WO2021154897A1 - Photohardenable compositions including an upconverting component and methods - Google Patents

Abstract

Photohardenable compositions for forming three-dimensional objects including (i) a hardenable resin component; (ii) an upconverting component; (iii) a photoinitiator; and (iv) a thixotrope are disclosed. Methods for forming three-dimensional objects are also disclosed.

Description

PHOTOHARDENABLE COMPOSITIONS INCLUDING AN UPCONVERTING COMPONENT

AND METHODS

CLAIM OF PRIORITY

This application claims priority to U.S. Provisional Patent Application No. 62/966,945 filed January 28, 2020, U.S. Provisional Patent Application No. 63/003,051 filed March 31, 2020, U.S. Provisional Patent Application No. 63/003,078 filed March 31, 2020, U.S. Provisional Patent Application No.63/091,863 filed October 14, 2020, U.S. Provisional Patent Application No. 63/121,906 filed December 05, 2020, and U.S. Provisional Patent Application No. 63/121,905 filed December 05, 2020, each of which is hereby incorporated herein by reference in its entirety for all purposes.

TECHNICAL FIELD OF THE INVENTION

The present relates to the technical field of three-dimensional printing and related materials.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to photohardenable compositions and methods for printing a three-dimensional object. The photohardenable compositions and methods include a hardenable resin component, and upconverting component for absorbing excitation light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths, and a photoinitiator that is activatable upon excitation by upconverted light emitted by the upconverting component in the second range of wavelengths, and a thixotrope.

In accordance with one aspect of the present invention, there is provided a photohardenable composition for forming a three-dimensional object, the composition comprising: (i) a hardenable resin component comprising a monomer, an oligomer, a pre-polymer, or a polymer, or a mixture including one or more of any of the foregoing; (ii) an upconverting component for absorbing excitation light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths; (iii) a photoinitiator, the photoinitiator being activatable upon excitation by upconverted light emitted by the upconverting component in the second range of wavelengths for initiating hardening of the photohardenable composition; and (iv) a thixotrope to at least partially restrict movement of the three-dimensional object or one or more regions thereof in the photohardenable composition during formation. In accordance with another aspect of the present invention, there is provided a photohardenable composition for forming a three-dimensional object in a volume of the photohardenable composition, the composition comprising: (i) a hardenable resin component comprising a monomer, an oligomer, or a polymer, or a mixture including any one or more of any of the foregoing; (ii) an upconverting component for absorbing excitation light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths; (iii) a photoinitiator, the photoinitiator being activatable upon excitation by upconverted light emitted by the upconverting component in the second range of wavelengths for initiating hardening of the photohardenable composition; and (iv) a thixotrope to at least partially restrict movement of the three-dimensional object in the volume of the photohardenable composition during formation.

In accordance with still another aspect of the invention, there is provided a method of forming a three-dimensional object in a volume of a photohardenable composition, the method comprising: (a) providing a volume of the photohardenable composition included within a container wherein at least a portion of the container is optically transparent so that the photohardenable composition is accessible by excitation light; (b) directing excitation light in the first range of wavelengths into the volume of the photohardenable composition, wherein the excitation light has an excitation intensity so that local hardening of the photohardenable composition is achieved at a selected location within the volume of the photohardenable composition; and (c) optionally repeating step (b) at the same or a different selected location within the volume of the photohardenable composition until the three-dimensional object is formed, wherein the photohardenable composition comprises: (i) a hardenable resin component comprising a monomer, an oligomer, a pre-polymer, or a polymer, or a mixture including one or more of any of the foregoing; (ii) an upconverting component for absorbing excitation light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths; (iii) a photoinitiator, the photoinitiator being activatable upon excitation by upconverted light emitted by the upconverting component in the second range of wavelengths for initiating hardening of the photohardenable composition; and (iv) a thixotrope to at least partially restrict movement of the three-dimensional object or one or more regions thereof in the photohardenable composition during formation.

In accordance with yet another aspect of the invention, there is provided a method of forming a three-dimensional object, comprising: (a) providing a volume of the photohardenable composition included within a container wherein at least a portion of the container is optically transparent so that the photohardenable composition is accessible by excitation light; (b) directing excitation light in the first range of wavelengths into the volume of the photohardenable composition, wherein the excitation light has an excitation intensity so that local hardening of the photohardenable composition is achieved at a selected location within the volume of the photohardenable composition; and (c) optionally repeating step (b) at the same or a different selected location within the volume of the photohardenable composition until the three-dimensional object is formed, wherein the photohardenable composition a photohardenable composition for forming a three-dimensional object, the composition comprises: (i) a hardenable resin component comprising a monomer, an oligomer, or a polymer, or a mixture including any one or more of any of the foregoing; (ii) an upconverting component for absorbing excitation light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths; (iii) a photoinitiator, the photoinitiator being activatable upon excitation by upconverted light emitted by the upconverting component in the second range of wavelengths for initiating hardening of the photohardenable composition; and (iv) a thixotrope to at least partially restrict movement of the three-dimensional object in the volume of the photohardenable composition during formation.

The foregoing, and other aspects and embodiments described herein and contemplated by this disclosure all constitute embodiments of the present invention.

It should be appreciated by those persons having ordinary skill in the art(s) to which the present invention relates that any of the features described herein in respect of any particular aspect and/or embodiment of the present invention can be combined with one or more of any of the other features of any other aspects and or embodiments of the present invention described herein, with modifications as appropriate to ensure compatibility of the combinations. Such combinations are considered to be part of the present invention contemplated by this disclosure.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.

Other embodiments will be apparent to those skilled in the art from consideration of the description, from the claims, and from practice of the invention disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

Various aspects and embodiments of the present invention will be further described in the following detailed description. The present invention relates to photohardenable compositions and methods for printing a three-dimensional object. The photohardenable compositions and methods include a hardenable resin component, and upconverting component for absorbing excitation light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths, and a photoinitiator that is activatable upon excitation by upconverted light emitted by the upconverting component in the second range of wavelengths, and a thixotrope. Inclusion of a thixotrope advantageously can at least partially restrict movement of the three-dimensional object in the volume of the photohardenable composition during formation.

In accordance with one aspect of the present invention, there is provided a photohardenable composition for forming a three-dimensional object, the composition comprising: (i) a hardenable resin component comprising a monomer, an oligomer, a pre-polymer, or a polymer, or a mixture including one or more of any of the foregoing; (ii) an upconverting component for absorbing excitation light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths; (iii) a photoinitiator, the photoinitiator being activatable upon excitation by upconverted light emitted by the upconverting component in the second range of wavelengths for initiating hardening of the photohardenable composition; and (iv) a thixotrope to at least partially restrict movement of the three-dimensional object or one or more regions thereof in the photohardenable composition during formation.

In accordance with another aspect of the present invention, there is provided a photohardenable composition for forming a three-dimensional object in a volume of the photohardenable composition, the composition comprising: (i) a hardenable resin component comprising a monomer, an oligomer, or a polymer, or a mixture including any one or more of any of the foregoing; (ii) an upconverting component for absorbing excitation light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths; (iii) a photoinitiator, the photoinitiator being activatable upon excitation by upconverted light emitted by the upconverting component in the second range of wavelengths for initiating hardening of the photohardenable composition; and (iv) a thixotrope to at least partially restrict movement of the three-dimensional object in the volume of the photohardenable composition during formation.

Photohardenable compositions in accordance with the present invention can further include one or more additives. Examples of additives include, but are not limited to, a light blocker, a defoamer, a stabilizer, an oxygen scavenger, and a non-reactive solvent diluent. Any additive can be a single additive or a mixture of additives. For example, a light blocker additive can comprise a single light blocker or a mixture of two or more light blockers. Additives are preferably selected so that they do not react with the hardenble resin component, upconverting component, photoinitiator, thixotrope, or other additives that may be included in the photohardenable composition.

A photohardenable composition in accordance with the present invention is particularly well-suited for use in three-dimensional-printing methods and systems, especially volumetric three- dimensional-printing methods and systems.

Advantageously, inclusion of a thixotrope in a photohardenable composition in accordance with the present invention can facilitate forming three-dimensional objects without the need for support structures employed in conventional layer-by-layer three-dimensional or additive manufacturing processes to provide mechanical support to the object being fabricated where, for example, a region of the object is not fully supported by previously formed layers. Avoiding the use of support structures also avoids the step of removing support structures from the object after printing which can lead to surface deformations or other flaws in the object being formed.

Inclusion of a thixotrope in a photohardenable composition in accordance with the present invention can further advantageously facilitate forming a three-dimensional object at a selected position in a volume of the photopolymerizable composition with a minimal displacement of the object in the volume of photohardenable composition during formation. Preferably the minimal displacement is an amount of movement that is acceptable for precisely producing the intended object geometry during the time interval required to form the object. Most preferably, the position of the object in the volume of the photohardenable composition remains fixed position during formation of the object.

Preferably the three-dimensional object is fully suspended in the volume of the photohardenable composition.

The photopolymerizable composition preferably displays non-Newtonian rheological behavior. For photopolymerizable liquids that display non-Newtonian rheological behavior, preferred steady shear viscosities are less than 30,000 centipoise, more preferably less than 10,000 centipoise, and most preferably less than 1,000 centipoise. (Steady shear viscosity refers to the viscosity after the thixotrope network has broken up.)

Preferably, the hardenable resin included in the photohardenable composition is selected to achieve an optically transparent or clear liquid, which is desirable in processes and systems in which light, e.g., excitation light, is directed into the composition or light, e.g., upconverted light, is emitted from species included in the composition.

Photopolymerizable compositions in accordance with the present invention can be pourable, which is particularly desirable for handling purposes and for use of the compositions in three- dimensional printing processes and systems.

The photohardenable composition can have a viscosity in a range from about 0.5 centipoise to about 10,000,000 centipoise.

Examples of viscosities under the conditions in which the method is carried out, that may be useful include, for example, but without limitation, greater than 1 centipoise, greater than 1,000 centipoise, and greater than 5,000 centipoise.

