JP7652850B2 - Liquid hybrid UV/vis radiation curable resin composition for additive manufacturing - Google Patents

Description

Detailed Description of the Invention

[Technical field]
The present invention relates to liquid compositions for additive manufacturing processes that are hybrid curable in the UV or visible spectral range.

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.S. Provisional Patent Application No. 62/172,489, filed June 8, 2015, the entire contents of which are hereby incorporated by reference as if fully set forth herein.

[background]
[001] Additive manufacturing processes for producing three-dimensional objects are known. Additive manufacturing processes utilize computer-aided design (CAD) data of an object to build a three-dimensional part, which may be formed from liquid resin, powder, or other materials.

[002] A well-known, but not limiting, example of an additive manufacturing process is stereolithography (SL). Stereolithography is a process for the rapid production of models, prototypes, patterns, and production parts for certain applications. SL uses CAD data of an object and converts it into a thin cross-section of a three-dimensional object. The data is loaded into a computer, which controls a laser that traces the pattern of the cross-section through a liquid radiation-curable resin composition contained in a vat, solidifying a thin layer of resin corresponding to the cross-section. The solidified layer is recoated with resin, and another cross-section is traced by the laser to cure another layer of resin on top of the previous layer. This process is repeated, layer by layer, until the three-dimensional object is complete. When initially formed, the three-dimensional object is generally not fully cured and is called a "green model." Although not required, the green model may be subjected to a post-cure to improve the mechanical properties of the finished part. An example of the SL process is described, for example, in U.S. Pat. No. 4,575,330.

[003] Lasers have traditionally served as the radiation source of choice for 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 wave (CW) or Q-switched pulsed. CW lasers provide continuous laser energy and can be used in fast scanning processes. Historically, several types of lasers have been used for stereolithography, traditionally with peak spectral output in the wavelength range of 193 nm to 355 nm, although other wavelengths exist. The light emitted from lasers is monochromatic; that is, a significant percentage of the total spectral output is within a very narrow wavelength range. Laser-based additive manufacturing systems in the industry have become most prevalent, operating with a peak spectral output of 355 nm.

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

[005] To eliminate some of the drawbacks associated with laser-based systems, other additive manufacturing systems have begun to utilize image projection technology as the source of actinic radiation. One example of this is liquid crystal display (LCD), a technology well known in other industries such as the manufacture of televisions and computer monitors. Another, but not limiting, example is that developed by Texas Instruments and called Digital Light Processing (DLP®). DLP systems use pixel-equivalent micromirrors known as digital micromirror devices (DMDs) controlled by and affixed to microchips to selectively transmit light from an input source and project that light in a desired output pattern or mask. DLP technology was developed for use in image projection systems as an alternative display system to LCD-based technology. The exceptional image sharpness, brightness, and uniformity associated with DLP systems are extremely useful in additive manufacturing where image resolution and precision are critical, since the boundaries of the three-dimensional object that is cured and produced are ultimately defined by the boundaries of the projected light. Additionally, image projection systems such as LCDs and DLPs offer a theoretical speed advantage in that an entire cross-sectional layer can be exposed and cured simultaneously. Furthermore, in that respect, while the curing time required in laser-based systems is directly proportional to the complexity of the cross-section being scanned, image projection systems are said to be cross-section independent, i.e., the exposure time for a given layer does not change as the shape complexity of any given layer increases. This makes them particularly suitable for parts produced by additive manufacturing that have complex and detailed geometries.

[006] DLPs and LCDs are not alternatives to generating light themselves, but rather provide a way to process light emitted from existing light sources into a more desirable pattern. Therefore, a combined input light source is still needed. The light input to an image projection system can come from any source, including traditional lamps and even lasers, but more commonly the input light is collimated from one or more light emitting diodes (LEDs).

[007] LEDs are semiconductor devices that utilize the phenomenon of electroluminescence to generate light. Currently, LED light sources for additive manufacturing systems generally emit at wavelengths between 300 and 475 nm, with typical peak spectral outputs at 365 nm, 375 nm, 395 nm, 401 nm, 405 nm, and 420 nm. For a more detailed discussion of LED light sources, see the textbook "Light-Emitting Diodes," by E. Fred Schubert, 2nd Edition, © E. Fred Schubert 2006, Cambridge University Press. LEDs offer the advantage of theoretically operating near their peak efficiency for longer durations than other light sources. Additionally, they are typically more energy efficient and less expensive to maintain, thus reducing initial and ongoing costs of ownership over laser-based optical systems.

[008] Thus, various additive manufacturing systems utilize one of the following non-limiting example 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.

[009] Recently, newer additive manufacturing systems, regardless of optical configuration, have begun to frequently utilize light sources that emit radiation at wavelengths longer than the traditional 355 nm output. Other systems have shifted away from monochromatic light sources in favor of light sources that emit light with a broader spectral power distribution. Thus, such newer systems incorporating laser/DLP, LED, LED/DLP, or LED/LCD based optical configurations have begun to operate with peak spectral outputs at longer wavelengths and with broader spectral distributions than was previously common. The wavelengths utilized therein have shifted away from 355 nm toward the visible spectrum, with some even having peak spectral outputs within the visible range. Such longer wavelengths (i.e., 375 nm to 500 nm) are traditionally referred to as "UV/vis".

[010] Some of the reasons typically cited for the current trend towards increased use of optics in the UV/vis region include, but are not limited to, (1) the reduced cost (both initial and maintenance costs) of light sources operating in the UV/vis range, as well as (2) the fact that UV/vis light sources emit lower energy radiation and, all else being equal, are less damaging to human tissue than sources that operate deeper into the UV region. Thus, they are less harmful in the event of accidental exposure than those that operate deeper in the UV region. As additive manufacturing continues to grow in popularity in consumer, "production consumer," and industrial market segments, the need for additive modeling systems that utilize lower cost, less hazardous sources of actinic radiation to cure liquid photopolymers will become increasingly important.

[011] However, the benefits gained from the use of UV/vis light source/optical systems are not without significant trade-offs. The biggest drawback so far has been the relatively large difficulty associated with developing photopolymers suitable for systems utilizing UV/vis optics. One of the main reasons for this is the natural phenomenon that longer wavelength light has lower energy, as well as the fact that the intensity of commercial light sources typically decreases with increasing wavelength of peak spectral output. Thus, while a traditional 355 nm laser-based light system may deliver an irradiance of 1500 W/ ^cm2 to a resin surface, commercial systems operating at about 400 nm are known to deliver an irradiance of roughly only about 1/1000 of that value to a resin surface. In fact, the irradiance delivered to a resin surface by UV/vis optics in existing 365 nm or 405 nm DLP-based commercial additive manufacturing systems can be as low as 0.1 W/ ^cm2 or even 0.0002 W/ ^cm2 in some of the more economical desktop units. This relatively reduced radiation energy/intensity makes it more difficult to photopolymerize radiation curable resins with such UV/vis optics unless the exposure time is prohibitively long. This in turn significantly increases part build times, thereby negating the theoretical speed advantage of photomask display systems. Furthermore, there are fewer photoinitiation systems on the market to promote photopolymerization at such longer UV/vis wavelengths, especially cationic photoinitiation systems.

[012] Due to the challenges outlined above, there are a limited number of photopolymers available for modern optical systems operating in the UV/vis region, compared to the many options available for systems operating deeper into the UV region, such as 355 nm laser-based systems.

[013] It is known that radically polymerizable resins exist for systems utilizing UV/vis optics. Such resins generally consist of one or more (meth)acrylate compounds (or other free radically polymerizable organic compounds) along with a free radical photoinitiator for radical generation. One such radically curable system is described in U.S. Pat. No. 5,418,112. Although radically polymerizable resins will cure easily even under the relatively lower energy and intensity provided by UV/vis optics, they are not suitable for all additive manufacturing applications. First, (meth)acrylate-based resins that are considered suitable for additive manufacturing processes have traditionally produced cured parts with insufficient mechanical properties for incorporation into many end uses. Thus, parts are typically produced that are not robust enough for non-prototyping applications. Also, such resins exhibit deformation issues, such as residual strain due to shrinkage differences upon curing, typically producing warped or misshapen parts. Such issues are exacerbated with larger platform additive manufacturing machines. In this case, as the cured object grows, the effects of cumulative shrinkage differences amplify part warpage or misshapenness. These distortion problems can be partially corrected through software that compensates for known shrinkage rates by modifying the CAD files that generate the solid three-dimensional part. However, software corrections are insufficient to fully compensate for distortion in parts with intricate, complex shapes or that require tight dimensional tolerances over long distances.

[014] Other well-known types of resins suitable for use in additive manufacturing systems are "hybrid" curable resins, i.e., those that include (1) an epoxy, oxetane, or other type of cationically polymerizable compound, (2) one or more cationic photoinitiators, (3) an acrylate resin or other type of free radically polymerizable compound, and (4) one or more free radical photoinitiators. Examples of such hybrid curable systems are described, for example, in U.S. Pat. No. 5,434,196. Such resins have long been known to result in cured parts produced by additive manufacturing processes with superior mechanical properties compared to all-acrylate based resins. In addition, hybrid curable systems are superior to all-acrylate systems in that they are less susceptible to the differential shrinkage problems that have long plagued all-acrylate systems.

[015] However, because the ring-opening process of cationic polymerization generally occurs slower and requires more activation energy than free radical polymerization, it is inherently more difficult to ensure proper curing of such formulations for additive manufacturing applications or satisfactory "building" of three-dimensional objects. Also, even if hybrid curable resins are at least partially cured after exposure to actinic radiation, green models produced therefrom have insufficient mechanical strength (or "green strength") for use in many additive manufacturing applications, as measured, for example, by elastic modulus or fracture strength. Such problems are significantly exacerbated with UV/vis optics emitting lower energy and intensity radiation than with conventional systems.

[016] Due to limitations of cationic polymerization, there are no known hybrid liquid radiation-curable resins for additive manufacturing that are commercially suitable for use in more modern additive manufacturing systems that utilize UV/vis optics. Furthermore, there are no known liquid radiation-curable resins for additive manufacturing (e.g., hybrid curable ones) that are suitable for additive manufacturing systems that utilize UV/vis optics and that simultaneously have both (1) a sufficiently fast curing rate and (2) the ability to impart sufficient mechanical strength and shrinkage deformation resistance to the cured three-dimensional part.

[017] From the above, it is apparent that a heretofore unmet need exists to provide a hybrid curable liquid radiation resin composition suitable for use in additive manufacturing systems utilizing UV/vis optics that can produce three-dimensional parts having mechanical properties at least comparable to existing hybrid curable materials designed for traditional laser-based 355 nm systems.

[Brief Overview]
[018] A first aspect of the invention is a liquid UV/vis radiation curable composition for additive manufacturing comprising a cationically curable component further comprising a cycloaliphatic epoxy component that undergoes cationic polymerization, at least one free radically curable component that undergoes free radical polymerization, a cationic photoinitiator, and a free radical photoinitiator, wherein after exposing the liquid UV/vis radiation curable composition to UV/vis optics emitting radiation having a peak spectral output at 400 nm and a dose to a surface of the liquid UV/vis radiation curable composition of at least 2 mW/ ^cm2 for at least 10 seconds, the cycloaliphatic epoxy component achieves a _T95 value of about 70 seconds or less and a plateau conversion of at least about 20%.

