WO2020089746A1

WO2020089746A1 - Method of additively manufacturing an article and articles made thereby

Info

Publication number: WO2020089746A1
Application number: PCT/IB2019/059132
Authority: WO
Inventors: Brian Gray Price; Viswanathan Kalyanaraman; Cameron RoyAl YOUNGSTROM
Original assignee: Sabic Global Technologies B.V.
Priority date: 2018-10-30
Filing date: 2019-10-24
Publication date: 2020-05-07

Abstract

A method of making an article by additive manufacturing includes forming a first layer of a thermoplastic composition having a plurality of thermoplastic polymer particles in the presence of a first gas, wherein the first gas is introduced prior to forming the first layer, and wherein the first gas has a permeability in the thermoplastic polymer composition that is at least two times the permeability of nitrogen in the thermoplastic composition; heating at least a portion of the first layer with a directed energy source to provide a fused first layer; forming a second layer of the thermoplastic composition on the fused first layer in the presence of the first gas; heating at least a portion of the second layer with the directed energy source to provide a fused second layer; and optionally, repeating the forming and heating to provide the article. The method can be particularly useful for forming articles having reduced amounts of bubbles or voids.

Description

METHOD OF ADDITIVELY MANUFACTURING AN ARTICLE AND ARTICLES MADE

THEREBY

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to European patent application No. EP18203545.1, filed October 30, 2019, which incorporated herein by reference in its entirety.

BACKGROUND

[0001] Three-dimensional (3D) printing (also known as additive manufacturing, or “AM”) refers to any process that may be used to make a three-dimensional product. Additive processes are used in 3D printing where successive layers of material are applied to form a product or part. These parts can be almost any shape or geometry and are produced from a 3D model on a computer or other electronic device.

[0002] A variety of additive manufacturing processes are currently available. The main differences between processes are in the way layers are deposited to create parts and in the materials that are used. Some methods melt or soften material to produce the layers, while others cure liquid materials using different technologies, or cut thin layers to shape and join them together. Selective laser melting (SLM), direct metal laser sintering (DMLS), selective laser sintering (SLS), fused deposition modeling (FDM), and fused filament fabrication (FFF) are types of additive manufacturing methods that melt or soften material to produce the layers.

[0003] Selective laser sintering (SLS), for example, is an additive manufacturing technique that may use a laser as the power source to sinter powdered material, such as a polymer or metal. The system aims the laser at points in space as defined by a 3D model, binding the material together to create a solid structure. SLS, as well as the other AM

techniques mentioned, have mainly been used for rapid prototyping and for low-volume production of component parts.

[0004] A drawback to additive manufacturing processes such as selective laser sintering can be excessive bubble formation, arising from trapped gases in the interstices between the particles to be sintered. For some thermoplastic materials, bubble formation has been a significant technical limitation preventing their use to the extent that is desired.

[0005] Accordingly, there remains a need in the art for an improved additive

manufacturing process (e.g., an improved selective laser sintering process) that can

advantageously reduce or eliminate the formation of bubbles in additively manufactured parts from thermoplastic materials. SUMMARY

[0006] A method of making an article by additive manufacturing comprises forming a first layer of a thermoplastic composition comprising a plurality of thermoplastic polymer particles in the presence of a first gas, wherein the first gas is introduced prior to forming the first layer, and wherein the first gas has a permeability in the thermoplastic polymer composition that is at least two times the permeability of nitrogen in the thermoplastic composition; heating at least a portion of the first layer with a directed energy source to provide a fused first layer; forming a second layer of the thermoplastic composition on the fused first layer in the presence of the first gas; heating at least a portion of the second layer with the directed energy source to provide a fused second layer; and optionally, repeating the forming and heating to provide the article, preferably wherein the article comprises at least 2, or at least 5 layers, or at least 10 layers, or at least 20 layers.

[0007] A three-dimensional article can be made by the method disclosed herein, wherein the article comprises a plurality of fused layers comprising the thermoplastic composition.

[0008] A three-dimensional article made by a laser sintering process comprises a plurality of fused layers comprising a thermoplastic composition, wherein the article is substantially free of bubbles.

[0009] The above described and other features are exemplified by the following figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following figures are exemplary embodiments wherein the like elements are numbered alike.

[0011] FIG. 1 is a cross-sectional view of an illustration of an exemplary printer used for selective laser sintering (SLS).

[0012] FIG. 2 is an optical microscope image of a polycarbonate part made by a conventional SFS process showing large isolated voids in the part.

[0013] FIG. 3 depicts a pictorial process according to an embodiment in when a moving gas bar sweeps the build area of a SFS printer immediately following the writing of a layer.

[0014] FIG. 4 is a photograph of polycarbonate parts formed by sintering powder via heat under various atmospheres, from left to right: nitrogen, air, helium, and helium followed by nitrogen.

[0015] FIG. 5 is an optical micrograph of an SFS-printed part in a helium atmosphere with no helium purge.

[0016] FIG. 6 is an optical micrograph of an SFS-printed part in a nitrogen atmosphere. [0017] FIG. 7A is an optical micrograph of an SLS-printed part in a nitrogen atmosphere after a helium purge and FIG. 7B an SLS-printed part in a helium atmosphere after a helium purge.

DETAILED DESCRIPTION

[0018] The present inventors have advantageously discovered an improved process for additively manufacturing thermoplastic articles, whereby bubble formation can be significantly reduced or eliminated. The method is particularly advantageous in a selective laser sintering (SLS) process. Selective laser sintering (SLS) involves sintering of very fine powders layer by layer from the bottom up until the product is completed. The layer by layer formation is accomplished by laser sintering a first layer onto a platform. The platform then lowers, and a fresh layer of powder is swept over the previously sintered layer, and the next layer is sintered or added on top of the previously built one.

[0019] An example of an SLS printer is shown in FIG. 1 (shown without the laser writing system for simplicity). The powder to be used in the printer is initially placed in feed reservoirs 1 and 4. As each new layer is to be deposited into the build area 3, the piston 6 for the build area is lowered by the desired layer thickness. The piston for the feed reservoir that donates the powder is raised by the amount required to provide sufficient powder to the build area, accounting for density differences between the feed reservoir and the build area. The feed roller 5 moves across the feed reservoir (the roller can rotate in either direction, depending on the implementation) where it picks up the powder that has been raised above the plane defined by the lowest line of the roller and its direction of motion. This powder is deposited into the build area, where the powder level has been lowered by the build area piston to receive the additional powder. Once the roller has cleared the build area, the build area is ready for the laser (not shown in FIG. 1) to write the next layer of the part (or parts) being built. Subsequent layers can be added in the same way. In a dual reservoir system as depicted in FIG. 1, the powder for the next layer is obtained from the opposite reservoir and transferred to the build area in the opposite direction. Not shown in FIG. 1 is a containment system that is generally present proximate the printer. This containment system can be swept with an inert gas such as nitrogen to improve the safety of the process.

[0020] During the sintering process, gases present in the interstices between the particles of the powder can become trapped in the molten thermoplastic material, creating voids or bubbles that persist in the final part. FIG. 2 shows an optical microscope image of a

polycarbonate part made by SLS in which many voids are clearly visible. The scale bar in FIG.

