Three-dimensional printing fusing agent

Abstract

An example of a fusing agent includes cesium tungsten oxide nanoparticles present in an amount ranging from about 0.01 wt% active to about 1 wt% active, based on a total weight of the fusing agent, and a liquid vehicle. The liquid vehicle includes water and a co-solvent mixture including from about 0.1 wt% active to about 10 wt% active of benzyl alcohol and from about 10 wt% active to about 40 wt% active of a co-solvent to improve miscibility between the benzyl alcohol and the water, where the wt% active of the benzyl alcohol of the co-solvent are each based on the total weight of the liquid vehicle.

Description

THREE-DIMENSIONAL PRINTING FUSING AGENTBACKGROUND

[0001] A three-dimensional (3D) printing process is a form of additive manufacturing that can be used to form 3D solid parts, e.g., using a digital model. 3D printing is often used in rapid product prototyping, mold generation, mold master generation, and short run manufacturing. Some additive 3D printing techniques involve the iterative application of successive layers of one or more materials, such as one or more build material composition(s), fusing agent(s), and the like. In some of these additive 3D printing techniques, at least partial curing, thermal merging / fusing, melting, sintering, etc. of the build material composition(s) may be used to form 3D solid parts, and the mechanism for material coalescence may depend upon the type of build material composition(s) used. For some materials, at least partial melting may be accomplished using heat-assisted extrusion, and for some other materials, curing or fusing may be accomplished using photonic energy sources, such as ultra-violet light or infrared light. 3D printing techniques may be used to generate 3D printed parts with various properties, such as parts having a desired color.BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Features of examples of the present disclosure will become apparent by reference to the following detailed description and drawings, in which like reference numerals correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals or features having a previously described function may or may not be described in connection with other drawings in which they appear.

[0003] Fig. 1 is a flow diagram illustrating a 3D printing method that utilizes an example of the 3D printing fusing agent disclosed herein;

[0004] Fig. 2 is a schematic illustration of a 3D printing method that utilizes an example of the 3D printing fusing agent disclosed herein;

[0005] Fig. 3 is a photograph, reproduced in black and white, of 3D objects formed using an example of the 3D printing fusing agent disclosed herein (shown inthe top half of the figure) and 3D objects formed using a comparative 3D printing fusing agent (shown in the bottom half of the figure); and

[0006] Fig. 4 is a graphical representation of the results of a color test between objects generated using an example of the 3D printing fusing agent disclosed herein and an object generated using a comparative fusing agent, with sample names being shown on the x axis and L* values being shown on the y axis.DETAILED DESCRIPTION

[0007] Some three-dimensional (3D) printing methods utilize an energy absorbing substance (e.g., an energy absorber) to pattern a build material composition, thereby forming a patterned region of build material composition. In these methods, an entire layer of the build material composition is exposed to radiation, and the patterned region of the build material composition is coalesced / fused and becomes a layer of a 3D printed object. In the patterned region, the energy absorbing substance is capable of at least partially penetrating into voids between the particles of the build material composition, and is also capable of spreading onto an exterior surface of particles within the build material composition. The energy absorbing substance is also capable of converting absorbed radiation energy into thermal energy, which may be used to coalesce / fuse build material particles that have been patterned with the energy absorbing substance.Fusing / coalescing causes the build material particles to join or blend to form a single entity (i. e. , the layer of the 3D part). Fusing / coalescing may involve at least partial thermal merging, melting, binding, and / or some other mechanism that causes the build material composition to form the layer of the 3D object.

[0008] Some 3D printing methods / techniques utilize a fusing agent including an energy absorber to achieve build material coalescence, and these methods / techniques may result in strongly colored 3D objects or 3D object layers, depending on the energy absorber and the other components that are used in the method. For example, some of these methods utilize darkly colored energy absorbers (e.g., black energy absorbers), and the darkly colored energy absorbers may result in the production of darkly-colored objects. The dark color may be undesirable for some 3D printedobjects, for example, where a white color or an off-white color is desired. Further, difficulties can be encountered when endeavoring to incorporate low-tint energy absorbers into fusing agents while still maintaining the fusing agent’s jettability (e.g., via inkjet applicators) and the fusing agent’s ability to absorb enough radiation to desirably heat and coalesce the build material particles.

[0009] Disclosed herein is a three-dimensional (3D) printing fusing agent that is capable of producing white and off-white 3D objects and that is jettable, e.g., via inkjet applicators. In some instances, 3D objects formed using the 3D printing fusing agent disclosed herein exhibit a color of the build material composition that is used to form the object or object layers, and this color may be white or off-white. Examples of the 3D printing fusing agent disclosed herein include a low loading of cesium tungsten oxide nanoparticles, benzyl alcohol, water, and a co-solvent to improve miscibility between the benzyl alcohol and the water. The low loading of the cesium tungsten oxide nanoparticles in the 3D printing fusing agent has been found to sufficiently coalesce the build material composition without substantially imparting color to the 3D object / layer being formed.

[0010] The cesium tungsten oxide nanoparticles may also be referred to herein as “CWO nanoparticles.”

[0011] The terms “3D printing fusing agent,” “3D fusing agent,” and “fusing agent” are used interchangeably herein.

[0012] Throughout this disclosure, a weight percentage that is referred to as “wt% active” refers to the loading of an active component of a stock formulation that is present, e.g., in the 3D printing fusing agent, etc. For example, particles of an energy absorber, such as cesium tungsten oxide nanoparticles, may be present in a waterbased formulation (e.g., a stock solution or dispersion) before being incorporated into the 3D printing fusing agent. In this example, the wt% active of the energy absorber accounts for the loading (as a weight percent) of the energy absorber solids that are present in the 3D fusing agent, and does not account for the weight of the other components (e.g., water, etc.) that are present in the stock solution or dispersion with the energy absorber. The term “wt%,” without the term actives, refers to the loading(e.g., in the fusing agent) of a 100% active component that does not include other nonactive components therein.

[0013] 3D Printing Fusing Agent

[0014] Disclosed herein is a fusing agent, including: cesium tungsten oxide nanoparticles present in an amount ranging from about 0.01 wt% active to about 1 wt% active, based on a total weight of the 3D printing fusing agent; and a liquid vehicle, including: water, and a co-solvent mixture including from about 0.1 wt% active to about 10 wt% active of benzyl alcohol and from about 10 wt% active to about 40 wt% active of a co-solvent to improve miscibility between the benzyl alcohol and the water, wherein the wt% of the benzyl alcohol and the wt% of the co-solvent are based on the total weight of the fusing agent. The various components of the fusing agent will now be described.

[0015] Cesium tungsten oxide nanoparticles

[0016] In an example, the cesium tungsten oxide nanoparticles have a general formula of CsxW03, where 0<x<1 .

[0017] The cesium tungsten oxide nanoparticles may be present in the fusing agent in a relatively low amount, due, in part, to the presence of the co-solvent mixture in the fusing agent. Benzyl alcohol in the co-solvent mixture is a plasticizer that can reduce the amount of infrared radiation required to adequately melt and coalesce the polymeric build particles by locally reducing the melting temperature in the polymer bed during 3D printing. Alternatively, the presence of benzyl alcohol in the fusing agent can be used to reduce the concentration of CWO in the fusing agent, such that an equivalent amount of radiation can adequately fuse a fusing agent prepared with a lower concentration of CWO, resulting in whiter final parts (due in part to the lowered concentration of CWO in the fusing agent). Accordingly, the final 3D object / layer (that is formed using the fusing agent) may retain the original color of the build material composition used to form the object (e.g., white or off-white) due, in part, to the low amount of cesium tungsten oxide nanoparticles in the fusing agent.

[0018] In an example, the amount of cesium tungsten oxide nanoparticles in the fusing agent ranges from about 0.01 wt% active to about 1 wt% active, or from about0.1 wt% active to about 0.9 wt% active, or from about 0.5 wt% active to about 1 wt% active, or from about 0.25 wt% active to about 0.75 wt% active, or from about 0.1 wt% active to about 0.5 wt% active. In a specific example, the cesium tungsten oxide nanoparticles are present in the fusing agent at about 0.8 wt% active. In each of these examples, the wt% active of the cesium tungsten oxide nanoparticles is based on a total weight of the fusing agent.

[0019] In an example, the cesium tungsten oxide nanoparticles have a volume weighted mean diameter ranging from about 0.001 pm to about 0.025 pm. The cesium tungsten oxide nanoparticles may have any desirable shape, such as spherical, hexagonal, irregular, flat (e.g., in flake form), etc.

[0020] The cesium tungsten oxide nanoparticles are capable of absorbing electromagnetic energy at certain wavelengths, and thus the cesium tungsten oxide nanoparticles may function as an energy absorber in the 3D printing fusing agent. In an example, the cesium tungsten oxide nanoparticles have substantial absorption at wavelengths ranging from about 800 nm to about 4000 nm. As used herein “substantial absorption” means that at least 80% of radiation having wavelengths within the specified range is absorbed by the substance being referred to (i.e. , cesium tungsten oxide nanoparticles). Even at the low loadings set forth herein, the cesium tungsten oxide nanoparticles are capable of absorbing and converting absorbed radiation into a sufficient amount of thermal energy to fuse / coalesce build material particles that have been patterned with the fusing agent (as will be described in more detail in regard to the methods disclosed herein).