[019] A first aspect of the present invention is a method for producing a liquid UV/vis radiation curable composition comprising: a cationically curable component that undergoes cationic polymerization, the cationically curable component further comprising a cycloaliphatic epoxy component and an oxetane component; a free radically curable component that undergoes free radical polymerization; and a photoinitiator package further comprising a cationic photoinitiator, a vinyl ether diluent monomer, and a free radical photoinitiator, wherein when the liquid UV/vis radiation curable composition is exposed to UV/vis optics emitting radiation having a peak spectral output at 400 nm and at a dose of 2 mW/ ^cm2 on the surface of the liquid UV/vis radiation curable composition for 10 seconds, the cycloaliphatic epoxy component exhibits the following properties: (i) a T of about 70 seconds or less, more preferably about 55 seconds or less, more preferably about 53 seconds or less, more preferably about 50 seconds or less. and (ii) a plateau conversion of at least about ₂₀ %, more preferably at least about 30%, more preferably at least about 36%, more preferably at least about 43%, and the oxetane component achieves the following properties: (i) a T ₉₅ value of about 50 seconds or less, more preferably less than about 42 seconds, more preferably less than about 34 seconds, more preferably less than about 23 seconds; and (ii) a plateau conversion of at least about 29%, more preferably at least about 34%, more preferably at least about 50%, more preferably at least about 59%.

[020] A second aspect of the present invention is a liquid radiation curable composition for additive manufacturing comprising: (a) a cationically polymerizable component; (b) an iodonium salt cationic photoinitiator; (c) a photosensitizer for photosensitizing component (b); (d) a reducing agent for reducing component (b); (e) a free radically polymerizable component; and optionally (f) a free radical photoinitiator; and the composition is curable with UV/vis optics providing a dose of 20 mJ/ ^cm2 and emitting radiation with a peak spectral intensity between about 375 nm and about 500 nm, more preferably between about 380 nm and about 450 nm, more preferably between about 390 nm and about 425 nm, more preferably between about 395 nm and about 410 nm.

[021] A second aspect of the invention is a liquid radiation curable composition for additive manufacturing comprising a cationically polymerizable component, an iodonium salt cationic photoinitiator, a photosensitizer for photosensitizing the iodonium salt cationic photoinitiator, a first reducing agent for reducing the iodonium salt cationic photoinitiator, a free radically polymerizable component, optionally a free radical photoinitiator, and a second reducing agent for reducing the iodonium salt cationic photoinitiator having an electron donating substituent attached to a vinyl group, the composition being curable with UV/vis optics providing a dose of 20 mJ/ ^cm2 and emitting 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.

（式中、ＲはＣ_１～Ｃ_２０脂肪族鎖を含有する）
で示される約０．５ｗｔ．％～約３ｗｔ．％の化合物と、フリーラジカル重合性成分と、ジフェニル（２，４，６－トリメチルベンゾイル）ホスフィンオキシドフリーラジカル光開始剤と、を含み、２０ｍＪ／ｃｍ^２の線量を与えるかつピークスペクトル強度で約３７５ｎｍ～約５００ｎｍ、より好ましくは約３８０ｎｍ～約４５０ｎｍ、より好ましくは約３９０ｎｍ～約４２５ｎｍの放射線を放出するＵＶ／ｖｉｓ光学素子により硬化可能である、付加造形用液状放射線硬化性組成物である。 [022] A third aspect of the present invention is a polymerizable composition comprising about 30 wt. % to about 80 wt. % of at least one cationically polymerizable component further comprising a cycloaliphatic epoxide and an oxetane, about 1 wt. % to about 8 wt. % of a sulfonium salt cationic photoinitiator having an absorbance of less than 0.01 at 400 nm, and a compound represented by the following formula (V):

where R contains a _C1 - _C20 aliphatic chain.
^% of a compound represented by the formula:

[023] A fourth aspect of the present invention is a method for forming a three-dimensional article by an additive manufacturing system utilizing UV/vis optics, comprising the steps of: (1) providing a liquid radiation curable composition for additive manufacturing of any of the first, second, or third aspects of the present invention; (2) providing a first liquid layer of a liquid radiation curable resin; (3) forming a first cured layer by imagewise exposing the first liquid layer to actinic radiation using a UV/vis optical configuration to form an imaged cross-section; and (4) forming a first cured layer. (5) forming a new layer of liquid radiation curable resin in contact with the cured layer; (6) imagewise exposing the new layer to actinic radiation to form an additional imaged cross-section; and (7) repeating steps (4) and (5) a sufficient number of times to build a three-dimensional article, wherein the UV/vis optics emit radiation with a peak spectral intensity between about 375 nm and about 500 nm, more preferably between about 380 nm and about 450 nm, and more preferably between about 395 nm and about 410 nm.

[024] A fifth aspect of the present invention is a three-dimensional part formed by the process according to the fourth aspect of the present invention using the liquid radiation curable composition of any of the first, second or third aspects of the present invention.

FIG. 1 is a plot showing RT-FTIR (under 365 nm cure conditions) conversion of cycloaliphatic epoxide in Plastcure ABS3650, a commercially available liquid hybrid radiation curable composition for additive manufacturing designed to be suitable for additive manufacturing machines operating at a peak spectral intensity of 365 nm. FIG. 2 is a plot showing RT-FTIR (under 365 nm cure conditions) conversion of oxetanes in Plastcure ABS3650. FIG. 3 is a plot showing RT-FTIR (under 400 nm cure conditions) conversion of cycloaliphatic epoxides in liquid hybrid radiation curable compositions for additive manufacturing utilizing a photoinitiator package that uses photoinitiators purported to be useful at 400 nm wavelength. FIG. 4 is a plot showing RT-FTIR (under 400 nm cure conditions) conversion of oxetanes in a liquid hybrid radiation curable composition for additive manufacturing utilizing a photoinitiator package that uses photoinitiators purported to be useful at 400 nm wavelength. FIG. 5 is a plot showing RT-FTIR (under 365 nm cure conditions) conversion of cycloaliphatic epoxides in liquid hybrid radiation curable compositions for additive manufacturing utilizing a photoinitiation package designed to be suitable for additive manufacturing machines operating at a peak spectral intensity of 365 nm. FIG. 6 is a plot showing RT-FTIR (under 365 nm cure conditions) conversion of oxetanes in a liquid hybrid radiation curable composition for additive manufacturing utilizing a photoinitiation package designed to be suitable for additive manufacturing machines operating at a peak spectral intensity of 365 nm. FIG. 7 is a plot showing RT-FTIR (under 400 nm cure conditions) conversion of cycloaliphatic epoxide in a liquid hybrid radiation curable composition for additive manufacturing according to the present invention. FIG. 8 is a plot showing RT-FTIR (under 400 nm cure conditions) conversion of oxetanes in a liquid hybrid radiation curable composition for additive manufacturing according to the present invention. FIG. 9 is a plot showing RT-FTIR (under 400 nm cure conditions) conversion of cycloaliphatic epoxide in a liquid hybrid radiation curable composition for additive manufacturing according to the present invention. FIG. 10 is a plot showing RT-FTIR (under 400 nm cure conditions) conversion of oxetanes in a liquid hybrid radiation curable composition for additive manufacturing according to the present invention. FIG. 11 is a plot showing RT-FTIR (under 400 nm cure conditions) conversion of cycloaliphatic epoxide in a liquid hybrid radiation curable composition for additive manufacturing according to the present invention. FIG. 12 is a plot showing RT-FTIR (under 400 nm cure conditions) conversion of oxetanes in a liquid hybrid radiation curable composition for additive manufacturing according to the present invention. FIG. 13 is a plot showing RT-FTIR (under 400 nm cure conditions) conversion of cycloaliphatic epoxide in a liquid hybrid radiation curable composition for additive manufacturing according to the present invention. FIG. 14 is a plot showing RT-FTIR (under 400 nm cure conditions) conversion of oxetanes in a liquid hybrid radiation curable composition for additive manufacturing according to the present invention.

Detailed Description
[033] Throughout this document, "UV/vis" is defined as the region of the electromagnetic spectrum from 375 nanometers (nm) to 500 nanometers (nm).

[034] Thus, throughout this document, "UV/vis optics" is defined as any electrical, mechanical, or electromechanical system that generates and directs/displays actinic radiation operating with a peak spectral intensity between 375 nm and 500 nm. Non-limiting examples of UV/vis optics include lasers, LEDs, 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.

[035] A first embodiment of the present invention comprises:
a cationically curable component that undergoes cationic polymerization, the cationically curable component further comprising a cycloaliphatic epoxy component and an oxetane component;
a free radically curable component that undergoes free radical polymerization;
The following:
a cationic photoinitiator;
a vinyl ether diluent monomer;
a free radical photoinitiator;
a light initiation package further comprising:
Including,
When the liquid UV/vis radiation curable composition is exposed to UV/vis optics emitting radiation having a peak spectral output at 400 nm and a dose of 2 mW/ ^cm2 applied to the surface of the liquid UV/vis radiation curable composition for 10 seconds,
The cycloaliphatic epoxy component has the following properties:
i. a _T95 value of about 70 seconds or less, more preferably about 55 seconds or less, more preferably about 53 seconds or less, more preferably about 50 seconds or less;
ii. a plateau conversion of at least about 20%, more preferably at least about 30%, more preferably at least about 36%, more preferably at least about 43%;
and the oxetane moiety has the following properties:
i. a _T95 value of about 50 seconds or less, more preferably less than about 42 seconds, more preferably less than about 34 seconds, more preferably less than about 23 seconds;
ii. a plateau conversion of at least about 29%, more preferably at least about 34%, more preferably at least about 50%, more preferably at least about 59%;
To achieve
A liquid UV/vis radiation curable composition for additive manufacturing.

Cationically Curable Component
[036] According to one embodiment, the radiation curable liquid resin for additive manufacturing of the present invention comprises at least one cationically polymerizable component, which is a component that undergoes cationically or in the presence of an acid generator initiated polymerization. The cationically polymerizable component may be a monomer, oligomer, and/or polymer and may contain aliphatic, aromatic, cycloaliphatic, arylaliphatic, heterocyclic moieties, and any combination thereof. Preferably, the cationically polymerizable component comprises at least one cycloaliphatic compound. Suitable cyclic ether compounds may contain cyclic ether groups as side groups or as groups forming part of an alicyclic or heterocyclic ring system.

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

[038] 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 cationic 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-vinylepoxy Bicyclohexane, 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), bicyclohexyl-3,3'-epoxide, -O-, -S-, -SO-, -SO _2- , -C( _CH3 ) _2- , _-CBr2- , -C( _CBr3 ) _2- , -C( _CF3 ) _2- , -C( _CCl3 ) _2- , or -CH _{( C6H5} )-bonded bis(3,4-epoxycyclohexyl), dicyclopentadiene diepoxide, di(3,4-epoxycyclohexylmethyl)ether of ethylene glycol, ethylene bis(3,4-epoxycyclohexanecarboxylate), epoxy hexahydrodioctyl phthalate, epoxy hexahydro-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 ether of aliphatic long-chain dibasic acids Glycidyl esters, monoglycidyl ethers of aliphatic higher alcohols, monoglycidyl ethers of phenol, cresol, butylphenol, or polyether alcohols obtained by addition of alkylene oxides to compounds, glycidyl esters of higher fatty acids, 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-(meth)-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-3-oxetanylmethoxy)ethyl]phenyl ether, isobutoxy methyl (3-ethyl-3-oxetanylmethyl) ether, 2-ethylhexyl (3-ethyl-3-oxetanylmethyl) ether, ethyl diethylene glycol (3-ethyl-3-oxetanylmethyl) ether, dicyclopentadiene (3-ethyl-3-oxetanylmethyl) ether, dicyclopentenyloxyethyl (3-ethyl-3-oxetanylmethyl) ether, dicyclopentenyl (3-ethyl-3-oxetanylmethyl) ether, tetrahydrofurfyl (3-ethyl-3-oxetanylmethyl) ether, 2-hydroxyethyl (3-ethyl-3-oxetanylmethyl) ether, 2-hydroxypropyl (3-ethyl-3-oxetanylmethyl) ether, and any combination thereof.

