WO2018119067A1 - Photopolymer ceramic dispersion - Google Patents

Photopolymer ceramic dispersion Download PDF

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Publication number
WO2018119067A1
WO2018119067A1 PCT/US2017/067583 US2017067583W WO2018119067A1 WO 2018119067 A1 WO2018119067 A1 WO 2018119067A1 US 2017067583 W US2017067583 W US 2017067583W WO 2018119067 A1 WO2018119067 A1 WO 2018119067A1
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dispersion
acrylate
group
meth
core particles
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PCT/US2017/067583
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French (fr)
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Kris Schmidt
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Basf Se
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/14—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on silica
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/10—Processes of additive manufacturing
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
    • C—CHEMISTRY; METALLURGY
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    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
    • C04B35/111—Fine ceramics
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/48—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on zirconium or hafnium oxides, zirconates, zircon or hafnates
    • C04B35/481—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on zirconium or hafnium oxides, zirconates, zircon or hafnates containing silicon, e.g. zircon
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/48—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on zirconium or hafnium oxides, zirconates, zircon or hafnates
    • C04B35/486—Fine ceramics
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/0037—Production of three-dimensional images
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/004—Photosensitive materials
    • G03F7/0047—Photosensitive materials characterised by additives for obtaining a metallic or ceramic pattern, e.g. by firing
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/004—Photosensitive materials
    • G03F7/027—Non-macromolecular photopolymerisable compounds having carbon-to-carbon double bonds, e.g. ethylenic compounds
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/004—Photosensitive materials
    • G03F7/038—Macromolecular compounds which are rendered insoluble or differentially wettable
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28B1/00—Producing shaped prefabricated articles from the material
    • B28B1/001—Rapid manufacturing of 3D objects by additive depositing, agglomerating or laminating of material
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/48—Organic compounds becoming part of a ceramic after heat treatment, e.g. carbonising phenol resins
    • C04B2235/483—Si-containing organic compounds, e.g. silicone resins, (poly)silanes, (poly)siloxanes or (poly)silazanes
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
    • C04B2235/54—Particle size related information
    • C04B2235/5418—Particle size related information expressed by the size of the particles or aggregates thereof
    • C04B2235/5436—Particle size related information expressed by the size of the particles or aggregates thereof micrometer sized, i.e. from 1 to 100 micron
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/60—Aspects relating to the preparation, properties or mechanical treatment of green bodies or pre-forms
    • C04B2235/602—Making the green bodies or pre-forms by moulding
    • C04B2235/6026—Computer aided shaping, e.g. rapid prototyping

Definitions

  • This disclosure generally relates to a photopolymer ceramic dispersion for additive fabrication. More specifically, the dispersion includes core particles and a surface treatment disposed on the core particles, wherein the core particles are microparticles and includes 5 weight percent or less of nanoparticles having a particle size of from 10 nanometers to 999 nanometers.
  • Additive fabrication processes for producing three dimensional objects are well known. Additive fabrication processes utilize computer-aided design (CAD) data of an object to build three-dimensional parts. These three-dimensional parts may be formed from liquid resins, powders, or other materials.
  • CAD computer-aided design
  • CAD data of an object is transformed into thin cross- sections of a three-dimensional object.
  • the data is loaded into a computer which controls a laser that traces a pattern of a cross section through a dispersion composition in a vat, solidifying a thin layer of the resin composition corresponding to the cross section.
  • the solidified layer is recoated with the resin composition and the laser traces another cross section to harden another layer of the resin composition on top of the previous layer.
  • the process is repeated layer by layer until the three-dimensional object is completed.
  • the three-dimensional object is, in general, not fully cured, and is called a "green model.” This process is also known as three-dimensional (3D) printing.
  • lasers used in stereolithography traditionally ranging from 193 nm to 355 nm in wavelength, although other wavelength variants exist.
  • the use of gas lasers to cure dispersion compositions is well known.
  • the delivery of laser energy in a stereolithography system can be Continuous Wave (CW) or Q-switched pulses.
  • CW lasers provide continuous laser energy and can be used in a high speed scanning process.
  • output power is limited which reduces the amount of curing that occurs during object creation.
  • Other methods of additive fabrication utilize lamps or light emitting diodes (LEDs). LEDs are semiconductor devices which utilize the phenomenon of electroluminescence to generate light.
  • LED UV light sources currently emit light at wavelengths between 300 and 475 nm, with 365 nm, 390 nm, 395 nm, 405 nm, and 415 nm being common peak spectral outputs.
  • Many additive fabrication applications require the green model to possess high mechanical strength (e.g. modulus of elasticity, fracture strength, etc.). This property, often referred to as "green strength,” is typically determined by the dispersion composition.
  • Some compositions include silica, e.g. to increase the heat deflection temperature and modulus or to make ceramic parts.
  • compositions tend to have (1) a high initial viscosity, (2) a poor viscosity stability, and (3) a tendency to phase separate, resulting in phenomena known as either "soft pack” or “hard pack,” and (4) high cure shrinkage resulting in distortion of the printed part.
  • compositions tend to phase separate over time when stored.
  • the silica may collect in the bottom of a storage container resulting in a phase separated composition.
  • the top part of the composition maybe a low- viscosity, largely unfilled portion, i.e., a portion that does not include sufficient loadings of the silica.
  • the bottom part maybe supersaturated with silica and high- viscosity.
  • the composition in the top portion cannot be used to produce green models with sufficient strength and stiffness and any resulting part will suffer high shrinkage and cracking during binder burnout and sintering due to the depletion of silica.
  • composition in the bottom part cannot be used because it is too viscous and has a concentration of silica that makes the final part unusable. Therefore, entire containers can become unusable or, at a minimum, must undergo further expensive and time consuming processing to be able to be used.
  • the silica settles at the bottom of the storage container and forms a soft pack.
  • the settled silica may be surrounded by partially polymerized resin, resulting in a wax-like consistency.
  • re-assimilation into a useable composition is possible, such a process requires frequent and often vigorous recirculation. This is a time- and energy- consuming maintenance process, and still does not obviate the composition's problematic viscosity.
  • the silica settles at the bottom of the storage container and forms a hard pack.
  • the silica forms very hard, rock-like structures. Such structures must be broken up by a drill or similar apparatus before re-assimilation is possible. Again, this is very time and energy intensive. Accordingly, there remains an opportunity for improvement.
  • Figure 1 is an infrared absorption spectra before and 30 min after UV exposure (350- 380 nm) for 4s with 540 mW/cm 2 for compositions of the Examples.
  • Figure 2 is a graph of typical conversion curves as a function of time for acrylate, oxetane, and epoxy compounds.
  • This disclosure provides a photopolymer ceramic dispersion for additive fabrication.
  • the dispersion includes a cationically polymerizable aliphatic epoxide, a cationically polymerizable oxetane, a free-radical polymerizable multifunctional (meth)acrylate, a cationic photo initiator, a free-radical photoinitiator, and a coated filler including core particles and a surface treatment disposed on the core particles.
  • the core particles include silica, alumina, zircon, or combinations thereof.
  • the surface treatment includes an organosilane.
  • the core particles are microparticles having a particle size of from 1 micrometer to 90 micrometers and wherein the core particles comprise 5 weight percent or less of nanoparticles having a particle size of from 10 nanometers to 999 nanometers.
  • This disclosure also provides a method of forming a ceramic article from the photopolymer ceramic dispersion.
  • the method includes the steps of applying a layer of the ceramic dispersion to a surface and selectively exposing the layer imagewise to actinic radiation to form an imaged cross-section.
  • the method also includes the steps of applying a second layer of the ceramic dispersion to the imaged cross-section and selectively exposing the second layer imagewise to actinic radiation to form a second imaged cross-section.
  • the method further includes the steps of repeating steps (C) and (D) to create a three-dimensional green ceramic article; and sintering the three-dimensional green ceramic article in a furnace to form the ceramic article.
  • This disclosure provides a photopolymer ceramic dispersion for additive fabrication, hereinafter described as a "dispersion.”
  • additive fabrication describes building parts in layers, as is well known in the art and as is described above.
  • photopolymer describes that the dispersion includes a free-radical initiator (e.g. a photoinitiator).
  • ceramic describes that the dispersion is used to form ceramic articles, also described in greater detail below.
  • dispensersion describes a composition that includes a continuous phase and a dispersed phase that is dispersed in the continuous phase.
  • the dispersion includes one or more cationicallypolymerizable compounds, one or more radically polymerizable compounds, one or more cationic photoinitiators, one or more free-radical photoinitiators, and one or more coated fillers.
  • the dispersion includes a cationicallypolymerizable aliphatic epoxide, a cationicallypolymerizable oxetane, a free-radical polymerizable multifunctional
  • (meth)acrylate (meth)acrylate, a cationic photoinitiator, a free-radical photoinitiator, and a coated filler, each of which is described in detail below.
  • the dispersion is, consists essentially of, or consists of, the one or more cationicallypolymerizable compounds, the one or more radically polymerizable compounds, the cationic photoinitiator, the free-radical photoinitiator, and the coated filler.
  • the dispersion is, consists essentially of, or consists of, the cationically polymerizable aliphatic epoxide, the cationicallypolymerizable oxetane, the free-radical polymerizable multifunctional (meth)acrylate, the cationic photoinitiator, the free-radical photoinitiator, and the coated filler.
  • the dispersion may be free of compounds that are not cationically polymerizable compounds (other than any required compounds of this disclosure which may or may not be cationically polymerizable), compounds that are not free radically curable, UV curable monomers that are not free-radical polymerizable multifunctional (meth)acrylates, other monomers that are polymerizable by free-radical mechanisms, other monomers that are polymerizable by non-UV and/or free-radical mechanisms, other polymers, additives of any type known in the art including any additives that are not the cationic photoinitiator, the free- radical photoinitiator, and the coated filler introduced above.
  • the dispersion is free of UV curable monomers that are not free-radical polymerizable multifunctional (meth)acrylates.
  • any one or more of these components may be present in an amount of less than 25, 20, 15, 10, 5, 4, 3, 2, 1, 0.1, 0.05, 0.01, etc, or any range thereof, based on a total weight of the dispersion.
  • all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
  • the dispersion typically includes the cationicallypolymerizable aliphatic epoxide, the cationically polymerizable oxetane, and the free-radical polymerizable multifunctional (meth)acrylate as a continuous phase (which may include soluble additives, initiators, etc. including any described below).
  • the dispersion also typically includes the coated filler as a dispersed phase that is dispersed in the continuous phase.
  • any one or more of the polymerizable components and/or organic components or solvents described herein maybe or form the continuous phase.
  • organic phase may be understood as the continuous phase of the dispersion.
  • the cationic polymerizable component maybe chosen from cyclic ether compounds, cyclic acetal compounds, cyclic thioethers compounds, spiro- orthoester compounds, cyclic lactone compounds, and vinyl ether compounds, and any combination thereof.
  • the dispersion includes a cationically polymerizable aliphatic epoxide.
  • the cationically polymerizable aliphatic epoxide is a multifunctional glycidyl ether, e.g. neopentyl glycol diglycidyl ether.
  • Suitable cationicallypolymerizable components include, but are not limited to, cyclic ether compounds such as epoxy compounds and oxetanes, cyclic lactone compounds, cyclic acetal compounds, cyclic thioether compounds, spiro orthoester compounds, and vinylether compounds.
  • cationically polymerizable components include 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, 2-(3,4- epoxycyclohexyl-5,5-spiro-3,4-epoxy)-cyclohexane-l,4-dioxane, bis(3,4- epoxycyclohexylmethyl)adipate, vinylcyclohexene oxide, 4-vinylepoxycyclohexane, vinylcyclohexene dioxide, limonene oxide, limonene dioxide, bis(3,4-epoxy-6- methylcyclohexylmethyl)adipate, 3,4-epoxy-6-methylcyclohexyl-3',4'-epoxy-6'- methylcyclohexanecarboxylate, .epsilon.-caprolactone-modified 3,4-epoxycyclohexylmethyl- 3',
  • the cationically polymerizable component may optionally also include polyfunctional materials including dendritic polymers such as dendrimers, linear dendritic polymers, dendrigraft polymers, hyperbranched polymers, star branched polymers, and hypergraft polymers with epoxy or oxetane functional groups.
  • dendritic polymers may include or be one type of polymerizable functional group or different types of polymerizable functional groups, for example, epoxy and oxetane functions.
  • the composition of the present disclosure also includes one or more mono or poly glycidylethers of aliphatic alcohols, aliphatic polyols, polyester polyols or polyether polyols.
  • components include 1,4-butanedioldiglycidylether, glycidylethers of polyoxyethylene and polyoxypropylene glycols and trio Is of molecular weights from about 200 to about 10,000; glycidylethers of polytetramethylene glycol or poly(oxyethylene-oxybutylene) random or block copolymers.
  • the cationically polymerizable component includes a polyfunctional glycidylether that lacks a cyclohexane ring in the molecule.
  • the cationically polymerizable component includes a neopentyl glycol diglycidyl ether.
  • the cationically polymerizable component includes a 1,4
  • Examples of commercially available polyfunctional glycidylethers are Erisys GE 22 (Erisys products are available from Emerald Performance Materials), Heloxy 48, Heloxy 67, Heloxy 68, Heloxy 107 (Heloxy modifiers are available from Momentive Specialty
  • the epoxide is 3,4-epoxycyclohexylmethyl-3',4- epoxycyclohexanecarboxylate (available as CELLOXIDE 202 IP from Daicel Chemical, 1,4- cyclohexanedimethanol diglycidyl ether (available as HELOXY 107 from Momentive), a mixture of dicyclohexyl diepoxide and nanosilica (available as NANOPDX), and any combination thereof.
  • CELLOXIDE 202 IP from Daicel Chemical
  • 1,4- cyclohexanedimethanol diglycidyl ether available as HELOXY 107 from Momentive
  • NANOPDX nanosilica
  • the cationic polymerizable component further includes at least two different epoxy components.
  • the cationic polymerizable component includes a cyclo aliphatic epoxy, for example, a cycloaliphatic epoxy with 2 or more than 2 epoxy groups.
  • the cationic polymerizable component includes an epoxy having an aromatic or aliphatic glycidyl ether group with 2 (difunctional) or more than 2 (polyfunctional) epoxy groups.
  • NPGDE conversion increases when combined with 20% neopentylglycol diacrylate (NPGDA) and increasing amounts (7-20%) of l,4-Bis[(3-ethyl-3- oxetanylmethoxy)methyl]benzene (Aron OXT-121), reaching 80-100% conversion 30 minutes after UV exposure.
  • NPGDE conversion can be further increased by the addition of 5% hydroxyethyl acrylate.
  • NPGDE conversion can be increased from 43% to 95% by combination with 5% or more of Celloxide 202 IP.
  • use of more than 7% Celloxide 202 IP increases the viscosity of the ceramic dispersion beyond the point of utility for 3D printing.
  • the cationic polymerizable component may be present, for example, in an amount from about 50 to about 80% by weight of an organic phase of the dispersion, in further embodiments from about 55 to about 70 wt % of the organic phase of the dispersion, and in further embodiments from about 58 to about 65 wt % of the organic phase of the dispersion. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
  • the dispersion also includes the cationically polymerizable oxetane.
  • the oxetane includes 1, 2 or more than 2 oxetane groups.
  • the cationically polymerizable oxetane is chosen from 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((l-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
  • the cationically polymerizable oxetane is chosen from 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, and combinations thereof.
  • the cationically polymerizable oxetane is typically included in an amount of from about 5 to about 30 wt % of the organic phase of the dispersion. In another embodiment, the cationically polymerizable oxetane is present in an amount from about 10 to about 25 wt % of the organic phase of the dispersion, and in yet another embodiment, the cationically polymerizable oxetane is present in an amount from 20 to about 30 wt % of the organic phase of the dispersion. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated. In various embodiments, the cationically polymerizable oxetane is chosen to increase the reaction rate of the cationically polymerizable aliphatic epoxide.
  • the dispersion includes at least one free-radical
  • polymerizable component that is, a component which undergoes polymerization initiated by free radicals.
  • the free-radical polymerizable components are monomers, oligomers, and/or polymers and can be monofunctional or polyfunctional materials, i.e., have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or up to 100 or more functional groups that can polymerize by free radical initiation such as aliphatic, aromatic, cycloaliphatic, arylaliphatic, heterocyclic moiety(ies), or any combination thereof.
  • polyfunctional materials include dendritic polymers such as dendrimers, linear dendritic polymers, dendrigraft polymers, hyperbranched polymers, star branched polymers, and hypergraft polymers.
  • the dendritic polymers may include one type of polymerizable functional group or different types of polymerizable functional groups, for example, acrylates and methacrylate functions.
  • Non-limiting examples of suitable free-radical polymerizable components include acrylates and methacrylates such as 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, acryloyl morpholine, (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, 2- hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, methyl (meth)acrylate, 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 (
  • ethoxydiethylene glycol (meth)acrylate benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, methoxyethylene glycol (meth)acrylate, ethoxyethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, diacetone
  • (meth)acrylamide beta-carboxyethyl (meth)acrylate, phthalic acid (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, butylcarbamethyl (meth)acrylate, n-isopropyl (meth)acrylamide fluorinated (meth)acrylate, 7-amino-3,7- dimethyloctyl (meth)acrylate.
  • Non-limiting examples of suitable multifunctional free-radical polymerizable components include those with (meth)acryloyl groups 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-[l,l- dimethyl-2- [( 1 -oxoallyl)oxy] ethyl]-5 -ethyl- 1 ,3 -dioxan-5 -yl]methyl acrylate; 3 ,9-bis( 1 , 1 - dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5- ]undecane di(meth)acrylate;
  • (meth)acryloyl groups such as trimethylolpropane tri(meth)acrylate, pent
  • di(meth)acrylate tricyclodecane diyl dimethyl di(meth)acrylate and alkoxylated versions (e.g., ethoxylated and/or propoxylated) of any of the preceding monomers, and triethylene glycol divinyl ether, and adducts of hydroxyethyl acrylate.
  • alkoxylated versions e.g., ethoxylated and/or propoxylated
  • the radically polymerizable component is a multifunctional (meth)acrylate.
  • the multifunctional (meth)acrylates may include all methacryloyl groups, all acryloyl groups, or any combination of methacryloyl and acryloyl groups.
  • the free-radical polymerizable component is chosen from propoxylated trimethylolpropane tri(meth)acrylate, and propoxylated neopentyl glycol di(meth)acrylate, and any combination thereof.
  • the multifunctional (meth)acrylate is chosen from trimethylolpropane tri(meth)acrylate, ethylene glycol di(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, tripropyleneglycol di(meth)acrylate, glycerol
  • the multifunctional (meth)acrylate has more than 2, more typically more than 3, and more typically greater than 4 functional groups.
  • the radically polymerizable component consists exclusively of a single multifunctional (meth)acrylate component.
  • the exclusive radically polymerizable component is tetra-functional, in further embodiments, the exclusive radically polymerizable component is penta-functional, and in further embodiments, the exclusive radically polymerizable component is hexa-functional.
  • the free-radical polymerizable component is chosen from dicyclopentadiene dimethanol diacrylate, [2-[l,l-dimethyl-2-[(l-oxoallyl)oxy]ethyl]-5-ethyl- l,3-dioxan-5-yl]methyl acrylate, propoxylated trimethylolpropane triacrylate, and propoxylated neopentyl glycol diacrylate, and any combination thereof.
  • the dispersion includes one or more of dicyclopentadiene dimethanol di(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, and/or propoxylated neopentyl glycol di(meth)acrylate, and more specifically one or more of dicyclopentadiene dimethanol diacrylate, propoxylated trimethylolpropane triacrylate, and/or propoxylated neopentyl glycol diacrylate.
  • the dispersion includes the free-radical polymerizable multifunctional (meth)acrylate.
  • This (meth)acrylate is able to polymerize with itself and/or with other acrylate monomers via free-radical polymerization initiated by exposure to UV light/energy.
  • a single type or more than one type of (meth)acrylate may be used.
  • the free-radical polymerizable multifunctional (meth)acrylate is used to produce rapid green strength formation.
  • the radically polymerizable component is further defined as a (meth)acrylate monomer which can be any monomer having at least one acrylate functional group and/or at least one methacrylate functional group.
  • the terminology "(meth)” describes that the "meth” group is optional and not required.
  • the monomer may be an "acrylate” monomer (without a methyl group) or a "methacrylate” monomer that includes a methyl group.
  • the (meth)acrylate monomer used herein is a compound selected from the group of aliphatic acrylates, aliphatic methacrylates, cycloaliphatic acrylates, cycloaliphatic methacrylates, and combinations thereof. It is to be understood that each of the compounds, the aliphatic acrylates, the aliphatic methacrylates, the cycloaliphatic acrylates, and the cycloaliphatic methacrylates, include an alkyl radical. The alkyl radicals of these compounds can include up to 20 carbon atoms.
  • the aliphatic acrylates that maybe selected as one of the (meth)acrylate monomers are selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, n- butyl acrylate, iso-butyl acrylate, tert-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, iso-octyl acrylate, iso-nonyl acrylate, iso-pentyl acrylate, tridecyl acrylate, stearyl acrylate, lauryl acrylate, and mixtures thereof.
  • the aliphatic methacrylates that maybe selected as one of the (meth)acrylate monomers are selected from the group consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, tert-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, iso- octyl methacrylate, iso-nonyl methacrylate, iso-pentyl methacrylate, tridecyl methacrylate, stearyl methacrylate, lauryl methacrylate, and mixtures thereof.
  • the cycloaliphatic acrylate that may be selected as one of the (meth)acrylate monomers is cyclohexyl acrylate
  • the cycloaliphatic methacrylate that maybe selected as one of the (meth)acrylate monomers is cyclohexyl methacrylate.
  • the above-mentioned radically polymerizable compounds can be used singly or in combination of two or more thereof.
  • the dispersion can include any suitable amount of the free-radical polymerizable components, for example, in certain embodiments, in an amount up to about 40 volume % of the organic phase of the dispersion, in certain embodiments, from about 2 to about 40 volume % of the organic phase of the dispersion, in other embodiments from about 5 to about 30 volume %, and in further embodiments from about 10 to about 20 volume % of the organic phase of the dispersion.
  • the acrylate monomer is present in an amount of greater than zero and up to about 40 volume % of the organic phase of the dispersion.
  • the acrylate monomer is present in amount of from 2 to 40, 5 to 40, 5 to 35, 5 to 30, 10 to 30, 10 to 25, 10 to 20, 15 to 30, 15 to 25, 15 to 20, or 1, 2, 3, 4, or 5, volume percent based on a total volume of the organic phase of the dispersion.
  • all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
  • the dispersion includes a cationic photoinitiator.
  • the cationic photoinitiator initiates cationic ring-opening polymerization upon irradiation of light.
  • any suitable cationic photoinitiator can be used, for example, those with cations chosen from onium salts, halonium salts, iodosyl salts, selenium salts, sulfonium salts, sulfoxonium salts, diazonium salts, metallocene salts, isoquinolinium salts, phosphonium salts, arsonium salts, tropylium salts, dialkylphenacylsulfonium salts, thiopyrilium salts, diaryl iodonium salts, triaryl sulfonium salts, ferrocenes,
  • di(cyclopentadienyliron)arene salt compounds di(cyclopentadienyliron)arene salt compounds, and pyridinium salts, and any combination thereof.
  • a cation of the cationic photoinitiator is chosen from aromatic diazonium salts, aromatic sulfonium salts, aromatic iodonium salts, metallocene based compounds, aromatic phosphonium salts, and any combination thereof.
  • the cation is a polymeric sulfonium salt or other aromatic heteroatom-including cations and naphthyl- sulfonium salts.
  • the cationic photoinitiator is chosen from triarylsulfonium salts, diaryliodonium salts, and metallocene based compounds, and any combination thereof.
  • Onium salts e.g., iodonium salts and sulfonium salts, and ferrocenium salts, have the advantage that they are generally more thermally stable.
  • the cationic photoinitiator has an anion chosen from BF 4 . " , AsFe “ , SbF 6 " , PF 6 ⁇ [B(CF 3 ) 4 ] “ , B(C 6 F 5 ) 4 “ , B[C 6 H 3 -3,5(CF 3 )2] 4 " , ⁇ ((1 ⁇ 43 ⁇ 4 ⁇ 1 ⁇ 4)4 " , B(C 6 H 3 F 2 ) 4 " , B[C 6 F 4 - 4(CF 3 )] 4 " , Ga(C 6 F 5 ) " , [(C6F 5 ) 3 B— C 3 H 3 N 2 — B(C 6 F 5 ) 3 ] " , [(C 6 F 5 ) 3 B— NH 2 — B(C 6 F 5 ) 3 ] " , tetrakis(3,5-difluoro-4-alkyloxyphenyl)borate, tetrakis(2,
  • tris(perfluoroalkyl)trifluorophosphates bis(perfluoroalkyl)tetrafluorophosphates, tris(pentafluoroethyl)trifluorophosphates, and (CHeBnBre) " , (CHeBnCle) " and other halogenated carborane anions.