[0021] In some examples, the cesium tungsten oxide nanoparticles are present in a dispersion before being incorporated into the fusing agent. In these examples, a stabilizer (e.g., beta-alanine) may be present in the dispersion to aid in preventing agglomeration of the cesium tungsten oxide nanoparticles while the nanoparticles are in the dispersion. In an example, the cesium tungsten oxide nanoparticles are present in the dispersion in an amount ranging from about 0.5 wt% to about 50 wt%, based on a total weight of the dispersion. In another example, the cesium tungsten oxide nanoparticles are present in the dispersion in an amount ranging from about 10 wt% to about 50 wt%, based on the total weight of the dispersion. In a specific example, thecesium tungsten oxide nanoparticles are present in the dispersion in an amount of about 20 wt%.

[0022] When included in the dispersion, the cesium tungsten oxide nanoparticles (prior to being incorporated into the 3D printing fusing agent) may be dispersed in water alone or in combination with an additional water-soluble or water- miscible co-solvent, such as 2-pyrrolidone, 1 -(2-hydroxyethyl)-2-pyrrolidone (HE2P), glycerol, 2-methyl-1 ,3-propanediol, 1 ,2-butane diol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, diethylene glycol butyl ether, other glycol ethers, or a combination thereof. It is to be understood that when the dispersion of cesium tungsten oxide nanoparticles is utilized, that the liquid components of the dispersion become part of the 3D printing fusing agent. The dispersion, when used, may be incorporated into the fusing agent so that the amount of the cesium tungsten oxide nanoparticles that is present in the 3D fusing agent (in terms of wt% active) conforms to any of the suitable ranges set forth herein (e.g., about 0.01 wt% active to about 1 wt% active, etc ).

[0023] Alternatively, solid cesium tungsten oxide nanoparticles may be added to the liquid vehicle at the low loading disclosed herein to form the fusing agent.

[0024] As described herein, the relatively low cesium tungsten oxide nanoparticle loadings used in the 3D fusing agent do not interfere with the jettability of the 3D fusing agent and may be used to generate 3D printed objects / layers that exhibit a color of or similar to a build material used to form the 3D objects / layers.

[0025] Liquid Vehicle

[0026] The 3D printing fusing agent further includes a liquid vehicle in addition to the cesium tungsten oxide nanoparticles.

[0027] The liquid vehicle includes a co-solvent mixture and water, and the cosolvent mixture includes benzyl alcohol and a co-solvent to improve miscibility between the benzyl alcohol and the water.

[0028] Benzyl alcohol is an aromatic alcohol with the formula C6H5CH2OH. As mentioned herein, the benzyl alcohol, when used in combination with the cesium tungsten oxide nanoparticles and the co-solvent in the 3D fusing agent, can be utilizedto generate 3D objects / object layers that exhibit a color of the build material composition used to form the 3D objects / object layers.

[0029] In one example, the benzyl alcohol is present in the fusing agent in an amount ranging from about 0.1 wt% active to about 10 wt% active. In other examples, the benzyl alcohol is present in the 3D printing fusing agent in an amount ranging from about 2 wt% active to about 9 wt% active, or from about 5 wt% active to about 10 wt% active. In a specific example, the benzyl alcohol is present in the 3D printing fusing agent at 1 wt% active. In another specific example, the benzyl alcohol is present in the 3D printing fusing agent at 2 wt% active. In still another specific example, the benzyl alcohol is present in the 3D printing fusing agent at 4 wt% active. In yet another specific example, the benzyl alcohol is present in the 3D printing fusing agent at 8 wt% active. In each of these examples, the wt% active of the benzyl alcohol is based on the total weight of the fusing agent. The upper limit of the benzyl alcohol set forth herein is selected, in part, to obtain a fusing agent with long term storage stability. For example, in some examples in which benzyl alcohol is present at greater than 10 wt%, agglomeration of the cesium tungsten oxide particles (in the fusing agent) may occur, which may result in destabilization of the cesium tungsten oxide particles within the fusing agent. It is to be understood, however, that the tungsten oxide nanoparticle loading and the liquid vehicle components (e.g., surfactant, stabilizer and / or chelator) and amounts may be adjusted to obtain an inkjettable and relatively stable formulation with a higher amount of benzyl alcohol (see Table 1 below).

[0030] The co-solvent mixture also includes the co-solvent, which is selected to improve miscibility between the benzyl alcohol and the water. This particular solvent may be considered a solvent for the benzyl alcohol, and is referred to herein as the “co-solvent” for brevity. The co-solvent may have a higher solubility for benzyl alcohol than for water. As such, the co-solvent improves the overall miscibility of liquid vehicle. The inclusion of the co-solvent enables the fusing agent to be prepared with a predetermined amount of benzyl alcohol that is desirable for solubilizing a build material during 3D printing and that is desirable for dispersing the (low loading) of cesium tungsten oxide nanoparticles.

[0031] In examples, the co-solvent has a boiling point of 150°C or higher. A wide variety of solvents for benzyl alcohol having a boiling point of 150°C or higher may be used. In an example, the co-solvent is selected from the group consisting of 1-(2-hydroxyethyl)-2-pyrrolidone, 1 ,5-pentanediol, 1 ,2-hexanediol, 2-pyrrolidinone, triethylene glycol, tetraethylene glycol, 2-methyl-1 ,3-propanediol, 1 ,6-hexanediol, tripropylene glycol methyl ether, 1 ,2-propanediol (i.e. , propylene glycol), diethylene glycol butyl either, polyethylene glycol having a weight average molecular weight ranging from about 190 Daltons to about 420 Daltons, glycerol, betaine, and combinations thereof. Some of these solvents, such as propylene glycol (bp ~188°C) and 1 -(2-hydroxyethyl)-2-pyrrolidone (bp ~ 175°C), have a boiling point higher than 170°C. Other of these solvents, such as triethylene glycol (bp ~ 285°C), tetraethylene glycol (bp ~ 327°C), propylene glycol 300 (bp > 220°C), propylene glycol 400 (bp ~ 290°C), and glycerol (bp ~290°C) have a boiling point higher than 200°C. In some instances, the co-solvent acts as a humectant in the fusing agent.

[0032] The total amount of the co-solvent (i.e., solvent for benzyl alcohol) that is included in the 3D fusing agent will depend, in part, upon the amount of benzyl alcohol that is included in the 3D printing fusing agent. The amount of benzyl alcohol and cosolvent present in the 3D printing fusing agent may also be expressed as a weight ratio. As an example, the benzyl alcohol and the co-solvent may be present (in the 3D printing fusing agent) at a weight ratio ranging from about 1 :6 to about 2:3. In another specific example, the benzyl alcohol and the solvent are present (in the 3D printing fusing agent) at a weight ratio of 1 :3. In one example, the co-solvent is present in the 3D printing fusing agent in an amount ranging from about 10 wt% active to about 40 wt% active, based on the total weight of the fusing agent. In other examples, the cosolvent is present in the 3D printing fusing agent in an amount ranging from about 15 wt% active to about 35 wt% active, or from about 20 wt% active to about 30 wt% active, based on the total weight of the fusing agent. In a specific example, the cosolvent is present in the liquid vehicle of the 3D printing fusing agent in the fusing agent at 19 wt% active, based on the total weight of the fusing agent.

[0033] In addition to the benzyl alcohol and the co-solvent, the solvent mixture of the fusing agent may also include one or more additional water soluble or watermiscible organic co-solvents. Classes of water soluble or water miscible organic cosolvents that may be used as the additional co-solvent in the liquid vehicle of the 3D printing fusing agent include aliphatic alcohols, aromatic alcohols, diols, glycol ethers, polyglycol ethers, lactams, formamides (substituted and unsubstituted), acetamides (substituted and unsubstituted), glycols, and long chain alcohols. Examples of these additional co-solvents include primary aliphatic alcohols, secondary aliphatic alcohols, 1 ,2-alcohols, 1 ,3-alcohols, 1 ,5-alcohols, other diols (e.g., 2-methyl-1 ,3-propanediol, etc.), ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higher homologs (Ce- C12) of polyethylene glycol alkyl ethers, triethylene glycol, tetraethylene glycol, tripropylene glycol methyl ether, N-alkyl caprolactams, unsubstituted caprolactams, 1 - methyl-2-pyrrolidone, 2-pyrrolidone, and the like. Other examples of suitable organic co-solvents include dimethyl sulfoxide (DMSO), isopropyl alcohol, ethanol, pentanol, acetone, or the like.

[0034] Regardless of whether the co-solvent is used alone or in combination with an additional co-solvent(s), the total amount of all co-solvent(s) present in the 3D printing fusing agent ranges from about 10 wt% active to about 40 wt% active, based on the total weight of the fusing agent. In other examples, the total amount of all cosolvents) ranges from about 15 wt% active to about 35 wt% active, or from about 20 wt% active to about 30 wt% active, based on the total weight of the fusing agent. In a specific example, the total amount of all co-solvents present in the fusing agent is 19 wt% active, based on the total weight of the fusing agent.