For printing a three-dimensional object that is floating within a volume of the photohardenable composition in a container or build chamber, a higher viscosity can be desirable for keeping the object that is being printed suspended. A photohardenable composition having a viscosity of about 1,000 centipoise or higher, 2,000 centipoise or higher, 4,000 centipoise or higher, or even higher can be preferred in this regard.

As mentioned above, the photopolymerizable composition preferably displays non- Newtonian rheological behavior. For photopolymerizable liquids that display non-Newtonian rheological behavior, preferred steady shear viscosities are less than 30,000 centipoise, more preferably less than 10,000 centipoise, and most preferably less than 1,000 centipoise. (Steady shear viscosity refers to the viscosity after the thixotrope network has been overcome. Shear rates suitable for measuring steady shear viscosity may range from about 0.00001 s ¹ to about 1000 s ¹.)

A photohardenable composition in accordance with the various aspects of the present invention can include from about 0.5 to about 95, preferably from about 50 to about 95, weight percent hardenable component; from about 0.1 to about 85, preferably from about 1 to about 20, weight percent upconverting component; from about 0.1 to about 25, preferably from about 0.5 to about 10, weight percent photoinitiator; and from about 0.05 to about 15, preferably from about 1 to about 10, weight percent thixotrope.

The hardenable composition can further include any one or more of the following: from about 0.005 to about 1 weight percent defoamer. from about 0.005 to about 10 weight percent light blocker. from about 0.00005 to about 1 weight percent stabilizer.

Unless otherwise indicated, specified weight percents are based on the total weight of the photohardenable composition.

Detailed information concerning the various components of photohardenable compositions in accordance with the present invention is provided below.

HARDENABLE RESIN COMPONENT

A hardenable resin component suitable for use in the photohardenable composition may be any hardenable resin suitable for hardening, e.g., by free-radical polymerization, cationic polymerization, anionic polymerization, insertion polymerization such as Ziegler-Natta or metallocene-catalyzed olefin polymerizations, ring opening polymerization (e.g. of epoxides, oxetanes, benzoxazines, silicones, lactones, carbonates, etc.), metathesis polymerization (e.g. of cyclic or acyclic olefins), condensation polymerization (e.g. polyesters, polyamides, polyurethanes), and cross-linking. Examples of hardenable resin components that may be included in the photohardenable composition include, for example, without limitation, monomers, oligomers such as dimers or trimers, pre -polymers, and polymers, or mixtures including one or more of the foregoing, such as, for example, without limitation, free-radically polymerizable or crosslinkable ethylenically-unsaturated species including, for example, acrylates, methacrylates, acrylamides, methacrylamides, vinyl ethers, vinyl esters, vinyl amides, vinyl imidazoles, vinyl oxazolidinones such as 5-methyl-3-vinyl-l,3-oxazolidin-2-one, vinyl carbazoles, maleimides, methylene malonates, allyl ethers, cyanoacrylates, cyclopolymerizable monomers such as methyl 2- ((allyloxy)methyl)acrylate, and certain vinyl compounds such as styrenes), as well as cationically- polymerizable monomers and oligomers and cationically -crosslinkable polymers (which are most commonly acid-initiated and which include, for example, epoxies, vinyl ethers, cyanate esters, oxetanes, lactones, lactams, cyclosiloxanes, benzoxazines, etc.), and the like, and mixtures thereof.

A non-limiting list of examples of such suitable hardenable resins include ethylenically- unsaturated species described, for example, by Palazzotto et al. in U.S. Pat. No. 5,545,676 at column 1, line 65, through column 2, line 26, that include mono-, di-, and poly-acrylates and methacrylates (for example, methyl acrylate, methyl methacrylate, ethyl acrylate, isopropyl methacrylate, n-hexyl acrylate, stearyl acrylate, allyl acrylate, glycerol diacrylate, glycerol triacrylate, ethyleneglycol diacrylate, diethyleneglycol diacrylate, triethyleneglycol dimethacrylate, 1,3-propanediol diacrylate,

1.3 -propanediol dimethacrylate, trimethylolpropane triacrylate, 1,2,4-butanetriol trimethacrylate,

1.4-cyclohexanediol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, sorbitol hexacrylate, bis[l-(2-acryloxy)]-p- ethoxyphenyldimethylmethane, bis[l-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane, trishydroxyethyl-isocyanurate trimethacrylate, the bis-acrylates and bis-methacrylates of polyethylene glycols of molecular weight about 200-500, copolymerizable mixtures of acrylated monomers such as those of U.S. Pat. No. 4,652,274, and acrylated oligomers such as those of U.S. Pat. No. 4,642,126); unsaturated amides (for example, methylene bis-acrylamide, methylene bis- methacrylamide, 1,6-hexamethylene bis-acrylamide, diethylene triamine tris- acrylamide and beta- methacrylaminoethyl methacrylate); vinyl compounds (for example, styrene, diallyl phthalate, divinyl succinate, divinyl adipate, and divinyl phthalate); and the like; and mixtures thereof. Suitable reactive polymers include polymers with pendant (meth)acrylate groups, for example, having from 1 to about 50 (meth) acrylate groups per polymer chain. Examples of such polymers include aromatic acid (meth) acrylate half ester resins. Other useful reactive polymers curable by free radical chemistry include those polymers that have a hydrocarbyl backbone and pendant peptide groups with free -radically polymerizable functionality attached thereto, such as those described in U.S. Pat. No. 5,235,015 (Ali et al.). Mixtures of two or more monomers, oligomers, and/or reactive polymers can be used if desired.

Suitable cationically-reactive species are described, for example, by Oxman et al. in U.S.

Pat. Nos. 5,998,495 and 6,025,406 and include epoxy resins. Such materials, broadly called epoxides, include monomeric epoxy compounds and epoxides of the polymeric type and can be aliphatic, alicyclic, aromatic, or heterocyclic. These materials generally have, on the average, at least 1 polymerizable epoxy group per molecule (preferably, at least about 1.5 and, more preferably, at least about 2). The polymeric epoxides include linear polymers having terminal epoxy groups (for example, a diglycidyl ether of a polyoxyalkylene glycol), polymers having skeletal oxirane units (for example, polybutadiene polyepoxide), and polymers having pendant epoxy groups (for example, a glycidyl methacrylate polymer or copolymer). The epoxides can be pure compounds or can be mixtures of compounds containing one, two, or more epoxy groups per molecule. These epoxy- containing materials can vary greatly in the nature of their backbone and substituent groups. For example, the backbone can be of any type and substituent groups thereon can be any group that does not substantially interfere with cationic cure at room temperature. Illustrative of permissible substituent groups include halogens, ester groups, ethers, sulfonate groups, siloxane groups, nitro groups, phosphate groups, and the like. The molecular weight of the epoxy-containing materials can vary from about 58 to about 100,000 or more.

Useful epoxy-containing materials include those which contain cyclohexene oxide groups such as epoxycyclohexanecarboxylates, typified by 3,4-epoxycyclohexylmethyl-3,4- epoxycyclohexanecarboxylate, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2- methylcyclohexane carboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate. A more detailed list of useful epoxides of this nature is set forth in U.S. Pat. No. 3,117,099.

Other epoxy-containing materials that are useful include glycidyl ether monomers. Examples are glycidyl ethers of polyhydric phenols obtained by reacting a polyhydric phenol with an excess of a chlorohydrin such as epichlorohydrin (for example, the diglycidyl ether of 2,2-bis- (2,3epoxypropoxyphenol)-propane). Additional examples of epoxides of this type are described in U.S. Pat. No. 3,018,262, and in Handbook of Epoxy Resins, Lee and Neville, McGraw-Hill Book Co., New York (1967).

Suitable hardenable resins also can include epoxy resins. Examples of such epoxy resins include octadecylene oxide, epichlorohydrin, styrene oxide, vinyl cyclohexene oxide, glycidol, glycidylmethacrylate, diglycidyl ethers of Bisphenol A, vinylcyclohexene dioxide, 3,4epoxycyclohexylmethyl-3,4-epoxycyclohexene carboxylate, 3,4-epoxy-6- methylcyclohexylmethyl-3,4-epoxy-6-methyl-cyclohexene carboxylate, bis(3,4-epoxy-6- methylcyclohexylmethyl) adipate, bis(2,3-epoxycyclopentyl) ether, aliphatic epoxy modified from polypropylene glycol, dipentene dioxide, epoxidized polybutadiene, silicone resin containing epoxy functionality, flame retardant epoxy resins, 1,4-butanediol diglycidyl ether of phenolformaldehyde novolak, resorcinol diglycidyl ether, bis(3,4-epoxycyclohexyl)adipate, 2-(3,4epoxycyclohexyl-5,5- spiro-3, 4-epoxy) cyclohexane-meta-dioxane, vinylcyclohexene monoxide 1,2-epoxyhexadecane, alkyl glycidyl ethers such as alkyl Cs-Cio glycidyl ether, alkyl C12-C14 glycidyl ether, butyl glycidyl ether, cresyl glycidyl ether, p-tert-butylphenyl glycidyl ether, polyfunctional glycidyl ethers such as diglycidyl ether of 1,4-butanediol, diglycidyl ether of neopentyl glycol, diglycidyl ether of cyclohexanedimethanol, trimethylol ethane triglycidyl ether, trimethylol propane triglycidyl ether, poly glycidyl ether of an aliphatic polyol, polyglycol diepoxide, bisphenol F epoxides, and 9,9-bis[4- (2,3 -epoxypropoxy )-pheny 1] fluorenone.

Other useful epoxy resins comprise copolymers of acrylic acid esters of glycidol (such as glycidylacrylate and glycidylmethacrylate) with one or more copolymerizable vinyl compounds. Examples of such copolymers are 1 : 1 styrene-glycidylmethacrylate, 1 : 1 methylmethacrylate- glycidylacrylate, and a 62.5:24:13.5 methylmethacrylate-ethyl acrylate-glycidylmethacrylate. Other useful epoxy resins are well known and contain such epoxides as epichlorohydrins, alkylene oxides (for example, propylene oxide), styrene oxide, alkenyl oxides (for example, butadiene oxide), and glycidyl esters (for example, ethyl glycidate).

