Liquid hybrid UV / visible radiation curable resin composition for additive manufacturing

Abstract

Disclosed are liquid radiation-curable compositions suitable for hybrid (i.e., cationic and free radical) polymerization when processed through an additive manufacturing apparatus utilizing an actinic radiation source having a peak spectral intensity in the UV / Vis region. According to one aspect, the composition has a first photoinitiator that is an iodonium salt of a non-fluorinated borate anion. According to another aspect, the composition is substantially free of Norrish Type I and / or Type II photoinitiators. Also disclosed are methods for manufacturing three-dimensional parts using a liquid radiation-curable composition suitable for hybrid polymerization through an additive manufacturing process utilizing an actinic radiation source having a peak spectral intensity in the UV / Vis region, as well as parts cured by the methods.

Description

Technical Field

[0001] The present invention relates to liquid compositions for additive manufacturing processes that are hybrid curable in the ultraviolet or visible spectrum.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Provisional Patent Application No. 62 / 893,969, filed on August 30, 2019, which is hereby incorporated by reference in its entirety as if fully set forth herein. Background Art

[0004] Additive manufacturing (AM) processes for producing three-dimensional objects are well known. AM uses computer-aided design (CAD) data of an object to construct a three-dimensional part. These three-dimensional parts can be formed from liquid resins, powders, or other materials.

[0005] A well-known, non-limiting example of an additive manufacturing process is stereolithography (SL). Stereolithography is a process used to quickly produce models, prototypes, patterns, and production parts in certain applications. SL uses CAD data of an object, where the data is transformed into a thin cross-section of the three-dimensional object. The data is loaded into a computer, which controls a laser that traces the pattern of the cross-section to radiate a curable resin through a liquid contained in a groove, thereby solidifying a thin layer of resin corresponding to the cross-section. The solidified layer is re-coated with resin, and the laser traces another cross-section to harden another layer of resin on top of the previous layer. The process is repeated layer by layer until the three-dimensional object is completed. When initially formed, the three-dimensional object is typically not fully cured and is referred to as a "green model." Although not required, the green model can be subjected to post-curing to enhance the mechanical properties of the manufactured part. For example, an example of the SL method is described in U.S. Patent No. 4,575,330.

[0006] Lasers have traditionally been used as the radiation source of choice in additive manufacturing processes such as stereolithography. The use of gas lasers to cure liquid radiation-curable resin compositions is well known. The delivery of laser energy in stereolithography systems can be continuous waves (CW) or Q-switched pulses. CW lasers provide continuous laser energy and can be used in high-speed scanning processes. Historically, several types of lasers have been used for stereolithography, with the wavelength range of their peak spectral output traditionally ranging from 193nm to 355nm, although other wavelength variants exist. The light emitted from the laser is monochromatic, that is, a high percentage of the total spectral output occurs within a very narrow wavelength range. Among the laser-based additive manufacturing systems in the industry, laser-based additive manufacturing systems operating with a peak spectral output of 355nm have become the most common.

[0007] However, laser-based systems, especially those operating at or near their peak spectral output at 355 nm, are not without drawbacks. The significant power output of such laser-based systems sometimes generates excessive heat at the point of irradiation, which can be detrimental to the resin. Furthermore, the use of any wavelength laser requires scanning point by point across the resin surface, a process that can be particularly time-consuming when the cross-sectional pattern to be cured is large or complex. Furthermore, systems based on 355 nm lasers are expensive and associated with high maintenance costs and energy consumption.

[0008] To overcome some of the shortcomings associated with laser-based systems, other additive manufacturing systems have begun to utilize image projection technology as the source of actinic radiation. One example is Liquid Crystal Display (LCD), a technology well known in other industries such as the manufacture of televisions and computer monitors. Another non-limiting example was developed by Texas Instruments and is called Digital Light Processing (DLP). ). A DLP system selectively transmits light from an input source and projects that light in a desired output pattern or mask using a pixel-representative microscope that is controlled by and attached to a microchip called a Digital Micromirror Device (DMD). DLP technology was developed for image projection systems as an alternative display system based on LCD technology. The superior image clarity, brightness, and uniformity associated with DLP systems make them well suited for additive manufacturing, where image resolution and accuracy are critical because the boundaries of the projected light ultimately define the boundaries of the three-dimensional object to be cured and created. In addition, image projection systems such as LCD and DLP offer a theoretical speed advantage because they enable the simultaneous exposure and curing of entire cross-sectional layers. Furthermore, whereas the curing time required in laser-based systems is proportional to the complexity of the cross-section to be scanned, image projection systems are referred to as cross-section independent, meaning that the exposure time for a given layer does not change as the complexity of the shape of any given layer increases. This makes them particularly suitable for parts with complex and detailed geometries created by additive manufacturing.

[0009] DLP and LCD are not themselves alternative methods of generating light; rather, they provide a way to process the light emitted from an existing light source into a more desirable pattern. Therefore, a coupled input light source is still required. Although the light input to the image projection system can come from any source, including conventional lamps or even lasers, it is more common for the input light to be collimated from one or more light emitting diodes (LEDs).

[0010] LEDs are semiconductor devices that use electroluminescence to generate light. Currently, LED light sources used in additive manufacturing systems emit light with wavelengths between 300 nm and 475 nm, with 365 nm, 375 nm, 395 nm, 401 nm, 405 nm, and 420 nm being common peak spectral outputs. See the textbook "Light-Emitting Diodes" by E. Fred Schubert, 2 nd Edition, For a more in-depth discussion of LED light sources, see E. Fred Schubert 2006, published by Cambridge University Press. LEDs offer the advantage that they can theoretically operate at near-peak efficiency for longer durations than other light sources. Furthermore, they are generally more energy-efficient and require less maintenance than laser-based optical systems, resulting in lower initial and ongoing costs of ownership.

[0011] Thus, various additive manufacturing systems have employed one of the following non-limiting examples of optical configurations: (1) laser only, (2) laser / DLP, (3) LED only, (4) LED / DLP, or (5) LED / LCD. Systems that do not utilize DLP technology may also incorporate other collimating or focusing lenses / mirrors to selectively direct light onto the liquid resin.

[0012] Recently, regardless of the optical configuration, newer additive manufacturing systems have begun to more frequently employ light sources that emit radiation at wavelengths greater than the traditional output at 355nm. Others have moved away from monochromatic light sources and instead opted for light sources that emit light with a broader spectral output distribution. Thus, such newer systems, incorporating optical configurations based on laser / DLP, LED, LED / DLP, or LED / LCD LED / LCD, have begun to operate at peak spectral outputs at longer wavelengths and broader spectral distributions than were previously common. The wavelengths employed have shifted from 355nm towards the visible spectrum, with some even having peak spectral outputs well into the visible range. Such longer wavelengths (i.e., from 375nm to 500nm) have heretofore been referred to as "UV / Visible light."

[0013] Some of the non-limiting reasons commonly cited for the current trend toward increasing use of optics in the UV / Vis region are: (1) the decreasing cost (both initial and maintenance costs) of light sources operating in the UV / Vis range, and (2) the fact that UV / Vis light sources emit radiation of lower energy than sources emitting deeper into the UV region and, all other things being equal, are less damaging to human tissue. This makes them less hazardous in the event of accidental exposure than those operating deeper into the UV region. As additive manufacturing continues to grow in popularity across consumer, "prosumer," and industrial market segments, the need for additive manufacturing systems that employ lower cost, less hazardous sources of actinic radiation to cure liquid photopolymers will become increasingly important.

[0014] However, the benefits of utilizing UV / Vis light sources / optical systems do not come without significant trade-offs. By far the greatest disadvantage is the relatively increased difficulty in developing suitable photopolymers for systems utilizing UV / Vis optics. One of the main reasons for this is that, in addition to the natural phenomenon of reduced energy at longer wavelengths, the intensity of commercial light sources typically decreases as the wavelength of peak spectral output increases. Thus, while conventional 355nm laser-based light systems may apply 1500W / cm2 of power at the resin surface, the power of these systems may be significantly reduced. 2However, commercial systems operating at around 400 nm are known to apply only about 1 / 1000 of this irradiance to the resin surface. In fact, on existing commercial additive manufacturing systems based on 365 nm or 405 nm DLP, the irradiance applied by UV / visible light optics to the resin surface can be as low as 0.1 W / cm 2 , or even as low as 0.0002W / cm for some more economical desktop units 2 These relatively reduced radiation energies / intensities make it more difficult for photopolymerization to occur in radiation-curable resins via such UV / Vis optics unless exposure times are excessively long. This, in turn, significantly increases part build time, negating the theoretical speed advantage of photomask display systems. Furthermore, there are relatively few photoinitiating systems on the market—particularly cationic photoinitiating systems—that promote photopolymerization at such long UV / Vis wavelengths.

[0015] The aforementioned challenges have resulted in a limited number of photopolymers available for modern optical systems operating in the UV / visible region relative to the various options available for systems operating deeper into the UV region, such as those based on 355 nm lasers.

[0016] Free-radically polymerizable resins are known to exist in systems employing UV / visible light optics. Such resins typically consist of one or more (meth)acrylate compounds (or other free-radically polymerizable organic compounds) and a free-radical photoinitiator for free-radical generation. U.S. Patent No. 5,418,112 describes one such free-radically curable system. Although free-radically polymerizable resins readily cure even at the relatively low energy and low intensity provided by UV / visible light optics, they are not suitable for all additive manufacturing applications. First, (meth)acrylate-based resins considered suitable for additive manufacturing processes have traditionally produced cured parts with insufficient mechanical properties to be incorporated into many end-use applications. Consequently, the parts they produce are generally not strong enough for non-prototype applications. Furthermore, due to residual strain caused by uneven shrinkage during curing, such resins often exhibit deformation issues, such as warping or deformation of parts. These issues are exacerbated on larger-platform additive manufacturing machines, where the cumulative uneven shrinkage effect amplifies part warping or deformation as the cured object becomes larger. These deformation issues can be partially corrected using software that takes into account known shrinkage by modifying the CAD files used to generate the solid 3D part. However, software corrections are not sufficient to fully compensate for the deformation of parts with intricate shapes or that require tight dimensional tolerances over long distances.

[0017] Another well-known type of resin suitable for use in additive manufacturing systems is a "hybrid" curable resin, or a resin comprising the following components: (1) an epoxy resin, an oxetane, or other type of cationic polymerizable compound; (2) one or more cationic photoinitiators; (3) an acrylate resin or other type of free radical polymerizable compound; and (4) one or more free radical photoinitiators. Examples of such hybrid curable systems are described, for example, in U.S. Patent No. 5,434,196. Such resins have long been known to result in cured parts produced by additive manufacturing processes having superior mechanical properties relative to all-acrylate based resins. Furthermore, hybrid curable systems are superior to all-acrylate systems because they are less susceptible to the uneven shrinkage problem that has long plagued all-acrylate systems.