[039] The cationically polymerizable component may also optionally contain multifunctional materials, including dendritic polymers such as dendrimers, linear dendritic polymers, dendrigraft polymers, hyperbranched polymers, star-branched polymers, hypergraft polymers, etc., having epoxy or oxetane functional groups. Dendritic polymers may contain one type of polymerizable functional group or different types of polymerizable functional groups, e.g., epoxy and oxetane functional groups.

[040] In an embodiment, the composition of the present invention also includes one or more mono- 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 polyoxyethylene and polyoxypropylene glycols and triols of molecular weight from 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 cationically polymerizable component includes a multifunctional glycidyl ether that does not have a cyclohexane ring in the molecule. In another specific embodiment, the cationically polymerizable component includes neopentyl glycol diglycidyl ether. In another specific embodiment, the cationically polymerizable component includes 1,4-cyclohexanedimethanol diglycidyl ether.

[041] Examples of preferred commercially available polyfunctional glycidyl ethers are Erisys™ GE22 (Erisys™ products are available from Emerald Performance Materials™), Heloxy™ 48, Heloxy™ 67, Heloxy™ 68, Heloxy™ 107 (Heloxy™ modifiers are available from Momentive Specialty Chemicals), and Grilonit® F713. Examples of preferred commercially available monofunctional glycidyl ethers are Heloxy(TM) 71, Heloxy(TM) 505, Heloxy(TM) 7, Heloxy(TM) 8, and Heloxy(TM) 61.

[042] In an embodiment, the epoxide is 3,4-epoxycyclohexylmethyl-3',4-epoxycyclohexanecarboxylate (available from Daicel Chemical as CELLOXIDE™ 202 IP or from Dow Chemical). available from Momentive as CYRACURE™ UVR-6105), hydrogenated bisphenol A epichlorohydrin based epoxy resin (available from Momentive as EPON™ 1510), 1,4-cyclohexanedimethanol diglycidyl ether (available from Momentive as HELOXY™ 107), hydrogenated bisphenol A diglycidyl ether (available from Momentive as EPON™ 825), a mixture of dicyclohexyl diepoxide and nanosilica (available as NANOPOX™), and any combination thereof.

（式中、Ｒは、炭素原子、エステル含有Ｃ_１～Ｃ_１０脂肪族鎖、またはＣ_１～Ｃ_１０アルキル鎖である）
で示される２個または２個超のエポキシ基を有する環式脂肪族エポキシを含む。 [043] In a specific embodiment, the cationically polymerizable component is a cycloaliphatic epoxy, for example, a cyclic epoxy represented by the following formula I:

where R is a carbon atom, an ester-containing C ₁ -C ₁₀ aliphatic chain, or a C ₁ -C ₁₀ alkyl chain.
The epoxy groups include cycloaliphatic epoxies having two or more epoxy groups, such as

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

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

を有する。 [046] In other embodiments of the present invention, the cationically polymerizable component also includes an oxetane component. In specific embodiments, the cationically polymerizable component includes an oxetane, for example, an oxetane containing one, two, or more than two oxetane groups. In other embodiments, the oxetane utilized is monofunctional and additionally has a hydroxyl group. According to embodiments, the oxetane has the following structure:

has.

[047] When utilized in the composition, the oxetane component is present in a preferred amount of about 5 to about 50 wt % of the resin composition. In other embodiments, the oxetane component is present in an amount of about 10 to about 25 wt % of the resin composition, and in yet other embodiments, the oxetane component is present in an amount of 20 to about 30 wt % of the resin composition.

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

[Free radical polymerizable compound]
[049] According to an embodiment of the present invention, the liquid radiation curable resin for additive manufacturing of the present invention comprises at least one free radically polymerizable component, i.e., a component that undergoes free radical initiated polymerization. The free radically polymerizable component can be a monomer, oligomer, and/or polymer, and can be a mono- or polyfunctional material, i.e., having 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 can contain aliphatic, aromatic, cycloaliphatic, arylaliphatic, heterocyclic moieties, or any combination thereof. Examples of polyfunctional materials include dendritic polymers, such as dendrimers, linear dendritic polymers, dendrigraft polymers, hyperbranched polymers, star-branched polymers, hypergraft polymers, etc. See, for example, US 2009/0093564 A1. Dendritic polymers can contain one type of polymerizable functional group or different types of polymerizable functional groups, for example, acrylate and methacrylate functional groups.

[050] Examples of free radical polymerizable components include isobornyl (meth)acrylate, bornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, dicyclopentanyl (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 (meth)acrylate, 2-hydroxybutyl (meth)acrylate, methyl (meth)acrylate. t, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, amyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (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 ) 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 and polypropylene glycol, mono(meth)acrylate, methoxyethylene glycol (meth)acrylate, ethoxyethyl Examples of acrylates and methacrylates include (meth)acrylate, methoxy polyethylene glycol (meth)acrylate, methoxy polypropylene glycol (meth)acrylate, diacetone (meth)acrylamide, beta-carboxyethyl (meth)acrylate, phthalic acid (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, butylcarbamylethyl (meth)acrylate, n-isopropyl (meth)acrylamide fluorinated (meth)acrylate, and 7-amino-3,7-dimethyloctyl (meth)acrylate.

[051] Examples of polyfunctional free radical polymerizable components 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, dicyclopentadiene dimethanol di(meth)acrylate, [2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxane-5-yl]methyl acrylate, 3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane di(meth)acrylate, acrylates, dipentaerythritol monohydroxypenta(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, propoxylated neopentyl glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polybutanediol di(meth)acrylate, tripropylene glycol di(meth)acrylate, glycerol tri(meth)acrylate, phosphate mono and di(meth)acrylates, _C7 to C ₂₀ alkyl di(meth)acrylate, 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 products (e.g., ethoxylated products and/or propoxylated products) of any of the above monomers, and Examples of such di(meth)acrylates include diol di(meth)acrylates which are adducts of ethylene oxide or propylene oxide to bisphenol A, di(meth)acrylates of diols which are adducts of ethylene oxide or propylene oxide to hydrogenated bisphenol A, epoxy (meth)acrylates which are (meth)acrylate adducts to bisphenol A diglycidyl ether, diacrylates of polyoxyalkylated bisphenol A, and adducts of triethylene glycol divinyl ether and hydroxyethyl acrylate.

[052] According to an embodiment, the radically polymerizable component is a multifunctional (meth)acrylate. The multifunctional (meth)acrylate may contain all methacryloyl groups, all acryloyl groups, or any combination of methacryloyl and acryloyl groups. In an embodiment, the free radically 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, dipentaerythritol monohydroxypenta(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, and propoxylated neopentyl glycol di(meth)acrylate, and any combination thereof.

[053] In an embodiment, the multifunctional (meth)acrylate has a functionality of more than two. According to other embodiments, the multifunctional (meth)acrylate has a functionality of more than three. In yet other embodiments, the multifunctional (meth)acrylate has a functionality of more than four. In other preferred embodiments, the radically polymerizable component consists exclusively of a single multifunctional (meth)acrylate component. In further embodiments, the exclusively radically polymerizable component is tetrafunctional, in further embodiments, the exclusively radically polymerizable component is pentafunctional, and in further embodiments, the exclusively radically polymerizable component is hexafunctional.

[054] In another embodiment, the free radically polymerizable component contains an aromatic (meth)acrylate. The aromatic acrylate is derived from, for example, but not limited to, bisphenol A, bisphenol S, or bisphenol F. In a particular embodiment, the aromatic is selected from the group consisting of bisphenol A diglycidyl ether diacrylate, dicyclopentadiene dimethanol diacrylate, [2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxane-5-yl]methyl acrylate, dipentaerythritol monohydroxypentaacrylate, propoxylated trimethylolpropane triacrylate, and propoxylated neopentyl glycol diacrylate, and any combination thereof. In an embodiment, the aromatic (meth)acrylate is difunctional.

[055] In specific embodiments, the liquid radiation curable resin for additive manufacturing of the present invention comprises one or more of bisphenol A diglycidyl ether di(meth)acrylate, dicyclopentadiene dimethanol di(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, and/or propoxylated neopentyl glycol di(meth)acrylate, more specifically one or more of bisphenol A diglycidyl ether diacrylate, dicyclopentadiene dimethanol diacrylate, dipentaerythritol pentaacrylate, propoxylated trimethylolpropane triacrylate, and/or propoxylated neopentyl glycol diacrylate.

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

[Cationic Photoinitiator]
[057] According to one embodiment, the liquid radiation curable resin composition comprises a cationic photoinitiator, which upon irradiation with light initiates cationic ring-opening polymerization.

[058] In embodiments, any suitable iodonium-based cationic photoinitiator can 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.

[059] In other embodiments, 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 other embodiments, the cation is a polymeric sulfonium salt, such as those described in U.S. Pat. No. 5,380,923 or U.S. Pat. No. 5,047,568, or other aromatic heteroatom-containing cations and naphthyl-sulfonium salts, such as those described in U.S. Pat. No. 7,611,817, U.S. Pat. No. 7,230,122, U.S. Pat. Appl. Pub. No. 2011/0039205, U.S. Pat. Appl. Pub. No. 2009/0182172, U.S. Pat. No. 7,678,528, EP 2,308,865, WO 2010046240, or EP 2,218,715. In other embodiments, 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, as well as ferrocenium salts, generally have the advantage of being more thermally stable.

[060] In certain embodiments, the cationic photoinitiator is _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 ]} ^- , [(C ₆ F ₅ ) ₃ B-NH ₂ -B(C ₆ F ₅ ) ₃ ] ⁻ , tetrakis(3,5-difluoro-4-alkyloxyphenyl)borate, tetrakis(2,3,5,6-tetrafluoro-4-alkyloxyphenyl)borate, perfluoroalkylsulfonate, tris[(perfluoroalkyl)sulfonyl]methide, bis[(perfluoroalkyl)sulfonyl]imide, perfluoroalkylphosphate, tris(perfluoroalkyl)trifluorophosphate, bis(perfluoroalkyl)tetrafluorophosphate, tris(pentafluoroethyl)trifluorophosphate, and (CH ₆ B ₁₁ Br ₆ ) ⁻ , (CH ₆ B ₁₁ Cl ₆ ) ⁻ , and other halogenated carborane anions.

[061] Reviews of other onium salt initiators and/or metallocene salts can be found in "UV Curing, Science and Technology", edited by S.P. Pappas, Technology Marketing Corp., 642 Westover Road, Stamford, Conn., U.S.A., "Chemistry & Technology of UV & EB Formulation for Coatings, Inks & Paints", Vol. 3, edited by P.K.T. Oldring, or J.P. Fouassier, J. Lavellee, "Photoinitiators for polymer synthesis" Wiley 2012 ISBN 978-3-527-33210-6.

[062] In an embodiment, the cationic photoinitiator has a cation selected from ^the group consisting of aromatic _sulfonium ^salts , aromatic iodonium salts, and metallocene-based compounds, with at least an anion selected from the group consisting of _SbF6- , _PF6- , B( _C6F5 ) _4- ^, [B( _CF3 ) ₄ ] ^- , tetrakis(3,5-difluoro- ₄ -methoxyphenyl)borate, perfluoroalkylsulfonates, perfluoroalkylphosphates, tris[(perfluoroalkyl)sulfonyl]methides, and [( _C2F5 ) _{3PF3 ]} ^- .

[063] Examples of cationic photoinitiators suitable for other embodiments 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(pentafluorophenyl)borate, tris(2,3,5,6-tetrafluoro-4-methyloxyphenyl)borate, tris(4-(4-acetylphenyl)thiophenyl)sulfonium tetrakis(pentafluorophenyl)borate (Irgacure® PAG290 from BASF), tris(4-(4-acetylphenyl)thiophenyl)sulfonium tris[(trifluoromethyl)sulfonyl]methide (Irgacure® GSID26-1 from BASF), tris(4-(4-acetylphenyl)thiophenyl)sulfonium hexafluorophosphate (Irgacure® 270 from BASF), and HS-1 available from San-Apro Ltd.

