USOO9353284B2
`
`(12) United States Patent
`Moussa
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 9,353,284 B2
`May 31, 2016
`
`(54) THREE DIMENSIONAL PRINTING
`MATERAL SYSTEMAND METHOD
`
`(71) Applicant: 3D Systems, Inc., Rock Hill, SC (US)
`
`(72) Inventor: Khalil Moussa, Chapel Hill, NC (US)
`
`(73) Assignee: 3D Systems, Inc., Rock Hill, SC (US)
`(*) Notice:
`Subject to any disclaimer, the term of this
`ded
`di
`d under 35
`patent 1s extended or adjusted under
`U.S.C. 154(b) by 145 days.
`
`(21) Appl. No.: 14/211,807
`
`(22) Filed:
`
`Mar 14, 2014
`
`(65)
`
`Prior Publication Data
`US 2014/0275317 A1
`Sep. 18, 2014
`
`(58) Field of Classification Search
`CPC ............. B29C 67/0081; C09D 1 1/101; C09D
`11/107: C09D 1 1/322; C09D 133/08
`See application file for complete search history.
`Ref
`Cited
`eeees e
`U.S. PATENT DOCUMENTS
`
`56
`(56)
`
`7,905,951 B2* 3/2011 Williams ............ B29C 67,0081
`106.31.13
`8, 157,908 B2 * 4/2012 Williams ............ B29C 67,0081
`106,400
`2008. O138515 A1* 6, 2008 Williams ............ B29C 67,0081
`427,222
`2011/O130489 A1* 6, 2011 Williams ............ B29C 67,0081
`524/47
`
`FOREIGN PATENT DOCUMENTS
`
`WO
`WO
`
`10, 2001
`O178696
`6, 2008
`2008073297
`OTHER PUBLICATIONS
`
`O
`O
`Related U.S. Application Data
`(60) Provisional application No. 61/787,591, filed on Mar.
`15, 2013.
`sa- - us
`
`PCT International Search Report the International Searching Author
`ity for PCT/US2014/027444 mailed Jul. 1, 2014 (5 pages).
`PCT Written Opinion of the International Searching Authority for
`PCT/US2014/027444 mailed Jul. 1, 2014 (6 pages).
`
`(51) Int. Cl.
`B29C 67/00
`C09D II/O
`C83/28
`CSF 2/50
`C09D 13.3/08
`C09D II/II
`C09D 1 1/107
`C09D II/322
`(52) U.S. Cl
`CPC
`- - - - - - C09D 133/08 (2013.01); B29C 67/0081
`(2013.01); C09D 1 1/101 (2013.01); C09D
`II/107 (2013.01); C09D 1 1/322 (2013.01)
`
`(2006.01)
`(2014.01)
`(2006.01)
`(2006.01)
`(2006.01)
`(2014.01)
`(2014.01)
`(2014.01)
`
`* cited by examiner
`Primary Examiner — Sanza McClendon
`(57)
`ABSTRACT
`A materials system and methods are provided to enable the
`formation of articles by 3D printing. In some embodiments, a
`materials system includes a Substantially dry particulate
`material that includes an insoluble filler, a soluble filler, and a
`transition metal catalyst. The materials system further com
`prises a fluid binder including a (meth)acrylate monomer, an
`allyl ether functional monomer and/or oligomer, and a free
`radical photoinitiator.
`22 Claims, 22 Drawing Sheets
`
`
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`1.
`THREE DIMIENSIONAL PRINTING
`MATERAL SYSTEMAND METHOD
`
`US 9,353,284 B2
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`CROSS REFERENCE TO RELATED
`APPLICATION
`
`This application claims priority pursuant to 35 U.S.C.S 119
`to U.S. Provisional Patent Application Ser. No. 61/787,591,
`filed on Mar. 15, 2013, which is hereby incorporated by
`reference in its entirety.
`
`10
`
`TECHNICAL FIELD
`
`This invention relates generally to rapid prototyping tech
`niques and, more particularly, to a three-dimensional (3D)
`printing material and method using a reduced rate cure.
`
`15
`
`BACKGROUND
`
`The field of rapid prototyping involves the production of
`prototype articles and Small quantities of functional parts, as
`well as structural ceramics and ceramic shell molds for metal
`casting, directly from computer-generated design data.