[0018] However, because the ring-opening process of cationic polymerization generally occurs more slowly and requires more activation energy than free-radical polymerization, it is inherently more difficult to ensure that such formulations for additive manufacturing applications fully cure, or successfully "build" a three-dimensional object. And even if curing does at least partially occur after the mixed curable resin is subjected to actinic radiation, the green models produced therefrom still have insufficient mechanical strength (or "green strength"), as measured by, for example, elastic modulus or fracture strength, for use in many additive manufacturing applications. Such problems are greatly exacerbated by the lower energy and intensity of the radiation emitted by UV / visible optics than by conventional systems.

[0019] Due to these limitations, few hybrid liquid radiation-curable resins for additive manufacturing are known to date that are suitable for use in more modern additive manufacturing systems employing UV / visible optics. Some are described in U.S. Patents Nos. 9,708,442 and 10,604,659, both assigned to DSMIP Assets BV. However, given the wide variety of additive manufacturing systems employing UV / visible optics, further solutions are still needed.

[0020] It would therefore be desirable to provide liquid radiation curable resins for additive manufacturing—hybrid curable or otherwise—that are suitable for use in additive manufacturing systems employing UV / visible light optics and that simultaneously (1) cure rapidly enough and (2) impart sufficient mechanical strength and resistance to shrinkage deformation to three-dimensional parts cured therefrom. Furthermore, or alternatively, it would be desirable to provide hybrid curable liquid radiation resin compositions that are suitable for use in additive manufacturing systems employing UV / visible light optics and that can produce three-dimensional parts having excellent precision and / or mechanical properties that are at least comparable to existing hybrid curable materials designed for conventional laser-based 355 nm systems. Summary of the Invention

[0021] Several embodiments of the present invention are described herein. According to a first aspect, the present invention relates to a radiation curable composition comprising a cationically curable component and a free radically curable component, the composition further comprising at least one first photoinitiator, the at least one first photoinitiator being an iodonium salt of a non-fluorinated borate anion. According to other embodiments of the first aspect, the non-fluorinated borate anion of the iodonium salt has the formula

[0022]

[0023] wherein R1-R4 are independently selected from the group consisting of alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl and heteroaryl, and further wherein (i) one or more substitutable carbon atoms of the alkyl, alkenyl or alkynyl group are optionally substituted with hydroxy, carboxyl, alkoxy, alkanoyl, hydroxyalkyl, carboxylalkyl, alkoxyalkyl or alkanoylalkyl, or (ii) one or more substitutable carbon atoms of the cycloalkyl, heterocycloalkyl, aryl or heteroaryl group are optionally substituted with alkyl, hydroxy, carboxyl, alkoxy, alkanoyl, hydroxyalkyl, carboxylalkyl, alkoxyalkyl or alkanoylalkyl.

[0024] According to further embodiments, the composition is substantially free of certain types of free radical photoinitiators, such as phosphorescent photoinitiators, Norrish Type I photoinitiators, and / or Norrish Type II photoinitiators.

[0025] According to a further embodiment, the composition additionally comprises a photosensitizer and / or a reducing agent. The reducing agent is preferably an electron-donating substituent bonded to a vinyl group, such as a multifunctional vinyl ether compound containing at least two vinyl groups per molecule.

[0026] A second aspect of the claimed invention describes a method of forming a three-dimensional article using any of the compositions according to the first aspect via an additive manufacturing system utilizing UV / visible light optics.

[0027] A third aspect of the claimed invention is a three-dimensional part formed by the second aspect of the invention using the liquid radiation curable composition of the first aspect of the invention. DETAILED DESCRIPTION

[0028] Throughout this document, "ultraviolet / visible light" is defined as the region of the electromagnetic spectrum from 375 nanometers (nm) to 500 nanometers (nm).

[0029] Therefore, throughout this document, "UV / Vis optics" is defined as any electrical, mechanical, or electromechanical system that generates and directs / displays actinic radiation operating at a peak spectral intensity between 375 nm and 500 nm. Specific non-limiting examples of UV / Vis optics include a laser, an LED, one or more LEDs coupled to a DLP display system, one or more LEDs coupled to an LCD display system, a laser coupled to a DLP display system, and a laser coupled to an LCD display system.

[0030] Furthermore, as used herein, "substantially free" means that a particular composition or component (as indicated above or below) is substantially free of a particular substance in an amount by weight, e.g., less than 0.1 wt%, or less than 0.05 wt%, or preferably less than 0.01 wt%, or about 0.00 wt% of a particular substance.

[0031] A first embodiment of the present invention is a radiation curable composition comprising a cationically curable component and a free radically curable component, the composition further comprising at least one first photoinitiator that is an iodonium salt of a non-fluorinated borate anion.

[0032] Thus, the composition according to the first aspect comprises a cationically curable component, a free radical polymerizable component and a photoinitiator. In a preferred embodiment, the composition comprises a free radical photoinitiator and a cationic photoinitiator. The composition may further comprise one or more photosensitizers, reducing agents and / or additives.

[0033] Cationic curable components

[0034] According to one embodiment, the liquid radiation-curable resin used in additive manufacturing of the present invention comprises at least one cationically polymerizable component; that is, a component that undergoes polymerization initiated by cations or in the presence of an acid generator. The cationically polymerizable component can be a monomer, oligomer, and / or polymer and can contain aliphatic, aromatic, cycloaliphatic, araliphatic, one or more heterocyclic moieties, and any combination thereof. Preferably, the cationically polymerizable component comprises at least one cycloaliphatic compound. Suitable cyclic ether compounds can contain cyclic ether groups as pendant groups or groups that form part of an alicyclic or heterocyclic ring system.

[0035] The cationically polymerizable component is selected from the group consisting of cyclic ether compounds, cyclic acetal compounds, cyclic thioether compounds, spiroorthoester compounds, cyclic lactone compounds, and any combination thereof.

[0036] Suitable cationically polymerizable components include cyclic ether compounds (such as epoxy compounds and oxetanes), cyclic lactone compounds, cyclic acetal compounds, cyclic thioether compounds, and spiroorthoester compounds. Specific examples of the cationically polymerizable component include: bisphenol A diglycidyl ether; bisphenol F diglycidyl ether; bisphenol S diglycidyl ether; brominated bisphenol A diglycidyl ether; brominated bisphenol F diglycidyl ether; brominated bisphenol S diglycidyl ether; epoxy novolac resin; hydrogenated bisphenol A diglycidyl ether; hydrogenated bisphenol F diglycidyl ether; hydrogenated bisphenol S diglycidyl ether; 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate; 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)-cyclohexane-1,4-dioxane; bis(3,4-epoxycyclohexylmethyl) adipate; vinylcyclohexene oxide; 4-vinylepoxycyclohexane Alkane; vinylcyclohexene dioxide; limonene oxide; limonene dioxide; bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate; 3,4-epoxy-6-methylcyclohexyl-3′,4′-epoxy-6′-methylcyclohexanecarboxylate; ε-caprolactone-modified 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate; trimethylcaprolactone-modified 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate; β-methyl-δ-valerolactone-modified 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate; methylenebis(3,4-epoxycyclohexane); biscyclohexyl-3,3′-epoxide, with -O- , -S-, -SO-, -SO2-, -C(CH3)2-, -CBr2-, -C(CBr3)2-, -C(CF3)2-, -C(CCl3)2-, or -CH(C6H5)- bonds; dicyclopentadiene diepoxide; bis(3,4-epoxycyclohexyl methyl) ether of ethylene glycol; ethylene bis(3,4-epoxycyclohexanecarboxylate); epoxyhexahydrodioctyl phthalate; epoxyhexahydro-di-2-ethylhexyl phthalate; 1,4-butanediol diglycidyl ether; 1,6-hexanediol diglycidyl ether; neopentyl glycol diglycidyl ether; glycerol triglycidyl ether; trimethylolpropane triglycidyl ether ; Polyethylene glycol diglycidyl ether; Polypropylene glycol diglycidyl ether; Diglycidyl ester of aliphatic long-chain dibasic acid; Monoglycidyl ether of aliphatic higher alcohol; Monoglycidyl ether of phenol, cresol, butylphenol; or polyether alcohols obtained by adding alkylene oxide to these compounds; Glycidyl ester of higher fatty acid; Epoxidized soybean oil; Epoxybutyl stearic acid; Epoxyoctyl stearic acid, Epoxidized linseed oil; Epoxidized polybutadiene; 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene; 3-ethyl-3-hydroxymethyloxetane; 3-ethyl-3-(3-hydroxypropyl)oxymethyloxetane; 3-ethyl-3-(4-hydroxybutyl)oxymethyloxetane;3-Ethyl-3-(5-hydroxypentyl)oxymethyloxetane; 3-ethyl-3-phenoxymethyloxetane; bis((1-ethyl(3-oxetanyl))methyl)ether; 3-ethyl-3-((2-ethylhexyloxy)methyl)oxetane; 3-ethyl-((triethoxysilylpropoxymethyl)oxetane; 3-(methyl)-allyloxymethyl-3-ethyloxetane; 3-hydroxymethyl-3-ethyloxetane; (3-ethyl-3-oxetanylmethoxy)methylbenzene; 4-fluoro-[1-(3-ethyl-3-oxetanylmethoxy)methyl]benzene; 4-methoxy-[1-(3-ethyl-3-oxetanylmethoxy)methyl]-benzene; [1-(3-ethyl

[0015] phenyl ether; isobutoxymethyl (3-ethyl-3-oxetanylmethyl) ether; 2-ethylhexyl (3-ethyl-3-oxetanylmethyl) ether; ethyldiethylene glycol (3-ethyl-3-oxetanylmethyl) ether; dicyclopentadiene (3-ethyl-3-oxetanylmethyl) ether; dicyclopentenyloxyethyl (3-ethyl-3-oxetanylmethyl) ether; dicyclopentenyl (3-ethyl-3-oxetanylmethyl) ether; tetrahydrofurfuryl (3-ethyl-3-oxetanylmethyl) ether; 2-hydroxyethyl (3-ethyl-3-oxetanylmethyl) ether; 2-hydroxypropyl (3-ethyl-3-oxetanylmethyl) ether, and any combination thereof.

[0037] The cationically polymerizable component may also optionally contain a multifunctional material, including dendritic polymers, such as dendritic macromolecules, linear dendritic polymers, dendritic graft polymers, hyperbranched polymers, star-branched polymers, and hypergrafted polymers having epoxy or oxetane functional groups. Dendritic polymers may contain one type of polymerizable functional group or different types of polymerizable functional groups, such as epoxy and oxetane functional groups.

[0038] In one embodiment, the composition of the present invention further comprises one or more monoglycidyl ethers or polyglycidyl ethers of aliphatic alcohols, aliphatic polyols, polyester polyols or polyether polyols. Examples of preferred components include 1,4-butanediol diglycidyl ether, glycidyl ethers of diols and triols of polyoxyethylene and polyoxypropylene having a molecular weight of about 200 to about 10,000; and glycidyl ethers of polytetramethylene glycol or poly(oxyethylene-oxybutylene) random or block copolymers. In a specific embodiment, the cationic polymerizable component comprises a multifunctional glycidyl ether lacking a cyclohexane ring in the molecule. In another specific embodiment, the cationic polymerizable component comprises neopentyl glycol diglycidyl ether. In another specific embodiment, the cationic polymerizable component comprises 1,4-cyclohexanedimethanol diglycidyl ether.