Useful epoxy-functional polymers include epoxy-functional silicones such as those described in U.S. Pat. No. 4,279,717 (Eckberg). These are polydimethylsiloxanes in which 1-20 mole % of the silicon atoms have been substituted with epoxyalkyl groups (preferably, epoxy cyclohexylethyl, as described in U.S. Pat. No. 5,753,346 (Kessel)).

Blends of various epoxy-containing materials can also be utilized. Such blends can comprise two or more weight average molecular weight distributions of epoxy-containing compounds (such as low molecular weight (below 200), intermediate molecular weight (about 200 to 10,000), and higher molecular weight (above about 10,000)). Alternatively or additionally, the epoxy resin can contain a blend of epoxy-containing materials having different chemical natures (such as aliphatic and aromatic) or functionalities (such as polar and non-polar). Other cationically-reactive polymers (such as vinyl ethers and the like) can additionally be incorporated, if desired.

Additional examples of epoxies include aromatic glycidyl epoxies and cycloaliphatic epoxies.

Suitable cationically-reactive species also include vinyl ether monomers, oligomers, and reactive polymers (for example, methyl vinyl ether, ethyl vinyl ether, tert-butyl vinyl ether, isobutyl vinyl ether, triethyleneglycol divinyl ether, trimethylpropane trivinyl ether, divinyl ether resins, and mixtures thereof. Blends (in any proportion) of one or more vinyl ether resins and/or one or more epoxy resins can also be utilized. Polyhydroxy-functional materials (such as those described, for example, in U.S. Pat. No. 5,856,373 (Kaisaki et al.)) can also be utilized in combination with epoxy- and/or vinyl ether-functional materials.

A hardenable resin component can comprise one or more multifunctional acrylate monomers. SR399 from Sartomer (which contains a pentaacrylate monomer) is an example of a preferred component for inclusion in the photohardenable composition.

Aliphatic urethane acrylates are also preferred hardenable resin components for inclusion in the photohardenable composition.

Mixtures of multifunctional acrylate monomers, such as SR399, and aliphatic urethane acrylates can also be used.

An acrylamide monomer can also be included in a photopolymerizable composition to act as a solvent for mixing the photoinitiator in the hardenable resin component.

Additional information concerning monomers, oligomers, prepolymers, and/or polymers that may be useful is described in WO2019/025717 of Baldeck, et al., published February 7, 2019, International Application No. Application No. PCT/US2019/063629, of Congreve, et al., filed November 27, 2019, and U.S. Patent No. 7,005,229 of Nirmal et al, issued February 28, 2006. each of which is hereby incorporated herein by reference in its entirety.

UPCONVERTING COMPONENT

An upconverting component can absorb excitation light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths.

An upconverting component can comprises one or more compositions that alone or in combination can absorb light at one or more wavelengths in a first range of wavelengths and emit light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths.

An upconverting component can preferably comprise upconverting nanoparticles for absorbing light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths. The upconverting nanoparticles preferably include a sensitizer and an annihilator, the sensitizer being selected to absorb light at one or more wavelengths in the first range of wavelengths and the annihilator being selected to emit light at one or more wavelengths in the second range of wavelengths after transfer of energy from the sensitizer to the annihilator, the second range of wavelengths being shorter than the first range of wavelengths.

Upconverting nanoparticles preferably have an average particle size less than the wavelength of the exciting light. Examples of preferred average particle sizes are less than 100 nm, less than 80 nm, less than 50 nm, less than 30 nm, less than 20 nm, although still larger, or smaller, nanoparticles can also be used. Most preferably, the upconverting nanoparticles have an average particle size creates no appreciable light scattering.

Examples of materials for use as sensitizers and annihilators are described in International Application No. PCT/US2019/063629, of Congreve, et al., filed November 27, 2019, S. Sanders, et al., “Photon Upconversion in Aqueous Nanodroplets”, J. Amer. Chem. Soc. 2019, 141, 9180-9184, and Beauti, Sumar, Abstract entitled “Search for New Chromophore Pairs for Triplet-Triplet Annihilation Upconversion” ISEF Projects Database, Finalist Abstract (2017), available at https://abstracts.societvforscience.org. each of the foregoing being hereby incorporated herein by reference in its entirety. WO2019/025717 of Baldeck, et al., published February 7, 2019, and International Application No. PCT/US2019/063629, of Congreve, et al., filed November 27, 2019 also provide additional information that may be useful concerning the concentration of the upconverting nanoparticles and the concentrations of the sensitizer and annihilator in the photohardenable composition.

An annihilator can comprise molecules capable of receiving a triplet exciton from a molecule of the sensitizer through triplet-triplet energy transfer, undergo triplet fusion with another annihilator molecule triplet to generate a higher energy singlet that emits light in a second range of wavelengths to excite the photoinitiator to initiate polymerization or cross-linking of the hardenable resin component. Examples of annihilators include, but are not limited to, polycyclic aromatic hydrocarbons, e.g., anthracene, anthracene derivatives (e.g., 9,10- bis(triisopropysilyl)ethynyl)anthracene, 9,10diphenyl anthracene (DPA) 9,10-dimethylanthracene (DMA2-chloro-9,10-diphenylanthracene), 2-carbonitrile-9,10-diphenylanthracene, 9,10 bis(phenylethynyl)anthracene (BPEA), 2-chloro-9,10-bis (phenylethynyl) anthracene (2CBPEA), 5,6,1 l,12-tetraphenylnaphthacene(rubrene), pyrene and or perylene (e.g., tetra-t-butyl perylene (TTBP). Mixtures including one or more of the foregoing can also be used. The above anthracene molecules can be substituted or unsubstituted and/or functionalized with a halogen. Preferred halogenated anthracene derivative include, for example, DPA or 9,10- bis(triisopropysilyl)ethynyl)anthracene further functionalized with a halogen (e.g., fluorine, chlorine, bromine, iodine), more preferably at the 2 or at the 2 and 6 position. Bromine can be a preferred halogen. Fluorescent organic dyes can be preferred.

A sensitizer can comprise at least one molecule capable of passing energy from a singlet state to a triplet state when it absorbs the photonic energy of excitation light in a first range of wavelengths. Examples of sensitizers include, but are not limited to, porphyrins, metalloporphyrins (e.g., palladium tetraphenyl tetrabutyl porphyrin (PdTPTBP), platinum octaethyl porphyrin (PtOEP), octaethyl-porphyrin palladium (PdOEP), palladium-tetraphenylporphyrin (PdTPP), palladium-meso- tetraphenyltetrabenzoporphyrin (PdPh4TBP), 1,4,8, 11,15, 18,22, 25-octabutoxyphthalocyanine (PdPc (OBu)), 2,3-butanedione (or diacetyl), which can be substituted or unsubstituted, derivatives of any of the foregoing, or a combination of several of the above molecules. Other examples of sensitizers include osmium sensitizers. See, for example, R. Haruki, et al, Chem. Commun., 2020, Advance Article accepted 13 May 2020 and published 13 May 2020, the abstract of which is available at https://doi.org/10.1039/D0CC02240C, which paper is hereby incorporated herein by reference.

The sensitizer preferably absorbs the excitation at one or more wavelengths in the first range of wavelengths in order to make maximum use of the energy thereof.

A consideration in selecting a photosensitizer/ annihilator pair may include the compatibility of the pair with the photoinitiator being used. Preferably upconverting nanoparticles include a core portion that includes the sensitizer and the annihilator in a liquid (e.g., oleic acid) and an encapsulating coating or a shell (e.g., silica) around the outer surface of the core portion. The core can comprise a micelle, that includes the sensitizer and annihilator in a liquid. (A micelle is typically formed from one or more surfactants, e.g., having a relatively hydrophilic portion and a relatively hydrophobic portion.) Examples of preferred upconverting nanoparticles include nanocapsules described in International Application No. PCT/US2019/063629, of Congreve, et ah, filed November 27, 2019 which is hereby incorporated herein by reference in its entirety. Other information concerning nanocapsules that may be useful includes International Publication No. WO2015/059179, of Landfester, et ah, which published April 30, 2015 and S. Sanders, et ah, “Photon Upconversion in Aqueous Nanodroplets”, J. Amer. Chem. Soc. 2019, 141, 9180-9184, each of which is hereby incorporated herein by reference in its entirety.

Upconverting nanoparticles can be surface treated to functionalize the surface thereof with functional groups for facilitating distribution of the nanoparticles in the hardenable resin component. Surfactants and other materials useful as surface treatments are commercially available. Examples of surface treatment materials for functionalizing the nanoparticle surfaces include, but are not limited to, poly-ethylene glycols, silanes, for example, but not limited to, PEG-silanes, (3- aminopropyl)triethoxysilane, (3-glycidyloxypropyl)trimethoxysilane, 2-

[methoxy(polyethyleneoxy)9-i2propyl]trimethoxysilane, 3-glycidoxypropyldimethoxymethylsilane, Isooctyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N- (triethoxysilylpropyl)-O-poly(ethylene oxide)4-6 urethane, 0-[Methoxy (polyethylene oxide)]-N- (triethoxysilylpropyl)carbamate, octadecyltrimethoxysilane, triethoxy vinylsilane, trimethoxy[2-(7- oxabicyclo[4.1.0]hept-3-yl)ethyl]silane, trimethoxyphenylsilane, vinyltrimethoxysilane, 3- (trimethoxysilyl)propyl methacrylate, N-[3-(trimethoxysilyl)propyl]aniline.

Photoinitiator

The photoinitiator can be readily selected by one of ordinary skill in the art, taking into account its suitability for the mechanism to be used to initiate polymerization as well as its suitability for and/or compatibility with the hardenable resin component to be polymerized.

A photoinitiator can comprise a single photoinitiator or a combination of photoinitiators or a photoinitiator system including two or more components, at least one of which is a photoinitiator.