`Two well-known methods for rapid prototyping include a
`selective laser sintering process and a liquid binder 3D print
`ing process. These techniques are similar, to the extent that
`they both use layering techniques to build three-dimensional
`articles. Both methods form Successive thin cross-sections of
`the desired article. The individual cross-sections are formed
`by bonding together adjacent grains of a granular, (i.e., par
`ticulate) material on a generally planar surface of a bed of the
`granular material. Each layer is bonded to a previously
`formed layer at the same time as the grains of each layer are
`bonded together to form the desired three-dimensional
`article. The laser-sintering and liquid binder techniques are
`advantageous because they create parts directly from com
`puter-generated design data and can produce parts having
`complex geometries. Moreover, 3D printing may be quicker
`and less expensive than machining of prototype parts or pro
`duction of cast or molded parts by conventional “hard' or
`“soft' tooling techniques that can take from a few weeks to
`several months, depending on the complexity of the item.
`An early 3D printing technique, described in U.S. Pat. No.
`5,204,055, incorporated herein by reference in its entirety,
`describes the use of an inkjet style printing head to deliver a
`liquid or colloidal binder material to sequentially applied
`layers of powdered material. The three-dimensional inkjet
`printing technique or liquid binder method involves applying
`a layer of a powdered material to a Surface using a counter
`roller. After the powdered material is applied to the surface,
`the inkjet printhead delivers a liquid binder in a predeter
`mined pattern to the layer of powder. The binder infiltrates
`into gaps in the powder material and hardens to bond the
`powder material into a solidified layer. The hardened binder
`also bonds each layer to the previous layer. After the first
`cross-sectional portion is formed, the previous steps are
`repeated, building Successive cross-sectional portions until
`the final article is formed. Optionally, an adhesive may be
`Suspended in a carrier that evaporates, leaving the hardened
`adhesive behind. The powdered material may be ceramic,
`plastic or a composite material. The liquid binder material
`may be organic or inorganic. Typical organic binder materials
`used are polymeric resins or ceramic precursors, such as
`polycarbosilaZane. Inorganic binders can be used where the
`binder is incorporated into the final articles. For example,
`silica can be used in Such an application.
`
`25
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`30
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`35
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`40
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`45
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`50
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`55
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`60
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`2
`It is also possible to perform ultraviolet cure of acrylate
`binders over particulate material. Acrylate binders provide
`several advantages. First of all, they are curable by ultraviolet
`(UV) light, thereby enabling a faster forming process than is
`possible with other typical curing methods. Secondly, they
`allow the formation of articles having surfaces with plastic
`appearances, thereby enabling more realistic modeling of
`various objects. Finally, because acrylate binders are essen
`tially solids, no evaporation takes place after the binders are
`printed, thereby allowing the formation of stable, tough struc
`tures.
`However, the fast curing mechanism of UV initiation of
`(meth)acrylate polymerization may cause excessive distor
`tion in free flowing particulate material, resulting in curling of
`the printed part, which may make the printing of parts having
`a thickness greater than 1 millimeter exceedingly difficult. To
`reduce curling due to fast curing, a first printed layer may be
`formed on a glass build plate, adhering thereto.
`
`SUMMARY
`
`In an embodiment of the invention, strong parts may be
`made by 3D printing over a particulate build material without
`a need for infiltration. Typical existing printing processes
`include a post-processing infiltration step to increase the
`strength of the printed article. Articles printed with the bind
`ers described herein have strengths comparable to that of
`infiltrated articles, e.g., about 20 MPa, thereby eliminating a
`need for the infiltration step.
`The fast curing mechanism of UV initiation of (meth)
`acrylate polymerization may cause curling and distortions to
`occur immediately due to shrinkage. Not intending to be
`bound by theory, the shrinkage may be due to the instanta
`neous decrease in free volume from the conversion of carbon
`carbon double bonds of the individual (meth)acrylate mono
`merto single carbon-carbon bonds to another (meth)acrylate
`monomer. This may hinder the production of articles thicker
`than 1 mm from free-flowing particulate build materials, as
`articles tend to be destroyed in the process. Again not intend
`ing to be bound by theory, it is believed that the slower curing
`mechanism of the initiation according to the present invention
`slows down the rate of carbon-carbon double bond conver
`sion into single bonds and thus reduces the immediate curling
`and distortion. Moreover, the acrylate-containing binder
`cures upon contact with the particulate material, thus provid
`ing the advantage of a stable two-component product.
