Thiol-ene inks for 3D printing

Abstract

The present invention relates to thiol-ene inks for 3D printing. In one aspect, inks for three-dimensional printing systems are described herein. In some embodiments, the inks described herein comprise a thiol monomer component and an ene monomer component. Additionally, in some cases, the inks described herein further comprise an additional (meth)acrylate monomer component that is different from the ene monomer component. In some such cases, the additional (meth)acrylate monomer component can be polymerized separately from the thiol and ene monomer components of the ink.

Description

[0001] Cross-referencing related applications

[0002] This application is a divisional application of parent application number 201780035334.4, filed April 6, 2017, entitled "Thiol-olefin ink for 3D printing". This application claims priority to U.S. Provisional Patent Application 62 / 319,533, filed April 7, 2016, under 35 U.S. SC §119(e), which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to inks, and more particularly, to inks for three-dimensional (3D) printing systems. Background Technology

[0004] Some commercially available 3D printers (such as 3D Systems, ProJet manufactured in Rock Hill, South Carolina) TM 3D printers use ink (also known as build material) that is ejected as a liquid through a printhead to form various 3D objects, articles, or parts. Other 3D printing systems also use ink, which is ejected through a printhead or otherwise dispensed onto a substrate. In some cases, the ink is solid at ambient temperature and transforms into a liquid at high inkjet temperatures. In other cases, the ink is liquid at ambient temperature. Additionally, in some cases, the ink may cure after dispensing and / or depositing onto the substrate.

[0005] Other 3D printers form 3D articles from reservoirs, barrels, or containers of fluid inks or build materials or powdered inks or build materials. In some cases, the ink or build material layers are selectively cured or bonded in a stepwise or layer-by-layer manner using adhesive materials or lasers, digital light processing (DLP) sources, or other energy sources to provide 3D articles.

[0006] Inks used in 3D printing systems can form a variety of articles for a variety of applications, including those described above. However, some inks used in 3D printing systems include (meth)acrylates as the initial curable material. Such inks can provide high printing resolution, but can also produce rigid and brittle or flexible but easily broken 3D printed articles. Therefore, there is a need for improved inks for 3D printing, including inks that can provide a combination of desirable properties such as high printing resolution and high toughness. Summary of the Invention

[0007] In one aspect, inks for 3D printers are described herein that, in some embodiments, can provide one or more advantages over prior inks. For example, in some embodiments, the inks described herein can be used to form 3D printed articles having high toughness and high resolution, among other desirable mechanical properties.

[0008] In some embodiments, the inks for 3D printing systems described herein include a thiol monomer component and an ethylenically unsaturated monomer component. The thiol monomer component can include one or more thiol-containing chemical species. Similarly, the ethylenically unsaturated monomer component can include one or more ethylenically unsaturated chemical species. The thiol monomer component and the ethylenically unsaturated monomer component can be selected to react with one another in a so-called thiol-ene reaction. Thus, the ethylenically unsaturated monomer component of the inks described herein can also be referred to as an "ene" monomer component.

[0009] Additionally, in some cases, the inks described herein also include an additional (meth)acrylate monomer component that is different from the ene monomer component. In some such cases, the additional (meth)acrylate monomer component can polymerize separately from the thiol and ene monomers of the ink. For example, in some cases, the thiol and ene monomers of the ink can be reacted with one another to form a first polymer network via a thiol-ene reaction, and the additional (meth)acrylate monomer of the ink can be reacted with itself to form a second polymer network. In these cases, the first and second polymer networks can be separate or distinct polymer networks. Additionally, in some embodiments, the first and second polymer networks together form an interpenetrating polymer network. Further, the first and second polymer networks can be formed via different polymerization processes.

[0010] In some embodiments, the additional (meth)acrylate monomer of the ink can also react with itself and can also react with the ene monomers of the ink. In such cases, only one polymer network can be formed. Additionally, in some embodiments, the ink includes thiol monomers and ene monomers, and the ene monomers are present in a stoichiometric excess compared to the thiol monomers. In some such cases, the ene monomers can react with the thiol monomers to provide a first polymer network (specifically, a thiol-ene polymer network), and can further react with themselves to provide a second polymer network (such as a separate (meth)acrylate network). Thus, in some such cases, an interpenetrating polymer network can be provided without an additional (meth)acrylate monomer that is different from the ene monomers.

[0011] The inks described herein can be particularly useful in 3D printing systems, such as contact stereolithography (cSLA) printing systems or other stereolithography (SLA) printing systems, in which the thiol monomer, the ene monomer, and optionally the additional (meth)acrylate monomer are combined prior to printing under conditions (e.g., time, temperature, and / or polymerization inhibitor conditions) insufficient for substantial thiol-ene reaction between the thiol monomer and the ene monomer (or the additional (meth)acrylate monomer) to occur prior to printing.

[0012] Alternatively, as described further below, 3D printing can be performed with multiple inks, in which a first ink comprises a thiol monomer and a second ink comprises an ene monomer. The second ink can also optionally comprise an additional (meth)acrylate monomer different from the ene monomer. Such a dual-ink system can be particularly useful in 3D printing systems, such as multi-jet modeling (MJM) systems, in which it can not be desirable to combine the thiol monomer with the ene monomer (or with the additional (meth)acrylate monomer) prior to printing. (It will be appreciated, however, that a "single" ink can also be used in MJM systems, provided that conditions are present that do not support premature reaction of the ink components (e.g., conditions provided by a strong polymerization inhibitor)). Thus, in another aspect, a kit for use in a 3D printing system is described herein. In some embodiments, such a kit comprises a first ink comprising a thiol monomer component and a second ink comprising an ene monomer component.

[0013] It will be appreciated that the inks described herein, whether "single" inks or multiple inks that are part of a kit, can comprise one or more additional components in addition to the monomers described above. For example, in some embodiments, the inks described herein further comprise one or more additives selected from colorants, inhibitors, stabilizers, photoinitiators, and photosensitizers.

[0014] In another aspect, the use of a composition for 3D printing is described herein, in which the composition comprises an ink or a kit as described above. For example, in some cases, the use of a composition for 3D printing is described herein, in which the composition comprises a thiol monomer and an ene monomer.

[0015] In yet another aspect, described herein are 3D printing systems. Such 3D printing systems can include the compositions described above for 3D printing, such as the compositions described above including inks or kits. In some embodiments, the 3D printing systems described herein include a 3D printer having at least one ink dispenser or ink reservoir, and the compositions described herein disposed in the ink dispenser or ink reservoir. The compositions can include any of the inks described herein for 3D printing. For example, in some cases, the 3D printing systems described herein include a 3D printer having at least one of an ink dispenser and an ink reservoir, and an ink disposed in the ink dispenser, ink reservoir, or both, wherein the ink includes a thiol monomer. Additionally, in some cases, such 3D printers further include a second ink dispenser or reservoir, and a second ink disposed in the second ink dispenser or reservoir, wherein the second ink includes an ene monomer.

[0016] In another aspect, described herein are methods of printing 3D articles, wherein the methods are performed with one or more of the inks described herein. In some cases, such methods include selectively jetting or otherwise depositing layers of an ink in a fluid state onto a substrate, wherein the ink includes a thiol monomer and an ene monomer component. Additionally, in some cases, the layers of ink are deposited in a layer-by-layer manner according to a 3D article image in a computer readable format. Additionally, in some embodiments, the methods described herein further include polymerizing or curing the thiol monomer and the ene monomer. Such curing can be performed in a layer-by-layer manner during the printing process, or, in a "post-processing" step, such as a curing step performed after the printing of all layers of the article is complete. Additionally, such curing can include reacting the thiol monomer with the ene monomer to form a thiol-ene polymerization product, also referred to as a "poly(thiol-ene)" or as a "thiol-ene polymer or oligomer," whenever it occurs in the process.

[0017] Additionally, in some cases, the inks used in the methods described herein include additional (meth)acrylate monomers that are different from the ene monomers that participate in thiol-ene polymerization. In such cases, the methods can further include curing the additional (meth)acrylate monomers with electromagnetic radiation, such as ultraviolet (UV) light or visible light. Such curing can include polymerizing the olefinic unsaturated moieties of the (meth)acrylate monomers to form poly(meth)acrylates. Additionally, in some cases, as described further herein, the poly(meth)acrylates and poly(thiol-ene) can together form an interpenetrating polymer network.

[0018] The methods of printing 3D articles described herein can be performed with a variety of, rather than a single, ink described herein. In some cases, such methods include selectively depositing a layer of a first ink in a fluid state on a substrate, and selectively depositing a layer of a second ink in a fluid state on the substrate, where the first ink and the second ink each comprise a first ink and a second ink of a kit described herein. In particular, the first ink can comprise a thiol monomer, and the second ink can comprise an ene monomer. Additionally, in some embodiments, the first ink and / or the second ink further comprises an additional (meth)acrylate monomer that is different from the ene monomer of the second ink. In some such cases, the methods further comprise photocuring the additional (meth)acrylate monomer, such as with UV light. Such curing can comprise polymerizing the ethylenically unsaturated portion of the additional (meth)acrylate monomer to form a poly(meth)acrylate. The methods described herein can further comprise curing the thiol monomer of the first ink and the ene monomer of the second ink, which can comprise reacting the thiol monomer with the ene monomer to form a poly(thiol-ene). In this way, the poly(meth)acrylate and the poly(thiol-ene) formed from the multiple inks can together form an interpenetrating polymer network.

[0019] Additionally, in other embodiments, the methods of printing 3D articles described herein need not include jetting or otherwise depositing one or more inks described herein on a substrate in accordance with digital data representative of a 3D article. Rather, in some cases, the methods of printing 3D articles described herein include maintaining an ink in a fluid state in a container, and selectively applying energy to the ink in the container to cure at least a portion of a first fluid layer of the ink to form a first cured layer defining a first cross-section of the article. The ink can comprise any of the inks described above. Additionally, such methods can further include elevating or lowering the first cured layer to provide a second fluid layer of the ink at a surface of the fluid ink in the container, and selectively applying energy to the ink in the container to cure at least a portion of the second fluid layer of the ink to form a second cured layer defining a second cross-section of the article. The first cross-section and the second cross-section are joined to one another in the z-direction.