[0035] In addition to the co-solvent mixture, the liquid vehicle further includes water. The water generally makes up a balance of the 3D fusing agent, relative to the other components included in the 3D fusing agent (e.g., the co-solvent mixture, the cesium tungsten oxide nanoparticles, and any additives included in the 3D fusing agent, as will be described herein). Thus, the amount of water that is included in the 3D printing fusing agent will generally depend upon the amount of each of the other components included in the 3D fusing agent. In an example, an amount of water in the 3D printing fusing agent ranges from 25 wt% to 90 wt%, based on the total weight of the fusing agent. In another example, the amount of water in the 3D printing fusing agent ranges from 70 wt% to 80 wt%, based on the total weight of the fusing agent.The water may be pure water, deionized water (DI water), distilled water, or any other suitable form of water.

[0036] Additive(s)

[0037] The 3D printing fusing agent may further include an additive selected from the group consisting of a humectant, a surfactant, an antimicrobial agent, a chelating agent, an anti-kogation agent, a pH adjuster, a stabilizer, and a combination thereof.

[0038] As such, in some examples, the 3D printing fusing agent comprises the cesium tungsten oxide nanoparticles, the liquid vehicle (as defined herein), and the additive. In one of these examples, the 3D printing fusing agent further comprises the stabilizer, the surfactant, and the anti-kogation agent. It is to be understood that in any of these examples, “the additive” refers to any of the aforementioned additives, including the combination of the listed additives.

[0039] In other examples, the 3D printing fusing agent consists of the cesium tungsten oxide nanoparticles, the liquid vehicle (as defined herein), and the additive, with no other components. It is to be understood that in these examples, “the additive” refers to any of the aforementioned additives, including the combination of two or more of the listed additives.

[0040] The 3D printing fusing agent may include a humectant as the additive. An example of a suitable humectant is ethoxylated glycerin having the following formula:in which the total of a+b+c ranges from about 5 to about 60, or in other examples, from about 20 to about 30. An example of the ethoxylated glycerin is LIPONIC® EG-1 (LEG-1 , glycereth-26, a+b+c=26, available from Lipo Chemicals).

[0041] In an example, the total amount of the humectant(s) present in the 3D printing fusing agent ranges from about 3 wt% active to about 10 wt% active, based on the total weight of the 3D printing fusing agent.

[0042] The 3D printing fusing agent may further include the surfactant as the additive. Suitable surfactant(s) for the 3D printing fusing agent include non-ionic or anionic surfactants. It may be desirable to select a surfactant that does not react with the benzyl alcohol. Some example surfactants include alkyl polyethylene oxides, alkyl phenyl polyethylene oxides, polyethylene oxide block copolymers, acetylenic polyethylene oxides, polyethylene oxide (di)esters, polyethylene oxide amines, dimethicone copolyols, substituted amine oxides, fluorosurfactants, and the like.Some specific examples include a self-emulsifiable, non-ionic wetting agent based on acetylenic diol chemistry (e g., SURFYNOL® SEF from Evonik Degussa), a non-ionic fluorosurfactant (e.g., CAPSTONE® fluorosurfactants, such as CAPSTONE® FS-35, from Chemours), an ethoxylated low-foam wetting agent (e.g., SURFYNOL® 440 or SURFYNOL® CT-111 from Evonik Degussa), an ethoxylated wetting agent and molecular defoamer (e.g., SURFYNOL® 420 from Evonik Degussa), non-ionic wetting agents and molecular defoamers (e.g., SURFYNOL® 104E from Evonik Degussa), and / or water-soluble, non-ionic surfactants (e.g., TERGITOL™ TMN-6, TERGITOL™ 15-S-7, or TERGITOL™ 15-S-9 (a secondary alcohol ethoxylate) from The Dow Chemical Company or TEGO® Wet 510 (organic surfactant) available from Evonik Degussa). Yet another suitable (anionic) surfactant includes alkyldiphenyloxide disulfonate (e.g., the DOWFAX™ series, such a 2A1 , 3B2, 8390, C6L, C10L, and 30599, from The Dow Chemical Company).

[0043] Whether a single surfactant is used or a combination of surfactants is used, the total amount of surfactant(s) in the 3D printing fusing agent may range from about 0.01 wt% active to about 5 wt% active. In another example, the total amount of surfactant(s) in the 3D printing fusing agent may range from about 0.05 wt% active to about 4 wt% active, or from about 0.1 wt% active to about 3 wt% active, or from about0.25 wt% active to about 2 wt% active, or from about 0.5 wt% active to about 1 .5 wt% active, or from about 0.75 wt% active to about 1 .25 wt% active, based on the total weight of the 3D printing fusing agent. In a specific example, the total amount of surfactant(s) present in the 3D printing fusing agent is 1 .25 wt% active. In each of these examples, the wt% active of the surfactant is based on the total weight of the fusing agent.

[0044] The 3D printing fusing agent may also include one or more antimicrobial agents as the additive. Antimicrobial agents are also known as biocides and / or fungicides. Examples of suitable antimicrobial agents include the NUOSEPT® (Ashland Inc.), UCARCIDE™ or KORDEK™ or ROCIMA™ (The Dow Chemical Company), PROXEL® (Arch Chemicals) series, ACTICIDE® B20 and ACTICIDE® M20 and ACTICIDE® MBL (blends of 2-methyl-4-isothiazolin-3-one (MIT), 1 ,2- benzisothiazolin-3-one (BIT) and Bronopol) (Thor Chemicals), AXIDE™ (Planet Chemical), NIPACIDE™ (Clariant), blends of 5-chloro-2-methyl-4-isothiazolin-3-one (CIT or CMIT) and MIT under the tradename KATHON™ (The Dow Chemical Company), and combinations thereof.

[0045] In an example, the total amount of antimicrobial agent(s) in the 3D printing fusing agent ranges from about 0.01 wt% active to about 0.1 wt% active based on the total weight of the 3D printing fusing agent.

[0046] Chelating agents (or sequestering agents) may be included in the 3D printing fusing agent (as an additive) to eliminate and / or mitigate any deleterious effects of heavy metal impurities. In an example, the chelating agent is selected from the group consisting of methylglycinediacetic acid, trisodium salt; 4,5-dihydroxy-1 ,3- benzenedisulfonic acid disodium salt monohydrate; ethylenediaminetetraacetic acid (EDTA); hexamethylenediamine tetra(methylene phosphonic acid), potassium salt; and combinations thereof. Methylglycinediacetic acid, trisodium salt (Na3MGDA) is commercially available as TRILON® M from BASF Corp. 4,5-dihydroxy-1 ,3- benzenedisulfonic acid disodium salt monohydrate is commercially available as TIRON™ monohydrate. Hexamethylenediamine tetra(methylene phosphonic acid), potassium salt is commercially available as DEQUEST® 2054 from Italmatch Chemicals.

[0047] Whether a single chelating agent is used or a combination of chelating agents is used, the total amount of chelating agent(s) in the 3D printing fusing agent may range from greater than 0 wt% active to about 0.5 wt% active, based on the total weight of the 3D printing fusing agent.

[0048] The 3D printing fusing agent may also include anti-kogation agent(s) that is / are to be jetted using thermal inkjet printing. “Kogation” refers to the deposit of dried printing liquid (e.g., 3D printing fusing agent) on a heating element of a thermal inkjet printhead. Anti-kogation agent(s) is / are included to assist in preventing the buildup of kogation.

[0049] Examples of suitable anti-kogation agents include oleth-3-phosphate (commercially available as CRODAFOS™ O3A or CRODAFOS™ N-3A) or dextran 500k. Other suitable examples of the anti-kogation agents include CRODAFOS™ HCE (phosphate-ester from Croda Int.), CRODAFOS® 010A (oleth-10-phosphate from Croda Int.), or DISPERSOGEN® LFH (polymeric dispersing agent with aromatic anchoring groups, acid form, anionic, from Clariant), etc. It is to be understood that any combination of the anti-kogation agents listed may be used.

[0050] The anti-kogation agent may be present in the 3D printing fusing agent in an amount ranging from about 0.1 wt% active to about 1 .5 wt% active, based on the total weight of the 3D printing fusing agent.

[0051] The 3D printing fusing agent may also include pH adjuster(s) as the additive. The type and amount of pH adjuster that is added may depend upon the initial pH of the 3D printing fusing agent and the desired final pH of the 3D fusing agent. If the initial pH is too high (e.g., above 12), an acid may be added to lower the pH, and if the initial pH is too low (below 7.5), a base may be added to increase the pH. Examples of suitable pH adjusters include metal hydroxide bases, such as potassium hydroxide (KOH), sodium hydroxide (NaOH), etc. In an example, the metal hydroxide base may be added to the 3D printing fusing agent in an aqueous solution. In another example, the metal hydroxide base may be added to the 3D printing fusing agent in an aqueous solution including 5 wt% of the metal hydroxide base (e.g., a 5 wt% potassium hydroxide aqueous solution). Examples of suitable acidic pH adjustersthat may be used include methane sulfonic acid, nitric acid, and phosphoric acid. The pH adjuster may be a buffer that helps to main the desired pH of the fusing agent.

[0052] In an example, the total amount of pH adjuster(s) in the 3D printing fusing agent ranges from greater than 0 wt% active to about 0.1 wt% active, based on the total weight of the 3D printing fusing agent.