`Both aerobic curing and anaerobic curing may be
`employed in embodiments of the invention. In contrast to
`existing processes where amines may be used as oxygen
`Scavengers solely in ultraviolet curing, allyl ethers, as
`described herein, may be employed as oxygen Scavengers in
`both ultraviolet curing and peroxide initiation.
`In an embodiment, the invention features a powder mate
`rial system for 3D printing including a Substantially dry par
`ticulate material that includes an insoluble filler, a soluble
`filler, and a transition metal catalyst. The dry particulate
`material is suitable for use in 3D printing to form an article
`having a plurality of layers, the layers including a reaction
`product of the particulate material and a non-aqueous fluid
`that contacts the particulate material during 3D printing.
`One or more of the following features may be included.
`The particulate material may possess an internal angle of
`friction greater than about 40° and less than about 70°. The
`particulate material may possess a critical Surface tension
`greater than about 20 dynes/cm. The particulate material may
`include about 50%-90% by weight of the insoluble filler,
`about 10-50% by weight of the soluble filler, and about 0.01
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`0.5% by weight of the transition metal catalyst, based on the
`total weight of the particulate material.
`The insoluble filler may include or consist essentially of
`Solid glass microspheres, hollow glass microspheres, Solid
`ceramic microspheres, hollow ceramic microspheres, potato 5
`starch, tabular alumina, calcium sulfate hemihydrate, calcium
`Sulfate dihydrate, calcium carbonate, ultra-high molecular
`weight polyethylene, polyamide, poly-cyclic-olefins, poly
`urethane, polypropylene and combinations thereof.
`The soluble filler may include or consist essentially of 10
`methyl methacrylate polymers, ethyl methacrylate polymers,
`butyl methacrylate polymers, polyvinylbutyral, and combi
`nations thereof. The soluble filler may have a weight average
`molecular weight between about 100,000 g/mol and about
`500,000 g/mol.
`The transition metal catalyst may include or consist essen
`tially of cobalt(II) octoate, cobalt(II) naphthenate, vanadium
`(II) octoate, manganese naphthenate and combinations
`thereof.
`The particulate material may include a pigment, e.g., about 20
`0.5 to 5% by weight, based on the total weight of the particu
`late material. The pigment may include or consist essentially
`of Zinc oxide, Zinc sulfide, barium sulfate, titanium dioxide,
`Zirconium silicate, lead carbonate, and hollow borosilicate
`glass spheres.
`The particulate material may include a processing aid, e.g.,
`about 0.01-2.0% by weight of the processing aid, based on the
`total weight of the particulate material. The processing aid
`may include or consist essentially of mineral oil, propylene
`glycol di(caprylate/caprate), petroleum jelly, propylene gly- 30
`col, di-isobutyl phthalate, di-isononyl phthalate, polyalkyle
`neoxide modified heptamethyltrisiloxanes, polyalkyleneox
`ide modified polydimethylsiloxanes, secondary ethoxylated
`alcohols, fluorinated hydrocarbons, saturated hydrocarbon
`resin tackifiers, and combinations thereof.
`In another aspect, the invention features a kit including a
`Substantially dry particulate material including an insoluble
`filler, a soluble filler, and a transition metal catalyst. The kit
`also includes a fluid binder including a (meth)acrylate mono
`mer, an allyl ether functional monomer and/or oligomer, and 40
`organic hydroperoxide. Alternatively, in some embodiments,
`the kit can include a free-radical photoinitiator instead of the
`organic hydroperoxide.
`One or more of the following features may be included.
`The fluid binder may have a contact angle of less than about 45
`25° on the particulate material. The fluid binder may include
`about 40%-95% by weight of the (meth)acrylate monomer,
`about 5-25% by weight of the allyl ether functional monomer/
`oligomer, and about 0.5-5% by weight of the organic hydro
`peroxide, based on the total weight of the fluid binder. Alter- 50
`natively, the organic hydroperoxide can be replaced by 0.01
`1% by weight photoinitiator, based on the total weight of the
`fluid binder. The fluid binder may also include 0-1% by
`weight of surfactant. The fluid binder may include a (meth)
`acrylate oligomer, e.g., about 10-40% by weight of the (meth) 55
`acrylate oligomer. The fluid binder may include a first accel
`erator, e.g., up to about 2% by weight of the first accelerator.
`The first accelerator may include dimethylacetoacetamide.
