Classifications

• • 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
  • 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
• • 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
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B19/00—Other methods of shaping glass
  • C03B19/06—Other methods of shaping glass by sintering, e.g. by cold isostatic pressing of powders and subsequent sintering, by hot pressing of powders, by sintering slurries or dispersions not undergoing a liquid phase reaction
  • C03B19/066—Other methods of shaping glass by sintering, e.g. by cold isostatic pressing of powders and subsequent sintering, by hot pressing of powders, by sintering slurries or dispersions not undergoing a liquid phase reaction for the production of quartz or fused silica articles
• • 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
• • 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 including a UV curable acrylate monomer and silica. More specifically, this composition includes a particular sheer thinning additive that minimizes silica sedimentation in the dispersion.
• 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 liquid radiation curable resin 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 run in wavelength, although other wavelength variants exist.
• the use of gas lasers to cure liquid radiation curable resin 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 liquid radiation curable resin 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, (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 may be a low -viscosity, largely unfilled portion, i.e., a portion that does not include sufficient loadings of the silica.
• the bottom part may be 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 a line graph showing sediment height as a function of an amount of the shear thinning additive.
• Figure 2 is a line graph showing viscosity of the dispersion as a function of an amount of the shear thinning additive.
• Figure 3 is a line graph showing sediment height as a function of an amount of the shear thinning additive.
• This disclosure provides a photopolymer ceramic dispersion for additive fabrication.
• the dispersion includes a UV curable acrylate monomer as a continuous phase.
• the dispersion also includes silica as a dispersed phase that is dispersed in the continuous phase in an amount of from 60 to 70 volume percent based on a total volume of the dispersion.
• the dispersion further includes a free-radical initiator and a shear thinning additive to minimize silica sedimentation in the dispersion.
• the shear thinning additive is chosen from bentonite clay, a urea-polyol-aliphatic copolymer, an acrylic copolymer, a modified hydrogenated castor oil, and combinations thereof.
• the dispersion has a viscosity from 500 to 4,000 cps at 25°C and 30 RPM using ASTM D 2196 - 99.
• This disclosure also provides a method of forming a ceramic article from a photopolymer ceramic dispersion.
• the method includes the steps of A. applying a layer of the ceramic dispersion to a surface and B. selectively exposing the layer imagewise 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 imagewise 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.
• 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 UV curable monomer, e.g. an acrylate monomer. In other words, the monomer is photo (or light) curable such that the dispersion itself is light curable to form a green model, described in greater detail below.
• 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 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.
• the dispersion typically includes a UV curable acrylate monomer as a continuous phase (which may include soluble additives, initiators, etc. including any described below), silica as a dispersed phase that is dispersed in the continuous phase in an amount of from 60 to 70 volume percent based on a total volume of the dispersion, a free-radical initiator, and a shear thinning additive to minimize silica sedimentation in the dispersion.
• a UV curable acrylate monomer as a continuous phase (which may include soluble additives, initiators, etc. including any described below)
• silica as a dispersed phase that is dispersed in the continuous phase in an amount of from 60 to 70 volume percent based on a total volume of the dispersion
• a free-radical initiator a free-radical initiator
• shear thinning additive to minimize silica sedimentation in the dispersion.
• the dispersion is, consists essentially of, or consists of, the UV curable acrylate monomer, the silica, the free-radical initiator, and the shear thinning additive.
• the dispersion may be free of UV curable monomers that are not 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 described herein that are not the shear thinning additive, any polymerization initiators that are not free-radical initiators, polymerization initiators that are not UV free-radical initiators, and/or fillers other than silica, etc., and/or combinations thereof.
• 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 the aforementioned values are hereby expressly contemplated.
• the dispersion includes a UV curable acrylate monomer.
• This monomer is able to polymerize with itself and/or with other acrylate monomers via free-radical polymerization initiated by exposure to UV light/energy.
• This monomer acts as the continuous (e.g. liquid) phase of the dispersion.