[0020] In another aspect, 3D printed articles are described herein. Such articles can be formed from one or more inks and / or with one or more of the methods described above.

[0021] These and other embodiments are described in more detail in the following detailed description. DETAILED DESCRIPTION

[0022] The embodiments described herein can be more readily understood by reference to the following Detailed Description and Examples. However, the elements, devices, and methods described herein are not limited to the specific embodiments provided in the Detailed Description and Examples. It is recognized that these embodiments are merely illustrative of the principles of the present disclosure. Numerous modifications and adaptions of the embodiments can be made by those skilled in the art without departing from the spirit and scope of the present disclosure.

[0023] In addition, it should be understood that all ranges disclosed herein include any and all sub-ranges subsumed therein. For example, a stated range of "1.0 to 10.0" should be considered to include any and all sub-ranges between (and inclusive of) the minimum value of 1.0 and the maximum value of 10.0, e.g., 1.0 to 5.3, or 4.7 to 10.0, or 3.6 to 7.9.

[0024] Unless explicitly stated otherwise, it should be understood that all ranges disclosed herein include the endpoints of the range. For example, it should be generally understood that the range "between 5 and 10" or "from 5 to 10" includes the endpoints 5 and 10.

[0025] In addition, when the phrase "at most" is used in connection with a quantity or amount, it should be understood that the quantity is at least a detectable amount or quantity. For example, a substance present in an "at most" specified amount can be present in a detectable amount and up to and including the specified amount.

[0026] The terms "three-dimensional printing system," "three-dimensional printer," "printing," and the like generally describe various solid freeform fabrication manufacturing techniques for fabricating three-dimensional articles or objects, by stereolithography, selective deposition, jetting, fused deposition modeling, multi-jet modeling, and other additive manufacturing techniques now known or hereafter known in the art for fabricating three-dimensional objects from a build material or ink.

[0027] I. Ink and kit for 3D printing

[0028] In one aspect, inks for 3D printers are described herein. In some embodiments, the inks described herein comprise a thiol monomer and an ene monomer. In addition, in some cases, the inks described herein further comprise an additional (meth)acrylate monomer different from the ene monomer. In addition, in some cases, the inks described herein further comprise a colorant, such as a molecular dye, a particulate inorganic pigment, or a particulate organic colorant. The inks described herein can also comprise one or more additives selected from the group consisting of inhibitors, stabilizers, photoinitiators, and photosensitizers.

[0029] Now turning to the specific components of the ink in detail, the inks described herein include a thiol monomer. It should be appreciated that the thiol "monomer" is not limited to a specific molecular weight or a specific chemical structure for purposes of reference herein. Rather, the thiol "monomer" can be any thiol-containing chemical species that is capable of reacting with an olefinically unsaturated chemical species in a thiol-ene reaction, such as a thiol-ene polymerization reaction, in which a thiol (S-H) moiety adds across both ends of a carbon-carbon double bond of an alkene to form a new carbon-sulfur covalent bond and a new carbon-hydrogen covalent bond. Additionally, the thiol "monomer" can include multiple thiol moieties. For example, in some cases, the thiol monomer includes two, three, or four thiol moieties.

[0030] Any thiol monomer that is consistent with the objects of the present disclosure can be used in the inks described herein. For example, in some cases, the thiol monomer includes an alkyl thiol, a thiol glycolate, or a thiol propionate. Additionally, in some cases, such alkyl thiol, thiol glycolate, or thiol propionate includes multiple thiol moieties, including at different ends of the monomer.

[0031] In some cases, the thiol monomer includes a chemical species having the structure of Formula (Al), Formula (A2), Formula (A3), Formula (A4), or (A5):

[0032]

[0033]

[0034] wherein R1, R2, R3, and R4 are each independently a linear or branched C1-C36 alkyl or alkylene, alkenyl or alkenylene, aryl or arylene, or heteroaryl or heteroarylene moiety, R5, R6, R7, and R8 are each independently H or CH3, a, b, c, and d are each independently an integer from 1 to 100, and m is an integer from 1 to 36. For example, in some cases, one or more of R1, R2, R3, and R4 is CH2 or CH2CH2, and R5, R6, R7, and R8 are each H.

[0035] Non-limiting examples of thiol monomers suitable for use in some embodiments described herein include pentaerythritol tetra(3-mercaptopropionate) (PETMP) (available from BRUNO BROCK under the trade designation THIOCURE PETMP, PETMP l.o., or PETMP sl), trimethylolpropane tri(3-mercaptopropionate) (TMPMP) (available from BRUNO BOCK), ethylene glycol di(3-mercaptopropionate) (GDMP) (available from BRUNO BOCK), pentaerythritol tetramercaptoacetate (PETMA) (available from BRUNO BOCK), trimethylolpropane trimercaptoacetate (TMPMA) (available from BRUNO BOCK), ethylene glycol dimercaptoacetate (GDMA) (available from BRUNO BOCK), ethoxylated trimethylolpropane tri(3-mercaptopropionate) (ETTMP) (available from BRUNO BOCK under the trade designation ETTMP 700 or ETTMP 1300, depending on molecular weight), propylene glycol 3-mercaptopropionate (PPGMP) (available from BRUNO BOCK under the trade designation PPGMP 800 or PPGMP 2200, depending on molecular weight), tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate (TEMPIC) (available from BRUNO BOCK), polycaprolactone tetra(3-mercaptopropionate) (available from BRUNO BOCK under the trade designation PCL4MP 1350), 2,3-bis((2-mercaptoethyl)thio)-l-propanethiol (DMPT) (available from BRUNO BOCK), dimercaptodiethyl sulfide (DMDS) (available from BRUNO BOCK), pentaerythritol tetra(3-mercaptobutyrate) (available from SHOWA DENKO under the trade designation KARENZ MTPE1), 1,4-bis(3-mercaptobutylyloxy)butane (available from SHOWA DENKO under the trade designation KARENZ MTBD1), and 1,3,5-tris(3-mercaptobutyloxethyl)-l,3,5-triazine-2,4,6(lH,3H,5H)-trione (available from SHOWA DENKO under the trade designation KARENZ MT NR1). Other thiol monomers can also be used in the inks described herein.

[0036] It should also be appreciated that the thiol monomer component of the inks described herein can comprise only one chemical species or multiple different chemical species. For example, in some cases, the thiol monomer of the inks described herein comprises multiple different thiol-containing species. Any combination of different thiol-containing species that are consistent with the objects of the present disclosure can be used in the inks described herein.

[0037] Additionally, the total amount of thiol monomer components may be present in the ink in any amount consistent with the purposes of this disclosure. For example, in some cases, the inks described herein contain up to 50% by weight, up to 40% by weight, up to 30% by weight, up to 25% by weight, or up to 20% by weight of thiol monomers, based on the total weight of the ink. In some cases, the inks contain 5-50% by weight, 5-40% by weight, 10-50% by weight, 10-40% by weight, 10-30% by weight, 10-20% by weight, 15-50% by weight, 15-40% by weight, 15-30% by weight, or 15-25% by weight of thiol monomers, based on the total weight of the ink.

[0038] The inks described herein also contain alkene monomers. It should be understood that alkene “monomers” are not limited to a specific molecular weight or chemical structure. Rather, alkene “monomers” can include any class of chemicals containing one or more alkene unsaturated moieties capable of reacting with thiol monomers in a thiol-alkene reaction to form a sulfur-carbon covalent bond.

[0039] Any olefin monomer consistent with the purposes of this disclosure may be used in the inks described herein. In some cases, the olefin monomer comprises a vinyl moiety, an allyl moiety, an propylene moiety, and / or a (meth)acrylate moiety, wherein the term "(meth)acrylate" includes acrylates or methacrylates or mixtures or combinations thereof. Additionally, the olefin monomers described herein may be monofunctional, difunctional, trifunctional, tetrafunctional, pentafunctional, or higher functional monomers. For illustrative purposes, a "monofunctional" monomer includes a class of chemicals comprising one olefin unsaturated moiety. Similarly, a "difunctional" monomer includes a class of chemicals comprising two olefin unsaturated moieties, a "trifunctional" monomer includes a class of chemicals comprising three olefin unsaturated moieties, a "tetrafunctional" monomer includes a class of chemicals comprising four olefin unsaturated moieties, and a "pentafunctional" monomer includes a class of chemicals comprising five olefin unsaturated (partial) moieties. Therefore, in some embodiments, the monofunctional olefin monomer of the ink described herein includes mono(meth)acrylate, the difunctional olefin monomer of the ink described herein includes di(meth)acrylate, the trifunctional olefin monomer of the ink described herein includes tri(meth)acrylate, the tetrafunctional olefin monomer of the ink described herein includes tetra(meth)acrylate, and the pentafunctional olefin monomer of the ink described herein includes penta(meth)acrylate. Other monofunctional, difunctional, trifunctional, tetrafunctional, and pentafunctional olefin monomers may also be used. In some cases, difunctional or higher-functionality olefin monomers are particularly preferred.