[0039] An example of a commercially available preferred polyfunctional glycidyl ether is Erisys TM GE 22 (Erisys TM Products are available from Emerald Performance Materials TM Purchased), Heloxy TM 48. Heloxy TM 67. Heloxy TM 68. Heloxy TM 107(Heloxy TM modifiers available from Momentive Specialty Chemicals), and F713. Examples of commercially available preferred monofunctional glycidyl ethers are Heloxy TM 71. Heloxy TM 505、Heloxy TM 7. Heloxy TM 8 and Heloxy TM 61.

[0040] In one embodiment, the epoxide is 3,4-epoxycyclohexylmethyl-3',4-epoxycyclohexanecarboxylate (available as CELLOXIDE TM 2021P was purchased from Daicel Chemical or as CYRACURE TM UVR-6105 is available from Dow Chemical), epoxy resin based on hydrogenated bisphenol A-epichlorohydrin (available as EPON TM 1510 available from Momentive), 1,4-cyclohexanedimethanol diglycidyl ether (available as HELOXY TM 107 available from Momentive), hydrogenated bisphenol A diglycidyl ether (available as EPON TM 825 available from Momentive), a mixture of dicyclohexyl diepoxide and nanosilica (available as NANOPOX TM and any combination thereof.

[0041] In one embodiment, the cationically polymerizable component includes a cycloaliphatic epoxy resin according to Formula I below, for example, a cycloaliphatic epoxy resin having 2 or more epoxy groups:

[0042]

[0043] Where R is a carbon atom, an ester-containing C1-C 10 Aliphatic chain, or C1-C 10Alkyl chain.

[0044] In another embodiment, the cationically polymerizable component includes an epoxy group having an aromatic or aliphatic glycidyl ether group with two (difunctional) or more than two (multifunctional) epoxy groups.

[0045] The above-mentioned cationically polymerizable compounds may be used alone or in combination of two or more thereof. In an embodiment of the present invention, the cationically polymerizable component further comprises at least two different epoxy components.

[0046] In other embodiments of the present invention, the cationically polymerizable component further comprises an oxetane component. In a specific embodiment, the cationically polymerizable component comprises an oxetane, for example, an oxetane containing one, two, or more than two oxetane groups. In another embodiment, the oxetane employed is monofunctional and additionally has a hydroxyl group. According to one embodiment, the oxetane has the following structure:

[0047]

[0048] If used in the composition, the oxetane component is suitably present in an amount of from about 5% to about 50% by weight of the resin composition. In another embodiment, the oxetane component is present in an amount of from about 10% to about 25% by weight of the resin composition, and in yet another embodiment, the oxetane component is present in an amount of from 20% to about 30% by weight of the resin composition.

[0049] Thus, the liquid radiation curable resin for additive manufacturing may comprise a suitable amount of a cationically curable component, for example, in certain embodiments, the amount of the cationically curable component is from about 10% to about 80% by weight of the resin composition, in further embodiments from about 20% to about 70% by weight of the resin composition, and in further embodiments from about 25% to about 65% by weight of the resin composition, in further preferred embodiments from about 30% to about 80% by weight of the resin composition, and more preferably from about 50% to about 85% by weight of the resin composition.

[0050] Free radical curable components

[0051] According to one embodiment of the present invention, the liquid radiation curable resin used for additive manufacturing of the present invention comprises at least one free radical curable component, i.e., a component that undergoes polymerization initiated by free radicals. Free radical polymerizable components are monomers, oligomers, and / or polymers; they are monofunctional or multifunctional materials, i.e., they have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ... 20 ... 30 ... 40 ... 50 ... 100 or more functional groups that can be polymerized by free radical initiation, and may contain aliphatic, aromatic, cycloaliphatic, aromatic aliphatic, one or more heterocyclic moieties, or any combination thereof. Examples of multifunctional materials include dendritic polymers, such as dendritic macromolecules, linear dendritic polymers, dendritic graft polymers, hyperbranched polymers, star-branched polymers, and hypergrafted polymers; see, for example, US2009 / 0093564 A1. Dendrimers may contain one type of polymerizable functional groups or different types of polymerizable functional groups, such as acrylate and methacrylate functional groups.

[0052] Examples of free radical curable or polymerizable components include acrylates and methacrylates, such as isobornyl (meth)acrylate, bornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, dicyclopentyl (meth)acrylate, dicyclopentenyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, 4-butylcyclohexyl (meth)acrylate, acryloylmorpholine, (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl ... hydroxybutyl ester, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, amyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, amyl (meth)acrylate, caprolactone acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, tridecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, methyl (meth)acrylate Oxyethylene glycol esters, ethoxyethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, diacetone (meth)acrylamide, β-carboxyethyl (meth)acrylate, phthalate (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, butylcarbamoylethyl (meth)acrylate, fluorinated n-isopropyl (meth)acrylamide (meth)acrylate, 7-amino-3,7-dimethyloctyl (meth)acrylate.

[0053] Examples of the polyfunctional free radical polymerizable component include those having a (meth)acryloyl group, such as trimethylolpropane tri(meth)acrylate, pentaerythritol (meth)acrylate, ethylene glycol di(meth)acrylate, bisphenol A diglycidyl ether di(meth)acrylate, dicyclopentadienyl dimethanol di(meth)acrylate, [2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxan-5-yl]methacrylate; 3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxane di(meth)acrylate; Spiro[5.5]undecyl ester; dipentaerythritol monohydroxypenta(meth)acrylate, trimethylolpropane propoxylated tri(meth)acrylate, neopentyl glycol propoxylated di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polybutylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, glycerol tri(meth)acrylate, mono(meth)acrylate phosphate and di(meth)acrylate phosphate, C7-C8 di(meth)acrylate 20 alkyl esters, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tricyclodecanediyldimethyl di(meth)acrylate, and alkoxylated versions (e.g., ethoxylated and / or propoxylated) of any of the foregoing monomers, as well as diol di(meth)acrylates that are ethylene oxide or propylene oxide adducts of bisphenol A, diol di(meth)acrylates that are ethylene oxide or propylene oxide adducts of hydrogenated bisphenol A, epoxy(meth)acrylates that are (meth)acrylate adducts of bisphenol A as diglycidyl ethers, diacrylates of polyoxyalkylated bisphenol A and triethylene glycol divinyl ether, and adducts of hydroxyethyl acrylate.

[0054] According to one embodiment, the radical polymerizable component is a multifunctional (meth)acrylate. The multifunctional (meth)acrylate may include all methacryloyl groups, all acryloyl groups, or any combination of methacryloyl groups and acryloyl groups. In one embodiment, the radical polymerizable component is selected from the group consisting of: bisphenol A diglycidyl ether di(meth)acrylate, ethoxylated or propoxylated bisphenol A or bisphenol F di(meth)acrylate, dicyclopentadiene dimethanol di(meth)acrylate, [2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxane-5-yl]methyl acrylate, monohydroxypentaerythritol penta(meth)acrylate, pentaerythritol penta(meth)acrylate, hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, and propoxylated neopentyl glycol di(meth)acrylate, and any combination thereof.

[0055] In one embodiment, the multifunctional (meth)acrylate has more than 2 functional groups. According to another embodiment, the multifunctional (meth)acrylate has more than 3 functional groups. In yet another embodiment, the multifunctional (meth)acrylate has more than 4 functional groups. In another preferred embodiment, the free radical polymerizable component consists only of a single multifunctional (meth)acrylate component. In other embodiments, the only free radical polymerizable component present is tetrafunctional, in other embodiments, the only free radical polymerizable component present is pentafunctional, and in other embodiments, the free radical polymerizable component is hexafunctional.

[0056] In another embodiment, the free radical polymerizable component comprises aromatic (meth) acrylate. As a non-limiting example, aromatic acrylate can be derived from bisphenol A, bisphenol S, or bisphenol F. In certain embodiments, the aromatic is selected from the group consisting of: bisphenol A diglycidyl ether diacrylate, dicyclopentadiene dimethanol diacrylate, acrylate [2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxane-5-yl]methyl ester, monohydroxypentaerythritol pentaacrylate, trimethylolpropane triacrylate and propoxylated neopentyl glycol diacrylate, and any combination thereof. In one embodiment, aromatic (meth) acrylate is difunctional.

[0057] In a specific embodiment, the liquid radiation curable resin for additive manufacturing of the present invention comprises one or more of the following: bisphenol A diglycidyl ether di(meth)acrylate, dicyclopentadiene dimethanol di(meth)acrylate, dipentaerythritol monohydroxy penta(meth)acrylate, trimethylolpropane propoxylate tri(meth)acrylate and / or neopentyl glycol propoxylate di(meth)acrylate, and more specifically comprises one or more of the following: bisphenol A diglycidyl ether diacrylate, dicyclopentadiene dimethanol diacrylate, dipentaerythritol pentaacrylate, trimethylolpropane propoxylate triacrylate and / or neopentyl glycol propoxylate diacrylate.

[0058] The above-mentioned free radical polymerizable compounds can be used alone or in combination of two or more thereof. The liquid radiation curable resin for additive manufacturing can contain any suitable amount of a free radical polymerizable component, for example, in certain embodiments, the amount of the free radical polymerizable component is up to about 50% by weight of the resin composition, in certain embodiments, from about 2% to about 40% by weight of the resin composition, in other embodiments, from about 5% to about 30% by weight of the resin composition, in further embodiments, from about 10% to about 20% by weight of the resin composition, in further preferred embodiments, from about 8% to about 50% by weight of the resin composition, and more preferably from about 15% to about 25% by weight of the resin composition.

[0059] Photoinitiator

[0060] In an embodiment according to the present invention, the composition comprises at least one photoinitiator. A photoinitiator is a compound that undergoes chemical changes due to the action of light (or a synergistic effect between the action of light and electronic excitation of a sensitizing dye) to produce at least one of free radicals, acids, and bases, which then initiate polymerization of one or more polymerizable species present in the corresponding composition. According to an embodiment of the first aspect of the present invention, the composition comprises a photoinitiator that can be used to effect polymerization of a free radical curable component, a cationically curable component, or both.

[0061] A photoinitiator that is capable of initiating polymerization of a free radical curable component (when subjected to light of an appropriate wavelength and / or intensity) is a free radical photoinitiator. A photoinitiator that is capable of initiating polymerization of a cationically curable component (when subjected to light of an appropriate wavelength and / or intensity) is a cationic photoinitiator. Specific photoinitiators can function as both free radical photoinitiators and cationic photoinitiators, but typically at least two different photoinitiators are employed to achieve this purpose. According to one embodiment, the liquid radiation curable resin composition comprises a photoinitiator system comprising at least one photoinitiator having a cationic initiation function and at least one photoinitiator having a free radical initiation function. In another embodiment, the photoinitiator system may comprise a photoinitiator that contains both free radical initiation and cationic initiation functions on the same molecule.