[0053] The 3D printing fusing agent may further include a stabilizer as the additive. The stabilizer aids in extending the shelf life of the 3D printing fusing agent and in maintaining the printability of the 3D fusing agent, and thus improves the overall stabilization of the fusing agent.

[0054] The stabilizer may be a zwitterionic stabilizer. While the zwitterionic stabilizer has an overall neutral charge, at least one area of the molecule has a positive charge (e.g., amino groups) and at least one other area of the molecule has a negative charge. The CWO nanoparticles may have a slight negative charge. The zwitterionic stabilizer molecules may orient around the slightly negative CWO nanoparticles with the positive area of the zwitterionic stabilizer molecules closest to the CWO nanoparticles and the negative area of the zwitterionic stabilizer molecules furthest away from the CWO nanoparticles. Then, the negative charge of the negative area of the zwitterionic stabilizer molecules may repel CWO nanoparticles from each other. The zwitterionic stabilizer molecules may form a protective layer around the CWO nanoparticles, and prevent them from coming into direct contact with each other and / or increase the distance between the particle surfaces (e.g., by a distance of from about 1 nm to about 2 nm). Thus, the zwitterionic stabilizer may prevent the CWO nanoparticles from agglomerating and / or settling in the fusing agent.

[0055] The zwitterionic stabilizer may be selected from the group consisting of C2to Cs betaines, C2to Cs aminocarboxylic acids having a solubility of at least 10 g in 100 g of water, taurine, and combinations thereof. Examples of the C2to Cs aminocarboxylic acids include beta-alanine, gamma-aminobutyric acid, glycine, and combinations thereof.

[0056] The zwitterionic stabilizer may be present in the 3D printing fusing agent in an amount of from about 0.2 wt% active to about 35 wt% active, based on the total weight of the fusing agent. When the zwitterionic stabilizer is the C2to Cs betaine, theC2 to Cs betaine may be present in an amount of from about 8 wt% to about 35 wt% active of the total weight of the fusing agent. When the zwitterionic stabilizer is the C2 to Cs aminocarboxylic acid, the C2 to Cs aminocarboxylic acid may be present in an amount of from about 0.5 wt% active to about 20 wt% active of the total weight of the fusing agent. When the zwitterionic stabilizer is taurine, taurine may be present in an amount of from about 2 wt% active to about 35 wt% active of the total weight of the primer fusing agent.

[0057] In this example, the weight ratio of the CWO nanoparticles to the zwitterionic stabilizer may be from 1 :10 to 10:1 ; or the weight ratio of the CWO nanoparticles to the zwitterionic stabilizer may be 1 :1.

[0058] As mentioned herein, the benzyl alcohol amount may be increased when the CWO nanoparticle loading is relatively low and the liquid vehicle is adjusted for inkjettability and storage stability. Additionally, benzyl alcohol may be excluded when the fusing agent is used in conjunction with an example of the assist agent disclosed herein that includes the benzyl alcohol. Table 1 illustrates an example of other formulations of the fusing agent that may be used.TABLE 1

[0059] Assist Agent

[0060] Some examples of the 3D printing methods described herein utilize an assist agent. The assist agent may be used to enhance the plasticizing effect from the solvents, which enables a lower amount of CWO nanoparticles to be used while yielding parts that appear white, even without the use of whitening additives in the build material composition.

[0061] In an example, the assist agent include the co-solvent of the fusing agent with which it is paired, optionally benzyl alcohol, a surfactant, a stabilizer, a pH adjuster, an anti-kogation agent, a chelating agent, and a balance of water. In an example, the assist agent consists of these components and no other components.

[0062] Any example of the surfactant, the stabilizer, the pH adjuster, the anti- kogation agent, and the chelating agent set forth herein for the fusing agent may be used in the assist agent in any of the amounts set forth herein for the fusing agent (except that the total is with respect to the total weight of the assist agent). Example amounts are provided in Table 2 below.

[0063] It is to be understood that when the fusing agent is to be used with the assist agent, the total amount of benzyl alcohol in the agent(s) (whether it is present in one agent or both agents) is about 30 wt%. For example, if the benzyl alcohol is contained in the fusing agent in the desired amount, the assist agent may not include benzyl alcohol. For another example, if the benzyl alcohol is contained in the assist agent in the desired amount, the fusing agent may not include benzyl alcohol.Alternatively, both agents may include some of the benzyl alcohol, so that the total between the two agents is up to 30 wt%, and in some instances, up to 10 wt%.

[0064] Table 2 illustrates an example of some formulations of the assist agent that may be used.TABLE 2

[0065] Detailing Agent

[0066] Some examples of the 3D printing methods described herein utilize a detailing agent. The detailing agent may include a surfactant, a DA co-solvent, and a balance of water. In an example, the detailing agent consists of these components and no other components. In another example, the detailing agent further includes additional components, such as anti-kogation agent(s), antimicrobial agent(s), and / or chelating agent(s), each of which is described above in reference to the 3D printing fusing agent.

[0067] The surfactant(s) that may be used in the detailing agent include any of the surfactants listed herein in reference to the 3D printing fusing agent. The total amount of surfactant(s) in the detailing agent may range from about 0.10 wt% active, to about 5 wt% active, based on a total weight of the detailing agent.

[0068] The DA co-solvent(s) that may be used in the detailing agent include any of the co-solvents or additional co-solvents listed above in reference to the 3D printing fusing agent. The total amount of the DA co-solvent(s) present in the detailing agent may range from about 1 wt% active to about 65 wt% active, based on the total weight of the detailing agent.

[0069] The examples of the detailing agent disclosed herein do not include a colorant. As such, the detailing agent may be colorless. As used herein, “colorless”means that the detailing agent is achromatic and does not include a colorant. The colorless detailing agent, in combination with the 3D printing fusing agent disclosed herein, may be used to generate 3D object layer(s) / object(s) exhibiting a color that is identical to the build material used to form the layer(s) / object(s).

[0070] The balance of the detailing agent is water. As such, the amount of water may vary depending upon the amounts of the other components that are included.

[0071] Polymeric Build Material Composition

[0072] The 3D printing fusing agent described herein may be suitable for printing on a polymeric build material composition (referred to interchangeably as the “build material composition” herein). Some examples of suitable polymeric materials for the polymeric build material composition include polyamides, polyacetals, polyolefins, styrene polymers and copolymers (e.g., polystyrene), fluoropolymers, acrylic polymers and copolymers, polyethers, polyaryletherketones, polyesters (e.g., a thermoplastic copolyester (TPC)), polycarbonates (PC), a thermoplastic polyurethane elastomer (TPU), a thermoplastic polyolefin elastomer (TPO), a thermoplastic vulcanizate (TPV), a polyether block amide (PEBA), or a combination thereof. In an example, the polymer material is selected from the group consisting of polyethylene, polyethylene terephthalate (PET), polystyrene (PS), polypropylene, high density polyethylene (HDPE), polyoxymethylene (POM), polyether ketone (PEK), polyether ether ketone (PEEK), polyetherketoneketone (PEKK), polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), acrylonitrile styrene acrylate (ASA), poly(methyl methacrylate) (PMMA), styrene acrylonitrile (SAN), styrene maleic anhydride (SMA), poly(vinyl chloride) (PVC), polyethylenimine (PEI), and combinations thereof.

[0073] In some examples, the polymeric build material composition is a polyamide build material composition including polyamide particles. Examples of suitable polyamides include polyamide-11 (PA 11 / nylon 11 ), polyamide-12 (PA 12 / nylon 12), polyamide-6 (PA 6 / nylon 6), polyamide-8 (PA 81 nylon 8), polyamide-9 (PA 9 / nylon 9), polyamide-66 (PA 66 / nylon 66), polyamide-612 (PA 612 / nylon612), polyam ide-812 (PA 812 I nylon 812), polyam ide-912 (PA 912 / nylon 912), etc.), a thermoplastic polyamide (TPA), and combinations thereof.

[0074] Any of the polymeric materials in the build material composition may be in the form of a powder or a powder-like material. The powder-like material includes, for example, short fibers having a length that is greater than its width. In some examples, the powder or powder-like material may be formed from, or may include, short fibers that may, for example, have been cut into short lengths from long strands or threads of material.

[0075] The polymeric material may be made up of similarly sized particles and / or differently sized particles. In an example, the average particle size of the polymeric material ranges from about 2 pm to about 225 pm. In another example, the average particle size of the polymeric material ranges from about 10 pm to about 130 pm. The term “average particle size,” as used herein, refers to a volume-weighted mean diameter of a particle distribution.

[0076] When the build material composition includes crystalline or semicrystalline polymeric material, the build material composition may have a wide processing window of greater than 5°C, which can be defined by the temperature range between the melting point and the re-crystallization temperature. In an example, the polymeric material in the build material composition may have a melting point ranging from about 50°C to about 300°C. As other examples, the polymeric material in the build material composition may have a melting point ranging from about 155°C to about 225°C, from about 155°C to about 215°C, about 160°C to about 200°C, from about 170°C to about 190°C, or from about 182°C to about 189°C. As still another example, the polymeric material in the build material composition may have a melting point of about 180°C.