  • the cationic photoinitiator has a cation chosen from aromatic sulfonium salts, aromatic iodonium salts, and metallocene based compounds with at least an anion chosen from SbFe " , PF 6 -, B(C6Fs) 4 " , [B(CF 3 ) 4 ] " , tetrakis(3,5-difluoro-4- methoxyphenyl)borate, perfluoroalkylsulfonates, perfluoroalkylpho sphates,
  • Examples of cationic photoinitiators useful for reaction at 300-475 nm, particularly at 365 nm UV light, without a sensitizer include 4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4- fluorophenyl)sulfonium hexafluoroantimonate, 4-[4-(3- chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfonium
  • Typical cationic photoinitiators include, either alone or in a mixture: bis[4- diphenylsulfoniumphenyl]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
  • the dispersion may be irradiated by laser or LED light operating at any wavelength in either the UV or visible light spectrum.
  • the irradiation is from a laser or LED emitting a wavelength of from 340 nm to 415 nm.
  • the laser or LED source emits a peak wavelength of about 340 nm, 355 nm, 365 nm, 375 nm, 385 nm, 395 nm, 405 nm, or 415 nm.
  • the dispersion includes an aromatic triaryl sulfonium salt cationic photoinitiator.
  • aromatic triaryl sulfonium salts as the cationic photoinitiator in dispersions is desirable in additive fabrication processes because the resulting dispersion attains a fast photospeed, good thermal-stability, and good photo- stability.
  • the cationic photoinitiator is an aromatic triaryl sulfonium salt that is more specifically an R-substituted aromatic thioether triaryl sulfonium
  • Yl, Y2, and Y3 are the same or different and wherein Yl, Y2, or Y3 are R- substituted aromatic thioether with R being an acetyl or halogen group.
  • Yl, Y2, and Y3 are the same. In another embodiment, Yl and Y2 are the same, but Y3 is different. In another embodiment, Yl, Y2, or Y3 are an R-substituted aromatic thioether with R being an acetyl or halogen group. Typically, Yl, Y2, or Y3 are a para-R-substituted aromatic thioether with R being an acetyl or halogen group.
  • Tris(4-(4- acetylphenyl)thiophenyl)sulfonium tetrakis(pentafluorophenyl)borate is known commercially as IRGACURE PAG-290 and is available from Ciba/BASF.
  • tetrakis(pentafluorophenyl)borate cationic photo initiator for instance, tris(4-(4- acetylphenyl)thiophenyl)sulfonium tetrakis(pentafluorophenyl)borate, is also more thermally- stable than some other cationic photoinitiators.
  • the improved thermal-stability allows dispersions for additive fabrication incorporating a triaryl sulfonium
  • tetrakis(pentafluorophenyl)borate cationic photo initiator instead of other conventional cationic photoinitiators to retain their viscosity at elevated temperatures for long periods of time.
  • the cationic photoinitiator is an aromatic triaryl sulfonium salt that possesses an anion represented by SbFe “ , PF6-, BF 4 “ , (CF3CF2)3PF3 “ (C6F5) 4 B “ ,
  • each of R 1 , R 2 , R 3 , R 5 and R 6 is independently an alkyl group, a hydroxy group, an alkoxy group, an alkylcarbonyl group, an arylcarbonyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an arylthiocarbonyl group, an acyloxy group, an arylthio group, an alkylthio group, an aryl group, a heterocyclic hydrocarbon group, an aryloxy group, an alkylsulfinyl group, an arylsulfinyl group, an alkylsulfonyl group, an arylsulfonyl group, a hydroxy(poly)alkyleneoxy group, an optionally substituted amino group, a cyano group, a nitro group, or a halogen atom
  • R 4 is an alkyl group, a hydroxy group, an alkoxy group, an alkylcarbonyl group
  • a particularly typical aromatic triaryl sulfonium cationic photoinitiator has an anion that is a fluoroalkyl-substituted fluorophosphate.
  • an aromatic triaryl sulfonium cationic photoinitiator having a fluoroalkyl-substituted fluorophosphate anion is the CPI-200 series (for example CPI-200K or CPI-2105) or 300 series, available from San- Apro Limited.
  • the dispersion includes a cationic polymerizable component in addition to an R-substituted aromatic thioether triaryl sulfonium
  • the dispersions for additive fabrication include cationic polymerizable components, free-radical photoinitiators, and free-radical polymerizable components.
  • the dispersions for additive fabrication include an R- substituted aromatic thioether triaryl sulfonium tetrakis(pentafluorophenyl)borate cationic photoinitiator and additional cationic photoinitiators and/or photosensitizers, along with a cationic polymerizable component and, optionally, free-radical polymerizable components and free-radical photoinitiators.
  • the dispersion can include any suitable amount of the cationic photoinitiator, for example, in certain embodiments, in an amount up to about 15% by weight of the dispersion composition, in certain embodiments, up to about 5% by weight of the dispersion composition, and in further embodiments from about 2% to about 10% by weight of the dispersion composition, and in other embodiments, from about 0.1% to about 5% by weight of the dispersion composition.
  • the amount of cationic photoinitiator is from about 0.2 wt % to about 4 wt % of the total dispersion composition, and in other embodiments from about 0.5 wt % to about 3 wt %. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
  • the dispersion may also contain various photoinitiators of different sensitivity to radiation of emission lines with different wavelengths to obtain a better utilization of a UV light source.
  • the use of known photoinitiators of different sensitivity to radiation of emission lines is well known in the art of additive fabrication, and may be selected in accordance with radiation sources of, for example, 351, nm 355 nm, 365 nm, 385 nm, and 405 nm.
  • all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
  • the dispersion depending on the wavelength of light used for curing the dispersion, it is desirable for the dispersion to include a photosensitizer.
  • photosensitizer is used to refer to any substance that either increases the rate of photoinitiated polymerization or shifts the wavelength at which polymerization occurs; see textbook by G. Odian, Principles of Polymerization, 3 rd Ed., 1991, page 222.
  • a variety of compounds can be used as photo sensitizers, including heterocyclic and fused-ring aromatic hydrocarbons, organic dyes, and aromatic ketones.
  • Examples of photo sensitizers include those chosen from methanones, xanthenones, pyrenemethanols, anthracenes, pyrene, perylene, quinones, xanthones, thioxanthones, benzoyl esters, benzophenones, and any combination thereof.
  • photosensitizers include those chosen from [4- [(4-methylphenyl)thio]phenyl]phenyl-methanone, 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,l 0-diethoxyanthracene, anthracene, anthraquinones, 2-methylanthraquinone, 2-eththr
  • the dispersion can include any suitable amount of the photo sensitizer, for example, in certain embodiments, in an amount up to about 10% by weight of the dispersion composition, in certain embodiments, up to about 5% by weight of the dispersion composition, and in further embodiments from about 0.05% to about 2% by weight of the dispersion composition. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
  • the dispersion includes a cationic photoinitiator in addition to, or in lieu of, an R-substituted aromatic thioether triaryl sulfonium
  • cationic photoinitiator tetrakis(pentafluorophenyl) borate cationic photoinitiator.
  • Any suitable cationic photoinitiator can be used, for example, those chosen from onium salts, halonium salts, iodosyl salts, selenium salts, sulfonium salts, sulfoxonium salts, diazonium salts, metallocene salts, isoquinolinium salts, phosphonium salts, arsonium salts, tropylium salts,
  • dialkylphenacylsulfonium salts thiopyrilium salts, diaryl iodonium salts, triaryl sulfonium salts, sulfonium antimonate salts, ferrocenes, di(cyclopentadienyliron)arene salt compounds, and pyridinium salts, and any combination thereof.
  • Onium salts e.g., iodonium salts, sulfonium salts and ferrocenes, have the advantage that they are thermally-stable.
  • Typical mixtures of cationic photoinitiators include a mixture of: bis[4- diphenylsulfoniumphenyl]sulfide bishexafluoroantimonate; thiophenoxyphenylsulfonium hexafluoroantimonate (available as Chivacure 1176 from Chitec); tris(4-(4- acetylphenyl)thiophenyl)sulfonium tetrakis(pentafluorophenyl)borate (Irgacure PAG-290 or GSID4480-1 from Ciba/BASF), iodonium, [4-(l-methylethyl)phenyl](4-methylphenyl)-, tetrakis(pentafluorophenyl)borate (available as Rhodorsil 2074 from Rhodia), 4-[4-(2- chlorobenzoyl)phenylthio]phenylbis(4-fluor
  • photosensitizers are useful in combination with photoinitiators in effecting cure with LED light sources emitting in the wavelength range of 300-475 nm.
  • suitable photosensitizers include: anthraquinones, such as 2- methylanthraquinone, 2-ethylanthraquinone, 2-tertbutylanthraquinone, 1- chloroanthraquinone, and 2-amylanthraquinone, thioxanthones and xanthones, such as isopropyl thioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, and l-chloro-4- propoxythioxanthone, methyl benzoyl formate (Darocur MBF from Ciba), methyl-2-benzoyl benzoate (Chivacure OMB from Chitec), 4-benzoyl-4'-methyl diphenyl sulphide
  • the photo sensitizer 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.
  • the photosensitizer is:
  • the dispersion can include any suitable amount of the photosensitizer, for example, in certain embodiments, in an amount up to about 10% by weight of the dispersion composition, in certain embodiments, up to about 5% by weight of the dispersion composition, and in further embodiments from about 0.05% to about 2% by weight of the dispersion composition.
  • photosensitizers when employed, other photoinitiators absorbing at shorter wavelengths can be used. Examples of such photoinitiators include: benzophenones, such as benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, and
  • 1-hydroxyphenyl ketones such as 1-hydroxycyclohexyl phenyl ketone, phenyl (l-hydroxyisopropyl)ketone, 2-hydroxy-l-[4-(2- hydroxyethoxyl)phenyl]-2-methyl- 1 -propanone, and 4-isopropylphenyl( 1 - hydroxyisopropyl)ketone, benzil dimethyl ketal, and oligo-[2-hydroxy-2-methyl-l-[4-(l- methylvinyl)phenyl]propanone] (Esacure KIP 150 from Lamberti).
  • 1-hydroxycyclohexyl phenyl ketone such as 1-hydroxycyclohexyl phenyl ketone, phenyl (l-hydroxyisopropyl)ketone, 2-hydroxy-l-[4-(2- hydroxyethoxyl)phenyl]-2-methyl- 1 -propanone, and 4-isopropylphenyl( 1 -
  • An additional photosensitizer or co-initiator maybe used to improve the activity of the cationic photoinitiator. It is for either increasing the rate of photoinitiated polymerization or shifting the wavelength at which polymerization occurs.
  • the sensitizer used in combination with the above-mentioned cationic photoinitiator is not particularly limited. 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 compounds disclosed by J. V. Crivello in Advances in Polymer Science, 62, 1 (1984), and by J. V. Crivello & K.
  • Dietliker "Photoinitiators for Cationic Polymerization” in Chemistry & technology of UV & EB formulation for coatings, inks & paints. Volume III, Photoinitiators for free radical and cationic polymerization, by K. Dietliker; [Ed. by P. K. T. Oldring], SITA Technology Ltd, London, 1991.
  • Specific examples include polyaromatic hydrocarbons and their derivatives such as anthracene, pyrene, perylene and their derivatives, thioxanthones, alpha-hydroxyalkylphenones, 4-benzoyl-4'-methyldiphenyl sulfide, acridine orange, and benzo flavin.
  • the dispersion can include any suitable amount of the other cationic photoinitiator or photosensitizer, for example, in certain embodiments, in an amount an amount from 0.1 to 10 wt % of the dispersion composition, in certain embodiments, from about 1 to about 8 wt % of the dispersion composition, and in further embodiments from about 2 to about 6 wt % of the dispersion composition. In one embodiment, the above ranges are particularly suitable for use with epoxy monomers.
  • the dispersion includes a photoinitiating system that is a photoinitiator having both cationic initiating function and free radical initiating function. Free-Radical Photoinitiator:
  • the dispersion also includes a free-radical initiator.
  • the free-radical initiator is a UV activated free-radical initiator.
  • the free-radical initiator is typically initiated by exposure to UV light which causes a radical to form, followed by propagation of that radical.
  • a non-UV initiated free-radical initiator may be used alone or in combination with a UV activated free-radical initiator.
  • the free-radical initiator may be described as a free-radical photoinitiator.
  • Free- radical photoinitiators are typically divided into those that form radicals by cleavage, known as "Norrish Type I" and those that form radicals by hydrogen abstraction, known as "Norrish type ⁇ ".
  • the Norrish type II photoinitiators typically require a hydrogen donor, which serves as the free-radical source.
  • the Norrish type II photoinitiators are generally slower than Norrish type I photoinitiators which are based on the unimolecular formation of radicals.
  • Norrish type II photoinitiators typically possess better optical absorption properties in the near-UV spectroscopic region.
  • Photolysis of aromatic ketones, such as benzophenone, thioxanthones, benzil, and quinones in the presence of hydrogen donors, such as alcohols, amines, or thiols leads to the formation of a radical produced from the carbonyl compound (ketyl-type radical) and another radical derived from the hydrogen donor.
  • the photopolymerization of vinyl monomers is typically initiated by the radicals produced from the hydrogen donor.
  • the ketyl radicals are typically not reactive toward vinyl monomers because of the steric hindrance and the delocalization of an unpaired electron.
  • the free-radical initiator is chosen from benzoylphosphine oxides, aryl ketones, benzophenones, hydroxylated ketones, 1 -hydroxyphenyl ketones, ketals, metallocenes, and combinations thereof.
  • the free-radical initiator is chosen from 2,4,6-trimethylbenzoyl diphenylphosphine oxide and 2,4,6-trimethylbenzoyl phenyl, ethoxyphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, 2- methyl-l-[4-(methylthio)phenyl]-2-mo holinopropanone-l,2-benzyl-2-(dim- ethylamino)-l- [4-(4-morpholinyl)phenyl]- 1 -butanone, 2-dimethylamino-2-(4-methyl-benzyl)- 1 -(4- morpholin-4-yl-phenyl)-butan-l-o- ne, 4-benzoyl-4'-methyl diphenyl sulphide, 4,4'- bis(diethylamino) benzophenone, and 4,4'-bis(N,N
  • dimethoxybenzophenone 1-hydroxycyclohexyl phenyl ketone, phenyl (1- hydroxyisopropyl)ketone, 2-hydroxy-l-[4-(2-hydroxyethoxyl)phenyl]-2-methyl-l-propanone, 4-isopropylphenyl(l-hydroxyisopropyl)ketone, oligo-[2-hydroxy-2 -methyl- l-[4-(l- methylvinyl)phenyl]propanone], camphorquinone, 4,4'-bis(diethylamino) benzophenone, benzil dimethyl ketal, bis(eta 5-2-4-cyclopentadien-l-yl) bis[2,6-difluoro-3-(lH-pyrrol-l- yl)phenyl]titanium, and combinations thereof.
  • the wavelength sensitivity of the dispersion typically, when forming the dispersion, the wavelength sensitivity of the
  • photoinitiator(s) present are evaluated to determine whether they will be activated by a chosen radiation source.
  • a chosen radiation source For light sources emitting in the 300-475 nm wavelength range, especially those emitting at 365 nm, 390 nm, or 395 nm, non-limiting examples of suitable free-radical initiators absorbing in these ranges include, but are not limited to,
  • benzoylphosphine oxides such as, 2,4,6-trimethylbenzoyl diphenylphosphine oxide (Lucirin TPO from BASF) and 2,4,6-trimethylbenzoyl phenyl, ethoxy phosphine oxide (Lucirin TPO- L from BASF), bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (Irgacure 819 or BAPO from Ciba), 2-methyl-l-[4-(methylthio)phenyl]-2-morpholinopropanone-l (Irgacure 907 from Ciba), 2-benzyl-2-(dimethylamino)-l-[4-(4-morpholinyl)phenyl]-l-butanone (Irgacure 369 from Ciba), 2-dime1hylamino-2-(4-me1hyl-benzyl)-l-(4-mo holin-4-yl
  • photosensitizers can be used, e.g. when using an LED light source.
  • suitable photosensitizers include: anthraquinones, such as 2- methylanthraquinone, 2-ethylanthraquinone, 2-tertbutylanthraquinone, 1- chloroanthraquinone, and 2-amylanthraquinone, thioxanthones and xanthones, such as isopropyl thioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, and l-chloro-4- propoxythioxanthone, methyl benzoyl formate (Darocur MBF from Ciba), methyl-2-benzoyl benzoate (Chivacure OMB from Chitec), 4-benzoyl-4'-methyl diphenyl sulphide (Chivacure BMS from Chitec), 4,
  • photosensitizers such as benzophenones, such as benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, dimethoxybenzophenone, and 1 -hydro xyphenyl ketones, such as 1- hydroxycyclohexyl phenyl ketone, phenyl (l-hydroxyisopropyl)ketone, 2-hydroxy-l-[4-(2- hroxyethoxy)phenyl]-2-methyl- 1 -propanone, and 4-isopropylphenyl( 1 - hydroxyisopropyl)ketone, benzil dimethyl ketal, and oligo-[2-hydroxy-2-methyl-l-[4-(l- methylvinyl)phenyl]propanone] (Esacure KIP 150 from Lamberti), and combinations thereof, can be used.
  • benzophenones such as benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, dim
  • free-radical initiators such as camphorquinone, 4,4'-bis(diethylamino) benzophenone (Chivacure EMK from Chitec), 4,4'-bis(N,N'-dimethylamino) benzophenone (Michler's ketone), bis(2,4,6- trimethylbenzoyl)-phenylphosphineoxide ("BAPO,” or Irgacure 819 from Ciba), and the visible light photoinitiators from Spectra Group Limited, Inc. such as H-Nu 470, H-Nu-535, H-Nu-635, H-Nu-Blue-640, and H-Nu-Blue-660, and combinations thereof, maybe used.
  • the light may be UVA radiation, which is radiation with a wavelength between about 320 and about 400 nm, UVB radiation, which is radiation with a wavelength between about 280 and about 320 nm, and/or UVC radiation, which is radiation with a wavelength between about 100 and about 280 nm.
  • UVA radiation which is radiation with a wavelength between about 320 and about 400 nm
  • UVB radiation which is radiation with a wavelength between about 280 and about 320 nm
  • UVC radiation which is radiation with a wavelength between about 100 and about 280 nm.
  • the dispersion may include any amount of the free-radical initiator so long as the other required components are present.
  • the free-radical initiator maybe present in an amount of greater than zero and up to about 10 wt % of the dispersion, from about 0.1 to about 10 wt % of the dispersion, or from about 1 to about 6 wt % of the dispersion.
  • all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
  • the dispersion also includes a coated filler.
  • the coated filler maybe the dispersed phase that is dispersed in the continuous phase described above.
  • the coated filler includes core particles and a surface treatment disposed on the core particles.
  • the core particles are chosen from glass or metal particles, glass powder, alumina, alumina hydrate, magnesium oxide, magnesium hydroxide, barium sulfate, calcium sulfate, calcium carbonate, magnesium carbonate, silicate mineral, diatomaceous earth, silica sand, silica powder, oxidation titanium, aluminum powder, bronze, zinc powder, copper powder, lead powder, gold powder, silver dust, glass fiber, titanic acid potassium whiskers, carbon whiskers, sapphire whiskers, verification rear whiskers, boron carbide whiskers, silicon carbide whiskers, silicon nitride whiskers, and combinations thereof.
  • the core particles include silica, alumina, zircon, or combinations thereof.
  • the core particles are 95-100 wt% silica.
  • the core particles are a combination of silica, 2 to 5 weight % of alumina, and 2 to 5 weight % of zircon.
  • the coated filler is present in an amount of from 55 to 70 volume percent based on a total volume of the dispersion. In various embodiments, the coated filler is present in 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, or 70, volume percent based on a total volume of the dispersion. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
  • the coated filler is further defined as particles, e.g.
  • the particles may be 90, 95, 99, or approximately 100 wt% of microparticles, nanoparticles, or a combination of microparticles and nanoparticles.
  • the core particles are microparticles having a particle size of from 1 micrometer to 90 micrometers and wherein the core particles include 5 weight percent or less of nanoparticles having a particle size of from 10 nanometers to 999 nanometers.
  • the coated filler has a particle size from 0.04 micrometers to 90 micrometers.
  • Particle size may be measured using laser diffraction particle size analysis in accordance with ISO13320:2009.
  • a suitable device for measuring the average particle diameter of nanoparticles is the LB-550 machine, available from Horiba Instruments, Inc, which measures particle diameter by dynamic light scattering. In various non-limiting embodiments, all values and ranges of values between the aforementioned values are hereby expressly contemplated.
  • the silica may include greater than 85 wt %, 90 wt %, or 95 wt % of silica (Si0 2 ).
  • Certain non-limiting examples of commercially available silica include Crystallite 3K-S, Crystallite NX-7, Crystallite MCC-4, Crystallite CMC-12, Crystallite A-l, Crystallite AA, Crystallite C, Crystallite D, Crystallite CMC-1, Crystallite C-66, Crystallite 5X, Crystallite 2A-2, Crystallite VX-S2, Crystallite VX-SR, Crystallite VX-X, Crystallite VX-S, Huselex RD-8, Huselex RD-120, Huselex MCF-4, Huselex GP-200T, Huselex ZA-30, Huselex RD-8, Huselex Y-40, Huselex E-2, Huselex Y- 60, Huselex E-l , Huselex E-2, Huselex FF, Huselex
  • Organosilicasol NPC-ST-30, Organosilicasol PMA-ST, Sunsphere H-31, Sunsphere H-32, Sunsphere H-51, Sunsphere H-52, Sunsphere H-121, Sunsphere H-122, Sunsphere L-31, Sunsphere L-51, Sunsphere L-121, Sunsphere NP-30, Sunsphere NP-100, and Sunsphere NP- 200 (Asahi Glass Co., Ltd.); Silstar MK-08 and MK-15 (Nippon Chemical Industrial Co., Ltd.); FB-48 (Denki Kagaku Kogyo K.K.); Nipsil SS-10, Nipsi:L SS-15, Nipsil SS-10A, Nipsil SS-20, Nipsil SS-30P, Nipsil SS-30S, Nipsil SS ⁇ O, Nipsil SS-50, Nipsil SS-50A, Nipsil SS-70, Nipsil SS-100, Nipsil SS-10F, Nipsil SS-50F, Nips
  • the coated filler is used to minimize hydrogen bonding in the dispersion which allows for customization of the viscosity of the dispersion.
  • the dispersion typically has a viscosity from 500 to 4,000 cps at 25 °C and 30 RPM using ASTM D 2196 - 99.
  • the viscosity is from 600 to 3, 900, from 700 to 3,800, from 800 to 3,700, from 900 to 3,600, from 1,000 to 3,500, from 1,100 to 3,400, from 1,200 to 3,300, from 1,300 to 3,200, from 1,400 to 3,100, from 1,500 to 3,000, from 1,600 to 2,900, from 1,700 to 2,800, from 1,800 to 2,700, from 1,900 to 2,600, from 2,000 to 2,500, from 2,100 to 2,400, or from 2,200 to 2,300, cps at 25°C and 30 RPM using ASTM D 2196 - 99.
  • all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
  • the core particles include silica.
  • the silica has all particles less than the layer thickness formed in 3D printing, otherwise particles larger than the layer thickness will be dragged across the build layer during recoating with the recoater doctor blade thus scoring the layer. While a single particle distribution can be used, a combination of multiple particle distributions can be used as binary and ternary
  • the ideal particle size ratio between two distributions of small particles and large particles is approximately 1 :7 and that the volume should be 25% of that of the volume of large particles.
  • lowest viscosity might be achieved when the volume loading of small particles is 27% in a binary mixture of large and small particles.
  • an ideal binary distribution could have average particle size distributions of about 60 ⁇ and about 8.6 ⁇ respectively and volume loading of about 73% large spheres and about 27% of small spheres.
  • a 100 ⁇ layer thickness using three particle size distributions may have average particle diameter ratios of about 60 ⁇ , 8.6 ⁇ and 1.2 ⁇ respectively, and volume loading of about 74% large spheres, 20% of mid-sized spheres, and 5% small spheres.
  • Non-spherical particles can form shear thinning dispersions and larger particles can form such suspensions more readily.
  • these dispersions Upon resting at zero shear, these dispersions can form large networked floes which can cause the viscosity of the dispersion to increase exponentially.
  • these floes Upon the application of shear force or vibration, these floes can break down and the viscosity of the dispersion is typically reduced.
  • the advantage of this property can be utilized to create a dispersion that is resistant to sedimentation through the formation of a high viscosity suspension upon standing at zero shear.
  • the largest particle component may be ground silica (shards) while the smallest and medium particle size distribution may be spherical for better particle packing and higher green part density.