[0062] In an embodiment, the liquid radiation-curable resin for additive manufacturing of the present invention comprises a free radical photoinitiator. Generally, free radical photoinitiators include those that form free radicals via a Norrish Type I or Type II mechanism. This mechanism is well known in the art to which the present invention is applied and is described, for example, in Parikh, A., Parikh, H., & Parikh, K. (2006). Norrish Type I and II Reaction (Cleavage). In Name Reactions in Organic Synthesis (pp. 325-329). Foundation Books. Such photoinitiators include those that form free radicals by cleavage, referred to as "Norrish Type I"; and those that form free radicals by hydrogen abstraction, referred to as "Norrish Type II". Norrish Type II photoinitiators require a hydrogen donor that acts as a source of free radicals. Because initiation is based on a bimolecular reaction, Norrish Type II photoinitiators are generally slower than Norrish Type I photoinitiators based on the unimolecular formation of free radicals. On the other hand, Norrish II type photoinitiators have better light absorption characteristics in the near UV spectral region. The photolysis of aromatic ketones (such as benzophenone, thioxanthone, benzil and quinone) in the presence of hydrogen donors (such as alcohols, amines or thiols) leads to the formation of free radicals (ketyl-type radicals) generated from carbonyl compounds and another free radical derived from the hydrogen donor. The photopolymerization of vinyl monomers is usually initiated by free radicals generated from hydrogen donors. Due to steric hindrance and the delocalization of unpaired electrons, ketyl groups are usually not reactive to vinyl monomers.

[0063] The inventors have now discovered that not all compounds suitable for promoting free radical polymerization, particularly for promoting the polymerization of radiation curable compositions in additive manufacturing processes utilizing UV / visible light sources, can be characterized under either of the two groups mentioned above. To the inventors' surprise, some photoinitiators are effective in promoting free radical (and potentially also cationic) polymerization, even though they do not utilize the Norrish Type I or Type II mechanism. Specific examples of this include certain iodonium salts, preferably iodonium salts of non-fluorinated borate anions. As used herein, "non-fluorinated" means free of fluorine atoms. In addition to being non-fluorinated, the anion of the iodonium salt compound is preferably non-halogenated. As used herein, "non-halogenated" means free of any halogen-based atoms.

[0064] In order to successfully formulate liquid radiation curable resins for additive manufacturing, it is of course necessary to examine the wavelength sensitivity of the photoinitiator or photoinitiators present in the resin composition to determine whether they will be activated by the radiation source selected to provide the curing light.

[0065] However, in one embodiment, the composition comprises an iodonium salt photoinitiator having the following structure:

[0066]

[0067] wherein R1-R4 are independently selected from the group consisting of alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl and heteroaryl, and further wherein (i) one or more substitutable carbon atoms of the alkyl, alkenyl or alkynyl group are optionally substituted with hydroxy, carboxyl, alkoxy, alkanoyl, hydroxyalkyl, carboxylalkyl, alkoxyalkyl or alkanoylalkyl, or (ii) one or more substitutable carbon atoms of the cycloalkyl, heterocycloalkyl, aryl or heteroaryl group are optionally substituted with alkyl, hydroxy, carboxyl, alkoxy, alkanoyl, hydroxyalkyl, carboxylalkyl, alkoxyalkyl or alkanoylalkyl.

[0068] In one embodiment, R1-R4 are independently selected from aryl, which is optionally substituted at one or more carbon atoms which may be substituted by alkyl or alkoxy. More specifically, R1-R4 can also be phenyl, which is optionally substituted independently by alkyl or alkoxy, wherein the alkyl portion of the alkyl or alkoxy group contains 1-10 carbon atoms.

[0069] In one embodiment, the non-fluorinated borate anion of the iodonium salt is tetraphenylborate according to the following structure:

[0070]

[0071] The cation of the iodonium salt of the non-fluorinated borate anion can be of any suitable type. In one embodiment, the iodonium salt has a diaryliodonium cation. In one embodiment, the cation is a diphenyliodonium salt having two phenyl groups optionally substituted with alkyl or alkoxy groups, wherein the alkyl portion of the alkyl or alkoxy group has 1 to 10 carbon atoms.

[0072] In one embodiment, the photoinitiator comprises one or both of iodonium salt cations having the following structures:

[0073]

[0074] In one embodiment, the photoinitiator comprises bis-4-cumyl iodonium tetraphenylborate or bis-4-tert-butyl iodonium tetraphenylborate. Such compounds are commercially available from Hampford Research as FP 5041 and FP 5028, respectively.

[0075] The inventors have discovered that when the photoinitiator comprises, consists of, or consists essentially of one or more of the iodonium salt photoinitiators described above, free radical and / or cationic polymerization can be maximized when the radiation-curable composition is subjected to an additive manufacturing system utilizing a light source using UV / optics. The inventors have further surprisingly discovered that by further adding more of other well-known free radical photoinitiators, polymerization efficiency may not be improved, and may even be inhibited. Thus, in one embodiment, the composition according to the first aspect is substantially free of any Norrish I-type photoinitiator. In another embodiment, the composition additionally or alternatively is free of any Norrish II-type photoinitiator. In one embodiment, the composition comprises less than about 0.1% by weight, or less than about 0.05% by weight, or less than about 0.01% by weight, or about 0.00% by weight of Norrish I-type and / or Norrish II-type photoinitiators.

[0076] According to one embodiment, the liquid radiation curable resin for additive manufacturing comprises at least one free radical photoinitiator, such as those selected from the group consisting of benzoylphosphine oxide, aryl ketones, benzophenones, hydroxylated ketones, 1-hydroxyphenyl ketones, ketals, metallocenes, and any combination thereof.

[0077] Nevertheless, in some embodiments, the composition may have other free radical photoinitiators. In one embodiment, the liquid radiation curable resin for additive manufacturing additionally comprises at least one free radical photoinitiator, such as, but not limited to, 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholino)phenyl]-1-butanone, 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one, 4-benzoyl-4′-methyldiphenyl sulfide, 4,4′-bis(diethylamino)benzophenone, and 4, 4′-bis(N,N′-dimethylamino)benzophenone (Michler’s ketone), benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, dimethoxybenzophenone, 1-hydroxycyclohexylphenyl ketone, phenyl(1-hydroxyisopropyl)ketone, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, 4-isopropylphenyl(1-hydroxyisopropyl)ketone, oligo-[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone], camphorquinone, 4,4′-bis(diethylamino)benzophenone, or benzildimethylketal, bis(η5-2-4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium, and any combination thereof.

[0078] For light sources emitting in the wavelength range of 300-475 nm, especially those emitting at 365 nm, 390 nm or 395 nm, examples of potentially suitable free radical photoinitiators absorbing in this region include: benzoylphosphine oxides, such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin TPO from BASF) and 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide (Lucirin TPO-L from BASF); bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819 or BAPO from Ciba); 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1 (Irgacure 907 from Ciba); 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholino)phenyl]-1-butanone (Irgacure 1007 from Ciba); Suitable examples include 2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one (Irgacure 379 from Ciba); 4-benzoyl-4′-methyldiphenyl sulfide (Chivacure BMS from Chitec); 4,4′-bis(diethylamino)benzophenone (Chivacure EMK from Chitec); and 4,4′-bis(N,N′-dimethylamino)benzophenone (Michler's ketone). Mixtures thereof are also suitable.

[0079] According to an embodiment of the present invention, the free radical photoinitiator may further include an acylphosphine oxide photoinitiator. Acylphosphine oxide photoinitiators are disclosed in, for example, U.S. Patent Nos. 4,324,744, 4,737,593, 5,942,290, 5,534,559, 6,020,528, 6,486,228, and 6,486,226. Acylphosphine oxide photoinitiators include bisacylphosphine oxide (BAPO) and monoacylphosphine oxide (MAPO). Although acylphosphine oxide photoinitiators are generally preferred for use with UV / visible light optics because they have good phosphono group delocalization under light irradiation, when using an iodonium salt photoinitiator with a non-fluorinated borate anion, such phosphorus-containing photoinitiators are not necessary and may not contribute much to curing or even not contribute to curing at all. Thus, in one embodiment, the composition is substantially free of phosphorus-containing free radical photoinitiators, or contains phosphorus-containing free radical photoinitiators in an amount of less than about 0.1 wt %, preferably less than about 0.05 wt %, or preferably less than about 0.01 wt %, or about 0.00 wt %.

[0080] Liquid radiation curable resins for additive manufacturing may include any suitable amount of a free radical photoinitiator as defined herein, for example, in an amount of up to about 10% by weight of the resin composition in certain embodiments, from about 0.1% to about 10% by weight of the resin composition in certain embodiments, and from about 1% to about 6% by weight of the resin composition in further embodiments.

[0081] According to some embodiments, the liquid radiation curable resin composition comprises a cationic photoinitiator. The cationic photoinitiator initiates cationic ring-opening polymerization upon exposure to light. In a preferred embodiment, the cationic photoinitiator comprises, consists of, or consists essentially of a cationic photoinitiator based on an iodonium salt.

[0082] In one embodiment, any suitable iodonium-based cationic photoinitiator may be used, such as those having a cation selected from the group consisting of diaryliodonium salts, triaryliodonium salts, aromatic iodonium salts, and any combination thereof.

[0083] In another embodiment, the cation of the cationic photoinitiator is selected from the group consisting of aromatic diazonium salts, aromatic sulfonium salts, aromatic iodonium salts, metallocene-based compounds, aromatic phosphonium salts, acylsulfonium salts, and any combination thereof. In another embodiment, the cation is a polymeric sulfonium salt, such as in US5380923 or US5047568, or other aromatic heteroatom-containing cations and naphthylsulfonium salts, such as in US7611817, US7230122, US2011 / 0039205, US2009 / 0182172, US7678528, EP2308865, WO2010046240 or EP2218715. In another embodiment, the cationic photoinitiator is selected from the group consisting of triarylsulfonium salts, diaryliodonium salts and metallocene-based compounds, and any combination thereof. Onium salts, such as iodonium and sulfonium salts, and ferrocenium salts, have the advantage that they are generally more thermally stable.

[0084] In a specific embodiment, the cationic photoinitiator has an anion selected from the group consisting of: BF4 - 、AsF6 - 、SbF6 - PF6 - 、[B(CF3)4] - 、B(C6F5)4 - 、B[C6H3-3,5(CF3)2]4 - 、B(C6H4CF3)4 - 、B(C6H3F2)4 -、B[C6F4-4(CF3)]4 - 、Ga(C6F5)4 - 、[(C6F5)3B-C3H3N2-B(C6F5)3] - 、[(C6F5)3B-NH2-B(C6F5)3] - , tetrakis(3,5-difluoro-4-alkoxyphenyl)borate anion, tetrakis(2,3,5,6-tetrafluoro-4-alkoxyphenyl)borate anion, perfluoroalkylsulfonate anion, tris[(perfluoroalkyl)sulfonyl]methide anion, bis[(perfluoroalkyl)sulfonyl]imide anion, perfluoroalkylphosphate anion, tris(perfluoroalkyl)trifluorophosphate anion, bis(perfluoroalkyl)tetrafluorophosphate anion, tris(pentafluoroethyl)trifluorophosphate anion and (CH6B 11 Br6) - 、(CH6B 11 Cl6) - and other halocarborane anions.