2 is 100 micrometers. [0021] The method according to the present disclosure includes forming a first layer of a thermoplastic composition comprising a plurality of thermoplastic polymer particles in the presence of a first gas, wherein the first gas has a permeability in the thermoplastic polymer composition that is at least two times the permeability of nitrogen in the thermoplastic composition; heating at least a portion of the first layer with a directed energy source to provide a fused first layer; forming a second layer of the thermoplastic composition on the fused first layer in the presence of the first gas; heating at least a portion of the second layer with the directed energy source to provide a fused second layer; and optionally, repeating the forming and heating to provide the article. Preferably, the article comprises at least 2 layers, or at least 5 layers, or at least 10 layers, or at least 20 layers, each layer comprising a fused layer of the thermoplastic composition.

[0022] Forming the first layer can comprise depositing the thermoplastic material on a target surface. The target surface can be a surface such as the build area shown in FIG. 1 and as described above. Forming the first layer is in the presence of the first gas. The first gas is introduced prior to forming the first layer of the thermoplastic composition (i.e., the system can be purged with the first gas prior to forming the first layer of the thermoplastic composition). Purging the system with the first gas can comprise purging the entire build chamber of the system, or by a directed purging towards one or more predetermined points within the build chamber. The purging prior to forming the first layer can be for a length of time effective to provide an atmosphere suitable for forming the first layer (i.e., to provide an atmosphere which consists essentially of the first gas). For example, the purging can be conducted for 10 to 15 minutes prior to forming the first layer in the build area.

[0023] The first gas has a high permeability in the thermoplastic composition. For simplicity, the permeability of a gas can be expressed in terms of the permeability relative to nitrogen gas (N₂), notated as P_rei (i.e., wherein N₂ has a relative permeability of 1.0). For example, the first gas can have a permeability in the thermoplastic composition relative to that of N₂ of at least 2.0, or at least 4.5, or at least 20, or at least 30. It will be understood that the actual permeability value of the first gas will depend on the identity of the first gas and the

thermoplastic composition, and such values can be determined by one of skill in the art. In some embodiments, gases suitable for use as the first gas include, but are not limited to, helium (P_rei 33.0), hydrogen (P_rei40.0), or a combination thereof. In some embodiments, the first gas contains no more than 5 volume percent of an impurity (i.e., no more than 5 volume percent of a gas having a permeability in the thermoplastic composition relative to that of N₂ of less than 2.0, or less than 1.8, preferably no more than 5 volume percent of a gas having a permeability in the thermoplastic composition less than that of the first gas). Thus, the first gas can have a purity of 95 volume percent or greater, or 98 volume percent or greater, or 99 volume percent or greater, or 99.9 volume percent or greater. For example, the first gas can have a purity of 95 volume percent, or 98 volume percent, or 99 volume percent, or 99.9 volume percent. In an aspect, the first gas is hydrogen or helium or a combination thereof, having a purity of 95 volume percent or greater, or 98 volume percent or greater, or 99 volume percent or greater, or 99.9 volume percent or greater. For example, the hydrogen or helium or a combination thereof can have a purity of 95 volume percent, or 98 volume percent, or 99 volume percent, or 99.9 volume percent.

[0024] After forming the first layer of the thermoplastic composition, at least a portion of the first layer can be heated to provide a fused first layer. The heating is done with a directed energy source. The energy source can be of sufficient power to heat a layer of the thermoplastic composition on the target area to create a fused layer. In some embodiments, the directed energy source can be laser beam. In some embodiments, sintering of the composition can be accomplished by application of electromagnetic radiation other than that produced by a laser. Other suitable sources of electromagnetic radiation can include, for example, infrared radiation sources, microwave generators, radiative heaters, lamps, or a combination thereof.

[0025] The heating of the first layer (and any subsequent layers) can be to a temperature that is effective to allow the thermoplastic polymer composition to flow to provide the corresponding fused layer. For example, the thermoplastic composition can be heated just enough to sinter the particles of the composition together, where the sintering temperature is less than the melting temperature (e.g., for a (semi)crystalline thermoplastic polymer). In some embodiments, the thermoplastic composition can be heated above a melting temperature of the thermoplastic composition to melt the particles. In some embodiments, the thermoplastic composition can be heated to a temperature between the glass transition temperature of the thermoplastic composition and the melting temperature of the thermoplastic composition. In some embodiments, when the thermoplastic composition comprises an amorphous thermoplastic polymer, the thermoplastic composition can be heated to a temperature greater than the glass transition temperature of the polymer. In other embodiments, when the thermoplastic composition comprises a crystalline thermoplastic polymer, the thermoplastic composition can be heated to a temperature greater than the melting temperature of the polymer. Thus, the temperature can be selected based on the identity of the thermoplastic composition, such that the heating temperature is greater than or equal to the glass transition temperature of the

thermoplastic polymer particles, or greater than or equal to the melting temperature of the thermoplastic polymer particles, or at least l0°C less than the decomposition temperature of the thermoplastic polymer particles. For example, the heating can be to a temperature of at least 200°C, or at least 250°C, or at least 275°C, or at least 300°C. In some embodiments, the heating can be to a temperature of less than 500°C.

[0026] After fusing the first layer, a second layer can be formed on the first fused layer and heated to form a second fused layer. The forming of the second layer (and any subsequent layers) is done in the presence of the first gas. The fused second layer is fused to the heated portion of the fused first layer. The process can be repeated until the desired number of layers is reached.

[0027] The thermoplastic polymer composition for use in the present method comprises a plurality of thermoplastic polymer particles. The thermoplastic polymer particles can have an average particle diameter (by volume) of 10 nanometer to 1 millimeter, preferably 1 micrometer to 1 millimeter, more preferably 50 to 600 micrometers, even more preferably 100 to 500 micrometers, even more preferably still 200 to 400 micrometers. Particle size can be determined, for example, using laser light scattering techniques such as static light scattering. In some embodiments, the polymer particles can be spherical polymer particles.

[0028] The thermoplastic particles comprise a thermoplastic polymer. As used herein, the term "thermoplastic" refers to a material that is plastic or deformable, can transform to a liquid when heated, and freezes to a brittle, glassy state when cooled sufficiently.