For example, the photoinitiators may form free radicals or cations upon initiation. Examples of photopolymerization initiators, but are not limited to, 2-isopropylthioxanthone, benzophenone, 2,2-azobisisobutyronitrile, camphorquinone, diphenyltrimethylbenzoylphosphine oxide (TPO), HCP (l-hydroxycyclohexylphenylketone), BAPO (phenylbis-2,4,6-(trimethylbenzoyl)phosphine oxide), Speedcure VLT (Bis(2,6-difluoro-3-(l -hydropyrrol- l-yl)phenyl)titanocene). Other examples include Norrish Type-1 and Norrish Type-2 initiators.

A preferred photoinitiator comprises a free-radical photoinitiator system including a ketocoumarin dye, an iodonium salt, and a borate salt which generates free radicals capable of hardening the hardenable resin component upon excitation of the ketocoumarin by upconverted light emitted by the upconverting component in the second range of wavelengths and energy and electron transfer reactions between the ketocoumarin and its reaction products

In a photohardenable composition including the above-described photoinitiator system including a ketocoumarin, borate salt, and iodonium salt, the composition can include: from about 0.005 to about 5 weight percent ketocoumarin based on the total weight of the hardenable component and the photoinitiator system; from about 0.005 to about 10 weight percent borate salt based on the total weight of the hardenable component and the photoinitiator system; and from about 0.1 to about 10 weight percent iodonium salt based on the total weight of the hardenable component and the photoinitiator system.

A photohardenable composition including the above photoinitiator system can include about 40 parts upconverting component to about 100 parts total of the hardenable component and photoinitiator system.

Following is information concerning the ketocoumarin dye, iodonium salt, and borate salt components included in the preferred free-radical photoinitiator system mentioned above.

The above-described photoinitiator system can be activated by upconverted light generated by the upconverting component in a second range of wavelengths from about 440 to about 510 nm and not activated by the excitation light being used.

Ketocoumarin Dyes

Ketocoumarin dyes suitable for use in the free -radical photoinitiator system include ketocoumarins that absorb upconverted light at one or more wavelengths in the second range of wavelengths. Examples include, without limitation, aminofunctional ketocoumarins; 3- ketocoumarins such as 3-(7-methoxy-3-coumarinoyl)-l-methylpyridinium p-toluenesulfonate; 4-(7- methoxy-3-coumarinoyl)-N,N,N-trimethylanilinium fluorosulfonate; sodium 4-(7-methoxy-3- coumarinoyl)benzoate; sodium 4-(7-methoxy-3-coumarinoyl)benzenesulfonate; 3-aroylcoismarins; 3,3'-carbonyibiscoumarins, including, but not limited to, 3,3’-carbonylbis(sodium 6- coumarincarboxylate), 3,3'-carbonylbis(6-coumarincarboxylic acid), 3,3’-carbonylbis(7- dialkylaminocoumarin) where each of the 3-ketocoumarinalkyl groups is independently a substituted or unsubstituted alkyl group, wherein an alkyl group is a aliphatic hydrocarbon chain containing 1-30 carbons, including, but not limited to, 3,3’-carbonylbis(7-diethylaminocoumarin), 3,3’-carbonylbis(7-di-(n-hexyl)aminocoumarin), and 3,3’-carbonylbis(7-(N-ethyl-N- propyl)aminocoumarin). Other ketocoumarins suitable for use in the present invention can be identified by the skilled artisan in the relevant art.

Additional examples of ketocoumarins that may be useful are described in U.S. Patent No. 4,366,228 of Specht, et al, issued December 28, 1982, U.S. Patent No. 7,005,229 of Nirmal et al, issued February 28, 2006, and D.P. Specht, et al., “Ketocoumarins A New Class of Triplet Sensitizers”, Tetrahedron Vol. 38, No. 9, pp 1203 to 1211, 1982, each of which is hereby incorporated herein by reference in its entirety.

Preferably a ketocoumarin dye is purified to remove at least a portion and preferably all impurities that absorb light in the first range of wavelengths. Purification can be carried out by recrystahization, column purification techniques, and other suitable purification methods readily identifiable by a person of ordinary skill in the relevant art.

Iodonium Salts

Iodonium salts suitable for inclusion in the free-radical photoinitiator system include those described by Palazzotto et al. in U.S. Pat. No. 5,545,676 at column 2, lines 28 through 46. Suitable iodonium salts are also described in U.S. Pat. Nos. 3,729,313, 3,741,769, 3,808,006, 4,250,053 and 4,394,403. The iodonium salt can be a simple salt (for example, containing an anion such as Cl , Br, G or C4H5 SO3 ) or a metal complex salt (for example, containing by way of example and without limitation, SbF₆, PF₆ , BF4 , tetrakis(perfluorophenyl)borate, SbFsOH , AsF₆). Examples of other counterions contained in an iodonium salt include by way of example, without limitation, perfluoro- 1-butanesulfonate, trifluoromethanesulfonate, or p-toluenesulfonate. Mixtures of iodonium salts can be used if desired.

Examples of useful aromatic iodonium complex salts include diphenyliodonium tetrafluoroborate; di(4-methylphenyl)iodonium tetrafluoroborate; phenyl-4-methylphenyliodonium tetrafluoroborate; di(4-heptylphenyl)iodonium tetrafluoroborate; di(3-nitrophenyl)iodonium hexafluorophosphate; di(4-chlorophenyl)iodonium hexafluorophosphate; di(naphthyl)iodonium tetrafluoroborate; di(4-trifluoromethylphenyl)iodonium tetrafluoroborate; diphenyliodonium hexafluorophosphate; di(4-methylphenyl)iodonium hexafluorophosphate; diphenyliodonium hexafluoroarsenate; di(4-phenoxyphenyl)iodonium tetrafluoroborate; phenyl-2-thienyliodonium hexafluorophosphate; 3,5-dimethylpyrazolyl-4-phenyliodonium hexafluorophosphate; diphenyliodonium hexafluoroantimonate; 2,2'-diphenyliodonium tetrafluoroborate; di(2,4- dichlorophenyl)iodonium hexafluorophosphate; di(4-bromophenyl)iodonium hexafluorophosphate; di(4-methoxyphenyl)iodonium hexafluorophosphate; di(3-carboxyphenyl)iodonium hexafluorophosphate; di(3-methoxycarbonylphenyl)iodonium hexafluorophosphate; di(3- methoxysulfonylphenyl)iodonium hexafluorophosphate; di(4-acetamidophenyl)iodonium hexafluorophosphate; di(2-benzothienyl)iodonium hexafluorophosphate; and diphenyliodonium hexafluoroantimonate; and the like; and mixtures thereof. Aromatic iodonium complex salts can be prepared by metathesis of corresponding aromatic iodonium simple salts (such as, for example, diphenyliodonium bisulfate) in accordance with the teachings of Beringer et al., J. Am. Chem. Soc. 81, 342 (1959).

Preferred iodonium salts include diaryl iodonium salts, including for example, but not limited to, diaryliodonium hexafluoroantimonate, diaryliodonium hexafluorophosphate, diphenyliodonium salts (such as diphenyliodonium chloride, diphenyliodonium hexafluorophosphate, and diphenyliodonium tetrafluoroborate), diaryliodonium triflate, (4-(2- hydroxytetradecyl-oxy)phenyl)phenyliodonium hexafluoroantimonate, (4- octoxyphenyl)phenyliodonium hexafluoroantimonate, bis(4-t-butylphenyl)iodonium hexafluorophosphate, diphenyliodonium tetraphenylborate, and mixtures thereof. A most preferred iodonium salt is bis(4-tert-butylphenyl)iodonium hexafluorophosphate.

Additional examples of iodonium salts that may be useful are described in U.S. Patent No. 8,087,354 of Teng, issued January 3, 2012 and U.S. Patent No. 7,005,229 of Nirmal et al, issued February 28, 2006, each of which is hereby incorporated herein by reference in its entirety.

Borate Salts

Preferred borate salts for use in the free-radical photoinitiator system include aryl borate salts (including for example alkyltriaryl borate salts, dialkyldiaryl borate salts, trialkylaryl borate salts), wherein the alkyl and aryl groups can be independently substituted or unsubstituted.

Examples of aryl borate salts having one aryl group in a molecule include sodium salt, lithium salt, potassium salt, magnesium salt, tetrabutyl ammonium salt, tetramethyl ammonium salt, tetraethyl ammonium salt, methyl pyridinium salt, ethyl pyridinium salt, butyl pyridinium salt, methyl quinolinium salt, ethyl quinolinium salt and butyl quinolinium salt of trialkylphenylboron, trialkyl(p-chlorophenyl)boron, trialkyl(p-fluorophenyl)boron, trialkyl(3,5- bistrifluoromethyl)phenylboron, trialkyl[3,5-bis ( 1 , 1 , 1 ,3,3,3-hcxafluoro-2-mcthoxy-2-propyl )- phenyl]boron, trialkyl(p-nitrophenyl)boron, tialkyl(m-nitophenyl)boron, trialkyl(p- butylphenyl)boron, tialkyl(m-butylphenyl)boron, trialkyl(m-butyloxyphenyl)boron, trialkyl(m- octyloxyphenyl)boron and trialkyl(p-octyloxyphenyl)boron (alkyl group is n-butyl group, n-octyl group, n-dodecyl group, etc.).

Examples of aryl borate salts having two aryl groups in one molecule include sodium salt, lithium salt, potassium salt, magnesium salt, tetrabutyl ammonium salt, tetramethyl ammonium salt, tetraethyl ammonium salt, methyl pyridinium salt, ethyl pyridinium salt, butyl pyridinium salt, methyl quinolinium salt, ethyl quinolinium salt and butyl quinolinium salt of dialkyldiphenylboron, dialkyldi(p-chlorophenyl)boron, dialkyldi(p-chlorophenyl)boron, dialky ldi(3, 5- bistrifluoromethyl)phenylboron, dialkyldi[3,5-bis( 1,1, 1,3,3, 3-hexafluoro-2-methoxy-2- propyl)phenyl]boron, dialkyldi(p-nitrophenyl)boron, dialkyldi(m-nitrophenyl)boron, dialkyldi(p- butylphenyl) boron, dialkyldi(m-butylphenyl)boron, dialkyldi(m-butyloxyphenyl)boron, dialkyldi(m-octyloxyphenyl)boron, and dialkyldi(p-octyloxyphenyl)boron (alkyl group is n-butyl group, n-octyl group, n-dodecyl group, etc.).