[064] In a preferred embodiment, the cationic photoinitiator component, either alone or in admixture, is selected from the group consisting of bis[4-diphenylsulfonium phenyl]sulfide bishexafluoroantimonate, thiophenoxyphenylsulfonium hexafluoroantimonate (available as Chivacure 1176 from Chitec), tris(4-(4-acetylphenyl)thiophenyl)sulfonium tetrakis(pentafluorophenyl)borate (Irgacure® PAG 290 from BASF), tris(4-(4-acetylphenyl)thiophenyl)sulfonium tris[(trifluoromethyl)sulfonyl]methide (available as Chivacure® 1176 from BASF), and bis[4-diphenylsulfonium phenyl]sulfide bishexafluoroantimonate (available as Chivacure® 1176 from Chitec). PF26-1), tris(4-(4-acetylphenyl)thiophenyl)sulfonium hexafluorophosphate (Irgacure® 270 from BASF), [4-(1-methylethyl)phenyl](4-methylphenyl)iodonium tetrakis(pentafluorophenyl)borate (available from Rhodia as Rhodorsil 2074), 4-[4-(2-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfonium hexafluoroantimonate (available from Adeka as SP-172), SP-300 from Adeka, and (PF26-1). _6-m (C _n F _2n+1 ) _m ^- (wherein m is an integer from 1 to 5 and n is an integer from 1 to 4) (available from San-Apro Ltd. as monovalent sulfonium salts CPI-200K or CPI-200S, TK-1 available from San-Apro Ltd., or HS-1 available from San-Apro Ltd.).

[065] In an 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 US Patent Publication No. 20120251841 to DSM IP Assets, B.V. and US Patent No. 6,368,769 to Asahi Denki Kogyo, which discuss aromatic triarylsulfonium salts with tetraarylborate anions, including tetrakis(pentafluorophenyl)borate, and the use of such compounds in stereolithography applications. Triarylsulfonium salts are disclosed, for example, in J Photopolymer Science & Tech (2000), 13(1), 117-118, and J Poly Science, Part A (2008), 46(11), 3820-29. Triarylsulfonium salts, such as Ar ₃ S+MXn ^- salts with complex metal halide anions such as BF ₄ ^- , AsF ₆ ^- , PF ₆ ^- , SbF ₆ ^- , are disclosed in J Polymr Sci, Part A (1996), 34(16), 3231-3253.

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

[067] In other embodiments, the cationic photoinitiator is an aromatic triarylsulfonium ^salt _having an ^anion represented _by ^SbF6- _{, PF6-} ^, _BF4- , ( _CF3CF2 ) ^3PF3- , ( _C6F5 ) _4B- , (( _{CF3 ) 2C6H3} ) _4B- ^, ( _C6F5 ) _4Ga- ^, ₍ ( _CF3 ) _{2C6H3 ) 4Ga-} ^, trifluoromethanesulfonate, nonafluorobutanesulfonate, methanesulfonate, butanesulfonate, benzenesulfonate, or p _- toluenesulfonate _. Such photoinitiators are described _{, for} example, in U.S. Pat. No. 8,617,787.

[068] Other cationic photoinitiators are aromatic triarylsulfonium cationic photoinitiators having an anion of a fluoroalkyl-substituted fluorophosphate. Commercially available examples of aromatic triarylsulfonium cationic photoinitiators having a fluoroalkyl-substituted fluorophosphate anion are the CPI 200 series (e.g., CPI-200K® or CPI-210S®) or 300 series available from San-Apro Co., Ltd.

[069] There are also several commercially available cationic photoinitiators designed to be particularly suitable for absorbing light at UV/vis wavelengths to generate photoreactive species. Incorporation of one or more such cationic photoinitiators into a liquid radiation curable composition for UV/vis curing may be accomplished via "direct" excitation of the photoinitiator. Some non-limiting examples of UV/vis direct excited cationic photoinitiators include Irgacure 261, Irgacure PAG 103, and Irgacure PAG 121 (each commercially available from BASF), R-Gen® 262 (η5-2,4-cyclopentadien-1-yl) [(1,2,3,4,5,6-η)-(1-methylethyl)benzene]-iron(I)-hexafluoroantimonate) (commercially available from Chitec Technology Co.), and CPI 400 series photoinitiators (available from San-Apro Co.).

[070] However, applicants have surprisingly found that the UV/vis directly excited cationic photoinitiators listed above are not suitable for achieving sufficient hybrid curing of compositions used in additive manufacturing processes utilizing UV/vis optics. Without wishing to be bound by any theory, it is speculated that because the free radical portions of the polymer network cure fairly quickly, the free radical curing portions of the resin build up viscosity and polymer structure to significantly reduce the molecular mobility of the slower curing cationic curing species, thereby significantly reducing the overall cure speed to unacceptably low rates. This problem is inherent to dual-cure hybrid resins and is exacerbated at the longer wavelengths, lower energies, and lower intensities typical of modern UV/vis optics. Thus, applicants have found that formulating a hybrid-cure radiation-curable composition suitable for UV/vis wavelengths for additive manufacturing is not achieved by simply changing the cationic photoinitiator of a hybrid resin suitable for UV curing with, for example, a 355 nm laser-based system. Thus, the inventors have discovered that such "direct excitation" mechanisms for achieving suitable hybrid curing are insufficient to address the processing realities of modern additive manufacturing systems that utilize UV/vis optics.

[071] More precisely, applicants have surprisingly discovered that a combination of one or more alternative mechanisms is instead required to achieve sufficient cure in additive manufacturing systems utilizing UV/vis optics. The first is via an "indirect excitation" mechanism. The second is via a free radical promoted cationic polymerization mechanism. The third is via a vinyl ether polymerization mechanism. As discussed further below, liquid radiation curable compositions for additive manufacturing made in accordance with the present invention synergistically utilize one or more of these mechanisms to achieve a suitable hybrid cure in additive manufacturing processes incorporating UV/vis optics.

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

Free Radical Photoinitiators
[073] In an embodiment, the liquid radiation curable resin for additive manufacturing of the present invention comprises a free radical photoinitiator. According to an embodiment, the liquid radiation curable resin composition comprises a photoinitiator system containing at least one photoinitiator having a cationic initiation functional group and at least one photoinitiator having a free radical initiation functional group. Additionally, the photoinitiator system may comprise a photoinitiator containing both free radical initiation functional groups and cationic initiation functional groups on the same molecule. A photoinitiator is a compound that undergoes a chemical change by the action of light or by the action of light in combination with the electronic excitation of a sensitizing dye to produce at least one of a radical, an acid, and a base.

[074] Typically, free radical photoinitiators are classified into those that generate radicals by cleavage, known as "Norrish type I," and those that generate radicals by hydrogen abstraction, known as "Norrish type II." Norrish type II photoinitiators require a hydrogen donor to function as a source of free radicals. Since initiation is based on a bimolecular reaction, Norrish type II photoinitiators are generally slower than Norrish type I photoinitiators, which are based on unimolecular generation of radicals. On the other hand, Norrish type II photoinitiators have better light absorption in the near-UV spectral region. Photolysis of aromatic ketones such as benzophenone, thioxanthone, benzil, and quinone in the presence of hydrogen donors such as alcohols, amines, and thiols produces radicals (ketyl type radicals) that originate from carbonyl compounds and other radicals derived from hydrogen donors. Photopolymerization of vinyl monomers is usually initiated by radicals that originate from hydrogen donors. Ketyl radicals are usually not reactive towards vinyl monomers due to steric hindrance and delocalization of the unpaired electron.

[075] To successfully formulate a liquid radiation curable resin for additive manufacturing, the wavelength sensitivity of the photoinitiator present in the resin composition must be examined to determine whether it will be activated by the radiation source selected to provide the curing light.

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

[077] In an embodiment, the liquid radiation curable resin for additive manufacturing is selected from the group consisting of 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 2,4,6-trimethylbenzoylphenyl, ethoxyphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1,2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one, 4-benzoyl-4'methyldiphenylsulfide, 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-hydroxycyclohexyl phenyl 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, benzyl dimethyl ketal, bis(η5-2-4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium, and any combination thereof.

[078] For light sources emitting in the wavelength range of 300 to 475 nm, particularly those emitting at 365 nm, 390 nm, or 395 nm, examples of suitable free radical photoinitiators that absorb in this region include benzoylphosphine oxides, such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin TPO from BASF) and 2,4,6-trimethylbenzoylphenyl,ethoxyphosphine 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]phosphine oxide, ... Examples of suitable photoinitiators include 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-2-morpholinopropanone-1 (Irgacure 907 manufactured by Ciba), 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone (Irgacure 369 manufactured by Ciba), 2-dimethylamino 2-(4-methyl-benzyl)-1-(4-morpholin-4-ylphenyl)-butan-1-one (Irgacure 379 manufactured by Ciba), 4-benzoyl-4'-methyldiphenyl sulfide (CibaCure BMS manufactured by Cheetech), 4,4'-bis(diethylamino)benzophenone (CibaCure EMK manufactured by Cheetech), and 4,4'-bis(N,N'-dimethylamino)benzophenone (Michler's ketone). Mixtures thereof are also suitable. These acylphosphine oxide photoinitiators are preferred because they have good delocalization of the phosphinoyl radicals upon irradiation with light.

[079] According to an embodiment of the present invention, the free radical photoinitiator is an acylphosphine oxide photoinitiator. Acylphosphine oxide photoinitiators are disclosed, for example, in U.S. Pat. Nos. 4,324,744, 4,737,593, 5,942,290, 5,534,559, 6,020,528, 6,486,228, and 6,486,226.

[080] The acylphosphine oxide photoinitiator is a bisacylphosphine oxide (BAPO) or a monoacylphosphine oxide (MAPO).

で示される。
[082]上記式中、Ｒ_５０は、Ｃ_１～Ｃ_１２アルキル、シクロヘキシル、あるいは置換されていないまたは１～４個のハロゲンもしくはＣ_１～Ｃ_８アルキルにより置換されたフェニルであり、Ｒ_５１およびＲ_５２は、それぞれ互いに独立して、Ｃ_１～Ｃ_８アルキルまたはＣ_１～Ｃ_８アルコキシであり、Ｒ_５３は、水素またはＣ_１～Ｃ_８アルキルであり、かつＲ_５４は、水素またはメチルである。 [081] Bisacylphosphine oxide photoinitiators have formula II:

As shown in the figure.
[082] In the above formula, R ₅₀ is C ₁ -C ₁₂ alkyl, cyclohexyl, or phenyl unsubstituted or substituted with 1 to 4 halogen or C ₁ -C ₈ alkyl, R ₅₁ and R ₅₂ are each independently C ₁ -C 8 alkyl or C ₁ -C ₈ alkoxy, R ₅₃ is hydrogen or C _{1 -C 8 alkyl} , and R ₅₄ is hydrogen or methyl.