[0077] When the build material composition includes thermoplastic polymeric material, the build material composition may have a melting range within the range of from about 130°C to about 250°C.

[0078] In some examples, the build material composition does not substantially absorb radiation having a wavelength within the range from 300 nm to 1400 nm. Thephrase “does not substantially absorb” means that the absorptivity of the build material composition at a particular wavelength is 25% or less (e.g., 20%, 10%, 5%, etc.).

[0079] In some examples, in addition to the polymeric material, the build material composition may include an antioxidant, a whitener, an antistatic agent, a flow aid, or a combination thereof. While several examples of these additives are provided, it is to be understood that these additives are selected to be thermally stable (i.e. , will not decompose) at the 3D printing temperatures.

[0080] Antioxidant(s) may be added to the build material composition to prevent or slow molecular weight decreases of the polymeric material and / or to prevent or slow discoloration (e.g., yellowing) by preventing or slowing oxidation of the polymeric material. In some examples, the polymeric material may discolor upon reacting with oxygen, and this discoloration may contribute to the discoloration of the build material composition. The antioxidant may be selected to minimize discoloration. In some examples, the antioxidant may be a radical scavenger. In these examples, the antioxidant may include IRGANOX® 1098 (benzenepropanamide, N,N'-1 ,6- hexanediylbis(3,5-bis(1 ,1 -dimethylethyl)-4-hydroxy)), IRGANOX® 254 (a mixture of 40% triethylene glycol bis(3-tert-butyl-4-hydroxy-5-methylphenyl), polyvinyl alcohol and deionized water), and / or other sterical ly hindered phenols. In other examples, the antioxidant may include a phosphite and / or an organic sulfide (e.g., a thioester). The antioxidant may be in the form of fine particles (e.g., having an average particle size of 5 pm or less) that are dry blended with the polymeric material. In an example, the antioxidant may be included in the build material composition in an amount ranging from about 0.01 wt% to about 5 wt%, based on a total weight of the build material composition. In other examples, the antioxidant may be included in the build material composition in an amount ranging from about 0.01 wt% to about 2 wt% or from about 0.2 wt% to about 1 wt%, based on the total weight of the build material composition.

[0081] Whitener(s) may be added to the build material composition to bring the L* of the build material composition closer to 100 (white) and / or improve visibility. It is to be understood, however, that some examples of the build material composition do not include the whitener because the 3D fusing agent disclosed herein is capable of generate relatively white 3D objects. Examples of suitable Whiteners include titaniumdioxide (TiO2), zinc oxide (ZnO), calcium carbonate (CaCOs), zirconium dioxide (ZrC>2), aluminum oxide (AI2O3), silicon dioxide (SiO2), boron nitride (BN), barium sulfate, and combinations thereof. In some examples, a stilbene derivative may be used as the whitener and a brightener. In these examples, the temperature(s) of the 3D printing process may be selected so that the stilbene derivative remains stable (i.e. , the 3D printing temperature does not thermally decompose the stilbene derivative). In an example, any of the aforementioned Whiteners may be included in the build material composition in an amount ranging from greater than 0 wt% to about 10 wt%, based on the total weight of the build material composition. The fusing agent disclosed herein exhibits little to no tint, and thus white to off-white 3D printed objects can be obtained when the build material composition excludes an additional whitener. In particular, whiter 3D printed objects are obtained when the combination of the fusing agent and the assist agent are used together, and thus, in these instances, the build material composition excludes an additional whitener.

[0082] Antistatic agent(s) may be added to the polymeric build material composition to suppress tribo-charging. Examples of suitable antistatic agents include aliphatic amines (which may be ethoxylated), aliphatic amides, quaternary ammonium salts (e.g., behentrimonium chloride or cocamidopropyl betaine), esters of phosphoric acid, polyethylene glycolesters, or polyols. Some suitable commercially available antistatic agents include HOSTASTAT® FA 38 (natural based ethoxylated alkylamine), HOSTASTAT® FE2 (fatty acid ester), and HOSTASTAT® HS 1 (alkane sulfonate), each of which is available from Clariant Int. Ltd.). In an example, the antistatic agent is added in an amount ranging from greater than 0 wt% to less than 5 wt%, based on the total weight of the polymeric build material composition.

[0083] Flow aid(s) may be added to improve the coating flowability of the polymeric build material composition. Flow aids may be particularly beneficial when the polymeric material in the build material composition has an average particle size less than 25 pm. The flow aid improves the flowability of the build material composition by reducing the friction, the lateral drag, and the tribocharge buildup (by increasing the particle conductivity). Examples of suitable flow aids include aluminum oxide (AI2O3), tricalcium phosphate (E341 ), powdered cellulose (E460(ii)), magnesiumstearate (E470b), sodium bicarbonate (E500), sodium ferrocyanide (E535), potassium ferrocyanide (E536), calcium ferrocyanide (E538), bone phosphate (E542), sodium silicate (E550), silicon dioxide (E551 ), calcium silicate (E552), magnesium trisilicate (E553a), talcum powder (E553b), sodium aluminosilicate (E554), potassium aluminum silicate (E555), calcium aluminosilicate (E556), bentonite (E558), aluminum silicate (E559), stearic acid (E570), and polydimethylsiloxane (E900). In an example, the flow aid is added in an amount ranging from greater than 0 wt% to less than 5 wt%, based on the total weight of the build material composition.

[0084] Printing Methods

[0085] An example of a 3D printing method utilizing the 3D printing fusing agent disclosed herein is shown and described in reference to Fig. 1.

[0086] Prior to execution of any examples of the method, it is to be understood that a controller may access data stored in a data store pertaining to a 3D part / object that is to be printed. For example, the controller may determine the number of layers of a build material composition that are to be formed, the locations at which the 3D printing fusing agent is to be deposited on each of the respective layers, etc.

[0087] Referring now to Fig. 1 , a flow diagram is depicted, illustrating an example 3D printing method 100 which utilizes the 3D printing fusing agent, in accordance with the present disclosure.

[0088] The method 100 shown in Fig. 1 includes applying a polymeric build material composition to form a build material layer (reference numeral 102); based on a 3D object model, selectively applying a fusing agent onto at least a portion of the build material layer, thereby forming a patterned portion, wherein the fusing agent includes: cesium tungsten oxide nanoparticles present in an amount ranging from about 0.01 wt% active to about 1 wt% active, based on a total weight of the fusing agent; and a liquid vehicle, including: water; and a co-solvent mixture including from about 0.1 wt% active to about 10 wt% active of benzyl alcohol and from about 10 wt% active to about 40 wt% active of a co-solvent to improve miscibility between the benzyl alcohol and the water (reference numeral 104); and exposing the build material layer to near-infrared radiation to selectively coalesce the patterned portion and form a 3Dobject layer at the patterned portion, wherein the wt% of the benzyl alcohol and the wt% of the co-solvent are each based on the total weight of the fusing agent (reference numeral 106).

[0089] Any example of the 3D printing fusing agent disclosed herein may be used in the method 100.

[0090] An example of the method 100 is shown schematically in Fig. 2. In Fig. 2, a layer 24 of the build material composition 22 is applied on a build area platform 26. It is to be understood that any of the polymeric build materials described herein may be used in the method 100 as the build material composition 22. A printing system may be used to apply the build material composition 22. The printing system may include the build area platform 26, a build material supply 28 containing the build material composition 22, and a build material distributor 30.

[0091] The build area platform 26 receives the build material composition 22 from the build material supply 28. The build area platform 26 may be moved in the directions as denoted by the arrow 33, e.g., along the z-axis, so that the build material composition 22 may be delivered to the build area platform 26 or to a previously formed layer. In an example, when the build material composition 22 is to be delivered, the build area platform 26 may be programmed to advance (e.g., downward) enough so that the build material distributor 30 can push the build material composition 22 onto the build area platform 26 to form a substantially uniform layer 24 of the build material composition 22 thereon. The build area platform 26 may also be returned to its original position, for example, when a new part is to be built.

[0092] The build material supply 28 may be a container, bed, or other surface that is to position the build material composition 22 between the build material distributor 30 and the build area platform 26. The build material supply 28 may include heaters so that the build material composition 22 is heated to a supply temperature ranging from about 25°C to about 150°C. In these examples, the supply temperature may depend, in part, on the build material composition 22 used and / or the 3D printer used. As such, the range provided is one example, and higher or lower temperatures may be used.

[0093] The build material distributor 30 may be moved in the directions as denoted by the arrow 32, e.g., along the y-axis, over the build material supply 28 and across the build area platform 26 to spread the layer 24 of the build material composition 22 over the build area platform 26. The build material distributor 30 may also be returned to a position adjacent to the build material supply 28 following the spreading of the build material composition 22. The build material distributor 30 may be a blade (e.g., a doctor blade), a roller, a combination of a roller and a blade, and / or any other device capable of spreading the build material composition 22 over the build area platform 26. For instance, the build material distributor 30 may be a counterrotating roller. In some examples, the build material supply 28 or a portion of the build material supply 28 may translate along with the build material distributor 30 such that build material composition 22 is delivered continuously to the build area platform 26.