[0085] A survey of other onium salt initiators and / or metallocene salts can be found in “UV Curing, Science and Technology”, (Editor SPP Appas, Technology Marketing Corp., 642 Westover Road, Stamford, Conn., USA) “Chemistry & Technology of UV & EB Formulation for Coatings, Inks & Paints”, Vol. 3 (edited by PKT Oldring), or JPF Foussier, J. Lavelee, “Photoinitiators for polymer synthesis” Wiley 2012 ISBN 978-3-527-33210-6.

[0086] In one embodiment, the cationic photoinitiator has a cation selected from the group consisting of aromatic sulfonium salts, aromatic iodonium salts, and metallocene-based compounds and at least one selected from the group consisting of SbF6 - PF6 - 、B(C6F5)4 - 、[B(CF3)4] - , tetrakis(3,5-difluoro-4-methoxyphenyl)borate anion, perfluoroalkylsulfonate anion, perfluoroalkylphosphate anion, tris[(perfluoroalkyl)sulfonyl]methide anion and [(C2F5)3PF3] - The group consisting of anions.

[0087] Examples of known cationic photoinitiators include 4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfonium hexafluoroantimonate, 4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfonium tetrakis(pentafluorophenyl)borate, 4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfonium tetrakis(3,5-difluoro-4-methyloxyphenyl)borate, 4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfonium tetrakis(2,3,5,6-tetrafluoro-4-methyloxyphenyl)borate, tris(4-(4-acetylphenyl)phenylthio)sulfonium tetrakis(pentafluorophenyl)borate (available from BASF). PAG 290), tris(4-(4-acetylphenyl)phenylthio)sulfonium tris[(trifluoromethyl)sulfonyl]methide (from BASF GSID 26-1), tris(4-(4-acetylphenyl)phenylthio)sulfonium hexafluorophosphate (from BASF 270), and HS-1 available from San-Apro Ltd.

[0088] Known cationic photoinitiators include the following, alone or in mixtures: bis[4-diphenylsulfoniumphenyl]sulfide bishexafluoroantimonate; thiophenoxyphenylsulfonium hexafluoroantimonate (available from Chitec as Chivacure 1176); tris(4-(4-acetylphenyl)phenylthio)sulfoniumtetrakis(pentafluorophenyl)borate (available from BASF as PAG 290); tris(4-(4-acetylphenyl)phenylthio)sulfonium tris[(trifluoromethyl)sulfonyl]methide (from BASF GSID26-1) and tris(4-(4-acetylphenyl)phenylthio)sulfonium hexafluorophosphate (from BASF 270); [4-(1-methylethyl)phenyl](4-methylphenyl)iodonium tetrakis(pentafluorophenyl)borate (available from Rhodia as Rhodorsil 2074); (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate (available from Hampford as OPPI FP5386); 4-[4-(2-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfonium hexafluoroantimonate (such as SP-172 from Adeka); SP-300 from Adeka, and 6-m (C n F 2n+1 ) m ) -An aromatic sulfonium salt wherein m is an integer from 1 to 5 and n is an integer from 1 to 4 (available as CPI-200K or CPI-200S, which are monovalent sulfonium salts from San-Apro Ltd.; TK-1 available from San-Apro Ltd., or HS-1 available from San-Apro Ltd.).

[0089] In one embodiment of the present invention, the liquid radiation curable resin for additive manufacturing comprises an aromatic triarylsulfonium salt cationic photoinitiator. The use of aromatic triarylsulfonium salts in additive manufacturing applications is known. See US20120251841 of DSMIP Assets, BV, U.S. Patent No. 6,368,769 of Asahi Denki Kogyo, which discusses aromatic triarylsulfonium salts with tetraarylborate anions (including tetrakis(pentafluorophenyl)borate anions), and the use of said compounds in stereolithography applications. Triarylsulfonium salts are disclosed in, for example, J Photopolymer Science & Tech (2000), 13(1), 117-118 and J Poly Science, Part A (2008), 46(11), 3820-29. - 、AsF6 - PF6 - and SbF6 - ) is disclosed in J Polymr Sci, Part A (1996), 34(16), 3231-3253.

[0090] An example of a triarylsulfonium tetrakis(pentafluorophenyl)borate cationic photoinitiator is tris(4-(4-acetylphenyl)phenylthio)sulfonium tetrakis(pentafluorophenyl)borate. Tris(4-(4-acetylphenyl)phenylthio)sulfonium tetrakis(pentafluorophenyl)borate is commercially available as PAG-290 is known and available from Ciba / BASF.

[0091] In another embodiment, the cationic photoinitiator is a photoinitiator having a structure consisting of SbF6 - PF6 - 、BF4 - 、(CF3CF2)3PF3 - 、(C6F5)4B - 、((CF3)2C6H3)4B - 、(C6F5)4Ga - 、((CF3)2C6H3)4Ga -Aromatic triarylsulfonium salts having an anion represented by 1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 61, 62, 63, 64, 6

[0092] Another cationic photoinitiator is an aromatic triarylsulfonium cationic photoinitiator having an anion that is a fluoroalkyl-substituted fluorophosphate. Commercial examples of aromatic triarylsulfonium cationic photoinitiators having a fluoroalkyl-substituted fluorophosphate anion are the CPI-200 series (e.g., CPI- or ).

[0093] The liquid radiation curable resin composition may include any suitable amount of cationic photoinitiator, for example, in an amount of up to about 15% by weight of the resin composition in certain embodiments, up to about 5% by weight of the resin composition in certain embodiments, and in other embodiments from about 2% to about 10% by weight of the resin composition, and in other embodiments from about 0.1% to about 5% by weight of the resin composition. In another embodiment, the amount of cationic photoinitiator is from about 0.2% to about 4% by weight of the total resin composition, and in other embodiments from about 0.5% to about 3% by weight.

[0094] photosensitizers

[0095] In some embodiments, depending on the wavelength of light used to cure the liquid radiation curable resin, it is desirable that the liquid radiation curable resin composition contain a photosensitizer. The term "photosensitizer" is used to refer to any substance that increases the rate of photoinduced polymerization or shifts the wavelength at which polymerization occurs; see the textbook G. Odian, Principles of Polymerization, 3 rd Ed., 1991, page 222. Materials operating according to the latter definition, when used in conjunction with a photoinitiator that would otherwise not absorb light of a particular wavelength, are said to operate by an "indirect excitation" mechanism using their associated photoinitiator. Applicants have exploited this mechanism to formulate compositions of the present invention that are suitable for curing by UV / visible light optics.

[0096] A variety of compounds can be used as photosensitizers, including heterocyclic and fused ring aromatic hydrocarbons, organic dyes, and aromatic ketones. Examples of photosensitizers include those selected from the group consisting of ketones, xanthone, pyrene methanol, anthracene, pyrene, perylene, quinone, xanthone, thioxanthone, benzoyl esters, benzophenone, and any combination thereof. Specific examples of photosensitizers include those selected from the group consisting of [4-[(4-methylphenyl)thio]phenyl]phenyl-ketone, isopropyl-9H-thioxanthen-9-one, 1-pyrene methanol, 9-(hydroxymethyl)anthracene, 9,10-diethoxyanthracene, 9,10-dimethoxyanthracene, 9,10-dipropoxyanthracene, 9,10-dibutoxyanthracene, 9-anthracenemethanol acetate, 2-ethyl-9,10-dimethoxyanthracene, 2-methyl-9,10-dimethoxyanthracene and combinations thereof.

[0097] The novel mixture may also contain various photoinitiators with varying sensitivities to radiation of different wavelengths to better utilize the UV light source. The use of known photoinitiators with varying sensitivities to radiation of different wavelengths is well known in the additive manufacturing field and can be selected based on, for example, the radiation source of 351 nm, 355 nm, 365 nm, 385 nm, and 405 nm. In this case, it is advantageous to select the various photoinitiators and use them in concentrations that result in equivalent light absorption with the radiation used.

[0098] In one embodiment, the photosensitizer is a fluorone, such as 5,7-diiodo-3-butoxy-6-fluorone, 5,7-diiodo-3-hydroxy-6-fluorone, 9-cyano-5,7-diiodo-3-hydroxy-6-fluorone, or the photosensitizer is

[0099] and any combination thereof.

[0100] When a photosensitizer is employed, other photoinitiators that absorb at shorter wavelengths may be used. Examples of such photoinitiators include benzophenones, such as benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, and dimethoxybenzophenone; and 1-hydroxyphenyl ketones, such as 1-hydroxycyclohexylphenyl ketone, phenyl(1-hydroxyisopropyl)ketone, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, and 4-isopropylphenyl(1-hydroxyisopropyl)ketone; benzil dimethyl ketal, and oligo-[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone] (Esacure KIP 150 from Lamberti).

[0101] It may be noted that some cationic photoinitiators have low absorption at preferred actinic wavelengths. For example, in one embodiment, an additive manufacturing application of interest utilizes UV light / optical devices with a peak intensity at approximately 400 nm. Ionium salts, such as Rhodorsil 2074 available from Rhodia Silicones, Irgacure 250 iodonium salt (4-methylphenyl) [4-(2-methylpropyl) phenyl] hexafluorophosphate (1-) available from Ciba, and UV9380c available from GE Silicones, have insufficient direct absorption at the preferred wavelengths and therefore require either excessive concentrations or a sensitizer. Therefore, triplet sensitizers (such as thioxanthone and Michler's ketone) are sometimes used to absorb actinic energy and then transfer that energy to the iodonium initiator in an efficient manner. However, some thioxanthones and Michler's ketones tend to form orange or red colors due to safety concerns, and although they have significant actinic absorption up to 430 nm, they are not very effective in sensitizing photoreactions at curing light wavelengths around 400 nm.

[0102] However, in one embodiment, chloropropylthioxanthone (CPTX) is a suitable sensitizer for iodonium initiators, particularly for use in stereolithography, because it has no significant light absorption above 500 nm and produces articles with less color.

[0103] In order to reduce the concentration of the sensitizer used in the formulation and prevent the adverse effects that a relatively large concentration of the sensitizer may have on the final physical properties of the composition, it is preferred to use a sensitizer with a high extinction coefficient at 400 nm. For example, in some cases, benzophenone can act as a triplet sensitizer, but at a laser wavelength of, for example, a tripled frequency YAG laser (Coherent AVIA Model No. 355-1800) operating at about 355 nm, the extinction coefficient is about 108 liters / mol-cm. On the other hand, CPTX using the same laser at the same laser wavelength of about 400 nm has an extinction coefficient of 2585 liters / mol-cm, which is almost X times that of benzophenone. This indicates that CPTX may require 1 / X of the concentration in the formulation to provide an equivalent light absorption effect. Thus, although not required, it is preferred that the sensitizer have an extinction coefficient greater than 300 L / mol-cm or higher, such as greater than 1000 L / mol-cm, preferably greater than 2000 L / mol-cm, at a curing light wavelength greater than 380 nm.