Examples of aryl borate salts having three aryl groups in one molecule include sodium salt, lithium salt, potassium salt, magnesium salt, tetrabutyl ammonium salt, tetramethyl ammonium salt, tetraethyl ammonium salt, methyl pyridinium salt, ethyl pyridinium salt, butyl pyridinium salt, methyl quinolinium salt, ethyl quinolinium salt and butyl quinolinium salt of monoalkyltriphenylboron, monoalkyltri(p-chlorophenyl)boron, monoalkyltri(p-chlorophenyl)boron, monoalkyltri(3,5-bistrifluoromethyl)phenylboron, monoalkyltri[3,5-bis( 1,1, 1,3,3, 3-hexafluoro-2- methoxy-2-propyl)-phenyl]bor on, monoalkyltri(p-nitrophenyl)boron, monoalkyltri(m- nitrophenyl)boron, monoalkyltri(p-butylphenyl)boron, monoalkyltri(m-butylphenyl)boron, monoalkyltri(m-butyloxyphenyl)boron, monoalkyltri(m-octyloxyphenyl)boron, and monoalkyltri(p- octyloxyphenyl)boron (alkyl group is n-butyl group, n-octyl group, n-dodecyl group, etc.).

Examples of aryl borate salts having four aryl groups in one molecule include sodium salt, lithium salt, potassium salt, magnesium salt, tetrabutyl ammonium salt, tetramethyl ammonium salt, tetraethyl ammonium salt, methyl pyridinium salt, ethyl pyridinium salt, butyl pyridinium salt, methyl quinolinium salt, ethyl quinolinium salt and butyl quinolinium salt of tetraphenylboron, tetrakis(p-fluorophenyl)boron, tetrakis(p-chlorophenyl)boron, tetrakis(3,5- bistrifluoromethyl)phenylboron, tetrakis [3,5-bis( 1,1,1 ,3,3,3-hexafluoro-2-methoxy-2- propyl)phenyl]boron, tetrakis(p-nitrophenyl)boron, tetrakis(m-nitrophenyl)boron, tetrakis(p- butylphenyl)boron, tetrakis(m-butylphenyl)boron, tetrakis(m-butyloxyphenyl)boron, tetrakis(m- octyloxyphenyl)boron, tetrakis(p-octyloxyphenyl)boron, (p-fluorophenyl)triphenylboron, (3,5- bistrifluoromethyl)phenyltriphenylboron, (p-nitrophenyl)triphenylboron, (m-butyloxyphenyl)- triphenylboron, (p-butyloxyphenyl)triphenylboron, (m-octyloxyphenyl)triphenylboron and (p- octyloxyphenyl)triphenylboron (alkyl group is n-butyl group, n-octyl group, n-dodecyl group, etc.).

Preferably the borate salt includes a quaternary ammonium or alkali metal counterion.

A preferred borate salt is borate salt comprises butyryl choline butyltriphenylborate.

An aryl borate salt may be used alone or with one or more other borate salts.

Additional examples of borate salts that may be useful are described in U.S. Patent No. 5,744,511 of Kazama, et al., issued April 28, 1998, U.S. Patent No. 7,005,229 of Nirmal et al, issued February 28, 2006, U.S. Patent No. 5,854,298 of McNay, et al., issued December 29, 1998, and W097/21737 of Spectra Group Limited, Inc., published June 19, 1997, each of which is hereby incorporated herein by reference in its entirety.

Additional information concerning the above-described free-radical photoinitiator system comprising: a ketocoumarin dye, an iodonium salt, and a borate salt and photohardenable compositions and methods including same can be found in U.S. Application No. 63/091,863 of Arndt, et al., filed October 14, 2020, which is hereby incorporated herein by reference in its entirety.

Information concerning other photoinitiators that may be useful can be found in WO2019/025717 of Baldeck et al., published February 7, 2019, and International Application No. Application No. PCT/US2019/063629, of Congreve, et al., filed November 27, 2019, each of which is hereby incorporated herein by reference in its entirety.

THIXOTROPES

Thixotropes suitable for inclusion in the photohardenable compositions of the present invention include, for example and without limitation, urea derivatives; modified urea compounds such as Rheobyk 410 and Rheobyk-D 410 available from BYK-Chemie GmbH, part of the ALTANA Group; fumed metal oxides (also referred to as pyrogenic metal oxides) including for example, but not limited to, fumed silica, fumed alumina; zirconia; precipitated metal oxides including for example, but not limited to, precipitated silica, precipitated alumina; unmodified and organo-modified phyllosilicate clays; dimer and trimer fatty acids; polyether phosphates; oxidized polyolefins; hybrid oxidized polyolefins with polyamide; alkali soluble/s wellable emulsions; cellulosic ethers; hydrophobically-modified alkali soluble emulsions; hydrophobically-modified ethylene oxide-based urethane; sucrose benzoate; ester terminated polyamides; tertiary amide terminated polyamides; polyalkyleneoxy terminated polyamides; polyether amides; acrylamidomethyl-subsituted cellulose ester polymers; polyethyleneimine; polyurea; organoclays; hydrogenated castor oil; organic base salts of a clay mineral (e.g., montmorillonite) and other silicate-type materials; aluminum, calcium, and zinc salts of fatty acids, such as 1 auric or stearic acid.

See U.S. Patent Nos. 6,548,593 of Merz, et al., issued April 15, 2003, and 9,376,602 of Walther, et al. issued June 28, 2016, which are hereby incorporated herein by reference in their entireties, for information relating to urea derivatives that may be useful as thixotropes.

Thermally reversible gellants such as ester terminated polyamides, tertiary amide terminated polyamides, polyalkyleneoxy terminated polyamides, and polyether amides, and combinations thereof, may be desirable for us as thixotropes. Examples include Crystasense LP1, Crystasense LP2, Crystasense LP3, Crystasense MP, Crystasense HP4, and Crystasense HP5 available from Croda.

Metal oxides that have been surface-treated to impart dispersibility characteristics compatible with the hardenable resin component may be desirable for use as thixotropes.

A thixotrope can be included in the photohardenable composition in an amount in a range from about 0.5 weight percent to about 15 weight percent of the photohardenable composition.

A thixotrope is preferably included in the photohardenable composition in an amount effective to at least partially restrict movement of the three-dimensional object or one or more regions thereof in the photohardenable composition during formation.

More preferably, the thixotrope is included in the composition in an amount effective to at least partially restrict movement of the three-dimensional object suspended (without contact with a container surface) in the volume of photohardenable composition during formation. Most preferably the position of the object in the volume of the photohardenable composition remains fixed position during formation of the object.

OTHER ADDITIVES

As mentioned above, photohardenable compositions in accordance with the present invention can further include one or more additives. Examples of additives include, but are not limited to, a light blockers, a defoamer, a stabilizer, an oxygen scavenger, and a non-reactive solvent diluent. Any additive can be a single additive or a mixture of additives. For example, a light blocker additive can comprise a single light blocker or a mixture of two or more light blockers. Additives are preferably selected so that they do not react with the hardenble resin component, upconverting component, photoinitiator, thixotrope, or any other additives that may be included in the photohardenable composition.

A light blocker can be included to control the spread of upconverted light and improve the selectivity and resolution of hardening. Preferable a light blocker has an absorption wavelength range that overlaps at least partially with the absorption wavelength range of the photoinitiator and the emission wavelength range of the upconverted light. Examples of preferred light blockers include azo dyes such as Sudan 1, Sudan 3, and other light blockers that can be readily identified by one of ordinary skill in the relevant art.

A light blocker can be included in a photohardenable composition that includes a photoinitiator system including a ketocoumarin, borate salt, and iodonium salt. In such case, the light blocker can be included in the photohardenable composition in an amount from about 0.0005 to about 1 weight percent light blocker based on the total weight of the hardenable component and the photoinitiator system.

A defoamer can be included to aid in removing bubbles introduced during processing and handling. A preferred defoamer is BYK 1798 (a silicone based defoamer) available from BYK- Chemie GmbH, part of the ALTANA Group.

A stabilizer can be included to improve shelf-life of the photohardenable composition and/or to control the level of cure and or spatial resolution during printing. An example of preferred stabilizer is TEMPO (2,2,6,6-tetramethylpiperidinooxy free radical available from Sigma- Aldrich). Examples of other stabilizers include, but are not limited to hindered phenols such as butylated hydroxy toluene; hydroquinone and its derivatives such as hydroquinone methyl ether; hindered amine light stabilizers; alkylated diphenylamines; and phosphite esters.

An oxygen scavenger can be included to react with oxygen (e.g., singlet oxygen, dissolved oxygen) present in the photohardenable composition. WO2019/025717 of Baldeck, et al., published February 7, 2019 provides information that may be useful regarding antioxidant additives.

A non-reactive solvent diluent can be included. Examples include, but are not limited to, acetone, amyl acetate, n-butanol, sec-butanol, tert-butanol, butyl acetate, cyclohexanone, decane, dimethylacetamide, dimethylformamide, dimethylsulfoxide, dipropylene glycol, dipropylene glycol methyl ether, ethanol, ethyl acetate, ethylene glycol, glycerol, heptane, isopropanol, isopropyl acetate, methyl ethyl ketone, N-methyl pyrrolidone, propylene carbonate, propylene glycol, propylene glycol diacetate, tetrahydrofuran, tripropylene glygol methyl ether, toluene, water, xylenes.