[0040] Additionally, in some cases, monofunctional, difunctional, trifunctional, tetrafunctional, and pentafunctional monomers can include relatively lower molecular weight species or relatively higher molecular weight species. For example, monomers can include or be "monomeric" or molecular species (i.e., species that are not themselves polymers or oligomers, are relatively lower molecular weight species, or are relatively lower viscosity species), or "oligomeric" species (i.e., species that are themselves polymers or oligomers, are relatively higher molecular weight species, or are relatively higher viscosity species) that are capable of undergoing additional polymerization (e.g., through one or more unsaturation points described herein). Thus, in some cases, a population of "monomeric" or molecular species in a monomer can have a uniform or well-defined molecular structure and / or formula throughout the population (e.g., can be represented by a specified mass of ethoxylated (4) bisphenol A diacrylate). In contrast, a population of "oligomeric" species in a monomer can have a varying molecular structure and / or formula throughout the population (e.g., can be represented by a specified mass of urethane acrylate having a non-uniform molecular weight distribution, or by a specified mass of ethoxylated polyethylene glycol having a distribution of ethylene glycol units and / or a distribution of ethoxy units within the population). Additionally, the weight average molecular weight of an "oligomeric" monomer can generally range from about 400 to 10,000, from about 600 to 10,000, or from about 500 to 7,000. In contrast, the molecular weight of a "monomeric" monomer can generally be less than 600, less than 500, less than 400, less than 300, less than 200, or less than 100. Additionally, in some embodiments, a "monomeric" monomer has a viscosity of 500 centipoise (cP) or less at 25 °C when determined according to ASTM D2983, and an "oligomeric" monomer has a viscosity of 1000 cP or more at 25 °C when determined according to ASTM D2983.

[0041] Generally, any monomeric olefin monomer consistent with the objects of the present disclosure can be used in the inks described herein. In some cases, the olefin monomer includes one or more (meth)acrylate species, such as one or more mono-functional, di-functional, tri-functional, tetra-functional, and / or penta-functional (meth)acrylates. For example, in some embodiments, the monomeric olefin monomer includes methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2- or 3-hydroxypropyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2- or 3-ethoxypropyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, cyclohexyl methacrylate, 2-phenoxyethyl acrylate, glycidyl acrylate, isodecyl acrylate, 2-phenoxyethyl (meth)acrylate, lauryl methacrylate, or combinations thereof. In some embodiments, the monomeric olefin monomer includes one or more allyl acrylate, allyl methacrylate, triethylene glycol di(meth)acrylate, tricyclodecane dimethanol diacrylate, and cyclohexane dimethanol diacrylate. Additionally, in some cases, the monomeric olefin monomer includes diacrylates and / or dimethacrylates of aliphatic, cycloaliphatic, or aromatic diols including 1,3- or 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, tripropylene glycol, 1,4- dihydroxymethyl cyclohexane, 2,2-bis(4-hydroxycyclohexyl)propane or bis(4- hydroxycyclohexyl)methane, hydroquinone, 4,4'-dihydroxydiphenyl, bisphenol A, bisphenol F, or bisphenol S. The olefin monomers described herein can also include 1,1- trimethylolpropane tri(meth)acrylate, pentaerythritol monohydroxy tri(meth)acrylate, dipentaerythritol monohydroxy penta(meth)acrylate, and / or bis(trimethylolpropane) tetra(meth)acrylate. Additionally, in some cases, the olefin monomer can include ethoxylated or propoxylated species such as ethoxylated or propoxylated neopentyl glycol, ethoxylated or propoxylated bisphenol A, ethoxylated or propoxylated bisphenol F, ethoxylated or propoxylated bisphenol S, ethoxylated or propoxylated 1,1,1-trimethylolpropane tri(meth)acrylate, or ethoxylated or propoxylated glycerol tri(meth)acrylate.

[0042] Additional non-limiting examples of commercially available monomeric olefin monomers useful in some embodiments described herein include the following: isobornyl acrylate (IBOA) available from SARTOMER under the trade designation SR506; isobornyl methacrylate available from SARTOMER under the trade designation SR 423A; triethylene glycol diacrylate available from SARTOMER under the trade designation SR272; triethylene glycol dimethacrylate available from SARTOMER under the trade designation SR205; tricyclodecane dimethanol diacrylate available from SARTOMER under the trade designation SR833S; tris(2-hydroxyethyl) isocyanurate triacrylate available from SARTOMER under the trade designation SR368; 2-phenoxyethyl acrylate available from SARTOMER under the trade designation SR339; ethoxylated (3 mol) bisphenol A diacrylate available from SARTOMER under the trade designation SR 349; and dipentaerythritol pentaacrylate available from SARTOMER under the trade designation SR 399 LV. Other commercially available monomeric olefin monomers can also be used.

[0043] Additionally, any oligomeric olefin monomer consistent with the objects of the present disclosure can be used in the inks described herein. For example, in some cases, the olefin monomer includes a polyester (meth)acrylate oligomer, a urethane (meth)acrylate oligomer, or an epoxy (meth)acrylate oligomer. Additionally, in some embodiments, the oligomeric olefin monomer described herein includes an aliphatic polyester urethane acrylate oligomer and / or an acrylate amine oligomeric resin, such as EBECRYL 7100. In some cases, the oligomeric olefin monomer described herein includes a polypropylene glycol mono(meth)acrylate or a polyethylene glycol mono(meth)acrylate. In some embodiments, the oligomeric olefin monomer includes a monofunctional aliphatic urethane (meth)acrylate. Additionally, in some cases, the oligomeric olefin monomer includes a diacrylate and / or dimethacrylate of an aliphatic, cycloaliphatic, or aromatic diol, including a polyethylene glycol, an ethoxylated or propoxylated neopentyl glycol, an ethoxylated or propoxylated bisphenol A, an ethoxylated or propoxylated bisphenol F, an ethoxylated or propoxylated bisphenol S, an ethoxylated or propoxylated 1,1,1-trishydroxymethylpropane tri(meth)acrylate, or an ethoxylated or propoxylated glycerol tri(meth)acrylate.

[0044] Some non-limiting examples of commercially available oligomeric olefin monomers useful in some embodiments described herein include the following: alkoxylated tetrahydrofurfuryl acrylate available from SARTOMER under the trade designation SR611; monofunctional urethane acrylate available from RAHN USA under the trade designation GENOMER 1122; and aliphatic urethane diacrylate available from ALLNEX under the trade designation EBECRYL 8402. Other commercially available oligomeric olefin monomers can also be used.

[0045] In some cases, urethane (meth)acrylates suitable for use in the inks described herein can be prepared by known methods, generally by reaction of a hydroxyl-terminated urethane with acrylic or methacrylic acid to give the corresponding urethane (meth)acrylate, or by reaction of an isocyanate-terminated prepolymer with a hydroxyalkyl acrylate or hydroxyalkyl methacrylate to give a urethane (meth)acrylate. Suitable methods are disclosed, inter alia, in EP-A 114982 and EP-A 133908. In some cases, the weight average molecular weight of these (meth)acrylate oligomers can be from about 400 to 10,000 or from about 500 to 7,000. Urethane (meth)acrylates can also be purchased from SARTOMER under the trade designations CN980, CN981, CN975, and CN2901, or from BOMAR Specialties Co. under the trade designation BR-741. In some embodiments described herein, the urethane (meth)acrylate oligomers have a viscosity of from about 140,000 centipoise (cP) to about 160,000 cP at about 50 °C, or a viscosity of from about 125,000 cP to about 175,000 cP at about 50 °C, when determined in a manner consistent with ASTM D2983. In some cases, the urethane (meth)acrylate oligomers have a viscosity of from about 100,000 cP to about 200,000 cP at about 50 °C, or a viscosity of from about 10,000 cP to about 300,000 cP at about 50 °C, when determined in a manner consistent with ASTM D2983.

[0046] It will be appreciated that the olefinic monomers of the inks described herein can comprise only one chemical species or multiple different chemical species. For example, in some cases, the olefinic monomers of the inks described herein comprise multiple different olefinically unsaturated species, such as one or more different monomeric (meth)acrylates and / or one or more different oligomeric (meth)acrylates. It will also be appreciated that where both oligomeric and monomeric species are included in the olefinic monomers of the inks described herein, the ratio of oligomeric species to monomeric species in the ink can be selected to provide an ink having a viscosity suitable for use in a desired 3D printing system, such as a 3D printing system that dispenses the ink with a piezoelectric print head or a stereolithographic 3D printing system.

[0047] Many of the foregoing examples of olefin monomers described herein are (meth)acrylates. In some embodiments, the use of such (meth)acrylates can be advantageous for some 3D printing applications. However, the olefin monomers can also be or include chemical species other than (meth)acrylates. Additionally, in some embodiments, the olefin monomers of the inks described herein exclude (meth)acrylates or are substantially free of (meth)acrylates. For reference purposes herein, an olefin monomer that is "substantially" free of (meth)acrylates can include less than 10% by weight, less than 5% by weight, less than 3% by weight, or less than 1% by weight of (meth)acrylates, based on the total weight of the olefin monomer.

[0048] In some embodiments, the olefin monomers include substituted or unsubstituted norbornene, vinyl ether, olefin, vinyl ester, N-vinyl amide, allyl ether, allyl triazine, allyl isocyanurate, maleimide (such as N-substituted maleimide), acrylonitrile, styrene, conjugated diene, or combinations thereof. Other non-(meth)acrylate olefin monomers can also be used.

[0049] The olefin monomers can be present in the inks described herein in any amount consistent with the objects of the present disclosure. In some cases, the olefin monomers (total) are present in an amount of up to about 90% by weight, up to about 80% by weight, up to about 70% by weight, up to about 60% by weight, up to about 50% by weight, up to about 40% by weight, up to about 30% by weight, or up to about 20% by weight, based on the total weight of the ink. In some cases, the inks described herein include about 10-90% by weight, 10-80% by weight, 10-70% by weight, 20-90% by weight, 20-85% by weight, 20-75% by weight, 20-70% by weight, 20-60% by weight, 20-50% by weight, 30-80% by weight, 30-70% by weight, 40-80% by weight, 40-70% by weight, 50-90% by weight, 50-80% by weight, or 50-70% by weight of olefin monomers, based on the total weight of the ink.