  • a ternary particle distribution having component distributions that deviate slightly from a 7:1 large particle to small particle ratio can be used.
  • the largest size distribution may be centered at 21 ⁇ , while the smallest size distribution may be centered at 0.9 ⁇ , and the medium size distribution may be centered at 4 ⁇ .
  • the size ratio of these distributions is about 5.3 and 4.4 respectively.
  • 2-5 wt% of aluminum oxide and 2-5 wt% zircon can be used to increase the strength of the ceramic article at high temperature.
  • Aluminum oxide and zircon can also function as UV absorbers and therefore can factor into the exposure characteristics of the formulation.
  • a ty ical silica formulation suitable for printing 100 ⁇ layers is set forth in the table below.
  • Teco-sphere Microdust is commercially available from Imerys Fused Materials Greenville, Inc., 109 Coile Street, Greeville, TN, USA.
  • Angular -200 is commercially available from Remet Corporation, 210 Commons Road, Utica, NY 13502-6395, USA.
  • RP-1 is commercially available Imerys Fused Materials Greenville, Inc., 109 Coile Street, Greeville, TN, USA.
  • A-10 is commercially available from Almatis Inc., 501 West Park Road, Leetsdale, Pa 15056, USA
  • Milled Zircon Fine Grind is commercially available from Remet Corporation, 210 Commons Road, Utica, NY 13502-6395, USA.
  • increasing the ceramic loading increases the viscosity and the probability of particle-particle interactions which decrease the sedimentation rate of the dispersion. Maximizing the ceramic loading can also increase the density of the ceramic article, decreases cracking and delamination flaws, and increase the mechanical strength of the ceramic article. As the ceramic loading reaches 64-66 volume percent for loading, the viscosity can begin to increase exponentially. Therefore, in various embodiments, 64 volume percent ceramic loading is used to maintain a formulation viscosity low enough for 3D printing.
  • the surface treatment that is disposed on the core particles may be disposed on and in direct contact with the core particles such that there is no intermediate layer between the surface treatment and the core particles or maybe disposed, and spaced apart from, the core particles. If disposed on and spaced apart from, there is typically one or more intermediate layers disposed between the surface treatment and the core particle.
  • the surface treatment is typically disposed on the surface of the core particles. Most typically, the surface treatment totally envelops or encapsulated the core particles. However, this is not required and less than total coverage, e.g.
  • the surface treatment may react with the surface of the core particles or may not react with the surface of the core particles.
  • the surface treatment maybe applied to the core particles in any method suitable in the art, e.g. spraying, pouring, dipping, coating, etc.
  • the surface treatment is or includes an organosilane.
  • organosilanes include vinyl trichlorosilane, vinyl tris (beta- methoxyethoxy) silane, vinyltriethoxy silane, vinyltrimethoxy silane, gamma- (methacryloxypropyl) trimethoxy silane, beta-(3,4-epoxycyclohexyl)ethyltrimethoxy silane, gamma-glycydoxypropyltrimethoxy silane, gamma-glycydoxypropylmethyl diethoxy silane, N-beta(aminoethyl) aminopropyltrimethoxy silane, N-beta-(aminoethyl)-gamma- aminopropylmethyldimethoxy silane, gamma-aminopropyltriethoxysilane, N-phenyl-gamma
  • the surface treatment is chosen from organosilane is chosen from dicyclopentyldimethoxysilane, (cyclohexyl)methyldimethoxysilane, 3 -acetoxyethylyltrimethoxysilane, 3 - acetoxypropyltrimethoxysilane, and combinations thereof.
  • the surface treatment is present in an amount of from 0.5 to 2 weight percent based on a total weight of the coated filler. In various embodiments, this amount is from 0.6 to 1.9, 0.7 to 1.8, 0.8 to 1.7, 0.9 to 1.6, 1 to 1.5, 1.1 to 1.4, 1.1 to 1.3, or 1.2 to 1.3, weight percent based on a total weight of the coated filler. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
  • the dispersion may also include, or be free of, or include less than 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, 0.1, 0.05, or 0.01, weight percent of one or more additives set forth below.
  • the dispersion may alternatively include 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 weight percent of one or more additive set forth below.
  • Such additives include, but are not limited to, those described in U.S. Pat. No. 5,665,792 and U.S. Pat. No. 6,099,787, the disclosure of each of which is hereby incorporated by reference relative to such additives in various non-limiting embodiments.
  • the additive is chosen from hydrocarbon carboxylic acid salts of group IA and IIA metals such as sodium bicarbonate, potassium bicarbonate, and rubidium carbonate, polyvinylpyrrolidones, polyacrylonitriles, and combinations thereof.
  • Other additives include dyes, pigments, antioxidants, wetting agents, photosensitizers, chain transfer agents, leveling agents, defoamers, surfactants, bubble breakers, antioxidants, acid scavengers, thickeners, flame retardants, silane coupling agents, ultraviolet absorbers, dispersion particles, core-shell particle impact modifiers, soluble polymers and block polymers.
  • all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
  • the dispersion also typically has a sedimentation rate that is at least 75, 80, 85, 90, 95, or 99, percent less as compared to an identical composition that is free of the sheer thinning additive.
  • the sedimentation rate is typically determined by the following method. However, any method in the art can be used.
  • One method includes providing a centrifuge to apply a gravitational force to the ceramic dispersion, placing a sample of the ceramic dispersion in a sample container in the centrifuge, applying a gravitational force of from 25G to 2000G to the ceramic dispersion in the centrifuge to precipitate an amount of the silica from the continuous phase thereby forming a sediment that comprises a topmost layer disposed on the sediment wherein the topmost layer comprises the metal particles to allow for visualization, and measuring the amount of the sediment in the ceramic dispersion.
  • the step of measuring can be further defined as, or include, or be, (i) calculating the height of the sediment as a percentage of the total height of the dispersion, and/or (ii) decanting the continuous phase and measuring the mass of the sediment to determine a mass percentage of the sediment based on the total mass of the dispersion before application of gravitational force.
  • calculating the height of the sediment as a percentage of the total height of the dispersion and/or (ii) decanting the continuous phase and measuring the mass of the sediment to determine a mass percentage of the sediment based on the total mass of the dispersion before application of gravitational force.
  • the method typically uses a centrifuge to exert centripetal forces on the dispersion that are many times the normal force of gravity. This increased G force accelerates particle segregation and precipitation.
  • Any centrifuge apparatus can be used. However, it tends to be easier to evaluate amounts of sediment in a quantitative manner when the centrifuge is oriented such that the centrifuge tubes containing the test dispersions are aligned with the direction of the centripetal force applied such that the resulting precipitate top surface is parallel with the top and bottom of the centrifuge tube. In this manner, the thickness of the precipitate can be readily measured simply by using a ruled scale such as a millimeter scale.
  • a swing-out type of centrifuge that allows the centrifuge tubes to swing into this described position may be used.
  • a centrifuge can be used that mounts the centrifuge tubes onto a flat circular plate that spins such as that found in the apparatus manufactured and marketed as a LUMiSizer.
  • a LUMiSizer 6112-24 dispersion analyzer is used. This analyzer is designed to accelerate and follow a precipitation process by shining a beam of light through the centrifuge tube while spinning. When using a dispersion that includes both large and small particles, large amounts of large particle precipitate maybe observed with the naked eye while the rest of the dispersion remains opaque to a probe of the
  • a first method decants the dispersion from the precipitate and measure the mass of the precipitate as a percentage of the total mass of the dispersion before applying the centrifuge centripetal force.
  • the second method aligns a ruled scale to the centrifuge tube and the distance between the bottom of the tube, the top of the dispersion, and the top of the precipitate and reports the height of the precipitate as a percentage of the total height of the dispersion.
  • the rate of spin of the centrifuge can be varied to minimize the testing time such that a measurable amount of precipitate can be observed while avoiding that all or most of the particles precipitated.
  • the acceleration applied to the dispersions is calculated by the following equations:
  • r circular radius from the center of rotation to the midpoint of the dispersion column (m)
  • ⁇ angular velocity (rad/s)
  • Samples can be prepared by pipetting the dispersions into centrifuge tubes to a height of 45 mm.
  • Polyamide centrifuge tubes can be used to prevent dissolution of the tubes by the acrylate monomers.
  • An acceleration force of 2000 G typically precipitates all particles, which is not desirable. 500 G of force may achieve the same undesirable result.
  • a rotation speed of about 600 RPM corresponding to 46 G may produce reproducibly measurable amounts of precipitate.
  • the time that the rotation is applied can then be varied to determine optimum test time.
  • Two test samples can then be removed from the centrifuge at 10 minute intervals. More specifically, the tubes can be spun for 10-60 minutes at 46x gravity (e.g. 600 rpm) at 25°C. Centrifugation can start with a full set of tubes (12 each).
  • centrifugation can then be paused to remove one tube for sediment measurement while the centrifugation continues with the rest of the tubes.
  • the height of the sediment and the total height of the dispersion can be measured with a scale having a precision of ⁇ 0.5 mm.
  • the appropriate acceleration can depend, at least in part, on the properties of the particles in the dispersion.
  • the G force is from 25 to 100, 30 to 95, 35 to 90, 40 to 85, 45 to 80, 50 to 75, 55 to 70, 60 to 65, 40 to 50, 40 to 45, or 45 to 50, G. In other embodiments, the G force is from 100 to 2000, 200 to 1900, 300 to 1800, 400 to 1700, 500 to 1600, 600 to 1500, 700 to 1400, 800 to 1300, 900 to 1200, or 1000 to 1100, G.
  • visualization of a sediment boundary can be customized by adding small fractions of pigment (0.1 w% of Oracet Blue 640). Without pigment, the interface of sediment and supernatant can be barely detectable as the instant dispersion typically does not have a clear supernatant. Instead, only the largest particles from the sediment tend to be apparent while the majority of the ceramic small particles remain suspended in the supernatant rendering it opaque.
  • pigment 0.1 w% of Oracet Blue 640
  • This disclosure also provides a method of forming the dispersion.
  • the method includes the steps of providing the cationicallypolymerizable aliphatic epoxide, providing the cationically polymerizable oxetane, providing the free-radical polymerizable multifunctional (meth)acrylate, providing the cationic photoinitiator, providing the free-radical photoinitiator, and providing the coated filler.
  • the method also includes the steps of combining the cationically polymerizable aliphatic epoxide, the cationically polymerizable oxetane, the free- radical polymerizable multifunctional (meth)acrylate, the cationic photoinitiator, the free- radical photoinitiator, and the coated filler to form the dispersion.
  • One or more of any of the aforementioned components can be combined with any one or more other components as a whole or in various parts.
  • silica particles in order to lower the dispersion viscosity sufficient for 3D printing and to avoid the presence of agglomerate particles greater than one print layer thickness, the silica particles must experience high shear during mixing in order to break up large silica agglomerates.
  • this silica concentrate is then mixed with the remaining liquid ingredients (e.g. a "photopolymer diluent") to reduce the dispersion viscosity suitable for 3D printing.
  • Silica photopolymer dispersions for example, can be prepared using high shear mixing, such as that provided by an anchor-double-helix mixer National Board No./U-l 131 manufactured by Chemineer or a 5 quart KitchenAid mixer using a KFE5T Flex Edge Beater available from Amazon.com. It some embodiments, it is important to have sufficient shear of the high viscosity silica concentrate in order to de-agglomerate the silica before reducing the viscosity by the addition of the photopolymer diluent.
  • Stirring can be continued in this manner for an additional two hours.
  • the stirring speed can be increased, however stirring speed should be moderated to maintain the temperature of the mixture below 50 °C in order to avoid polymerizing the dispersion.
  • This silica concentrate can then ne mixed with the remaining liquid ingredients ("photopolymer diluent") in order to reduce the dispersion viscosity suitable for 3D printing.
  • Chemineer vessel temperature of the vessel can be controlled by a cooling jacket in addition to agitation speed. Typically but not required, higher agitation speeds were used at the end of the mix time to ensure agglomeration break-up. Any high shear blade or paddle such as the double helix will provide enough shear to break agglomerations.
  • the dispersion can be used to form a ceramic article.
  • the ceramic article is not particularly limited and may be any known in the art.
  • the ceramic article is typically a ceramic core or ceramic shell which create a mold for the investment casting of nickel super alloy parts.
  • the dispersion can be used to form a ceramic article that is involved in the casting or formation of metal parts and many different types of casting.
  • This disclosure also provides a method of forming a ceramic article from the dispersion.
  • the method includes the steps of A. applying a layer of the ceramic dispersion to a surface and B. selectively exposing the layer image wise to actinic radiation to form an imaged cross-section.
  • the method also includes the steps of C. applying a second layer of the ceramic dispersion to the imaged cross-section and D. selectively exposing the second layer image wise to actinic radiation to form a second imaged cross-section.
  • the method also includes the steps of E. repeating steps (C) and (D) to create a three-dimensional green ceramic article and F. sintering the three-dimensional green ceramic article in a furnace to form the ceramic article.
  • the step of A. applying a layer of the ceramic dispersion to a surface maybe further defined as applying a layer of the dispersion having a thickness of from 50 to 100, 55 to 95, 60 to 90, 65 to 85, 70 to 80, or 75 to 80, ⁇ , to the surface.
  • the surface is not particularly limited and may be any known in the art.
  • typically all the layers in a part build have the same thickness, e.g. either 50 or 100 ⁇ .
  • the layers can be 150 or 200 ⁇ thick, but then the stair stepping on sloped surfaces may be too great.
  • a series of layers are build forming vertical walls at a high layer thickness while building the layers that form sloped or rounded surfaces at a smaller layer thickness. Thicker layers tend to build faster. However, it is desirable for the contour areas of the part to have stair step height minimized.
  • the step of applying is typically further defined as applying using a doctor blade controlled by a computer.
  • the doctor blade may have 1 -3 baffles wherein the blade may or may not be enclosed such that an applied partial vacuum pulls the dispersion up into the blade for assisted deposition onto the previous layer part surface.
  • the step of B. selectively exposing the layer image wise to actinic radiation may be further defined as exposure to UV laser in the 325-365 nm range directed by X-Y scanning mirrors onto a surface of the dispersion.
  • Computer control of mirrors maybe used to draw cross sections of the part such that only the part cross section selectively receives UV radiation.
  • a bank of LED lamps having wavelengths of 260, 265, 280, 310, 325 and 340 nm, 365, 375 and 385 nm, and/or 405 nm, or combinations thereof maybe reflected off a digital micro mirror array (DLP chip) to expose a layer cross section image on the surface of the dispersion such that only the part cross section selectively receives UV radiation.
  • DLP chip digital micro mirror array
  • the step of C. applying the second layer of the ceramic dispersion to the imaged cross-section may be the same as step A or may be different in one or more respects.
  • the second layer maybe the same as, or different from, the first layer with respect to composition, thickness, size, method of application, etc.
  • the step of D. selectively exposing the second layer image wise to actinic radiation to form the second imaged cross-section may be the same as step B or may be different in one or more respects.
  • the second layer may be selectively exposed in the same way or differently than the first layer, may be exposed to the same or different actinic radiation, and may have the same, more, or less of the second layer exposed to the radiation.
  • the step of E. repeating steps (C) and (D) to create the three-dimensional green ceramic article may occur once or many times.
  • steps (C) and (D) may be repeated as many times as chosen by one of skill in the art, e.g. 50 to 5,000, times.
  • the step of F. sintering the three-dimensional green ceramic article in a furnace to form the ceramic article is typically further defined as heating at a temperature of from 1100-1600 °C in the furnace.
  • the times and temperatures maybe any known in the art.
  • the furnace type may also be any known in the art.
  • the method may be alternatively described as three-dimensionally printing the green ceramic article.
  • the method may include any one or more steps known in the art as related to three-dimensional printing.
  • one of more steps of the method maybe as described in:
  • the method may also include the step of post-curing the three-dimensional green ceramic article prior to the step of sintering. Even though most of the dispersion has typically been solidified during the part building process by the radiation provided, the part typically has only been partially polymerized.
  • the step of post-curing may be further described as when SL parts are postcured to essentially complete the polymerization process and to improve the final mechanical strength of the green ceramic article.
  • a 3D Systems Inc. postcure apparatus PCA
  • PCA postcure apparatus
  • the PCA has a turntable that provides for a more distributed actinic UV emission exposure.
  • the standard postcure time is this apparatus is 60 minutes.
  • a Prodways L5000 machine can be used and the specific parameters can be chosen by one of skill in the art.
  • a laser based stereolithography system can be used.
  • UV 3D printing that exposes photopolymer layers through a glass plate from the bottom (rather than printing from the top exposed to free air) can be used.
  • the parameters, cycle times, etc. can be chosen by one of skill in the art.
  • the green ceramic article may be cured, partially cured, or uncured, e.g. by UV radiation.
  • the green ceramic article may include cured, partially cured, or uncured monomers, as described above.
  • the green ceramic article is cured using a UV exposure sufficient to cure 200% of a layer thickness (i.e., overcure of 100 ⁇ on a 100 ⁇ layer).
  • the green ceramic article typically has a flexural modulus greater than 10 MPa, greater than 40 MPa, greater than 100 MPa, as measured by ASTM D790.
  • the combination of ceramic photopolymer formulation and UV exposure should form a green article having acceptable green strength, as described above, and a curl factor less than 3, typically less than 2 and most typically less than 1.5 as determined by the method described in Rapid Prototyping & Manufacturing: Fundamentals of StereoLithography, January 15, 1992 by Paul F. Jacobs, which is expressly incorporated herein by reference in its entirety relative to various non-limiting embodiments.
  • FTIR can be used to follow the rate of conversion of the individual epoxy, oxetane, and acrylate components to polymer within formulations containing these monomers and catalyzed with 2% Irgacure 184 (UV free radical initiator) and 2%triarylsulfonium hexafluoroantimonate (UV cationic initiator).
  • Irgacure 184 UV free radical initiator
  • 2%triarylsulfonium hexafluoroantimonate UV cationic initiator
  • the acrylate component reacts immediately via free radical polymerization to form a rigid gel that creates the form of the green body that resists the deformation forces of the 3D printing recoating process while the epoxy component reacts slowly over minutes or hours via cationic polymerization.
  • the shrinkage due to the polymerization can be distributed over time and therefore many 3D printing layers such that shrinkage occurs about the center of mass of 3D printed object.
  • the green flexural strength of a standard flexural test sample according to ASTM D790 measured 3 hours after its construction can be used as a relative indication of the initial green strength of a single layer.
  • a green ceramic article cured using a UV exposure sufficient to cure 200% of a layer thickness can have a flexural modulus greater than 10 MPa, typically greater than 40 MPa, and most typically greater than 100 MPa as measured by ASTM D790.
  • the combination of ceramic photopolymer formulation and UV exposure can form a green article having acceptable green strength, as described above, and a curl factor less than 3, typically less than 2 and most typically less than 1.5 as determined by the method described in Rapid Prototyping & Manufacturing: Fundamentals of StereoLithography, January 15, 1992 by Paul F. Jacobs.
  • the acrylate component(s) must reach full conversion immediately and that the epoxy components) conversion reach 30-50% conversion in the first 5 minutes after UV exposure and that the epoxy conversion continues slowly over the following 30 minutes to reach 60- 100% conversion.
  • the concentration of the slowly converting epoxy components) of the formulation can be maximized to be 50-80% of the monomer formulation.
  • the monomer components must have viscosities below 30 MPa-s. Higher viscosity monomers maybe included if they are minor components of the formulation, for example 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, 275 mPa-s, at 5 wt % of the mass of the ceramic photopolymer formulation.
  • each of the cationically polymerizable aliphatic epoxide, the cationically polymerizable oxetane, and the multifunctional (meth)acrylate independently has a viscosity of less than 30 mPas s as determined using ASTM D 2196 - 99.
  • the viscosity of the dispersion when silica loading is high, for example 60 percent by volume, can be high and form a thick paste.
  • Dispersants that coat the surfaces of the silica can be added to such formulations to reduce the viscosity to 1-2 Pa-s.
  • the best dispersants are salts of tertiary amines and these are highly effective. Unfortunately, these tertiary amines react immediately with the cationic photoinitiator in an acid-base reaction and over the longer term these tertiary amines catalyze the polymerization of epoxies significantly shortening the useful life of the dispersion.
  • an alternative treatment must be used that passivates at least some portion of the OH groups on surface of the fillers.
  • Surface treating filler with an organosilane reduces hydrogen bonding between particles thereby reducing the viscosity of the dispersion.
  • the organosilane is typically hydrolyzed by water and subsequently reacts with OH (e.g. silanol) groups on the surface of the filler thereby permanently passivating the surfaces. This can also reduce shear thinning behavior of because the surfaces no longer have free hydroxyl groups interacting between particles. Therefore, a balance between viscosity reduction and shear thinning is sought.
  • Organosilane candidates were evaluated in the following base formula: Silica 79.3% 64.3%
  • silica were added to 65 ml ethanol while stirring in a stainless steel beaker surrounded in a water bath within a sonicator. The suspension was then sonicated for 30 minutes to de-agglomerate the silica. (3-acryloxypropyl)trimethoxysilane was then added while stirring and the suspension was acidified with two drops of acetic acid to produce a pH of 4-5, and the requisite amount of water was added. The suspension was then heated to 60 0 C for one hour and then covered and stored at room temperature overnight to allow the reaction to complete. The suspension was then washed with acetone, centrifuged to separate all of the silica, dried at 60 °C for 16 hours to drive off the alcohol reaction product, and heated at 100 °C for one hour to drive off the residual water.
  • Ethanol was chosen as the solvent because it competes with the condensation polymerization side reaction of silane to form polysiloxane, which should be minimized or eliminated.
  • silanes below were screened in the base formula set forth above using 12.8 mmol of silane per 100 g of silica and the viscosity of each is reported. Conclusions drawn from the results set forth below are that silanes having short alkyl side chains, aliphatic rings or acrylic functionalities produce the lowest formulation viscosity while those silanes having long chains or other functional groups that occupy a large volume or bipodal silanes produce high formulation viscosity. (Cyclohexyl)methyldimethoxysilane,
  • dicyclopentyldimethoxysilane, (methacryloxymethyl)methyldimethoxysilane, 3- (methacryloxypropyl)trimethoxysilane, 3-(acryloxypropyl)trimethoxysilane, 3- acetoxypropyltrimethoxysilane were the better candidates and
  • silica sediment that forms on the bottom of a 3D printing vat after long standing has the tendency to polymerize through the linking of the silica particles via the methacryloxypropyl moieties on their surfaces. The probability of this event is increased in the low oxygen environment of a sediment cake. This polymerized sediment cannot be re-suspended. Changing the silane to one having an inert side chain, for example 3-acetoxypropyltrimethoxysilane tends to eliminate this problem.
  • triethoxysilylpropoxy(polyetheneoxy)dodecanoate can be the best candidate from the aforementioned all acrylate photopolymer formula screening, such a formulation can have a very high viscosity when used in an epoxy-oxetane-acrylate photopolymer formulation where it produces a viscosity of 22 Pa-s at 10 RPM.
  • Celloxide 2021P is commercially available from Daicel Corporation, Konan, Minato-ku, Tokyo 108-8230, Japan or Daicel (U.S.A.), Inc., One Parker Plaza, 400 Kelby Street, Fort Lee, New Jersey 07024, USA functions as a cationically cured aliphatic epoxy monomer and acts as a UV curable binder for ceramic component particles.
  • Celloxide 202 IP from Daicel Corporation is typical due to its low viscosity and thermal stability relative to other manufacturers.
  • the typical concentration of Celloxide 2021P 3,4- epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate is 5-14 wt %, and more typically 5-7 wt % of the mass of the organic binder phase of the formulation.
  • ERISYSTM GE-20 is commercially available from CVC Thermoset
  • Neopentylglycol diepoxide produces a rigid high modulus polymer having a high glass transition temperature due to its germinal dimethyl groups' steric hindrance of bond rotation about the central carbon chain.
  • concentration of ERISYSTM GE-20 neopentylglycol diepoxide is 50-80%, more typically 59-68% of the mass of the organic binder phase of the formulation.
  • ARON OXETA E OXT-221 is commercially available from Toagosei America Inc., 1450 West Main Street, West Jefferson, OH43162, USA or Sanyo Corporation of America, 500 Fifth Avenue, Suite 3620, New York, NY 10110, USA functions as a low viscosity cationically cured oxetane monomer that accelerates the polymerization rate of aliphatic epoxies when used at 7-20% concentration of the mass of the organic binder phase of the formulation and assisted by 5% hydro xyethyl acrylate of the mass of the organic binder phase of the formulation or 1-5% OXT-101 of the mass of the organic binder phase of the formulation.
  • OXT-221 also acts as a minor component UV curable binder for ceramic component particles.
  • the typical concentration of ARON OXETANE OXT-221 is 5-20%, more typically 5-7% of the mass of the organic binder phase of the formulation.