`A 1 mm penetration hardening rate of the Substantially dry
`particulate material upon application of the fluid binder can 60
`be selected from a range of 0.01/min to 1.0/min. The dry
`particulate material may include a pigment and/or a process
`ing aid.
`In yet another aspect, a method for forming an article by 3D
`printing includes the step of providing a Substantially dry 65
`particulate material including a plurality of adjacent particles,
`the particulate material comprising a transition metal cata
`
`4
`lyst. A fluid binder is applied to at least some of the plurality
`of particles in an amount Sufficient to bond those particles
`together to define at least a portion of the article, the fluid
`binder including a (meth)acrylate monomer, a (meth)acrylate
`oligomer, anallyl ether functional monomer and/or oligomer,
`and an organic hydroperoxide. Alternatively, in some
`embodiments, the organic hydroperoxide is replaced by a
`photoinitiator.
`One or more of the following features may be included. In
`Some embodiments, the transition metal catalyst may induce
`decomposition of the organic hydroperoxide to generate free
`radicals and the free radicals may initiate anaerobic polymer
`ization of the (meth)acrylate monomer and oligomer, and
`aerobic polymerization of the allyl ether functional mono
`mer? oligomer. Alternatively, in other embodiments, the pho
`toinitiator and the transition metal catalyst may act coopera
`tively, with or without the presence of activating or initiating
`radiation, to generate free radicals. In Such embodiments, the
`free radicals can initiate anaerobic polymerization of the
`(meth)acrylate monomer and oligomer, and aerobic polymer
`ization of the allyl ether functional monomer? oligomer.
`If desired, the fluid binder may also include a first accel
`erator. The particulate material may include an insoluble
`filler, a soluble filler, a pigment, and/or a processing aid.
`
`BRIEF DESCRIPTION OF THE FIGURES
`
`The following drawings are not necessarily to scale,
`emphasis instead being placed generally upon illustrating the
`principles of the invention. The foregoing and other features
`and advantages of the present invention, as well as the inven
`tion itself, will be more fully understood from the following
`description of exemplary and preferred embodiments, when
`read together with the accompanying drawings, in which:
`FIG. 1 is a schematic view of a first layer of a mixture of
`particulate material of an embodiment of the invention depos
`ited onto a movable Surface of a container on which an article
`is to be built, before any fluid has been delivered;
`FIG. 2 is a schematic view of an inkjet nozzle delivering a
`fluid to a portion of the layer of particulate material of FIG. 1
`in a predetermined pattern;
`FIG. 3 is a schematic view of a final article of an embodi
`ment of the invention enclosed in the container, the article
`made by a series of steps illustrated in FIG. 2 and embedded
`in the loose unactivated particles;
`FIG. 4 is a schematic view of the final article of FIG. 3;
`FIG. 5 is a graph illustrating a typical response from the
`Washburn infiltration method to determine the material con
`stant and contact angle of a fluid against a particulate mate
`rial;
`FIG. 6a is a magnified image of the particulate material
`consisting primarily of glass microspheres and a soluble filler
`as the secondary component;
`FIG. 6b is a magnified image of the particulate material
`consisting of a 50/50 blend by bulk volume of glass micro
`spheres and calcium sulfate hemihydrates with a soluble filler
`as the third component;
`FIG. 7 is a plot of flexural strength and flexural distance at
`break of particulate materials using soluble fillers with vary
`ing molecular weights.
`FIG. 8 is a Zisman plot of a particulate material using a
`mineral oil processing aid;
`FIG. 9 is a Zisman plot of a particulate material using a
`combination of mineral oil and a secondary ethoxylated alco
`hol Surfactant as a processing aid;
`
`EX. 1028
`APPLE INC. / Page 25 of 39
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`US 9,353,284 B2
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`5
`FIGS. 10a and 10b are laser profilometer images compar
`ing the effect of properand poor binder wetting on the bottom
`Surfaces of articles;
`FIG. 11 is a Zisman plot of a particulate material using a
`combination of a saturated hydrocarbon resin and mineral oil
`as a processing aid;
`FIG. 12 is a graph illustrating a hardness development
`response of a particulate material and a fluid binder,
`FIG. 13 is the transformed plot of FIG. 12, plotting the
`natural logarithm of the force measured against time;
`FIG. 14 is a diagram illustrating the aerobic cure response
`time of thin-walled articles;
`FIG. 15 is a schematic diagram of a test part used to
`determine aerobic cure response;
`FIG. 16 is a graph illustrating the internal friction angle of
`various powders;
`FIGS. 17a and 17b are laser profilometer images compar
`ing the effect of particulate materials with high internal angle
`of friction on finished article properties;
`FIG. 17c is a CAD drawing of the part portion printed in
`FIGS. 17a and 17b,
`FIGS.18a and 18b are laser profilometer images compar
`ing the effect of particulate material with low internal angle of
`friction on finished article properties; and
`FIG. 18c is a CAD drawing of the part portion printed in
`FIGS. 18a and 18b.