[0104] Although CPTX can be used to increase the activity of cationic photoinitiators, the sensitizers used in combination with the above-mentioned cationic photoinitiators are not necessarily limited thereto. A variety of compounds can be used as photosensitizers, including heterocyclic and condensed-ring aromatic hydrocarbons, organic dyes, and aromatic ketones. Examples of sensitizers include J. V. Crivello in Advances in Polymer Science, 62, 1 (1984), and by J. V. Crivello & K. Dietliker, "Photoinitiators for Cationic Polymerization" in Chemistry & technology of UV & EB formulation for coatings, inks & paints. Volume III, Photoinitiators for free radical and cationic polymerization. by K. Dietliker; [Ed. by PKT Oldring], SITA Technology Ltd, London, 1991. Specific examples include polycyclic aromatic hydrocarbons and their derivatives, such as anthracene, pyrene, perylene and their derivatives, substituted thioxanthones, α-hydroxyalkylphenols, 4-benzoyl-4′-methyldiphenyl sulfide, acridine orange, and benzoflavin.

[0105] In one embodiment, the liquid radiation curable composition for additive manufacturing according to the first aspect of the present invention comprises a photosensitizer having a structure according to the following structure:

[0106]

[0107] Where R contains C1-C 20 Aliphatic chain.

[0108] In one embodiment, the photosensitizer employed is an anthracene-based photoinitiator. Commercially available photosensitizers of this type include Anthracure TM UVS-1101 and UVS-1331.

[0109] The photosensitizer is present in any suitable amount from about 0.5 wt% to about 10 wt%, more preferably 0.5 wt% to 3 wt%.

[0110] Liquid radiation curable resins for additive manufacturing may contain any suitable amount of additional cationic photoinitiators or photosensitizers, for example, in amounts ranging from 0.1% to 10% by weight of the resin composition in certain embodiments, from about 1% to about 8% by weight of the resin composition in certain embodiments, and from about 2% to about 6% by weight of the resin composition in further embodiments. In one embodiment, the above ranges are particularly suitable for epoxy resin monomers. In another embodiment, the photosensitizer may be used in an amount ranging from about 0.05% to about 2% by weight of the total composition into which it is incorporated.

[0111] reducing agent

[0112] As used herein, a reducing agent is a component that loses or "donates" one or more electrons to a cationic photoinitiator component in a redox chemical reaction during polymerization of a liquid radiation composition for additive manufacturing according to the present invention. For present purposes, such components are still considered reducing agents, even though they may not readily donate electrons until they form or decompose into free radicals upon dissociation, or have entered an excited state upon exposure to actinic radiation of UV / visible wavelengths. Therefore, they may alternatively be referred to herein as "activated reducing agents."

[0113] Photoinitiated cationic polymerization of monomers such as epoxides and vinyl ethers plays an essential role in hybrid-cure additive manufacturing applications. Due to the additives used in different applications, the wavelength flexibility of photoinitiation becomes a fundamental factor in determining the curing performance of a particular formulation when targeting specific spectral sensitivities. Consequently, photoinitiator systems for cationic polymerizations that are particularly sensitive to longer wavelengths, such as those emitted by modern UV / visible optics, are becoming increasingly important. Many existing photoinitiator systems for cationic polymerization are based on the use of certain onium salts, such as diphenyliodonium salts, triphenylsulfonium salts, and alkoxypyridinium salts. However, these salts do not absorb significantly, if at all, in the UV / visible spectrum unless additional chromophores are incorporated into the salt structure. Therefore, it is important to find alternative ways to comprehensively expand the sensitivity range of readily available onium salts to UV / visible wavelengths, particularly given that commercially available photoinitiators that have been designed to absorb in the UV / visible spectrum are unsuitable for incorporation into hybrid-cure systems for additive manufacturing for other reasons.

[0114] This is known to be achieved by a mechanism known as indirect excitation, with the aid of a combination of sensitizers. Furthermore, onium salts act as electron acceptors in redox reactions with free radicals, electron donor compounds in charge transfer complexes, and sensitizers for long-lived electronic excited states. Among these methods, so-called "free radical-promoted" cationic polymerization appears to be another effective and flexible way to generate cationic species capable of initiating cationic polymerization of monomers. The overall mechanism involves the oxidation of photochemically formed radicals by onium salts (On+) with a suitable reduction potential:

[0115] R·+ON+→R+ (1).

[0116] Latent reducing agents, believed to aid free radical-promoted cationic polymerization, generally include some of the free radical photoinitiators mentioned above, such as acylphosphine oxides, as well as amines, benzoin and its derivatives, o-phthalaldehyde, polysilanes, and compounds having electron-donating substituents attached to vinyl groups, such as vinyl ethers or vinyl halides, to name a few.

[0117] Amines are known to be effective hydrogen donors and readily form free radicals via a chain transfer mechanism, which can reduce the cationic photoinitiator with which they are associated. Therefore, in certain embodiments, they can act as suitable reducing agents. However, caution is advised when including such compounds in hybrid radiation-curable compositions for additive manufacturing, as the nitrogen atoms they contain are known to inhibit cationic polymerization reactions in other ways.

[0118] Several systems exist for generating oxidizable free radicals in the presence of UV / visible light sources. For example, free radicals formed by irradiating a system containing a xanthene dye and an aromatic amine can act as reducing agents for diphenyliodonium salts. Similarly, when used in conjunction with an onium salt, dimanganese decacarbonyl-organic halide combinations are effective reducing agents for cationic polymerization at UV / visible wavelengths. Furthermore, commercial titanocene-type photoinitiators, such as Irgacure 784, can be used as a reducing agent source generated by irradiation with visible light.

[0119] Preferably, the reducing agent comprises, consists of, consists essentially of a component having electron-donating substituents attached to a vinyl group. Such components may further provide a mechanism by which cationic cure of liquid radiation-curable compositions for additive manufacturing systems employing UV / visible light optics is improved. Such compounds (e.g., vinyl ethers) are avoided in many modern commercial hybrid curable compositions subjected to additive manufacturing systems employing conventional UV-based radiation sources because the compounds tend to (1) generate excessive heat due to their exothermic reaction of rapid polymerization; and (2) initiate copolymerization and concomitant heterogeneous polymers, thereby producing three-dimensional parts with inconsistent and inferior physical properties. However, if used in conjunction with other required components according to the present invention, their inclusion in compositions tailored for systems utilizing UV / visible light optics with lower energy / intensity becomes desirable. Specifically, the inclusion of additional components having electron-donating substituents attached to vinyl groups synergistically improves polymerization.

[0120] A preferred example of a component having an electron-donating substituent attached to a vinyl group is a vinyl ether. Vinyl ethers can be produced from a variety of starting materials (e.g., ethers, esters, or biscarbamates, or vinyl ether-terminated (poly)carbamates or carbonates). Some non-limiting examples of each include the following:

[0121] Vinyl ether monomers from the ether group: Specific examples of polyfunctional vinyl ethers include divinyl ethers such as ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, isobutyl vinyl ether, butylene glycol divinyl ether, butanediol divinyl ether, ether), hexanediol divinyl ether, cyclohexanediol divinyl ether, bisphenol A alkylene oxide divinyl ether, and bisphenol F alkylene oxide divinyl ether; and polyfunctional vinyl ethers, such as trimethylolethane trivinyl ether, trimethylolpropane trivinyl ether, ditrimethylolpropane tetravinyl ether, glycerol trivinyl ether, pentaerythritol tetravinyl ether, pentaerythritol divinyl ether, dipentaerythritol pentavinyl ether, dipentaerythritol hexavinyl ether, ethylene oxide adducts of trimethylolpropane trivinyl ether, propylene oxide adducts of trimethylolpropane trivinyl ether, ethylene oxide adducts of ditrimethylolpropane tetravinyl ether, propylene oxide adducts of ditrimethylolpropane tetravinyl ether, ethylene oxide adducts of pentaerythritol tetravinyl ether, propylene oxide adducts of pentaerythritol tetravinyl ether, ethylene oxide adducts of dipentaerythritol hexavinyl ether, propylene oxide adducts of dipentaerythritol hexavinyl ether.

[0122] Vinyl ether monomers from esters or biscarbamates: Specific examples of polyfunctional vinyl ethers include divinyl adipate, divinyl terephthalate, and divinylcyclohexyl diacrylate. Bis[4-(vinyloxy)butyl]adipate ( 4060), bis[4-(vinyloxy)butyl]succinate ( 4030), bis[4-(vinyloxy)butyl]isophthalate ( 4010), bis[4-(vinyloxymethyl)cyclohexylmethyl]glutarate ( 4020), tris[4-(vinyloxy)butyl] trimellitate ( 5015), bis[4-(vinyloxymethyl)cyclohexylmethyl]isophthalate ( 4040), bis[4-(vinyloxy)butyl](4-methyl-1,3-phenylene)biscarbamate ( 4220) and bis[4-(vinyloxy)butyl](methylenebis-4,1-phenylene)biscarbamate ( 4210) etc.

[0123] Vinyl ether-terminated urethane or carbonate: Specific examples of polyfunctional vinyl ethers include polyurethane or polycarbonate terminated with hydroxy vinyl ether, wherein the polyurethane or polycarbonate has at least one hydroxyl group and at least one vinyl ether group in the molecule. For example, 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 2-hydroxypropyl vinyl ether, 2-hydroxyisopropyl vinyl ether, 4-hydroxybutyl vinyl ether, 3-hydroxybutyl vinyl ether, 2-hydroxybutyl vinyl ether, 3-hydroxyisobutyl vinyl ether, 2-hydroxyisobutyl vinyl ether, 1-methyl-3-hydroxypropyl vinyl ether, 1-methyl-2-hydroxypropyl vinyl ether, 1-hydroxymethylpropyl vinyl ether, 4-hydroxycyclohexyl vinyl ether, 1,6-hexanediol monovinyl ether, 1,4-cyclohexanedimethanol monovinyl ether, 1,3-cyclohexanediol monovinyl ether, Hexanedimethanol monovinyl ether, 1,2-cyclohexanedimethanol monovinyl ether, p-xylene glycol monovinyl ether, m-xylene glycol monovinyl ether, o-xylene glycol monovinyl ether, diethylene glycol monovinyl ether, triethylene glycol monovinyl ether, tetraethylene glycol monovinyl ether, pentaethylene glycol monovinyl ether, oligoethylene glycol monovinyl ether, polyethylene glycol monovinyl ether, dipropylene glycol monovinyl ether, tripropylene glycol monovinyl ether, tetrapropylene glycol monovinyl ether, derivatives thereof such as pentapropylene glycol monovinyl ether, oligopropylene glycol monovinyl ether and polypropylene glycol monovinyl ether, and the like.

[0124] In a preferred embodiment, the component having an electron-donating substituent attached to the vinyl group is one or more of the following: vinyl ether, vinyl ester, vinyl sulfide, n-vinyl carbazole, n-vinyl pyrrolidone, n-vinyl caprolactam, allyl ether, and vinyl carbonate.

[0125] In another preferred embodiment, the component having electron donating substituents attached to the vinyl group is multifunctional. As used herein, "multifunctional" means that the vinyl ether has at least two vinyl groups per molecule.