  • ARON OXETANE OXT-101 is commercially available from Toagosei America Inc., 1450 West Main Street, West Jefferson, OH43162, USA or Sanyo Corporation of America, 500 Fifth Avenue, Suite 3620, New York, NY 10110, USA functions as a low viscosity cationically cured oxetane monomer that accelerates the polymerization rate and extent of conversion of aliphatic epoxies when used at 2-5% concentration of the mass of the organic binder phase of the formulation.
  • OXT-101 also acts as a minor component UV curable binder for ceramic component particles. The typical concentration of ARON
  • OXETANE OXT-221 is 1-7% of the mass of the organic binder phase of the formulation.
  • Sartomer SR 247 is commercially available from Arkema Inc., 900 First Avenue, King of Prussia, Pennsylvania 19406, USA functions as a free radically cured acrylic monomer having low viscosity that produces high green strength during the 3D printing process. Neopentylglycol diacrylate produces a rigid high modulus polymer having a high glass transition temperature due to germinal dimethyl groups' steric hindrance of bond rotation about the central carbon chain. Sartomer SR 247 also acts as a UV curable binder for ceramic component particles. The typical concentration of Sartomer SR 247 neopentylglycol diacrylate is 15-25%, more typically 20% of the mass of the organic binder phase of the formulation.
  • Hydroxyethyl acrylate is commercially available from BASF Corp., 100 Park Avenue, Florham Park, NJ 07932, USA functions as a free radically cured acrylic monomer having low viscosity that accelerates the polymerization rate and extent of conversion of aliphatic epoxies when used at 5% concentration. Hydroxyethyl acrylate also acts as a minor component UV curable binder for ceramic component particles. The typical concentration of hydroxyethyl acrylate is 1-5%, more typically 1% of the mass of the organic binder phase of the formulation.
  • Irgacure 184 is commercially available from BASF Corp., 100 Park Avenue, Florham Park, NJ 07932, USA functions as a UV free radical photo initiator for initiating acrylate polymerization.
  • the UV penetration depth, Dp is controlled by the concentration of the free radical initiator, cationic initiator, alumina, and zircon concentrations.
  • the free radical initiator concentration typically must be sufficient to produce sufficient strength in a single part layer to resist the layer recoating forces and to limit the UV light penetration depth.
  • the typical free radical initiator concentration is 1-5 wt %, and more typically 3 wt % of the mass of the organic binder phase of the formulation.
  • Triarylsulfonium hexafluoroantimonate is commercially available as
  • Chivacure 1176 from Chitec Technology Co., Ltd. 1980 Post Oak Boulevard, Suite 1500 Houston, TX 77056, USA functions as a UV cationic photoinitiator for initiating epoxy and oxetane polymerization.
  • the UV penetration depth, Dp is controlled by the concentration of the free radical initiator, cationic initiator, alumina, and zircon concentrations.
  • the cationic initiator concentration must be sufficient to fully polymerize the epoxy and oxetane components.
  • the typical cationic initiator concentration is approximately 2-3 times that of the free radical initiator concentration, more typically 2.3 times that of the free radical initiator concentration.
  • the typical concentration of the cationic initiator is 5-9 wt %, and more typically 7 wt % of the mass of the organic binder phase of the formulation.
  • Base stabilizers N,N-dimethylbenzylamine and sodium carbonate are commercially available from Sigma-Aldrich Corp., St. Louis, MO, USA and function as proton absorbers for stabilization of cationically cured epoxies and oxetanes.
  • Sodium carbonate is added to the formulation as a 15 wt % aqueous solution or dissolved in the water used to hydrolyze the organo silane.
  • the typical concentration of N,N-dimethylbenzylamine is 0.001-0.01%, more typically 0.005% of the entire mass of the formulation.
  • the typical concentration of sodium carbonate is 0.02-0.05%, more typically 0.03% of the entire mass of the formulation.
  • Silica functions as the ceramic component which, after binder burnout and sintering, forms the ceramic mold for investment casting.
  • the typical silica concentration is 55-67 volume %, more typically 63-64 volume % of the entire volume of the formulation.
  • 3-acetoxypropyltrimethoxysilane is commercially available from Gelest Inc., 11 East Steel Rd., Morrisville Pa 19067, USA, functions as a silane surface treatment for the silica particles.
  • Surface treating the silica particle surfaces with an organosilane reduces hydrogen bonding between particles thereby reducing the viscosity of the formulation.
  • 3- acetoxypropyltrimethoxysilane is hydrolyzed by water subsequently reacts with silanol groups on the silica surfaces.
  • silica surface is passivated and the 3-acetoxypropysilyl moiety is then inert to reaction with acrylates or epoxies or oxetanes and compatible with these monomers having similar chemical polarity. While silanation of the silica surface reduces the formulation viscosity, it also reduces the shear thinning behavior of the formulation because the silica surfaces no longer have hydroxyl groups interacting between particles. The extent of silanation of the silica surface is therefore a balance between the objectives of viscosity reduction and shear thinning that helps stabilize the suspension to sedimentation.
  • the silica sediment that forms on the bottom of the 3D printing vat after long standing has the tendency to polymerize through the linking of the silica particles via the methacryloxypropyl moieties on their surfaces.
  • the probability of this event is increased in the low oxygen environment of the sediment cake.
  • the polymerized sediment cannot be re-suspended.
  • the typical silica concentration is 0.2-3 wt %, more typically 0.5-2.5 wt %, and most typically 2% of the mass of silica contained in the formulation.
  • the silica particles may experience high shear during mixing in order to break up large silica agglomerates. This can require slow addition of the silica powder to all of the dispersion liquid ingredients, except the organosilane and water, followed by continuous shear mixing of this high viscosity paste for several hours. The organosilane can then be added causing reduction of the viscosity of the preparation from a thick stiff paste to a soft paste that flows.
  • the water required for hydrolysis of the silane can then be added in order to silanate the surfaces of the de-agglomerated silica. Addition of the organosilane at the beginning of the preparation process may cause the silica agglomerates to become chemically bound together preventing the de-agglomeration process.
  • silica photopolymers were prepared using a 5 quart or 8 quart Kitchenaid kitchen mixer available from Amazon.com. Sufficient shear of the high viscosity silica concentrate can be important in order to de-agglomerate the silica before reducing the viscosity by the addition of the silane and water. All of the ingredients except the silica, silane, and water components were added to the mixer equipped with the nylon coated flat beater for the 5 quart mixer or the burnished metal flat beater for the 8 quart mixer. These liquid ingredients were then mixed on the slowest speed setting for 10 minutes.
  • the silica powder was then added in small aliquots such that the consistency did not go beyond the paste stage while allowing sufficient mixing between aliquot additions to reduce the viscosity back to a high viscosity liquid.
  • the silica addition usually requires 45 -60 minutes.
  • the stirrer is then changed to the flex edge beater in order to increase the shear force for breaking up silica agglomerates by having a smaller clearance between the stir blade and the mixing bowl wall. Stirring is continued in this manner for an additional two hours.
  • the stirring speed can be increased, however stirring speed should be moderated to maintain the temperature of the mixture below 50 °C in order to avoid polymerizing the dispersion.
  • the silane and water is then added and mixing continued for an additional 15 minutes.
  • the mixture is then allowed to rest in the dark for 24 hours at room temperature to allow the silane to hydrolyze and react with the surface of the silica particles.
  • Triethoxysilanes require approximately eight times longer to hydrolyze than trimethoxysilanes, so additional reaction time must be allowed when using triethoxysilanes.
  • FTIR was used to follow the rate of conversion of the individual epoxy, oxetane, and acrylate components to polymer within formulations containing these monomers and catalyzed with 2% Irgacure 184 (UV free radical initiator) and 2%triarylsulfonium hexafluoroantimonate (UV cationic initiator).
  • the area under the absorption curve between 802 - 819 cm-1 (absorption peak at 810 cm-1) was integrated and its attenuation with time was used to follow the acrylate monomer conversion with a precision of +/- 5%.
  • NPGDE neopentylglycol diepoxide
  • Celloxide 202 IP 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate
  • Spectra are recorded a) before UV exposure (reference spectrum), b) during/after UV exposure each 1.25 s for 1.25 min (first spectrum with start of exposure) and c) thereafter each 60 s over 30 minutes.
  • Raw spectra are processed using OPUS 7.0 software. All spectra are baseline- corrected and normalized with respect to the region 2700-3050 cm-1 (CH polymer backbone signal) to compensate for variation of film thickness between samples.
  • the different chemical families' conversion degrees are calculated from the absorption bands and with spectrum integration algorithms as summarized in the table below and in Figure 1.
  • the conversion degree of a chemical family is defined as the ratio of its absorption band integral before and after exposure.
  • Figure 2 shows typical conversion curves as a function of time for acrylate, oxetane, and epoxy compounds.
  • a range of "at least 10" inherently includes a subrange of from at least 10 to 35, a subrange of from at least 10 to 25, a subrange of from 25 to 35, and so on, and each subrange maybe relied upon individually and/or collectively and provides adequate support for specific embodiments within the scope of the appended claims.
  • an individual number within a disclosed range may be relied upon and provides adequate support for specific embodiments within the scope of the appended claims.
  • a range "of from 1 to 9" includes various individual integers, such as 3, as well as individual numbers including a decimal point (or fraction), such as 4.1 , which may be relied upon and provide adequate support for specific embodiments within the scope of the appended claims.

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Abstract

A photopolymer ceramic dispersion for additive fabrication is provided. The dispersion includes a cationicallypolymerizable aliphatic epoxide, a cationically polymerizable oxetane, a free-radical polymerizable multifunctional (meth)acrylate, a cationic photo initiator, a free-radical photoinitiator, and a coated filler including core particles and a surface treatment disposed on the core particles. The core particles include silica, alumina, zircon, or combinations thereof. The surface treatment includes an organosilane. The core particles are microparticles having a particle size of from (1) micrometer to (90) micrometers and wherein the core particles comprise (5) weight percent or less of nanoparticles having a particle size of from (10) nanometers to (999) nanometers.

Description

PHOTOPOLYMER CERAMIC DISPERSION
FIELD OF THE DISCLOSURE
[0001] This disclosure generally relates to a photopolymer ceramic dispersion for additive fabrication. More specifically, the dispersion includes core particles and a surface treatment disposed on the core particles, wherein the core particles are microparticles and includes 5 weight percent or less of nanoparticles having a particle size of from 10 nanometers to 999 nanometers.
BACKGROUND
[0002] Additive fabrication processes for producing three dimensional objects are well known. Additive fabrication processes utilize computer-aided design (CAD) data of an object to build three-dimensional parts. These three-dimensional parts may be formed from liquid resins, powders, or other materials.
[0003] In stereolithography (SL), CAD data of an object is transformed into thin cross- sections of a three-dimensional object. The data is loaded into a computer which controls a laser that traces a pattern of a cross section through a dispersion composition in a vat, solidifying a thin layer of the resin composition corresponding to the cross section. The solidified layer is recoated with the resin composition and the laser traces another cross section to harden another layer of the resin composition on top of the previous layer. The process is repeated layer by layer until the three-dimensional object is completed. When initially formed, the three-dimensional object is, in general, not fully cured, and is called a "green model." This process is also known as three-dimensional (3D) printing.
[0004] There are several types of lasers used in stereolithography, traditionally ranging from 193 nm to 355 nm in wavelength, although other wavelength variants exist. The use of gas lasers to cure dispersion compositions is well known. The delivery of laser energy in a stereolithography system can be Continuous Wave (CW) or Q-switched pulses. CW lasers provide continuous laser energy and can be used in a high speed scanning process. However, their output power is limited which reduces the amount of curing that occurs during object creation. Other methods of additive fabrication utilize lamps or light emitting diodes (LEDs). LEDs are semiconductor devices which utilize the phenomenon of electroluminescence to generate light. At present, LED UV light sources currently emit light at wavelengths between 300 and 475 nm, with 365 nm, 390 nm, 395 nm, 405 nm, and 415 nm being common peak spectral outputs. [0005] Many additive fabrication applications require the green model to possess high mechanical strength (e.g. modulus of elasticity, fracture strength, etc.). This property, often referred to as "green strength," is typically determined by the dispersion composition. Some compositions include silica, e.g. to increase the heat deflection temperature and modulus or to make ceramic parts. However, such compositions tend to have (1) a high initial viscosity, (2) a poor viscosity stability, and (3) a tendency to phase separate, resulting in phenomena known as either "soft pack" or "hard pack," and (4) high cure shrinkage resulting in distortion of the printed part.
[0006] As the amount of silica is increased in such a composition, the viscosity of the composition increases, resulting in decreased workability and processing speed. At the same time, the composition must have sufficient viscosity stability over time. Viscosity should not significantly increase over time or additional processing problems can result.
[0007] Furthermore, such compositions tend to phase separate over time when stored. For example, the silica may collect in the bottom of a storage container resulting in a phase separated composition. The top part of the composition maybe a low- viscosity, largely unfilled portion, i.e., a portion that does not include sufficient loadings of the silica. The bottom part maybe supersaturated with silica and high- viscosity. The composition in the top portion cannot be used to produce green models with sufficient strength and stiffness and any resulting part will suffer high shrinkage and cracking during binder burnout and sintering due to the depletion of silica. The composition in the bottom part cannot be used because it is too viscous and has a concentration of silica that makes the final part unusable. Therefore, entire containers can become unusable or, at a minimum, must undergo further expensive and time consuming processing to be able to be used.
[0008] In one scenario, the silica settles at the bottom of the storage container and forms a soft pack. The settled silica may be surrounded by partially polymerized resin, resulting in a wax-like consistency. Although re-assimilation into a useable composition is possible, such a process requires frequent and often vigorous recirculation. This is a time- and energy- consuming maintenance process, and still does not obviate the composition's problematic viscosity.
[0009] In another scenario, the silica settles at the bottom of the storage container and forms a hard pack. In such a scenario, the silica forms very hard, rock-like structures. Such structures must be broken up by a drill or similar apparatus before re-assimilation is possible. Again, this is very time and energy intensive. Accordingly, there remains an opportunity for improvement. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0010] Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
[0011] Figure 1 is an infrared absorption spectra before and 30 min after UV exposure (350- 380 nm) for 4s with 540 mW/cm2 for compositions of the Examples.
[0012] Figure 2 is a graph of typical conversion curves as a function of time for acrylate, oxetane, and epoxy compounds.
SUMMARY OF THE DISCLOSURE
[0013] This disclosure provides a photopolymer ceramic dispersion for additive fabrication. The dispersion includes a cationically polymerizable aliphatic epoxide, a cationically polymerizable oxetane, a free-radical polymerizable multifunctional (meth)acrylate, a cationic photo initiator, a free-radical photoinitiator, and a coated filler including core particles and a surface treatment disposed on the core particles. The core particles include silica, alumina, zircon, or combinations thereof. The surface treatment includes an organosilane. The core particles are microparticles having a particle size of from 1 micrometer to 90 micrometers and wherein the core particles comprise 5 weight percent or less of nanoparticles having a particle size of from 10 nanometers to 999 nanometers.
[0014] This disclosure also provides a method of forming a ceramic article from the photopolymer ceramic dispersion. The method includes the steps of applying a layer of the ceramic dispersion to a surface and selectively exposing the layer imagewise to actinic radiation to form an imaged cross-section. The method also includes the steps of applying a second layer of the ceramic dispersion to the imaged cross-section and selectively exposing the second layer imagewise to actinic radiation to form a second imaged cross-section. The method further includes the steps of repeating steps (C) and (D) to create a three-dimensional green ceramic article; and sintering the three-dimensional green ceramic article in a furnace to form the ceramic article.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0015] This disclosure provides a photopolymer ceramic dispersion for additive fabrication, hereinafter described as a "dispersion." The terminology "additive fabrication" describes building parts in layers, as is well known in the art and as is described above. The terminology "photopolymer" describes that the dispersion includes a free-radical initiator (e.g. a photoinitiator). The terminology "ceramic" describes that the dispersion is used to form ceramic articles, also described in greater detail below. The terminology "dispersion" describes a composition that includes a continuous phase and a dispersed phase that is dispersed in the continuous phase.
[0016] In one embodiment, the dispersion includes one or more cationicallypolymerizable compounds, one or more radically polymerizable compounds, one or more cationic photoinitiators, one or more free-radical photoinitiators, and one or more coated fillers. In other embodiments, the dispersion includes a cationicallypolymerizable aliphatic epoxide, a cationicallypolymerizable oxetane, a free-radical polymerizable multifunctional
(meth)acrylate, a cationic photoinitiator, a free-radical photoinitiator, and a coated filler, each of which is described in detail below.
[0017] In various embodiments, the dispersion is, consists essentially of, or consists of, the one or more cationicallypolymerizable compounds, the one or more radically polymerizable compounds, the cationic photoinitiator, the free-radical photoinitiator, and the coated filler. In other embodiments, the dispersion is, consists essentially of, or consists of, the cationically polymerizable aliphatic epoxide, the cationicallypolymerizable oxetane, the free-radical polymerizable multifunctional (meth)acrylate, the cationic photoinitiator, the free-radical photoinitiator, and the coated filler.
[0018] For example, in embodiments that "consist essentially of the aforementioned components, the dispersion may be free of compounds that are not cationically polymerizable compounds (other than any required compounds of this disclosure which may or may not be cationically polymerizable), compounds that are not free radically curable, UV curable monomers that are not free-radical polymerizable multifunctional (meth)acrylates, other monomers that are polymerizable by free-radical mechanisms, other monomers that are polymerizable by non-UV and/or free-radical mechanisms, other polymers, additives of any type known in the art including any additives that are not the cationic photoinitiator, the free- radical photoinitiator, and the coated filler introduced above. In various embodiments, the dispersion is free of UV curable monomers that are not free-radical polymerizable multifunctional (meth)acrylates. Alternatively, any one or more of these components may be present in an amount of less than 25, 20, 15, 10, 5, 4, 3, 2, 1, 0.1, 0.05, 0.01, etc, or any range thereof, based on a total weight of the dispersion. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated. [0019] The dispersion typically includes the cationicallypolymerizable aliphatic epoxide, the cationically polymerizable oxetane, and the free-radical polymerizable multifunctional (meth)acrylate as a continuous phase (which may include soluble additives, initiators, etc. including any described below). The dispersion also typically includes the coated filler as a dispersed phase that is dispersed in the continuous phase.
[0020] Any one or more of the polymerizable components and/or organic components or solvents described herein maybe or form the continuous phase. Also, throughout this disclosure, the terminology "organic phase" may be understood as the continuous phase of the dispersion.
Cationic Polymerizable Component:
[0021] In various embodiments, the cationic polymerizable component maybe chosen from cyclic ether compounds, cyclic acetal compounds, cyclic thioethers compounds, spiro- orthoester compounds, cyclic lactone compounds, and vinyl ether compounds, and any combination thereof. In various embodiments, the dispersion includes a cationically polymerizable aliphatic epoxide. In various embodiments, the cationically polymerizable aliphatic epoxide is a multifunctional glycidyl ether, e.g. neopentyl glycol diglycidyl ether. Suitable cationicallypolymerizable components include, but are not limited to, cyclic ether compounds such as epoxy compounds and oxetanes, cyclic lactone compounds, cyclic acetal compounds, cyclic thioether compounds, spiro orthoester compounds, and vinylether compounds. Specific non-limiting examples of cationically polymerizable components include 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, 2-(3,4- epoxycyclohexyl-5,5-spiro-3,4-epoxy)-cyclohexane-l,4-dioxane, bis(3,4- epoxycyclohexylmethyl)adipate, vinylcyclohexene oxide, 4-vinylepoxycyclohexane, vinylcyclohexene dioxide, limonene oxide, limonene dioxide, bis(3,4-epoxy-6- methylcyclohexylmethyl)adipate, 3,4-epoxy-6-methylcyclohexyl-3',4'-epoxy-6'- methylcyclohexanecarboxylate, .epsilon.-caprolactone-modified 3,4-epoxycyclohexylmethyl- 3',4'-epoxycyclohexane carboxylates, trimethylcaprolactone-modified 3,4- epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylates, .beta.-methyl-.delta.- valerolactone-modified 3 ,4-epoxycyclohexcylmethyl-3 ',4'-epoxycyclohexane carboxylates, methylenebis(3,4-epoxycyclohexane), bicyclohexyl-3,3'-epoxide, bis(3,4-epoxycyclohexyl) with a linkage of -0-, --S-, -SO-, -S02-, -C(CH3)2-, -CBr2~, -C(CBr3)2-, - C(CF3)2~, -C(CC13)2~, or -CH(C6H5)~ dicyclopentadiene diepoxide, di(3,4- epoxycyclohexylmethyl) ether of ethylene glycol, ethylenebis(3,4- epoxycyclohexanecarboxylate), epoxyhexahydrodioctylphthalate, epoxyhexahydro-di-2- ethylhexyl phthalate, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, neopentylglycol diglycidyl ether, glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, diglycidyl esters of aliphatic long-chain dibasic acids, monoglycidyl ethers of aliphatic higher alcohols, monoglycidyl ethers of phenol, cresol, butyl phenol, or polyether alcohols obtained by the addition of alkylene oxide to these compounds, glycidyl esters of higher fatty acids, epoxidized soybean oil, epoxybutylstearic acid, epoxyoctylstearic acid, epoxidized linseed oil, epoxidized polybutadiene, l,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene, and any combination thereof. One or more of these components can be combined with any one or more other components as a whole or in various parts.
[0022] The cationically polymerizable component may optionally also include polyfunctional materials including dendritic polymers such as dendrimers, linear dendritic polymers, dendrigraft polymers, hyperbranched polymers, star branched polymers, and hypergraft polymers with epoxy or oxetane functional groups. The dendritic polymers may include or be one type of polymerizable functional group or different types of polymerizable functional groups, for example, epoxy and oxetane functions.
[0023] In one embodiment, the composition of the present disclosure also includes one or more mono or poly glycidylethers of aliphatic alcohols, aliphatic polyols, polyester polyols or polyether polyols. Examples of components include 1,4-butanedioldiglycidylether, glycidylethers of polyoxyethylene and polyoxypropylene glycols and trio Is of molecular weights from about 200 to about 10,000; glycidylethers of polytetramethylene glycol or poly(oxyethylene-oxybutylene) random or block copolymers. In a specific embodiment, the cationically polymerizable component includes a polyfunctional glycidylether that lacks a cyclohexane ring in the molecule. In another specific embodiment, the cationically polymerizable component includes a neopentyl glycol diglycidyl ether. In another specific embodiment, the cationically polymerizable component includes a 1,4
cyclohexanedimethanol diglycidyl ether.
[0024] Examples of commercially available polyfunctional glycidylethers are Erisys GE 22 (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.RTM. F713. Examples of commercially available monofunctional glycidylethers are Heloxy 71, Heloxy 505, Heloxy 7, Heloxy 8, and Heloxy 61.
[0025] In an embodiment, the epoxide is 3,4-epoxycyclohexylmethyl-3',4- epoxycyclohexanecarboxylate (available as CELLOXIDE 202 IP from Daicel Chemical, 1,4- cyclohexanedimethanol diglycidyl ether (available as HELOXY 107 from Momentive), a mixture of dicyclohexyl diepoxide and nanosilica (available as NANOPDX), and any combination thereof.
[0026] The above-mentioned cationically polymerizable compounds can be used singly or in combination of two or more thereof. In embodiments of the disclosure, the cationic polymerizable component further includes at least two different epoxy components. In a specific embodiment, the cationic polymerizable component includes a cyclo aliphatic epoxy, for example, a cycloaliphatic epoxy with 2 or more than 2 epoxy groups. In another specific embodiment, the cationic polymerizable component includes an epoxy having an aromatic or aliphatic glycidyl ether group with 2 (difunctional) or more than 2 (polyfunctional) epoxy groups.
[0027] In various non-limiting embodiments, it is important that the polymerization of epoxy components) is minimized (30-50% conversion) in the first 5 minutes after UV exposure and that the epoxy conversion continue slowly over the thereafter to reach 70-100% conversion after 30 minutes in order to minimize the curl shrinkage distortion of a fabricated part.
Aliphatic epoxies alone typically reach a conversion of 34% and 60% for neopentylglycol diepoxide (NPGDE) and 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (Celloxide 2021P), respectively, which is typically insufficient for adequate cure of the 3D printed parts. Therefore, aliphatic epoxies are typically combined with oxetanes and acrylates in order to create adequately cured 3d printed parts. The concentrations set forth below typically indicate percent by weight of the organic phase of the dispersion. In one embodiment, NPGDE conversion increases when combined with 20% neopentylglycol diacrylate (NPGDA) and increasing amounts (7-20%) of l,4-Bis[(3-ethyl-3- oxetanylmethoxy)methyl]benzene (Aron OXT-121), reaching 80-100% conversion 30 minutes after UV exposure. In other embodiments, at lower concentrations (7-10%) of Aron OXT-121, NPGDE conversion can be further increased by the addition of 5% hydroxyethyl acrylate. In further embodiments, with 20% NPGDA and without the assistance of oxetanes, NPGDE conversion can be increased from 43% to 95% by combination with 5% or more of Celloxide 202 IP. In still further embodiments, use of more than 7% Celloxide 202 IP increases the viscosity of the ceramic dispersion beyond the point of utility for 3D printing.