In accordance with still another aspect of the invention, there is provided a method of forming a three-dimensional object in a volume of a photohardenable composition, the method comprising: (a) providing a volume of the photohardenable composition included within a container wherein at least a portion of the container is optically transparent so that the photohardenable composition is accessible by excitation light; (b) directing excitation light in the first range of wavelengths into the volume of the photohardenable composition, wherein the excitation light has an excitation intensity so that local hardening of the photohardenable composition is achieved at a selected location within the volume of the photohardenable composition; and (c) optionally repeating step (b) at the same or a different selected location within the volume of the photohardenable composition until the three-dimensional object is formed, wherein the photohardenable composition a photohardenable composition for forming a three-dimensional object, the composition comprises: (i) a hardenable resin component comprising a monomer, an oligomer, a pre-polymer, or a polymer, or a mixture including one or more of any of the foregoing;

(ii) an upconverting component for absorbing excitation light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths;

(iii) a photoinitiator, the photoinitiator being activatable upon excitation by upconverted light emitted by the upconverting component in the second range of wavelengths for initiating hardening of the photohardenable composition; and (iv) a thixotrope to at least partially restrict movement of the three-dimensional object or one or more regions thereof in the photohardenable composition during formation.

In accordance with yet another aspect of the invention, there is provided a method of forming a three-dimensional object, comprising: (a) providing a volume of the photohardenable composition included within a container wherein at least a portion of the container is optically transparent so that the photohardenable composition is accessible by excitation light; (b) directing excitation light in the first range of wavelengths into the volume of the photohardenable composition, wherein the excitation light has an excitation intensity so that local hardening of the photohardenable composition is achieved at a selected location within the volume of the photohardenable composition; and (c) optionally repeating step (b) at the same or a different selected location within the volume of the photohardenable composition until the three-dimensional object is formed, wherein the photohardenable composition a photohardenable composition for forming a three-dimensional object, the composition comprises: (i) a hardenable resin component comprising a monomer, an oligomer, or a polymer, or a mixture including any one or more of any of the foregoing; (ii) an upconverting component for absorbing excitation light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths; (iii) a photoinitiator, the photoinitiator being activatable upon excitation by upconverted light emitted by the upconverting component in the second range of wavelengths for initiating hardening of the photohardenable composition; and (iv) a thixotrope to at least partially restrict movement of the three-dimensional object in the volume of the photohardenable composition during formation.

A suitable first range of wavelengths can be from about 400 to about 800 nm. Preferably the first range of wavelengths is from about 605 nm to about 650 nm, from about 520 to about 540 nm, from about 425 to about 460 nm, from about 680 nm to about 740 nm.

A suitable second range of wavelengths can be from about 300 nm to about 600 nm. Preferably the second range of wavelength is from about 400 nm to about 500 nm, from about 360 nm to about 420 nm, about 420 nm to about 480 nm, from about 440 to about 460 nm, from about 440 nm to about 510 nm, from about 460 nm to about 530 nm.

Power densities or intensities of excitation light directed into the volume of photohardenable composition to cause hardening (e.g., by polymerization, crosslinking) to occur may be, without limitation, less than 1000 W/cm², less than 500 W/cm², less than 100 W/cm², less than 50 W/cm², less than 10 W/cm², less than 5 W/cm², less than 1 W/cm², less than 500 mW/cm², less than 100 mW/cm², etc.

Most preferably, a nonlinear, such as a quadratic, relationship exists between the power of the excitation light and emission from the annihilator when a sensitizer and annihilator are included in the photohardenable composition.

Optionally, the excitation light can be temporally and or spatially modulated. Optionally, the intensity of the excitation light can be modulated. Optionally, source drive modulation can be used to adjust the absolute power of the light beam.

Spatially modulated excitation light can be created by known spatial modulation techniques, including, for example, a liquid crystal display (LCD), a digital micromirror device (DMD), or a microLED array. Other known spatial modulation techniques can be readily identified by those of ordinary skill in the relevant art.

Methods in accordance with the present invention can be useful for printing three- dimensional objects from photohardenable compositions that demonstrate non-Newtonian behavior and which can be solidified at volumetric positions impinged upon by excitation light in the first range of wavelengths by upconversion-induced photopolymerization, crosslinking, or hardening. Preferably, the upconversion comprises triplet upconversion (or triplet-triplet annihilation, TTA) which may be used to produce light of a higher energy relative to light used to photoexcite the sensitizer or annihilator. Most preferably, the sensitizer absorbs low energy light and upconverts it by transferring energy to the annihilator, where two triplet excitons may combine to produce a higher energy singlet exciton that may emit high-frequency or shorter-wavelength light, e.g., via annihilation upconversion.

A method of the present invention includes providing a volume of a photohardenable composition included within a container wherein at least a portion of the container is optically transparent so that the photohardenable composition is accessible by excitation light. Preferably, the entire container is optically transparent.

Optically transparent portions of a container can be constructed from a material comprising, for example, but not limited to, glass, quartz, fluoropolymers (e.g., Teflon FEP, Teflon AF, Teflon PFA), cyclic olefin copolymers, polymethyl methacrylate (PMMA), polynorbornene, sapphire, or transparent ceramic.

Examples of container shapes include, but are not limited to, a cylindrical container having a circular or oval cross-section, a container having straight sides with a polygonal cross-section or a rectangular or square cross-section.

Preferably the optically transparent portion(s) of the container is (are) also optically flat.

Optionally, one or more filters are added to at least a surface of any optically transparent portions of the container to block undesired light, e.g., with a wavelength the same as the upconverted light (e.g., light in the second range of wavelengths), to prevent unintentional curing.

Preferably the photohardenable composition is degassed, purged or sparged with an inert gas before or after being introduced into the container and is maintained under inert conditions, e.g., under an inert atmosphere, while in the container which is preferably closed during printing. This can prevent introduction of oxygen into the container while the three-dimensional object is being printed or formed. Preferably the container is sealed or otherwise closed in an air-tight manner to prevent introduction of oxygen into the container during printing. The seal or other closing techniques that may be used should not be permanent so at least that the printed objects and unpolymerized material can be removed from the container. In certain instances, depending, for example, upon the materials used, the photohardenable composition is preferably substantially oxygen free (e.g., less than 50 ppm oxygen) during printing.

In the method described herein, the container may be rotated to provide additional angles of illumination or projection of excitation light into the volume of photohardenable composition contained therein. This can be of assistance in patterning object volumes or surfaces more accurately or it can be used as a means of providing multiple exposure of a given feature from different angles.

In the method described herein, the container may be stationary while a beam or optical projection of excitation light is being directed into the photohardenable composition.

The methods disclosed herein can also include the use commercially available optical projection and filtering techniques that can assist in providing a very narrow depth of focus or systems that employ two or more optical projection methods at once.

Before printing, a digital file of the object to be printed is obtained. If the digital file is not of a format that can be used to print the object, the digital file is then converted to a format that can be used to print the object. An example of a typical format that can be used for printing includes, but is not limited to, an STL file. Typically, the STL file is then sliced into two-dimensional layers with use of three-dimensional slicer software and converted into G-Code or a set of machine commands, which facilitates building the object. See B. Redwood, et ah, “The 3D Printing Handbook - Technologies, designs applications”, 3D HUBS B.V. 2018.

Examples of sources of the excitation light source for use in the methods described herein include laser diodes, such as those available commercially, light emitting diodes, DMD projection systems, micro-LED arrays, vertical cavity lasers (VCLs). In some embodiments, the excitation radiation source (e.g., the light source) is a light-emitting diode (LED).

The excitation light can be directing into the volume of photohardenable composition in a continuous or intermittent manner. Intermittent excitation can include random on and off application of light or periodic application of light. Examples of periodic application of light includes pulsing. Excitation can alternatively be applied as a combination of both continuous excitation light and intermittent light, including, for example, the application of intermittent excitation light that is preceded or followed by irradiation with continuous light.

The methods of the present invention can further include post-treatment of the three- dimensional object(s) formed. Examples of post-treatments include, but are not limited to, washing, post-curing (e.g., by light, e-beam, heat, non-ionizing radiation, ionizing radiation, pressure, humidity, or simultaneous or sequential combinations of techniques), metrology, freeze-dry processing, critical point drying, and packaging.

Photohardenable compositions in accordance with the present invention are suitable for use as a photopolymerizable liquid in the methods and/or systems described in any of U.S. Patent Application No. 62/966,945 of Kazlas, filed January 28, 2020, U.S. Patent Application No. 63/003,051 of Kazlas, filed March 31, 2020, U.S. Patent Application No. 63/003,078 of Eric M. Arndt filed March 31, 2020, U.S. Patent Application No. 63/034,164 of Peter T. Kazlas, et al., filed June 3, 2020, and U.S. Patent Application No. 63/034,184 of Karen Twietmeyer, et ah, filed June 3, 2020, each of the foregoing being hereby incorporated herein by reference in its entirety.

Other information concerning optical systems that may useful in connection with the various aspects of the present inventions includes Texas Instruments Application Report DLPA022- July 2010 entitled “DLP™ System Optics”; Texas Instruments “TI DL^R Technology for 3D Printing - Design scalable high-speed stereolithography [sic] systems using TI DLP technology” 2016;

Texas Instruments “DLP65000.65 1018p MVSP Type A DMD”, DLP6500, DLPS040A-October 2014 - Revised October 2016; and Y-H Lee, et al., “Fabrication of Periodic 3D Nanostructuration for Optical Surfaces by Holographic Two-Photon-Polymerization”, Int’l Journal of Information and Electronics Engineering, Vol 6, No. 3, May 2016, each of the foregoing being hereby incorporated herein by reference in its entirety.

When used as a characteristic of a portion of a container or build chamber, “optically transparent” refers to having high optical transmission to the wavelength of light being used, and “optically flat” refers to being non-distorting (e.g., optical wavefronts entering the portion of the container or build chamber remain largely unaffected).

EXAMPLES

The examples provided herein are provided as examples and not limitations, wherein a number of modifications of the exemplified compositions and processes are contemplated and within the scope of the present invention.