Thermoplastics are typically high molecular weight polymers. The thermoplastic polymer can be crystalline, semi-crystalline, or amorphous. The terms“amorphous” and“crystalline” as used herein have their usual meanings in the polymer art. For example, in an amorphous polymer the molecules can be oriented randomly and can be intertwined, and the polymer can have a glasslike, transparent appearance. In crystalline polymers, the polymer molecules can be aligned in ordered regions. In the polymer art, some types of crystalline polymers are sometimes referred to as semi-crystalline polymers. The term“crystalline” as used herein refers to both crystalline and semi-crystalline polymers. In some embodiments, a crystalline thermoplastic polymer can have a percent crystallinity of at least 20%, for example 20 to 80%, preferably, at least 25%, for example 25 to 60%, or 25 to 30%, more preferably at least 27%, for example 27 to 40%. The term“percent crystallinity” or“% crystallinity” as used herein, refers to the portion of the polymer that has a crystalline form. The percentage is based upon the total weight of the crystalline polymer. In some embodiments, the thermoplastic polymer is amorphous. In some embodiments, an amorphous thermoplastic polymer has less than 20% crystallinity, or less than 15% crystallinity, or less than 10% crystallinity, or less than 1% crystallinity, or 0%

crystallinity. In some embodiments, the thermoplastic polymer can be an amorphous polymer that does not exhibit a melting point. [0029] Examples of thermoplastic polymers that can be used include polyacetals (e.g., polyoxyethylene and polyoxymethylene), poly(Ci-₆ alkyl)acrylates, polyacrylamides, polyamides (e.g., aliphatic polyamides, polyphthalamides, and polyaramides), polyamideimides, polyanhydrides, polyarylates, polyarylene ethers (e.g., polyphenylene ethers), polyarylene sulfides (e.g., polyphenylene sulfides), polyarylsulfones (e.g., polyphenylsulfones),

polybenzothiazoles, polybenzoxazoles, polycarbonates (including polycarbonate copolymers such as polycarbonate-siloxanes, polycarbonate-esters, and polycarbonate-ester-siloxanes), polyesters (e.g., polyethylene terephthalates, polybutylene terephthalates, polyarylates, and polyester copolymers such as polyester-ethers), polyetherimides (including copolymers such as polyetherimide-siloxane copolymers), a polyarylether ketone (which is inclusive of

polyetheretherketones, polyetherketoneketones, and polyetherketones), polyethersulfones, polyimides (including copolymers such as polyimide-siloxane copolymers), poly(Ci-₆ alkyl)methacrylates, polymethacrylamides, polynorbomenes (including copolymers containing norbornenyl units), polyolefins (e.g., polyethylene s, polypropylenes, polytetrafluoroethylenes, and their copolymers, for example ethylene-alpha-olefin copolymers), polyoxadiazoles, polyoxymethylenes, polyphthalides, polysilazanes, polysiloxanes, polystyrenes (including copolymers such as acrylonitrile-butadiene-styrene (ABS) and methyl methacrylate-butadiene- styrene (MBS)), polysulfides, poly sulfonamides, polysulfonates, polysulfones, polythioesters, polytriazines, polyureas, polyurethanes, polyvinyl alcohols, polyvinyl esters, polyvinyl ethers, polyvinyl halides, polyvinyl ketones, polyvinyl thioethers, polyvinylidene fluorides, or the like, or a combination thereof. In an embodiment, the thermoplastic polymer particles can comprise polycarbonate, polyetherimide, polyarylether ketone, nylon, acrylonitrile-butadiene-styrene, polyphenylsulfone, or a combination thereof. Polycarbonates, polyetherimides, and

combinations thereof can be especially useful.

[0030] In some embodiments, the thermoplastic polymer particles comprise a polycarbonate. “Polycarbonate” as used herein means a homopolymer or copolymer having repeating structural carbonate units of formula (1)

wherein at least 60 percent of the total number of R¹ groups are aromatic, or each R¹ contains at least one C₆-30 aromatic group. Specifically, each R¹ can be derived from a dihydroxy compound such as an aromatic dihydroxy compound of formula (2) or a bisphenol of formula

(3).

In formula (2), each R^h is independently a halogen atom, for example bromine, a Ci-io hydrocarbyl group such as a C_HO alkyl, a halogen-substituted Ci-io alkyl, a C_6-io aryl, or a halogen-substituted C_6-io aryl, and n is 0 to 4.

[0031] In formula (3), R^a and R^b are each independently a halogen, C1-12 alkoxy, or C1-12 alkyl, and p and q are each independently integers of 0 to 4, such that when p or q is less than 4, the valence of each carbon of the ring is filled by hydrogen. In an embodiment, p and q is each 0, or p and q is each 1, and R^a and R^b are each a C1-3 alkyl group, specifically methyl, disposed meta to the hydroxy group on each arylene group. X^a is a bridging group connecting the two hydroxy-substituted aromatic groups, where the bridging group and the hydroxy substituent of each C₆ arylene group are disposed ortho, meta, or para (specifically para) to each other on the C₆ arylene group, for example, a single bond, -0-, -S-, -S(O)-, -S(0)₂-, -C(O)-, or a Ci-is organic group, which can be cyclic or acyclic, aromatic or non-aromatic, and can further comprise heteroatoms such as halogens, oxygen, nitrogen, sulfur, silicon, or phosphorous. For example, X^a can be a substituted or unsubstituted C3-18 cycloalkylidene; a C1-25 alkylidene of the formula - C(R^c)(R^d) - wherein R^c and R^d are each independently hydrogen, C1-12 alkyl, C1-12 cycloalkyl, C7-12 arylalkyl, C1-12 heteroalkyl, or cyclic C7-12 heteroarylalkyl; or a group of the formula - C(=R^e)- wherein R^e is a divalent C1-12 hydrocarbon group.

[0032] Examples of bisphenol compounds include 4,4'-dihydroxybiphenyl, 1,6- dihydroxynaphthalene, 2,6-dihydroxynaphthalene, bis(4-hydroxyphenyl)methane, bis(4- hydroxyphenyl)diphenylmethane, bis(4-hydroxyphenyl)-l-naphthylmethane, l,2-bis(4- hydroxyphenyl)ethane, l,l-bis(4-hydroxyphenyl)-l-phenylethane, 2-(4-hydroxyphenyl)-2-(3- hydroxyphenyl)propane, bis(4-hydroxyphenyl)phenylmethane, 2,2-bis(4-hydroxy-3- bromophenyl)propane, 1,1 -bis (hydroxyphenyl)cyclopentane, l,l-bis(4- hydroxyphenyl)cyclohexane, 1 , 1 -bis(4-hydroxyphenyl)isobutene, 1 , 1 -bis(4- hydroxyphenyl)cyclododecane, trans-2,3-bis(4-hydroxyphenyl)-2-butene, 2,2-bis(4- hydroxyphenyl)adamantane, alpha, alpha'-bis(4-hydroxyphenyl)toluene, bis(4- hydroxyphenyl)acetonitrile, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(3-ethyl-4- hydroxyphenyl)propane, 2,2-bis(3-n-propyl-4-hydroxyphenyl)propane, 2,2-bis(3-isopropyl-4- hydroxyphenyl)propane, 2,2-bis(3-sec-butyl-4-hydroxyphenyl)propane, 2,2-bis(3-t-butyl-4- hydroxyphenyl)propane, 2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane, 2,2-bis(3-allyl-4- hydroxyphenyl)propane, 2,2-bis(3-methoxy-4-hydroxyphenyl)propane, 2,2-bis(4- hydroxyphenyl)hexafluoropropane, l,l-dichloro-2,2-bis(4-hydroxyphenyl)ethylene, 1,1- dibromo-2,2-bis(4-hydroxyphenyl)ethylene, l,l-dichloro-2,2-bis(5-phenoxy-4- hydroxyphenyl)ethylene, 4,4'-dihydroxybenzophenone, 3,3-bis(4-hydroxyphenyl)-2-butanone,