[0028] The cationic polymerizable component may be present, for example, in an amount from about 50 to about 80% by weight of an organic phase of the dispersion, in further embodiments from about 55 to about 70 wt % of the organic phase of the dispersion, and in further embodiments from about 58 to about 65 wt % of the organic phase of the dispersion. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
Cationicallv Polvmerizable Oxetane:
[0029] The dispersion also includes the cationically polymerizable oxetane. In various embodiments, the oxetane includes 1, 2 or more than 2 oxetane groups.
[0030] In various embodiments, the cationically polymerizable oxetane is chosen from 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((l-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, isobutoxymethyl(3 -ethyl-3 -oxetanylmethyl)ether, 2- ethylhexyl(3 -ethyl-3 -oxetanylmethyl)ether, ethyldiethylene glycol(3-ethyl-3- oxetanylmethyl)ether, dicyclopentadiene (3-ethyl-3-oxetanylmethyl)ether,
dicyclopentenyloxyethyl(3-ethyl-3-oxetanylmethyl)ether, dicyclopentenyl(3-ethyl-3- oxetanylmethyl)ether, tetrahydrofurfuyl(3-ethyl-3-oxetanylmethyl)ether, 2-hydroxyethyl(3- ethyl-3 -oxetanylmethyl)ether, 2-hydroxypropyl(3 -ethyl-3 -oxetanylmethyl)ether, and combinations thereof. In other embodiments, the cationically polymerizable oxetane is chosen from 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, and combinations thereof.
[0031] The cationically polymerizable oxetane is typically included in an amount of from about 5 to about 30 wt % of the organic phase of the dispersion. In another embodiment, the cationically polymerizable oxetane is present in an amount from about 10 to about 25 wt % of the organic phase of the dispersion, and in yet another embodiment, the cationically polymerizable oxetane is present in an amount from 20 to about 30 wt % of the organic phase of the dispersion. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated. In various embodiments, the cationically polymerizable oxetane is chosen to increase the reaction rate of the cationically polymerizable aliphatic epoxide.
Free-Radical Polymerizable Component:
[0032] In various embodiments, the dispersion includes at least one free-radical
polymerizable component, that is, a component which undergoes polymerization initiated by free radicals. The free-radical polymerizable components are monomers, oligomers, and/or polymers and can be monofunctional or polyfunctional materials, i.e., have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or up to 100 or more functional groups that can polymerize by free radical initiation such as aliphatic, aromatic, cycloaliphatic, arylaliphatic, heterocyclic moiety(ies), or any combination thereof. Examples of polyfunctional materials include dendritic polymers such as dendrimers, linear dendritic polymers, dendrigraft polymers, hyperbranched polymers, star branched polymers, and hypergraft polymers. The dendritic polymers may include one type of polymerizable functional group or different types of polymerizable functional groups, for example, acrylates and methacrylate functions.
[0033] Non-limiting examples of suitable free-radical polymerizable components include acrylates and methacrylates such as 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, acryloyl morpholine, (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, 2- hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, methyl (meth)acrylate, 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, tridecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl
(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, butoxyethyl (meth)acrylate,
ethoxydiethylene glycol (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, methoxyethylene glycol (meth)acrylate, ethoxyethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, diacetone
(meth)acrylamide, beta-carboxyethyl (meth)acrylate, phthalic acid (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, butylcarbamethyl (meth)acrylate, n-isopropyl (meth)acrylamide fluorinated (meth)acrylate, 7-amino-3,7- dimethyloctyl (meth)acrylate.
[0034] Non-limiting examples of suitable multifunctional free-radical polymerizable components include those with (meth)acryloyl groups 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-[l,l- dimethyl-2- [( 1 -oxoallyl)oxy] ethyl]-5 -ethyl- 1 ,3 -dioxan-5 -yl]methyl acrylate; 3 ,9-bis( 1 , 1 - dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5- ]undecane di(meth)acrylate;
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, tripropyleneglycol di(meth)acrylate, glycerol tri(meth)acrylate, phosphoric acid mono- and di(meth)acrylates, C7-C20 alkyl di(meth)acrylates, tris(2- hydroxyethyl)isocyanurate tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate
di(meth)acrylate, tricyclodecane diyl dimethyl di(meth)acrylate and alkoxylated versions (e.g., ethoxylated and/or propoxylated) of any of the preceding monomers, and triethylene glycol divinyl ether, and adducts of hydroxyethyl acrylate.
[0035] In one embodiment, the radically polymerizable component is a multifunctional (meth)acrylate. The multifunctional (meth)acrylates may include all methacryloyl groups, all acryloyl groups, or any combination of methacryloyl and acryloyl groups. In an embodiment, the free-radical polymerizable component is chosen from propoxylated trimethylolpropane tri(meth)acrylate, and propoxylated neopentyl glycol di(meth)acrylate, and any combination thereof. In another embodiment, the multifunctional (meth)acrylate is chosen from trimethylolpropane tri(meth)acrylate, ethylene glycol di(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, tripropyleneglycol di(meth)acrylate, glycerol
tri(meth)acrylate, and combinations thereof.
[0036] In a typical embodiment, the multifunctional (meth)acrylate has more than 2, more typically more than 3, and more typically greater than 4 functional groups. In another typical embodiment, the radically polymerizable component consists exclusively of a single multifunctional (meth)acrylate component. In further embodiments, the exclusive radically polymerizable component is tetra-functional, in further embodiments, the exclusive radically polymerizable component is penta-functional, and in further embodiments, the exclusive radically polymerizable component is hexa-functional.
[0037] In another embodiment, the free-radical polymerizable component is chosen from dicyclopentadiene dimethanol diacrylate, [2-[l,l-dimethyl-2-[(l-oxoallyl)oxy]ethyl]-5-ethyl- l,3-dioxan-5-yl]methyl acrylate, propoxylated trimethylolpropane triacrylate, and propoxylated neopentyl glycol diacrylate, and any combination thereof.
[0038] In other embodiments, the dispersion includes one or more of dicyclopentadiene dimethanol di(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, and/or propoxylated neopentyl glycol di(meth)acrylate, and more specifically one or more of dicyclopentadiene dimethanol diacrylate, propoxylated trimethylolpropane triacrylate, and/or propoxylated neopentyl glycol diacrylate.
[0039] In various embodiments, the dispersion includes the free-radical polymerizable multifunctional (meth)acrylate. This (meth)acrylate is able to polymerize with itself and/or with other acrylate monomers via free-radical polymerization initiated by exposure to UV light/energy. A single type or more than one type of (meth)acrylate may be used. Typically the free-radical polymerizable multifunctional (meth)acrylate is used to produce rapid green strength formation.
[0040] In various embodiments, the radically polymerizable component is further defined as a (meth)acrylate monomer which can be any monomer having at least one acrylate functional group and/or at least one methacrylate functional group. In other words, the terminology "(meth)" describes that the "meth" group is optional and not required. Thus, the monomer may be an "acrylate" monomer (without a methyl group) or a "methacrylate" monomer that includes a methyl group. It is typical that the (meth)acrylate monomer used herein is a compound selected from the group of aliphatic acrylates, aliphatic methacrylates, cycloaliphatic acrylates, cycloaliphatic methacrylates, and combinations thereof. It is to be understood that each of the compounds, the aliphatic acrylates, the aliphatic methacrylates, the cycloaliphatic acrylates, and the cycloaliphatic methacrylates, include an alkyl radical. The alkyl radicals of these compounds can include up to 20 carbon atoms.
[0041] The aliphatic acrylates that maybe selected as one of the (meth)acrylate monomers are selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, n- butyl acrylate, iso-butyl acrylate, tert-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, iso-octyl acrylate, iso-nonyl acrylate, iso-pentyl acrylate, tridecyl acrylate, stearyl acrylate, lauryl acrylate, and mixtures thereof. The aliphatic methacrylates that maybe selected as one of the (meth)acrylate monomers are selected from the group consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, tert-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, iso- octyl methacrylate, iso-nonyl methacrylate, iso-pentyl methacrylate, tridecyl methacrylate, stearyl methacrylate, lauryl methacrylate, and mixtures thereof. The cycloaliphatic acrylate that may be selected as one of the (meth)acrylate monomers is cyclohexyl acrylate, and the cycloaliphatic methacrylate that maybe selected as one of the (meth)acrylate monomers is cyclohexyl methacrylate.
[0042] The above-mentioned radically polymerizable compounds can be used singly or in combination of two or more thereof. The dispersion can include any suitable amount of the free-radical polymerizable components, for example, in certain embodiments, in an amount up to about 40 volume % of the organic phase of the dispersion, in certain embodiments, from about 2 to about 40 volume % of the organic phase of the dispersion, in other embodiments from about 5 to about 30 volume %, and in further embodiments from about 10 to about 20 volume % of the organic phase of the dispersion. In various embodiments, the acrylate monomer is present in an amount of greater than zero and up to about 40 volume % of the organic phase of the dispersion. In other embodiments, the acrylate monomer is present in amount of from 2 to 40, 5 to 40, 5 to 35, 5 to 30, 10 to 30, 10 to 25, 10 to 20, 15 to 30, 15 to 25, 15 to 20, or 1, 2, 3, 4, or 5, volume percent based on a total volume of the organic phase of the dispersion. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
[0043] In various embodiments, each of said cationically polymerizable aliphatic epoxide, said cationically polymerizable oxetane, and said multifunctional (meth)acrylate
independently has a viscosity of less than 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 15, 10, or 5, mPas s as determined using ASTM D 2196 - 99. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
Cationic Photoinitiator:
[0044] In accordance with an embodiment, the dispersion includes a cationic photoinitiator. The cationic photoinitiator initiates cationic ring-opening polymerization upon irradiation of light. In one embodiment, any suitable cationic photoinitiator can be used, for example, those with cations chosen from onium salts, halonium salts, iodosyl salts, selenium salts, sulfonium salts, sulfoxonium salts, diazonium salts, metallocene salts, isoquinolinium salts, phosphonium salts, arsonium salts, tropylium salts, dialkylphenacylsulfonium salts, thiopyrilium salts, diaryl iodonium salts, triaryl sulfonium salts, ferrocenes,
di(cyclopentadienyliron)arene salt compounds, and pyridinium salts, and any combination thereof.
[0045] In another embodiment, a cation of the cationic photoinitiator is chosen from aromatic diazonium salts, aromatic sulfonium salts, aromatic iodonium salts, metallocene based compounds, aromatic phosphonium salts, and any combination thereof. In another embodiment, the cation is a polymeric sulfonium salt or other aromatic heteroatom-including cations and naphthyl- sulfonium salts. In another embodiment, the cationic photoinitiator is chosen from triarylsulfonium salts, diaryliodonium salts, and metallocene based compounds, and any combination thereof. Onium salts, e.g., iodonium salts and sulfonium salts, and ferrocenium salts, have the advantage that they are generally more thermally stable.
[0046] In one embodiment, the cationic photoinitiator has an anion chosen from BF4.", AsFe", SbF6 ", PF6\ [B(CF3)4]", B(C6F5)4 ", B[C6H3-3,5(CF3)2]4 ", Β((¼¾α¼)4", B(C6H3F2)4 ", B[C6F4- 4(CF3)]4 ", Ga(C6F5) ", [(C6F5)3B— C3H3N2— B(C6F5)3]", [(C6F5)3B— NH2— B(C6F5)3]" , tetrakis(3,5-difluoro-4-alkyloxyphenyl)borate, tetrakis(2,3,5,6-tetrafluoro-4- alkyloxyphenyl)borate, perfluoroalkylsulfonates, tris[(perfluoroalkyl)sulfonyl]methides, bis[(perfluoroalkyl)sulfonyl]imides, perfluoroalkylphosphates,
tris(perfluoroalkyl)trifluorophosphates, bis(perfluoroalkyl)tetrafluorophosphates, tris(pentafluoroethyl)trifluorophosphates, and (CHeBnBre)", (CHeBnCle)" and other halogenated carborane anions.
[0047] In one embodiment, the cationic photoinitiator has a cation chosen from aromatic sulfonium salts, aromatic iodonium salts, and metallocene based compounds with at least an anion chosen from SbFe", PF6-, B(C6Fs)4 ", [B(CF3)4]", tetrakis(3,5-difluoro-4- methoxyphenyl)borate, perfluoroalkylsulfonates, perfluoroalkylpho sphates,
tris[(perfluoroalkyl)sulfonyl]methides, and [(C2F5)3PF3]\
[0048] Examples of cationic photoinitiators useful for reaction at 300-475 nm, particularly at 365 nm UV light, without a sensitizer include 4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4- fluorophenyl)sulfonium hexafluoroantimonate, 4-[4-(3- chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfonium
tetrakis(pentafluorophenyl)borate, 4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4- fluorophenyl)sulfonium tetrakis(3,5-difluoro-4-methyloxyphenyl)borate, 4-[4-(3- chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfonium tetrakis(2,3,5,6-tetrafluoro-4- methyloxyphenyl)borate, tris(4-(4-acetylphenyl)thiophenyl) sulfonium
tetrakis(pentafluorophenyl)borate (Irgacure PAG 290 from BASF), tris(4-(4- acetylphenyl)thiophenyl)sulfonium tris[(trifluoromethyl)sulfonyl]methide (Irgacure GSID 26-1 from BASF), tris(4-(4-acetylphenyl)thiophenyl)sulfonium hexafluorophosphate (Irgacure 270 from BASF), and HS-1 available from San-Apro Ltd.
[0049] Typical cationic photoinitiators include, either alone or in a mixture: bis[4- diphenylsulfoniumphenyl]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 (Irgacure GSID 26-1 from BASF), and tris(4-(4- acetylphenyl)thiophenyl)sulfonium hexafluorophosphate (Irgacure 270 from BASF), [4-(l- methylethyl)phenyl](4-methylphenyl) iodonium tetrakis(pentafluorophenyl)borate (available as Rhodorsil 2074 from Rhodia), 4-[4-(2-chlorobenzoyl)phenylthio]phenylbis(4- fluorophenyl)sulfon- ium hexafluoroantimonate (as SP-172 from Adeka), SP-300 from Adeka, and aromatic sulfonium salts with anions of (PF6-m(CnF2n+i)m) where m is an integer from 1 to 5, and n is an integer from 1 to 4 (available as CPI-200K or CPI-200S, which are monovalent sulfonium salts from San-Apro Ltd., TK-1 available from San-Apro Ltd., or HS- 1 available from San-Apro Ltd.)
[0050] In various embodiments, the dispersion may be irradiated by laser or LED light operating at any wavelength in either the UV or visible light spectrum. In particular embodiments, the irradiation is from a laser or LED emitting a wavelength of from 340 nm to 415 nm. In particular embodiments, the laser or LED source emits a peak wavelength of about 340 nm, 355 nm, 365 nm, 375 nm, 385 nm, 395 nm, 405 nm, or 415 nm.
[0051] In one embodiment of the disclosure, the dispersion includes an aromatic triaryl sulfonium salt cationic photoinitiator. The use of aromatic triaryl sulfonium salts as the cationic photoinitiator in dispersions is desirable in additive fabrication processes because the resulting dispersion attains a fast photospeed, good thermal-stability, and good photo- stability.
[0052] In a typical embodiment, the cationic photoinitiator is an aromatic triaryl sulfonium salt that is more specifically an R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photoinitiator, having a
tetrakis(pentafluorophenyl)borate anion and a cation of the following formula (I):
Figure imgf000017_0001
wherein Yl, Y2, and Y3 are the same or different and wherein Yl, Y2, or Y3 are R- substituted aromatic thioether with R being an acetyl or halogen group.
[0053] In one embodiment, Yl, Y2, and Y3 are the same. In another embodiment, Yl and Y2 are the same, but Y3 is different. In another embodiment, Yl, Y2, or Y3 are an R-substituted aromatic thioether with R being an acetyl or halogen group. Typically, Yl, Y2, or Y3 are a para-R-substituted aromatic thioether with R being an acetyl or halogen group.
[0054] A particularly typical R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photo initiator is tris(4-(4- acetylphenyl)thiophenyl)sulfonium tetrakis(pentafluorophenyl)borate. Tris(4-(4- acetylphenyl)thiophenyl)sulfonium tetrakis(pentafluorophenyl)borate is known commercially as IRGACURE PAG-290 and is available from Ciba/BASF.
[0055] An R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photo initiator, for instance, tris(4-(4- acetylphenyl)thiophenyl)sulfonium tetrakis(pentafluorophenyl)borate, is also more thermally- stable than some other cationic photoinitiators. The improved thermal-stability allows dispersions for additive fabrication incorporating a triaryl sulfonium
tetrakis(pentafluorophenyl)borate cationic photo initiator instead of other conventional cationic photoinitiators to retain their viscosity at elevated temperatures for long periods of time.
[0056] In another embodiment, the cationic photoinitiator is an aromatic triaryl sulfonium salt that possesses an anion represented by SbFe", PF6-, BF4 ", (CF3CF2)3PF3"(C6F5)4B",
((CF3)2C6¾)4B", (CeFs^Ga", ((CF3)2C6H3)4Ga", trifluoromethanesulfonate,
nonafluorobutanesulfonate, methanesulfonate, butanesulfonate, benzenesulfonate, or p- toluenesulfonate, and a cation of the following formula (II):
Figure imgf000018_0001
wherein each of R1, R2, R3, R5 and R6 is independently an alkyl group, a hydroxy group, an alkoxy group, an alkylcarbonyl group, an arylcarbonyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an arylthiocarbonyl group, an acyloxy group, an arylthio group, an alkylthio group, an aryl group, a heterocyclic hydrocarbon group, an aryloxy group, an alkylsulfinyl group, an arylsulfinyl group, an alkylsulfonyl group, an arylsulfonyl group, a hydroxy(poly)alkyleneoxy group, an optionally substituted amino group, a cyano group, a nitro group, or a halogen atom, R4 is an alkyl group, a hydroxy group, an alkoxy group, an alkylcarbonyl group, an alkoxycarbonyl group, an acyloxy group, an alkylthio group, a heterocyclic hydrocarbon group, an alkylsulfinyl group, an alkylsulfonyl group, a hydroxy(poly)alkyleneoxy group, an optionally substituted amino group, a cyano group, a nitro group, or a halogen atom, m1 to m6 is the number of occurrences of each of R1 to R6, such that each of m1, m4, and m6 is an integer of 0 to 5, and each of m2, m3, and m5 each is an integer of 0 to 4. Such photoinitiators are described in, for example, U.S. Pat. No. 8,617,787, which is expressly incorporated herein by reference in various non-limiting embodiments.
[0057] A particularly typical aromatic triaryl sulfonium cationic photoinitiator has an anion that is a fluoroalkyl-substituted fluorophosphate. Commercial examples of an aromatic triaryl sulfonium cationic photoinitiator having a fluoroalkyl-substituted fluorophosphate anion is the CPI-200 series (for example CPI-200K or CPI-2105) or 300 series, available from San- Apro Limited.
[0058] In various embodiments, the dispersion includes a cationic polymerizable component in addition to an R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl)borate or fluoroalkyl-substituted fluorophosphate cationic photoinitiator. In other embodiments, the dispersions for additive fabrication include cationic polymerizable components, free-radical photoinitiators, and free-radical polymerizable components. In some embodiments, the dispersions for additive fabrication include an R- substituted aromatic thioether triaryl sulfonium tetrakis(pentafluorophenyl)borate cationic photoinitiator and additional cationic photoinitiators and/or photosensitizers, along with a cationic polymerizable component and, optionally, free-radical polymerizable components and free-radical photoinitiators.
[0059] The dispersion can include any suitable amount of the cationic photoinitiator, for example, in certain embodiments, in an amount up to about 15% by weight of the dispersion composition, in certain embodiments, up to about 5% by weight of the dispersion composition, and in further embodiments from about 2% to about 10% by weight of the dispersion composition, and in other embodiments, from about 0.1% to about 5% by weight of the dispersion composition. In a further embodiment, the amount of cationic photoinitiator is from about 0.2 wt % to about 4 wt % of the total dispersion composition, and in other embodiments from about 0.5 wt % to about 3 wt %. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
[0060] The dispersion may also contain various photoinitiators of different sensitivity to radiation of emission lines with different wavelengths to obtain a better utilization of a UV light source. The use of known photoinitiators of different sensitivity to radiation of emission lines is well known in the art of additive fabrication, and may be selected in accordance with radiation sources of, for example, 351, nm 355 nm, 365 nm, 385 nm, and 405 nm. In this context it is advantageous for the various photoinitiators to be selected such, and employed in a concentration such, that equal optical absorption is produced with the emission lines used. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
Photosensitizer:
[0061] In some embodiments, depending on the wavelength of light used for curing the dispersion, it is desirable for the dispersion to include a photosensitizer. The term
"photosensitizer" is used to refer to any substance that either increases the rate of photoinitiated polymerization or shifts the wavelength at which polymerization occurs; see textbook by G. Odian, Principles of Polymerization, 3rd Ed., 1991, page 222. A variety of compounds can be used as photo sensitizers, including heterocyclic and fused-ring aromatic hydrocarbons, organic dyes, and aromatic ketones. Examples of photo sensitizers include those chosen from methanones, xanthenones, pyrenemethanols, anthracenes, pyrene, perylene, quinones, xanthones, thioxanthones, benzoyl esters, benzophenones, and any combination thereof. Particular examples of photosensitizers include those chosen from [4- [(4-methylphenyl)thio]phenyl]phenyl-methanone, 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,l 0-diethoxyanthracene, anthracene, anthraquinones, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tertbutylanthraquinone, 1-chloroanthraquinone, 2- amylanthraquinone, thioxanthones and xanthones, isopropyl thioxanthone, 2- chlorothioxanthone, 2,4-diethylthioxanthone, l-chloro-4-propoxythioxanthone, methyl benzoyl formate (Darocur MBF from BASF), methyl-2 -benzoyl benzoate (Chivacure OMB from Chitec), 4-benzoyl-4'-methyl diphenyl sulphide (Chivacure BMS from Chitec), 4,4'- bis(diethylamino) benzophenone (Chivacure EMK from Chitec), and any combination thereof.
[0062] The dispersion can include any suitable amount of the photo sensitizer, for example, in certain embodiments, in an amount up to about 10% by weight of the dispersion composition, in certain embodiments, up to about 5% by weight of the dispersion composition, and in further embodiments from about 0.05% to about 2% by weight of the dispersion composition. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
[0063] In accordance with an embodiment, the dispersion includes a cationic photoinitiator in addition to, or in lieu of, an R-substituted aromatic thioether triaryl sulfonium
tetrakis(pentafluorophenyl) borate cationic photoinitiator. Any suitable cationic photoinitiator can be used, for example, those chosen from onium salts, halonium salts, iodosyl salts, selenium salts, sulfonium salts, sulfoxonium salts, diazonium salts, metallocene salts, isoquinolinium salts, phosphonium salts, arsonium salts, tropylium salts,
dialkylphenacylsulfonium salts, thiopyrilium salts, diaryl iodonium salts, triaryl sulfonium salts, sulfonium antimonate salts, ferrocenes, di(cyclopentadienyliron)arene salt compounds, and pyridinium salts, and any combination thereof. Onium salts, e.g., iodonium salts, sulfonium salts and ferrocenes, have the advantage that they are thermally-stable.
[0064] Typical mixtures of cationic photoinitiators include a mixture of: bis[4- diphenylsulfoniumphenyl]sulfide bishexafluoroantimonate; thiophenoxyphenylsulfonium hexafluoroantimonate (available as Chivacure 1176 from Chitec); tris(4-(4- acetylphenyl)thiophenyl)sulfonium tetrakis(pentafluorophenyl)borate (Irgacure PAG-290 or GSID4480-1 from Ciba/BASF), iodonium, [4-(l-methylethyl)phenyl](4-methylphenyl)-, tetrakis(pentafluorophenyl)borate (available as Rhodorsil 2074 from Rhodia), 4-[4-(2- chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfon- ium hexafluoroantimonate (as SP-172) and SP-300 (both available from Adeka).
[0065] Additionally, photosensitizers are useful in combination with photoinitiators in effecting cure with LED light sources emitting in the wavelength range of 300-475 nm. Examples of suitable photosensitizers include: anthraquinones, such as 2- methylanthraquinone, 2-ethylanthraquinone, 2-tertbutylanthraquinone, 1- chloroanthraquinone, and 2-amylanthraquinone, thioxanthones and xanthones, such as isopropyl thioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, and l-chloro-4- propoxythioxanthone, methyl benzoyl formate (Darocur MBF from Ciba), methyl-2-benzoyl benzoate (Chivacure OMB from Chitec), 4-benzoyl-4'-methyl diphenyl sulphide (Chivacure BMS from Chitec), 4,4'-bis(diethylamino) benzophenone (Chivacure EMK from Chitec).