UPCONVERTING NANOCAPSULE SYNTHESIS

Distilled water, titrated to pH 10.5 with sodium hydroxide (200 niL), is chilled over an ice bath and then poured into to a Vitamix Blender (Amazon.com) in an inert atmosphere. Tire stock solution containing sensitizer and annihilate· (1.45 mL) is carefully dispensed into the water in one portion (stock solution: PdTBTP (0.5 mg/niL and Br-TIPS anthracene (10 mg/niL) in 99% oleic acid)). The solution is blended for 60 s at the maximum speed, and the emulsion is transferred to the flask and immediately stirred at high speed. (3-ammopropyl)triethoxysiIane (0.75 mL, Acros Organics) is added until the mixture becomes transparent, and then 5K MPEG-Silane (4 g, Nanosoft Polymers) is immediately added to prevent capsule aggregation. After 10 minutes tetraethyl orthosilicate (TEOS, 36 mL, Sigma Aldrich) is added in one portion. The flask is sealed with a septum and the solution is stirred vigorously for 30 minutes at room temperature. Then, the flask is heated to 65 °C at constant pressure for 2 days. The reaction crude is allowed to cool to room temperature, poured into a centrifuge tube, and centrifuged at 7000 rpm for one hour at room temperature (18-22 °C), after which the pellet is discarded. Tire solution is then centrifuged at 7000 rpm for 14 hours at room temperature. After the second centrifuge, the Upcon verting Nanocapsule (UCNC) paste is transferred from the glovebox to a round bottom flask where 100 mL of ethanol and 10 mL of water, as well as 2 mL of 30% NH30H and is stirred until a homogeneous solution is formed. To this solution is added at 60 degrees Celsius 6 mL of 3-(Trimethoxysilyl)propyl methacrylate. The solution is stirred 24 hours at 60 degrees Celsius, then centrifuged at 6000 RPM for 8 hours to obtain the solid capsule paste, discarding the ethanol. This paste is redispersed in 100 mL of N,N-dimethylacrylamide and stirred 4 hours at 60 degrees Celsius to remove any external sensitizer that might remain, and centrifuged one more time at 6000 RPM for 8 hours to obtain the final capsule paste that is dispersed at 60 wt% in N,N-dimefhylacrylamide for subsequent dispersion into resin.

RESIN MIXING PROCEDURE

45 mg 3,3'-carbonyl-bis(7-diethylaminocoumarin) (recrystallized three times from o- dichlorobenzene via hexane vapor diffusion, 99%, Acros Organics) is weighed out and added to a 40-mL amber septum-top scintillation vial. 30 mg butyrylcholine triphenylbutylborate (Borate V, Spectra Group Limited, Inc.) is weighed out and added to the vial. 300 mg bis(4-tert- butylphenyl)iodonium hexafluorophosphate (98%, Sigma Aldrich) is weighed out and added to the vial. 4.5 mg Sudan I (technical grade, Sigma Aldrich) is weighed out and added to the vial. 0.75 g N,N-dimethylacrylamide (99.5%, Sigma Aldrich) is added to the vial by disposable plastic pipet, and the vial is placed in a heating block at 65°C for 5 min. The vial is vortexed for 20 s to complete dissolution of the powders. 6.0 g capsules dispersion (35.0 wt% capsules dry weight in N,N- dimethylacrylamide; see procedure below) is added to the vial by disposable plastic pipet. The vial is mixed in a speedmixer (model DAC 150.1 FVZ-K, Flacktek) for 1 min at 3100 rpm. 10.5 g difunctional aliphatic urethane acrylate (Genomer 4259, Rahn) is added to the vial by large bore plastic syringe. The vial is speedmixed for 1 min at 3100 rpm. 3.0 g dipentaerythritol pentaacrylate (SR 399, Sartomer) is added to the vial by large bore plastic syringe. 15 pL defoamer (BYK 1798) is added to the vial by capillary piston pipette. The vial is speedmixed for 1 min at 3100 rpm. 0.75 g thixotrope (Rheobyk 410, BYK) is added to the vial by disposable plastic pipet. The vial is speedmixed for 1 min at 2100 rpm. The vial is transferred to the glovebox, and 90 pL 0.1 w/v% 2,2,6,6-tetramethylpiperidinooxy free radical (98%, Sigma Aldrich) solution in N,N- dimethyl acrylamide is added by micropipette. The vial is resealed, placed in a heating block at 45 °C, and then sparged with pure nitrogen for 12 min.

CAPSULE DISPERSION PROCEDURE

To make a dispersion of capsules suitable for mixing into resin, a quantity of capsule slurry (typically 2 g to 100 g) obtained from centrifugation is transferred to a suitable plastic jar. The jar is mixed in a speedmixer (model DAC 150.1 FVZ-K, Flacktek) to mix the capsules and distribute the capsules evenly in the bottom of the jar. A small quantity (about 0.1-1 g) of mixed capsule slurry is placed in a disposable aluminum pan. The masses of the sample and pan are recorded. The mass of the remaining capsule slurry in the jar is recorded. The pan is placed in a vacuum oven set 130°C to dry under vacuum for at least 2 hr. The pan is removed from the oven and the combined mass of dried samples and pan is recorded. The solids fraction of the capsule slurry is calculated as the dried capsules mass (difference in final and empty pan masses) divided by the initial sample mass times 100%. A typical range of solids fraction in the capsule slurry is about 35 wt% to about 70 wt%. A quantity of N,N-dimethylacrylamide is added to the jar containing the remaining capsule slurry to adjust the solids content to 35 wt%. The jar is speedmixed until a homogeneous dispersion is obtained. Mixing time and speed is adjusted based on the consistency of the material. Typical mixing speeds and times are 3500 rpm and 3 min. The mixing may be conducted multiple times at the same or different speeds and times. If any nondispersable material remains, the dispersion is poured or pressed through a disposable paint strainer (190 pm mesh) into a new jar for storage.

Other information that may be useful in connection with the photohardenable compositions and methods of the present invention includes WO 2020/113018 A1 of the President And Fellows Of Harvard College, published June 4, 2020, U.S. Patent Application No. 62/911,125 of Congreve, et ah, filed October 4, 2019, U.S. Patent Application No. 62/911,128 of Congreve, et ah, filed October 4, 2019, U.S. Application No. 63/013,457 of Congreve, et ah, filed April 22, 2020, U.S. Patent Application No. 62/966,945 of Kazlas, filed January 28, 2020, U.S. Patent Application No. 63/003,051 of Kazlas, filed March 31, 2020, U.S. Patent Application No. 63/003,078 of Eric M. Arndt filed March 31, 2020, U.S. Patent Application No. 63/034,164 of Peter T. Kazlas, et ah, filed June 3, 2020, and U.S. Patent Application No. 63/034,184 of Karen Twietmeyer, et ah, filed June 3, 2020, and U.S. Application No. 63/091,863 of Arndt, et ah, Filed October 14, 2020. As used herein, the singular forms "a", "an" and "the" include plural unless the context clearly dictates otherwise. Thus, for example, reference to an emissive material includes reference to one or more of such materials.

Applicant specifically incorporates the entire contents of all cited references in this disclosure. Further, when an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range.

Other embodiments of the present invention will be apparent to those skilled in the art from consideration of the present specification and practice of the present invention disclosed herein. It is intended that the present specification and examples be considered as exemplary only with a true scope and spirit of the invention being indicated by the following claims and equivalents thereof.

Claims

WHAT IS CLAIMED IS:

1. A photohardenable composition for forming a three-dimensional object, the composition comprising:

(i) a hardenable resin component comprising a monomer, an oligomer, a pre-polymer, or a polymer, or a mixture including one or more of any of the foregoing;

(ii) an upconverting component for absorbing excitation light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths;

(iii) a photoinitiator, the photoinitiator being activatable upon excitation by upconverted light emitted by the upconverting component in the second range of wavelengths for initiating hardening of the photohardenable composition; and

(iv) a thixotrope to at least partially restrict movement of the three-dimensional object or one or more regions thereof in the photohardenable composition during formation.

2. A photohardenable composition for forming a three-dimensional object in a volume of the photohardenable composition, the composition comprising:

(i) a hardenable resin component comprising a monomer, an oligomer, or a polymer, or a mixture including any one or more of any of the foregoing;

(ii) an upconverting component for absorbing excitation light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths;

(iii) a photoinitiator, the photoinitiator being activatable upon excitation by upconverted light emitted by the upconverting component in the second range of wavelengths for initiating hardening of the photohardenable composition; and

(iv) a thixotrope to at least partially restrict movement of the three-dimensional object in the volume of the photohardenable composition during formation.

3. The photohardenable composition of claim 1 or 2 wherein the thixotrope comprises a urea derivative.

4. The photohardenable composition of claim 1 or 2 wherein the thixotrope comprises a fumed metal oxide.

5. The photohardenable composition of claim 1 or 2 wherein the thixotrope comprises a precipitated metal oxide.

6. The photohardenable composition of claim 1 or 2 wherein the thixotrope comprises a non polymeric compound.

7. The photohardenable composition of claim 1 wherein the thixotrope is included in the composition in an amount effective to at least partially restrict movement of the three-dimensional object or one or more regions thereof in the photohardenable composition during formation.

8. The photohardenable composition of claim 2 wherein the thixotrope is included in the composition in an amount effective to at least partially restrict movement of the three-dimensional object in the volume of photohardenable composition during formation.

9. The photohardenable composition of claim 1 or 2 wherein the monomer, oligomer, pre polymer, or polymer comprises an ethylenically-unsaturated species.

10. The photohardenable composition of claim 1 or 2 wherein the monomer, oligomer, pre polymer, or polymer comprises an epoxide species.

11. The photohardenable composition of claim 1 or 2 wherein the hardenable resin component comprises a free-radically -polymerizable resin.

12. The photohardenable composition of claim 1 or 2 wherein the hardenable resin component comprises a cross-linkable resin.

13. The photohardenable composition of claim 1 or 2 wherein the hardenable resin component comprises one or more multifunctional acrylate monomers.

14. The photohardenable composition of claim 1 or 2 wherein the hardenable resin component comprises an aliphatic urethane acrylate.

15. The photohardenable composition of claim 1 or 2 wherein the hardenable resin component comprises an aliphatic urethane acrylate monomer and a multifunctional acrylate monomer.

16. The photohardenable composition of claim 15 wherein the hardenable resin component further comprises an acrylamide monomer.

17. The photohardenable composition of claim 1 or 2 wherein the upconverting component comprises a sensitizer and an annihilator, the sensitizer being selected to absorb excitation light at one or more wavelengths in the first range of wavelengths and the annihilator being selected to emit light at one or more wavelengths in the second range of wavelengths after transfer of energy from the sensitizer to the annihilator, the second range of wavelengths being shorter than the first range of wavelengths.