[0126] One or more of the above-mentioned components having electron-donating substituents attached to the vinyl group may be employed in the compositions according to the present invention in any suitable amount and may be selected individually or in combination of one or more of the types listed herein. In a preferred embodiment, the component having electron-donating substituents attached to the vinyl group is present in an amount of from about 1% to about 25% by weight relative to the total weight of the composition, more preferably from about 5% to about 20% by weight relative to the total weight of the composition, and more preferably from about 5% to about 12% by weight relative to the total weight of the composition. In another embodiment, the component having electron-donating substituents attached to the vinyl group is present in an amount of from 1% to 15% by weight, more preferably from 1% to 10% by weight, and more preferably from 3% to about 8% by weight.

[0127] additive

[0128] Stabilizers are typically added to the resin composition to further prevent viscosity buildup, such as during use in solid imaging processes. Useful stabilizers include those described in U.S. Patent No. 5,665,792. The presence of a stabilizer is optional. In a specific embodiment, the liquid radiation-curable resin composition for additive manufacturing comprises from 0.1% to 3% by weight of a stabilizer.

[0129] Other possible additives include organic and inorganic fillers, dyes, pigments, antioxidants, wetting agents, defoamers, chain transfer agents, leveling agents, defoamers, surfactants, etc. As will be understood by those skilled in the art, such additives are known and can generally be employed as required for a particular application.

[0130] The liquid radiation curable resin composition for additive manufacturing of the present invention may further comprise one or more additives selected from the group consisting of defoamers, antioxidants, surfactants, acid scavengers, pigments, dyes, thickeners, flame retardants, silane coupling agents, ultraviolet absorbers, resin particles, core-shell particle impact modifiers, soluble polymers and block polymers.

[0131] In addition, many known liquid radiation curable resin compositions for increasing material manufacturing use hydroxyl functional compounds to enhance the characteristics of the parts made of resin combination. If present, any hydroxyl can be used for specific purposes. If present, the hydroxyl-containing material preferably contains one or more primary or secondary aliphatic hydroxyl groups. The hydroxyl group can be inside or at the end of the molecule. Monomer, oligomer or polymer can be used. The hydroxyl equivalent (that is, the number average molecular weight divided by the hydroxyl number) is preferably in the range of 31 to 5000. If present, relative to the gross weight of resin combination, the resin combination preferably comprises at the most 10 wt %, more preferably at the most 5 wt %, and most preferably at the most 2 wt % of one or more non-radical polymerizable hydroxyl functional compounds.

[0132] A second aspect of the claimed invention is a method of forming a three-dimensional article by an additive manufacturing system utilizing UV / visible light optics, the method comprising:

[0133] (1) Providing a liquid radiation curable composition for additive manufacturing according to the first aspect of the present invention;

[0134] (2) establishing a first liquid layer of liquid radiation curable resin;

[0135] (3) imagewise exposing the first liquid layer to actinic radiation through a UV / visible light optics arrangement to form an imagewise cross-section, thereby forming a first solidified layer;

[0136] (4) forming a new layer of liquid radiation curable resin in contact with the first cured layer;

[0137] (5) imagewise exposing the new layer to actinic radiation to form additional imaged cross sections; and

[0138] (6) repeating steps (4) and (5) a sufficient number of times to construct a three-dimensional article;

[0139] wherein the UV / visible optical device emits radiation with a peak spectral intensity of about 375 nm to about 500 nm, more preferably about 380 nm to about 450 nm, more preferably about 390 nm to about 425 nm, more preferably about 395 nm to about 410 nm.

[0140] The liquid radiation curable composition provided in the second aspect of the present invention as described above must be suitable for curing by the additive manufacturing system utilizing ultraviolet / visible light optics. Such compositions are described in the first aspect of the present invention. When setting up the first liquid layer or forming a new layer of liquid radiation curable resin, the layer can have any suitable thickness and shape, and depends on the additive manufacturing process utilized. For example, it can be selectively distributed by spraying, or it can be added by immersing the previously cured layer in a resin tank, thereby producing a layer with substantially uniform thickness, which is a typical case of most stereolithography processes. In another non-limiting embodiment, it can alternatively be transferred by a perfusator or dispenser via a foil, film or carrier of predetermined thickness.

[0141] In the foregoing, "exposing" refers to irradiation with actinic radiation. As previously mentioned, the liquid radiation composition of the present invention for additive manufacturing, as described herein, is particularly suitable for imparting a hybrid cure via UV / visible light optics. In one embodiment, the UV / visible light optics utilize one or more LEDs as a light source. In one embodiment, the light source is a laser. In one embodiment, the LED or laser light source is coupled to a DLP or LCD image projection system. In embodiments where the image projection system includes an LCD display, the light source can be configured to emit only actinic radiation above 400 nm to minimize the deleterious effects of UV wavelengths on LCD component parts.

[0142] A third aspect of the claimed invention is a three-dimensional part formed by the second aspect of the invention using the liquid radiation curable composition of the first aspect of the invention.

[0143] The following examples further illustrate the present invention but, of course, should not be construed as limiting the scope of the invention in any way.

[0144] Example

[0145] These examples illustrate embodiments of the liquid radiation curable resin for additive manufacturing of the present invention. Table 1 describes the various components of the liquid radiation curable resin for additive manufacturing used in this example.

[0146] Table 1

[0147]

[0148] Test Method

[0149] In order to measure the polymerization rate (curing speed) of each embodiment, real-time Fourier transform infrared (FTIR) spectroscopy was used. In order to improve data acquisition frequency and resolution, a mercury cadmium telluride (MCT) detector was used. Instead of transmission mode, an attenuated total reflection (ATR) setting was used. All polymerization rate measurements were performed using a Thermo Scientific Nicolet 8700. The following table shows the experimental condition settings for the measurements. Under these conditions, a total of 41 spectra were acquired for 200 seconds per measurement:

[0150] Scan times 4 Resolution 4 Types of Data Collected real time Configuration file type Ramp Timing Save 200 seconds Use repetition time (seconds) 5

[0151] For UV / visible light control, a Digital Light Lab LED spotlight (wavelength 385 nm, intensity 5 mW) and a controller (AccuCure Optical Rheometer) were used. The calibration continuous mode was selected. The light intensity and duration (exposure time) were selected before the measurement.

[0152] In order to measure, a few drops of selected samples are placed in the center of the ATR crystal group (setup). Then, a film of about 3 mils (± 0.4 mils) is coated on the top of the ATR crystal using the Bode pull-down bar (draw down bird bar) of 3 mils (± 0.4 mils). After applying a coating of 3 mil, the LED lamp is immediately kept on the top of the ATR setup, and the hole is positioned in the center of the support. Then start real-time FTIR scanning. Once 1 spectrum is obtained, the light source is turned on to start polymerization. Based on the above program input, a spectrum is obtained every 5 seconds, which lasts for a total of 200 seconds. A total of 41 spectra are obtained in each experiment.

[0153] The relationship between polymerization conversion and time is calculated based on the change in the specific IR peak representing each functional group. The figure above shows an example of the change in IR peak. To calculate the conversion of each relevant functional group, the peak height or peak area is calculated appropriately according to the following table:

[0154]

[0155] Utilize the raw data obtained, it is important to remove the first one to two data points, because the experimental curing speed process has an unknown short time delay between turning on the FTIR detection equipment and the light source for curing the sample. In order to solve any uncertainty associated with the amount of statistical noise generated by these preliminary data points, three sets of curve fitting are generated for each data set. In each case, the model equation to be fitted to the data set is Conv=a(1-e(-b*(time-c))). For this purpose, Microsoft Excel14.0.7116.5000 version (32 bit) with data analysis attachment is used to fit the raw data.

[0156] In the first case, the entire data set (including the first two data points) is fitted. In the second case, the entire data set minus the first data point is fitted. In the third case, the entire data set minus the first and second data points is fitted. In each case, a curve fit coefficient r is created. 2 The first data point above 1% conversion and whose curve fit combination yields an r above 0.90 was selected. 2 The data set was used, and the obtained curve fitting equation results were used to further calculate the curing speed at 95% plateau conversion rate. 2 If it is below 0.90, rerun the data again.

[0157] As described above, the data were fit to an equation of the form Conv = a(1 - e(-b*(time - c))) where "Conv" is the conversion % as measured by the FTIR peak ratio, time is the exposure duration, "a" is the plateau conversion, "b" is the resulting derived cure rate coefficient used to calculate cure rate, and "c" is the resulting derived cure induction time. Once the data were fitted, the software generated an experimentally derived equation where the numerical parameters of "a", "b", and "c" were determined from the experimental data and the fit. For cationic curable materials (i.e., epoxies and oxetanes), "c" does not have any meaning since there is no cure induction time. Therefore, in this case, "c" was ignored. The variable "a" was used as the plateau conversion under the cure conditions used and represents the overall asymptotic degree of conversion of the components. The variable "b" was used to calculate the cure rate via the equation T 95 = ln(.05 / b) to calculate the conversion rate of "a" to 95% platform (T 95The calculated conversions of the three different polymerizable components (epoxy resin, oxetane and acrylate) at 100 seconds are reported in Table 3 below.

[0158] Examples 1 to 13

[0159] First, a base resin for additive manufacturing was prepared by combining an oxetane component, a cycloaliphatic epoxide component, a polyol component, a glycidyl ether epoxide component, and an acrylate component according to methods well known in the art. Details of the so-called "control" are provided in Table 2 below. The full composition of Formulations 1 to 13, along with conversion test results using a 5 mW, 385 nm UV / Visible light source, are provided in Table 3.

[0160] Table 2

[0161] Control Package. Values ​​are listed in parts by weight

[0162] Component\Formula Base resin 1 Celloxide 2021P 54.0 OXT-101 9.0 PolyTHF-1000 (polytetramethylene glycol with a MW of 1000) 18.0 CN 110 (bisphenol A diglycidyl diacrylate) 18.0 Total (per weight portion) 99.0

[0163] Table 3 Unless otherwise stated, the values ​​are listed in parts by weight

[0164]

[0165] Discussion of the results

[0166] The data in Table 3 demonstrate that various embodiments according to the present invention are suitable for promoting hybrid cure under UV / visible light exposure conditions. Notably, when comparing Formulation 1 with Formulations 10 to 12, the addition of Norrish Type I or Type II photoinitiators did not significantly improve cure performance. In fact, the presence of phosphine-containing photoinitiators (BAPO and TPO; see Examples 10 to 11) actually degraded cure performance.

[0167] Additional exemplary embodiments

[0168] A first additional exemplary embodiment is a radiation curable composition comprising:

[0169] a first photoacid generator, said photoacid generator having an iodonium salt cation and a borate anion containing no fluorine atom; preferably wherein said cation has one of the following structures:

[0170] (bis (4-cumyl iodonium tetraphenylborate; CAS 1158840-74-4, or

[0171] (Bis(4-tert-butylphenyl)iodonium tetraphenylborate CAS131725-16-1;

[0172] And preferably, the cation has the following structure:

[0173]

[0174] b. a second photoacid generator, preferably an iodonium salt;

[0175] c. an electron-donating substituent attached to a vinyl group; for example, a vinyl ether;

[0176] d. Optionally, a photosensitizer;

[0177] e. a polymerizable component; and

[0178] f. Optionally, an additive component comprising one or more stabilizers;

[0179] The composition is preferably substantially free of free radical photoinitiators having phosphorus atoms; or substantially free of Norrish type I photoinitiators; or substantially free of Norrish type II photoinitiators.