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`DETAILED DESCRIPTION
`
`6
`Referring to FIG. 2, an ink-jet style nozzle 28 delivers a
`fluid binder 26 to at least a portion 30 of the layer or film of the
`particulate mixture 20 in a two-dimensional pattern. In some
`embodiments, the fluid binder 26 delivered to the particulate
`material 20 includes a (meth)acrylate functional monomer, an
`allylic functional monomer? oligomer, and an organic hydro
`peroxide. Alternatively, in other embodiments, the organic
`hydroperoxide may be replaced by a photoinitiator as
`described further hereinbelow. Surprisingly, it has been found
`that a sufficiently slow cure rate can be achieved with the
`appropriate use of a photoinitiator, as described herein. The
`fluid binder 26 may also include a surfactant, an accelerator,
`and/or a (meth)acrylate functional oligomer. In some cases,
`the fluid binder 26 further comprises colloidal silica. Accord
`ing to the printing method, the fluid binder 26 is delivered to
`the layer or film of particulate material 20 in any predeter
`mined two-dimensional pattern (circular, in the figures, for
`purposes of illustration only), using any convenient mecha
`nism, such as a drop-on-demand (DOD) printhead driven by
`Software in accordance with article model data from a com
`puter-assisted-design (CAD) system.
`The first portion 30 of the particulate material 20 activates
`the fluid binder 26, causing the fluid binder 26 to initiate
`polymerization into a solid that adheres together the particu
`late mixture to form a conglomerate of the particulate mate
`rial 20 (powder) and fluid binder 26. The conglomerate
`defines an essentially solid circular layer that becomes a
`cross-sectional portion of an intermediate article 38 (see, e.g.,
`FIGS. 3 and 4). As used herein, “activates’ is meant to define
`a change in state in the fluid binder 26 from essentially stable
`to reactive. This definition encompasses the decomposition of
`the organic hydroperoxide in the fluid binder 26 once in
`contact with the transition metal in the particulate material 20,
`when an organic hydroperoxide is present Similarly, when a
`photoinitiator is present, this definition also encompasses the
`decomposition of the photoinitiator in the fluid binder 26
`once in contact with the transition metal in the particulate
`material 20 and/or in the presence of activating or initiating
`electromagnetic radiation (not shown). Such as UV radiation
`or other radiation capable of generating a free radical or other
`decomposition in the photoinitiator. When the fluid initially
`comes into contact with the particulate mixture, it immedi
`ately flows outwardly (on a microscopic scale) from the point
`of impact by capillary suction, dissolving the soluble filler
`within a time period. Such as 30 seconds to one minute. A
`typical droplet of fluid binder has a volume of about 50
`picoliters (pL), and spreads to a diameter of about 100
`micrometers (um) after coming into contact with the particu
`late mixture. As the fluid binder dissolves the soluble filler,
`the fluid viscosity increases dramatically, arresting further
`migration of the fluid from the initial point of impact. Within
`a few minutes, the fluid with soluble filler dissolved therein
`flows and adheres to the insoluble filler, forming adhesive
`bonds between the insoluble filler particulate material. The
`fluid binder is capable of bonding together an amount of the
`particulate mixture that is several times the mass of a droplet
`of the fluid. As the reactive monomers/oligomer of the fluid
`binder polymerize, the adhesive bonds harden, joining the
`insoluble filler particulate material and, optionally, pigment
`into a rigid structure, which becomes a cross-sectional por
`tion of the final article 40
`Any dry particulate mixture 32 that was not exposed to the
`fluid remains loose and free-flowing on the movable surface
`22. The dry particulate mixture is typically left in place until
`formation of the intermediate article 38 is complete. Leaving
`the dry, loose particulate mixture in place ensures that the
`intermediate article 38 is fully Supported during processing,
`
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`
`Embodiments described herein can be understood more
`readily by reference to the following detailed description,
`examples, and drawings. Elements, apparatus and methods
`described herein, however, are not limited to the specific
`embodiments presented in the detailed description, examples,
`and drawings. It should be recognized that these embodi
`ments are merely illustrative of the principles of the present
`invention. Numerous modifications and adaptations will be
`readily apparent to those of skill in the art without departing
`from the spirit and scope of the invention.