• the acrylate monomer may be an acrylate or a methacrylate.
• the acrylate monomer may be a multifunctional acrylate or polyfunctional acrylate. A single type or more than one type of UV curable acrylate monomer may be used.
• Suitable non-limiting examples include isobornyl (meth)acrylate, bornyl
• 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
• di(meth)acrylate dicyclopentadiene dimethanol di(meth)acrylate, [2-[l, l-dimethyl-2-[(l- oxoallyl)oxy]ethyl]-5-ethyl-l,3-dioxan-5-yl]methyl acrylate; 3,9-bis(l, l-dimethyl-2- hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5- ]undecane di(meth)acrylate; dipentaerythritol monohydroxy penta(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(
• the acrylate monomer is a polyfunctional (meth)acrylate that may include all methacryloyl groups, all acryloyl groups, or any combination of methacryloyl and acryloyl groups.
• the acrylate monomer is chosen from propoxylated trimethylolpropane tri(meth)acrylate, and propoxylated neopentyl glycol di(meth)acrylate, and combinations thereof.
• the acrylate monomer has more than 2, more than 3, or more than 4 functional groups.
• the acrylate monomer may have exactly 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, functional groups.
• the acrylate monomer consists exclusively of a single polyfunctional (meth)acrylate component.
• the acrylate monomer is chosen from dicyclopentadiene dimethanol diacrylate, [2- [1,1 -dimethyl - 2-[(l-oxoallyl)oxy]ethyl]-5-ethyl-l,3-dioxan-5-yl]methyl acrylate, propoxylated
• the acrylate monomer may be dicyclopentadiene dimethanol di(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, and/or propoxylated neopentyl glycol di(meth)acrylate, and more specifically, dicyclopentadiene dimethanol diacrylate, propoxylated trimethylolpropane triacrylate, and/or propoxylated neopentyl glycol diacrylate.
• the UV curable acrylate monomer 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 may be 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 may be 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 may be selected as one of the (meth)acrylate monomers is cyclohexyl methacrylate.
• the above-mentioned acrylate monomers can be used singly or in combination of two or more.
• the dispersion can include any suitable amount of the acrylate monomer so long as the silica is present in an amount of from 60 to 70 volume percent based on a total volume of the dispersion and the free-radical initiator and the shear thinning additive are also present in the dispersion.
• the dispersion is free of UV curable monomers that are not acrylates.
• the acrylate monomer is present in an amount of greater than zero and up to about 40 volume % 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 dispersion. In various non-limiting embodiments, all values and ranges of values between the aforementioned values are hereby expressly contemplated.
• the dispersion also includes the silica.
• the silica is the dispersed phase that is dispersed in the acrylate monomer continuous phase described above. In other words, silica particles are dispersed in the acrylate monomer, which is typically liquid or liquid-like.
• the silica is present in an amount of from 60 to 70 volume percent based on a total volume of the dispersion. In various embodiments, the silica is present in 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 the aforementioned values are hereby expressly contemplated.
• the silica is further defined as silica particles, e.g.
• the silica may be 90, 95, 99, or approximately 100 wt% of microparticles, nanoparticles, or a combination of microparticles and nanoparticles.
• the silica comprises a combination of microparticles having a particle size of from 1 to 90 micrometers and nanoparticles having a particle size of from 10 to 500 nanometers, in a ratio of average particle size of
• the silica comprises a combination of microparticles having a particle size of from 1 to 90 micrometers and nanoparticles having a particle size of from 10 to 1000 nanometers, in a ratio of average particle size of microparticles:nanoparticles of from 1 :2 to 1 :200. In other non-limiting embodiments, these ratios can be reversed. In various non-limiting embodiments, all values and ranges of values between and including 1 and 90 micrometers, 10 and 500 nanometers, and 1 :2 and 1 :200, are hereby expressly contemplated for use.