[0094] The build material supply 28 may supply the build material composition 22 into a position so that it is ready to be spread onto the build area platform 26. The build material distributor 30 may spread the supplied build material composition 22 onto the build area platform 26. The controller (not shown) may process “control build material supply” data, and in response, control the build material supply 28 to appropriately position the particles of the build material composition 22, and may process “control spreader” data, and in response, control the build material distributor 30 to spread the build material composition 22 over the build area platform 26 to form the layer 24. In Fig. 2, one build material layer 24 has been formed.

[0095] The layer 24 has a substantially uniform thickness across the build area platform 26. In an example, the build material layer 24 has a thickness ranging from about 50 pm to about 120 pm. In another example, the thickness of the build material layer 24 ranges from about 30 pm to about 300 pm. It is to be understood that thinner or thicker layers may also be used. For example, the thickness of the build material layer 24 may range from about 20 pm to about 500 pm. The layer thickness may be about 2x (i.e. , 2 times) the average diameter of the polymeric material at a minimum for finer part definition. In some examples, the layer thickness may be about 1 2x the average diameter of the polymeric material in the build material composition 22.

[0096] After the build material composition 22 has been applied, and prior to further processing, the build material layer 24 may be exposed to heating. In an example, the heating temperature may be below the melting point or melting range of the polymeric material in the build material composition 22. As examples, the preheating temperature may range from about 5°C to about 50°C below the melting point or the lowest temperature of the melting range of the polymeric material. In an example, the pre-heating temperature ranges from about 50°C to about 205°C. In still another example, the pre-heating temperature ranges from about 100°C to about 190°C. It is to be understood that the pre-heating temperature may depend, in part, on the build material composition 22 used. As such, the ranges provided are some examples, and higher or lower temperatures may be used.

[0097] Pre-heating the layer 24 may be accomplished by using any suitable heat source that exposes all of the build material composition 22 in the layer 24 to the heat. Examples of the heat source include a thermal heat source (e.g., a heater (not shown) integrated into the build area platform 26 (which may include sidewalls)) or a radiation source 34.

[0098] After the layer 24 is formed, and in some instances is pre-heated, the 3D printing fusing agent 12 is selectively applied on at least some of the build material composition 22 in the layer 24 to form a patterned portion 36.

[0099] The amount of the 3D printing fusing agent 12 that is applied per unit of the build material composition 22 in the patterned portion 36 may be sufficient to absorb and convert enough electromagnetic radiation so that the build material composition 22 in the patterned portion 36 will coalesce / fuse. The amount of the 3D printing fusing agent 12 that is applied per unit of the build material composition 22 may depend, at least in part, on the cesium tungsten oxide nanoparticle loading in the 3D printing fusing agent 12, and the polymeric material in the build material composition 22. In particular, the concentration of the CWO nanoparticles in the 3D printing fusing agent 12 can be considered. This concentration can be used to determine how much 3D printing fusing agent 12 to apply to achieve a weight ratio of 3D printing fusing agent 12 to build material composition 22 for acceptable layer-by- layer fusing. Thus, if applying the 3D printing fusing agent 12 (10 wt%) to the buildmaterial composition 22 (90 wt%) at about a 1 :9 weight ratio, then the CWO nanoparticles to build material composition 22 weight ratio (as applied) can be from about 1 :9000 to about 1 :450. If more (up to 20 wt%) or less (down to 5 wt%) of the 3D printing fusing agent 12 is applied to the build material composition 22, then these ratios can be adjusted accordingly. That stated, the weight ratio of the CWO nanoparticles to the build material composition 22 (as applied) in some more specific examples can be from about 1 : 1000 to about 1 : 100, from about 1 :800 to about 1 :150, or from about 1 :500 to about 1 :200, for example.

[0100] The 3D fusing agent 12 may be dispensed from an applicator 17. The applicator 17 may include a thermal inkjet printhead, a piezoelectric printhead, a continuous inkjet printhead, etc. in fluid communication with a fluid reservoir / container, and the selective application of the 3D fusing agent 12 may be accomplished by thermal inkjet printing, piezo electric inkjet printing, continuous inkjet printing, etc. The controller may process data, and in response, control the applicator 17 to deposit the 3D printing fusing agent 12 onto pre-determined portion(s) of the build material composition 22 to generate the patterned portion 36.

[0101] In some examples, the method 100 further comprises selectively applying, based on the 3D object model, a detailing agent 16 onto another portion of the build material layer 24 outside of the patterned portion 36 (e.g., at an unpatterned portion 38 as shown in Fig. 2).

[0102] As shown in Fig. 2, the detailing agent 16 may be selectively applied to the portion(s) 38 of the layer 24. The portion(s) 38 are not patterned with the 3D printing fusing agent 12 and thus are not to become part of a final 3D object layer 40. Thermal energy generated during radiation exposure may propagate into the surrounding portion(s) 38 that do not have the 3D printing fusing agent 12 applied thereto. The propagation of thermal energy may be inhibited, and thus the coalescence of the non-patterned build material portion(s) 38 may be prevented, when the detailing agent 16 is applied to these portion(s) 38.

[0103] In some other examples (not shown in Fig. 2), the detailing agent 16 may also or alternatively be applied to the patterned portion 36 or a portion of the patterned portion 36. The detailing agent 16 may be applied to the patterned portion 36 toprovide a cooling effect so that the build material does not overheat and / or to lower the extent of fusing in the area patterned with both the 3D printing fusing agent 12 and the detailing agent 16. In these examples, the amount of the detailing agent 16 that is applied should be low enough so that fusing is not completely inhibited. In other examples, the detailing agent 16 and the 3D printing fusing agent 12 may intermingle at the edge(s) between the patterned portion 36 and the portion(s) 38.

[0104] The detailing agent 16 may be dispensed from an applicator 17’. The applicator 17’ may include a thermal inkjet printhead, a piezoelectric printhead, a continuous inkjet printhead, etc. in fluid communication with a fluid reservoir / container, and the selective application of the detailing agent 16 may be accomplished by thermal inkjet printing, piezo electric inkjet printing, continuous inkjet printing, etc. The controller may process data, and in response, control the applicator 17’ to deposit the detailing agent 16 onto pre-determined portion(s) of the build material composition 22 to generate the portion(s) 38.

[0105] In some examples, the method 100 further comprises selectively applying, based on the 3D object model, an assist agent (not shown) onto the patterned portion 36 of the build material layer 24 (i.e. , at the same portion(s) where the fusing agent 12 is applied).

[0106] The assist agent may be dispensed from yet another applicator (not shown). This applicator may be part of the 3D printing system along with the applicator 17, or applicators 17 and 17’. Similar to the applicators 17, 17’, the applicator used for dispensing the assist agent may also include a thermal inkjet printhead, a piezoelectric printhead, a continuous inkjet printhead, etc. in fluid communication with a fluid reservoir / container, and the selective application of the assist agent may be accomplished by thermal inkjet printing, piezo electric inkjet printing, continuous inkjet printing, etc. The controller may process data, and in response, control the applicator to deposit the assist agent onto pre-determined portion(s), e.g., portion(s) 36 of the build material composition 22 to increase the plasticizing effect, and thus enhance fusing.

[0107] It is to be understood that the selective application of any of the 3D printing fusing agent 12 and / or the detailing agent 16 and / or the assist agent may beaccomplished in a single printing pass or in multiple printing passes. In some examples, the agent(s) is / are selectively applied in a single printing pass. In some other examples, the agent(s) is / are selectively applied in multiple printing passes. In one of these examples, the number of printing passes ranges from 2 to 4. It may be desirable to apply the 3D printing fusing agent 12 and / or the detailing agent 16 and / or the assist agent in multiple printing passes to increase the amount, e.g., of the CWO nanoparticles, etc. that is applied to the build material composition 22, to avoid liquid splashing, to avoid displacement of the build material composition 22, etc.

[0108] After the 3D printing fusing agent 12 and / or detailing agent 16 and / or the assist agent are selectively applied in the specific portion(s) 36, 38 of the layer 24, the entire layer 24 of the build material composition 22 is exposed to electromagnetic radiation (shown as EMR in Fig. 2).

[0109] The electromagnetic radiation is emitted from the radiation source 34. The radiation source 34 may include one or more infrared radiation (IR) lamps, IR emitting diodes, or another broad spectrum light source emitting the desired wavelength(s).

[0110] The length of time the electromagnetic radiation is applied for, or energy exposure time, may be dependent, for example, on one or more of: characteristics of the radiation source 34; characteristics of the build material composition 22; and / or characteristics of the 3D printing fusing agent 12. In an example, a single point of the build material layer 24 is exposed to electromagnetic radiation for a period of time ranging from 0.01 second to 1 second.

[0111] It is to be understood that the electromagnetic radiation exposure may be accomplished in a single radiation event or in multiple radiation events. The term “event,” as used herein, refers to one period of exposure of electromagnetic radiation from the radiation source 34. In an example, a radiation event may occur as a pass of a moveable radiation source 34 over the build material layer 24 (similar to a printing pass). In an example, the exposing of the build material composition 22 is accomplished in multiple radiation events. In a specific example, the number of radiation events ranges from 1 to 8. In still another specific example, the exposure of the build material composition 22 to electromagnetic radiation may be accomplished in3 radiation events. It may be desirable to expose the build material composition 22 to electromagnetic radiation in multiple radiation events to counteract a cooling effect that may be brought on by the amount of the 3D printing fusing agent 12, alone or in combination with the assist agent, or the detailing agent 16 that is applied to the build material layer 24. Additionally, it may be desirable to expose the build material composition 22 to electromagnetic radiation in multiple radiation events to sufficiently elevate the temperature of the build material composition 22 in the portion(s) 36 without over heating the build material composition 22 in the non-patterned portion(s) 38.