1.6-bis(4-hydroxyphenyl)-l,6-hexanedione, ethylene glycol bis(4-hydroxyphenyl)ether, bis(4- hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl) sulfoxide, bis(4- hydroxyphenyl)sulfone, 9,9-bis(4-hydroxyphenyl)fluorene, 2,7-dihydroxypyrene, 6,6'- dihydroxy-3,3,3',3'- tetramethylspiro(bis)indane ("spirobiindane bisphenol"), 3,3-bis(4- hydroxyphenyl)phthalimide, 2,6-dihydroxydibenzo-p-dioxin, 2,6-dihydroxythianthrene, 2,7- dihydroxyphenoxathin, 2,7-dihydroxy-9, lO-dimethylphenazine, 3,6-dihydroxydibenzofuran,

3.6-dihydroxydibenzothiophene, and 2,7-dihydroxycarbazole; resorcinol, substituted resorcinol compounds such as 5-methyl resorcinol, 5-ethyl resorcinol, 5-propyl resorcinol, 5-butyl resorcinol, 5-t-butyl resorcinol, 5-phenyl resorcinol, 5-cumyl resorcinol, 2,4,5,6-tetrafluoro resorcinol, 2,4,5,6-tetrabromo resorcinol, or the like; catechol; hydroquinone; substituted hydroquinones such as 2-methyl hydroquinone, 2-ethyl hydroquinone, 2-propyl hydroquinone, 2-butyl hydroquinone, 2-t-butyl hydroquinone, 2-phenyl hydroquinone, 2-cumyl hydroquinone,

2.3.5.6-tetramethyl hydroquinone, 2,3,5,6-tetra-t-butyl hydroquinone, 2,3,5,6-tetrafluoro hydroquinone, 2,3,5,6-tetrabromo hydroquinone, or the like.

[0033] Specific dihydroxy compounds include resorcinol, 2,2-bis(4-hydroxyphenyl) propane (“bisphenol A” or“BPA”), 3,3-bis(4-hydroxyphenyl) phthalimidine, 2-phenyl-3,3’- bis(4-hydroxyphenyl) phthalimidine (also known as N-phenyl phenolphthalein bisphenol, “PPPBP”, or 3,3-bis(4-hydroxyphenyl)-2-phenylisoindolin-l-one), l,l-bis(4-hydroxy-3- methylphenyl)cyclohexane, and l,l-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane

(isophorone bisphenol).

[0034] In some embodiments, the thermoplastic composition comprises polyetherimide. Polyetherimides comprise more than 1, for example 2 to 1000, or 5 to 500, or 10 to 100 structural units of formula (4)

wherein each R is independently the same or different, and is a substituted or unsubstituted divalent organic group, such as a substituted or unsubstituted C₆-20 aromatic hydrocarbon group, a substituted or unsubstituted straight or branched chain C4-20 alkylene group, a substituted or unsubstituted C3-8 cycloalkylene group, in particular a halogenated derivative of any of the foregoing. In some embodiments R is divalent group of one or more of the following formulas

(5)

wherein Q¹ is -0-, -S-, -C(O)-, -S0₂-, -SO-, -P(R^a)(=0)- wherein R^a is a Ci-s alkyl or C_6-i2 aryl, -

C_yH_2y- wherein y is an integer from 1 to 5 or a halogenated derivative thereof (which includes perfluoroalkylene groups), or -(C₆H_IO)_z- wherein z is an integer from 1 to 4. In some

embodiments R is m-phenylene, p-phenylene, or a diarylene sulfone, in particular bis(4,4’- phenylene)sulfone, bis(3, 4’-phenylene) sulfone, bis(3,3’-phenylene)sulfone, or a combination comprising at least one of the foregoing. In some embodiments, at least 10 mole percent or at least 50 mole percent of the R groups contain sulfone groups, and in other embodiments no R groups contain sulfone groups.

[0035] Further in formula (4), T is -O- or a group of the formula -O-Z-O- wherein the divalent bonds of the -O- or the -O-Z-O- group are in the 3,3', 3,4', 4,3', or the 4,4' positions, and Z is an aromatic C₆-24 monocyclic or polycyclic moiety optionally substituted with 1 to 6 Ci-s alkyl groups, 1 to 8 halogen atoms, or a combination comprising at least one of the foregoing, provided that the valence of Z is not exceeded. Exemplary groups Z include groups of formula (6)

wherein R^a and R^b are each independently the same or different, and are a halogen atom or a monovalent C1-6 alkyl group, for example; p and q are each independently integers of 0 to 4; c is 0 to 4; and X^a is a bridging group connecting the hydroxy-substituted aromatic groups, where the bridging group and the hydroxy substituent of each C₆ arylene group are disposed ortho, meta, or para (specifically para) to each other on the C₆ arylene group. The bridging group X^a can be a single bond, -O-, -S-, -S(O)-, -S(0)₂-, -C(O)-, or a C_MS organic bridging group. The Ci-i₈ organic bridging group can be cyclic or acyclic, aromatic or non-aromatic, and can further comprise heteroatoms such as halogens, oxygen, nitrogen, sulfur, silicon, or phosphorous. The Cms organic group can be disposed such that the C₆ arylene groups connected thereto are each connected to a common alkylidene carbon or to different carbons of the Ci-is organic bridging group. A specific example of a group Z is a divalent group of formula (6a)

wherein Q is -0-, -S-, -C(O)-, -SO2-, -SO-, -P(R^a)(=0)- wherein R^a is a Ci-s alkyl or C_6-i2 aryl, or -C_yH2_y- wherein y is an integer from 1 to 5 or a halogenated derivative thereof (including a perfluoroalkylene group). In a specific embodiment Z is a derived from bisphenol A, such that Q in formula (6a) is 2,2-isopropylidene.

[0036] In an embodiment in formula (4), R is m-phenylene, p-phenylene, or a combination comprising at least one of the foregoing, and T is -O-Z-O- wherein Z is a divalent group of formula (6a). Alternatively, R is m-phenylene, p-phenylene, or a combination comprising at least one of the foregoing, and T is -O-Z-O wherein Z is a divalent group of formula (6a) and Q is 2,2-isopropylidene. Such materials are available under the trade name ULTEM from SABIC. Alternatively, the polyetherimide can be a copolymer comprising additional structural polyetherimide units of formula (4) wherein at least 50 mole percent (mol%) of the R groups are bis(4,4’-phenylene)sulfone, bis(3,4’-phenylene)sulfone, bis(3,3’- phenylene)sulfone, or a combination comprising at least one of the foregoing and the remaining R groups are p-phenylene, m-phenylene or a combination comprising at least one of the foregoing; and Z is 2,2-(4-phenylene)isopropylidene, i.e., a bisphenol A moiety, an example of which is commercially available under the trade name EXTEM from SABIC.