[0050] In some embodiments, the inks described herein also include an additional (meth)acrylate monomer component that is different from the olefin monomer component of the ink. The use of such additional (meth)acrylate monomers is particularly desirable in embodiments in which the olefin monomer does not contain or is substantially free of (meth)acrylate groups. As described above, in some such cases, the additional (meth)acrylate monomers can be polymerized or cured separately from the thiol and olefin monomers of the ink. For example, in some cases, the thiol and olefinically unsaturated monomers of the ink can be caused to react with one another to form a first polymer network via thiol-ene polymerization, and the additional (meth)acrylate monomers of the ink can be caused to react with one another to form a second polymer network. In such cases, the first and second polymer networks can be separate or distinct polymer networks formed via separate or distinct polymerization processes. Additionally, in some embodiments, the first and second polymer networks can together form an interpenetrating polymer network.

[0051] The use of two different polymerization processes, such as a thiol-ene polymerization process and a separate (meth)acrylate polymerization process, can allow a 3D printed article formed from the thiol monomers, olefin monomers, and additional (meth)acrylate monomers described herein to be cured in multiple stages rather than in a single manner. Additionally, the different stages of curing can be temporally separated from one another, and / or can be spatially separated from one another within the geometry of the 3D article. For example, in some embodiments, a first monomer (or pair of monomers, such as a pair of thiol and olefin monomers) can be cured during printing of the 3D article to provide a printed article having sufficient green strength to be handled and / or exhibiting a desired feature resolution, and a second monomer (or pair of monomers) can be cured after printing, such as by placing the article in an oven to thermally cure the second monomer (it will be appreciated that, in this context, "printing" includes the process of forming a printed article by providing successive layers or cross-sections of the article, and excludes any "post-printing" or "post-processing" steps, such as impregnating the printed article with an impregnant or heating the printed article). In other cases, a first monomer (or pair of monomers) is cured or polymerized within a first region of the 3D printed article, and a second monomer (or pair of monomers) is cured or polymerized within a second region of the 3D printed article, where the first and second regions are different regions.

[0052] Additionally, dual polymerization or curing can also be provided, including in a temporally or spatially separated manner, without an additional (meth)acrylate monomer that is different from the olefin monomer. For example, in some embodiments, the ink includes a thiol monomer and an olefin monomer, and the olefin monomer is present in a stoichiometric excess compared to the thiol monomer. In some such cases, the olefin monomer can react with the thiol monomer to provide a first polymer network (in particular, a thiol-ene polymer network), and can further react with itself to provide a second polymer network (such as a separate poly(meth)acrylate network).

[0053] Any additional (meth)acrylate monomer consistent with the objects of the present disclosure can be used in the inks described herein. Generally, any (meth)acrylate species or combination of (meth)acrylate species described above in the context of the olefin monomer can also be used as an additional (meth)acrylate monomer for the inks described herein. It should also be appreciated that the additional (meth)acrylate monomer for the inks described herein can comprise only one (meth)acrylate species or multiple different (meth)acrylate species. For example, in some embodiments, the additional (meth)acrylate monomer for the inks described herein comprises a monomeric (meth)acrylate described above and an oligomeric (meth)acrylate described above.

[0054] The additional (meth)acrylate monomer can be present in the inks described herein in any amount consistent with the objects of the present disclosure. In some cases, the additional (meth)acrylate monomer(s) is present in an amount of up to about 80 wt%, up to about 70 wt%, up to about 60 wt%, up to about 50 wt%, up to about 40 wt%, up to about 30 wt%, up to about 20 wt%, or up to about 10 wt%, based on the total weight of the ink. In some cases, the inks described herein comprise about 5-80 wt%, 10-70 wt%, 10-60 wt%, 15-80 wt%, 20-75 wt%, 20-65 wt%, 20-50 wt%, 20-40 wt%, 30-70 wt%, 30-60 wt%, 40-70 wt%, 40-60 wt%, 50-80 wt%, or 50-70 wt% of the additional (meth)acrylate monomer(s), based on the total weight of the ink.

[0055] In addition to the monomers described above, the inks described herein can also comprise one or more components. For example, the inks described herein can also comprise a colorant, such as a molecular dye, a particulate inorganic pigment, or a particulate organic colorant. The inks described herein can also comprise one or more additives selected from the group consisting of inhibitors and stabilizers. The inks described herein can also comprise one or more photoinitiators and / or one or more photosensitizers.

[0056] The inks can comprise any colorant consistent with the objects of the present disclosure. The colorant for the inks described herein can be a particulate colorant, such as a particulate pigment or a molecular colorant, such as a molecular dye. Any such particulate or molecular colorant consistent with the objects of the present disclosure can be used. For example, in some cases, the colorant for the inks comprises an inorganic pigment, such as Ti02and / or ZnO. In some embodiments, the colorant for the inks comprises a colorant for RGB, sRGB, CMY, CMYK, L*a*b*, or Colorants of the color scheme. In some cases, one or more colorants of the inks described herein exhibit a white color. In other cases, the colorants exhibit a black color. Some non-limiting examples of colorants suitable for use in some embodiments described herein include SUN UV DJ 107, SUN UV DJ 150, SUN UV DJ 322, SUN UV DJ 350, SUN UV DJ 354, RJA D3010-FX-Y150, RJAD3410-FX-Y150, RJA D3410-FX-K, PENN COLOR 9B898, and PENN COLOR 9B989. Additionally, in some cases, the particulate colorants described herein have an average particle size of less than about 5 pm or less than about 1 pm. In some cases, the particulate colorants described herein have an average particle size of less than about 500 nm, such as an average particle size of less than about 400 nm, less than about 300 pm, less than about 250 nm, less than about 200 nm, or less than about 150 pm. In some cases, the particulate colorants have an average particle size of about 50-5000 nm, about 50-1000 nm, or about 50-500 nm.

[0057] The colorants can be present in the inks described herein in any amount consistent with the objects of the present disclosure. In some cases, the colorants are present in an amount of up to about 2% by weight, or in an amount of about 0.005-2% by weight, 0.01-2% by weight, 0.01-1.5% by weight, 0.01-1% by weight, 0.01-0.5% by weight, 0.1-2% by weight, 0.1-1% by weight, 0.1-0.5% by weight, or 0.5-1.5% by weight, based on the total weight of the ink.

[0058] Additionally, in some embodiments, the inks described herein further comprise one or more polymerization inhibitors and / or stabilizers. Polymerization inhibitors can be added to the inks to provide additional thermal stability to the composition. Any polymerization inhibitor consistent with the objects of the present disclosure can be used. Additionally, the polymerization inhibitor can delay or reduce the rate of polymerization, and / or prevent polymerization from occurring for a period of time or “induction time” until the polymerization inhibitor is consumed. Additionally, in some cases, the polymerization inhibitors described herein are “additive” inhibitors. The inhibitors described herein can also be “chain transfer” inhibitors. In some cases, suitable polymerization inhibitors include methoxyhydroquinone (MEHQ).

[0059] In some embodiments, the stabilizing agent includes one or more antioxidants. The stabilizing agent can include any antioxidant consistent with the objects of the present disclosure. In some cases, suitable antioxidants include various aryl compounds, including butylated hydroxytoluene (BHT), which can also be used as a polymerization inhibitor in some embodiments described herein. More generally, a single species can be used as both a stabilizing agent and a polymerization inhibitor. In some cases, multiple inhibitors and / or stabilizing agents can also be used, where different inhibitors and / or stabilizing agents provide different effects and / or synergistic effects.

[0060] The polymerization inhibitor and / or stabilizing agent can be present in the ink in any amount consistent with the objects of the present disclosure. In some embodiments, the polymerization inhibitor is present in an amount of about 0.01% by weight to about 2% by weight or about 0.05% by weight to about 1% by weight. Similarly, in some cases, the stabilizing agent is present in the ink in an amount of about 0.1% by weight to about 5% by weight, about 0.5% by weight to about 4% by weight, about 0.5% by weight to about 1.5% by weight, or about 1% by weight to about 3% by weight, based on the total weight of the ink.

[0061] The inks described herein can also include one or more photoinitiators. Any photoinitiator consistent with the objects of the present disclosure can be used. In some cases, the photoinitiator includes an a-cleavage type (single molecule decomposition process) photoinitiator or a hydrogen abstraction photoinitiator-tertiary amine synergist, operable to absorb light between about 250 nm and about 400 nm or between about 300 nm and about 385 nm, to generate free radicals. Examples of a-cleavage photoinitiators are Irgacure 184 (CAS 947-19-3), Irgacure 369 (CAS 119313-12-1), and Irgacure 819 (CAS 162881-26-7). An example of a photoinitiator-amine combination is Darocur BP (CAS 119-61-9) with diethylaminoethyl methacrylate.

[0062] Additionally, in some cases, the photoinitiator includes benzoin classes (including benzoin, benzoin ethers (such as benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether, benzoin phenyl ether), and benzoin acetate), acetophenones (including acetophenone, 2,2-dimethoxyacetophenone, and 1,1-dichloroacetophenone), benzil, benzil ketals (such as benzil dimethyl ketal and benzil diethyl ketal), anthraquinones (including 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, and 2-pentylanthraquinone), triphenylphosphine, benzoylphosphine oxides (such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin TPO)), benzophenones (such as benzophenone and 4,4'-bis(N,N'-dimethylamino)benzophenone), thioxanthone classes and xanthone classes, acridine derivatives, phenazine derivatives, quinoxaline derivatives, or 1-phenyl-1,2-propanedione, 2-0-benzoyl oxime, 1-aminophenyl ketones, or 1-hydroxyphenyl ketones (such as 1-hydroxycyclohexyl phenyl ketone, phenyl 1-hydroxyisopropyl ketone, and 4-isopropylphenyl 1-hydroxyisopropyl ketone).