[0112] The 3D printing fusing agent 12, e.g., the CWO nanoparticles, enhances the absorption of the radiation, converts the absorbed radiation to thermal energy, and promotes the transfer of the thermal heat to the build material composition 22 in contact therewith. In an example, the 3D printing fusing agent 12 sufficiently elevates the temperature of the build material composition 22 in the portion 36 to a temperature above the melting point or within the melting range of the polymeric material, allowing coalescing / fusing (e.g., thermal merging, melting, binding, etc.) of the build material composition 22 to take place. The application of the electromagnetic radiation forms the 3D object layer 40.

[0113] In some examples, the electromagnetic radiation has a wavelength ranging from 800 nm to 4000 nm. Radiation having wavelengths within the provided ranges may be substantially absorbed (e.g., 80% or more of the applied radiation is absorbed) by the 3D printing fusing agent 12 (e.g., by the cesium tungsten oxide nanoparticles included therein) and may heat the build material composition 22 in contact therewith. Further, the radiation may not be substantially absorbed (e.g., 25% or less of the applied radiation is absorbed) by the non-patterned build material composition 22 in portion(s) 38.

[0114] After the 3D object layer 40 is formed, additional layer(s) may be formed thereon to create an example of the 3D object. To form the next layer, additional build material composition 22 may be applied on the layer 40. The 3D printing fusing agent 12, alone or in combination with the assist agent, is then selectively applied on at least a portion of the additional build material composition 22, according to the 3D objectmodel. The detailing agent 16 may be applied in any area of the additional build material composition 22 where coalescence is not desirable. After the fusing agent 12 and / or detailing agent 16 and / or the assist agent is / are applied, the entire additional layer of the additional build material composition 22 is exposed to electromagnetic radiation in the manner described herein. The application of additional build material composition 22, the selective application of the 3D printing fusing agent 12, alone or in combination with the assist agent, or the detailing agent 16, and the electromagnetic radiation exposure may be repeated for a predetermined number of cycles to form the final 3D object in accordance with the 3D object model. As such, some examples of the method 100 include repeating the applying of the build material composition 22, the selectively applying of the 3D printing fusing agent 12, alone or in combination with the assist agent, and the exposing, to form a predetermined number of 3D object layers 40 and a 3D printed object.

[0115] As described, the 3D objects generated using the 3D printing fusing agent 12, such as the object formed from individual layers 40, may appear white or exhibit the color of the build material composition 22, due in part to the low loading of the cesium tungsten oxide nanoparticles in the 3D fusing agent 12.

[0116] In the examples disclosed herein, a 3D object may be printed in any orientation. For example, the 3D object can be printed from bottom to top, top to bottom, on its side, at an angle, or any other orientation. The orientation of the 3D object can also be formed in any orientation relative to the layering of the build material composition 22. For example, the 3D object can be formed in an inverted orientation or on its side relative to the layering of the build material composition 22. The orientation of the build within each layer 24 can be selected in advance or even by the user at the time of printing, for example.

[0117] Printed article

[0118] Examples of the method(s) described herein may be used to generate individual 3D object layers that make up a three-dimensional (3D) printed article / part, including: coalesced polymeric build material; and from about 0.001 wt% to about 1wt%, based on a total weight of the 3D printed article, of cesium tungsten oxide nanoparticles.

[0119] Even though the 3D printed article contains the cesium tungsten oxide nanoparticles, the 3D printed article exhibits a color of the polymeric build material (used to form the article). By “exhibits a color,” it is meant that the 3D object being referred to closely resembles the color of the build material used to 3D print the object. For example, the L* value of a 3D printed part that exhibits the color of the build material is within 25 of the L* value of the build material. In an example, the 3D object layer (forming the 3D printed article) has an L* value ranging from 85 to 95, as the term “L*” is defined hereinbelow in regard to the examples.

[0120] In some examples, the 3D printed article further comprises benzyl alcohol. It is to be understood that at least some of the benzyl alcohol may be evaporated during the 3D printing process, but in some instances, residual amounts may remain in the 3D object. In an example, the amount of residual benzyl alcohol that remains in the printed part ranges from about 0.01 wt% to about 5 wt%.

[0121] It is to be understood that other components of the build material composition (e.g., whitener, etc.) and components of the 3D printing fusing agent that do not evaporate are also present in the 3D printed article. The weight percentage of each component will depend on the amount in the build material composition and / or 3D printing fusing agent, the dimensions of the part, the amount of the 3D printing fusing agent applied, the evaporation rate (if any) of the components, and other like conditions or parameters.

[0122] Three-dimensional (3D) Printing Kit

[0123] Further described herein are examples of a three-dimensional (3D) printing kit. The 3D printing kit includes: a polymeric build material composition; and a fusing agent, comprising: cesium tungsten oxide nanoparticles present in an amount ranging from about 0.01 wt% active to about 1 wt% active, based on a total weight of the fusing agent; and a liquid vehicle, including: water; and a co-solvent mixture including from about 0.1 wt% active to about 10 wt% active of benzyl alcohol and from about 10 wt% active to about 40 wt% active of a co-solvent to improve miscibilitybetween the benzyl alcohol and the water, wherein the wt% of the benzyl alcohol and the wt% of the co-solvent are each based on the total weight of the fusing agent.

[0124] The polymeric build material composition and the fusing agent in the kit may be any of the examples disclosed herein. Thus, the co-solvent included in the fusing agent in the 3D printing kit may be any co-solvent described herein that improves miscibility between the benzyl alcohol and the water. In some examples, the fusing agent included in the 3D printing kit may further include the additive. In one specific example, the fusing agent in the 3D printing kit further comprises a stabilizer, a surfactant, and an anti-kogation agent. It is to be understood, however, that any of the additives described herein (including the combination of two or more additives) may be included in the fusing agent of the 3D printing kit. In another example of the 3D printing kit, the polymeric build material composition is a polyamide. Some examples of the 3D printing kit further include the detailing agent. Other examples of the 3D printing kit further include the assist agent. Still other examples of the 3D printing kit further include the detailing agent and the assist agent. In some examples of the 3D printing kit, the benzyl alcohol and the solvent are present in the 3D printing fusing agent in a weight ratio ranging from about 1 :6 to about 2:3.

[0125] Examples of the fluid kit are suitable for printing on the polymeric build materials described herein.EXAMPLES

[0126] Example 1

[0127] A comparative 3D printing fusing agent (referred to herein as “Comp. FA 1”) and four example 3D printing fusing agents (referred to herein as “Ex. FA 2,” “Ex. FA 3,” “Ex. FA4,” “Ex. FA 5”) were each prepared. The example formulations included water, different amounts of benzyl alcohol, a co-solvent to improve miscibility between the benzyl alcohol and the water, an anti-kogation agent, a surfactant, and betaalanine. The comparative formulation was the same as the example formulations, except that it did not include any benzyl alcohol.

[0128] The components of the comparative formulation and the example formulations are shown in Table 3. All of the components included in bothformulations were >99 wt% active, except for the 2-pyrrolidinone (which was 95 wt% active) and the cesium tungsten oxide nanoparticle dispersion, which included 20% active cesium tungsten oxide nanoparticles. The wt% values provided in Table 3 represent the wt% active of each component that was present in each formulation, based on a total weight of the formulation:TABLE 3

[0129] The example formulations were printed using a thermal inkjet printer to determine the printability and decap performance. To test the printability and decap performance, a reference line of each example formulation was printed from a printhead that was not uncapped (i.e. , was not exposed to air). Then, the printhead was left uncapped (i.e., exposed to air) for a predetermined amount of time (e.g., 9 seconds) before the example formulation was ejected again from the printhead. The print results indicated very good decap performance and nozzle health. Thus, each of the example 3D printing fusing agents exhibited acceptable 2D printing or jetting performance.

[0130] Comp. FA 1 and Ex. FA 2 were then used in a 3D printing process to generate comparative and example 3D printed objects. Some of the comparative and example 3D printed objects were type V dogbones, which are shown in Fig. 3 (discussed below). Ex. FA 2 was selected, in part, due to the high amount of benzyl alcohol.

[0131] The polymeric build material used to generate all of the 3D printed objects was polyamide-12. The polyamide-12 build material was spread out into thin layers having a thickness of about 80 pm. Comp. FA 1 and Ex. FA 2 were inkjet printed, independently, on each build material layer. Ex. FA 2 was printed at about 16.9 ng I voxel and Comp. FA 1 was printed at about 2.8 ng / voxel. Each patterned layer was exposed to IR radiation. This process of spreading, inkjet printing, and exposing was repeated 50 times for each object (e.g., for 50 patterned layers) to form each dogbone. Eight comparative 3D objects (i.e. , dogbones) and eight example 3D objects (i.e., dogbones) were generated.