[0037] In some embodiments, the polyetherimide can be a copolymer that optionally comprises additional structural imide units that are not polyetherimide units, for example imide units of formula (7)

wherein R is as described in formula (4) and each V is the same or different, and is a substituted or unsubstituted C6-20 aromatic hydrocarbon group, for example a tetravalent linker of the formulas

wherein W is a single bond, -0-, -S-, -C(O)-, -S0₂-, -SO-, a C ms hydrocarbylene group, - P(R^a)(=0)- wherein R^a is a Ci-s alkyl or C_6-i2 aryl, or -C_yH_2y- wherein y is an integer from 1 to 5 or a halogenated derivative thereof (which includes perfluoroalkylene groups). These additional structural imide units preferably comprise less than 20 mol% of the total number of units, and more preferably can be present in amounts of 0 to 10 mol% of the total number of units, or 0 to 5 mol% of the total number of units, or 0 to 2 mol% of the total number of units. In some embodiments, no additional imide units are present in the polyetherimide.

[0038] The polyetherimide can be prepared by any of the methods known to those skilled in the art, including the reaction of an aromatic bis(ether anhydride) of formula (8) or a chemical equivalent thereof, with an organic diamine of formula (9)

(8) H₂N-R-NH₂ (9)

wherein T and R are defined as described above. Copolymers of the polyetherimides can be manufactured using a combination of an aromatic bis(ether anhydride) of formula (8) and an additional bis(anhydride) that is not a bis(ether anhydride), for example pyromellitic dianhydride or bis(3,4-dicarboxyphenyl) sulfone dianhydride.

[0039] Illustrative examples of aromatic bis(ether anhydride)s include 2,2-bis[4-(3,4- dicarboxyphenoxy)phenyl]propane dianhydride (also known as bisphenol A dianhydride or BPADA), 3,3-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride; 4,4'-bis(3,4- dicarboxyphenoxy)diphenyl ether dianhydride; 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride; 4,4'-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride; 4,4'-bis(3,4- dicarboxyphenoxy)diphenyl sulfone dianhydride; 4,4'-bis(2,3-dicarboxyphenoxy)diphenyl ether dianhydride; 4,4'-bis(2,3-dicarboxyphenoxy)diphenyl sulfide dianhydride; 4,4'-bis(2,3- dicarboxyphenoxy)benzophenone dianhydride; 4,4'-bis(2,3-dicarboxyphenoxy)diphenyl sulfone dianhydride; 4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl-2, 2-propane dianhydride; 4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl ether dianhydride; 4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride; 4-(2,3- dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)benzophenone dianhydride; 4,4’- (hexafluoroisopropylidene)diphthalic anhydride; and 4-(2,3-dicarboxyphenoxy)-4'-(3,4- dicarboxyphenoxy)diphenyl sulfone dianhydride. A combination of different aromatic bis(ether anhydride)s can be used. [0040] Examples of organic diamines include 1, 4-butane diamine, l,5-pentanediamine, l,6-hexanediamine, l,7-heptanediamine, l,8-octanediamine, l,9-nonanediamine, 1,10- decanediamine, l,l2-dodecanediamine, l,l8-octadecanediamine, 3- methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine, 4- methylnonamethylenediamine, 5-methylnonamethylenediamine, 2,5- dimethylhexamethylenediamine, 2,5-dimethylheptamethylenediamine, 2, 2- dimethylpropylenediamine, N-methyl-bis (3-aminopropyl) amine, 3- methoxyhexamethylenediamine, l,2-bis(3-aminopropoxy) ethane, bis (3-aminopropyl) sulfide, l,4-cyclohexanediamine, bis-(4-aminocyclohexyl) methane, m-phenylenediamine, p- phenylenediamine, 2,4-diaminotoluene, 2,6-diaminotoluene, m-xylylenediamine, p- xylylenediamine, 2-methyl-4, 6-diethyl- l,3-phenylene-diamine, 5-methyl-4, 6-diethyl- 1,3- phenylene-diamine, benzidine, 3,3’-dimethylbenzidine, 3,3’-dimethoxybenzidine, 1,5- diaminonaphthalene, bis(4-aminophenyl) methane, bis(2-chloro-4-amino-3,5-diethylphenyl) methane, bis(4-aminophenyl) propane, 2,4-bis(p-amino-t-butyl) toluene, bis(p-amino-t- butylphenyl) ether, bis(p-methyl-o-aminophenyl) benzene, bis(p-methyl-o-aminopentyl) benzene, 1, 3-diamino-4-isopropylbenzene, bis(4-aminophenyl) sulfide, bis-(4-aminophenyl) sulfone (also known as 4,4'-diaminodiphenyl sulfone (DDS)), and bis(4-aminophenyl) ether.

Any regioisomer of the foregoing compounds can be used. C_M alkylated or poly(Ci-₄) alkylated derivatives of any of the foregoing can be used, for example a polymethylated 1,6- hexanediamine. Combinations of these compounds can also be used. In some embodiments the organic diamine is m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, or a combination comprising at least one of the foregoing.

[0041] The polyetherimide can have a melt index of 0.1 to 10 grams per minute (g/min), as measured by American Society for Testing Materials (ASTM) D1238 at 340 to 370°C, using a 6.7 kilogram (kg) weight. In some embodiments, the polyetherimide has a weight average molecular weight (Mw) of 1,000 to 150,000 grams/mole (Dalton), as measured by gel permeation chromatography, using polystyrene standards. In some embodiments the polyetherimide has an Mw of 10,000 to 80,000 Daltons. Such polyetherimides typically have an intrinsic viscosity greater than 0.2 deciliters per gram (dl/g), or, more specifically, 0.35 to 0.7 dl/g as measured in m-cresol at 25 °C.

[0042] In addition to the thermoplastic polymer, the thermoplastic polymer particles can optionally further comprise an additive. An additive composition can be used, comprising one or more additives selected to achieve a desired property, with the proviso that the additive(s) are also selected so as to not significantly adversely affect a desired property of the thermoplastic composition. The additive composition or individual additives can be mixed at a suitable time during the mixing of the components for forming the composition. The additive composition can include an impact modifier, flow modifier, filler (e.g., a particulate polytetrafluoroethylene (PTFE), glass, carbon, mineral, or metal), reinforcing agent (e.g., glass fibers), antioxidant, heat stabilizer, light stabilizer, ultraviolet (UV) light stabilizer, UV absorbing additive, plasticizer, lubricant, release agent (such as a mold release agent), antistatic agent, anti-fog agent, antimicrobial agent, colorant (e.g, a dye or pigment), surface effect additive, radiation stabilizer, flame retardant, anti-drip agent (e.g., a PTFE-encapsulated styrene- acrylonitrile copolymer (TSAN)), or a combination comprising one or more of the foregoing. In general, the additives are used in the amounts generally known to be effective. For example, the total amount of the additive composition (other than any impact modifier, filler, or reinforcing agent) can be 0.001 to 10.0 wt%, or 0.01 to 5 wt%, each based on the total weight of the polymer in the composition. In some embodiments, the thermoplastic polymer particles preferably comprise a flow agent, a mold release agent, or a combination thereof.