[0063] The photoinitiator can also include photoinitiators operable with HeCd laser radiation sources, including acetophenones, 2,2-dialkoxybenzophenones, and 1-hydroxyphenyl ketones (such as 1-hydroxycyclohexyl phenyl ketone or 2-hydroxyisopropyl phenyl ketone (= 2-hydroxy-2,2-dimethylacetophenone)). Additionally, in some cases, the photoinitiator includes photoinitiators operable with Ar laser radiation sources, including benzil ketals, such as benzil dimethyl ketal. In some embodiments, the photoinitiator includes an a-hydroxyphenyl ketone, benzil dimethyl ketal, or 2,4,6-trimethylbenzoyldiphenylphosphine oxide, or mixtures thereof.

[0064] Another class of photoinitiators that can be included in the inks described herein includes ionic dye-counterion compounds that are capable of absorbing actinic radiation and generating free radicals for polymerization initiation. Some ionic dye-counterion compounds and the manner in which they operate are disclosed in EP-A-0 223 587 and U.S. Patents 4,751,102, 4,772,530, and 4,772,541.

[0065] The photoinitiator can be present in the inks described herein in any amount consistent with the objects of the present disclosure. In some embodiments, the photoinitiator is present in the ink in an amount of up to about 5% by weight, based on the total weight of the ink. In some cases, the photoinitiator is present in an amount of about 0.1% by weight to about 5% by weight.

[0066] Additionally, in some embodiments, the inks described herein further comprise one or more photosensitizers. Generally, such photosensitizers can be added to the ink to improve the efficacy of one or more photoinitiators that can also be present. In some cases, the photosensitizer comprises isopropyl thioxanthone (ITX) or 2-chlorothioxanthone (CTX).

[0067] The photosensitizer can be present in the ink in any amount consistent with the objects of the present disclosure. In some embodiments, the photosensitizer is present in an amount of about 0.1% by weight to about 2% by weight or about 0.5% by weight to about 1% by weight, based on the total weight of the ink.

[0068] Some non-limiting examples of inks according to the present disclosure are provided in Tables I and II below. Specifically, Table I and Table II each provide the weight percentages of different components of exemplary inks, where the weight percentages are based on the total weight of the ink. In Table I, the table heading "Thiol" refers to the thiol monomer, "Enes" refers to the ene monomer, "AMM" refers to the additional (meth)acrylate monomer, "PI" refers to the photoinitiator, "Stab." refers to the stabilizer, and "Colorant" refers to the colorant. In Table II, "Mono." refers to the monomeric (meth)acrylate, and "Olig." refers to the oligomeric (meth)acrylate.

[0069] Table I. Ink Components.

[0070] Ink ]]> ​ Thiol ]]> ​ Alkenes ]]> ​ AMM ]]> ​ PI ]]> ​ Stab. ]]> ​ Colorant ]]> ​ 1 5-40 5-40 15-60 0.5-2.5 0.2-2 0-2 2 5-30 5-30 35-60 1-2 0.2-1.5 0-2 3 5-20 5-20 55-70 0.5-3 0.2-1 0.1-1 4 10-40 10-40 15-70 1-5 0.5-2.5 0.1-0.5 5 10-30 10-30 35-70 0.1-3 0.5-5 0.1-1.5 6 15-25 15-25 45-70 0.1-2 1-5 0.005-2

[0071] Table II. Ink Components.

[0072] Ink ]]> ​ Mono. ]]> ​ Mono. ]]> ​ Olig .]]> ​ P I ]]> Stab. ]]> ​ Colorant ]]> ​ 7 5-40 10-60 5-60 0.5-2.5 0.2-2 0.01-2 8 5-40 10-50 10-50 1-4 0.1-1 0-2 9 15-25 20-50 10-50 0.5-3 0.2-1 0.1-1 10 15-25 20-50 10-50 1-5 0.5-2.5 0.1-0.5

[0073] As described above, 3D printing can be performed according to the present disclosure with a single ink that is capable of forming a polymer or oligomer from a thiol monomer, an ene monomer, and optionally an additional (meth)acrylate monomer. However, 3D printing can also be performed with a combination of different inks that, when combined, are capable of forming a polymer or oligomer from a thiol monomer, an ene monomer, and optionally an additional (meth)acrylate monomer. Accordingly, in another aspect, a kit for use in a 3D printing system is described herein. In some embodiments, such a kit comprises a first ink comprising a thiol monomer and a second ink comprising an ene monomer. Additionally, in some cases, the first ink and / or the second ink further comprises an additional (meth)acrylate monomer. The first ink and / or the second ink can also comprise a photoinitiator, an inhibitor, a stabilizer, and / or a colorant.

[0074] In addition, it should also be appreciated that the thiol monomers, ene monomers, additional (meth)acrylate monomers, photoinitiators, inhibitors, stabilizers, and colorants of the kits described herein can include any of the thiol monomers, ene monomers, additional (meth)acrylate monomers, photoinitiators, inhibitors, stabilizers, and colorants described herein with respect to the "single" ink. In addition, it should also be appreciated that the first or second ink of the kits described herein can include a plurality of thiol species or mixtures thereof, a plurality of ene species or mixtures thereof, a plurality of additional (meth)acrylate species or mixtures thereof, a plurality of photoinitiators or mixtures thereof, a plurality of inhibitors or mixtures thereof, a plurality of stabilizers or mixtures thereof, and / or a plurality of colorants or mixtures thereof. Generally, any combination or mixture of the different thiol species, ene species, additional (meth)acrylate species, photoinitiators, inhibitors, stabilizers, and / or colorants described herein can be used in the first ink and / or second ink of the kits described herein. However, in some cases, the inks of the kits described herein do not both contain a thiol species and an ene species (such as a (meth)acrylate).

[0075] In addition, the inks of the kits described herein can be used simultaneously or sequentially in a 3D printing process. In addition, in some cases, the inks of the kits can together provide different monomers or curable species that form different polymer networks. In some such cases, the different monomers and / or polymer networks of the different inks of the kits can be cured in a temporally separate manner and / or in a spatially separate manner within the geometry of the 3D article, as described above with respect to the single ink. For example, in some embodiments, the monomers (or pair of monomers) of the first (and / or second) ink can be cured during the printing of the 3D article to provide a printed article having sufficient green strength to be handled and / or exhibiting a desired feature resolution, and the different monomers (or pair of monomers) of the second (and / or first) ink can be cured after printing, such as by placing the article in an oven to thermally cure the second monomers. Similarly, in other cases, the monomers (or pair of monomers) of the first ink are cured or polymerized within a first region of the 3D printed article, and the monomers (or pair of monomers) of the second ink are cured or polymerized within a second region of the 3D printed article.

[0076] Additionally, during 3D printing, the two inks of the kits described herein can be used in separate ink dispensers or "channels" of a 3D printing system, or can be combined to form a single composition for use in forming a 3D article, as further described below. Additionally, it should be appreciated that a "channel" of a 3D printing system can refer to the mechanism by which a single substance is deposited from an ink dispenser, such as a print head. For example, a channel of a print head can refer to a specific substance ejection orifice of a print head that is separate or associated with any substance conduit, substance storage compartment, and / or other hardware or software combination of a 3D printing system. A channel can also refer to an entire print head that is separate or associated with the printing of a single specific substance from the channel.

[0077] The inks described herein, whether "single" inks or part of a kit, can exhibit a variety of desirable properties. For example, the inks described herein can have any freezing point, melting point, and / or other phase transition temperature that is consistent with the objects of the present disclosure. In some cases, the inks have freezing points and melting points that are consistent with the temperatures used in some 3D printing systems, including 3D printing systems designed for use with phase change inks. In some embodiments, the inks have a freezing point greater than about 40 °C. For example, in some cases, the inks have a freezing point that is centered in a range from about 45 °C to about 55 °C, or from about 50 °C to about 80 °C. In some cases, the inks have a freezing point that is less than about 40 °C, or less than about 30 °C.

[0078] Additionally, in some embodiments described herein, the inks exhibit a "sharp" freezing point or other phase transition. For example, in some cases, the inks freeze over a narrow temperature range, such as a range of about 1-10 °C, about 1-8 °C, or about 1-5 °C. In some embodiments, the inks having a "sharp" freezing point freeze over a temperature range of X ± 2.5 °C, where X is the temperature at which the freezing point is centered (e.g., X = 65 °C).

[0079] Additionally, in some cases, the inks described herein are fluid at the inkjet temperatures encountered in some 3D printing systems. Additionally, in some embodiments, the inks solidify once deposited on a surface during the manufacture of a three-dimensional printed article or object. Alternatively, in other cases, the inks remain substantially fluid after deposition on a surface. In some embodiments, the solidification of the inks occurs through a phase change of the ink or ink component. The phase change can include a liquid-to-solid phase change or a liquid-to-semi-solid phase change. Additionally, in some cases, the solidification of the inks includes an increase in viscosity of the ink, such as an increase in viscosity from a low viscosity state to a high viscosity state. The solidification of the inks can also occur due to the hardening or curing of the inks.

[0080] Additionally, in some embodiments, the inks described herein have viscosity properties consistent with the requirements and parameters of one or more 3D printing systems (such as multi-jet modeling or stereolithography printing systems) when uncured. For example, in some cases, the inks described herein have a dynamic viscosity of about 8.0 cP to about 14.0 cP or about 9.0 cP to about 14.0 cP at a temperature of the jetting temperature of the system, such as about 80 °C, when determined according to ASTM Standard D2983 (e.g., using a Brookfield Model DV-II+ viscometer). In some embodiments, the inks have a dynamic viscosity of about 9.5-12.5 cP or about 10.5-12.5 cP at a temperature of about 80 °C. In some cases, the inks have a viscosity of about 8.0-10.0 cP at a temperature of about 85-87 °C. In some embodiments, the inks described herein have a dynamic viscosity of about 8.0-19.0 cP, about 8.0-13.5 cP, about 11.0-14.0 cP, about 11.5-13.5 cP, or about 12.0-13.0 cP at a temperature of about 65 °C, when determined according to ASTM D2983. In other cases, the inks described herein exhibit a dynamic viscosity of about 200-2000 cP, about 200-900 cP, about 300-900 cP, about 300-800 cP, about 400-1000 cP, about 400-900 cP, about 400-800 cP, about 400-600 cP, about 450-550 cP, about 500-700 cP, about 500-600 cP, or about 500-550 cP at 30 °C when uncured, as determined according to ASTM D2983. In some cases, the inks described herein exhibit a dynamic viscosity of less than about 100 cP or greater than about 1000 cP when uncured, as determined according to ASTM D2983.