18. The photohardenable composition of claim 1 or 2 wherein the upconverting component comprises upconverting nanoparticles for absorbing light at one or more wavelengths in a first range of wavelengths and emitting light at one or more wavelengths in a second range of wavelengths, the second range of wavelengths being shorter than the first range of wavelengths.

19. The photohardenable composition of claim 1 or 2 wherein the upconverting component comprises upconverting nanoparticles including a sensitizer and an annihilator, the sensitizer being selected to absorb excitation light at one or more wavelengths in a first range of wavelengths and the annihilator being selected to emit light at one or more wavelengths in a second range of wavelengths after transfer of energy from the sensitizer to the annihilator, the second range of wavelengths being shorter than the first range of wavelengths.

20. The photohardenable composition of claim 18 wherein at least a portion of the upconverting nanoparticles include a core portion including the sensitizer and annihilator in a medium and an encapsulating shell over at least a portion, and preferably substantially all, of an outer surface of the core portion.

21. The photohardenable composition of claim 20 wherein at least a portion of the cores comprise a micelle including the sensitizer and the annihilator.

22. The photohardenable composition of claim 20 wherein the shell comprises silica.

23. The photohardenable composition of claim 20 wherein the nanoparticles further include functional groups at the outer surface thereof.

24. The photohardenable composition of claim 17 wherein the annihilator comprises molecules capable of receiving a triplet exciton from a molecule of the sensitizer through triplet-triplet energy transfer, undergo triplet fusion with another annihilator molecule triplet to generate a higher energy singlet that emits light in the second range of wavelengths.

25. The photohardenable composition of claim 19 wherein the annihilator comprises molecules capable of receiving a triplet exciton from a molecule of the sensitizer through triplet-triplet energy transfer, undergo triplet fusion with another annihilator molecule triplet to generate a higher energy singlet that emits light in the second range of wavelengths.

26. The photohardenable composition of claim lor 2 wherein the upconverting component is capable of upconverting at least a portion and preferably all of the absorbed excitation light via triplet-triplet annihilation.

27. The photohardenable composition of claim 1 or 2 further comprising one or more additives.

28. The photohardenable composition of claim 1 or 2 further comprising a defoamer.

29. The photohardenable composition of claim 1 or 2 further comprising a light blocker.

30. The photohardenable composition of claim 1 or 2 further comprising a stabilizer.

31. The photohardenable composition of claim 1 or 2 wherein the photoinitiator comprises a free-radical photoinitiator system activatable upon excitation by upconverted light emitted by the upconverting component in the second range of wavelengths, the photoinitiator comprising: a ketocoumarin dye, an iodonium salt, and a borate salt.

32. The photohardenable composition of claim 31 further comprising a light blocker having an absorption wavelength range that overlaps at least partially with the absorption wavelength range of the free -radical photoinitiator system and the emission wavelength range of the upconverted light.

33. The photohardenable composition of claim 31 wherein the photoinitiator is activatable by upconverted light generated by the upconverting component in the second range of wavelengths from about 440 to about 510 nm and not activated by excitation light in the first range of wavelengths.

34. The photohardenable composition of claim 1 or 2 wherein the photoinitiator initiates polymerization or cross-linking of the hardenable resin component by free radical reactions.

35. The photohardenable composition of claim 1 or 2 wherein the first range of wavelengths is from about 400 nm to about 800 nm.

36. The photohardenable composition of claim 1 or 2 wherein the first range of wavelengths is from about 605 nm to about 650 nm.

37. The photohardenable composition of claim 1 or 2 wherein the first range of wavelengths is from about 520 nm to about 540 nm.

38. The photohardenable composition of claim 1 or 2 wherein the first range of wavelengths is from about 425 nm to about 460 nm.

39. The photohardenable composition of claim 1 or 2 wherein the excitation light has a wavelength of about 638 nm plus or minus 10 nm.

40. The photohardenable composition of claim 1 or 2 wherein the second range of wavelengths is from about 300 nm to about 600 nm.

41. The photohardenable composition of claim 1 or 2 wherein the second range of wavelengths includes wavelengths from about 440 nm to about 510 nm.

42. The photohardenable composition of claim 1 or 2 wherein the second range of wavelengths includes wavelengths from about 440 nm to about 460 nm.

43. The photohardenable composition of claim 1 or 2 wherein the second range of wavelengths is from about 400 to about 500 nm.

44. The photohardenable composition of claim 1 or 2 wherein the second range of wavelengths is from about 420 to about 480.

45. The photohardenable composition of claim 1 or 2 wherein the second range of wavelengths is from about 360 nm to about 420 nm.

46. The photohardenable composition of claim 1 or 2 wherein the second range of wavelengths is from about 460 nm to about 530 nm.

47. The photohardenable composition of claim 31 wherein the photohardenable composition includes: from about 0.005 to about 5 weight percent ketocoumarin based on the total weight of the hardenable component and the photoinitiator system; from about 0.005 to about 10 weight percent borate salt based on the total weight of the hardenable resin component and the photoinitiator system; and from about 0.1 to about 10 weight percent iodonium salt based on the total weight of the hardenable resin component and the photoinitiator system.

48. The photohardenable composition of claim 31 wherein the photohardenable composition includes: from about 0.0005 to about 1 weight percent light blocker based on the total weight of the hardenable resin component and the photoinitiator system.

49. The photohardenable composition of claim 1 or 2 wherein the photohardenable composition includes about 40 parts upconverting component to about 100 parts total of the hardenable resin component and photoinitiator.

50. The photohardenable composition of claim 1 or 2 wherein the composition includes: from about 0.5 to about 95 weight percent hardenable component; from about 0.1 to about 85 weight percent upconverting component; from about 0.1 to about 25 weight percent photoinitiator; and from about 0.05 to about 15 weight percent thixotrope.

51. The photohardenable composition of claim 50 further including from about 0.005 to about 1 weight percent defoamer.

52. The photohardenable composition of claim 50 further including from about 0.005 to about 10 weight percent light blocker.

53. The photohardenable composition of claim 50 further including from about 0.00005 to about 1 weight percent stabilizer.

54. The photohardenable composition of claim 50 further including: from about 0.005 to about 1 weight percent defoamer; about 0.00005 to about 1 weight percent stabilizer; and from about 0.00005 to about 1 weight percent stabilizer.

55. The photohardenable composition of claim 17 wherein the sensitizer comprises a substituted or unsubstituted porphyrin or derivative thereof, a substituted or unsubstituted metalloporhyrin or derivative thereof, or a mixture including any one or more of the foregoing.

56. The photohardenable composition of claim 19 wherein the sensitizer comprises a substituted or unsubstituted porphyrin or derivative thereof, a substituted or unsubstituted metalloporhyrin or derivative thereof, or a mixture including any one or more of the foregoing.

57. The photohardenable composition of claim 17 wherein the annihilator comprises a substituted or unsubstituted anthracene or derivative thereof, or a mixture including any one or more of the foregoing.

58. The photohardenable composition of claim 19 wherein the annihilator comprises a substituted or unsubstituted anthracene or derivative thereof, or a mixture including any one or more of the foregoing.

59. The photohardenable composition of claim 17 wherein the sensitizer and the annihilator are capable of upconverting at least a portion and preferably all of the absorbed excitation light via triplet-triplet annihilation.

60. The photohardenable composition of claim 19 wherein the sensitizer and the annihilator are capable of upconverting at least a portion and preferably all of the absorbed excitation light via triplet-triplet annihilation.

61. The photohardenable composition of claim 1 or 2 wherein the photohardenable composition exhibits non-Newtonian behavior.

62. A method of forming a three-dimensional object, comprising:

(a) providing a volume of the photohardenable composition of claim 1 included within a container wherein at least a portion of the container is optically transparent so that the photohardenable composition is accessible by excitation light;

(b) directing excitation light in the first range of wavelengths into the volume of the photohardenable composition, wherein the excitation light has an excitation intensity so that local hardening of the photohardenable composition is achieved at a selected location within the volume of the photohardenable composition; and

(c) optionally repeating step (b) at the same or a different selected location within the volume of the photohardenable composition until the three-dimensional object is formed.

63. A method of forming a three-dimensional object in a volume of a photohardenable composition, the method comprising:

(a) providing a volume of the photohardenable composition of claim 2 included within a container wherein at least a portion of the container is optically transparent so that the photohardenable composition is accessible by excitation light;

(b) directing excitation light in the first range of wavelengths into the volume of the photohardenable composition, wherein the excitation light has an excitation intensity so that local hardening of the photohardenable composition is achieved at a selected location within the volume of the photohardenable composition; and

(c) optionally repeating step (b) at the same or a different selected location within the volume of the photohardenable composition until the three-dimensional object is formed.

64. The method of claim 62 or 63 wherein the photohardenable composition has a steady shear viscosity less than 30,000 centipoise.

65. The method of claim 62 or 63 wherein the photohardenable composition has a steady shear viscosity less than 10,000 centipoise.

66. The method of claim 62 or 63 wherein the photohardenable composition has a steady shear viscosity less than 1,000 centipoise.

67. The method of claim 62 or 63 wherein the excitation light has a power density less than 1000 W/cm²·

68. The method of claim 62 or 63 wherein the excitation light has a power density less than 100 W/cm².

69. The method of claim 62 or 63 wherein the excitation light has a power density less than 1 W/cm².

70. The method of claim 62 or 63 wherein the upconverting component upconverts at least a portion and preferably all of the absorbed excitation light via triplet-triplet annihilation.

71. The method of claim 62 or 63 wherein the three-dimensional object is suspended in the volume during formation.

72. The method of claim 71 wherein the three-dimensional object remains at a fixed position or is minimally displaced in the photohardenable composition during formation.

73. The photohardenable composition of claim 1 or 2 wherein the first range of wavelengths is from about 680 nm to about 730 nm.

74. The new, useful, and unobvious processes, machines, manufactures, and compositions of matter, as shown and described herein.