[083] For example, R ₅₀ is C ₂ -C ₁₀ alkyl, cyclohexyl, or phenyl unsubstituted or substituted with 1-4 C ₁ -C ₄ alkyl, Cl, or Br. In other embodiments, R ₅₀ is C ₃ -C ₈ alkyl, cyclohexyl, or phenyl unsubstituted or substituted in the 2, 3, 4, or 2,5 positions with C ₁ -C ₄ alkyl. For example, R ₅₀ is C ₄ -C ₁₂ alkyl or cyclohexyl, R ₅₁ and R ₅₂ are each, independently of the others, C ₁ -C ₈ alkyl or C ₁ -C ₈ alkoxy, and R ₅₃ is hydrogen or C ₁ -C ₈ alkyl. For example, R ₅₁ and R ₅₂ are C ₁ -C ₄ alkyl or C ₁ -C ₄ alkoxy, and R ₅₃ is hydrogen or C ₁ -C ₄ alkyl. In other embodiments, R ₅₁ and R ₅₂ are methyl or methoxy, and R ₅₃ is hydrogen or methyl. For example, R ₅₁ , R ₅₂ , and R ₅₃ are methyl. In other embodiments, R ₅₁ , R ₅₂ , and R 53 are methyl, and R ₅₄ is hydrogen. In other embodiments, _{R 50 is} a C ₃ -C ₈ alkyl. For example, R ₅₁ and R ₅₂ are methoxy, _{R 53} and R ₅₄ are hydrogen, and R 50 is isooctyl. For example, R ₅₀ is isobutyl. For example, R ₅₀ is phenyl. The bisacylphosphine oxide photoinitiator of the present invention is, for example, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (CAS# 162881-26-7) or bis(2,4,6-trimethylbenzoyl)-(2,4-bis-pentyloxyphenyl)phosphine oxide.

で示される。上記式中、Ｒ_１およびＲ_２は、互いに独立して、Ｃ_１～Ｃ_１２アルキル、ベンジル、置換されていないまたはハロゲン、Ｃ_１～Ｃ_８アルキル、および／もしくはＣ_１～Ｃ_８アルコキシにより１～４回置換されたフェニルであり、あるいはシクロヘキシルまたは－ＣＯＲ_３基であり、あるいはＲ_１は－ＯＲ_４であり、Ｒ_３は、置換されていないまたはＣ_１～Ｃ_８アルキル、Ｃ_１～Ｃ_８アルコキシ、Ｃ_１～Ｃ_８アルキルチオ、および／もしくはハロゲンにより１～４回置換されたフェニルであり、かつＲ_４は、Ｃ_１～Ｃ_８アルキル、フェニル、またはベンジルである。たとえば、Ｒ_１は－ＯＲ_４である。たとえば、Ｒ_２は、置換されていないまたはハロゲン、Ｃ_１～Ｃ_８アルキル、および／もしくはＣ_１～Ｃ_８アルコキシにより１～４回置換されたフェニルである。たとえば、Ｒ_３は、置換されていないまたはＣ_１～Ｃ_８アルキルにより１～４回置換されたフェニルである。たとえば、本発明のモノアシルホスフィンオキシドは、２，４，６－トリメチルベンゾイルエトキシフェニルホスフィンオキシドまたは２，４，６－トリメチルベンゾイルジフェニルホスフィンオキシドである。 [084] Monoacylphosphine oxide photoinitiators have formula III:

In the above formula, R ₁ and R ₂ are each independently C ₁ -C ₁₂ alkyl, benzyl, phenyl which is unsubstituted or substituted 1-4 times with halogen, C ₁ -C ₈ alkyl, and/or C ₁ -C ₈ alkoxy, or a cyclohexyl or -COR ₃ group, or R ₁ is -OR ₄ , R ₃ is phenyl which is unsubstituted or substituted 1-4 times with C ₁ -C ₈ alkyl, C ₁ -C ₈ alkoxy, C ₁ -C ₈ alkylthio, and/or halogen, and R ₄ is C ₁ -C ₈ alkyl, phenyl, or benzyl. For example, R ₁ is -OR _4. For example, R ₂ is phenyl which is unsubstituted or substituted 1-4 times with halogen, C ₁ -C ₈ alkyl, and/or C ₁ -C ₈ alkoxy. For example, R ₃ is phenyl that is unsubstituted or substituted 1 to 4 times with C ₁ -C ₈ alkyl. For example, the monoacylphosphine oxide of the present invention is 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide or 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

[085] The radiation curable liquid resin for additive manufacturing may include a free radical photoinitiator as component (d) in any suitable amount, for example, in certain embodiments up to about 10 wt % of the resin composition, in certain embodiments from about 0.1 to about 10 wt % of the resin composition, and in further embodiments from about 1 to about 6 wt % of the resin composition.

[Light Initiation Package]
[086] According to certain embodiments, one or more cationic and/or free radical photoinitiators are included in the resin composition together with a diluent monomer. The cationic and free radical photoinitiators are as discussed herein, and any suitable diluent may be used. Typical liquid diluents for dispersing certain cationic photoinitiators include (poly)propylene glycol or (poly)propylene carbonate. Surprisingly, the inventors have discovered that the use of vinyl ethers as diluent monomers or dispersants in combination with at least one cationic photoinitiator results in improved photopolymerization efficacy when subjected to curing under UV/vis optical conditions according to the present invention.

[087] In an embodiment, the cationic photoinitiator is present in an amount of about 8 wt % to about 50 wt %, more preferably about 30 wt % to about 45 wt %, the vinyl ether diluent monomer is present in an amount of about 25 wt % to about 90 wt %, more preferably about 40 wt % to about 60 wt %, and the free radical photoinitiator is present in an amount of about 8 wt % to about 30 wt %, more preferably about 10 wt % to about 25 wt %, based on the total weight of the photoinitiator package, provided that the cationic photoinitiator is at least partially dissolved in solution with the vinyl ether diluent monomer in a ratio of 0.1:1 to 1:1.

[088] A second aspect of the claimed invention comprises:
(a) a cationically polymerizable component;
(b) an iodonium salt cationic photoinitiator; and
(c) a photosensitizer for photosensitizing component (b); and
(d) a first reducing agent for reducing component (b); and
(e) a free radically polymerizable component; and
(f) optionally a free radical photoinitiator;
(g) a second reducing agent for reducing component (b), the second reducing agent having an electron donating substituent attached to the vinyl group; and
Including,
curable by UV/vis optics providing a dose of 20 mJ/ ^cm2 and emitting radiation with a peak spectral intensity between about 375 nm and about 500 nm, more preferably between about 380 nm and about 450 nm, more preferably between about 390 nm and about 425 nm, more preferably between about 395 nm and about 410 nm;
A liquid radiation curable composition for additive manufacturing.

[089] The cationically polymerizable component, free radically polymerizable component, and free radical photoinitiator according to the first aspect of the invention are similarly suitable for use in the second aspect of the claimed invention. Moreover, the above description of the iodonium salt cationic photoinitiator according to the first aspect of the claimed invention is also similarly suitable for use in the second aspect of the claimed invention. In a preferred embodiment, the iodonium salt cationic photoinitiator is a diphenyliodonium salt. Some suitable diphenyliodonium salt photoinitiators are, for example, (4-methylphenyl)[4-(2-methylpropyl)phenyl]-, hexafluorophosphate, [4-(1-methylethyl)phenyl](4-methylphenyl)-, tetrakis(pentafluorophenyl)borate(1-) (bis(4-dodecylphenyl)iodonium hexafluoroantimonate), and (bis(4-tert-butylphenyl)iodonium hexafluorophosphate).

[Photosensitizer]
[090] In some embodiments, depending on the wavelength of light used to cure the liquid radiation curable resin, it is desirable for the liquid radiation curable resin composition to contain a photosensitizer. The term "photosensitizer" is used to mean any substance that either increases the rate of photoinitiated polymerization or shifts the wavelength at which polymerization occurs. See the textbook (G. Odian, Principles of Polymerization, 3rd Edition, 1991, p. 222). Substances that operate under the latter definition and that are used in conjunction with photoinitiators that do not otherwise absorb light of a particular wavelength are said to operate by an "indirect excitation" mechanism with their associated photoinitiator. Applicants have utilized this mechanism to formulate compositions of the present invention that are suitable for curing with UV/vis optics.

[091] 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 methanone, xanthenone, pyrenemethanol, anthracene, pyrene, perylene, quinone, xanthone, thioxanthone, benzoyl ester, benzophenone, and any combination thereof. Specific examples of photosensitizers include [4-[(4-methylphenyl)thio]phenyl]phenylmethanone, isopropyl-9H-thioxanthen-9-one, 1-pyrenemethanol, 9-(hydroxymethyl)anthracene, 9,10-diethoxyanthracene, 9,10-dimethoxyanthracene, 9,10-dipropoxyanthracene, 9,10-dibutyloxyanthracene, 9-anthracenemethanol acetate, 2-ethyl-9,10-dimethoxyanthracene, 2-methyl-9,10-dimethoxyanthracene, 2-t-butyl-9,10-dimethoxyanthracene, 2-ethyl-9,10-diethoxyanthracene, and 2-methyl-9,10-diethoxyanthracene, anthracene, anthraquinone, 2-methylanthracene, laquinone, 2-ethyl anthraquinone, 2-tert-butyl anthraquinone, 1-chloro anthraquinone, 2-amyl anthraquinone, thioxanthone and xanthone, isopropyl thioxanthone, 2-chloro thioxanthone, 2,4-diethyl thioxanthone, 1-chloro-4-propoxy thioxanthone, methyl benzoyl formate (Darocur MBF from BASF), methyl-2-benzoyl benzoate (Civacure OMB from Cheetech), 4-benzoyl-4'-methyldiphenyl sulfide (Civacure BMS from Cheetech), 4,4'-bis(diethylamino)benzophenone (Civacure EMK from Cheetech), and any combination thereof.

[092] The novel mixtures may also contain various photoinitiators with different sensitivities to emission line radiation of different wavelengths in order to achieve better utilization of the UV light source. The use of known photoinitiators with different sensitivities to emission line radiation is well known in the additive manufacturing art and may be selected according to the radiation sources, for example 351 nm, 355 nm, 365 nm, 385 nm, and 405 nm. In this context, it is advantageous to select various photoinitiators and use them in concentrations that result in equal light absorption at the emission lines used.

およびそれらの任意の組合せである。 [093] In embodiments, the photosensitizer is a fluorone, e.g., 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

and any combination thereof.

[094] When a photosensitizer is utilized, other photoinitiators that absorb at shorter wavelengths can be used. Examples of such photoinitiators include benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, and dimethoxybenzophenone, and 1-hydroxyphenyl ketones such as 1-hydroxycyclohexyl phenyl 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 KIP150 from Lamberti).

[095] It may be noted that some cationic photoinitiators have low absorption at the preferred actinic wavelengths. For example, in embodiments, UV/optics with peak intensity at about 400 nm are utilized in additive manufacturing applications of interest. For example, iodonium salts such as Rhodolsil 2074 available from Rhodia Silicones, Irgacure 250 Iodonium, (4-methylphenyl)[4-(2-methylpropyl)phenyl]hexafluorophosphate(1-) available from Ciba, and UV9380c available from GE Silicones have poor direct absorption at the preferred wavelengths and therefore require excess concentration or require a sensitizer. Thus, triplet sensitizers such as thioxanthone and Michler's ketone may be used to absorb actinic energy and efficiently transfer the energy to the iodonium initiator. However, some thioxanthones and Michler's ketones tend to produce an orange or red color, pose safety concerns, and, although they have significant actinic absorption up to 430 nm, are not very effective at sensitizing the photoreaction at curing light wavelengths of about 400 nm.

[096] However, in embodiments, chloropropylthioxanthone (CPTX) is a preferred sensitizer for iodonium initiators, particularly for use in stereolithography, because it does not have significant light absorption above 500 nm and forms articles with less coloration.

[097] In order to reduce the concentration of sensitizer used in the formulation and to prevent possible adverse effects from relatively high concentrations of sensitizer on the final physical properties of the composition, it is preferable to use a sensitizer with a high extinction coefficient at 400 nm. For example, benzophenone may act as a triplet sensitizer in some cases, but at a laser wavelength of, for example, a frequency tripled YAG laser (Coherent AVIA model #355-1800) operating at about 355 nm, the extinction coefficient is on the order of 108 liters/mole cm. On the other hand, CPTX has an extinction coefficient of approximately X times that of benzophenone, or 2585 liters/mole cm, using the same laser at the same laser wavelength of about 400 nm. This suggests that CPTX may require a concentration of 1/X in the formulation to provide an equivalent light absorption effect. Thus, it is preferred, but not required, that the sensitizer has an extinction coefficient of 300 liters/mole cm or more, for example, greater than 1000 liters/mole cm, and preferably greater than 2000 liters/mole cm, at a curing light wavelength greater than 380 nm.