[0066] In one embodiment, the photo sensitizer 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. In other embodiments, the photosensitizer is:
Figure imgf000021_0001
, or any combination thereof.
[0067] The dispersion can include any suitable amount of the photosensitizer, for example, in certain embodiments, in an amount up to about 10% by weight of the dispersion composition, in certain embodiments, up to about 5% by weight of the dispersion composition, and in further embodiments from about 0.05% to about 2% by weight of the dispersion composition. [0068] When photosensitizers are employed, other photoinitiators absorbing at shorter wavelengths can be used. Examples of such photoinitiators include: benzophenones, such as benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, and
dimethoxybenzophenone, and 1-hydroxyphenyl ketones, such as 1-hydroxycyclohexyl phenyl ketone, phenyl (l-hydroxyisopropyl)ketone, 2-hydroxy-l-[4-(2- hydroxyethoxyl)phenyl]-2-methyl- 1 -propanone, and 4-isopropylphenyl( 1 - hydroxyisopropyl)ketone, benzil dimethyl ketal, and oligo-[2-hydroxy-2-methyl-l-[4-(l- methylvinyl)phenyl]propanone] (Esacure KIP 150 from Lamberti).
[0069] An additional photosensitizer or co-initiator maybe used to improve the activity of the cationic photoinitiator. It is for either increasing the rate of photoinitiated polymerization or shifting the wavelength at which polymerization occurs. The sensitizer used in combination with the above-mentioned cationic photoinitiator is not particularly limited. 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 compounds disclosed by J. V. Crivello in Advances in Polymer Science, 62, 1 (1984), and by J. V. Crivello & K. Dietliker, "Photoinitiators for Cationic Polymerization" in Chemistry & technology of UV & EB formulation for coatings, inks & paints. Volume III, Photoinitiators for free radical and cationic polymerization, by K. Dietliker; [Ed. by P. K. T. Oldring], SITA Technology Ltd, London, 1991. Specific examples include polyaromatic hydrocarbons and their derivatives such as anthracene, pyrene, perylene and their derivatives, thioxanthones, alpha-hydroxyalkylphenones, 4-benzoyl-4'-methyldiphenyl sulfide, acridine orange, and benzo flavin.
[0070] The dispersion can include any suitable amount of the other cationic photoinitiator or photosensitizer, for example, in certain embodiments, in an amount an amount from 0.1 to 10 wt % of the dispersion composition, in certain embodiments, from about 1 to about 8 wt % of the dispersion composition, and in further embodiments from about 2 to about 6 wt % of the dispersion composition. In one embodiment, the above ranges are particularly suitable for use with epoxy monomers. In accordance with an embodiment, the dispersion includes a photoinitiating system that is a photoinitiator having both cationic initiating function and free radical initiating function. Free-Radical Photoinitiator:
[0071] The dispersion also includes a free-radical initiator. Typically, the free-radical initiator is a UV activated free-radical initiator. For example, the free-radical initiator is typically initiated by exposure to UV light which causes a radical to form, followed by propagation of that radical. However, a non-UV initiated free-radical initiator may be used alone or in combination with a UV activated free-radical initiator.
[0072] The free-radical initiator may be described as a free-radical photoinitiator. Free- radical photoinitiators are typically divided into those that form radicals by cleavage, known as "Norrish Type I" and those that form radicals by hydrogen abstraction, known as "Norrish type Π". The Norrish type II photoinitiators typically require a hydrogen donor, which serves as the free-radical source. As the initiation is based on a bimolecular reaction, the Norrish type II photoinitiators are generally slower than Norrish type I photoinitiators which are based on the unimolecular formation of radicals. However, Norrish type II photoinitiators typically possess better optical absorption properties in the near-UV spectroscopic region. Photolysis of aromatic ketones, such as benzophenone, thioxanthones, benzil, and quinones, in the presence of hydrogen donors, such as alcohols, amines, or thiols leads to the formation of a radical produced from the carbonyl compound (ketyl-type radical) and another radical derived from the hydrogen donor. The photopolymerization of vinyl monomers is typically initiated by the radicals produced from the hydrogen donor. The ketyl radicals are typically not reactive toward vinyl monomers because of the steric hindrance and the delocalization of an unpaired electron.
[0073] In various embodiments, the free-radical initiator is chosen from benzoylphosphine oxides, aryl ketones, benzophenones, hydroxylated ketones, 1 -hydroxyphenyl ketones, ketals, metallocenes, and combinations thereof. In other embodiments, the free-radical initiator is chosen from 2,4,6-trimethylbenzoyl diphenylphosphine oxide and 2,4,6-trimethylbenzoyl phenyl, ethoxyphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, 2- methyl-l-[4-(methylthio)phenyl]-2-mo holinopropanone-l,2-benzyl-2-(dim- ethylamino)-l- [4-(4-morpholinyl)phenyl]- 1 -butanone, 2-dimethylamino-2-(4-methyl-benzyl)- 1 -(4- morpholin-4-yl-phenyl)-butan-l-o- ne, 4-benzoyl-4'-methyl diphenyl sulphide, 4,4'- bis(diethylamino) benzophenone, and 4,4'-bis(N,N'-dimethylamino) benzophenone (Michler's ketone), benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone,
dimethoxybenzophenone, 1-hydroxycyclohexyl phenyl ketone, phenyl (1- hydroxyisopropyl)ketone, 2-hydroxy-l-[4-(2-hydroxyethoxyl)phenyl]-2-methyl-l-propanone, 4-isopropylphenyl(l-hydroxyisopropyl)ketone, oligo-[2-hydroxy-2 -methyl- l-[4-(l- methylvinyl)phenyl]propanone], camphorquinone, 4,4'-bis(diethylamino) benzophenone, benzil dimethyl ketal, bis(eta 5-2-4-cyclopentadien-l-yl) bis[2,6-difluoro-3-(lH-pyrrol-l- yl)phenyl]titanium, and combinations thereof.
[0074] Typically, when forming the dispersion, the wavelength sensitivity of the
photoinitiator(s) present are evaluated to determine whether they will be activated by a chosen radiation source. For light sources emitting in the 300-475 nm wavelength range, especially those emitting at 365 nm, 390 nm, or 395 nm, non-limiting examples of suitable free-radical initiators absorbing in these ranges include, but are not limited to,
benzoylphosphine oxides, such as, 2,4,6-trimethylbenzoyl diphenylphosphine oxide (Lucirin TPO from BASF) and 2,4,6-trimethylbenzoyl phenyl, ethoxy phosphine oxide (Lucirin TPO- L from BASF), bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (Irgacure 819 or BAPO from Ciba), 2-methyl-l-[4-(methylthio)phenyl]-2-morpholinopropanone-l (Irgacure 907 from Ciba), 2-benzyl-2-(dimethylamino)-l-[4-(4-morpholinyl)phenyl]-l-butanone (Irgacure 369 from Ciba), 2-dime1hylamino-2-(4-me1hyl-benzyl)-l-(4-mo holin-4-yl-phenyl)-butan-l- o- ne (Irgacure 379 from Ciba), 4-benzoyl-4'-methyl diphenyl sulphide (Chivacure BMS from Chitec), 4,4'-bis(diethylamino) benzophenone (Chivacure EMK from Chitec), and 4,4'- bis(N,N'-dimethylamino) benzophenone (Michler's ketone). Also suitable are combinations thereof.
[0075] Additionally, photosensitizers can be used, e.g. when using an LED light source. Non-limiting examples of suitable photosensitizers include: anthraquinones, such as 2- methylanthraquinone, 2-ethylanthraquinone, 2-tertbutylanthraquinone, 1- chloroanthraquinone, and 2-amylanthraquinone, thioxanthones and xanthones, such as isopropyl thioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, and l-chloro-4- propoxythioxanthone, methyl benzoyl formate (Darocur MBF from Ciba), methyl-2-benzoyl benzoate (Chivacure OMB from Chitec), 4-benzoyl-4'-methyl diphenyl sulphide (Chivacure BMS from Chitec), 4,4'-bis(diethylamino) benzophenone (Chivacure EMK from Chitec).
[0076] For light sources emitting in the wavelength range of 100 to 300 nm, photosensitizers such as benzophenones, such as benzophenone, 4-methyl benzophenone, 2,4,6-trimethyl benzophenone, dimethoxybenzophenone, and 1 -hydro xyphenyl ketones, such as 1- hydroxycyclohexyl phenyl ketone, phenyl (l-hydroxyisopropyl)ketone, 2-hydroxy-l-[4-(2- hroxyethoxy)phenyl]-2-methyl- 1 -propanone, and 4-isopropylphenyl( 1 - hydroxyisopropyl)ketone, benzil dimethyl ketal, and oligo-[2-hydroxy-2-methyl-l-[4-(l- methylvinyl)phenyl]propanone] (Esacure KIP 150 from Lamberti), and combinations thereof, can be used. [0077] For light sources emitting in the wavelength range of 475 to 900 nm, free-radical initiators such as camphorquinone, 4,4'-bis(diethylamino) benzophenone (Chivacure EMK from Chitec), 4,4'-bis(N,N'-dimethylamino) benzophenone (Michler's ketone), bis(2,4,6- trimethylbenzoyl)-phenylphosphineoxide ("BAPO," or Irgacure 819 from Ciba), and the visible light photoinitiators from Spectra Group Limited, Inc. such as H-Nu 470, H-Nu-535, H-Nu-635, H-Nu-Blue-640, and H-Nu-Blue-660, and combinations thereof, maybe used.
[0078] Referring back to the UV light used to initiate polymerization of the acrylate monomer, the light may be UVA radiation, which is radiation with a wavelength between about 320 and about 400 nm, UVB radiation, which is radiation with a wavelength between about 280 and about 320 nm, and/or UVC radiation, which is radiation with a wavelength between about 100 and about 280 nm.
[0079] The dispersion may include any amount of the free-radical initiator so long as the other required components are present. For example, the free-radical initiator maybe present in an amount of greater than zero and up to about 10 wt % of the dispersion, from about 0.1 to about 10 wt % of the dispersion, or from about 1 to about 6 wt % of the dispersion. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
Coated Filler:
[0080] The dispersion also includes a coated filler. The coated filler maybe the dispersed phase that is dispersed in the continuous phase described above. The coated filler includes core particles and a surface treatment disposed on the core particles. In various
embodiments, the core particles are chosen from glass or metal particles, glass powder, alumina, alumina hydrate, magnesium oxide, magnesium hydroxide, barium sulfate, calcium sulfate, calcium carbonate, magnesium carbonate, silicate mineral, diatomaceous earth, silica sand, silica powder, oxidation titanium, aluminum powder, bronze, zinc powder, copper powder, lead powder, gold powder, silver dust, glass fiber, titanic acid potassium whiskers, carbon whiskers, sapphire whiskers, verification rear whiskers, boron carbide whiskers, silicon carbide whiskers, silicon nitride whiskers, and combinations thereof. In other embodiments, the core particles include silica, alumina, zircon, or combinations thereof. In further embodiments, the core particles are 95-100 wt% silica. In further embodiments, the core particles are a combination of silica, 2 to 5 weight % of alumina, and 2 to 5 weight % of zircon.
[0081] In various embodiments, the coated filler is present in an amount of from 55 to 70 volume percent based on a total volume of the dispersion. In various embodiments, the coated filler is present in 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, or 70, volume percent based on a total volume of the dispersion. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
[0082] In various embodiments, the coated filler is further defined as particles, e.g.
microparticles and/or nanoparticles, that are coated. For example, the particles may be 90, 95, 99, or approximately 100 wt% of microparticles, nanoparticles, or a combination of microparticles and nanoparticles. For example, in various embodiments, the core particles are microparticles having a particle size of from 1 micrometer to 90 micrometers and wherein the core particles include 5 weight percent or less of nanoparticles having a particle size of from 10 nanometers to 999 nanometers. In other embodiments, the coated filler has a particle size from 0.04 micrometers to 90 micrometers.
[0083] Particle size may be measured using laser diffraction particle size analysis in accordance with ISO13320:2009. A suitable device for measuring the average particle diameter of nanoparticles is the LB-550 machine, available from Horiba Instruments, Inc, which measures particle diameter by dynamic light scattering. In various non-limiting embodiments, all values and ranges of values between the aforementioned values are hereby expressly contemplated.
[0084] If the core particle is silica or includes silica, the silica may include greater than 85 wt %, 90 wt %, or 95 wt % of silica (Si02). Certain non-limiting examples of commercially available silica include Crystallite 3K-S, Crystallite NX-7, Crystallite MCC-4, Crystallite CMC-12, Crystallite A-l, Crystallite AA, Crystallite C, Crystallite D, Crystallite CMC-1, Crystallite C-66, Crystallite 5X, Crystallite 2A-2, Crystallite VX-S2, Crystallite VX-SR, Crystallite VX-X, Crystallite VX-S, Huselex RD-8, Huselex RD-120, Huselex MCF-4, Huselex GP-200T, Huselex ZA-30, Huselex RD-8, Huselex Y-40, Huselex E-2, Huselex Y- 60, Huselex E-l , Huselex E-2, Huselex FF, Huselex X, Huselex ZA-20, IMSIL A-25, IMSIL A-15, IMSIL A-10, and IMSIL A-8, (Ryushin Co., Ltd.); ORGANOSILICASOL MEK-EC- 2102, Organosilicasol MEK-EC-2104, Organosilicasol MEK-AC-2202, Organosilicasol MEK-AC-4101, Organosilicasol MEK-AC-5101, Organosilicasol MIBK-SD, Organosilicasol MIBK-SD-L, Organosilicasol DMAC-ST, Organosilicasol EG-ST, Organosilicasol IP A-ST, Organosilicasol IPA-ST-L, Organosilicasol IPA-ST-L-UP, Organosilicasol IPA-ST-ZL, Organosilicasol MA-ST-M, Organosilicasol MEK-ST, Organosilicasol MEK-ST-L,
Organosilicasol MEK-ST-UP, Organosilicasol MIBK-ST, Organosilicasol MT-ST,
Organosilicasol NPC-ST-30, Organosilicasol PMA-ST, Sunsphere H-31, Sunsphere H-32, Sunsphere H-51, Sunsphere H-52, Sunsphere H-121, Sunsphere H-122, Sunsphere L-31, Sunsphere L-51, Sunsphere L-121, Sunsphere NP-30, Sunsphere NP-100, and Sunsphere NP- 200 (Asahi Glass Co., Ltd.); Silstar MK-08 and MK-15 (Nippon Chemical Industrial Co., Ltd.); FB-48 (Denki Kagaku Kogyo K.K.); Nipsil SS-10, Nipsi:L SS-15, Nipsil SS-10A, Nipsil SS-20, Nipsil SS-30P, Nipsil SS-30S, Nipsil SS^O, Nipsil SS-50, Nipsil SS-50A, Nipsil SS-70, Nipsil SS-100, Nipsil SS-10F, Nipsil SS-50F, Nipsil SS-50B, Nipsil SS-50C, Nipsil SS-72F, Nipsil SS-170X, Nipsil SS-178B, Nipsil E150K, Nipsil E-150J, Nipsil E- 1030, Nipsil ST-4, Nipsil E-170, Nipsil E-200, Nipsil E-220, Nipsil E-200A, Nipsil E-1009, Nipsil E-220A, Nipsil E-1011, NipsilE-K300, Nipsil HD, Nipsil HD-2, Nipsil N-300A, Nipsil L-250, Nipsil G-300, Nipsil E-75, Nipsil E-743, and Nipsil E-74P (Nippon Silica Industry, Ltd.). In other embodiments, the silica is as described in U.S. Pat. No. 6,013,714, which is expressly incorporated herein by reference in various non-limiting embodiments relative to the silica.
[0085] The coated filler is used to minimize hydrogen bonding in the dispersion which allows for customization of the viscosity of the dispersion. The dispersion typically has a viscosity from 500 to 4,000 cps at 25 °C and 30 RPM using ASTM D 2196 - 99. In various embodiments, the viscosity is from 600 to 3, 900, from 700 to 3,800, from 800 to 3,700, from 900 to 3,600, from 1,000 to 3,500, from 1,100 to 3,400, from 1,200 to 3,300, from 1,300 to 3,200, from 1,400 to 3,100, from 1,500 to 3,000, from 1,600 to 2,900, from 1,700 to 2,800, from 1,800 to 2,700, from 1,900 to 2,600, from 2,000 to 2,500, from 2,100 to 2,400, or from 2,200 to 2,300, cps at 25°C and 30 RPM using ASTM D 2196 - 99. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
[0086] In various embodiments, the core particles include silica. In some embodiments, the silica has all particles less than the layer thickness formed in 3D printing, otherwise particles larger than the layer thickness will be dragged across the build layer during recoating with the recoater doctor blade thus scoring the layer. While a single particle distribution can be used, a combination of multiple particle distributions can be used as binary and ternary
distributions pack more densely, thus increasing the density of the ultimate ceramic article, and the sedimentation rate of the dispersion is typically reduced. In various embodiments, the ideal particle size ratio between two distributions of small particles and large particles is approximately 1 :7 and that the volume should be 25% of that of the volume of large particles. However, lowest viscosity might be achieved when the volume loading of small particles is 27% in a binary mixture of large and small particles. [0087] In other embodiments, a 100 μπι layer thickness might have a first particle distribution centered at about 60 μ (dso=60) and for a Gaussian distribution have a standard deviation of about 9 μπι. This can ensure that all of the particles would have a diameter less than 100 μπι. In other embodiments, an ideal binary distribution could have average particle size distributions of about 60 μπι and about 8.6 μπι respectively and volume loading of about 73% large spheres and about 27% of small spheres. A 100 μπι layer thickness using three particle size distributions may have average particle diameter ratios of about 60 μπι, 8.6 μπι and 1.2 μπι respectively, and volume loading of about 74% large spheres, 20% of mid-sized spheres, and 5% small spheres.
[0088] Non-spherical particles, especially shard or plate forms, can form shear thinning dispersions and larger particles can form such suspensions more readily. Upon resting at zero shear, these dispersions can form large networked floes which can cause the viscosity of the dispersion to increase exponentially. Upon the application of shear force or vibration, these floes can break down and the viscosity of the dispersion is typically reduced. The advantage of this property can be utilized to create a dispersion that is resistant to sedimentation through the formation of a high viscosity suspension upon standing at zero shear.
[0089] In various embodiments, the largest particle component may be ground silica (shards) while the smallest and medium particle size distribution may be spherical for better particle packing and higher green part density. In other embodiments, a ternary particle distribution having component distributions that deviate slightly from a 7:1 large particle to small particle ratio can be used. The largest size distribution may be centered at 21 μπι, while the smallest size distribution may be centered at 0.9 μπι, and the medium size distribution may be centered at 4 μπι. The size ratio of these distributions is about 5.3 and 4.4 respectively.
Figure imgf000028_0001
[0090] In other embodiments, 2-5 wt% of aluminum oxide and 2-5 wt% zircon can be used to increase the strength of the ceramic article at high temperature. Aluminum oxide and zircon can also function as UV absorbers and therefore can factor into the exposure characteristics of the formulation. In various embodiments, a ty ical silica formulation suitable for printing 100 μπι layers is set forth in the table below.
Figure imgf000029_0001
[0091] In other embodiments, a formulation suitable for printing 50 μ layers is found in the table below.
Figure imgf000029_0002
[0092] * indicates that the Angular -200 as delivered from Remet was sifted through a 325 mesh sieve.
[0093] ** indicates that the RP-1 as delivered from Imerys was sifted through a 325 mesh sieve.
[0094] Teco-sphere Microdust is commercially available from Imerys Fused Materials Greenville, Inc., 109 Coile Street, Greeville, TN, USA.
[0095] Angular -200 is commercially available from Remet Corporation, 210 Commons Road, Utica, NY 13502-6395, USA.
[0096] RP-1 is commercially available Imerys Fused Materials Greenville, Inc., 109 Coile Street, Greeville, TN, USA.
[0097] A-10 is commercially available from Almatis Inc., 501 West Park Road, Leetsdale, Pa 15056, USA [0098] Milled Zircon Fine Grind is commercially available from Remet Corporation, 210 Commons Road, Utica, NY 13502-6395, USA.
[0099] In other embodiments, increasing the ceramic loading increases the viscosity and the probability of particle-particle interactions which decrease the sedimentation rate of the dispersion. Maximizing the ceramic loading can also increase the density of the ceramic article, decreases cracking and delamination flaws, and increase the mechanical strength of the ceramic article. As the ceramic loading reaches 64-66 volume percent for loading, the viscosity can begin to increase exponentially. Therefore, in various embodiments, 64 volume percent ceramic loading is used to maintain a formulation viscosity low enough for 3D printing.
Surface Treatment:
[00100] Referring back, the surface treatment that is disposed on the core particles may be disposed on and in direct contact with the core particles such that there is no intermediate layer between the surface treatment and the core particles or maybe disposed, and spaced apart from, the core particles. If disposed on and spaced apart from, there is typically one or more intermediate layers disposed between the surface treatment and the core particle. The surface treatment is typically disposed on the surface of the core particles. Most typically, the surface treatment totally envelops or encapsulated the core particles. However, this is not required and less than total coverage, e.g. 99, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5, percent of the surface area of the core particles may be covered by the surface treatment. The surface treatment may react with the surface of the core particles or may not react with the surface of the core particles. The surface treatment maybe applied to the core particles in any method suitable in the art, e.g. spraying, pouring, dipping, coating, etc.
[00101] In various embodiments, the surface treatment is or includes an organosilane. Suitable non-limiting examples of organosilanes include vinyl trichlorosilane, vinyl tris (beta- methoxyethoxy) silane, vinyltriethoxy silane, vinyltrimethoxy silane, gamma- (methacryloxypropyl) trimethoxy silane, beta-(3,4-epoxycyclohexyl)ethyltrimethoxy silane, gamma-glycydoxypropyltrimethoxy silane, gamma-glycydoxypropylmethyl diethoxy silane, N-beta(aminoethyl) aminopropyltrimethoxy silane, N-beta-(aminoethyl)-gamma- aminopropylmethyldimethoxy silane, gamma-aminopropyltriethoxysilane, N-phenyl-gamma- amino propyl trimethoxy silane, gamma-mercaptopropyl trimethoxysilane, and gamma- chloropropyltrimethoxy silane. In other embodiments, the surface treatment is chosen from organosilane is chosen from dicyclopentyldimethoxysilane, (cyclohexyl)methyldimethoxysilane, 3 -acetoxyethylyltrimethoxysilane, 3 - acetoxypropyltrimethoxysilane, and combinations thereof.
[00102] The surface treatment is present in an amount of from 0.5 to 2 weight percent based on a total weight of the coated filler. In various embodiments, this amount is from 0.6 to 1.9, 0.7 to 1.8, 0.8 to 1.7, 0.9 to 1.6, 1 to 1.5, 1.1 to 1.4, 1.1 to 1.3, or 1.2 to 1.3, weight percent based on a total weight of the coated filler. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
Additives:
[00103] The dispersion may also include, or be free of, or include less than 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, 0.1, 0.05, or 0.01, weight percent of one or more additives set forth below. The dispersion may alternatively include 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 weight percent of one or more additive set forth below. Such additives include, but are not limited to, those described in U.S. Pat. No. 5,665,792 and U.S. Pat. No. 6,099,787, the disclosure of each of which is hereby incorporated by reference relative to such additives in various non-limiting embodiments. In various embodiments, the additive is chosen from hydrocarbon carboxylic acid salts of group IA and IIA metals such as sodium bicarbonate, potassium bicarbonate, and rubidium carbonate, polyvinylpyrrolidones, polyacrylonitriles, and combinations thereof. Other additives include dyes, pigments, antioxidants, wetting agents, photosensitizers, chain transfer agents, leveling agents, defoamers, surfactants, bubble breakers, antioxidants, acid scavengers, thickeners, flame retardants, silane coupling agents, ultraviolet absorbers, dispersion particles, core-shell particle impact modifiers, soluble polymers and block polymers. In various non-limiting embodiments, all values and ranges of values between and including the aforementioned values are hereby expressly contemplated.
Physical Properties:
[00104] In various non-limiting embodiments, the dispersion also typically has a sedimentation rate that is at least 75, 80, 85, 90, 95, or 99, percent less as compared to an identical composition that is free of the sheer thinning additive. The sedimentation rate is typically determined by the following method. However, any method in the art can be used.
[00105] One method includes providing a centrifuge to apply a gravitational force to the ceramic dispersion, placing a sample of the ceramic dispersion in a sample container in the centrifuge, applying a gravitational force of from 25G to 2000G to the ceramic dispersion in the centrifuge to precipitate an amount of the silica from the continuous phase thereby forming a sediment that comprises a topmost layer disposed on the sediment wherein the topmost layer comprises the metal particles to allow for visualization, and measuring the amount of the sediment in the ceramic dispersion. The step of measuring can be further defined as, or include, or be, (i) calculating the height of the sediment as a percentage of the total height of the dispersion, and/or (ii) decanting the continuous phase and measuring the mass of the sediment to determine a mass percentage of the sediment based on the total mass of the dispersion before application of gravitational force. Each is described in greater detail below.