[0081] Additionally, in some embodiments, the inks described herein can exhibit a combination of one or more desirable characteristics. For example, in some cases, the inks have one or more of the following properties in the uncured state:

[0082] 1. a freezing point of less than about 30 °C, less than about 25 °C, or less than about 15 °C;

[0083] 2. a viscosity of about 9-14 cP at 70-95 °C, or about 400-1000 cP at 25-35 °C; and

[0084] 3. thermal stability for at least 6 months at room temperature (25 °C).

[0085] As noted above, viscosity can be determined in accordance with ASTM D2983 (e.g., using a Brookfield Model DV-II+ viscometer). Additionally, for reference purposes herein, a "thermally stable" substance exhibits a change in viscosity of no greater than about 35% over a specified period (e.g., 3 days) when measured at a specified temperature (e.g., room temperature) at the beginning and end of the period. In some embodiments, the change in viscosity is no greater than about 30% or no greater than about 20%, based on the greater viscosity value. In some cases, the change in viscosity is between about 10% and about 20% or between about 25% and about 30%. Additionally, in some embodiments, the change in viscosity is an increase in viscosity.

[0086] In addition to those described above in the cured state or in the "green" state, the inks described herein can also exhibit a variety of other desirable properties. As used herein, an "cured" state ink includes an ink comprising a curable substance or polymerizable component that has at least partially polymerized and / or crosslinked or has largely polymerized and / or crosslinked. For example, in some cases, a cured ink is at least about 51% polymerized or crosslinked or at least about 60% polymerized or crosslinked. In some embodiments, a cured ink is at least about 70%, at least about 80%, at least about 90%, or at least about 95% polymerized or crosslinked. In some cases, a cured ink is between about 50% and about 99% polymerized or crosslinked. A "green" state ink can be less than 50%, less than 40%, less than 30%, or less than about 20% polymerized or crosslinked. In some cases, an ink in the green state is 5-50%, 5-40%, 5-30%, 10-50%, 10-40%, 10-30%, 20-50%, 20-40%, 30-50%, or 30-40% polymerized or crosslinked. Additionally, as will be appreciated by one of ordinary skill in the art, the "green" state of an ink can be defined as the state of the ink during or after the layer-by-layer 3D printing process described herein but prior to having performed a post-processing curing step.

[0087] In some cases, the inks described herein have an elongation at break of about 10-400%, 10-300%, 10-200%, 10-100%, 10-8%, 10-40%, 10-30%, 10-20%, 15-400%, 15-300%, 15-100%, 15-30%, 50-400%, 50-300%, 50-200%, 50-100%, 100-400%, 100-300%, 100-200%, 200-400%, 200-300%, or 300-400% when cured or in a green state when measured according to ASTM D638. Additionally, in some cases, the cured or green inks described herein can have a tensile strength of about 3500-7000 psi or about 4000-6000 psi when measured according to ASTM D638. Additionally, in some embodiments, the cured or green inks described herein can have a tensile modulus of about 100-400 ksi or about 150-300 ksi when measured according to ASTM D638.

[0088] Additionally, in some cases, the inks described herein can exhibit a variety of the aforementioned properties when cured. For example, in some embodiments, the inks have a tensile strength of about 4000-6000 psi when measured according to ASTM D638 when cured; a tensile modulus of about 150-300 ksi when measured according to ASTM D638; and an elongation at break of about 10-400% when measured according to ASTM D638 when cured.

[0089] The inks described herein can be prepared in any manner consistent with the objects of the present disclosure. For example, in some embodiments, a method of preparing the inks described herein includes the steps of mixing the ink components, melting the mixture, and filtering the melted mixture. In some cases, the melting of the mixture is performed at a temperature of about 75 °C or in the range of about 75 °C to about 85 °C. In some embodiments, the inks described herein are prepared by placing all of the components of the ink into a reaction vessel and heating the resulting mixture to a temperature in the range of about 75 °C to about 85 °C while stirring. Heating and stirring are continued until the mixture reaches a substantially homogenized, molten state. Generally, the molten mixture can be filtered while in a flowable state to remove any large undesirable particles that can interfere with the inkjet or extrusion or other printing process. The filtered mixture can then be allowed to cool to ambient temperature and stored until ready for use in a 3D printing system. In other cases, the components of the ink are mixed at ambient temperature (e.g., 20-25 °C) without heating, or with minimal heating (e.g., heating to a temperature of 30-45 °C). Such methods can still include filtering the resulting liquid mixture.

[0090] II. Use of the composition for 3D printing

[0091] In another aspect, described herein is a use of a composition for 3D printing, wherein the composition comprises an ink or a kit described above. For example, in some cases, described herein is a use of a composition for 3D printing, wherein the composition comprises an ink comprising a thiol monomer and an ene monomer. However, any ink or plurality of inks described above in Section I can be used for 3D printing.

[0092] III. 3D printing system

[0093] In another aspect, described herein is a 3D printing system. Such a 3D printing system can use or comprise a composition described above for 3D printing, such as a composition comprising an ink, a plurality of inks, or a kit described above. In some embodiments, a 3D printing system described herein comprises a 3D printer having at least one of an ink dispenser and an ink reservoir, and an ink described herein disposed in the ink dispenser, the ink reservoir, or both. The ink comprises, consists of, or consists essentially of any ink described above in Section I. Additionally, in some cases, a 3D printing system described herein comprises a 3D printer having a first ink dispenser and a second ink dispenser, a first ink disposed in the first ink dispenser, and a second ink disposed in the second ink dispenser. The first ink and the second ink each comprise, consist of, or consist essentially of a first ink and a second ink described above in Section I.

[0094] Generally, any 3D printer consistent with the objects of the present disclosure can comprise or include an ink described herein, including in an ink dispenser and / or reservoir. For example, in some embodiments, a 3D printer comprises an inkjet or so-called multi-jet modeling (MJM) type 3D printer. In other cases, a 3D printer comprises a stereolithography (SLA) type 3D printer, a digital light processing (DLP) type 3D printer, or a contact SLA (cSLA) type printer. Other 3D printers can also be used.

[0095] IV. Method of printing a 3D article

[0096] In another aspect, described herein is a method of printing a 3D article or object. A method of printing a 3D article or object described herein can comprise forming a 3D article from a plurality of ink layers described herein in a layer-by-layer manner. Any ink described above in Section I can be used. For example, in some cases, an ink comprises a thiol monomer and an ene monomer. Other inks described herein can also be used. Additionally, in some cases, a method described herein comprises selectively depositing an ink layer in a fluid state on a substrate.

[0097] Additionally, the methods described herein can also include curing or polymerizing one or more monomers or curable species of the ink, such as the thiol monomers and the ene monomers of the ink. Additionally, where the ink includes multiple monomers having different polymerization processes or curing mechanisms, the different monomers can be cured or polymerized in separate curing or polymerization steps, at different time periods and / or in different spatial regions of the ink layer. Additionally, the different monomers can be cured or polymerized in different ways.

[0098] For example, in some cases, the ink used in the methods described herein includes thiol monomers, ene monomers, and additional (meth)acrylate monomers that are different from the ene monomers. In some such cases, the methods described herein include curing or polymerizing the olefinic unsaturated portion of the (meth)acrylate monomers to form a poly(meth)acrylate. For example, the (meth)acrylate monomers can be cured or polymerized with UV light. Additionally, in some embodiments, the methods also include separately curing or polymerizing the thiol monomers and the ene monomers. Such curing or polymerization can include reacting the thiol monomers with the ene monomers to form a poly(thiol-ene). Additionally, in some cases, the reaction of the thiol monomers with the ene monomers is thermally initiated. In other embodiments, the reaction of the thiol monomers with the ene monomers is photo-initiated. However, in some such cases, the photo-curing of the additional (meth)acrylate monomers is performed with a different wavelength or intensity of light than the photo-curing of the thiol monomers and the ene monomers. The reaction of the thiol monomers with the ene monomers can also be initiated with the same light that initiates the polymerization of the additional (meth)acrylate monomers. Additionally, in some cases, the heat energy released from the photo-initiated polymerization of the (meth)acrylate monomers initiates the reaction of the thiol monomers with the ene monomers.

[0099] Curing or polymerizing one or more of the curable species or monomers described herein can be performed in any manner consistent with the objectives of the present disclosure. For example, in some cases, a deposited ink layer can be polymerized or cured prior to depositing another or adjacent ink layer. Accordingly, in some cases, the methods of printing 3D articles described herein also include exposing the ink layer to electromagnetic radiation having a wavelength and intensity sufficient to cure at least one monomer (or pair of monomers) of the ink, where curing can include polymerizing one or more polymerizable moieties or functional groups of one or more monomer (or pair of monomers) components. In some embodiments, UV light or visible light is used.