[0043] When present, the flow agent can be a particulate inorganic material having a median particle size of 10 micrometers or less. The flow agent can include, for example, a hydrated silica, amorphous alumina, a glassy silica, a glassy phosphate, a glassy borate, a glassy oxide, titania, talc, mica, a fumed silica, kaolin, attapulgite, calcium silicate, alumina, magnesium silicate, and the like, or a combination thereof. The flow agent can be present in an amount sufficient to allow the thermoplastic polymer particles to flow and level on the build surface of the laser sintering apparatus. An exemplary flow agent is a fumed silica. When present, the flow agent can be included in an amount of up to 5 weight percent, for example 0.01 to 5 weight percent, or 0.05 to 1 weight percent, or 0.1 to 0.25 weight percent, based on the total weight of the composition.

[0044] In some embodiments, the method can optionally further comprise exposing the fused first layer to a second gas for a predetermined time prior to forming the second layer, wherein the second gas has a permeability in the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas, preferably less than 0.1 times the

permeability of the first gas, more preferably less than 0.05 times the permeability of the first gas. The exposure to the second gas can be repeated for each fused layer prior to forming and fusing any subsequent layers. Thus, a specific embodiment is a method of making an article by additive manufacturing, the method comprising forming a first layer of a thermoplastic composition comprising a plurality of thermoplastic polymer particles in the presence of a first gas, wherein the first gas has a permeability in the thermoplastic polymer composition that is at least two times the permeability of nitrogen in the thermoplastic composition; heating at least a portion of the first layer with a directed energy source to provide a fused first layer; exposing the fused first layer to a second gas for a predetermined time, wherein the second gas has a permeability in the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas, preferably less than 0.1 times the permeability of the first gas, more preferably less than 0.05 times the permeability of the first gas; forming a second layer of the thermoplastic composition on the fused first layer in the presence of the first gas; heating at least a portion of the second layer with the directed energy source to provide a fused second layer; and exposing the fused second layer to the second gas for a predetermined time; and optionally, repeating the forming, heating, and exposing to provide the article. The first gas and other process parameters such as temperature can be as already described above.

[0045] The second gas has a permeability in the thermoplastic composition that is less than the permeability of the first gas in the thermoplastic composition. Thus, suitable second gases can be selected depending on the identity of the thermoplastic composition and the first gas. Preferably, the second gas has a permeability of the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas, preferably less than 0.1 times the permeability of the first gas, more preferably less than 0.05 times the permeability of the first gas. For example, the second gas can have a permeability relative to nitrogen in the

thermoplastic composition of less than or equal to 1, or less than or equal to 0.75, or less than or equal to 0.5, or less than or equal to 0.25, provided that the permeability of the second gas is less than or equal to 0.25 times the permeability of the first gas. In some embodiments, gases suitable for use as the second gas include, but are not limited to, nitrogen, argon, or a

combination thereof.

[0046] In some embodiments, the second gas contains no more than 5 volume percent of an impurity (i.e., no more than 5 volume percent of a gas having a permeability that is greater than the permeability of the first gas, preferably no more than 5 volume percent of a gas having a permeability that is greater than or equal to 0.25 times the permeability of the first gas). Thus, the second gas can have a purity of 95 volume percent or greater, or 98 volume percent or greater, or 99 volume percent or greater, or 99.9 volume percent or greater. For example, the second gas can have a purity of 95 volume percent, or 98 volume percent, or 99 volume percent, or 99.9 volume percent. In an aspect the second gas is nitrogen, argon, or a combination thereof, having a purity of 95 volume percent or greater, or 98 volume percent or greater, or 99 volume percent or greater, or 99.9 volume percent or greater.

[0047] The predetermined time during which the fused layer is exposed to the second gas can be, for example, up to 500 minutes, or 15 seconds to 500 minutes, or 2 minutes to 250 minutes, or 5 minutes to 100 minutes, or 5 minutes to 60 minutes, or 5 to 30 minutes, or 10 to 20 minutes, or 15 seconds to 1 minute, or 1 to 5 minutes, or 5 to 20 minutes, or 1 second to 20 minutes, or 1 second to 5 minutes, or 1 to 60 seconds. Subsequent to this time period, the process can be repeated to form one or more additional layers.

[0048] An exemplary system used to carry out the method according to this embodiment is shown in FIG. 3, where the same SLS printer shown in FIG. 1 has been adapted to include a moving gas bar 7, which sweeps the second gas over the build area immediately following each layer writing process.

[0049] The method described herein can be used to provide additively manufactured articles (e.g., by SLS). In particular, the articles provided by the process described herein can be substantially free of bubbles.“Bubbles” as used herein can also refer to voids, microbubbles, pinholes, and other similar defects. As used herein, the articles are“substantially free” of bubbles or voids when the articles contain, on average, fewer than 1 bubble per square centimeter, determined by optical or scanning microscopy. In some embodiments, the articles do not contain any bubbles or voids that are detectable by optical microscopy. In some embodiments, the articles can be substantially free of bubbles or voids having an average diameter of less than or equal to 100 micrometers, or less than or equal to 60 micrometers, or less than or equal to 50 micrometers. Where the bubbles or voids are not spherical, the above mentioned diameter can be applied to the longest dimension of the bubble or void (i.e., the articles can be free of bubbles or voids having a longest dimension that is less than or equal to 100 micrometers). In some embodiments, fewer than one bubble per square centimeter (on average) is visually observed in the article, either by eye of by use of an optical microscope, and preferably no bubbles or voids are visually observed in the article, either by eye or by use of an optical microscope. Additionally, additively manufactured articles made by the process disclosed herein can advantageously have isotropic mechanical properties, a density equal to that of the natural material density, and a high optical clarity for unfilled, amorphous materials.

[0050] This disclosure is further illustrated by the following examples, which are non limiting.

EXAMPLES

[0051] Materials used for the following examples are summarized in Table 1.

Table 1

[0052] The PC particles were made by grinding pellets of 1300 grade PC from SABIC. The resulting PC powder was passed through a 35 US mesh sieve, providing particles having a maximum particle size of about 500 micrometers.

[0053] In the present example, a hotplate was used as the heat source and an aluminum pan was used as the mold. The PC powder was added to the pan, and then pan was placed in a closed container to control the atmosphere. The closed container was purged with air or helium for 10 minutes. Following the 10 minute purge, the entire container was placed on a hot plate preheated to 320°C for 30 minutes. After 15 minutes of heating, the container was opened to quickly switch the atmosphere to replace the helium with air for one example. The container was closed again, and the heating was continued for 15 minutes. As a comparative example, the same procedure was carried out except that the system was not purged with helium (i.e., conducted completely in the presence of nitrogen). For each example, the formed part was removed from the aluminum pan and evaluated for the presence of bubbles and other artifacts. Photographs of each part are shown in FIG. 4. In the photograph of FIG. 4, the resulting parts formed (from left to right) in nitrogen (comparative), air, helium, and helium followed by a purge with nitrogen are shown. As can be seen from FIG. 4, the PC part formed in the comparative example was filled with bubbles, and the part has contracted slightly upon cooling, resulting in a concave lower surface (shown facing upward in the photograph). The part formed under air has fewer remaining voids than the part formed under N₂. Both parts formed under helium exhibit almost no voids. Upon closer inspection, the part formed under He only has a few more voids than the part formed under He followed by N_2. The part formed with the helium purge, shown at the right, was also free of any contraction effects.