[0180] A first aspect of a second additional exemplary embodiment is a radiation curable composition comprising a free radical polymerizable component, a cationically polymerizable component, a free radical photoinitiator component, and a cationic photoinitiator component;

[0181] wherein the free radical photoinitiator component is substantially free of Norrish Type I photoinitiator, or contains less than 0.1 wt%, or less than 0.05 wt%, or less than 0.01 wt% of Norrish Type I photoinitiator.

[0182] Another aspect of the second additional exemplary embodiment is a radiation curable composition according to the first aspect of the second additional exemplary embodiment, wherein the free radical photoinitiator component is essentially free of Norrish Type II photoinitiator, or contains less than 0.1 weight percent, or less than 0.05 weight percent, or less than 0.01 weight percent Norrish Type II photoinitiator.

[0183] Another aspect of the second additional exemplary embodiment is a radiation curable composition according to any of the foregoing aspects of the second additional exemplary embodiment, wherein the composition is essentially free of or contains less than 0.1 wt %, or less than 0.05 wt %, or less than 0.01 wt % of a Norrish Type I photoinitiator.

[0184] Another aspect of the second additional exemplary embodiment is a radiation curable composition according to any of the foregoing aspects of the second additional exemplary embodiment, wherein the free radical photoinitiator component comprises, consists essentially of, or consists of one or more iodonium salt-based photoinitiators.

[0185] Another aspect of the second additional exemplary embodiment is a radiation curable combination according to the previous aspect of the second additional exemplary embodiment, wherein the iodonium salt-based photoinitiator comprises a borate-containing anion.

[0186] Another aspect of the second additional exemplary embodiment is a radiation curable composition according to any of the previous two aspects of the second additional exemplary embodiment, wherein the iodonium salt-based photoinitiator comprises a tetraphenylborate anion.

[0187] Another aspect of the second additional exemplary embodiment is a radiation curable composition according to any of the preceding aspects of the second additional exemplary embodiment, wherein the cationic photoinitiator component comprises, consists of, or consists essentially of one or more iodonium salt-based cationic photoinitiators.

[0188] Another aspect of the second additional exemplary embodiment is a radiation curable composition according to any of the preceding aspects of the second additional exemplary embodiment, wherein the free radical polymerizable component comprises, consists of, or consists essentially of one or more (meth)acrylate functional compounds.

[0189] Another aspect of the second additional exemplary embodiment is a radiation curable composition according to any of the preceding aspects of the second additional exemplary embodiment, wherein the cationically polymerizable component comprises, consists of, or consists essentially of one or more epoxy-functional compounds and / or oxetane-functional compounds.

[0190] Another aspect of the second additional exemplary embodiment is a radiation curable composition according to any of the preceding aspects of the second additional exemplary embodiment, wherein the cationically polymerizable component comprises, consists of, or consists essentially of one or more cycloaliphatic epoxides, glycidyl ether epoxides, and / or oxetanes.

[0191] Another aspect of the second additional exemplary embodiment is a radiation curable composition according to any of the foregoing aspects of the second additional exemplary embodiment, further comprising a photosensitizer.

[0192] Another aspect of the second additional exemplary embodiment is a radiation curable composition according to any of the foregoing aspects of the second additional exemplary embodiment, further comprising a multifunctional vinyl ether compound.

[0193] Another aspect of the second additional exemplary embodiment is a radiation curable combination according to the foregoing aspect of the second additional exemplary embodiment, wherein the multifunctional vinyl ether compound has at least two vinyl groups.

[0194] Another aspect of the second additional exemplary embodiment is a radiation curable composition according to any of the foregoing aspects of the second additional exemplary embodiment, further comprising one or more additives.

[0195] Another aspect of the second additional exemplary embodiment is a radiation curable composition according to any of the preceding aspects of the second additional exemplary embodiment, wherein, relative to the weight of the entire composition:

[0196] The free radical polymerizable component is present in an amount of 5% to 50% by weight;

[0197] The cationically polymerizable component is present in an amount of 20% to 90% by weight;

[0198] The free radical photoinitiator component is present in an amount of 0.025 wt % to 5 wt %;

[0199] The cationic photoinitiator component is present in an amount of 0.5% to 8% by weight;

[0200] and the additive is present in a range of 0% to 40% by weight;

[0201] The weight of all components herein equals 100%.

[0202] Unless otherwise indicated, the term wt% refers to the amount by mass of a particular component relative to the entire liquid radiation curable composition for additive manufacturing into which it is incorporated.

[0203] Unless otherwise indicated herein or obviously contradictory to the context, otherwise in the context of describing the present invention (especially in the context of the following claims) the use of the terms "one" and "an" and "the" and similar indicators should be interpreted as covering both the singular and the plural. Unless otherwise indicated, the terms "comprise", "have", "include" and "contain" should be interpreted as open terms (that is, meaning "including but not limited to"). Unless otherwise indicated herein, the description of value ranges herein is only intended to be used as a shorthand method for quoting each individual value falling within the scope, and each individual value is incorporated into this specification as if it were individually quoted herein. Unless otherwise indicated herein or obviously contradictory to the context, all methods described herein can be carried out in any suitable order. Unless otherwise claimed, the use of any and all examples or illustrative language (such as "such as") provided herein is only intended to better illustrate the present invention, rather than to limit the scope of the present invention. Any language in the specification should not be interpreted as representing that any unclaimed element is essential for the practice of the present invention.

[0204] The preferred embodiments of the present invention are described herein, including the best mode known to the inventor for implementing the present invention. After reading the foregoing description, variations of those preferred embodiments will be apparent to those of ordinary skill in the art. The inventors hope that the skilled person will appropriately adopt such variations, and the inventors hope to practice the present invention in a manner different from that specifically described herein. Therefore, the present invention includes all modifications and equivalents of the subject matter described in the appended claims herein as allowed by applicable law. In addition, unless otherwise specified herein or clearly contradicted by the context, the present invention encompasses any combination of all possible variations of the above-mentioned elements.

[0205] While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as claimed.

Claims

1. A radiation curable composition comprising a cationically curable component and a free radically curable component, the composition further comprising at least one first photoinitiator, the at least one first photoinitiator being an iodonium salt of a non-fluorinated borate anion, in, The cationically curable component comprises at least one cycloaliphatic compound, wherein the free radical curable component comprises at least one acrylate or methacrylate, wherein the radiation curable composition is used for additive manufacturing, and Wherein, the radiation curable composition includes a photosensitizer.

2. The radiation curable composition of claim 1, wherein the iodonium salt of a non-fluorinated borate anion is an iodonium salt of a non-halogenated borate anion.

3. The radiation curable composition of claim 1 , wherein the non-fluorinated borate anion of the iodonium salt has the formula: wherein R1-R4 are independently selected from the group consisting of alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl and heteroaryl, and further wherein (i) one or more substitutable carbon atoms of the alkyl, alkenyl or alkynyl group are optionally substituted with hydroxy, carboxyl, alkoxy, alkanoyl, hydroxyalkyl, carboxylalkyl, alkoxyalkyl or alkanoylalkyl, or (ii) one or more substitutable carbon atoms of the cycloalkyl, heterocycloalkyl, aryl or heteroaryl group are optionally substituted with alkyl, hydroxy, carboxyl, alkoxy, alkanoyl, hydroxyalkyl, carboxylalkyl, alkoxyalkyl or alkanoylalkyl.

4. The radiation curable composition according to claim 3, wherein R1 to R4 are independently selected from aryl groups, which are optionally substituted on one or more substitutable carbon atoms with alkyl or alkoxy groups.

5. The radiation curable composition of claim 4, wherein R1 to R4 are each phenyl, optionally independently substituted with an alkyl group or an alkoxy group, wherein the alkyl group or the alkyl portion of the alkoxy group has 1 to 10 carbon atoms.

6. The radiation curable composition of claim 5, wherein the non-fluorinated borate anion of the iodonium salt is a tetraphenylborate anion having the formula:

7. The radiation curable composition according to any one of claims 1 to 6, wherein the iodonium salt of a non-fluorinated borate anion has a diaryliodonium cation.

8. The radiation curable composition according to claim 7, wherein the diaryliodonium cation of the iodonium salt is a diphenyliodonium salt having two phenyl groups optionally substituted with an alkyl or alkoxy group, wherein the alkyl portion of the alkyl or alkoxy group has 1 to 10 carbon atoms.

9. The radiation curable composition according to claim 8, wherein the diphenyliodonium cation of the iodonium salt is a bis-4-cumyliodonium cation or a bis-4-tert-butyliodonium cation having the following structure:

10. The radiation curable composition of claim 1, wherein the first photoinitiator is bis (4-cumyl iodonium tetraphenylborate) or bis (4-tert-butyl iodonium tetraphenylborate).

11. The radiation curable composition of claim 1 , wherein the composition contains less than about 0.1 wt. % by weight of a phosphorus-containing free radical photoinitiator.

12. The radiation curable composition of claim 1, wherein the composition contains a Norrish Type I and / or Norrish Type II photoinitiator in an amount of less than 0.1 wt% by weight.

13. The radiation curable composition of claim 1, wherein the cationically curable component comprises a cycloaliphatic epoxy compound and an oxetane compound.

14. The radiation curable composition of claim 13, wherein the composition emits a peak spectral output of 375-405 nm and an irradiance of 2 mW / cm2 at the surface of the composition. 2 When the cycloaliphatic epoxy compound is subjected to an ultraviolet / visible light optics irradiated with an irradiation agent for 10 seconds, the conversion rate of the cycloaliphatic epoxy compound is at least about 35%, or at least about 40%, or at least about 45%, and the conversion rate of the oxetane compound is at least about 40%, or at least about 45%, or at least about 50%.

15. The radiation curable composition of claim 1, wherein the first photoinitiator is present in the composition in an amount of about 0.1 wt% to about 1 wt%.

16. The radiation curable composition of claim 1 , further comprising a second photoinitiator in addition to the first photoinitiator, the second photoinitiator being an iodonium salt cationic initiator, wherein the iodonium salt cationic initiator as the second photoinitiator is present in the composition in an amount of about 0.5 wt % to about 8 wt %.

17. The radiation curable composition of claim 1, further comprising a reducing agent, wherein the reducing agent has an electron donating substituent bonded to a vinyl group.

18. The radiation curable composition according to claim 17, wherein the reducing agent comprises or consists of a vinyl ether compound.

19. The radiation curable composition of claim 1, wherein the photosensitizer is present in the composition in an amount of about 0.05 wt% to about 0.8 wt% by weight.

20. The radiation curable composition of any one of claims 17-18, wherein the reducing agent is present in the composition in an amount of about 1 wt% to about 10 wt% by weight.

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