[0100] Similarly, thermal curing can also be performed. In some embodiments, thermal curing is performed with thermal energy or heat provided by the photocuring steps described herein, including thermal energy released by the photoinitiated polymerization of (meth)acrylate monomers, as described above. Thermal curing can also be performed by heating the ink (or article formed from the ink) with a thermal energy source, such as an oven. Thermal curing can be performed during the layer-by-layer printing of the article or after the layer-by-layer printing of the article. For example, in some cases, the article is heated in a "post-processing" step, such as by placing the pre-formed article in an oven or other enclosure at an elevated temperature. In some such cases, the article can be heated at a temperature sufficient to cure previously uncured monomers of the ink from which the article is formed and for a period of time, in contrast to heating at a lower temperature and / or for a shorter period of time, such as can be used to melt away or away support material from a completed 3D article. In some cases, however, the support material, if present, can be melted away from the completed 3D article concurrently with thermal curing of the ink monomers.

[0101] As described above, the methods of printing 3D articles described herein can include forming the 3D article from multiple layers of multiple inks described herein in a layer-by-layer manner, rather than from a single ink. For example, in some embodiments, the method includes forming the 3D article from a plurality of first ink layers and a plurality of second ink layers. In some such cases, the method of printing the 3D article includes selectively depositing a first ink layer in a fluid state on a substrate and selectively depositing a second ink layer in a fluid state on the substrate, wherein the first ink and the second ink each include a first ink and a second ink described in Section I above. For example, the first ink can include thiol monomers and the second ink can include alkenyl monomers.

[0102] As with the "single" ink, the methods described herein that use multiple different inks can also include curing the multiple monomers or curable species of the inks, including in separate curing steps performed at different times and / or in different spatial regions of one or more ink layers. Additionally, as described further herein, the different monomers or curable species can be cured in different ways. For example, in some embodiments, the second ink includes additional (meth)acrylate monomers and the method further includes photocuring the additional (meth)acrylate monomers of the second ink with UV light, followed by thermal or photocuring the thiol monomers and the alkenyl monomers.

[0103] Generally, one ink layer or multiple ink layers can be deposited according to a 3D article image in a computer readable format. In some embodiments, the ink is deposited according to preselected computer aided design (CAD) parameters. Additionally, in some cases, one or more ink layers described herein have a thickness of about 10 μιη to about 100 μιη, about 10 μιη to about 80 μιη, about 10 μιη to about 50 μιη, about 20 μιη to about 100 μιη, about 20 μιη to about 80 μιη, or about 20 μιη to about 40 μιη. Other thicknesses are also possible.

[0104] Additionally, it should be appreciated that the methods of printing 3D articles described herein can include so-called multi-jet modeling or stereolithographic 3D printing methods. For example, in some cases, the multi-jet methods of printing 3D articles include selectively depositing one or more of the ink layers described herein in a fluid state onto a substrate, such as a build pad of a 3D printing system. Additionally, in some embodiments, the methods described herein further include supporting at least one of the one or more ink layers with a support material. Any support material consistent with the objects of the present disclosure can be used.

[0105] Additionally, in some embodiments, a preselected amount of an ink described herein is heated to a suitable temperature and jetted through a print head or multiple print heads of a suitable inkjet printer to form a layer on a print pad in a print chamber. In some cases, each ink layer is deposited according to preselected CAD parameters. In some embodiments, a suitable print head for depositing the inks is a piezoelectric print head. Additional suitable print heads for depositing the inks and support materials described herein are commercially available from a number of inkjet printer manufacturers. For example, in some cases, a print head from Xerox, Hewlett Packard, or Ricoh can be used.

[0106] Additionally, in some embodiments, the inks described herein remain substantially fluid upon deposition. Alternatively, in other cases, the inks exhibit a phase change upon deposition and / or cure upon deposition. Additionally, in some cases, the temperature of the printing environment can be controlled such that the jetted droplets of ink cure upon contact with the receiving surface. In other embodiments, the jetted droplets of ink do not cure upon contact with the receiving surface, remaining in a substantially fluid state. Additionally, in some cases, upon deposition of each layer, the deposited material is planarized prior to deposition of the next layer and cured with electromagnetic (e.g., UV) radiation. Optionally, a number of layers can be deposited prior to planarization and curing, or multiple layers can be deposited and cured, followed by deposition of one or more layers, then planarization without curing. Planarization prior to curing the material corrects the thickness of one or more layers by flattening the dispensed material to remove excess material and create a uniformly smooth exposed or planar upward surface on the support platform of the printer. In some embodiments, planarization is accomplished with a squeegee device, such as a roller, which can be counter-rotated in one or more print directions, but not in one or more other print directions. In some cases, the squeegee device includes a roller and a squeegee that removes excess material from the roller. Additionally, in some cases, the squeegee device is heated. It should be noted that in some embodiments, the consistency of the inks described herein that are jetted prior to curing should desirably be sufficiently viscous to maintain their shape without being overly draggy for the planarizer.

[0107] Additionally, in use, the support material can be deposited in a manner consistent with that described above with respect to the ink. For example, the support material can be deposited according to preselected CAD parameters such that the support material is adjacent to or continuous with one or more ink layers. In some embodiments, the jetted droplets of support material solidify or set upon contact with the receiving surface. In some cases, the deposited support material is also subjected to planarization.

[0108] Layered deposition of the ink and support material can be repeated until a 3D article has been formed. In some embodiments, the method of printing a 3D article further comprises removing the support material from the ink.

[0109] A 3D article can also be formed from the inks described herein using stereolithography (SLA), contact SLA (cSLA), or digital light processing (DLP) 3D printing. For example, in some cases, the method of printing a 3D article comprises maintaining one or more inks described herein in a fluid state in a container and selectively applying energy to the one or more inks in the container to solidify at least a portion of a fluid layer of the ink to form a solidified layer defining a cross-section of the 3D article. Additionally, the methods described herein can further comprise lifting or lowering the solidified layer of the ink to provide a new or second fluid layer of the ink that is not solidified at the surface of the fluid ink in the container, followed by again selectively applying energy to the ink in the container to solidify at least a portion of the new or second fluid layer of the ink to form a second solidified layer defining a second cross-section of the 3D article. Additionally, the first and second cross-sections of the 3D article can be joined or bonded to one another in the z-direction (or a build direction equivalent to the above-mentioned lifting or lowering direction) by the application of energy to solidify the ink. Additionally, selectively applying energy to the ink in the container can comprise applying electromagnetic radiation, such as UV radiation or visible radiation, having sufficient energy to solidify the ink. In some cases, the UV light has an average wavelength of 320-380 nm, 340-370 nm, or 350-360 nm. In some cases, the solidification radiation is provided by a computer-controlled laser beam or a DLP light source or projector. Additionally, in some cases, lifting or lowering the solidified layer of the ink is performed with a lifter platform disposed in the container of fluid ink. The methods described herein can also comprise planarizing the new fluid layer of ink provided by lifting or lowering the lifter platform. In some cases, such planarization can be performed by a squeegee or roller.

[0110] It should also be appreciated that the foregoing process can be repeated as many times as necessary to provide a 3D article. For example, in some cases, the process can be repeated "n" times, where n can be up to about 100,000, up to about 50,000, up to about 10,000, up to about 5,000, up to about 1,000, or up to about 500. Accordingly, in some embodiments, the method of printing a 3D article described herein can include selectively applying energy to the ink in the container to solidify at least a portion of the n-th fluid ink layer to form an n-th solidified layer defining an n-th cross-section of the 3D article, lifting or lowering the n-th solidified ink layer to provide an (n+1)-th non-solidified ink layer at the surface of the fluid ink in the container, selectively applying energy to the (n+1)-th ink layer in the container to solidify at least a portion of the (n+1)-th ink layer to form an (n+1)-th solidified layer defining an (n+1)-th cross-section of the 3D article, lifting or lowering the (n+1)-th solidified ink layer to provide an (n+2)-th non-solidified ink layer at the surface of the fluid ink in the container, and continuing to repeat the foregoing steps to form the 3D article. In addition, it should be appreciated that one or more steps of the methods described herein, such as the step of selectively applying energy to the ink layer, can be performed in accordance with a 3D article image in a computer readable format. General methods of 3D printing using stereolithography are also described, inter alia, in U.S. Patents 5,904,889 and 6,558,606.

[0111] The printing processes described above can provide 3D printed articles having high feature resolution from the inks described herein. For purposes of reference herein, the "feature resolution" of an article can be the smallest controllable physical feature size of the article. The feature resolution of an article can be described in units of distance, such as micrometers (pm), or in dots per inch (dpi). Those of ordinary skill in the art will appreciate that a higher feature resolution corresponds to a higher dpi value, but to a lower distance value (pm). In some cases, articles formed from the deposition or solidification of the inks described herein can have a feature resolution of about 500 pm or less, about 200 pm or less, about 100 pm or less, or about 50 pm or less, including at elevated temperatures. In some embodiments, the articles have a feature resolution of between about 50 pm and about 500 pm, between about 50 pm and about 200 pm, between about 50 pm and about 100 pm, or between about 100 pm and about 200 pm. Accordingly, in some cases, the articles described herein have a feature resolution of at least about 100 dpi, at least about 200 dpi, at least about 250 dpi, at least about 400 dpi, or at least about 500 dpi. In some cases, the feature resolution of the article is between about 100 dpi and about 600 dpi, between about 100 dpi and about 250 dpi, or between about 200 dpi and about 600 dpi.

[0112] V. 3D printed article

[0113] In another aspect, 3D printed articles are described herein. In some embodiments, the 3D printed articles are formed from one or more inks described herein. Any of the inks described above in Section I can be used. For example, in some cases, the 3D articles are formed from a single ink described herein, such as an ink comprising a thiol monomer, an ene monomer, and an additional (meth)acrylate monomer different from the ene monomer. Additionally, upon curing, the thiol monomer and the ene monomer can together form a poly(thiol-ene). Similarly, upon curing, the additional (meth)acrylate monomer can form a poly(meth)acrylate. In some such cases, the poly(thiol-ene) and the poly(meth)acrylate together form an interpenetrating polymer network.