[098] Although it is taught that CPTX may be used to improve the activity of cationic photoinitiators, the sensitizers used in combination with the cationic photoinitiators described above are not necessarily limited thereto. A variety of compounds can be used as photosensitizers, including heterocyclic and fused ring aromatic hydrocarbons, organic dyes, and aromatic ketones. Examples of sensitizers include those described in J. V. Crivello, Advances in Polymer Science, Vol. 62, No. 1 (1984), and J. V. Crivello and K. and compounds disclosed in "Photoinitiators for Cationic Polymerization" by K. Dietliker, Chemistry & technology of UV & EB formulation for coatings, inks & paints, Vol. III, Photoinitiators for free radical and cationic polymerization by K. Dietliker, [P. K. T. Oldring, ed.], 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-hydroxyalkylphenones, 4-benzoyl-4'-methyldiphenyl sulfide, acridine orange, and benzoflavins.

[099] The radiation curable liquid resin for additive manufacturing may include other cationic photoinitiators or photosensitizers in any suitable amount, for example, in certain embodiments, 0.1-10 wt % of the resin composition, in certain embodiments, about 1 to about 8 wt % of the resin composition, and in further embodiments, about 2 to about 6 wt % of the resin composition. In embodiments, the above ranges are particularly suitable for use with epoxy monomers. In other embodiments, the photosensitizer may be utilized in an amount of about 0.05 wt % to about 2 wt % of the total composition in which it is incorporated.

[Reducing Agent]
[0100] As used herein, a reducing agent refers to a component that loses one or more electrons, i.e., "donates" one or more electrons to a cationic photoinitiator component in a redox chemical reaction upon polymerization of the present invention's liquid radiation-based additive manufacturing compositions. Even if such a component does not have the ability to readily donate an electron until it generates a free radical, i.e., decomposes into a free radical after dissociation, or is otherwise excited upon exposure to UV/vis wavelength actinic radiation, it is still considered a reducing agent for purposes of the present invention. For this reason, it may alternatively be referred to herein as an "activated reducing agent."

[0101] Photoinitiated cationic polymerization of monomers such as epoxides and vinyl ethers plays a necessary role in hybrid-curing additive manufacturing applications. Due to the use of additives in a variety of applications, wavelength flexibility of photoinitiation is a fundamental factor in determining the curing performance of a particular formulation when targeting a specific spectral sensitivity. Photoinitiating systems for cationic polymerization that are sensitive to longer wavelengths, especially those emitted by modern UV/vis optics, are therefore gaining in importance. Many of the existing photoinitiating systems for cationic polymerization are based on the use of onium salts, such as diphenyliodonium salts, triphenylsulfonium salts, and alkoxypyridinium salts. However, these salts do not absorb significantly (if at all) in the UV/vis spectrum unless additional chromophores are incorporated into the salt structure. Therefore, it is important to find alternative ways to synthetically extend the sensitivity range of readily available onium salts to UV/vis wavelengths, especially in light of the fact that commercially available photoinitiators already designed to absorb in the UV/vis spectral range are not suitable for incorporation into hybrid curing systems for additive manufacturing for other reasons.

[0102] As discussed herein, applicants have achieved their objectives at least in part through a mechanism called indirect excitation, utilizing a combination of sensitizers. Besides, onium salts act as electron acceptors in redox reactions using free radicals, electron donor compounds of charge transfer complexes, and long-lived electronic excited states of sensitizers, respectively. Among these methods, the so-called "free radical promoted" cationic polymerization appears to be an additional effective and flexible way to generate cationic species capable of initiating the cationic polymerization of monomers. The overall mechanism involves the oxidation of photochemically formed radicals by onium salts (On+) with suitable reduction potentials.
R・+ON+→R+ (1)

[0103] Reducing agents suitable for promoting free radical promoted cationic polymerization generally include some of the free radical photoinitiators listed above, such as acylphosphine oxides, along with amines, benzoin and its derivatives, o-phthalaldehyde, polysilanes, and compounds having electron donating substituents attached to the vinyl group, such as vinyl ethers and vinyl halides, to name a few.

[0104] Amines are considered to be efficient hydrogen donors and will readily form free radicals that reduce associated cationic photoinitiators via chain transfer mechanisms. Thus, in certain embodiments, they can act as suitable reducing agents. However, care should be taken when including such compounds in hybrid radiation-curable additive manufacturing compositions, as the nitrogen atoms they contain are known to tend to otherwise inhibit cationic polymerization reactions.

[0105] There are several systems that generate oxidizing radicals in the presence of a UV/vis light source. For example, radicals formed by irradiating a system containing a xanthene dye and an aromatic amine can function as reducing agents for diphenyliodonium salts. Similarly, dimanganese decacarbonyl-organohalide combinations are effective reducing agents for cationic polymerization at UV/vis wavelengths when used in combination with onium salts. Additionally, commercially available titanocene-type photoinitiators such as Irgacure 784 can be used as a source of reducing agent generated by irradiation with visible light.

[0106] Acylphosphine oxides and acylphosphanates of various structures have been used as photoinitiators for free radical polymerization. Extensive studies of the photochemistry of acylphosphine oxides have shown that they undergo α-scission with fairly high quantum yields.

[0107] In embodiments, acylphosphine oxides, at least when combined with a second reducing agent having an electron donating substituent attached to the vinyl group, are suitable reducing agents that contribute to promoting cationic polymerization of suitable monomers at UV/vis wavelengths. Cationic polymerization of tetrahydrofuran and butyl vinyl ether can be readily initiated upon irradiation at UV/vis wavelengths in the presence of bisacylphosphine oxides and diphenyliodonium salts. Without wishing to be bound by theory, it is believed that the photoinitiated bisacylphosphine oxides readily abstract hydrogen from a suitable donor (e.g., solvent or monomer) to become a reducing agent when used in conjunction with a cationic photoinitiator. The resulting carbon-centered radical is converted to a carbocation by reaction with PhI+ ions to initiate cationic polymerization. As disclosed herein, it has been found that acylphosphine oxides, more preferably substituted acylphosphine oxides, when combined with suitable onium salts, such as iodonium and pyridinium salts, are efficient and effective reducing agents for promoting free cationic polymerization at UV/vis curing wavelengths. The proposed initiation mechanism appears to involve the photogeneration of phosphinoyl and benzoyl radicals in the first step. The phosphinoyl radical is then oxidized by an onium salt to produce a phosphonium ion capable of initiating polymerization of the monomer. The efficiency of the latter step should be controlled by the redox potential of the onium salt and the electron delocalization (p character) of the phosphinoyl radical. Thus, one embodiment of the present invention is to maximize the redox potential between the onium salt and the acylphosphine oxide free radical photoinitiator while simultaneously searching for an acylphosphine oxide with maximum electron delocalization (p character) so that the effect of this mechanism is maximized at 400 nm wavelength light and maximum cationic cure speed is achieved.

により表される。上記式中、Ａｒ_１は、置換または非置換の芳香族基であり、Ｒ_１は、Ａｒ_１、Ｃ_２～Ｃ_２０脂肪族鎖、またはＣ_２～Ｃ_２０アルキル鎖であり、かつＲ_２は、Ｒ_１であるかまたは１個以上の置換もしくは非置換のアシルフェニル基を含有する。 [0108] In embodiments, the reducing agent for reducing the cationic photoinitiator is represented by the following formula IV:

In the above formula, Ar ₁ is a substituted or unsubstituted aromatic group, R ₁ is Ar ₁ , a C ₂ -C ₂₀ aliphatic chain, or a C ₂ -C ₂₀ alkyl chain, and R ₂ is R ₁ or contains one or more substituted or unsubstituted acylphenyl groups.

[0109] The liquid radiation curable resin for additive manufacturing may include a reducing agent for reducing the cationic photoinitiator, for example, in certain embodiments, in an amount of 0.01 to 30 wt %, in other preferred embodiments, in an amount of 0.01 to 10 wt % of the resin composition, in other certain embodiments, about 1 to about 8 wt % of the resin composition, and in further embodiments, about 2 to about 6 wt % of the resin composition. In embodiments, the above ranges are particularly suitable when an iodonium salt photoinitiator is used in combination. In embodiments, the same reducing agent component may function simultaneously as a free radical photoinitiator and a reducing agent, thereby promoting both free radical and cationic polymerizations simultaneously. In other embodiments, the reducing agent may be utilized in an amount of about 0.05 wt % to about 4 wt % of the total composition in which it is incorporated.

[Reducing Agents Having Electron-Donating Substituents Attached to Vinyl Groups]
[0110] The inclusion of an additional component having an electron donating substituent attached to the vinyl group can further provide a mechanism for improving the cationic curing of liquid radiation curable compositions for additive modeling systems utilizing UV/vis optics. Such compounds, such as vinyl ethers, are avoided in many modern commercial hybrid curable compositions for additive modeling systems utilizing traditional UV-based radiation sources because of their (1) tendency to generate excess heat due to rapid polymerization exothermic reactions, and (2) tendency to result in copolymerization and concomitant non-uniform polymers to produce three-dimensional parts with inconsistent and poor physical properties. Nevertheless, the inventors have surprisingly found that their incorporation into compositions tailored to systems utilizing UV/vis optics with lower energy/intensity becomes desirable when combined with other necessary components according to the present invention. Specifically, the inventors have further found that the inclusion of an additional component having an electron donating substituent attached to the vinyl group surprisingly improves polymerization synergistically with the presence of components that induce other reaction mechanisms cited herein (i.e., indirect excitation and free radical promoted cationic polymerization).

[0111] A preferred example of a component having an electron donating substituent attached to the vinyl group is a vinyl ether. Vinyl ethers can be produced from a variety of starting materials, such as ethers, esters, or biscarbamates, or vinyl ether terminated (poly)urethanes or carbonates. Some non-limiting examples of each include:

[0112] Vinyl ether monomers from ethers: 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, hexanediol divinyl ether, cyclohexanediol divinyl ether, bisphenol A alkylene oxide divinyl ether, and bisphenol F alkylene oxide divinyl ether, as well as polyfunctional vinyl ethers, such as trimethylolethane trivinyl ether, trimethylolpropane trivinyl ether, ditrimethylolpropane trivinyl ether, divinyloxyethyl ... Examples of the vinyl ether include ethylene oxide adduct of trimethylolpropane trivinyl ether, glycerol trivinyl ether, pentaerythritol tetravinyl ether, pentaerythritol divinyl ether, dipentaerythritol pentavinyl ether, dipentaerythritol hexavinyl ether, ethylene oxide adduct of trimethylolpropane trivinyl ether, propylene oxide adduct of trimethylolpropane trivinyl ether, ethylene oxide adduct of ditrimethylolpropane tetravinyl ether, propylene oxide adduct of ditrimethylolpropane tetravinyl ether, ethylene oxide adduct of pentaerythritol tetravinyl ether, propylene oxide adduct of pentaerythritol tetravinyl ether, ethylene oxide adduct of dipentaerythritol hexavinyl ether, and propylene oxide adduct of dipentaerythritol hexavinyl ether.