[0054] Parts were made using a selective laser sintering (SLS) process. In a first example, prior to forming the part, the system was purged with helium for 10 minutes at 1200 liters/hour with the system exhaust open. As shown in FIG. 5, when the purge was conducted with the exhaust open it was not sufficient to reduce the bubbles present in the final printed part. While slightly reduced, the bubbles present in the part shown in FIG. 5 are comparable to the bubbles present in a part formed in a nitrogen atmosphere, as shown in FIG. 6.

[0055] FIG. 7 shows the results from forming a part by SLS in the presence of nitrogen (FIG. 7A) compared to in the presence of helium (FIG. 7B, with a helium purge conducted for 10 minutes at 1200 liters per hour, with the exhaust closed, prior to forming the part, as well as in the presence of helium during forming the part). In each of FIG. 7A and 7B, the part shown on the left is the as-printed part, and the part shown on the right is after polishing. Unsintered material is removed from the exterior of the part by polishing to reveal the bulk of the sintered material. As can be seen from FIG. 7B, conducting the helium purge prior to and during forming the part resulted in a SLS-printed part with reduced defects and good clarity. In contrast, an SLS-printed part formed in the presence of a nitrogen atmosphere was opaque, even after a helium purge. These examples demonstrate the importance of the purge step with the first gas prior to forming the part. Even when sintered in the presence of the first gas, the example of FIG. 5 shows that without a sufficient purge, the resulting part can exhibit undesirable bubbles or defects.

[0056] This disclosure further encompasses the following aspects.

[0057] Aspect 1: A method of making an article by additive manufacturing, the method comprising: forming a first layer of a thermoplastic composition comprising a plurality of thermoplastic polymer particles in the presence of a first gas, wherein the first gas is introduced prior to forming the first layer, and wherein the first gas has a permeability in the thermoplastic polymer composition that is at least two times the permeability of nitrogen in the thermoplastic composition; heating at least a portion of the first layer with a directed energy source to provide a fused first layer; forming a second layer of the thermoplastic composition on the fused first layer in the presence of the first gas; heating at least a portion of the second layer with the directed energy source to provide a fused second layer; and optionally, repeating the forming and heating to provide the article, preferably wherein the article comprises at least 2 layers, or at least 5 layers, or at least 10 layers, or at least 20 layers.

[0058] Aspect 2: The method of aspect 1, wherein the method further comprises exposing the fused first layer to a second gas for a predetermined time prior to forming the second layer, wherein the second gas has a permeability in the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas, preferably less than 0.1 times the permeability of the first gas, more preferably less than 0.05 times the permeability of the first gas; and exposing the fused second layer to the second gas for a predetermined time prior to repeating and forming additional layers.

[0059] Aspect 3: A method of making an article by additive manufacturing, the method comprising: forming a first layer of a thermoplastic composition comprising a plurality of thermoplastic polymer particles in the presence of a first gas, wherein the first gas has a permeability in the thermoplastic polymer composition that is at least two times the permeability of nitrogen in the thermoplastic composition; heating at least a portion of the first layer with a directed energy source to provide a fused first layer; exposing the fused first layer to a second gas for a predetermined time, wherein the second gas has a permeability in the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas, preferably less than 0.1 times the permeability of the first gas, more preferably less than 0.05 times the permeability of the first gas; forming a second layer of the thermoplastic composition on the fused first layer in the presence of the first gas; heating at least a portion of the second layer with the directed energy source to provide a fused second layer; and exposing the fused second layer to the second gas for a predetermined time; and optionally, repeating the forming, heating, and exposing to provide the article, preferably wherein the article comprises at least 2 layers, or at least 5 layers, or at least 10 layers, or at least 20 layers.

[0060] Aspect 4: The method of any one of aspects 1 to 3, wherein forming the first layer comprises depositing the thermoplastic composition on a target surface.

[0061] Aspect 5: The method of any of aspects 1 to 4, wherein heating the layers is to a temperature effective to cause the thermoplastic polymer composition to flow to provide the corresponding fused layer.

[0062] Aspect 6: The method of any one of aspects 1 to 5, wherein the directed energy source is a laser beam.

[0063] Aspect 7: The method of any one of aspects 1 to 6, wherein the thermoplastic polymer particles comprise polycarbonate, polyetherimide, polyarylether ketone, nylon, acrylonitrile-butadiene-styrene, polyphenylsulfone, or a combination thereof, preferably polycarbonate.

[0064] Aspect 8: The method of any one of aspects 1 to 7, wherein heating is at a temperature that is greater than or equal to the glass transition temperature of the thermoplastic polymer particles, or greater than or equal to the melting temperature of the thermoplastic polymer particles, or at least l0°C less than the decomposition temperature of the thermoplastic polymer particles.

[0065] Aspect 9: The method of any one of aspects 2 to 8, wherein the predetermined time up to 500 minutes, or 15 seconds to 500 minutes, or 2 minutes to 250 minutes, or 5 minutes to 100 minutes, or 5 minutes to 60 minutes, or 5 to 30 minutes, or 10 to 20 minutes, or 15 seconds to 1 minute, or 1 to 5 minutes, or 5 to 20 minutes, or 1 second to 20 minutes, or 1 second to 5 minutes, or 1 to 60 seconds.

[0066] Aspect 10: The method of any one of aspects 1 to 9, wherein the first gas comprises helium, hydrogen, or a combination thereof.

[0067] Aspect 11: The method of any one of aspects 2 to 10, wherein second gas comprises nitrogen, argon, or a combination thereof.

[0068] Aspect 12: The method of any one of aspects 1 to 11, wherein the thermoplastic composition further comprises an additive.

[0069] Aspect 13: The method of aspect 12, wherein the additive comprises a flow agent, a mold release agent, or a combination thereof. [0070] Aspect 14: A three-dimensional article made by the method of any one of aspects 1 to 13, wherein the article comprises a plurality of fused layers comprising the thermoplastic composition.

[0071] Aspect 15: The article of aspect 14, wherein the article is substantially free of bubbles.

[0072] Aspect 16: A three-dimensional article made by a laser sintering process, wherein the article comprises a plurality of fused layers comprising a thermoplastic composition, and wherein the article is substantially free of bubbles.

[0073] The compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any appropriate materials, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any materials (or species), steps, or components, that are otherwise not necessary to the achievement of the function or objectives of the compositions, methods, and articles.

[0074] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. “Combinations” is inclusive of blends, mixtures, alloys, reaction products, and the like. The terms“first,”“second,” and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms“a” and“an” and“the” do not denote a limitation of quantity and are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly

contradicted by context. “Or” means“and/or” unless clearly stated otherwise. Reference throughout the specification to“some embodiments,”“an embodiment,” and so forth, means that a particular element described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. The term “combination thereof’ as used herein includes one or more of the listed elements, and is open, allowing the presence of one or more like elements not named. In addition, it is to be

understood that the described elements may be combined in any suitable manner in the various embodiments.