[00106] In one embodiment, the method typically uses a centrifuge to exert centripetal forces on the dispersion that are many times the normal force of gravity. This increased G force accelerates particle segregation and precipitation. Any centrifuge apparatus can be used. However, it tends to be easier to evaluate amounts of sediment in a quantitative manner when the centrifuge is oriented such that the centrifuge tubes containing the test dispersions are aligned with the direction of the centripetal force applied such that the resulting precipitate top surface is parallel with the top and bottom of the centrifuge tube. In this manner, the thickness of the precipitate can be readily measured simply by using a ruled scale such as a millimeter scale. A swing-out type of centrifuge that allows the centrifuge tubes to swing into this described position may be used. Alternatively, a centrifuge can be used that mounts the centrifuge tubes onto a flat circular plate that spins such as that found in the apparatus manufactured and marketed as a LUMiSizer.
[00107] In various embodiments, a LUMiSizer 6112-24 dispersion analyzer is used. This analyzer is designed to accelerate and follow a precipitation process by shining a beam of light through the centrifuge tube while spinning. When using a dispersion that includes both large and small particles, large amounts of large particle precipitate maybe observed with the naked eye while the rest of the dispersion remains opaque to a probe of the
LUMiSizer 6112-24.
[00108] A first method decants the dispersion from the precipitate and measure the mass of the precipitate as a percentage of the total mass of the dispersion before applying the centrifuge centripetal force. The second method aligns a ruled scale to the centrifuge tube and the distance between the bottom of the tube, the top of the dispersion, and the top of the precipitate and reports the height of the precipitate as a percentage of the total height of the dispersion.
[00109] The rate of spin of the centrifuge can be varied to minimize the testing time such that a measurable amount of precipitate can be observed while avoiding that all or most of the particles precipitated. The acceleration applied to the dispersions is calculated by the following equations:
ac = v2 / r
2
= ω r
= (2 π ns)2 r
= (2 π nwm/ 60)2 r
where
ac = centripetal acceleration (mJs2 )
v = tangential velocity (m/s)
r = circular radius from the center of rotation to the midpoint of the dispersion column (m) ω = angular velocity (rad/s)
ns = revolutions per second (1/s)
nrpm = revolutions per min (l/min)
[00110] Samples can be prepared by pipetting the dispersions into centrifuge tubes to a height of 45 mm. Polyamide centrifuge tubes can be used to prevent dissolution of the tubes by the acrylate monomers. An acceleration force of 2000 G typically precipitates all particles, which is not desirable. 500 G of force may achieve the same undesirable result. A rotation speed of about 600 RPM corresponding to 46 G may produce reproducibly measurable amounts of precipitate. The time that the rotation is applied can then be varied to determine optimum test time. Two test samples can then be removed from the centrifuge at 10 minute intervals. More specifically, the tubes can be spun for 10-60 minutes at 46x gravity (e.g. 600 rpm) at 25°C. Centrifugation can start with a full set of tubes (12 each). Every 10 min, centrifugation can then be paused to remove one tube for sediment measurement while the centrifugation continues with the rest of the tubes. The height of the sediment and the total height of the dispersion can be measured with a scale having a precision of ± 0.5 mm.
[00111] The appropriate acceleration can depend, at least in part, on the properties of the particles in the dispersion. In one embodiment, an acceleration that produces
approximately 46 G is sufficient when the particles are ceramic particles (D50 = 9 μπι, mainly including silica particles with a small fraction of alumina and also zircon particles as large as 90 μπι). In various embodiments, the G force is from 25 to 100, 30 to 95, 35 to 90, 40 to 85, 45 to 80, 50 to 75, 55 to 70, 60 to 65, 40 to 50, 40 to 45, or 45 to 50, G. In other embodiments, the G force is from 100 to 2000, 200 to 1900, 300 to 1800, 400 to 1700, 500 to 1600, 600 to 1500, 700 to 1400, 800 to 1300, 900 to 1200, or 1000 to 1100, G. [00112] In other embodiments, visualization of a sediment boundary can be customized by adding small fractions of pigment (0.1 w% of Oracet Blue 640). Without pigment, the interface of sediment and supernatant can be barely detectable as the instant dispersion typically does not have a clear supernatant. Instead, only the largest particles from the sediment tend to be apparent while the majority of the ceramic small particles remain suspended in the supernatant rendering it opaque.
Method of Forming the Dispersion:
[00113] This disclosure also provides a method of forming the dispersion. The method includes the steps of providing the cationicallypolymerizable aliphatic epoxide, providing the cationically polymerizable oxetane, providing the free-radical polymerizable multifunctional (meth)acrylate, providing the cationic photoinitiator, providing the free-radical photoinitiator, and providing the coated filler. The method also includes the steps of combining the cationically polymerizable aliphatic epoxide, the cationically polymerizable oxetane, the free- radical polymerizable multifunctional (meth)acrylate, the cationic photoinitiator, the free- radical photoinitiator, and the coated filler to form the dispersion. One or more of any of the aforementioned components can be combined with any one or more other components as a whole or in various parts.
[00114] In various non-limiting embodiments, in order to lower the dispersion viscosity sufficient for 3D printing and to avoid the presence of agglomerate particles greater than one print layer thickness, the silica particles must experience high shear during mixing in order to break up large silica agglomerates. This requires preparation of a silica paste concentrate ("silica concentrate") through slow addition of the 86.7%w silica powder to a mixture of 1.7%w of the dispersant Variquat CC 42 NS with 11.6%w of the main acrylic monomer while mixing, followed by continuous shear mixing of this high viscosity paste for several hours. In various embodiments, this silica concentrate is then mixed with the remaining liquid ingredients (e.g. a "photopolymer diluent") to reduce the dispersion viscosity suitable for 3D printing.
[00115] Silica photopolymer dispersions, for example, can be prepared using high shear mixing, such as that provided by an anchor-double-helix mixer National Board No./U-l 131 manufactured by Chemineer or a 5 quart KitchenAid mixer using a KFE5T Flex Edge Beater available from Amazon.com. It some embodiments, it is important to have sufficient shear of the high viscosity silica concentrate in order to de-agglomerate the silica before reducing the viscosity by the addition of the photopolymer diluent. For example, to a 5 quart KitchenAid mixer equipped with the nylon coated flat beater, 0.10 Kg of the dispersant Variquat CC 42 NS and 0.7 Kg of the acrylic monomer can be added. These liquid ingredients can then be mixed on the slowest speed setting for 1 minute. The silica powder can then be added in small aliquots such that the consistency does not go beyond the paste stage while allowing sufficient mixing between aliquot additions to reduce the viscosity back to a high viscosity liquid. The silica addition usually requires 45-60 minutes. The stirrer can then be changed to the flex edge beater in order to increase the shear force for breaking up silica agglomerates by having a smaller clearance between the stir blade and the mixing bowl wall. Stirring can be continued in this manner for an additional two hours. As the viscosity decreases due to silica de-agglomeration the stirring speed can be increased, however stirring speed should be moderated to maintain the temperature of the mixture below 50 °C in order to avoid polymerizing the dispersion. This silica concentrate can then ne mixed with the remaining liquid ingredients ("photopolymer diluent") in order to reduce the dispersion viscosity suitable for 3D printing.
[00116] In mix vessels that are equipped with temperature control such as the
Chemineer vessel, temperature of the vessel can be controlled by a cooling jacket in addition to agitation speed. Typically but not required, higher agitation speeds were used at the end of the mix time to ensure agglomeration break-up. Any high shear blade or paddle such as the double helix will provide enough shear to break agglomerations.
Ceramic Article:
[00117] The dispersion can be used to form a ceramic article. The ceramic article is not particularly limited and may be any known in the art. For example, the ceramic article is typically a ceramic core or ceramic shell which create a mold for the investment casting of nickel super alloy parts. In other embodiments, the dispersion can be used to form a ceramic article that is involved in the casting or formation of metal parts and many different types of casting.
Method of Forming the Ceramic Article:
[00118] This disclosure also provides a method of forming a ceramic article from the dispersion. The method includes the steps of A. applying a layer of the ceramic dispersion to a surface and B. selectively exposing the layer image wise to actinic radiation to form an imaged cross-section. The method also includes the steps of C. applying a second layer of the ceramic dispersion to the imaged cross-section and D. selectively exposing the second layer image wise to actinic radiation to form a second imaged cross-section. The method also includes the steps of E. repeating steps (C) and (D) to create a three-dimensional green ceramic article and F. sintering the three-dimensional green ceramic article in a furnace to form the ceramic article.
[00119] The step of A. applying a layer of the ceramic dispersion to a surface maybe further defined as applying a layer of the dispersion having a thickness of from 50 to 100, 55 to 95, 60 to 90, 65 to 85, 70 to 80, or 75 to 80, μπι, to the surface. Moreover, the surface is not particularly limited and may be any known in the art. For example, typically all the layers in a part build have the same thickness, e.g. either 50 or 100 μπι. However, the layers can be 150 or 200 μπι thick, but then the stair stepping on sloped surfaces may be too great. In various embodiments, a series of layers are build forming vertical walls at a high layer thickness while building the layers that form sloped or rounded surfaces at a smaller layer thickness. Thicker layers tend to build faster. However, it is desirable for the contour areas of the part to have stair step height minimized.
[00120] The step of applying is typically further defined as applying using a doctor blade controlled by a computer. The doctor blade may have 1 -3 baffles wherein the blade may or may not be enclosed such that an applied partial vacuum pulls the dispersion up into the blade for assisted deposition onto the previous layer part surface.
[00121] The step of B. selectively exposing the layer image wise to actinic radiation may be further defined as exposure to UV laser in the 325-365 nm range directed by X-Y scanning mirrors onto a surface of the dispersion. Computer control of mirrors maybe used to draw cross sections of the part such that only the part cross section selectively receives UV radiation. Alternatively, a bank of LED lamps having wavelengths of 260, 265, 280, 310, 325 and 340 nm, 365, 375 and 385 nm, and/or 405 nm, or combinations thereof, maybe reflected off a digital micro mirror array (DLP chip) to expose a layer cross section image on the surface of the dispersion such that only the part cross section selectively receives UV radiation. The step of C. applying the second layer of the ceramic dispersion to the imaged cross-section may be the same as step A or may be different in one or more respects. For example, the second layer maybe the same as, or different from, the first layer with respect to composition, thickness, size, method of application, etc.
[00122] The step of D. selectively exposing the second layer image wise to actinic radiation to form the second imaged cross-section may be the same as step B or may be different in one or more respects. For example, the second layer may be selectively exposed in the same way or differently than the first layer, may be exposed to the same or different actinic radiation, and may have the same, more, or less of the second layer exposed to the radiation. [00123] The step of E. repeating steps (C) and (D) to create the three-dimensional green ceramic article may occur once or many times. For example, steps (C) and (D) may be repeated as many times as chosen by one of skill in the art, e.g. 50 to 5,000, times.
[00124] The step of F. sintering the three-dimensional green ceramic article in a furnace to form the ceramic article is typically further defined as heating at a temperature of from 1100-1600 °C in the furnace. Typically, the times and temperatures maybe any known in the art. Moreover, the furnace type may also be any known in the art.
[00125] Moreover, the method may be alternatively described as three-dimensionally printing the green ceramic article. As such, the method may include any one or more steps known in the art as related to three-dimensional printing. In various non-limiting embodiments, one of more steps of the method maybe as described in:
(A) Rapid Prototyping & Manufacturing: Fundamentals of StereoLithography, January 15, 1992 by Paul F. Jacobs;
(B) Stereolithography & Other RP&M Technologies: From Rapid Prototyping to Rapid Tooling by Paul F Jacobs, 1995;
(C) US Pat. No. 4,093,017;
(D) Integrally Cored Ceramic Investment Casting Mold Fabricated By Ceramic Stereolithography by Chang- Jun Bae;
(E) Parametric Study And Optimization Of Ceramic Stereolithography by Kahn Chia Wu; and/or
(F) Towards Inert Cores for Investment Casting by Martin Riley, each of which is expressly incorporated herein in their entirety relative to the method in various non-limiting embodiments.
[00126] The method may also include the step of post-curing the three-dimensional green ceramic article prior to the step of sintering. Even though most of the dispersion has typically been solidified during the part building process by the radiation provided, the part typically has only been partially polymerized. The step of post-curing may be further described as when SL parts are postcured to essentially complete the polymerization process and to improve the final mechanical strength of the green ceramic article. A 3D Systems Inc. postcure apparatus (PCA) can be used which is essentially an "oven" with UV light sources that radiate and reflect within the device. The PCA has a turntable that provides for a more distributed actinic UV emission exposure. The standard postcure time is this apparatus is 60 minutes. [00127] In various embodiments, a Prodways L5000 machine can be used and the specific parameters can be chosen by one of skill in the art. In other embodiments, a laser based stereolithography system can be used. Still further, UV 3D printing that exposes photopolymer layers through a glass plate from the bottom (rather than printing from the top exposed to free air) can be used. In all of these systems, the parameters, cycle times, etc. can be chosen by one of skill in the art.
Green Ceramic Article:
[00128] This disclosure also provides the green ceramic article itself. The green ceramic article may be cured, partially cured, or uncured, e.g. by UV radiation. In other words, the green ceramic article may include cured, partially cured, or uncured monomers, as described above. In various embodiments, the green ceramic article is cured using a UV exposure sufficient to cure 200% of a layer thickness (i.e., overcure of 100 μπι on a 100 μπι layer). In such embodiments, the green ceramic article typically has a flexural modulus greater than 10 MPa, greater than 40 MPa, greater than 100 MPa, as measured by ASTM D790. The combination of ceramic photopolymer formulation and UV exposure should form a green article having acceptable green strength, as described above, and a curl factor less than 3, typically less than 2 and most typically less than 1.5 as determined by the method described in Rapid Prototyping & Manufacturing: Fundamentals of StereoLithography, January 15, 1992 by Paul F. Jacobs, which is expressly incorporated herein by reference in its entirety relative to various non-limiting embodiments.
Additional Embodiments:
[00129] In various embodiments, FTIR can be used to follow the rate of conversion of the individual epoxy, oxetane, and acrylate components to polymer within formulations containing these monomers and catalyzed with 2% Irgacure 184 (UV free radical initiator) and 2%triarylsulfonium hexafluoroantimonate (UV cationic initiator). For example, the area under the absorption curve between 802 - 819 cm"1 (absorption peak at 810 cm"1) can be integrated and its attenuation with time used to follow the acrylate monomer conversion with a precision of +/- 5%. The area under the absorption curve between 880 - 942 cm"1
(absorption peak at 910-920 cm"1 depending on the epoxy molecule) can be integrated and its attenuation with time was used to follow the epoxy monomer conversion with a certainty of +/- 9%. The area under the absorption curve between 957 - 1007 cm"1 (absorption peak at 980 cm"1) can be integrated and its attenuation with time was used to follow the oxetane monomer conversion with a precision of +/- 7%. However, the baseline of this oxetane absorption peak can be confounded by the overlap of a static portion of the epoxy absorption curve such that the oxetane conversion could not be exactly determined beyond 90%.
[00130] In various embodiments, to have successful 3D printing of low curl shrinkage distortion ceramic photopolymers including epoxies, oxetanes and acrylates, the acrylate component reacts immediately via free radical polymerization to form a rigid gel that creates the form of the green body that resists the deformation forces of the 3D printing recoating process while the epoxy component reacts slowly over minutes or hours via cationic polymerization. Using this formulation strategy, the shrinkage due to the polymerization can be distributed over time and therefore many 3D printing layers such that shrinkage occurs about the center of mass of 3D printed object. If all of the polymerization shrinkage takes place immediately, as can happen with a 100% acrylate binder formulation, a rigid first layer can be created and the second layer then applies all of its polymerization shrinkage forces upon the first layer causing the layers to distort and curl upward. This curl shrinkage distortion causes at least inaccuracy and deformation of the part relative to its CAD dimensions and at worst causes the recoating blade to collide with the partially formed part thus catastrophically terminating the part building process. Further, it is important that the acrylate(s) together with initial epoxy and oxetane reactions produce a polymer binder that produces sufficient green strength to resist the deformation forces of the 3D printing recoating process. While it maybe difficult or impossible to quantitatively determine the green flexural strength of a single layer within the first 3-5 minutes after its formation, the green flexural strength of a standard flexural test sample according to ASTM D790 measured 3 hours after its construction can be used as a relative indication of the initial green strength of a single layer. A green ceramic article cured using a UV exposure sufficient to cure 200% of a layer thickness (i. e. overcure of 100 μ on a 100 μ layer) can have a flexural modulus greater than 10 MPa, typically greater than 40 MPa, and most typically greater than 100 MPa as measured by ASTM D790. The combination of ceramic photopolymer formulation and UV exposure can form a green article having acceptable green strength, as described above, and a curl factor less than 3, typically less than 2 and most typically less than 1.5 as determined by the method described in Rapid Prototyping & Manufacturing: Fundamentals of StereoLithography, January 15, 1992 by Paul F. Jacobs. In some embodiments, the acrylate component(s) must reach full conversion immediately and that the epoxy components) conversion reach 30-50% conversion in the first 5 minutes after UV exposure and that the epoxy conversion continues slowly over the following 30 minutes to reach 60- 100% conversion. Moreover, the concentration of the slowly converting epoxy components) of the formulation can be maximized to be 50-80% of the monomer formulation.
Furthermore, in some embodiments, the monomer components must have viscosities below 30 MPa-s. Higher viscosity monomers maybe included if they are minor components of the formulation, for example 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, 275 mPa-s, at 5 wt % of the mass of the ceramic photopolymer formulation. In other embodiments, each of the cationically polymerizable aliphatic epoxide, the cationically polymerizable oxetane, and the multifunctional (meth)acrylate independently has a viscosity of less than 30 mPas s as determined using ASTM D 2196 - 99.
[00131] In various non-limiting embodiments, any one or more components, compounds, reactaiits, solvents, additive, method steps, pieces of equipment, etc. described in one or both of concurrently filed U.S. Provisional Patent Applications for BASF Docket Numbers: 129568 and 160760, ma e used herein. Both of these applications are hereby expressly incorporated herein by reference in their entireties in various non-limiting embodiments.
EXAMPLES
[00132] In various embodiments, when silica loading is high, for example 60 percent by volume, the viscosity of the dispersion can be high and form a thick paste. Dispersants that coat the surfaces of the silica can be added to such formulations to reduce the viscosity to 1-2 Pa-s. The best dispersants are salts of tertiary amines and these are highly effective. Unfortunately, these tertiary amines react immediately with the cationic photoinitiator in an acid-base reaction and over the longer term these tertiary amines catalyze the polymerization of epoxies significantly shortening the useful life of the dispersion. Consequently, for formulations including epoxides, an alternative treatment must be used that passivates at least some portion of the OH groups on surface of the fillers. Surface treating filler with an organosilane reduces hydrogen bonding between particles thereby reducing the viscosity of the dispersion. The organosilane is typically hydrolyzed by water and subsequently reacts with OH (e.g. silanol) groups on the surface of the filler thereby permanently passivating the surfaces. This can also reduce shear thinning behavior of because the surfaces no longer have free hydroxyl groups interacting between particles. Therefore, a balance between viscosity reduction and shear thinning is sought.
[00133] Organosilane candidates were evaluated in the following base formula:
Figure imgf000040_0001
Silica 79.3% 64.3%
Variquat CC 42
1.6% 3%
NS
Laromer HDDA 15.4% 27%
Laromer LR 8863
(ethoxylated 1.7% 2.8%
TMPTA)
Irgacure 184 2.01% 3.0%
100.0% 100.0%
Viscosity @ 50
1330
RPM (mPa-s)
[00134] It can be important to determine the concentration of silanol groups on the silica surfaces in order to accurately compare different silanes having different molecular weights and to determine the optimum amount of silane to use for a given amount of silica so that the viscosity is minimized without leaving behind unreacted silane and possibly to retain at least some shear thinning behavior by leaving some silica silanol groups unreacted.
Experiments were performed varying the amount of (3-acryloxypropyl)trimethoxysilane in the base formulation in table above. Three moles of water are required to hydrolyze one mole of (3-acryloxypropyl)trimethoxysilane. While there is some water already present on the silica surface, additional water must be added to fully hydrolyze the silane. 3.6 moles of water, a 20% excess, were added to the formulation containing (3- acryloxypropyl)trimethoxysilane in order to insure full hydrolysis of the silane. The silica was pretreated with silane before adding the silica to the base formulation above according to the following procedure:
[00135] 200 g silica were added to 65 ml ethanol while stirring in a stainless steel beaker surrounded in a water bath within a sonicator. The suspension was then sonicated for 30 minutes to de-agglomerate the silica. (3-acryloxypropyl)trimethoxysilane was then added while stirring and the suspension was acidified with two drops of acetic acid to produce a pH of 4-5, and the requisite amount of water was added. The suspension was then heated to 60 0 C for one hour and then covered and stored at room temperature overnight to allow the reaction to complete. The suspension was then washed with acetone, centrifuged to separate all of the silica, dried at 60 °C for 16 hours to drive off the alcohol reaction product, and heated at 100 °C for one hour to drive off the residual water.
[00136] Ethanol was chosen as the solvent because it competes with the condensation polymerization side reaction of silane to form polysiloxane, which should be minimized or eliminated.
[00137] The results in the table below show the formulation viscosity at varying concentrations of (3-acryloxypropyl)trimethoxysilane as a percentage of the mass of silica. Here, viscosity is used as a proxy indicator of the fraction of silanol groups passivated with organic silyl groups. These results indicate that all of the silanol groups on the silica particle surfaces are reacted and passivated when (3-acryloxypropyl)trimethoxysilane is present at 2 wt % of the mass of silica (25.6 mmol of silane for 200 )and that further quantities of silane have no effect.
Figure imgf000042_0001
[00138] The silanes below were screened in the base formula set forth above using 12.8 mmol of silane per 100 g of silica and the viscosity of each is reported. Conclusions drawn from the results set forth below are that silanes having short alkyl side chains, aliphatic rings or acrylic functionalities produce the lowest formulation viscosity while those silanes having long chains or other functional groups that occupy a large volume or bipodal silanes produce high formulation viscosity. (Cyclohexyl)methyldimethoxysilane,
dicyclopentyldimethoxysilane, (methacryloxymethyl)methyldimethoxysilane, 3- (methacryloxypropyl)trimethoxysilane, 3-(acryloxypropyl)trimethoxysilane, 3- acetoxypropyltrimethoxysilane were the better candidates and
triethoxysilylpropoxy(polyetheneoxy)dodecanoate are the better candidates for use herein. Viscosity at 12 rpm
Name
(mPa-s)
Triethoxysilylpropoxy(polyethyleneoxy)dodecanoate
978
(Available from Gelest Inc.)
3-(Glycidoxypropyl)trimethoxysilane
5748
(Available from Gelest Inc.)
2-(3,4-Epoxycyclohexyl)ethyltrimethoxysilane
15557
(Available from Gelest Inc.)
(Cyclohexyl)methyldimethoxysilane
Wacker Silane CHM Dimethoxy 1923
(Available from Wacker Chemie AG)
Dicyclopentyldimethoxysilane
Wacker Silane CP2 Dimethoxy 1693
(Available from Wacker Chemie AG)
n-Octyltrimethoxysilane
37913
(Available from Gelest Inc.)
Hexadecyltrimethoxysilane
Wacker Silane 25013 VP 18100
(Available from Wacker Chemie AG)
N-[3-(Trimethoxysilyl)propyl]hexadecanamide Higher Than (Available from Gelest Inc.) Detection Limit
(Methacryloxymethyl)methyldimethoxysilane
Wacker Geniosil XL 32 1252
(Available from Wacker Chemie AG)
3-(Methacryloxypropyl)trimethoxysilane
1223
(Available from Gelest Inc.)
3 -(Acryloxypropyl)trimethoxysilane
1957
(Available from Gelest Inc.)
1 ,2-Bis(triethoxysilyl)ethane
15571
(Available from Gelest Inc.)
1 ,2-Bis(trimethoxysilyl)decane
18435
(Available from Gelest Inc.)
3 -acetoxypropyltrimethoxysilane 1220 (Available from Gelest Inc.)
[00139] Using 12.8 mmol of silane per 100 g of silica significantly reduces or eliminates shear thinning while using 6.4 mmol of silane per 100 g of silica retains at least some of the innate shear thinning behavior of the silica.