[0113] Vinyl ether monomers from esters or biscarbamates: Specific examples of polyfunctional vinyl ethers such as divinyl adipate, divinyl terephthalate, divinylcyclohexyl dicarboxylate. Bis[4-(vinyloxy)butyl]adipate (Vectomer® 4060), bis[4-(vinyloxy)butyl]succinate (Vectomer® 4030), bis[4-(vinyloxy)butyl]isophthalate (Vectomer® 4010), bis[4-(vinyloxymethyl)cyclohexylmethyl]glutarate (Vectomer® 4020), tris[4-(vinyloxy)butyl] Trimellitate (Vectomer® 5015), bis[4-(vinyloxymethyl)cyclohexylmethyl]isophthalate (Vectomer® 4040), bis[4-(vinyloxy)butyl](4-methyl-1,3-phenylene)biscarbamate (Vectomer® 4220), and bis[4-(vinyloxy)butyl](methylenedi-4,1-phenylene)biscarbamate (Vectomer® 4210).

[0114] Vinyl ether-terminated urethane or carbonate: Specific examples of polyfunctional vinyl ethers such as polyurethanes and polycarbonates end-capped with hydroxyvinyl ethers having at least a hydroxyl group and at least a 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-cyclohexanedimethanol monovinyl ether, 1,2-cyclohexanediol monovinyl ether, Methanol 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, and derivatives thereof, such as pentapropylene glycol monovinyl ether, oligopropylene glycol monovinyl ether, and polypropylene glycol monovinyl ether.

[0115] In preferred embodiments, the component having an electron donating substituent attached to the vinyl group is one or more of the following: vinyl ether, vinyl ester, vinyl thioether, n-vinyl carbazole, n-vinyl pyrrolidone, n-vinyl caprolactam, allyl ether, and vinyl carbonate.

[0116] In another preferred embodiment, the component having an electron donating substituent attached to the vinyl group is polyfunctional.

[0117] Any suitable amount of one or more of the above listed components having an electron donating substituent attached to the vinyl group can be used in the compositions of the present invention and may be selected alone or in combination of one or more of the types listed herein. In a preferred embodiment, the component having an electron donating substituent attached to the vinyl group is present in an amount of about 1 wt. % to about 25 wt. %, more preferably about 5 wt. % to about 20 wt. %, more preferably about 5 wt. % to about 12 wt. %, based on the total weight of the composition. In another embodiment, the component having an electron donating substituent attached to the vinyl group is present in an amount of 1 wt. % to 15 wt. %, more preferably 1 wt. % to 10 wt. %, more preferably 3 wt. % to about 8 wt. %.

[Other ingredients]
[0118] To further prevent viscosity increase, e.g., during use in solid imaging processes, stabilizers are often added to the resin composition. Useful stabilizers include those described in U.S. Pat. No. 5,665,792. The presence of a stabilizer is optional. In a specific embodiment, the radiation curable liquid resin composition for additive manufacturing comprises 0.1 wt % to 3 wt % of a stabilizer.

[0119] Other useful additives include organic and inorganic fillers, dyes, pigments, antioxidants, wetting agents, foam disintegrators, chain transfer agents, leveling agents, defoamers, surfactants, and the like. Such additives are known and are generally available as desired for a particular application, as would be understood by one of ordinary skill in the art.

[0120] The liquid radiation-curable resin composition for additive manufacturing of the present invention may further contain one or more additives selected from the group consisting of a bubble disintegrator, an antioxidant, a surfactant, an acid scavenger, a pigment, a dye, a thickener, a flame retardant, a silane coupling agent, an ultraviolet absorber, a resin particle, a core-shell particle impact modifier, a soluble polymer, and a block polymer.

[0121] Additionally, many of the known liquid radiation curable resin compositions for additive manufacturing use hydroxy-functional compounds to improve the properties of parts made from the resin composition. Any hydroxy group, if present, may be used for a specific purpose. If present, the hydroxyl-containing material preferably contains one or more primary or secondary aliphatic hydroxyls. The hydroxyl groups may be internal or terminal. Monomers, oligomers, or polymers may be used. The hydroxyl equivalent weight, i.e., the number average molecular weight divided by the number of hydroxyl groups, is preferably in the range of 31 to 5000. If present, the resin composition preferably contains at most 10 wt %, more preferably at most 5 wt %, and most preferably at most 2 wt %, of one or more non-free-radically polymerizable hydroxy-functional compounds, based on the total weight of the resin composition.

[ratio]
[0122] Surprisingly, the inventors have found that compositions according to the present invention can be specifically optimized for curing by certain additive manufacturing processes utilizing UV/vis optics by controlling the ratios of the various necessary components relative to one another. In a preferred embodiment, the weight ratio of iodonium salt cationic photoinitiator, photosensitizer, first reducing agent, and second reducing agent having an electron donating substituent attached to a vinyl group is about 2:2:1:2 to about 20:1:5:25, more preferably about 10:1:2:12. If the amount of iodonium salt cationic photoinitiator is too high, the radiation absorption becomes too significant and interferes with the ability to cure to a sufficient depth of the layer. If it is too low relative to the other components, cationic curing is initiated but not to the level required to produce a three-dimensional part with adequate green strength. The amount of photosensitizer should generally not exceed the amount of iodonium salt cationic photoinitiator, but should be present in an amount sufficient to allow indirect excitation of said cationic photoinitiator. The reducing agent should also generally not exceed the amount of cationic photoinitiator being reduced, but should likewise be present in an amount sufficient to promote free radical promoted cationic polymerization. Finally, the component having an electron donating substituent attached to the vinyl group can be present in a maximum amount by weight compared to the other components listed above to fully enable additional cationic polymerization mechanisms, but should not be present in a disproportionately large amount as this may accelerate the cure, resulting in uncontrolled exothermic reactions and excessive heat generation.

[0123] In other embodiments, the ratio of iodonium salt cationic photoinitiator to photosensitizer is from 1:3 to 10:1. In embodiments, the ratio of iodonium salt cationic photoinitiator to reducing agent is from 1:5 to 10:1.

（式中、ＲはＣ_１～Ｃ_２０脂肪族鎖を含有する）
で示される約０．５ｗｔ．％～約３ｗｔ．％の化合物と、
（ｄ）フリーラジカル重合性成分と、
（ｅ）ジフェニル（２，４，６－トリメチルベンゾイル）ホスフィンオキシドフリーラジカル光開始剤と、
を含み、
２０ｍＪ／ｃｍ^２の線量を与えるかつピークスペクトル強度で約３７５ｎｍ～約５００ｎｍ、より好ましくは約３８０ｎｍ～約４５０ｎｍ、より好ましくは約３９０ｎｍ～約４２５ｎｍの放射線を放出するＵＶ／ｖｉｓ光学素子により硬化可能である、
付加造形用液状放射線硬化性組成物である。 [0124] A third aspect of the claimed invention comprises:
(a) about 30 wt. % to about 80 wt. % of at least one cationically polymerizable component further comprising a cycloaliphatic epoxide and an oxetane;
(b) about 1 wt. % to about 8 wt. % of a sulfonium salt cationic photoinitiator having an absorbance of less than 0.01 at 400 nm;
(c) a compound of formula (V):

where R contains a _C1 - _C20 aliphatic chain.
About 0.5 wt. % to about 3 wt. % of a compound represented by
(d) a free radically polymerizable component; and
(e) diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide free radical photoinitiator; and
Including,
curable by UV/vis optics providing a dose of 20 mJ/ ^cm2 and emitting radiation with a peak spectral intensity between about 375 nm and about 500 nm, more preferably between about 380 nm and about 450 nm, more preferably between about 390 nm and about 425 nm;
A liquid radiation curable composition for additive manufacturing.

[0125] According to another aspect of the invention, the cationic photoinitiator used in formulating the liquid radiation curable composition for additive manufacturing that is curable by UV/vis optics is a sulfonium salt. The above description of the sulfonium salt cationic photoinitiator according to the first aspect of the claimed invention is equally suitable for use in this third aspect of the claimed invention. In a preferred embodiment of the third aspect of the invention, the cationic photoinitiator is a triarylsulfonium salt. In a preferred embodiment, the (triaryl)sulfonium salt cationic photoinitiator has a very low direct absorbance at UV/vis wavelengths in practice. In an embodiment, the (triaryl)sulfonium salt photoinitiator used has an absorbance at 400 nm of less than 0.05, more preferably less than 0.01, more preferably less than 0.005, and most preferably less than 0.001. As described, applicants have surprisingly found that indirect excitation of cationic photoinitiators is a preferred mechanism for initiating cationic polymerization of liquid radiation-curable compositions for additive manufacturing using UV/vis optics, as compared to direct excitation of cationic photoinitiators that have significant absorbance at 400 nm.

で示されるカチオンを有するトリアリールスルホニウム塩である。 [0126] In embodiments, the sulfonium salt cationic photoinitiator has the following structure:

It is a triarylsulfonium salt having a cation represented by the formula:

[0127] In embodiments, the triarylsulfonium salt further has a hexafluoroantimonate or hexafluorophosphate counterion.

[0128] In embodiments, the sulfonium salt cationic photoinitiator is present in the composition in any suitable amount, from 0.01 wt % to 15 wt %, in other embodiments from 1 wt % to 8 wt %, and in other embodiments from 2 wt % to 5 wt %.

[0129] Additionally, the cationically polymerizable and free radically polymerizable components of the first and second aspects of the invention are similarly suitable for use in the claimed third aspect of the invention.

[0130] The liquid radiation curable composition for additive manufacturing according to the third aspect of the invention also contains a free radical photoinitiator. The description of the free radical photoinitiator according to the first and second aspects of the invention is generally suitable for use in the claimed third aspect of the invention as well. However, in a preferred embodiment, the free radical photoinitiator comprises diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide. Furthermore, the inventors have surprisingly found that in an embodiment, the free radical photoinitiator component can produce improved curability in combination with a sulfonium salt cationic photoinitiator when the free radical photoinitiator component has less than 50% of compounds containing two or more carboxyl groups, preferably less than 33% of compounds containing two or more carboxyl groups, based on the total amount of free radical photoinitiator present in the composition.

（式中、ＲはＣ_１～Ｃ_２０脂肪族鎖を含有する）
で示される構造を有する。 [0131] The liquid radiation curable composition for additive manufacturing according to the third aspect of the present invention also contains a photosensitizer. In embodiments, the photosensitizer may generally be selected according to the description of the photosensitizer according to the second aspect of the present invention. In a preferred embodiment, the photosensitizer utilized has the following formula (V):

where R contains a _C1 - _C20 aliphatic chain.
It has the structure shown below.

[0132] In a preferred embodiment of the third aspect of the invention, the photosensitizer utilized is an anthracene-based photoinitiator. Commercially available products of such photosensitizers include Anthracure™ UVS-1101 and UVS-1331 available from Kawasaki Chemical.

[0133] The photosensitizer is present in any suitable amount from about 0.5 wt. % to about 10 wt. %, more preferably from 0.5 wt. % to 3 wt. %.

[0134] A fourth aspect of the claimed invention is a method of forming a three-dimensional article with an additive fabrication system utilizing UV/vis optics, comprising:
(1) providing a liquid radiation curable composition for additive manufacturing according to the first, second or third aspect of the present invention;
(2) providing a first liquid layer of a liquid radiation curable resin;
(3) forming a first cured layer by imagewise exposing the first liquid layer to actinic radiation using a UV/vis optical configuration to form an imaged cross-section;
(4) forming a new layer of liquid radiation curable resin in contact with the first cured layer;
(5) imagewise exposing the new layer to actinic radiation to form additional imageable cross-sections;
(6) repeating steps (4) and (5) a sufficient number of times to build a three-dimensional article; and
Including,
the UV/vis optics emit radiation with a peak spectral intensity between about 375 nm and about 500 nm, more preferably between about 380 nm and about 450 nm, more preferably between about 390 nm and about 425 nm, more preferably between about 395 nm and about 410 nm;
This is the method.