`In addition, all ranges disclosed herein are to be understood
`to encompass any and all Subranges Subsumed therein. For
`example, a stated range of “1.0 to 10.0’ should be considered
`to include any and all Subranges beginning with a minimum
`value of 1.0 or more and ending with a maximum value of
`10.0 or less, e.g., 1.0 to 5.3, or 4.7 to 10.0, or 3.6 to 7.9.
`45
`All ranges disclosed herein are also to be considered to
`include the end points of the range, unless expressly stated
`otherwise. For example, a range of “between 5 and 10 should
`generally be considered to include the end points 5 and 10.
`Further, when the phrase “up to is used in connection with
`an amount or quantity, it is to be understood that the amount
`is at least a detectable amount or quantity. For example, a
`material present in an amount “up to a specified amount can
`be present from a detectable amount and up to and including
`the specified amount.
`Three Dimensional Printing
`Referring to FIG. 1, in accordance with a printing method
`using the materials system of the present invention, a layer or
`film of a particulate material 20, i.e., an essentially dry, and
`free-flowing powder, is applied on a linearly movable Surface
`22 of a container 24. The layer or film of particulate material
`20 may be formed in any Suitable manner, for example using
`a counter-roller. The particulate material 20 applied to the
`surface 22 includes an insoluble filler material, a soluble filler
`material, and a transition metal catalyst. The particulate mate
`rial 20 may also include a pigment and/or a processing aid
`material.
`
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`EX. 1028
`APPLE INC. / Page 26 of 39
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`

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`US 9,353,284 B2
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`allowing features such as overhangs, undercuts, and cavities
`to be defined and formed without the need to use supplemen
`tal Support structures. After formation of the first cross-sec
`tional portion of the intermediate article 38, the movable
`Surface 22 is indexed downwardly, in an embodiment, and the
`process is repeated.
`Using, for example, a counter-rolling mechanism, a second
`film or layer of the particulate mixture is then applied over the
`first layer, covering both the rigid first cross-sectional portion,
`and any proximate loose particulate mixture. A second appli
`cation of fluid binder follows in the manner described above,
`dissolving the soluble filler and forming adhesive bonds
`between at least a portion of the previous cross-sectional
`formed portion, the insoluble filler particulate material, and,
`optionally, pigment of the second layer, and hardening to
`form a second rigid cross-sectional portion added to the first
`rigid cross-sectional portion of the final article. The movable
`Surface 22 is again indexed downward.
`The previous steps of applying a layer of particulate mix
`ture, including the soluble filler, applying the fluid binder, and
`indexing the movable surface 22 downward are repeated until
`the intermediate article 38 is completed. Referring to FIG. 3,
`the intermediate article 38 may be any shape. Such as cylin
`drical. At the end of the process, only a top surface 34 of the
`intermediate article 38 is visible in the container 24. The
`intermediate article 38 is typically completely immersed in a
`surrounding bed 36 of dry and loose particulate material.
`Alternatively, an article could be formed in layers upward
`from an immovable platform, by Successively depositing,
`Smoothing, and printing a series of Such layers.
`Referring to FIG. 4, the dry and loose particulate material
`may be removed from the intermediate article 38 by pressur
`ized airflow or a vacuum. After removal of the dry and loose
`particulate material from the intermediate article 38, a post
`processing treatment may be performed, such as heating in an
`oven, painting, etc. to define a final article 40, having the same
`shape as intermediate article 38, but with additional desired
`characteristics, such as a smooth Surface appearance, neutral
`chroma, high lightness, toughness, strength, and/or flexibil
`ity.
`Particulate Material
`One preferred embodiment of a particulate material suit
`able for 3D printing, such as a Substantially dry particulate
`material, includes or consists essentially of the following,
`wherein the listed weight percents are based on the total
`weight of the particulate material:
`
`insoluble filler
`soluble filler
`pigment
`transition metal catalyst
`processing aids
`
`SO-90