[0114] The 3D printed articles described herein can also be formed from a plurality of different inks. For example, in some embodiments, the 3D printed articles are formed from a first ink and a second ink described above in Section I. In some such cases, the first ink comprises a thiol monomer and the second ink comprises an ene monomer. The first and / or second ink can also comprise an additional (meth)acrylate monomer different from the ene monomer. Additionally, as described above, this additional (meth)acrylate monomer of the first or second ink can form a polymer network (specifically, a poly(meth)acrylate) network that is different from the polymer network (specifically, a poly(thiol-ene)) formed from the thiol and ene monomers. Additionally, in some cases, the two polymer networks together form an interpenetrating polymer network.

[0115] Some embodiments described herein are also illustrated in the following non-limiting examples.

[0116] Examples

[0117] Inks for 3D printing

[0118] An ink according to one embodiment described herein was prepared as follows. First, 15-25 wt% pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), 10-50 wt% oligomeric (meth)acrylate, and 20-50 wt% monomeric (meth)acrylate, 1-4 wt% photoinitiator, and 0.1-1 wt% polymerization inhibitor were mixed together in the manner described above in Section I and provided in a liquid state. Specifically, the ink components were combined and mixed. With stirring, the mixture was heated to a temperature of about 60-75 °C. Heating and stirring were continued until the mixture reached a substantially homogenized liquid state. The liquid mixture was then filtered to remove particulates.

[0119] After the ink was prepared, various 3D articles were formed using the ink with a cSLA 3D printing system. The resulting articles were very tough, soft, and not brittle under all test conditions.

[0120] All patent documents mentioned herein are incorporated by reference in their entirety. Various embodiments of the application are described in fulfillment of different objects of the application. It should be recognized that these embodiments are only examples of the principles of the application. Many improvements and modifications can be made without departing from the spirit and scope of the application.

Claims

1. An ink for use in a three-dimensional printing system, the ink comprising: 10-40% by weight of a thiol monomer; 10-60% by weight of a monomeric (meth)acrylate; and 5-60% by weight of an oligomeric (meth)acrylate, based on the total weight of the ink, wherein the thiol monomer comprises pentaerythritol tetra(3-mercaptopropionate) (PETMP).

2. The ink of claim 1, further comprising: 0.1-5% by weight of a photoinitiator, based on the total weight of the ink.

3. The ink of claim 1, further comprising: 0.05-1.5% by weight of an inhibitor and / or stabilizer, based on the total weight of the ink.

4. An ink for use in a three-dimensional printing system, the ink comprising: 10-40% by weight of a thiol monomer; 5-40% by weight of an olefinic monomer; and 10-60% by weight of a (meth)acrylate monomer different from the olefinic monomer, based on the total weight of the ink, wherein the thiol monomer comprises pentaerythritol tetra(3-mercaptopropionate) (PETMP).

5. The ink of claim 4, wherein the (meth)acrylate monomer comprises a monomeric (meth)acrylate and an oligomeric (meth)acrylate.

6. A method of printing a three-dimensional article, the method comprising: selectively depositing layers of an ink in a fluid state on a substrate, wherein the ink comprises the ink of claim 1.

7. The method of claim 6, wherein the layers of ink are deposited according to a three-dimensional article image in a computer readable format.

8. The method of claim 6, wherein the ink comprises an olefinic monomer and a (meth)acrylate monomer different from the olefinic monomer of the ink, and the method further comprises curing the (meth)acrylate monomer with UV light.

9. The method of claim 8, further comprising thermally curing the thiol monomer and the olefinic monomer.

10. An ink for use in a three-dimensional printing system, comprising: 10 to 30 % by weight of a thiol monomer, the thiol monomer comprising pentaerythritol tetra(3-mercaptobutyrate); and up to 90 % by weight of at least one of an olefinic monomer and an olefinic oligomer, based on the total weight of the ink, wherein the thiol monomer is present in at least a detectable amount.

11. The ink of claim 10, further comprising 0.1-5% by weight of a photoinitiator, based on the total weight of the ink.

12. The ink of claim 10, wherein the thiol monomer comprises a plurality of different thiol- containing species.

13. The ink of claim 10, further comprising a (meth)acrylate monomer different from the at least one of an olefinic monomer and an olefinic oligomer.

14. The ink of claim 10, comprising up to 20% by weight of the thiol monomer.

15. The ink of claim 10, further comprising an inhibitor and / or a stabilizer.

16. A kit for use in a three-dimensional printing system, the kit comprising: a first ink comprising 10 to 30 % by weight of a thiol monomer, the thiol monomer comprising pentaerythritol tetra(3-mercaptobutyrate); and a second ink comprising at least one of an olefinic monomer and an olefinic oligomer, the olefinic monomer or olefinic oligomer comprising an ethylenically unsaturated moiety; wherein The thiol monomers and the olefin monomers do not bind prior to printing.

17. The kit of claim 16, wherein the second ink comprises (meth)acrylate monomers different from the at least one olefin monomer and olefin oligomer.

18. The kit of claim 16, wherein the first ink comprises a plurality of different thiol- containing species.

19. The kit of claim 16, wherein at least one of the first ink and the second ink comprises 0.1-5% by weight photoinitiator, based on the total weight of the first ink and the second ink.

20. The kit of claim 17, wherein at least one of the first ink and the second ink comprises an inhibitor and / or a stabilizer.

21. The kit of claim 17, wherein the first ink comprises a plurality of thiol moieties.

22. A printed three-dimensional article formed from the ink of claim 10.

23. A method of printing a three-dimensional article, comprising: selectively depositing layers of ink in a fluid state onto a substrate, wherein the ink comprises the ink of claim 10.

24. The method of claim 23, wherein the layers are deposited according to an image of the three-dimensional article in a computer readable format.

25. The method of claim 23, wherein the ink comprises (meth)acrylate monomers different from the at least one olefin monomer and olefin oligomer, and the method comprises further UV curing the (meth)acrylate monomers.

26. The method of claim 23, further comprising thermally curing the thiol monomers and the at least one olefin monomer and olefin oligomer.

27. A method of printing a three-dimensional article, comprising: storing the ink in a liquid state in a container; selectively applying energy to the ink in the container to cure at least a portion of a first fluid layer of the ink to form a first cured layer defining a first cross-section of the article; raising or lowering the first cured layer to provide a second fluid layer of the ink at a surface of the fluid ink in the container; and selectively applying energy to the ink in the container to cure at least a portion of the second fluid layer of the ink to form a second cured layer defining a second cross-section of the article, the first cross-section and the second cross-section being joined to one another in a z-direction, wherein the ink comprises the ink of any one of claims 10-15.

28. The method of claim 27, further comprising repeating the raising or lowering step and the subsequent selectively applying energy step n times to form the three-dimensional object, wherein n is an integer up to 100,000.

29. The method of claim 28, further comprising thermally curing the formed three- dimensional article after printing.

30. The method of claim 29, wherein thermally curing the formed three-dimensional article comprises reacting the thiol monomers with the olefin monomers and olefin oligomers.

31. The method of claim 30, wherein selectively applying energy to the ink in the container comprises selectively exposing the ink to UV radiation.

32. The method of claim 31, wherein exposing the ink to UV radiation at least partially cures (meth)acrylate monomers of the ink. ​ 33. An ink for a three-dimensional printing system, comprising: 15-40 % by weight thiol monomer; 10-60 % by weight monomeric (meth)acrylate; and 5-60 % by weight oligomeric (meth)acrylate, based on the total weight of the ink, wherein the thiol monomer comprises pentaerythritol tetra(3-mercaptopropionate) (PETMP).

34. The ink of claim 33, further comprising an inhibitor and / or a stabilizer.

35. An ink for a three-dimensional printing system, comprising: 15-40 % by weight thiol monomer; 5-40 % by weight ene monomer; and 10-60 % by weight (meth)acrylate monomer different from the ene monomer, based on the total weight of the ink, wherein the thiol monomer comprises pentaerythritol tetra(3-mercaptopropionate) (PETMP).

36. The ink of claim 35, further comprising an inhibitor and / or a stabilizer.

37. A kit for a three-dimensional printing system, the kit comprising: a first ink comprising 15 to 30 % by weight thiol monomer, the thiol monomer comprising pentaerythritol tetra(3-mercaptopropionate) (PETMP), and a second ink comprising at least one of an ene monomer and an ene oligomer, the ene monomer or ene oligomer comprising an ethylenically unsaturated moiety; wherein the thiol monomer and the ene monomer do not combine prior to printing.

38. A kit for a three-dimensional printing system, the kit comprising: a first ink comprising 10-40% by weight thiol monomer, based on the total weight of the ink, the thiol monomer comprising pentaerythritol tetra(3-mercaptopropionate) (PETMP); and a second ink comprising an ene monomer; and wherein the thiol monomer and the ene monomer do not combine prior to printing.

39. The kit of claim 38, wherein the first ink comprises 15 to 25% by weight of the thiol monomer.

40. An ink for a three-dimensional printing system, comprising: 10-40 % by weight thiol monomer; and 5-40 % by weight ene monomer; based on the total weight of the ink wherein the ink is substantially free of (meth)acrylate and the thiol monomer comprises pentaerythritol tetra(3-mercaptopropionate).

41. The ink of claim 40, wherein the ene monomer is a substituted or unsubstituted norbornene, vinyl ether, olefin, vinyl ester, N-vinyl amide, allyl ether, allyl triazine, allyl isocyanurate, maleimide, acrylonitrile, styrene, conjugated diene, or a combination thereof.

42. An ink for a three-dimensional printing system, comprising: 10-40 % by weight thiol monomer; 5-40 % by weight ene monomer; and 10-60 % by weight (meth)acrylate monomer; based on the total weight of the ink wherein the (meth)acrylate monomer comprises urethane (meth)acrylate and the thiol monomer comprises pentaerythritol tetra(3-mercaptopropionate).

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