometry of the optical article; filling the mold with excess optical composition; securing the mold with a fastener; exposing the mold to UV light and heat; removing the optical article from the mold.

[0126] Aspect 11 is the method of Aspect 10, wherein filling the mold with excess optical composition comprises filling the mold with an amount of optical composition such that any grooves or defects in a surface of the optical article is filled with the excess optical composition; wherein exposing the mold to UV light and heat cures the excess optical composition within the grooves or defects in the surface of the optical article.

[0127] Aspect 12 is the method of any one of Aspects 10-11, wherein the optical article removed from the mold has a percent haze of less than 2 % haze, as determined by ASTM D1003.

[0128] Aspect 13 is the method of any one of Aspects 10-12, wherein the optical article removed from the mold has a hardness of at least 120 N / mm2, as measured by DIN EN ISO 14577-1.

[0129] Aspect 14 is the method of any one of Aspects 10-13, wherein the optical article removed from the mold has a surface roughness of less than 0.2 pm.

[0130] Aspect 15 is the method of any one of Aspects 10-14, wherein the optical article comprises a transmittance value higher than 80%, as measured according to ASTM D 1003-9.

[0131] Aspect 16 is the method of any one of Aspects 10-15, wherein the optical geometry of the optical article comprises at least one of a planar, plano-convex, double-convex, plano-concave, double-concave, positive achromatic, and aspheric geometry.

[0132] Aspect 17 is the method of any one of Aspects 7-16, wherein printing the optical article comprises printing successive layers each with a layer thickness from 0.1 pm to 10 pm.

[0133] Aspect 18 is the method of any one of Aspects 7-17, wherein printing the optical article using vat photopolymerization comprises a bottom exposure time of 20 seconds to 32 seconds.

[0134] Aspect 19 is the method of any one of Aspects 7-18, wherein printing the optical article using vat photopolymerization comprises an off time of 0.1 seconds to 5 seconds.

[0135] Aspect 20 is the method of any one of Aspects 7-19, wherein printing the optical article using vat photopolymerization comprises printing 2 base layers to 7 base layers of the optical article.

Claims

CLAIMSWhat is claimed is:

1. An optical composition for vat photopolymerization, comprising:a monomer or a blend of monomers comprising at least one of a (meth) acrylate and / or a thio-(meth)acrylate functional group;0.20 mass % to 3.0 mass % of a photoinitiator;0.40 mass % to 2.2 mass % of a UV absorber; and0.40 mass % to 2.2 mass % of a hindered amine light stabilizer (HALS), based on a total mass of the optical composition.

2. The optical composition of claim 1, wherein the monomer or the blend of monomers comprises two or more (meth)acrylate and / or thio-(meth)acrylate functional groups.

3. The optical composition of either claim 1 or claim 2, wherein the UV absorber comprises at least one of a benzophenone and a triazine.

4. The optical composition of any one of claims 1-3, wherein the photoinitiator comprises an acylphosphine oxide type 1 photoinitiator.

5. The optical composition of any one of claims 1-4, wherein the UV absorber comprises an absorption range from 300 nm to 405 nm.

6. The optical composition of any one of claims 1-5, further comprising 0.0001 wt. % to 0.0005 wt. % of at least one additive;wherein the at least one additive is one of a pigment, a fixed tint dye, an antioxidant, a polymerization modifier, a photosensitizers, and an internal mold release agent.

7. A method of forming an optical article, the optical article comprising an optical surface that defines an optical geometry, comprising:printing the optical article of a predetermined curved or flat boundary using vat photopolymerization, the curved or flat boundary defining the optical geometry;wherein the optical article is printed such that the optical surface of the optical article extends in a z-axis, the z-axis being perpendicular to a print surface the optical article is printed on; andwherein the vat photopolymerization comprises an optical composition, the optical composition comprising:a monomer or a blend of monomers comprising at least one of a (meth) acrylate and thio-(meth)acrylate functional group;0.20 mass % to 3.0 mass % of a photoinitiator;0.40 mass % to 2.2 mass % of a UV absorber; and 0.40 mass % to 2.2 mass % of a hindered amine light stabilizer (HALS), based on a total mass of the optical composition.

8. The method of claim 7, further comprising printing support structures for the optical article, the support structures anchoring the optical article along a periphery edge of the optical article to the print surface.

9. The method of claim 8, further comprising removing the support structures from the optical article.

10. The method of any one of claims 7-9, further comprising:enclosing the optical article in a mold, the mold having a hollow portion defining a mold optical geometry, wherein the mold optical geometry is substantially similar to the optical geometry of the optical article;filling the mold with excess optical composition;securing the mold with a fastener;exposing the mold to UV light and heat;removing the optical article from the mold.

11. The method of claim 10, wherein filling the mold with excess optical composition comprises filling the mold with an amount of optical composition such that any grooves or defects in a surface of the optical article is filled with the excess optical composition;wherein exposing the mold to UV light and heat cures the excess optical composition within the grooves or defects in the surface of the optical article.

12. The method of any one of claims 10-11, wherein the optical article removed from the mold has a percent haze of less than 2 % haze, as determined by ASTM D1003.

13. The method of any one of claims 10-12, wherein the optical article removed from the mold has a hardness of at least 120 N / mm2, as measured by DIN EN ISO 14577-1.

14. The method of any one of claims 10-13, wherein the optical article removed from the mold has a surface roughness of less than 0.2 pm.

15. The method of any one of claims 10-14, wherein the optical article comprises a transmittance value higher than 80%, as measured according to ASTM D 1003-9.

16. The method of any one of claims 10-15, wherein the optical geometry of the optical article comprises at least one of a planar, plano-convex, double-convex, plano-concave, double-concave, positive achromatic, and aspheric geometry.

17. The method of any one of claims 7-16, wherein printing the optical article comprises printing successive layers each with a layer thickness from 0.1 pm to 10 pm.

18. The method of any one of claims 7-17, wherein printing the optical article using vat photopolymerization comprises a bottom exposure time of 20 seconds to 32 seconds.

19. The method of any one of claims 7-18, wherein printing the optical article using vat photopolymerization comprises an off time of 0.1 seconds to 5 seconds.

20. The method of any one of claims 7-19, wherein printing the optical article using vat photopolymerization comprises printing 2 base layers to 7 base layers of the optical article.

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