[0132] A photograph of four of the dogbones generated using Ex. FA 2 and one of the dogbones generated using Comp. FA 1 was taken. A black and white reproduction of the photograph is shown in Fig. 3. The originally colored image of this black and white reproduction illustrated that the example objects - produced using Ex. FA 2 - exhibited a color that was closer to the color of the build material that was used to form the object (which in this example is off white) compared to the comparative object - produced using Comp. FA 1 . The visual results were confirmed with L* measurements.

[0133] The L* measurements were taken using an X-rite® eXact™ spectrophotometer. L* is a measure for lightness / whiteness ranging from black (L*= 0) to white (L*= 100). The L* value of the build material that was used to generate the 3D printed object was close to 100. The L* results are shown in Table 4 and are graphically represented in Fig. 4 (for both the bottom and the top of each part). Table 4 identifies the sample 3D objects by the fusing agent with which they were prepared, and also depicts the location of the 3D object where the measurement was taken (top or bottom) and the L* value.TABLE 4

[0134] The L* values indicate that Ex. FA 2 did not introduce a darker color to 3D printed object. Visually, the 3D object had a color similar to that of the build material composition, and the L* values confirmed the visual observation (with L* values ranging from 89.1 to 91.1 ). In comparison, 3D printed objects generated with Comp. FA 1 had a color that was darker than those generated using the example composition, with L* values ranging from 86.3 to 88.4.

[0135] The results for the 3D object formed with Ex. FA 2 illustrate that the low loading of the cesium tungsten oxide nanoparticles enables sufficient absorption for creating a mechanically strong 3D printed object, and imparts little to no color of the cesium tungsten oxide nanoparticles to the 3D printed object, such that the 3D printed object exhibits the color of the originally used build material composition.

[0136] Example 2

[0137] Five additional comparative 3D printing fusing agents (referred to herein as “Comp. FA 6,” “Comp. FA 7,” “Comp. FA 8,” “Comp. FA 9,” and “Comp. FA 10,” respectively) were prepared.

[0138] The components of each of Comp. FA 6, Comp. FA 7, Comp. FA 8, Comp. FA 9, and Comp. FA 10 are shown in Table 5. All of the components included in both formulations were >99 wt% active, except for the 2-pyrrolidinone (which was 95 wt% active) and the cesium tungsten oxide nanoparticle dispersion, which included 20% active cesium tungsten oxide nanoparticles. The wt% values provided in Table 5represent the wt% active of each component that was present in each comparative formulation, based on a total weight of the respective formulation:TABLE 5

[0139] Each of Comp. FA 6, Com. FA 7, Comp. FA 8, Comp. FA 9, and Comp. FA 10 exhibited particle agglomeration, which, in some instances, is believed to interfere with the fusing agents’ capacity to be efficiently jetted (e.g., from an inkjet printhead). This stands in contrast to the properties of each of Ex. FA 2-5 (in Example 1 ), none of which exhibited particle agglomeration. In Comp. FA 6-9, the agglomeration may have been due to the relatively high amount of the cesium tungsten oxide nanoparticles, and in Comp. FA 10, the agglomeration may have been due to the relatively high amount of the co-solvent.

[0140] It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range. For example, from about0.01 wt% active to about 8 wt% active should be interpreted to include not only the explicitly recited limits of from about 0.01 wt% active to about 10 wt% active, but also to include individual values, such as about 1 wt% active, about 2 wt% active, about 4 wt% active, about 8 wt% active, etc., and sub-ranges, such as from about 1 wt% active to about 7 wt% active, from about 2 wt% active to about 6 wt% active, from about 3 wt% active to about 5 wt% active, etc.

[0141] Furthermore, when “about” is utilized to describe a value, this is meant to encompass minor variations (up to + / - 10%) from the stated value.

[0142] Reference throughout the specification to “one example”, “another example”, “an example”, and so forth, means that a particular element (e.g., feature, structure, and / or characteristic) described in connection with the example is included in at least one example described herein, and may or may not be present in other examples. In addition, it is to be understood that the described elements for any example may be combined in any suitable manner in the various examples unless the context clearly dictates otherwise.

[0143] In describing and claiming the examples disclosed herein, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0144] While several examples have been described in detail, it is to be understood that the disclosed examples may be modified. Therefore, the foregoing description is to be considered non-limiting.

Claims

What is claimed is:

1. A fusing agent, comprising: cesium tungsten oxide nanoparticles present in an amount ranging from about 0.01 wt% active to about 1 wt% active, based on a total weight of the fusing agent; and a liquid vehicle, including: water; and a co-solvent mixture including from about 0.1 wt% active to about 10 wt% active of benzyl alcohol and from about 10 wt% active to about 40 wt% active of a co-solvent to improve miscibility between the benzyl alcohol and the water, wherein the wt% active of the benzyl alcohol and the wt% active of the co-solvent are each based on the total weight of the fusing agent.

2. The fusing agent as defined in claim 1 , wherein the co-solvent is selected from the group consisting of 1 -(2-hydroxyethyl)-2-pyrrolidone, 1 ,5-pentanediol, 1 ,2- hexanediol, 2-pyrrolidinone, triethylene glycol, tetraethylene glycol, 2-methyl-1 ,3- propanediol, 1 ,6-hexanediol, tripropylene glycol methyl ether, 1 ,2-propanediol, diethylene glycol butyl either, polyethylene glycol having a weight average molecular weight ranging from about 190 Daltons to about 420 Daltons, glycerol, betaine, and combinations thereof.

3. The fusing agent as defined in claim 1 , further comprising a zwitterionic stabilizer selected from the group consisting of C2 to Cs betaines, C2 to Cs aminocarboxylic acids having a solubility of at least 10 g in 100 g of water, taurine, and combinations thereof.

4. The fusing agent as defined in claim 1 , wherein the cesium tungsten oxide nanoparticles have a volume weighted mean diameter ranging from about 0.005 pm to about 0.01 pm.

5. The fusing agent as defined in claim 1 , further comprising: a stabilizer;a surfactant; and an anti-kogation agent.

6. A three-dimensional (3D) printing kit, comprising: a polymeric build material composition; and a fusing agent, comprising: cesium tungsten oxide nanoparticles present in an amount ranging from about 0.01 wt% active to about 1 wt% active, based on a total weight of the fusing agent; and a liquid vehicle, including: water; and a co-solvent mixture including from about 0.1 wt% active to about 10 wt% active of benzyl alcohol and from about 10 wt% active to about 40 wt% active of a co-solvent to improve miscibility between the benzyl alcohol and the water, wherein the wt% active of the benzyl alcohol and the wt% active of the co-solvent are each based on the total weight of the fusing agent.

7. The 3D printing kit as defined in claim 6, wherein the co-solvent in the fusing agent is selected from the group consisting of 1-(2-hydroxyethyl)-2-pyrrolidone, 1 ,5- pentanediol, 1 ,2-hexanediol, 2-pyrrolidinone, triethylene glycol, tetraethylene glycol, 2- methyl-1 ,3-propanediol, 1 ,6-hexanediol, tripropylene glycol methyl ether, 1 ,2- propanediol, diethylene glycol butyl either, polyethylene glycol having a weight average molecular weight ranging from about 190 Daltons to about 420 Daltons, glycerol, betaine, and combinations thereof.

8. The 3D printing kit as defined in claim 6, wherein the fusing agent further comprises a zwitterionic stabilizer selected from the group consisting of C2to C8betaines, C2to C8aminocarboxylic acids having a solubility of at least 10 g in 100 g of water, taurine, and combinations thereof.

9. The 3D printing kit as defined in claim 6, wherein the cesium tungsten oxide nanoparticles in the fusing agent have a volume weighted mean diameter ranging from about 0.005 pm to about 0.01 pm.

10. The 3D printing kit as defined in claim 6, wherein the fusing agent further comprises: a stabilizer; a surfactant; and an anti-kogation agent.11 . The 3D printing kit as defined in claim 6, wherein the polymeric build material composition is a polyamide.

12. The 3D printing kit as defined in claim 6, further comprising a detailing agent.

13. A method of three-dimensional (3D) printing, comprising: applying a polymeric build material composition to form a build material layer; based on a 3D object model, selectively applying a fusing agent onto at least a portion of the build material layer, thereby forming a patterned portion, wherein the fusing agent includes: cesium tungsten oxide nanoparticles present in an amount ranging from about 0.01 wt% active to about 1 wt% active, based on a total weight of the fusing agent; and a liquid vehicle, including: water; and a co-solvent mixture including from about 0.1 wt% active to about10 wt% active of benzyl alcohol and from about 10 wt% active to about 40 wt% active of a co-solvent to improve miscibility between the benzyl alcohol and the water, wherein the wt% active of the benzyl alcohol andthe wt% active of the co-solvent are each based on the total weight of the fusing agent; and exposing the build material layer to near-infrared radiation to selectively coalesce the patterned portion and form a 3D object layer at the patterned portion.

14. The method as defined in claim 13, further comprising selectively applying, based on the 3D object model, a detailing agent onto an other portion of the build material layer outside of the patterned portion.

15. The method as defined in claim 13, wherein the 3D object layer has an L* value ranging from 85 to 95.

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