[0135] The liquid radiation curable composition provided in the above-mentioned aspects of the invention should be suitable for curing by an additive manufacturing system utilizing UV/vis optics. Such compositions are particularly described in the first, second, and third aspects of the invention. When providing the first liquid layer or forming a new layer of liquid radiation curable resin, the layer can be of any suitable thickness and shape and will depend on the additive manufacturing process being utilized. For example, it can be selectively dispensed by jetting or can be added by dipping an already cured layer into a vat of resin to produce a layer of substantially uniform thickness, as is common in most stereolithography processes. In other non-limiting embodiments, a cartridge or dispenser can be used to alternatively transfer a predetermined thickness through a foil, film, or carrier.

[0136] In the above, "exposure" means exposure to actinic radiation. As stated above, the liquid radiation compositions for additive manufacturing of the present invention described herein are particularly suitable for applying hybrid cure via UV/vis optics. In an embodiment, the UV/vis optics utilizes one or more LEDs as a light source. In an embodiment, the light source is a laser. In an embodiment, the LED or laser light source is coupled to a DLP or LCD image projection system. In an embodiment where the image projection system includes an LCD display, the light source may be configured to emit actinic radiation exclusively above 400 nm to minimize the deleterious effects of UV wavelengths on the LCD components.

[0137] A fifth aspect of the claimed invention is a three-dimensional part formed according to the fourth aspect of the invention using a liquid radiation curable composition of the first, second, or third aspect of the invention.

[0138] The following examples further illustrate the present invention but, of course, should not be construed as in any way limiting its scope.

[Example]
[0139] These examples illustrate embodiments of the radiation curable liquid resin for additive manufacturing of the present invention. Table 1 lists the various components of the radiation curable liquid resin for additive manufacturing used in the examples of the present invention.

[Test Method]
[0140] Real-time Fourier transform infrared (FTIR) spectroscopy was used to measure the polymerization rate (cure speed) of each example. A mercury cadmium telluride (MCT) detector was used to increase the data acquisition frequency and thus the resolution. An attenuated total reflectance (ATR) configuration was used instead of transmission mode. All polymerization rate measurements were performed using a Thermo Scientific Nicolet 8700 model. The experimental condition settings for the measurements are shown in the table below. Under these conditions, a total of 41 spectra were obtained for each measurement in 200 seconds.

[0141] For UV/Vis light control, Digital Light Lab LED spot lamps (365 nm, 395 nm, and 400 nm) and a controller (AccuCure Photo Rheometer) were used. Calibrated continuous mode was selected. Light intensity and duration (exposure time) were selected before measurements.

[0142] For the measurement, a few drops of the selected sample were placed in the center of the ATR crystal setup. A 3 mil (±0.4 mil) drawdown bird bar was then used to coat approximately a 3 mil film (±0.4 mil) on the ATR crystal. Immediately after application of the 3 mil coating, an LED lamp was held above the ATR setup and positioned in the hole in the center of the holder. A real-time FTIR scan was then started. After acquiring one spectrum, the light source was turned on to start the polymerization. Based on the above program inputs, each spectrum was acquired every 5 seconds for a total of 200 seconds. A total of 41 spectra were acquired for each experiment.

[0143] Polymerization conversion versus time was calculated based on the specific IR peak changes representing each functional group. Examples of IR peak changes are shown in the images above. To calculate the conversion of each relevant functional group, the peak height or peak area was calculated according to the following table, as appropriate.

[0144] When using the raw data obtained, it was important to remove the first one or two data points because the experimental cure speed procedure has an unknown short time lag between the turn-on of the FTIR detector and the turn-on of the light source used to cure the sample. To compensate for any uncertainty associated with the amount of statistical noise generated by these preliminary data points, three curve fits were generated for each data set. In each case, the model equation used to fit the data sets was Conv=a(1-e(-b*(time-c))). For this purpose, the raw data was fitted using Microsoft Excel version 14.0.7116.5000 (32-bit) with the Data Analysis add-on.

[0145] In the first case, the entire data set (including the first two data points) was fitted. In the second case, the entire data set was fitted minus the first data point. In the third case, the entire data set was fitted minus the first and second data points. In both cases, a curve fit coefficient ^r2 was generated. Data sets with a first data point with a conversion rate greater than 1% and whose combined curve fit yielded an ^r2 greater than 0.90 were selected for use, and the resulting curve fit equation was used for further calculation of the cure speed at 95% of the plateau conversion. If the curve fit coefficient ^r2 was less than 0.90, the data was rerun again.

[0146] As discussed above, the data was fitted to an equation of the form Conv = a(1 - e(-b * (time - c))), where "Conv" is the % conversion measured by FTIR peak ratio, time is the duration of exposure, "a" is the plateau conversion, "b" is the derived cure speed factor used to calculate cure speed, and "c" is the derived cure induction time. After fitting the data, the software created an empirically derived equation with the numerical parameters "a", "b", and "c" determined from the experimental data and the fit. For cationically curable materials (i.e., epoxies and oxetanes), "c" has no meaning since there is no cure induction time. Therefore, in such cases, "c" was ignored. The variable "a" was used as the plateau conversion under the cure conditions used, and represents the overall asymptotic range to which the components were converted. The variable "b" was used to calculate the time to 95% plateau conversion ( _T95 ) of "a" by the formula _T95 = ln(.05/b). _T95 is listed in Tables 2, 3, and 4 as appropriate (and if available).

[Examples 1 to 8]
[0147] First, an additive modeling base resin 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 known in the art.

[0148] Irgacure PAG 103 (used in Comparative Example 1) and Irgacure PAG 121 (used in Comparative Example 2) are available from BASF and are specifically promoted as non-ionic cationic photoacid photoinitiators for cationically curable resins with significant absorbance in the UV/vis spectrum. CPI 400 (used in Comparative Example 3) is a cationic photoinitiator available from Sun-Apro with significant absorbance at 400 nm. The three above-listed cationic photoinitiators would be expected to be suitable candidates for possible incorporation into liquid hybrid radiation curable compositions for additive manufacturing systems utilizing UV/vis optics.

[0149] The _T95 and plateau conversion of the cycloaliphatic epoxy component are calculated as described in the Test Methods section above.

[0150] Comparative Example 4 utilizes a photoinitiation package shown to be suitable for curing at a wavelength of 365 nm. It is therefore useful for benchmarking against the inventive examples provided in Table 3 using the same base resin.

[Discussion of results]
[0151] Table 1 is the base resin used for most of the formulations in Tables 2, 3, and 4.

[0152] In Table 2, known commercial techniques used for 365 nm cure applications are used to establish acceptable levels of performance using the RT-FTIR methods described herein. These test results will be used to benchmark the results in Tables 3 and 4 to establish acceptance criteria.

[0153] In Table 3, cationic photoinitiators are used that are known to absorb in the UV/vis spectral range and are expected to be suitable for incorporation into liquid hybrid radiation curable compositions for additive modeling systems with a direct excitation mechanism utilizing UV/vis optics. However, as can be seen, none of these alternative methods approach the cure performance of the benchmark in Table 2 made at 365 nm. Three different photoinitiators were identified by their suppliers as useful for curing at wavelengths of about 405 nm. Of all three tested, only CPI-400 showed some measurable cure activity. The data generated from this experiment was entered into the curve fitting software described in the Test Methods section above, but the ^r2 values never achieved acceptable levels as the data was statistically so insignificant in the tests. Thus, while not statistically significant to demonstrate actual _T95 and plateau conversion, the data in Table 3 and Figures 3 and 4 are nevertheless instructive in showing how poorly such photoinitiators perform utilizing a direct excitation mechanism.

[0154] Table 4 shows tests based on the inventive concepts discussed herein as cured at 400 nm (at the listed intensities and durations). As can be seen, the examples all achieve results that are comparable to and even better than the 365 nm acceptance criteria established in Table 2. A shorter time to reach 95% of the plateau, _T95 , is desirable, while a higher plateau conversion is desirable.

[0155] Unless otherwise specified, the term wt. % refers to the amount by weight of a particular component incorporated relative to the total radiation-curable liquid composition for additive manufacturing.

[0156] The use of the terms "a," "an," and "the" and similar reference words in connection with the description of the present invention (particularly in connection with the claims which follow) should be construed to encompass both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms "comprising," "having," "including," and "containing" should be construed as open-ended terms (i.e., meaning "including, but not limited to") unless otherwise noted. The recitation of ranges of values herein is intended to serve as a shorthand notation for individually referring to each individual value falling within the range, unless otherwise specified herein, and each individual value is incorporated herein as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise specified herein or otherwise clearly contradicted by context. The use of any examples or exemplary language provided herein (e.g., "such as") is intended merely to facilitate a better understanding of the invention and does not impose limitations on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[0157] Preferred embodiments of the invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of such preferred embodiments will become apparent to those of skill in the art upon reading the foregoing description. The inventors anticipate that such variations will be utilized by those of skill in the art as appropriate, and it is the intention of the inventors that the invention be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the present invention unless otherwise indicated herein or otherwise clearly contradicted by context.

[0158] Although the present invention has been described in detail with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention as claimed.

Claims (10)

(a) 30 to 80% by weight of a cationically polymerizable component;
(b) an iodonium salt cationic photoinitiator; and
(c) 0.05 to 6 weight percent of a photosensitizer for photosensitizing component (b);
(d) a reducing agent for reducing component (b), the reducing agent comprising a vinyl ether monomer produced from an ether as a starting material ;
(e) 8 to 25 weight percent of a free radically polymerizable component;
optionally (f) a free radical photoinitiator;
Including,
A liquid radiation curable composition for additive manufacturing that is curable with UV/vis optics providing a dose of 20 mJ/ ^cm2 and emitting radiation between 375 nm and 500 nm with a peak spectral intensity. The liquid radiation-curable composition for additive manufacturing of claim 1, wherein component (d) further comprises a free radical photoinitiator configured to reduce component (b) upon exposure to UV/vis wavelength actinic radiation to generate free radicals upon dissociation. The liquid radiation-curable composition for additive manufacturing according to claim 1 or 2, wherein component (a) additionally comprises a glycidyl ether epoxy selected from the group consisting of bisphenol A-based glycidyl ethers, bisphenol S-based glycidyl ethers, and bisphenol F-based glycidyl ethers. The liquid radiation-curable composition for additive manufacturing according to any one of claims 1 to 3, wherein component (b) is a diphenyliodonium salt. 5. The radiation curable liquid composition for additive manufacturing of claim 4, wherein the diphenyliodonium salt is selected from the group consisting of (4-methylphenyl)[4-(2-methylpropyl)phenyl] iodonium hexafluorophosphate , [4-(1-methylethyl)phenyl](4-methylphenyl)iodonium tetrakis(pentafluorophenyl)borate(1-), (bis(4-dodecylphenyl)iodonium hexafluoroantimonate), and (bis(4-tert-butylphenyl)iodonium hexafluorophosphate). The liquid radiation-curable composition for additive manufacturing according to any one of claims 1 to 5, wherein component (c) is thioxanthone. The liquid radiation-curable composition for additive manufacturing according to claim 6, wherein the thioxanthone is further selected from the group consisting of chloropropoxythioxanthone and isopropylthioxanthone. The free radical photoinitiator has the following formula (IV):

where Ar ₁ is a substituted or unsubstituted aromatic group, R ₁ is Ar ₁ or a C ₂ -C ₂₀ aliphatic chain, and R ₂ is R ₁ or contains one or more substituted or unsubstituted acylphenyl groups.
The liquid radiation curable composition for additive manufacturing according to any one of claims 2 to 7, wherein The liquid radiation-curable composition for additive manufacturing according to any one of claims 1 to 8, wherein component (f) is not optional and is hydroxycyclohexyl phenyl ketone. 10. The radiation curable liquid composition for additive manufacturing according to any one of claims 1 to 9, wherein the vinyl ether monomer is a multifunctional vinyl ether monomer.

Images