[00140] When the organic chain of the silane is reactive with acrylates, for example methacryloxypropyltrimethoxysilane, silica sediment that forms on the bottom of a 3D printing vat after long standing has the tendency to polymerize through the linking of the silica particles via the methacryloxypropyl moieties on their surfaces. The probability of this event is increased in the low oxygen environment of a sediment cake. This polymerized sediment cannot be re-suspended. Changing the silane to one having an inert side chain, for example 3-acetoxypropyltrimethoxysilane tends to eliminate this problem.
[00141] These examples attempt to achieve a low curl shrinkage distortion formula via an epoxy-oxetane-acrylate organic phase of the photopolymer dispersion. Silanation work with epoxy-oxetane-acrylate formulas was accomplished by adding the silane directly to the dispersion without going through the laborious steps of pre-silanating the silica before adding the silica to the organic components of the dispersion. Although
triethoxysilylpropoxy(polyetheneoxy)dodecanoate can be the best candidate from the aforementioned all acrylate photopolymer formula screening, such a formulation can have a very high viscosity when used in an epoxy-oxetane-acrylate photopolymer formulation where it produces a viscosity of 22 Pa-s at 10 RPM.
Figure imgf000044_0001
Neopentylglycol diacrylate
Hydroxyethyl Acrylate 1.0% 4.9% 1.0% 5.0%
Irgacure 184 0.6% 3.0% 0.6% 3.0%
Triarylsulfonium
1.4% 6.9% 1.4% 7.0% hexafluoroantimonate
Base stabilizer* 0.005% 0.025% 0.03% 0.15%
Silica (64volume %) 76.8% 76.9%
3 -acetoxypropyltrimethoxysilane 2.2% 2.2%
excess water (20w% of silane) 0.6% 0.6%
Total 100.0% 100.0%
Viscosity (mPa-s) @ 10 RPM 4992 3900
*Base stabilizer = N,N-dimethylbenzylamine Sodium carbonate
[00142] Celloxide 2021P is commercially available from Daicel Corporation, Konan, Minato-ku, Tokyo 108-8230, Japan or Daicel (U.S.A.), Inc., One Parker Plaza, 400 Kelby Street, Fort Lee, New Jersey 07024, USA functions as a cationically cured aliphatic epoxy monomer and acts as a UV curable binder for ceramic component particles. Celloxide 202 IP from Daicel Corporation is typical due to its low viscosity and thermal stability relative to other manufacturers. The typical concentration of Celloxide 2021P 3,4- epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate is 5-14 wt %, and more typically 5-7 wt % of the mass of the organic binder phase of the formulation.
[00143] ERISYS™ GE-20 is commercially available from CVC Thermoset
Specialties, 844 N. Lenola Road, Moorestown, New Jersey 08057, USA functions as a low viscosity cationically cured aliphatic epoxy monomer and acts as a UV curable binder for ceramic component particles. Neopentylglycol diepoxide produces a rigid high modulus polymer having a high glass transition temperature due to its germinal dimethyl groups' steric hindrance of bond rotation about the central carbon chain. The typical concentration of ERISYS™ GE-20 neopentylglycol diepoxide is 50-80%, more typically 59-68% of the mass of the organic binder phase of the formulation. [00144] ARON OXETA E OXT-221 is commercially available from Toagosei America Inc., 1450 West Main Street, West Jefferson, OH43162, USA or Sanyo Corporation of America, 500 Fifth Avenue, Suite 3620, New York, NY 10110, USA functions as a low viscosity cationically cured oxetane monomer that accelerates the polymerization rate of aliphatic epoxies when used at 7-20% concentration of the mass of the organic binder phase of the formulation and assisted by 5% hydro xyethyl acrylate of the mass of the organic binder phase of the formulation or 1-5% OXT-101 of the mass of the organic binder phase of the formulation. OXT-221 also acts as a minor component UV curable binder for ceramic component particles. The typical concentration of ARON OXETANE OXT-221 is 5-20%, more typically 5-7% of the mass of the organic binder phase of the formulation.
[00145] ARON OXETANE OXT-101 is commercially available from Toagosei America Inc., 1450 West Main Street, West Jefferson, OH43162, USA or Sanyo Corporation of America, 500 Fifth Avenue, Suite 3620, New York, NY 10110, USA functions as a low viscosity cationically cured oxetane monomer that accelerates the polymerization rate and extent of conversion of aliphatic epoxies when used at 2-5% concentration of the mass of the organic binder phase of the formulation. OXT-101 also acts as a minor component UV curable binder for ceramic component particles. The typical concentration of ARON
OXETANE OXT-221 is 1-7% of the mass of the organic binder phase of the formulation.
[00146] Sartomer SR 247 is commercially available from Arkema Inc., 900 First Avenue, King of Prussia, Pennsylvania 19406, USA functions as a free radically cured acrylic monomer having low viscosity that produces high green strength during the 3D printing process. Neopentylglycol diacrylate produces a rigid high modulus polymer having a high glass transition temperature due to germinal dimethyl groups' steric hindrance of bond rotation about the central carbon chain. Sartomer SR 247 also acts as a UV curable binder for ceramic component particles. The typical concentration of Sartomer SR 247 neopentylglycol diacrylate is 15-25%, more typically 20% of the mass of the organic binder phase of the formulation.
[00147] Hydroxyethyl acrylate is commercially available from BASF Corp., 100 Park Avenue, Florham Park, NJ 07932, USA functions as a free radically cured acrylic monomer having low viscosity that accelerates the polymerization rate and extent of conversion of aliphatic epoxies when used at 5% concentration. Hydroxyethyl acrylate also acts as a minor component UV curable binder for ceramic component particles. The typical concentration of hydroxyethyl acrylate is 1-5%, more typically 1% of the mass of the organic binder phase of the formulation. [00148] Irgacure 184 is commercially available from BASF Corp., 100 Park Avenue, Florham Park, NJ 07932, USA functions as a UV free radical photo initiator for initiating acrylate polymerization. The UV penetration depth, Dp, is controlled by the concentration of the free radical initiator, cationic initiator, alumina, and zircon concentrations. The free radical initiator concentration typically must be sufficient to produce sufficient strength in a single part layer to resist the layer recoating forces and to limit the UV light penetration depth. The typical free radical initiator concentration is 1-5 wt %, and more typically 3 wt % of the mass of the organic binder phase of the formulation.
[00149] Triarylsulfonium hexafluoroantimonate is commercially available as
Chivacure 1176 from Chitec Technology Co., Ltd. 1980 Post Oak Blvd, Suite 1500 Houston, TX 77056, USA functions as a UV cationic photoinitiator for initiating epoxy and oxetane polymerization. The UV penetration depth, Dp, is controlled by the concentration of the free radical initiator, cationic initiator, alumina, and zircon concentrations. The cationic initiator concentration must be sufficient to fully polymerize the epoxy and oxetane components. The typical cationic initiator concentration is approximately 2-3 times that of the free radical initiator concentration, more typically 2.3 times that of the free radical initiator concentration. The typical concentration of the cationic initiator is 5-9 wt %, and more typically 7 wt % of the mass of the organic binder phase of the formulation.
[00150] Base stabilizers N,N-dimethylbenzylamine and sodium carbonate are commercially available from Sigma-Aldrich Corp., St. Louis, MO, USA and function as proton absorbers for stabilization of cationically cured epoxies and oxetanes. Sodium carbonate is added to the formulation as a 15 wt % aqueous solution or dissolved in the water used to hydrolyze the organo silane. The typical concentration of N,N-dimethylbenzylamine is 0.001-0.01%, more typically 0.005% of the entire mass of the formulation. The typical concentration of sodium carbonate is 0.02-0.05%, more typically 0.03% of the entire mass of the formulation.
[00151] Silica functions as the ceramic component which, after binder burnout and sintering, forms the ceramic mold for investment casting. The typical silica concentration is 55-67 volume %, more typically 63-64 volume % of the entire volume of the formulation.
[00152] 3-acetoxypropyltrimethoxysilane is commercially available from Gelest Inc., 11 East Steel Rd., Morrisville Pa 19067, USA, functions as a silane surface treatment for the silica particles. Surface treating the silica particle surfaces with an organosilane reduces hydrogen bonding between particles thereby reducing the viscosity of the formulation. 3- acetoxypropyltrimethoxysilane is hydrolyzed by water subsequently reacts with silanol groups on the silica surfaces. Once this reaction occurs the silica surface is passivated and the 3-acetoxypropysilyl moiety is then inert to reaction with acrylates or epoxies or oxetanes and compatible with these monomers having similar chemical polarity. While silanation of the silica surface reduces the formulation viscosity, it also reduces the shear thinning behavior of the formulation because the silica surfaces no longer have hydroxyl groups interacting between particles. The extent of silanation of the silica surface is therefore a balance between the objectives of viscosity reduction and shear thinning that helps stabilize the suspension to sedimentation. When the organic chain of the silane is reactive with acrylates, for example methacryloxypropyltrimethoxysilane, the silica sediment that forms on the bottom of the 3D printing vat after long standing has the tendency to polymerize through the linking of the silica particles via the methacryloxypropyl moieties on their surfaces. The probability of this event is increased in the low oxygen environment of the sediment cake. The polymerized sediment cannot be re-suspended. The typical silica concentration is 0.2-3 wt %, more typically 0.5-2.5 wt %, and most typically 2% of the mass of silica contained in the formulation.
Dispersion Preparation Procedure:
[00153] In various non-limiting embodiments, several steps are required in order to successfully prepare a functional photopolymer dispersion. In order to lower the dispersion viscosity sufficient for 3D printing and to avoid the presence of agglomerate particles greater than one layer thickness, the silica particles may experience high shear during mixing in order to break up large silica agglomerates. This can require slow addition of the silica powder to all of the dispersion liquid ingredients, except the organosilane and water, followed by continuous shear mixing of this high viscosity paste for several hours. The organosilane can then be added causing reduction of the viscosity of the preparation from a thick stiff paste to a soft paste that flows. The water required for hydrolysis of the silane can then be added in order to silanate the surfaces of the de-agglomerated silica. Addition of the organosilane at the beginning of the preparation process may cause the silica agglomerates to become chemically bound together preventing the de-agglomeration process.
[00154] In some embodiments, silica photopolymers were prepared using a 5 quart or 8 quart Kitchenaid kitchen mixer available from Amazon.com. Sufficient shear of the high viscosity silica concentrate can be important in order to de-agglomerate the silica before reducing the viscosity by the addition of the silane and water. All of the ingredients except the silica, silane, and water components were added to the mixer equipped with the nylon coated flat beater for the 5 quart mixer or the burnished metal flat beater for the 8 quart mixer. These liquid ingredients were then mixed on the slowest speed setting for 10 minutes. The silica powder was then added in small aliquots such that the consistency did not go beyond the paste stage while allowing sufficient mixing between aliquot additions to reduce the viscosity back to a high viscosity liquid. The silica addition usually requires 45 -60 minutes. The stirrer is then changed to the flex edge beater in order to increase the shear force for breaking up silica agglomerates by having a smaller clearance between the stir blade and the mixing bowl wall. Stirring is continued in this manner for an additional two hours. As the viscosity decreases due to silica de-agglomeration the stirring speed can be increased, however stirring speed should be moderated to maintain the temperature of the mixture below 50 °C in order to avoid polymerizing the dispersion. The silane and water is then added and mixing continued for an additional 15 minutes. The mixture is then allowed to rest in the dark for 24 hours at room temperature to allow the silane to hydrolyze and react with the surface of the silica particles. Triethoxysilanes require approximately eight times longer to hydrolyze than trimethoxysilanes, so additional reaction time must be allowed when using triethoxysilanes.
Additional Experiments:
[00155] FTIR was used to follow the rate of conversion of the individual epoxy, oxetane, and acrylate components to polymer within formulations containing these monomers and catalyzed with 2% Irgacure 184 (UV free radical initiator) and 2%triarylsulfonium hexafluoroantimonate (UV cationic initiator). The area under the absorption curve between 802 - 819 cm-1 (absorption peak at 810 cm-1) was integrated and its attenuation with time was used to follow the acrylate monomer conversion with a precision of +/- 5%. The area under the absorption curve between 880 - 942 cm-1 (absorption peak at 910-920 cm-1 depending on the epoxy molecule) was integrated and its attenuation with time was used to follow the epoxy monomer conversion with a certainty of +/- 9%. The area under the absorption curve between 957 - 1007 cm-1 (absorption peak at 980 cm-1) was integrated and its attenuation with time was used to follow the oxetane monomer
[00156] The above FTIR method of determining individual component conversion rate was used to create and optimize the photopolymer binder for the ceramic photopolymer formulations that would satisfy the curl shrinkage distortion, green strength, and viscosity constraints.
[00157] Using the method above it was found that the free radical polymerization reached 90-95% conversion almost immediately as expected regardless of combination with or without oxetane and/or epoxy components. Using the method above it was found that oxetanes alone reached a conversion of 10%, 35% and 50% for 3-Ethyl-3- hydroxymethyloxetane (Aron OXT-101), l,4-Bis[(3-ethyl-3- oxetanylmethoxy)methyl]benzene (Aron OXT-121), 3-Ethyl-3-{[(3-ethyloxetane-3- yl)methoxy]methyl}oxetane (Aron OXT-221) respectively. Using the method above it was found that aliphatic epoxies alone reached a conversion of 10% and 60% for neopentylglycol diepoxide (NPGDE) and 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (Celloxide 202 IP) respectively. However it was found that NPGDE conversion increased when combined with increasing amounts of OXT-221 reaching 35-90% conversion. NPGDE conversion did not appreciably increase when combined with OXT-101. Celloxide 2021P conversion did not appreciably increase when combined with oxetane compounds, perhaps this is because Celloxide 202 IP is already more reactive on its own due to the strained epoxy ring structure of that molecule. Celloxide 202 IP conversion did not appreciably increase when combined with acrylate compounds. Further and surprisingly, it was found that the combination of 20% neopentylglycol diacrylate (NPGDA) with NPGDE increases the conversion of NPGDE from 10% to 20% and the combination of 20% NPGDA with 7- 14%Celloxide 2021P and the balance of NPGDE increases the conversion of Celloxide 2021P and NPGDA to 80-85%. Even more surprising, the addition of 2-5% hydroxyethyl acrylate (HEA) to these combinations of 7-14%Celloxide 202 IP and the balance of NPGDE further increases the conversion of Celloxide 2021P and NPGDA to 90-100%. Similarly surprising is that 10-20% OXT221 with 20% NPGDA with 5% HEA with the balance of NPGDE increases the conversion of NPGDE to 100% while similar formulations containing 0-5% OXT221 only convert 20-25% of the NPGDE to polymer.
[00158] In additional experiments, measurements are performed with a Bruker IFS-66 Fourier transform infrared spectrometer (range: mid-infrared 3600-700 cm-1; resolution: 8 cm-1). Samples are prepared by draw-down of 10 μπι thick films with a doctor blade on a 30 x 8 mm KBr crystal. Polymerization is triggered by UV exposure (350-380 nm) for 4s at 540 mW/cm2 with an Omnicure S2000 exposure unit (high-pressure mercury-vapor lamp equipped with 365 nm notch filter having 30 nm spectral width; fiber-optic direction of exposure to the sample from the top with a total dose of 2080 mJ/cm2 over 4 seconds. The sample is purged with nitrogen to prevent oxygen inhibition effects.
[00159] Spectra are recorded a) before UV exposure (reference spectrum), b) during/after UV exposure each 1.25 s for 1.25 min (first spectrum with start of exposure) and c) thereafter each 60 s over 30 minutes. [00160] Raw spectra are processed using OPUS 7.0 software. All spectra are baseline- corrected and normalized with respect to the region 2700-3050 cm-1 (CH polymer backbone signal) to compensate for variation of film thickness between samples. The different chemical families' conversion degrees are calculated from the absorption bands and with spectrum integration algorithms as summarized in the table below and in Figure 1. The conversion degree of a chemical family is defined as the ratio of its absorption band integral before and after exposure. Moreover, Figure 2 shows typical conversion curves as a function of time for acrylate, oxetane, and epoxy compounds.
Figure imgf000051_0001
[00161] All combinations of the aforementioned embodiments throughout the entire disclosure are hereby expressly contemplated in one or more non-limiting embodiments even if such a disclosure is not described verbatim in a single paragraph or section above. In other words, an expressly contemplated embodiment may include any one or more elements described above selected and combined from any portion of the disclosure.
[00162] One or more of the values described above may vary by ± 5%, ± 10%, ± 15%, ± 20%, ± 25%, etc. so long as the variance remains within the scope of the disclosure.
Unexpected results may be obtained from each member of a Markush group independent from all other members. Each member maybe relied upon individually and or in combination and provides adequate support for specific embodiments within the scope of the appended claims. The subject matter of all combinations of independent and dependent claims, both singly and multiply dependent, is herein expressly contemplated. The disclosure is illustrative including words of description rather than of limitation. Many modifications and variations of the present disclosure are possible in light of the above teachings, and the disclosure maybe practiced otherwise than as specifically described herein.
[00163] It is also to be understood that any ranges and subranges relied upon in describing various embodiments of the present disclosure independently and collectively fall within the scope of the appended claims, and are understood to describe and contemplate all ranges including whole and/or fractional values therein, even if such values are not expressly written herein. One of skill in the art readily recognizes that the enumerated ranges and subranges sufficiently describe and enable various embodiments of the present disclosure, and such ranges and subranges maybe further delineated into relevant halves, thirds, quarters, fifths, and so on. As just one example, a range "of from 0.1 to 0.9" maybe further delineated into a lower third, i.e. from 0.1 to 0.3, a middle third, i.e. from 0.4 to 0.6, and an upper third, i.e. from 0.7 to 0.9, which individually and collectively are within the scope of the appended claims, and maybe relied upon individually and/or collectively and provide adequate support for specific embodiments within the scope of the appended claims. In addition, with respect to the language which defines or modifies a range, such as "at least," "greater than," "less than," "no more than," and the like, it is to be understood that such language includes subranges and/or an upper or lower limit. As another example, a range of "at least 10" inherently includes a subrange of from at least 10 to 35, a subrange of from at least 10 to 25, a subrange of from 25 to 35, and so on, and each subrange maybe relied upon individually and/or collectively and provides adequate support for specific embodiments within the scope of the appended claims. Finally, an individual number within a disclosed range may be relied upon and provides adequate support for specific embodiments within the scope of the appended claims. For example, a range "of from 1 to 9" includes various individual integers, such as 3, as well as individual numbers including a decimal point (or fraction), such as 4.1 , which may be relied upon and provide adequate support for specific embodiments within the scope of the appended claims.

Claims

CLAIMS What is claimed is:
1. A photopolymer ceramic dispersion for additive fabrication comprising: a cationically polymerizable aliphatic epoxide;
a cationically polymerizable oxetane;
a free-radical polymerizable multifunctional (meth)acrylate;
a cationic photoinitiator;
a free-radical photoinitiator; and
a coated filler comprising core particles and a surface treatment disposed on said core particles, wherein said core particles comprise silica, alumina, zircon, or combinations thereof and said surface treatment comprises an organosilane,
wherein said core particles are microparticles having a particle size of from 1 micrometer to 90 micrometers and wherein said core particles comprise 5 weight percent or less of nanoparticles having a particle size of from 10 nanometers to 999 nanometers
2. The dispersion of claim 1 wherein said coated filler is present in an amount of from 55 to 70 volume percent based on a total volume of said dispersion.
3. The dispersion of claim 1 or 2 wherein said surface treatment is present in an amount of from 0.5 to 2 weight percent based on a total weight of said coated filler.
4. The dispersion of any one of claims 1 to 3 wherein said core particles are a combination of silica, 2 to 5 weight % of alumina, and 2 to 5 weight % of zircon.
5. The dispersion of any one of claims 1 to 4 wherein said organosilane is chosen from dicyclopentyldimethoxysilane, (cyclohexyl)methyldimethoxysilane, 3- acetoxyethylyltrimethoxysilane, 3-acetoxypropyltrimethoxysilane, and combinations thereof.
6. The dispersion of any one of claims 1 to 5 wherein said cationically polymerizable aliphatic epoxide is a multifunctional glycidyl ether.
7. The dispersion of claim 6 wherein said multifunctional glycidyl ether is neopentyl glycol diglycidyl ether.
8. The dispersion of any one of claims 1 to 7 wherein each of said cationically polymerizable aliphatic epoxide, said cationically polymerizable oxetane, and said multifunctional (meth)acrylate independently has a viscosity of less than 30 mPas s as determined using ASTM D 2196 - 99.
9. The dispersion of any one of claims 1 to 8 wherein said cationic photoinitiator is an R-substituted aromatic thioether triaryl sulfonium or iodonium
tetrakis(pentafluorophenyl) borate cationic photoinitiator with a
tetrakis anion and a cation of the following formula (I):
Figure imgf000054_0001
wherein Yl , Y2, and Y3 are the same or different and wherein each of Yl, Y2, and Y3 is an R-substituted aromatic thioether wherein R is an acetyl or halogen group.
10. The dispersion of any one of claims 1 to 8 wherein said cationic photoinitiator comprises an anion chosen from SbF6_, PF6-, BF4 ", (CF3CF2)3PF3, (CeFi ', ((CF3)2C6H3)4B", (C6Fs)4Ga", ((CF3)2C6H3)4Ga", trifluoromethanesulfonate, nonafluorobutanesulfonate, methanesulfonate, butanesulfonate, benzenesulfonate, and p-toluenesulfonate, and also com rises a cation of the following formula:
Figure imgf000054_0002
1 2 3 5 6
wherein each of R , R , R , R , and R is independently an alkyl group, a hydroxy group, an alkoxy group, an alkylcarbonyl group, an arylcarbonyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an arylthiocarbonyl group, an acyloxy group, an arylthio group, an alkylthio group, an aryl group, a heterocyclic hydrocarbon group, an aryloxy group, an alkylsulfinyl group, an arylsulfinyl group, an alkylsulfonyl group, an arylsulfonyl group, a hydroxy(poly)alkyleneoxy group, an optionally substituted amino group, a cyano group, a nitro group, or a halogen atom,
wherein R4 is an alkyl group, a hydroxy group, an alkoxy group, an alkylcarbonyl group, an alkoxycarbonyl group, an acyloxy group, an alkylthio group, a heterocyclic hydrocarbon group, an alkylsulfinyl group, an alkylsulfonyl group, a
hydroxy(poly)alkyleneoxy group, an optionally substituted amino group, a cyano group, a nitro group, or a halogen atom, and
wherein each of m1 to m6 is the number of occurrences of each of R1 to R6 such that each of m1, m4, and m6 is an integer from 0 to 5, and each of m2, m3, and m5 is an integer from 0 to 4.
11. The dispersion of any one of claims 1 to 10 wherein said cationically polymerizable oxetane is chosen from 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, and combinations thereof.
12. The dispersion of any one of claims 1 to 11 wherein said multifunctional (meth)acrylate is chosen from trimethylolpropane tri(meth)acrylate, ethylene glycol di(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, tripropyleneglycol
di(meth)acrylate, glycerol tri(meth)acrylate, and combinations thereof.
13. The dispersion of any one of claims 1 to 12 that is free of UV curable monomers that are not free-radical polymerizable multifunctional (meth)acrylates.
14. The dispersion of any one of claims 1 to 13 wherein said coated filler has a particle size from 0.04 micrometers to 90 micrometers.
15. The dispersion of any one of claims 1 to 14 wherein said dispersion has a viscosity from 500 to 4,000 cps at 25 °C and 30 RPM using ASTM D 2196 - 99.
16. A ceramic article formed from said dispersion of any one of claims 1 to 15.
17. A method of forming a ceramic article from a photopolymer ceramic dispersion comprising a cationically polymerizable aliphatic epoxide, a cationically polymerizable oxetane, a free-radical polymerizable multifunctional (meth)acrylate, a cationic photo initiator, a free-radical photoinitiator, and a coated filler comprising core particles and a surface treatment disposed on the core particles, wherein the core particles comprise silica, alumina, zircon, or combinations thereof and the surface treatment comprises an organosilane, wherein the core particles are microparticles having a particle size of from 1 micrometer to 90 micrometers and wherein the core particles comprise 5 weight percent or less of nanoparticles having a particle size of from 10 nanometers to 999 nanometers, said method comprising the steps of:
applying a layer of the ceramic dispersion to a surface;
selectively exposing the layer imagewise to actinic radiation to form an imaged cross-section;
applying a second layer of the ceramic dispersion to the imaged cross-section; selectively exposing the second layer imagewise to actinic radiation to form a second imaged cross-section;
repeating steps (C) and (D) to create a three-dimensional green ceramic article; and
sintering the three-dimensional green ceramic article in a furnace to form the ceramic article.
18. The method of claim 17 that is further defined as a method of three- dimensionally printing the green ceramic article.
19. The method of claim 17 or 18 further comprising the step of post-curing the three-dimensional green ceramic article prior to the step of sintering.
20. The method of any one of claims 17 to 19 wherein the step of sintering is further defined as burning away the dispersion in the furnace to form the ceramic article.
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