• nanoparticles may be described as those particles having a mean particle size of from between 1 nanometer (nm) to 999 nm.
• Microparticles may be alternatively described as those particles having a mean particle size of from 1 micrometer ( ⁇ ) to 999 ⁇ .
• the silica comprises particles having a particle size (distribution) of from 0.04 micrometers to 90 micrometers. In various non- limiting embodiments, all values and ranges of values between and including all values above are hereby expressly contemplated for use.
• 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 (S1O 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 X, Huselex ZA-20, IMSIL A-25,
• the silica may be surface treated with a silane coupling agent.
• Silane coupling agents which can be used for this purpose 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
• 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 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, benzophenone s, 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, ethoxy phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, 2- methyl- 1 - [4-(methylthio)phenyl] -2-morpholinopropanone- 1 ,2-benzyl-2-(dim- ethylamino)- 1 - [4-(4-morpholinyl)phenyl] - 1 -butanone, 2-dimethylamino-2-(4-methyl -benzyl)- 1 -(4- mo holin-4-yl-phenyl)-butan-l-o- ne, 4-benzoyl-4'-methyl diphenyl sulphide, 4,4'- bis(diethylamino) benzophenone, and 4,4'--
• dimethoxybenzophenone 1-hydroxycyclohexyl phenyl ketone, phenyl (1- hydroxyisopropyl)ketone, 2-hydroxy- 1 - [4-(2-hydroxyethoxyl)phenyl] -2-methyl- 1 -propanone, 4-isopropylphenyl( 1 -hydroxyisopropyl)ketone, oligo- [2-hydroxy-2-methyl- 1 - [4-( 1 - methylvinyl)phenyl] propanone], camphorquinone, 4,4'-bis(diethylamino) benzophenone, 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-mo holinopropanone-l (Irgacure 907 from Ciba), 2-benzyl-2-(dimethylamino)-l-[4-(4-mo holinyl)phenyl]-l-butanone (Irgacure 369 from Ciba), 2-dimethylamino-2-(4-methyl-benzyl)-l-(4-mo holin-4-y
• 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-hydroxyphenyl 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(l- 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, dimethoxybenzophenone
• 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, may be 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 may be 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 the
• the dispersion also includes a shear thinning additive to minimize silica
• the shear thinning additive may be alternatively described as an anti-settling agent.
• the shear thinning additive is chosen from bentonite clay, a urea- polyol-aliphatic copolymer, an acrylic copolymer, a modified hydrogenated castor oil, and combinations thereof.
• the shear thinning additive is the bentonite clay.
• the shear thinning additive is the urea-polyol-aliphatic copolymer.
• the shear thinning additive is the acrylic polymer.
• the shear thinning additive is a modified hydrogenated castor oil.
• the shear thinning additive that may be used is commercially available as BYK 410, 420, or 430.
• the acrylic copolymer has the following structure:
• each of R 1 and R 2 is independently a group (C n H 2n )OH wherein n is from 15 to 20.
• n may be 15, 16, 17, 18, 19, or 20.
• the OH group may be present at any location on the chain of R 1 and R 2 .
• R 1 and R 2 may have the same or different chain lengths.
• the acrylic copolymer is N,N'-Ethane-l,2-diylbis(12-
• the acrylic copolymer is Attagel 50 available from BASF.
• the shear thinning additive is the urea-polyol
• the shear thinning additive is the urea-polyol-aliphatic copolymer having the structure:
• the shear thinning additive is a modified hydrogenated castor oil.
• the modified hydrogenated castor oil may be EFKA RM1900 from BASF. Additives:
• 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, poly aery lonitriles, 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.
• group IA and IIA metals such as sodium bicarbonate, potassium bicarbonate, and rubidium carbonate
• polyvinylpyrrolidones polyvinylpyrrolidones
• poly aery lonitriles and combinations thereof.
• Other additives include dyes, pigments, antioxidants, wetting agents, photosens
• 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 25 G 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.
• 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.