[0075] Unless specified to the contrary herein, all test standards are the most recent standard in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears.

[0076] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this application belongs. All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0077] Compounds are described using standard nomenclature. For example, any position not substituted by any indicated group is understood to have its valency filled by a bond as indicated, or a hydrogen atom. A dash

that is not between two letters or symbols is used to indicate a point of attachment for a substituent. For example, -CHO is attached through carbon of the carbonyl group.

[0078] As used herein, the term“hydrocarbyl,” whether used by itself, or as a prefix, suffix, or fragment of another term, refers to a residue that contains only carbon and hydrogen. The residue can be aliphatic or aromatic, straight-chain, cyclic, bicyclic, branched, saturated, or unsaturated. It can also contain combinations of aliphatic, aromatic, straight chain, cyclic, bicyclic, branched, saturated, and unsaturated hydrocarbon moieties. However, when the hydrocarbyl residue is described as substituted, it may, optionally, contain heteroatoms over and above the carbon and hydrogen members of the substituent residue. Thus, when specifically described as substituted, the hydrocarbyl residue can also contain one or more carbonyl groups, amino groups, hydroxyl groups, or the like, or it can contain heteroatoms within the backbone of the hydrocarbyl residue. The term "alkyl" means a branched or straight chain, unsaturated aliphatic hydrocarbon group, e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, t-butyl, n- pentyl, s-pentyl, and n- and s-hexyl. “Alkenyl” means a straight or branched chain, monovalent hydrocarbon group having at least one carbon-carbon double bond (e.g., ethenyl (-HC=CH₂)). “Alkoxy” means an alkyl group that is linked via an oxygen (i.e., alkyl-O-), for example methoxy, ethoxy, and sec-butyloxy groups. "Alkylene" means a straight or branched chain, saturated, divalent aliphatic hydrocarbon group (e.g., methylene (-CH₂-) or, propylene (-(CH₂)₃- )).“Cycloalkylene” means a divalent cyclic alkylene group, -C_nH_2n-x, wherein x is the number of hydrogens replaced by cyclization(s). “Cycloalkenyl” means a monovalent group having one or more rings and one or more carbon-carbon double bonds in the ring, wherein all ring members are carbon (e.g., cyclopentyl and cyclohexyl). "Aryl" means an aromatic hydrocarbon group containing the specified number of carbon atoms, such as phenyl, tropone, indanyl, or naphthyl. “Arylene” means a divalent aryl group. “Alkylarylene” means an arylene group substituted with an alkyl group. “Arylalkylene” means an alkylene group substituted with an aryl group (e.g., benzyl). The prefix "halo" means a group or compound including one more of a fluoro, chloro, bromo, or iodo substituent. A combination of different halo groups (e.g., bromo and fluoro), or only chloro groups can be present. The prefix“hetero” means that the compound or group includes at least one ring member that is a heteroatom (e.g., 1, 2, or 3 heteroatom(s)), wherein the heteroatom(s) is each independently N, O, S, Si, or P. “Substituted” means that the compound or group is substituted with at least one (e.g., 1, 2, 3, or 4) substituents that can each independently be a C_1-9 alkoxy, a C_1-9 haloalkoxy, a nitro (-NO₂), a cyano (-CN), a C_1-6 alkyl sulfonyl (-S(=0)₂-alkyl), a C_6-i2 aryl sulfonyl (-S(=0)₂-aryl), a thiol (-SH), a thiocyano (-SCN), a tosyl (CH3C6H4SO2-), a C3-12 cycloalkyl, a C2-12 alkenyl, a C5-12

cycloalkenyl, a C_6-i2 aryl, a C_7-13 arylalkylene, a C_4-12 heterocycloalkyl, and a C_3-12 heteroaryl instead of hydrogen, provided that the substituted atom’s normal valence is not exceeded. The number of carbon atoms indicated in a group is exclusive of any substituents. For example - CH₂CH₂CN is a C₂ alkyl group substituted with a nitrile.

[0079] While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.

Claims

CLAIMS What is claimed is:

1. A method of making an article by additive manufacturing, the method comprising: forming a first layer of a thermoplastic composition comprising a plurality of thermoplastic polymer particles in the presence of a first gas, wherein the first gas is introduced prior to forming the first layer, and wherein the first gas has a permeability in the thermoplastic polymer composition that is at least two times the permeability of nitrogen in the thermoplastic composition;

heating at least a portion of the first layer with a directed energy source to provide a fused first layer;

forming a second layer of the thermoplastic composition on the fused first layer in the presence of the first gas;

heating at least a portion of the second layer with the directed energy source to provide a fused second layer; and

optionally, repeating the forming and heating to provide the article, preferably wherein the article comprises at least 2, or at least 5 layers, or at least 10 layers, or at least 20 layers.

2. The method of claim 1, wherein the method further comprises

exposing the fused first layer to a second gas for a predetermined time prior to forming the second layer, wherein the second gas has a permeability in the thermoplastic composition that is less than or equal to 0.25 times the permeability of the first gas, preferably less than 0.1 times the permeability of the first gas, more preferably less than 0.05 times the permeability of the first gas; and

exposing the fused second layer to the second gas for a predetermined time prior to repeating and forming additional layers.

3. The method of claim 1 or 2, wherein forming the first layer comprises depositing the thermoplastic composition on a target surface.

4. The method of any of claims 1 to 3, wherein heating the layers is to a temperature effective to cause the thermoplastic polymer composition to flow to provide the corresponding fused layer.

5. The method of any one of claims 1 to 4, wherein the directed energy source is a laser beam.

6. The method of any one of claims 1 to 5, wherein the thermoplastic polymer particles comprise polycarbonate, polyetherimide, polyarylether ketone, nylon, acrylonitrile-butadiene- styrene, polyphenylsulfone, or a combination thereof, preferably polycarbonate.

7. The method of any one of claims 1 to 6, wherein heating is at a temperature that is greater than or equal to the glass transition temperature of the thermoplastic polymer particles, or greater than or equal to the melting temperature of the thermoplastic polymer particles, or at least lO°C less than the decomposition temperature of the thermoplastic polymer particles.

8. The method of any one of claims 2 to 7, wherein the predetermined time is up to 500 minutes.

9. The method of any one of claims 1 to 8, wherein the first gas comprises helium, hydrogen, or a combination thereof.

10. The method of any one of claims 2 to 9, wherein second gas comprises nitrogen, argon, or a combination thereof.

11. The method of any one of claims 1 to 10, wherein the thermoplastic composition further comprises an additive.

12. The method of claim 11, wherein the additive comprises a flow agent, a mold release agent, or a combination thereof.

13. A three-dimensional article made by the method of any one of claims 1 to 12, wherein the article comprises a plurality of fused layers comprising the thermoplastic composition.

14. The article of claim 13, wherein the article is substantially free of bubbles.

15. A three-dimensional article made by a laser sintering process, wherein the article comprises a plurality of fused layers comprising a thermoplastic composition, and wherein the article is substantially free of bubbles.