• 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.
• 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 may be observed with the naked eye while the rest of the dispersion remains opaque to a probe of the LUMiSizer 6112- 24.
• 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.
• 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 UV curable acrylate monomer, providing the silica, providing the free-radical initiator, and providing the sheer thinning additive.
• the method also includes the steps of combining the UV curable acrylate monomer, the silica, the free- radical initiator, and the sheer thinning additive to form the dispersion.
• One or more of these 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.
• temperature of the vessel can be controlled by a cooling jacket in addition to agitation speed.
• 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 may be 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. For example, typically all the layers in a part build have the same thickness, e.g. either 50 or 100 ⁇ . However, 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 built forming vertical walls at a high layer thickness while building the layers that form sloped or rounded surfaces at a smaller layer thickness.
• 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 may be 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 may be 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.
• the second layer may be 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.
• 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 may be 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 may be 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.
• 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 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, preferably less than 2 and most preferably 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.
• 160762 and 160760 may be used herein. Both of these applications are hereby expressly incorporated herein by reference in their entireties in various non-limiting embodiments.
• a series of dispersions are formed in accordance with this disclosure.
• a comparative dispersion is also formed.
• the Dispersions and Comparative Dispersions are evaluated to determine sedimentation and viscosity as set forth in the Table below wherein all values are in weight percent unless otherwise indicated.
• Variquat CC 42 NS is a dispersant, Poly[oxy(methyl-l,2-ethanediyl)], a-[2- (diethylmethylammonio)ethyl]-w -hydroxy-, chloride, manufactured by Evonik Corporation of Hopewell, VA 23860, USA.
• Laromer HDDA is hexanediol diacrylate manufactured by BASF Corp., 100 Park Avenue, Florham Park, NJ 07932, USA and functions as a UV curable binder.
• Laromer LR 8863 ethoxylated trimethylolpropane triacrylate (ethoxylated TMPTA) manufactured by BASF Corp., 100 Park Avenue, Florham Park, NJ 07932, USA and functions as a UV curable binder that increases the strength of the green body.
• Sartomer SR247 (NPGDA) and functions as a UV curable binder producing very high green strength and very low curl distortion factor.
• DPGDA Dipropyleneglycol diacrylate
• DCPA Dicyclopentadienyl diacrylate
• Byk 410 is the shear thinning additive manufactured by BYK USA Inc., 524 South Cherry Street, Wallingsford, CT 06492, USA.
• Irgacure 184 is manufactured by BASF Corp., 100 Park Avenue, Florham Park, NJ 07932, USA and functions as a UV free radical photoinitiator for initiating acrylate polymerization.
• the sedimentation rate is determined using a method described above and is tabulated below for various concentrations of shear thinning anti-settling additives together with viscosity of those formulations measured using an Anton-Parr MCR 301 plate-plate rheometer.
• the shear thinning additive will, at very low
• BYK 410, BYK 420, Bentone SD2, and EFKA RM 1900 are the most effective causing the sedimentation rate to go to zero under the test conditions.
• BYK 410 achieves this at 0.25 wt%
• BYK 420 achieves this at 0.5 wt %
• Bentone SD2 achieves this at 0.8 wt%
• EFKA RM 1900 achieves this at 1.25 wt%.
• BYK 410, BYK 420, and Bentone SD2 achieve this without appreciably increasing the formulation viscosity (less than 1500 MPa-s).
• shear thinning additives reduces the sedimentation rate of dispersions without appreciably increasing the formulation viscosity thus enabling the 3D printing of ceramic parts having constant ceramic density throughout the build process and even through successive 3D print jobs.
• shear thinning additives reduce sedimentation rate by as much as a factor 12, both using the accelerated test metric and in real time at 1G.
• 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 may be further delineated into relevant halves, thirds, quarters, fifths, and so on. As just one example, a range "of from 0.1 to 0.9" may be further delineated into a lower third, i.e.
• 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 may be 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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